linux/net/ipv4/tcp_input.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * INET         An implementation of the TCP/IP protocol suite for the LINUX
   4 *              operating system.  INET is implemented using the  BSD Socket
   5 *              interface as the means of communication with the user level.
   6 *
   7 *              Implementation of the Transmission Control Protocol(TCP).
   8 *
   9 * Authors:     Ross Biro
  10 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  11 *              Mark Evans, <evansmp@uhura.aston.ac.uk>
  12 *              Corey Minyard <wf-rch!minyard@relay.EU.net>
  13 *              Florian La Roche, <flla@stud.uni-sb.de>
  14 *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
  15 *              Linus Torvalds, <torvalds@cs.helsinki.fi>
  16 *              Alan Cox, <gw4pts@gw4pts.ampr.org>
  17 *              Matthew Dillon, <dillon@apollo.west.oic.com>
  18 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  19 *              Jorge Cwik, <jorge@laser.satlink.net>
  20 */
  21
  22/*
  23 * Changes:
  24 *              Pedro Roque     :       Fast Retransmit/Recovery.
  25 *                                      Two receive queues.
  26 *                                      Retransmit queue handled by TCP.
  27 *                                      Better retransmit timer handling.
  28 *                                      New congestion avoidance.
  29 *                                      Header prediction.
  30 *                                      Variable renaming.
  31 *
  32 *              Eric            :       Fast Retransmit.
  33 *              Randy Scott     :       MSS option defines.
  34 *              Eric Schenk     :       Fixes to slow start algorithm.
  35 *              Eric Schenk     :       Yet another double ACK bug.
  36 *              Eric Schenk     :       Delayed ACK bug fixes.
  37 *              Eric Schenk     :       Floyd style fast retrans war avoidance.
  38 *              David S. Miller :       Don't allow zero congestion window.
  39 *              Eric Schenk     :       Fix retransmitter so that it sends
  40 *                                      next packet on ack of previous packet.
  41 *              Andi Kleen      :       Moved open_request checking here
  42 *                                      and process RSTs for open_requests.
  43 *              Andi Kleen      :       Better prune_queue, and other fixes.
  44 *              Andrey Savochkin:       Fix RTT measurements in the presence of
  45 *                                      timestamps.
  46 *              Andrey Savochkin:       Check sequence numbers correctly when
  47 *                                      removing SACKs due to in sequence incoming
  48 *                                      data segments.
  49 *              Andi Kleen:             Make sure we never ack data there is not
  50 *                                      enough room for. Also make this condition
  51 *                                      a fatal error if it might still happen.
  52 *              Andi Kleen:             Add tcp_measure_rcv_mss to make
  53 *                                      connections with MSS<min(MTU,ann. MSS)
  54 *                                      work without delayed acks.
  55 *              Andi Kleen:             Process packets with PSH set in the
  56 *                                      fast path.
  57 *              J Hadi Salim:           ECN support
  58 *              Andrei Gurtov,
  59 *              Pasi Sarolahti,
  60 *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
  61 *                                      engine. Lots of bugs are found.
  62 *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
  63 */
  64
  65#define pr_fmt(fmt) "TCP: " fmt
  66
  67#include <linux/mm.h>
  68#include <linux/slab.h>
  69#include <linux/module.h>
  70#include <linux/sysctl.h>
  71#include <linux/kernel.h>
  72#include <linux/prefetch.h>
  73#include <net/dst.h>
  74#include <net/tcp.h>
  75#include <net/inet_common.h>
  76#include <linux/ipsec.h>
  77#include <asm/unaligned.h>
  78#include <linux/errqueue.h>
  79#include <trace/events/tcp.h>
  80#include <linux/jump_label_ratelimit.h>
  81#include <net/busy_poll.h>
  82
  83int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
  84
  85#define FLAG_DATA               0x01 /* Incoming frame contained data.          */
  86#define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
  87#define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
  88#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
  89#define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
  90#define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
  91#define FLAG_ECE                0x40 /* ECE in this ACK                         */
  92#define FLAG_LOST_RETRANS       0x80 /* This ACK marks some retransmission lost */
  93#define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
  94#define FLAG_ORIG_SACK_ACKED    0x200 /* Never retransmitted data are (s)acked  */
  95#define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
  96#define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
  97#define FLAG_SET_XMIT_TIMER     0x1000 /* Set TLP or RTO timer */
  98#define FLAG_SACK_RENEGING      0x2000 /* snd_una advanced to a sacked seq */
  99#define FLAG_UPDATE_TS_RECENT   0x4000 /* tcp_replace_ts_recent() */
 100#define FLAG_NO_CHALLENGE_ACK   0x8000 /* do not call tcp_send_challenge_ack()  */
 101#define FLAG_ACK_MAYBE_DELAYED  0x10000 /* Likely a delayed ACK */
 102
 103#define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 104#define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
 105#define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
 106#define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
 107
 108#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
 109#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
 110
 111#define REXMIT_NONE     0 /* no loss recovery to do */
 112#define REXMIT_LOST     1 /* retransmit packets marked lost */
 113#define REXMIT_NEW      2 /* FRTO-style transmit of unsent/new packets */
 114
 115#if IS_ENABLED(CONFIG_TLS_DEVICE)
 116static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ);
 117
 118void clean_acked_data_enable(struct inet_connection_sock *icsk,
 119                             void (*cad)(struct sock *sk, u32 ack_seq))
 120{
 121        icsk->icsk_clean_acked = cad;
 122        static_branch_deferred_inc(&clean_acked_data_enabled);
 123}
 124EXPORT_SYMBOL_GPL(clean_acked_data_enable);
 125
 126void clean_acked_data_disable(struct inet_connection_sock *icsk)
 127{
 128        static_branch_slow_dec_deferred(&clean_acked_data_enabled);
 129        icsk->icsk_clean_acked = NULL;
 130}
 131EXPORT_SYMBOL_GPL(clean_acked_data_disable);
 132
 133void clean_acked_data_flush(void)
 134{
 135        static_key_deferred_flush(&clean_acked_data_enabled);
 136}
 137EXPORT_SYMBOL_GPL(clean_acked_data_flush);
 138#endif
 139
 140static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
 141                             unsigned int len)
 142{
 143        static bool __once __read_mostly;
 144
 145        if (!__once) {
 146                struct net_device *dev;
 147
 148                __once = true;
 149
 150                rcu_read_lock();
 151                dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
 152                if (!dev || len >= dev->mtu)
 153                        pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
 154                                dev ? dev->name : "Unknown driver");
 155                rcu_read_unlock();
 156        }
 157}
 158
 159/* Adapt the MSS value used to make delayed ack decision to the
 160 * real world.
 161 */
 162static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
 163{
 164        struct inet_connection_sock *icsk = inet_csk(sk);
 165        const unsigned int lss = icsk->icsk_ack.last_seg_size;
 166        unsigned int len;
 167
 168        icsk->icsk_ack.last_seg_size = 0;
 169
 170        /* skb->len may jitter because of SACKs, even if peer
 171         * sends good full-sized frames.
 172         */
 173        len = skb_shinfo(skb)->gso_size ? : skb->len;
 174        if (len >= icsk->icsk_ack.rcv_mss) {
 175                icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
 176                                               tcp_sk(sk)->advmss);
 177                /* Account for possibly-removed options */
 178                if (unlikely(len > icsk->icsk_ack.rcv_mss +
 179                                   MAX_TCP_OPTION_SPACE))
 180                        tcp_gro_dev_warn(sk, skb, len);
 181        } else {
 182                /* Otherwise, we make more careful check taking into account,
 183                 * that SACKs block is variable.
 184                 *
 185                 * "len" is invariant segment length, including TCP header.
 186                 */
 187                len += skb->data - skb_transport_header(skb);
 188                if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
 189                    /* If PSH is not set, packet should be
 190                     * full sized, provided peer TCP is not badly broken.
 191                     * This observation (if it is correct 8)) allows
 192                     * to handle super-low mtu links fairly.
 193                     */
 194                    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
 195                     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
 196                        /* Subtract also invariant (if peer is RFC compliant),
 197                         * tcp header plus fixed timestamp option length.
 198                         * Resulting "len" is MSS free of SACK jitter.
 199                         */
 200                        len -= tcp_sk(sk)->tcp_header_len;
 201                        icsk->icsk_ack.last_seg_size = len;
 202                        if (len == lss) {
 203                                icsk->icsk_ack.rcv_mss = len;
 204                                return;
 205                        }
 206                }
 207                if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
 208                        icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
 209                icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
 210        }
 211}
 212
 213static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
 214{
 215        struct inet_connection_sock *icsk = inet_csk(sk);
 216        unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
 217
 218        if (quickacks == 0)
 219                quickacks = 2;
 220        quickacks = min(quickacks, max_quickacks);
 221        if (quickacks > icsk->icsk_ack.quick)
 222                icsk->icsk_ack.quick = quickacks;
 223}
 224
 225void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
 226{
 227        struct inet_connection_sock *icsk = inet_csk(sk);
 228
 229        tcp_incr_quickack(sk, max_quickacks);
 230        inet_csk_exit_pingpong_mode(sk);
 231        icsk->icsk_ack.ato = TCP_ATO_MIN;
 232}
 233EXPORT_SYMBOL(tcp_enter_quickack_mode);
 234
 235/* Send ACKs quickly, if "quick" count is not exhausted
 236 * and the session is not interactive.
 237 */
 238
 239static bool tcp_in_quickack_mode(struct sock *sk)
 240{
 241        const struct inet_connection_sock *icsk = inet_csk(sk);
 242        const struct dst_entry *dst = __sk_dst_get(sk);
 243
 244        return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
 245                (icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
 246}
 247
 248static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
 249{
 250        if (tp->ecn_flags & TCP_ECN_OK)
 251                tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
 252}
 253
 254static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
 255{
 256        if (tcp_hdr(skb)->cwr) {
 257                tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 258
 259                /* If the sender is telling us it has entered CWR, then its
 260                 * cwnd may be very low (even just 1 packet), so we should ACK
 261                 * immediately.
 262                 */
 263                inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
 264        }
 265}
 266
 267static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
 268{
 269        tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
 270}
 271
 272static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
 273{
 274        struct tcp_sock *tp = tcp_sk(sk);
 275
 276        switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
 277        case INET_ECN_NOT_ECT:
 278                /* Funny extension: if ECT is not set on a segment,
 279                 * and we already seen ECT on a previous segment,
 280                 * it is probably a retransmit.
 281                 */
 282                if (tp->ecn_flags & TCP_ECN_SEEN)
 283                        tcp_enter_quickack_mode(sk, 2);
 284                break;
 285        case INET_ECN_CE:
 286                if (tcp_ca_needs_ecn(sk))
 287                        tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
 288
 289                if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
 290                        /* Better not delay acks, sender can have a very low cwnd */
 291                        tcp_enter_quickack_mode(sk, 2);
 292                        tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
 293                }
 294                tp->ecn_flags |= TCP_ECN_SEEN;
 295                break;
 296        default:
 297                if (tcp_ca_needs_ecn(sk))
 298                        tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
 299                tp->ecn_flags |= TCP_ECN_SEEN;
 300                break;
 301        }
 302}
 303
 304static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
 305{
 306        if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
 307                __tcp_ecn_check_ce(sk, skb);
 308}
 309
 310static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
 311{
 312        if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
 313                tp->ecn_flags &= ~TCP_ECN_OK;
 314}
 315
 316static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
 317{
 318        if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
 319                tp->ecn_flags &= ~TCP_ECN_OK;
 320}
 321
 322static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
 323{
 324        if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
 325                return true;
 326        return false;
 327}
 328
 329/* Buffer size and advertised window tuning.
 330 *
 331 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
 332 */
 333
 334static void tcp_sndbuf_expand(struct sock *sk)
 335{
 336        const struct tcp_sock *tp = tcp_sk(sk);
 337        const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
 338        int sndmem, per_mss;
 339        u32 nr_segs;
 340
 341        /* Worst case is non GSO/TSO : each frame consumes one skb
 342         * and skb->head is kmalloced using power of two area of memory
 343         */
 344        per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
 345                  MAX_TCP_HEADER +
 346                  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 347
 348        per_mss = roundup_pow_of_two(per_mss) +
 349                  SKB_DATA_ALIGN(sizeof(struct sk_buff));
 350
 351        nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
 352        nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
 353
 354        /* Fast Recovery (RFC 5681 3.2) :
 355         * Cubic needs 1.7 factor, rounded to 2 to include
 356         * extra cushion (application might react slowly to EPOLLOUT)
 357         */
 358        sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
 359        sndmem *= nr_segs * per_mss;
 360
 361        if (sk->sk_sndbuf < sndmem)
 362                WRITE_ONCE(sk->sk_sndbuf,
 363                           min(sndmem, sock_net(sk)->ipv4.sysctl_tcp_wmem[2]));
 364}
 365
 366/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
 367 *
 368 * All tcp_full_space() is split to two parts: "network" buffer, allocated
 369 * forward and advertised in receiver window (tp->rcv_wnd) and
 370 * "application buffer", required to isolate scheduling/application
 371 * latencies from network.
 372 * window_clamp is maximal advertised window. It can be less than
 373 * tcp_full_space(), in this case tcp_full_space() - window_clamp
 374 * is reserved for "application" buffer. The less window_clamp is
 375 * the smoother our behaviour from viewpoint of network, but the lower
 376 * throughput and the higher sensitivity of the connection to losses. 8)
 377 *
 378 * rcv_ssthresh is more strict window_clamp used at "slow start"
 379 * phase to predict further behaviour of this connection.
 380 * It is used for two goals:
 381 * - to enforce header prediction at sender, even when application
 382 *   requires some significant "application buffer". It is check #1.
 383 * - to prevent pruning of receive queue because of misprediction
 384 *   of receiver window. Check #2.
 385 *
 386 * The scheme does not work when sender sends good segments opening
 387 * window and then starts to feed us spaghetti. But it should work
 388 * in common situations. Otherwise, we have to rely on queue collapsing.
 389 */
 390
 391/* Slow part of check#2. */
 392static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
 393{
 394        struct tcp_sock *tp = tcp_sk(sk);
 395        /* Optimize this! */
 396        int truesize = tcp_win_from_space(sk, skb->truesize) >> 1;
 397        int window = tcp_win_from_space(sk, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]) >> 1;
 398
 399        while (tp->rcv_ssthresh <= window) {
 400                if (truesize <= skb->len)
 401                        return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
 402
 403                truesize >>= 1;
 404                window >>= 1;
 405        }
 406        return 0;
 407}
 408
 409static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 410{
 411        struct tcp_sock *tp = tcp_sk(sk);
 412        int room;
 413
 414        room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
 415
 416        /* Check #1 */
 417        if (room > 0 && !tcp_under_memory_pressure(sk)) {
 418                int incr;
 419
 420                /* Check #2. Increase window, if skb with such overhead
 421                 * will fit to rcvbuf in future.
 422                 */
 423                if (tcp_win_from_space(sk, skb->truesize) <= skb->len)
 424                        incr = 2 * tp->advmss;
 425                else
 426                        incr = __tcp_grow_window(sk, skb);
 427
 428                if (incr) {
 429                        incr = max_t(int, incr, 2 * skb->len);
 430                        tp->rcv_ssthresh += min(room, incr);
 431                        inet_csk(sk)->icsk_ack.quick |= 1;
 432                }
 433        }
 434}
 435
 436/* 3. Try to fixup all. It is made immediately after connection enters
 437 *    established state.
 438 */
 439void tcp_init_buffer_space(struct sock *sk)
 440{
 441        int tcp_app_win = sock_net(sk)->ipv4.sysctl_tcp_app_win;
 442        struct tcp_sock *tp = tcp_sk(sk);
 443        int maxwin;
 444
 445        if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
 446                tcp_sndbuf_expand(sk);
 447
 448        tp->rcvq_space.space = min_t(u32, tp->rcv_wnd, TCP_INIT_CWND * tp->advmss);
 449        tcp_mstamp_refresh(tp);
 450        tp->rcvq_space.time = tp->tcp_mstamp;
 451        tp->rcvq_space.seq = tp->copied_seq;
 452
 453        maxwin = tcp_full_space(sk);
 454
 455        if (tp->window_clamp >= maxwin) {
 456                tp->window_clamp = maxwin;
 457
 458                if (tcp_app_win && maxwin > 4 * tp->advmss)
 459                        tp->window_clamp = max(maxwin -
 460                                               (maxwin >> tcp_app_win),
 461                                               4 * tp->advmss);
 462        }
 463
 464        /* Force reservation of one segment. */
 465        if (tcp_app_win &&
 466            tp->window_clamp > 2 * tp->advmss &&
 467            tp->window_clamp + tp->advmss > maxwin)
 468                tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
 469
 470        tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
 471        tp->snd_cwnd_stamp = tcp_jiffies32;
 472}
 473
 474/* 4. Recalculate window clamp after socket hit its memory bounds. */
 475static void tcp_clamp_window(struct sock *sk)
 476{
 477        struct tcp_sock *tp = tcp_sk(sk);
 478        struct inet_connection_sock *icsk = inet_csk(sk);
 479        struct net *net = sock_net(sk);
 480
 481        icsk->icsk_ack.quick = 0;
 482
 483        if (sk->sk_rcvbuf < net->ipv4.sysctl_tcp_rmem[2] &&
 484            !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
 485            !tcp_under_memory_pressure(sk) &&
 486            sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
 487                WRITE_ONCE(sk->sk_rcvbuf,
 488                           min(atomic_read(&sk->sk_rmem_alloc),
 489                               net->ipv4.sysctl_tcp_rmem[2]));
 490        }
 491        if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
 492                tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
 493}
 494
 495/* Initialize RCV_MSS value.
 496 * RCV_MSS is an our guess about MSS used by the peer.
 497 * We haven't any direct information about the MSS.
 498 * It's better to underestimate the RCV_MSS rather than overestimate.
 499 * Overestimations make us ACKing less frequently than needed.
 500 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
 501 */
 502void tcp_initialize_rcv_mss(struct sock *sk)
 503{
 504        const struct tcp_sock *tp = tcp_sk(sk);
 505        unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
 506
 507        hint = min(hint, tp->rcv_wnd / 2);
 508        hint = min(hint, TCP_MSS_DEFAULT);
 509        hint = max(hint, TCP_MIN_MSS);
 510
 511        inet_csk(sk)->icsk_ack.rcv_mss = hint;
 512}
 513EXPORT_SYMBOL(tcp_initialize_rcv_mss);
 514
 515/* Receiver "autotuning" code.
 516 *
 517 * The algorithm for RTT estimation w/o timestamps is based on
 518 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
 519 * <http://public.lanl.gov/radiant/pubs.html#DRS>
 520 *
 521 * More detail on this code can be found at
 522 * <http://staff.psc.edu/jheffner/>,
 523 * though this reference is out of date.  A new paper
 524 * is pending.
 525 */
 526static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 527{
 528        u32 new_sample = tp->rcv_rtt_est.rtt_us;
 529        long m = sample;
 530
 531        if (new_sample != 0) {
 532                /* If we sample in larger samples in the non-timestamp
 533                 * case, we could grossly overestimate the RTT especially
 534                 * with chatty applications or bulk transfer apps which
 535                 * are stalled on filesystem I/O.
 536                 *
 537                 * Also, since we are only going for a minimum in the
 538                 * non-timestamp case, we do not smooth things out
 539                 * else with timestamps disabled convergence takes too
 540                 * long.
 541                 */
 542                if (!win_dep) {
 543                        m -= (new_sample >> 3);
 544                        new_sample += m;
 545                } else {
 546                        m <<= 3;
 547                        if (m < new_sample)
 548                                new_sample = m;
 549                }
 550        } else {
 551                /* No previous measure. */
 552                new_sample = m << 3;
 553        }
 554
 555        tp->rcv_rtt_est.rtt_us = new_sample;
 556}
 557
 558static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
 559{
 560        u32 delta_us;
 561
 562        if (tp->rcv_rtt_est.time == 0)
 563                goto new_measure;
 564        if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
 565                return;
 566        delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
 567        if (!delta_us)
 568                delta_us = 1;
 569        tcp_rcv_rtt_update(tp, delta_us, 1);
 570
 571new_measure:
 572        tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
 573        tp->rcv_rtt_est.time = tp->tcp_mstamp;
 574}
 575
 576static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 577                                          const struct sk_buff *skb)
 578{
 579        struct tcp_sock *tp = tcp_sk(sk);
 580
 581        if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
 582                return;
 583        tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
 584
 585        if (TCP_SKB_CB(skb)->end_seq -
 586            TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
 587                u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
 588                u32 delta_us;
 589
 590                if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
 591                        if (!delta)
 592                                delta = 1;
 593                        delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
 594                        tcp_rcv_rtt_update(tp, delta_us, 0);
 595                }
 596        }
 597}
 598
 599/*
 600 * This function should be called every time data is copied to user space.
 601 * It calculates the appropriate TCP receive buffer space.
 602 */
 603void tcp_rcv_space_adjust(struct sock *sk)
 604{
 605        struct tcp_sock *tp = tcp_sk(sk);
 606        u32 copied;
 607        int time;
 608
 609        trace_tcp_rcv_space_adjust(sk);
 610
 611        tcp_mstamp_refresh(tp);
 612        time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
 613        if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
 614                return;
 615
 616        /* Number of bytes copied to user in last RTT */
 617        copied = tp->copied_seq - tp->rcvq_space.seq;
 618        if (copied <= tp->rcvq_space.space)
 619                goto new_measure;
 620
 621        /* A bit of theory :
 622         * copied = bytes received in previous RTT, our base window
 623         * To cope with packet losses, we need a 2x factor
 624         * To cope with slow start, and sender growing its cwin by 100 %
 625         * every RTT, we need a 4x factor, because the ACK we are sending
 626         * now is for the next RTT, not the current one :
 627         * <prev RTT . ><current RTT .. ><next RTT .... >
 628         */
 629
 630        if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf &&
 631            !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
 632                int rcvmem, rcvbuf;
 633                u64 rcvwin, grow;
 634
 635                /* minimal window to cope with packet losses, assuming
 636                 * steady state. Add some cushion because of small variations.
 637                 */
 638                rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
 639
 640                /* Accommodate for sender rate increase (eg. slow start) */
 641                grow = rcvwin * (copied - tp->rcvq_space.space);
 642                do_div(grow, tp->rcvq_space.space);
 643                rcvwin += (grow << 1);
 644
 645                rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
 646                while (tcp_win_from_space(sk, rcvmem) < tp->advmss)
 647                        rcvmem += 128;
 648
 649                do_div(rcvwin, tp->advmss);
 650                rcvbuf = min_t(u64, rcvwin * rcvmem,
 651                               sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
 652                if (rcvbuf > sk->sk_rcvbuf) {
 653                        WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
 654
 655                        /* Make the window clamp follow along.  */
 656                        tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
 657                }
 658        }
 659        tp->rcvq_space.space = copied;
 660
 661new_measure:
 662        tp->rcvq_space.seq = tp->copied_seq;
 663        tp->rcvq_space.time = tp->tcp_mstamp;
 664}
 665
 666/* There is something which you must keep in mind when you analyze the
 667 * behavior of the tp->ato delayed ack timeout interval.  When a
 668 * connection starts up, we want to ack as quickly as possible.  The
 669 * problem is that "good" TCP's do slow start at the beginning of data
 670 * transmission.  The means that until we send the first few ACK's the
 671 * sender will sit on his end and only queue most of his data, because
 672 * he can only send snd_cwnd unacked packets at any given time.  For
 673 * each ACK we send, he increments snd_cwnd and transmits more of his
 674 * queue.  -DaveM
 675 */
 676static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
 677{
 678        struct tcp_sock *tp = tcp_sk(sk);
 679        struct inet_connection_sock *icsk = inet_csk(sk);
 680        u32 now;
 681
 682        inet_csk_schedule_ack(sk);
 683
 684        tcp_measure_rcv_mss(sk, skb);
 685
 686        tcp_rcv_rtt_measure(tp);
 687
 688        now = tcp_jiffies32;
 689
 690        if (!icsk->icsk_ack.ato) {
 691                /* The _first_ data packet received, initialize
 692                 * delayed ACK engine.
 693                 */
 694                tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
 695                icsk->icsk_ack.ato = TCP_ATO_MIN;
 696        } else {
 697                int m = now - icsk->icsk_ack.lrcvtime;
 698
 699                if (m <= TCP_ATO_MIN / 2) {
 700                        /* The fastest case is the first. */
 701                        icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
 702                } else if (m < icsk->icsk_ack.ato) {
 703                        icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
 704                        if (icsk->icsk_ack.ato > icsk->icsk_rto)
 705                                icsk->icsk_ack.ato = icsk->icsk_rto;
 706                } else if (m > icsk->icsk_rto) {
 707                        /* Too long gap. Apparently sender failed to
 708                         * restart window, so that we send ACKs quickly.
 709                         */
 710                        tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
 711                        sk_mem_reclaim(sk);
 712                }
 713        }
 714        icsk->icsk_ack.lrcvtime = now;
 715
 716        tcp_ecn_check_ce(sk, skb);
 717
 718        if (skb->len >= 128)
 719                tcp_grow_window(sk, skb);
 720}
 721
 722/* Called to compute a smoothed rtt estimate. The data fed to this
 723 * routine either comes from timestamps, or from segments that were
 724 * known _not_ to have been retransmitted [see Karn/Partridge
 725 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
 726 * piece by Van Jacobson.
 727 * NOTE: the next three routines used to be one big routine.
 728 * To save cycles in the RFC 1323 implementation it was better to break
 729 * it up into three procedures. -- erics
 730 */
 731static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
 732{
 733        struct tcp_sock *tp = tcp_sk(sk);
 734        long m = mrtt_us; /* RTT */
 735        u32 srtt = tp->srtt_us;
 736
 737        /*      The following amusing code comes from Jacobson's
 738         *      article in SIGCOMM '88.  Note that rtt and mdev
 739         *      are scaled versions of rtt and mean deviation.
 740         *      This is designed to be as fast as possible
 741         *      m stands for "measurement".
 742         *
 743         *      On a 1990 paper the rto value is changed to:
 744         *      RTO = rtt + 4 * mdev
 745         *
 746         * Funny. This algorithm seems to be very broken.
 747         * These formulae increase RTO, when it should be decreased, increase
 748         * too slowly, when it should be increased quickly, decrease too quickly
 749         * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
 750         * does not matter how to _calculate_ it. Seems, it was trap
 751         * that VJ failed to avoid. 8)
 752         */
 753        if (srtt != 0) {
 754                m -= (srtt >> 3);       /* m is now error in rtt est */
 755                srtt += m;              /* rtt = 7/8 rtt + 1/8 new */
 756                if (m < 0) {
 757                        m = -m;         /* m is now abs(error) */
 758                        m -= (tp->mdev_us >> 2);   /* similar update on mdev */
 759                        /* This is similar to one of Eifel findings.
 760                         * Eifel blocks mdev updates when rtt decreases.
 761                         * This solution is a bit different: we use finer gain
 762                         * for mdev in this case (alpha*beta).
 763                         * Like Eifel it also prevents growth of rto,
 764                         * but also it limits too fast rto decreases,
 765                         * happening in pure Eifel.
 766                         */
 767                        if (m > 0)
 768                                m >>= 3;
 769                } else {
 770                        m -= (tp->mdev_us >> 2);   /* similar update on mdev */
 771                }
 772                tp->mdev_us += m;               /* mdev = 3/4 mdev + 1/4 new */
 773                if (tp->mdev_us > tp->mdev_max_us) {
 774                        tp->mdev_max_us = tp->mdev_us;
 775                        if (tp->mdev_max_us > tp->rttvar_us)
 776                                tp->rttvar_us = tp->mdev_max_us;
 777                }
 778                if (after(tp->snd_una, tp->rtt_seq)) {
 779                        if (tp->mdev_max_us < tp->rttvar_us)
 780                                tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
 781                        tp->rtt_seq = tp->snd_nxt;
 782                        tp->mdev_max_us = tcp_rto_min_us(sk);
 783
 784                        tcp_bpf_rtt(sk);
 785                }
 786        } else {
 787                /* no previous measure. */
 788                srtt = m << 3;          /* take the measured time to be rtt */
 789                tp->mdev_us = m << 1;   /* make sure rto = 3*rtt */
 790                tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
 791                tp->mdev_max_us = tp->rttvar_us;
 792                tp->rtt_seq = tp->snd_nxt;
 793
 794                tcp_bpf_rtt(sk);
 795        }
 796        tp->srtt_us = max(1U, srtt);
 797}
 798
 799static void tcp_update_pacing_rate(struct sock *sk)
 800{
 801        const struct tcp_sock *tp = tcp_sk(sk);
 802        u64 rate;
 803
 804        /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
 805        rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
 806
 807        /* current rate is (cwnd * mss) / srtt
 808         * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
 809         * In Congestion Avoidance phase, set it to 120 % the current rate.
 810         *
 811         * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
 812         *       If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
 813         *       end of slow start and should slow down.
 814         */
 815        if (tp->snd_cwnd < tp->snd_ssthresh / 2)
 816                rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio;
 817        else
 818                rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio;
 819
 820        rate *= max(tp->snd_cwnd, tp->packets_out);
 821
 822        if (likely(tp->srtt_us))
 823                do_div(rate, tp->srtt_us);
 824
 825        /* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
 826         * without any lock. We want to make sure compiler wont store
 827         * intermediate values in this location.
 828         */
 829        WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
 830                                             sk->sk_max_pacing_rate));
 831}
 832
 833/* Calculate rto without backoff.  This is the second half of Van Jacobson's
 834 * routine referred to above.
 835 */
 836static void tcp_set_rto(struct sock *sk)
 837{
 838        const struct tcp_sock *tp = tcp_sk(sk);
 839        /* Old crap is replaced with new one. 8)
 840         *
 841         * More seriously:
 842         * 1. If rtt variance happened to be less 50msec, it is hallucination.
 843         *    It cannot be less due to utterly erratic ACK generation made
 844         *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
 845         *    to do with delayed acks, because at cwnd>2 true delack timeout
 846         *    is invisible. Actually, Linux-2.4 also generates erratic
 847         *    ACKs in some circumstances.
 848         */
 849        inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
 850
 851        /* 2. Fixups made earlier cannot be right.
 852         *    If we do not estimate RTO correctly without them,
 853         *    all the algo is pure shit and should be replaced
 854         *    with correct one. It is exactly, which we pretend to do.
 855         */
 856
 857        /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
 858         * guarantees that rto is higher.
 859         */
 860        tcp_bound_rto(sk);
 861}
 862
 863__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
 864{
 865        __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 866
 867        if (!cwnd)
 868                cwnd = TCP_INIT_CWND;
 869        return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 870}
 871
 872/* Take a notice that peer is sending D-SACKs */
 873static void tcp_dsack_seen(struct tcp_sock *tp)
 874{
 875        tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
 876        tp->rack.dsack_seen = 1;
 877        tp->dsack_dups++;
 878}
 879
 880/* It's reordering when higher sequence was delivered (i.e. sacked) before
 881 * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
 882 * distance is approximated in full-mss packet distance ("reordering").
 883 */
 884static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
 885                                      const int ts)
 886{
 887        struct tcp_sock *tp = tcp_sk(sk);
 888        const u32 mss = tp->mss_cache;
 889        u32 fack, metric;
 890
 891        fack = tcp_highest_sack_seq(tp);
 892        if (!before(low_seq, fack))
 893                return;
 894
 895        metric = fack - low_seq;
 896        if ((metric > tp->reordering * mss) && mss) {
 897#if FASTRETRANS_DEBUG > 1
 898                pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
 899                         tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
 900                         tp->reordering,
 901                         0,
 902                         tp->sacked_out,
 903                         tp->undo_marker ? tp->undo_retrans : 0);
 904#endif
 905                tp->reordering = min_t(u32, (metric + mss - 1) / mss,
 906                                       sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
 907        }
 908
 909        /* This exciting event is worth to be remembered. 8) */
 910        tp->reord_seen++;
 911        NET_INC_STATS(sock_net(sk),
 912                      ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
 913}
 914
 915/* This must be called before lost_out is incremented */
 916static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
 917{
 918        if (!tp->retransmit_skb_hint ||
 919            before(TCP_SKB_CB(skb)->seq,
 920                   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
 921                tp->retransmit_skb_hint = skb;
 922}
 923
 924/* Sum the number of packets on the wire we have marked as lost.
 925 * There are two cases we care about here:
 926 * a) Packet hasn't been marked lost (nor retransmitted),
 927 *    and this is the first loss.
 928 * b) Packet has been marked both lost and retransmitted,
 929 *    and this means we think it was lost again.
 930 */
 931static void tcp_sum_lost(struct tcp_sock *tp, struct sk_buff *skb)
 932{
 933        __u8 sacked = TCP_SKB_CB(skb)->sacked;
 934
 935        if (!(sacked & TCPCB_LOST) ||
 936            ((sacked & TCPCB_LOST) && (sacked & TCPCB_SACKED_RETRANS)))
 937                tp->lost += tcp_skb_pcount(skb);
 938}
 939
 940static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
 941{
 942        if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
 943                tcp_verify_retransmit_hint(tp, skb);
 944
 945                tp->lost_out += tcp_skb_pcount(skb);
 946                tcp_sum_lost(tp, skb);
 947                TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 948        }
 949}
 950
 951void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
 952{
 953        tcp_verify_retransmit_hint(tp, skb);
 954
 955        tcp_sum_lost(tp, skb);
 956        if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
 957                tp->lost_out += tcp_skb_pcount(skb);
 958                TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 959        }
 960}
 961
 962/* This procedure tags the retransmission queue when SACKs arrive.
 963 *
 964 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
 965 * Packets in queue with these bits set are counted in variables
 966 * sacked_out, retrans_out and lost_out, correspondingly.
 967 *
 968 * Valid combinations are:
 969 * Tag  InFlight        Description
 970 * 0    1               - orig segment is in flight.
 971 * S    0               - nothing flies, orig reached receiver.
 972 * L    0               - nothing flies, orig lost by net.
 973 * R    2               - both orig and retransmit are in flight.
 974 * L|R  1               - orig is lost, retransmit is in flight.
 975 * S|R  1               - orig reached receiver, retrans is still in flight.
 976 * (L|S|R is logically valid, it could occur when L|R is sacked,
 977 *  but it is equivalent to plain S and code short-curcuits it to S.
 978 *  L|S is logically invalid, it would mean -1 packet in flight 8))
 979 *
 980 * These 6 states form finite state machine, controlled by the following events:
 981 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
 982 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
 983 * 3. Loss detection event of two flavors:
 984 *      A. Scoreboard estimator decided the packet is lost.
 985 *         A'. Reno "three dupacks" marks head of queue lost.
 986 *      B. SACK arrives sacking SND.NXT at the moment, when the
 987 *         segment was retransmitted.
 988 * 4. D-SACK added new rule: D-SACK changes any tag to S.
 989 *
 990 * It is pleasant to note, that state diagram turns out to be commutative,
 991 * so that we are allowed not to be bothered by order of our actions,
 992 * when multiple events arrive simultaneously. (see the function below).
 993 *
 994 * Reordering detection.
 995 * --------------------
 996 * Reordering metric is maximal distance, which a packet can be displaced
 997 * in packet stream. With SACKs we can estimate it:
 998 *
 999 * 1. SACK fills old hole and the corresponding segment was not
1000 *    ever retransmitted -> reordering. Alas, we cannot use it
1001 *    when segment was retransmitted.
1002 * 2. The last flaw is solved with D-SACK. D-SACK arrives
1003 *    for retransmitted and already SACKed segment -> reordering..
1004 * Both of these heuristics are not used in Loss state, when we cannot
1005 * account for retransmits accurately.
1006 *
1007 * SACK block validation.
1008 * ----------------------
1009 *
1010 * SACK block range validation checks that the received SACK block fits to
1011 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1012 * Note that SND.UNA is not included to the range though being valid because
1013 * it means that the receiver is rather inconsistent with itself reporting
1014 * SACK reneging when it should advance SND.UNA. Such SACK block this is
1015 * perfectly valid, however, in light of RFC2018 which explicitly states
1016 * that "SACK block MUST reflect the newest segment.  Even if the newest
1017 * segment is going to be discarded ...", not that it looks very clever
1018 * in case of head skb. Due to potentional receiver driven attacks, we
1019 * choose to avoid immediate execution of a walk in write queue due to
1020 * reneging and defer head skb's loss recovery to standard loss recovery
1021 * procedure that will eventually trigger (nothing forbids us doing this).
1022 *
1023 * Implements also blockage to start_seq wrap-around. Problem lies in the
1024 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1025 * there's no guarantee that it will be before snd_nxt (n). The problem
1026 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1027 * wrap (s_w):
1028 *
1029 *         <- outs wnd ->                          <- wrapzone ->
1030 *         u     e      n                         u_w   e_w  s n_w
1031 *         |     |      |                          |     |   |  |
1032 * |<------------+------+----- TCP seqno space --------------+---------->|
1033 * ...-- <2^31 ->|                                           |<--------...
1034 * ...---- >2^31 ------>|                                    |<--------...
1035 *
1036 * Current code wouldn't be vulnerable but it's better still to discard such
1037 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1038 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1039 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1040 * equal to the ideal case (infinite seqno space without wrap caused issues).
1041 *
1042 * With D-SACK the lower bound is extended to cover sequence space below
1043 * SND.UNA down to undo_marker, which is the last point of interest. Yet
1044 * again, D-SACK block must not to go across snd_una (for the same reason as
1045 * for the normal SACK blocks, explained above). But there all simplicity
1046 * ends, TCP might receive valid D-SACKs below that. As long as they reside
1047 * fully below undo_marker they do not affect behavior in anyway and can
1048 * therefore be safely ignored. In rare cases (which are more or less
1049 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1050 * fragmentation and packet reordering past skb's retransmission. To consider
1051 * them correctly, the acceptable range must be extended even more though
1052 * the exact amount is rather hard to quantify. However, tp->max_window can
1053 * be used as an exaggerated estimate.
1054 */
1055static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1056                                   u32 start_seq, u32 end_seq)
1057{
1058        /* Too far in future, or reversed (interpretation is ambiguous) */
1059        if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1060                return false;
1061
1062        /* Nasty start_seq wrap-around check (see comments above) */
1063        if (!before(start_seq, tp->snd_nxt))
1064                return false;
1065
1066        /* In outstanding window? ...This is valid exit for D-SACKs too.
1067         * start_seq == snd_una is non-sensical (see comments above)
1068         */
1069        if (after(start_seq, tp->snd_una))
1070                return true;
1071
1072        if (!is_dsack || !tp->undo_marker)
1073                return false;
1074
1075        /* ...Then it's D-SACK, and must reside below snd_una completely */
1076        if (after(end_seq, tp->snd_una))
1077                return false;
1078
1079        if (!before(start_seq, tp->undo_marker))
1080                return true;
1081
1082        /* Too old */
1083        if (!after(end_seq, tp->undo_marker))
1084                return false;
1085
1086        /* Undo_marker boundary crossing (overestimates a lot). Known already:
1087         *   start_seq < undo_marker and end_seq >= undo_marker.
1088         */
1089        return !before(start_seq, end_seq - tp->max_window);
1090}
1091
1092static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1093                            struct tcp_sack_block_wire *sp, int num_sacks,
1094                            u32 prior_snd_una)
1095{
1096        struct tcp_sock *tp = tcp_sk(sk);
1097        u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1098        u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1099        bool dup_sack = false;
1100
1101        if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1102                dup_sack = true;
1103                tcp_dsack_seen(tp);
1104                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1105        } else if (num_sacks > 1) {
1106                u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1107                u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1108
1109                if (!after(end_seq_0, end_seq_1) &&
1110                    !before(start_seq_0, start_seq_1)) {
1111                        dup_sack = true;
1112                        tcp_dsack_seen(tp);
1113                        NET_INC_STATS(sock_net(sk),
1114                                        LINUX_MIB_TCPDSACKOFORECV);
1115                }
1116        }
1117
1118        /* D-SACK for already forgotten data... Do dumb counting. */
1119        if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
1120            !after(end_seq_0, prior_snd_una) &&
1121            after(end_seq_0, tp->undo_marker))
1122                tp->undo_retrans--;
1123
1124        return dup_sack;
1125}
1126
1127struct tcp_sacktag_state {
1128        u32     reord;
1129        /* Timestamps for earliest and latest never-retransmitted segment
1130         * that was SACKed. RTO needs the earliest RTT to stay conservative,
1131         * but congestion control should still get an accurate delay signal.
1132         */
1133        u64     first_sackt;
1134        u64     last_sackt;
1135        struct rate_sample *rate;
1136        int     flag;
1137        unsigned int mss_now;
1138};
1139
1140/* Check if skb is fully within the SACK block. In presence of GSO skbs,
1141 * the incoming SACK may not exactly match but we can find smaller MSS
1142 * aligned portion of it that matches. Therefore we might need to fragment
1143 * which may fail and creates some hassle (caller must handle error case
1144 * returns).
1145 *
1146 * FIXME: this could be merged to shift decision code
1147 */
1148static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1149                                  u32 start_seq, u32 end_seq)
1150{
1151        int err;
1152        bool in_sack;
1153        unsigned int pkt_len;
1154        unsigned int mss;
1155
1156        in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1157                  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1158
1159        if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1160            after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1161                mss = tcp_skb_mss(skb);
1162                in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1163
1164                if (!in_sack) {
1165                        pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1166                        if (pkt_len < mss)
1167                                pkt_len = mss;
1168                } else {
1169                        pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1170                        if (pkt_len < mss)
1171                                return -EINVAL;
1172                }
1173
1174                /* Round if necessary so that SACKs cover only full MSSes
1175                 * and/or the remaining small portion (if present)
1176                 */
1177                if (pkt_len > mss) {
1178                        unsigned int new_len = (pkt_len / mss) * mss;
1179                        if (!in_sack && new_len < pkt_len)
1180                                new_len += mss;
1181                        pkt_len = new_len;
1182                }
1183
1184                if (pkt_len >= skb->len && !in_sack)
1185                        return 0;
1186
1187                err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
1188                                   pkt_len, mss, GFP_ATOMIC);
1189                if (err < 0)
1190                        return err;
1191        }
1192
1193        return in_sack;
1194}
1195
1196/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1197static u8 tcp_sacktag_one(struct sock *sk,
1198                          struct tcp_sacktag_state *state, u8 sacked,
1199                          u32 start_seq, u32 end_seq,
1200                          int dup_sack, int pcount,
1201                          u64 xmit_time)
1202{
1203        struct tcp_sock *tp = tcp_sk(sk);
1204
1205        /* Account D-SACK for retransmitted packet. */
1206        if (dup_sack && (sacked & TCPCB_RETRANS)) {
1207                if (tp->undo_marker && tp->undo_retrans > 0 &&
1208                    after(end_seq, tp->undo_marker))
1209                        tp->undo_retrans--;
1210                if ((sacked & TCPCB_SACKED_ACKED) &&
1211                    before(start_seq, state->reord))
1212                                state->reord = start_seq;
1213        }
1214
1215        /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1216        if (!after(end_seq, tp->snd_una))
1217                return sacked;
1218
1219        if (!(sacked & TCPCB_SACKED_ACKED)) {
1220                tcp_rack_advance(tp, sacked, end_seq, xmit_time);
1221
1222                if (sacked & TCPCB_SACKED_RETRANS) {
1223                        /* If the segment is not tagged as lost,
1224                         * we do not clear RETRANS, believing
1225                         * that retransmission is still in flight.
1226                         */
1227                        if (sacked & TCPCB_LOST) {
1228                                sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1229                                tp->lost_out -= pcount;
1230                                tp->retrans_out -= pcount;
1231                        }
1232                } else {
1233                        if (!(sacked & TCPCB_RETRANS)) {
1234                                /* New sack for not retransmitted frame,
1235                                 * which was in hole. It is reordering.
1236                                 */
1237                                if (before(start_seq,
1238                                           tcp_highest_sack_seq(tp)) &&
1239                                    before(start_seq, state->reord))
1240                                        state->reord = start_seq;
1241
1242                                if (!after(end_seq, tp->high_seq))
1243                                        state->flag |= FLAG_ORIG_SACK_ACKED;
1244                                if (state->first_sackt == 0)
1245                                        state->first_sackt = xmit_time;
1246                                state->last_sackt = xmit_time;
1247                        }
1248
1249                        if (sacked & TCPCB_LOST) {
1250                                sacked &= ~TCPCB_LOST;
1251                                tp->lost_out -= pcount;
1252                        }
1253                }
1254
1255                sacked |= TCPCB_SACKED_ACKED;
1256                state->flag |= FLAG_DATA_SACKED;
1257                tp->sacked_out += pcount;
1258                tp->delivered += pcount;  /* Out-of-order packets delivered */
1259
1260                /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1261                if (tp->lost_skb_hint &&
1262                    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1263                        tp->lost_cnt_hint += pcount;
1264        }
1265
1266        /* D-SACK. We can detect redundant retransmission in S|R and plain R
1267         * frames and clear it. undo_retrans is decreased above, L|R frames
1268         * are accounted above as well.
1269         */
1270        if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1271                sacked &= ~TCPCB_SACKED_RETRANS;
1272                tp->retrans_out -= pcount;
1273        }
1274
1275        return sacked;
1276}
1277
1278/* Shift newly-SACKed bytes from this skb to the immediately previous
1279 * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1280 */
1281static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
1282                            struct sk_buff *skb,
1283                            struct tcp_sacktag_state *state,
1284                            unsigned int pcount, int shifted, int mss,
1285                            bool dup_sack)
1286{
1287        struct tcp_sock *tp = tcp_sk(sk);
1288        u32 start_seq = TCP_SKB_CB(skb)->seq;   /* start of newly-SACKed */
1289        u32 end_seq = start_seq + shifted;      /* end of newly-SACKed */
1290
1291        BUG_ON(!pcount);
1292
1293        /* Adjust counters and hints for the newly sacked sequence
1294         * range but discard the return value since prev is already
1295         * marked. We must tag the range first because the seq
1296         * advancement below implicitly advances
1297         * tcp_highest_sack_seq() when skb is highest_sack.
1298         */
1299        tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1300                        start_seq, end_seq, dup_sack, pcount,
1301                        tcp_skb_timestamp_us(skb));
1302        tcp_rate_skb_delivered(sk, skb, state->rate);
1303
1304        if (skb == tp->lost_skb_hint)
1305                tp->lost_cnt_hint += pcount;
1306
1307        TCP_SKB_CB(prev)->end_seq += shifted;
1308        TCP_SKB_CB(skb)->seq += shifted;
1309
1310        tcp_skb_pcount_add(prev, pcount);
1311        WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
1312        tcp_skb_pcount_add(skb, -pcount);
1313
1314        /* When we're adding to gso_segs == 1, gso_size will be zero,
1315         * in theory this shouldn't be necessary but as long as DSACK
1316         * code can come after this skb later on it's better to keep
1317         * setting gso_size to something.
1318         */
1319        if (!TCP_SKB_CB(prev)->tcp_gso_size)
1320                TCP_SKB_CB(prev)->tcp_gso_size = mss;
1321
1322        /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1323        if (tcp_skb_pcount(skb) <= 1)
1324                TCP_SKB_CB(skb)->tcp_gso_size = 0;
1325
1326        /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1327        TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1328
1329        if (skb->len > 0) {
1330                BUG_ON(!tcp_skb_pcount(skb));
1331                NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1332                return false;
1333        }
1334
1335        /* Whole SKB was eaten :-) */
1336
1337        if (skb == tp->retransmit_skb_hint)
1338                tp->retransmit_skb_hint = prev;
1339        if (skb == tp->lost_skb_hint) {
1340                tp->lost_skb_hint = prev;
1341                tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1342        }
1343
1344        TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1345        TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
1346        if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1347                TCP_SKB_CB(prev)->end_seq++;
1348
1349        if (skb == tcp_highest_sack(sk))
1350                tcp_advance_highest_sack(sk, skb);
1351
1352        tcp_skb_collapse_tstamp(prev, skb);
1353        if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
1354                TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
1355
1356        tcp_rtx_queue_unlink_and_free(skb, sk);
1357
1358        NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
1359
1360        return true;
1361}
1362
1363/* I wish gso_size would have a bit more sane initialization than
1364 * something-or-zero which complicates things
1365 */
1366static int tcp_skb_seglen(const struct sk_buff *skb)
1367{
1368        return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1369}
1370
1371/* Shifting pages past head area doesn't work */
1372static int skb_can_shift(const struct sk_buff *skb)
1373{
1374        return !skb_headlen(skb) && skb_is_nonlinear(skb);
1375}
1376
1377int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from,
1378                  int pcount, int shiftlen)
1379{
1380        /* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE)
1381         * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need
1382         * to make sure not storing more than 65535 * 8 bytes per skb,
1383         * even if current MSS is bigger.
1384         */
1385        if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE))
1386                return 0;
1387        if (unlikely(tcp_skb_pcount(to) + pcount > 65535))
1388                return 0;
1389        return skb_shift(to, from, shiftlen);
1390}
1391
1392/* Try collapsing SACK blocks spanning across multiple skbs to a single
1393 * skb.
1394 */
1395static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1396                                          struct tcp_sacktag_state *state,
1397                                          u32 start_seq, u32 end_seq,
1398                                          bool dup_sack)
1399{
1400        struct tcp_sock *tp = tcp_sk(sk);
1401        struct sk_buff *prev;
1402        int mss;
1403        int pcount = 0;
1404        int len;
1405        int in_sack;
1406
1407        /* Normally R but no L won't result in plain S */
1408        if (!dup_sack &&
1409            (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1410                goto fallback;
1411        if (!skb_can_shift(skb))
1412                goto fallback;
1413        /* This frame is about to be dropped (was ACKed). */
1414        if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1415                goto fallback;
1416
1417        /* Can only happen with delayed DSACK + discard craziness */
1418        prev = skb_rb_prev(skb);
1419        if (!prev)
1420                goto fallback;
1421
1422        if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1423                goto fallback;
1424
1425        if (!tcp_skb_can_collapse_to(prev))
1426                goto fallback;
1427
1428        in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1429                  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1430
1431        if (in_sack) {
1432                len = skb->len;
1433                pcount = tcp_skb_pcount(skb);
1434                mss = tcp_skb_seglen(skb);
1435
1436                /* TODO: Fix DSACKs to not fragment already SACKed and we can
1437                 * drop this restriction as unnecessary
1438                 */
1439                if (mss != tcp_skb_seglen(prev))
1440                        goto fallback;
1441        } else {
1442                if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1443                        goto noop;
1444                /* CHECKME: This is non-MSS split case only?, this will
1445                 * cause skipped skbs due to advancing loop btw, original
1446                 * has that feature too
1447                 */
1448                if (tcp_skb_pcount(skb) <= 1)
1449                        goto noop;
1450
1451                in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1452                if (!in_sack) {
1453                        /* TODO: head merge to next could be attempted here
1454                         * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1455                         * though it might not be worth of the additional hassle
1456                         *
1457                         * ...we can probably just fallback to what was done
1458                         * previously. We could try merging non-SACKed ones
1459                         * as well but it probably isn't going to buy off
1460                         * because later SACKs might again split them, and
1461                         * it would make skb timestamp tracking considerably
1462                         * harder problem.
1463                         */
1464                        goto fallback;
1465                }
1466
1467                len = end_seq - TCP_SKB_CB(skb)->seq;
1468                BUG_ON(len < 0);
1469                BUG_ON(len > skb->len);
1470
1471                /* MSS boundaries should be honoured or else pcount will
1472                 * severely break even though it makes things bit trickier.
1473                 * Optimize common case to avoid most of the divides
1474                 */
1475                mss = tcp_skb_mss(skb);
1476
1477                /* TODO: Fix DSACKs to not fragment already SACKed and we can
1478                 * drop this restriction as unnecessary
1479                 */
1480                if (mss != tcp_skb_seglen(prev))
1481                        goto fallback;
1482
1483                if (len == mss) {
1484                        pcount = 1;
1485                } else if (len < mss) {
1486                        goto noop;
1487                } else {
1488                        pcount = len / mss;
1489                        len = pcount * mss;
1490                }
1491        }
1492
1493        /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1494        if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1495                goto fallback;
1496
1497        if (!tcp_skb_shift(prev, skb, pcount, len))
1498                goto fallback;
1499        if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
1500                goto out;
1501
1502        /* Hole filled allows collapsing with the next as well, this is very
1503         * useful when hole on every nth skb pattern happens
1504         */
1505        skb = skb_rb_next(prev);
1506        if (!skb)
1507                goto out;
1508
1509        if (!skb_can_shift(skb) ||
1510            ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1511            (mss != tcp_skb_seglen(skb)))
1512                goto out;
1513
1514        len = skb->len;
1515        pcount = tcp_skb_pcount(skb);
1516        if (tcp_skb_shift(prev, skb, pcount, len))
1517                tcp_shifted_skb(sk, prev, skb, state, pcount,
1518                                len, mss, 0);
1519
1520out:
1521        return prev;
1522
1523noop:
1524        return skb;
1525
1526fallback:
1527        NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1528        return NULL;
1529}
1530
1531static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1532                                        struct tcp_sack_block *next_dup,
1533                                        struct tcp_sacktag_state *state,
1534                                        u32 start_seq, u32 end_seq,
1535                                        bool dup_sack_in)
1536{
1537        struct tcp_sock *tp = tcp_sk(sk);
1538        struct sk_buff *tmp;
1539
1540        skb_rbtree_walk_from(skb) {
1541                int in_sack = 0;
1542                bool dup_sack = dup_sack_in;
1543
1544                /* queue is in-order => we can short-circuit the walk early */
1545                if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1546                        break;
1547
1548                if (next_dup  &&
1549                    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1550                        in_sack = tcp_match_skb_to_sack(sk, skb,
1551                                                        next_dup->start_seq,
1552                                                        next_dup->end_seq);
1553                        if (in_sack > 0)
1554                                dup_sack = true;
1555                }
1556
1557                /* skb reference here is a bit tricky to get right, since
1558                 * shifting can eat and free both this skb and the next,
1559                 * so not even _safe variant of the loop is enough.
1560                 */
1561                if (in_sack <= 0) {
1562                        tmp = tcp_shift_skb_data(sk, skb, state,
1563                                                 start_seq, end_seq, dup_sack);
1564                        if (tmp) {
1565                                if (tmp != skb) {
1566                                        skb = tmp;
1567                                        continue;
1568                                }
1569
1570                                in_sack = 0;
1571                        } else {
1572                                in_sack = tcp_match_skb_to_sack(sk, skb,
1573                                                                start_seq,
1574                                                                end_seq);
1575                        }
1576                }
1577
1578                if (unlikely(in_sack < 0))
1579                        break;
1580
1581                if (in_sack) {
1582                        TCP_SKB_CB(skb)->sacked =
1583                                tcp_sacktag_one(sk,
1584                                                state,
1585                                                TCP_SKB_CB(skb)->sacked,
1586                                                TCP_SKB_CB(skb)->seq,
1587                                                TCP_SKB_CB(skb)->end_seq,
1588                                                dup_sack,
1589                                                tcp_skb_pcount(skb),
1590                                                tcp_skb_timestamp_us(skb));
1591                        tcp_rate_skb_delivered(sk, skb, state->rate);
1592                        if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1593                                list_del_init(&skb->tcp_tsorted_anchor);
1594
1595                        if (!before(TCP_SKB_CB(skb)->seq,
1596                                    tcp_highest_sack_seq(tp)))
1597                                tcp_advance_highest_sack(sk, skb);
1598                }
1599        }
1600        return skb;
1601}
1602
1603static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
1604{
1605        struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
1606        struct sk_buff *skb;
1607
1608        while (*p) {
1609                parent = *p;
1610                skb = rb_to_skb(parent);
1611                if (before(seq, TCP_SKB_CB(skb)->seq)) {
1612                        p = &parent->rb_left;
1613                        continue;
1614                }
1615                if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
1616                        p = &parent->rb_right;
1617                        continue;
1618                }
1619                return skb;
1620        }
1621        return NULL;
1622}
1623
1624static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1625                                        u32 skip_to_seq)
1626{
1627        if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
1628                return skb;
1629
1630        return tcp_sacktag_bsearch(sk, skip_to_seq);
1631}
1632
1633static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1634                                                struct sock *sk,
1635                                                struct tcp_sack_block *next_dup,
1636                                                struct tcp_sacktag_state *state,
1637                                                u32 skip_to_seq)
1638{
1639        if (!next_dup)
1640                return skb;
1641
1642        if (before(next_dup->start_seq, skip_to_seq)) {
1643                skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
1644                skb = tcp_sacktag_walk(skb, sk, NULL, state,
1645                                       next_dup->start_seq, next_dup->end_seq,
1646                                       1);
1647        }
1648
1649        return skb;
1650}
1651
1652static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1653{
1654        return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1655}
1656
1657static int
1658tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1659                        u32 prior_snd_una, struct tcp_sacktag_state *state)
1660{
1661        struct tcp_sock *tp = tcp_sk(sk);
1662        const unsigned char *ptr = (skb_transport_header(ack_skb) +
1663                                    TCP_SKB_CB(ack_skb)->sacked);
1664        struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1665        struct tcp_sack_block sp[TCP_NUM_SACKS];
1666        struct tcp_sack_block *cache;
1667        struct sk_buff *skb;
1668        int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1669        int used_sacks;
1670        bool found_dup_sack = false;
1671        int i, j;
1672        int first_sack_index;
1673
1674        state->flag = 0;
1675        state->reord = tp->snd_nxt;
1676
1677        if (!tp->sacked_out)
1678                tcp_highest_sack_reset(sk);
1679
1680        found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1681                                         num_sacks, prior_snd_una);
1682        if (found_dup_sack) {
1683                state->flag |= FLAG_DSACKING_ACK;
1684                tp->delivered++; /* A spurious retransmission is delivered */
1685        }
1686
1687        /* Eliminate too old ACKs, but take into
1688         * account more or less fresh ones, they can
1689         * contain valid SACK info.
1690         */
1691        if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1692                return 0;
1693
1694        if (!tp->packets_out)
1695                goto out;
1696
1697        used_sacks = 0;
1698        first_sack_index = 0;
1699        for (i = 0; i < num_sacks; i++) {
1700                bool dup_sack = !i && found_dup_sack;
1701
1702                sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1703                sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1704
1705                if (!tcp_is_sackblock_valid(tp, dup_sack,
1706                                            sp[used_sacks].start_seq,
1707                                            sp[used_sacks].end_seq)) {
1708                        int mib_idx;
1709
1710                        if (dup_sack) {
1711                                if (!tp->undo_marker)
1712                                        mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1713                                else
1714                                        mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1715                        } else {
1716                                /* Don't count olds caused by ACK reordering */
1717                                if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1718                                    !after(sp[used_sacks].end_seq, tp->snd_una))
1719                                        continue;
1720                                mib_idx = LINUX_MIB_TCPSACKDISCARD;
1721                        }
1722
1723                        NET_INC_STATS(sock_net(sk), mib_idx);
1724                        if (i == 0)
1725                                first_sack_index = -1;
1726                        continue;
1727                }
1728
1729                /* Ignore very old stuff early */
1730                if (!after(sp[used_sacks].end_seq, prior_snd_una))
1731                        continue;
1732
1733                used_sacks++;
1734        }
1735
1736        /* order SACK blocks to allow in order walk of the retrans queue */
1737        for (i = used_sacks - 1; i > 0; i--) {
1738                for (j = 0; j < i; j++) {
1739                        if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1740                                swap(sp[j], sp[j + 1]);
1741
1742                                /* Track where the first SACK block goes to */
1743                                if (j == first_sack_index)
1744                                        first_sack_index = j + 1;
1745                        }
1746                }
1747        }
1748
1749        state->mss_now = tcp_current_mss(sk);
1750        skb = NULL;
1751        i = 0;
1752
1753        if (!tp->sacked_out) {
1754                /* It's already past, so skip checking against it */
1755                cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1756        } else {
1757                cache = tp->recv_sack_cache;
1758                /* Skip empty blocks in at head of the cache */
1759                while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1760                       !cache->end_seq)
1761                        cache++;
1762        }
1763
1764        while (i < used_sacks) {
1765                u32 start_seq = sp[i].start_seq;
1766                u32 end_seq = sp[i].end_seq;
1767                bool dup_sack = (found_dup_sack && (i == first_sack_index));
1768                struct tcp_sack_block *next_dup = NULL;
1769
1770                if (found_dup_sack && ((i + 1) == first_sack_index))
1771                        next_dup = &sp[i + 1];
1772
1773                /* Skip too early cached blocks */
1774                while (tcp_sack_cache_ok(tp, cache) &&
1775                       !before(start_seq, cache->end_seq))
1776                        cache++;
1777
1778                /* Can skip some work by looking recv_sack_cache? */
1779                if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1780                    after(end_seq, cache->start_seq)) {
1781
1782                        /* Head todo? */
1783                        if (before(start_seq, cache->start_seq)) {
1784                                skb = tcp_sacktag_skip(skb, sk, start_seq);
1785                                skb = tcp_sacktag_walk(skb, sk, next_dup,
1786                                                       state,
1787                                                       start_seq,
1788                                                       cache->start_seq,
1789                                                       dup_sack);
1790                        }
1791
1792                        /* Rest of the block already fully processed? */
1793                        if (!after(end_seq, cache->end_seq))
1794                                goto advance_sp;
1795
1796                        skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1797                                                       state,
1798                                                       cache->end_seq);
1799
1800                        /* ...tail remains todo... */
1801                        if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1802                                /* ...but better entrypoint exists! */
1803                                skb = tcp_highest_sack(sk);
1804                                if (!skb)
1805                                        break;
1806                                cache++;
1807                                goto walk;
1808                        }
1809
1810                        skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
1811                        /* Check overlap against next cached too (past this one already) */
1812                        cache++;
1813                        continue;
1814                }
1815
1816                if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1817                        skb = tcp_highest_sack(sk);
1818                        if (!skb)
1819                                break;
1820                }
1821                skb = tcp_sacktag_skip(skb, sk, start_seq);
1822
1823walk:
1824                skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1825                                       start_seq, end_seq, dup_sack);
1826
1827advance_sp:
1828                i++;
1829        }
1830
1831        /* Clear the head of the cache sack blocks so we can skip it next time */
1832        for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1833                tp->recv_sack_cache[i].start_seq = 0;
1834                tp->recv_sack_cache[i].end_seq = 0;
1835        }
1836        for (j = 0; j < used_sacks; j++)
1837                tp->recv_sack_cache[i++] = sp[j];
1838
1839        if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
1840                tcp_check_sack_reordering(sk, state->reord, 0);
1841
1842        tcp_verify_left_out(tp);
1843out:
1844
1845#if FASTRETRANS_DEBUG > 0
1846        WARN_ON((int)tp->sacked_out < 0);
1847        WARN_ON((int)tp->lost_out < 0);
1848        WARN_ON((int)tp->retrans_out < 0);
1849        WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1850#endif
1851        return state->flag;
1852}
1853
1854/* Limits sacked_out so that sum with lost_out isn't ever larger than
1855 * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1856 */
1857static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1858{
1859        u32 holes;
1860
1861        holes = max(tp->lost_out, 1U);
1862        holes = min(holes, tp->packets_out);
1863
1864        if ((tp->sacked_out + holes) > tp->packets_out) {
1865                tp->sacked_out = tp->packets_out - holes;
1866                return true;
1867        }
1868        return false;
1869}
1870
1871/* If we receive more dupacks than we expected counting segments
1872 * in assumption of absent reordering, interpret this as reordering.
1873 * The only another reason could be bug in receiver TCP.
1874 */
1875static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1876{
1877        struct tcp_sock *tp = tcp_sk(sk);
1878
1879        if (!tcp_limit_reno_sacked(tp))
1880                return;
1881
1882        tp->reordering = min_t(u32, tp->packets_out + addend,
1883                               sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
1884        tp->reord_seen++;
1885        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
1886}
1887
1888/* Emulate SACKs for SACKless connection: account for a new dupack. */
1889
1890static void tcp_add_reno_sack(struct sock *sk, int num_dupack)
1891{
1892        if (num_dupack) {
1893                struct tcp_sock *tp = tcp_sk(sk);
1894                u32 prior_sacked = tp->sacked_out;
1895                s32 delivered;
1896
1897                tp->sacked_out += num_dupack;
1898                tcp_check_reno_reordering(sk, 0);
1899                delivered = tp->sacked_out - prior_sacked;
1900                if (delivered > 0)
1901                        tp->delivered += delivered;
1902                tcp_verify_left_out(tp);
1903        }
1904}
1905
1906/* Account for ACK, ACKing some data in Reno Recovery phase. */
1907
1908static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1909{
1910        struct tcp_sock *tp = tcp_sk(sk);
1911
1912        if (acked > 0) {
1913                /* One ACK acked hole. The rest eat duplicate ACKs. */
1914                tp->delivered += max_t(int, acked - tp->sacked_out, 1);
1915                if (acked - 1 >= tp->sacked_out)
1916                        tp->sacked_out = 0;
1917                else
1918                        tp->sacked_out -= acked - 1;
1919        }
1920        tcp_check_reno_reordering(sk, acked);
1921        tcp_verify_left_out(tp);
1922}
1923
1924static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1925{
1926        tp->sacked_out = 0;
1927}
1928
1929void tcp_clear_retrans(struct tcp_sock *tp)
1930{
1931        tp->retrans_out = 0;
1932        tp->lost_out = 0;
1933        tp->undo_marker = 0;
1934        tp->undo_retrans = -1;
1935        tp->sacked_out = 0;
1936}
1937
1938static inline void tcp_init_undo(struct tcp_sock *tp)
1939{
1940        tp->undo_marker = tp->snd_una;
1941        /* Retransmission still in flight may cause DSACKs later. */
1942        tp->undo_retrans = tp->retrans_out ? : -1;
1943}
1944
1945static bool tcp_is_rack(const struct sock *sk)
1946{
1947        return sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION;
1948}
1949
1950/* If we detect SACK reneging, forget all SACK information
1951 * and reset tags completely, otherwise preserve SACKs. If receiver
1952 * dropped its ofo queue, we will know this due to reneging detection.
1953 */
1954static void tcp_timeout_mark_lost(struct sock *sk)
1955{
1956        struct tcp_sock *tp = tcp_sk(sk);
1957        struct sk_buff *skb, *head;
1958        bool is_reneg;                  /* is receiver reneging on SACKs? */
1959
1960        head = tcp_rtx_queue_head(sk);
1961        is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
1962        if (is_reneg) {
1963                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
1964                tp->sacked_out = 0;
1965                /* Mark SACK reneging until we recover from this loss event. */
1966                tp->is_sack_reneg = 1;
1967        } else if (tcp_is_reno(tp)) {
1968                tcp_reset_reno_sack(tp);
1969        }
1970
1971        skb = head;
1972        skb_rbtree_walk_from(skb) {
1973                if (is_reneg)
1974                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1975                else if (tcp_is_rack(sk) && skb != head &&
1976                         tcp_rack_skb_timeout(tp, skb, 0) > 0)
1977                        continue; /* Don't mark recently sent ones lost yet */
1978                tcp_mark_skb_lost(sk, skb);
1979        }
1980        tcp_verify_left_out(tp);
1981        tcp_clear_all_retrans_hints(tp);
1982}
1983
1984/* Enter Loss state. */
1985void tcp_enter_loss(struct sock *sk)
1986{
1987        const struct inet_connection_sock *icsk = inet_csk(sk);
1988        struct tcp_sock *tp = tcp_sk(sk);
1989        struct net *net = sock_net(sk);
1990        bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
1991
1992        tcp_timeout_mark_lost(sk);
1993
1994        /* Reduce ssthresh if it has not yet been made inside this window. */
1995        if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1996            !after(tp->high_seq, tp->snd_una) ||
1997            (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1998                tp->prior_ssthresh = tcp_current_ssthresh(sk);
1999                tp->prior_cwnd = tp->snd_cwnd;
2000                tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2001                tcp_ca_event(sk, CA_EVENT_LOSS);
2002                tcp_init_undo(tp);
2003        }
2004        tp->snd_cwnd       = tcp_packets_in_flight(tp) + 1;
2005        tp->snd_cwnd_cnt   = 0;
2006        tp->snd_cwnd_stamp = tcp_jiffies32;
2007
2008        /* Timeout in disordered state after receiving substantial DUPACKs
2009         * suggests that the degree of reordering is over-estimated.
2010         */
2011        if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
2012            tp->sacked_out >= net->ipv4.sysctl_tcp_reordering)
2013                tp->reordering = min_t(unsigned int, tp->reordering,
2014                                       net->ipv4.sysctl_tcp_reordering);
2015        tcp_set_ca_state(sk, TCP_CA_Loss);
2016        tp->high_seq = tp->snd_nxt;
2017        tcp_ecn_queue_cwr(tp);
2018
2019        /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
2020         * loss recovery is underway except recurring timeout(s) on
2021         * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
2022         */
2023        tp->frto = net->ipv4.sysctl_tcp_frto &&
2024                   (new_recovery || icsk->icsk_retransmits) &&
2025                   !inet_csk(sk)->icsk_mtup.probe_size;
2026}
2027
2028/* If ACK arrived pointing to a remembered SACK, it means that our
2029 * remembered SACKs do not reflect real state of receiver i.e.
2030 * receiver _host_ is heavily congested (or buggy).
2031 *
2032 * To avoid big spurious retransmission bursts due to transient SACK
2033 * scoreboard oddities that look like reneging, we give the receiver a
2034 * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
2035 * restore sanity to the SACK scoreboard. If the apparent reneging
2036 * persists until this RTO then we'll clear the SACK scoreboard.
2037 */
2038static bool tcp_check_sack_reneging(struct sock *sk, int flag)
2039{
2040        if (flag & FLAG_SACK_RENEGING) {
2041                struct tcp_sock *tp = tcp_sk(sk);
2042                unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2043                                          msecs_to_jiffies(10));
2044
2045                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2046                                          delay, TCP_RTO_MAX);
2047                return true;
2048        }
2049        return false;
2050}
2051
2052/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2053 * counter when SACK is enabled (without SACK, sacked_out is used for
2054 * that purpose).
2055 *
2056 * With reordering, holes may still be in flight, so RFC3517 recovery
2057 * uses pure sacked_out (total number of SACKed segments) even though
2058 * it violates the RFC that uses duplicate ACKs, often these are equal
2059 * but when e.g. out-of-window ACKs or packet duplication occurs,
2060 * they differ. Since neither occurs due to loss, TCP should really
2061 * ignore them.
2062 */
2063static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2064{
2065        return tp->sacked_out + 1;
2066}
2067
2068/* Linux NewReno/SACK/ECN state machine.
2069 * --------------------------------------
2070 *
2071 * "Open"       Normal state, no dubious events, fast path.
2072 * "Disorder"   In all the respects it is "Open",
2073 *              but requires a bit more attention. It is entered when
2074 *              we see some SACKs or dupacks. It is split of "Open"
2075 *              mainly to move some processing from fast path to slow one.
2076 * "CWR"        CWND was reduced due to some Congestion Notification event.
2077 *              It can be ECN, ICMP source quench, local device congestion.
2078 * "Recovery"   CWND was reduced, we are fast-retransmitting.
2079 * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
2080 *
2081 * tcp_fastretrans_alert() is entered:
2082 * - each incoming ACK, if state is not "Open"
2083 * - when arrived ACK is unusual, namely:
2084 *      * SACK
2085 *      * Duplicate ACK.
2086 *      * ECN ECE.
2087 *
2088 * Counting packets in flight is pretty simple.
2089 *
2090 *      in_flight = packets_out - left_out + retrans_out
2091 *
2092 *      packets_out is SND.NXT-SND.UNA counted in packets.
2093 *
2094 *      retrans_out is number of retransmitted segments.
2095 *
2096 *      left_out is number of segments left network, but not ACKed yet.
2097 *
2098 *              left_out = sacked_out + lost_out
2099 *
2100 *     sacked_out: Packets, which arrived to receiver out of order
2101 *                 and hence not ACKed. With SACKs this number is simply
2102 *                 amount of SACKed data. Even without SACKs
2103 *                 it is easy to give pretty reliable estimate of this number,
2104 *                 counting duplicate ACKs.
2105 *
2106 *       lost_out: Packets lost by network. TCP has no explicit
2107 *                 "loss notification" feedback from network (for now).
2108 *                 It means that this number can be only _guessed_.
2109 *                 Actually, it is the heuristics to predict lossage that
2110 *                 distinguishes different algorithms.
2111 *
2112 *      F.e. after RTO, when all the queue is considered as lost,
2113 *      lost_out = packets_out and in_flight = retrans_out.
2114 *
2115 *              Essentially, we have now a few algorithms detecting
2116 *              lost packets.
2117 *
2118 *              If the receiver supports SACK:
2119 *
2120 *              RFC6675/3517: It is the conventional algorithm. A packet is
2121 *              considered lost if the number of higher sequence packets
2122 *              SACKed is greater than or equal the DUPACK thoreshold
2123 *              (reordering). This is implemented in tcp_mark_head_lost and
2124 *              tcp_update_scoreboard.
2125 *
2126 *              RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
2127 *              (2017-) that checks timing instead of counting DUPACKs.
2128 *              Essentially a packet is considered lost if it's not S/ACKed
2129 *              after RTT + reordering_window, where both metrics are
2130 *              dynamically measured and adjusted. This is implemented in
2131 *              tcp_rack_mark_lost.
2132 *
2133 *              If the receiver does not support SACK:
2134 *
2135 *              NewReno (RFC6582): in Recovery we assume that one segment
2136 *              is lost (classic Reno). While we are in Recovery and
2137 *              a partial ACK arrives, we assume that one more packet
2138 *              is lost (NewReno). This heuristics are the same in NewReno
2139 *              and SACK.
2140 *
2141 * Really tricky (and requiring careful tuning) part of algorithm
2142 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2143 * The first determines the moment _when_ we should reduce CWND and,
2144 * hence, slow down forward transmission. In fact, it determines the moment
2145 * when we decide that hole is caused by loss, rather than by a reorder.
2146 *
2147 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2148 * holes, caused by lost packets.
2149 *
2150 * And the most logically complicated part of algorithm is undo
2151 * heuristics. We detect false retransmits due to both too early
2152 * fast retransmit (reordering) and underestimated RTO, analyzing
2153 * timestamps and D-SACKs. When we detect that some segments were
2154 * retransmitted by mistake and CWND reduction was wrong, we undo
2155 * window reduction and abort recovery phase. This logic is hidden
2156 * inside several functions named tcp_try_undo_<something>.
2157 */
2158
2159/* This function decides, when we should leave Disordered state
2160 * and enter Recovery phase, reducing congestion window.
2161 *
2162 * Main question: may we further continue forward transmission
2163 * with the same cwnd?
2164 */
2165static bool tcp_time_to_recover(struct sock *sk, int flag)
2166{
2167        struct tcp_sock *tp = tcp_sk(sk);
2168
2169        /* Trick#1: The loss is proven. */
2170        if (tp->lost_out)
2171                return true;
2172
2173        /* Not-A-Trick#2 : Classic rule... */
2174        if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
2175                return true;
2176
2177        return false;
2178}
2179
2180/* Detect loss in event "A" above by marking head of queue up as lost.
2181 * For non-SACK(Reno) senders, the first "packets" number of segments
2182 * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2183 * has at least tp->reordering SACKed seqments above it; "packets" refers to
2184 * the maximum SACKed segments to pass before reaching this limit.
2185 */
2186static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2187{
2188        struct tcp_sock *tp = tcp_sk(sk);
2189        struct sk_buff *skb;
2190        int cnt, oldcnt, lost;
2191        unsigned int mss;
2192        /* Use SACK to deduce losses of new sequences sent during recovery */
2193        const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;
2194
2195        WARN_ON(packets > tp->packets_out);
2196        skb = tp->lost_skb_hint;
2197        if (skb) {
2198                /* Head already handled? */
2199                if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
2200                        return;
2201                cnt = tp->lost_cnt_hint;
2202        } else {
2203                skb = tcp_rtx_queue_head(sk);
2204                cnt = 0;
2205        }
2206
2207        skb_rbtree_walk_from(skb) {
2208                /* TODO: do this better */
2209                /* this is not the most efficient way to do this... */
2210                tp->lost_skb_hint = skb;
2211                tp->lost_cnt_hint = cnt;
2212
2213                if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2214                        break;
2215
2216                oldcnt = cnt;
2217                if (tcp_is_reno(tp) ||
2218                    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2219                        cnt += tcp_skb_pcount(skb);
2220
2221                if (cnt > packets) {
2222                        if (tcp_is_sack(tp) ||
2223                            (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2224                            (oldcnt >= packets))
2225                                break;
2226
2227                        mss = tcp_skb_mss(skb);
2228                        /* If needed, chop off the prefix to mark as lost. */
2229                        lost = (packets - oldcnt) * mss;
2230                        if (lost < skb->len &&
2231                            tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
2232                                         lost, mss, GFP_ATOMIC) < 0)
2233                                break;
2234                        cnt = packets;
2235                }
2236
2237                tcp_skb_mark_lost(tp, skb);
2238
2239                if (mark_head)
2240                        break;
2241        }
2242        tcp_verify_left_out(tp);
2243}
2244
2245/* Account newly detected lost packet(s) */
2246
2247static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2248{
2249        struct tcp_sock *tp = tcp_sk(sk);
2250
2251        if (tcp_is_sack(tp)) {
2252                int sacked_upto = tp->sacked_out - tp->reordering;
2253                if (sacked_upto >= 0)
2254                        tcp_mark_head_lost(sk, sacked_upto, 0);
2255                else if (fast_rexmit)
2256                        tcp_mark_head_lost(sk, 1, 1);
2257        }
2258}
2259
2260static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2261{
2262        return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2263               before(tp->rx_opt.rcv_tsecr, when);
2264}
2265
2266/* skb is spurious retransmitted if the returned timestamp echo
2267 * reply is prior to the skb transmission time
2268 */
2269static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2270                                     const struct sk_buff *skb)
2271{
2272        return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2273               tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2274}
2275
2276/* Nothing was retransmitted or returned timestamp is less
2277 * than timestamp of the first retransmission.
2278 */
2279static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2280{
2281        return tp->retrans_stamp &&
2282               tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2283}
2284
2285/* Undo procedures. */
2286
2287/* We can clear retrans_stamp when there are no retransmissions in the
2288 * window. It would seem that it is trivially available for us in
2289 * tp->retrans_out, however, that kind of assumptions doesn't consider
2290 * what will happen if errors occur when sending retransmission for the
2291 * second time. ...It could the that such segment has only
2292 * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2293 * the head skb is enough except for some reneging corner cases that
2294 * are not worth the effort.
2295 *
2296 * Main reason for all this complexity is the fact that connection dying
2297 * time now depends on the validity of the retrans_stamp, in particular,
2298 * that successive retransmissions of a segment must not advance
2299 * retrans_stamp under any conditions.
2300 */
2301static bool tcp_any_retrans_done(const struct sock *sk)
2302{
2303        const struct tcp_sock *tp = tcp_sk(sk);
2304        struct sk_buff *skb;
2305
2306        if (tp->retrans_out)
2307                return true;
2308
2309        skb = tcp_rtx_queue_head(sk);
2310        if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2311                return true;
2312
2313        return false;
2314}
2315
2316static void DBGUNDO(struct sock *sk, const char *msg)
2317{
2318#if FASTRETRANS_DEBUG > 1
2319        struct tcp_sock *tp = tcp_sk(sk);
2320        struct inet_sock *inet = inet_sk(sk);
2321
2322        if (sk->sk_family == AF_INET) {
2323                pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2324                         msg,
2325                         &inet->inet_daddr, ntohs(inet->inet_dport),
2326                         tp->snd_cwnd, tcp_left_out(tp),
2327                         tp->snd_ssthresh, tp->prior_ssthresh,
2328                         tp->packets_out);
2329        }
2330#if IS_ENABLED(CONFIG_IPV6)
2331        else if (sk->sk_family == AF_INET6) {
2332                pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2333                         msg,
2334                         &sk->sk_v6_daddr, ntohs(inet->inet_dport),
2335                         tp->snd_cwnd, tcp_left_out(tp),
2336                         tp->snd_ssthresh, tp->prior_ssthresh,
2337                         tp->packets_out);
2338        }
2339#endif
2340#endif
2341}
2342
2343static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2344{
2345        struct tcp_sock *tp = tcp_sk(sk);
2346
2347        if (unmark_loss) {
2348                struct sk_buff *skb;
2349
2350                skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2351                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2352                }
2353                tp->lost_out = 0;
2354                tcp_clear_all_retrans_hints(tp);
2355        }
2356
2357        if (tp->prior_ssthresh) {
2358                const struct inet_connection_sock *icsk = inet_csk(sk);
2359
2360                tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2361
2362                if (tp->prior_ssthresh > tp->snd_ssthresh) {
2363                        tp->snd_ssthresh = tp->prior_ssthresh;
2364                        tcp_ecn_withdraw_cwr(tp);
2365                }
2366        }
2367        tp->snd_cwnd_stamp = tcp_jiffies32;
2368        tp->undo_marker = 0;
2369        tp->rack.advanced = 1; /* Force RACK to re-exam losses */
2370}
2371
2372static inline bool tcp_may_undo(const struct tcp_sock *tp)
2373{
2374        return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2375}
2376
2377/* People celebrate: "We love our President!" */
2378static bool tcp_try_undo_recovery(struct sock *sk)
2379{
2380        struct tcp_sock *tp = tcp_sk(sk);
2381
2382        if (tcp_may_undo(tp)) {
2383                int mib_idx;
2384
2385                /* Happy end! We did not retransmit anything
2386                 * or our original transmission succeeded.
2387                 */
2388                DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2389                tcp_undo_cwnd_reduction(sk, false);
2390                if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2391                        mib_idx = LINUX_MIB_TCPLOSSUNDO;
2392                else
2393                        mib_idx = LINUX_MIB_TCPFULLUNDO;
2394
2395                NET_INC_STATS(sock_net(sk), mib_idx);
2396        } else if (tp->rack.reo_wnd_persist) {
2397                tp->rack.reo_wnd_persist--;
2398        }
2399        if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2400                /* Hold old state until something *above* high_seq
2401                 * is ACKed. For Reno it is MUST to prevent false
2402                 * fast retransmits (RFC2582). SACK TCP is safe. */
2403                if (!tcp_any_retrans_done(sk))
2404                        tp->retrans_stamp = 0;
2405                return true;
2406        }
2407        tcp_set_ca_state(sk, TCP_CA_Open);
2408        tp->is_sack_reneg = 0;
2409        return false;
2410}
2411
2412/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2413static bool tcp_try_undo_dsack(struct sock *sk)
2414{
2415        struct tcp_sock *tp = tcp_sk(sk);
2416
2417        if (tp->undo_marker && !tp->undo_retrans) {
2418                tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
2419                                               tp->rack.reo_wnd_persist + 1);
2420                DBGUNDO(sk, "D-SACK");
2421                tcp_undo_cwnd_reduction(sk, false);
2422                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2423                return true;
2424        }
2425        return false;
2426}
2427
2428/* Undo during loss recovery after partial ACK or using F-RTO. */
2429static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2430{
2431        struct tcp_sock *tp = tcp_sk(sk);
2432
2433        if (frto_undo || tcp_may_undo(tp)) {
2434                tcp_undo_cwnd_reduction(sk, true);
2435
2436                DBGUNDO(sk, "partial loss");
2437                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2438                if (frto_undo)
2439                        NET_INC_STATS(sock_net(sk),
2440                                        LINUX_MIB_TCPSPURIOUSRTOS);
2441                inet_csk(sk)->icsk_retransmits = 0;
2442                if (frto_undo || tcp_is_sack(tp)) {
2443                        tcp_set_ca_state(sk, TCP_CA_Open);
2444                        tp->is_sack_reneg = 0;
2445                }
2446                return true;
2447        }
2448        return false;
2449}
2450
2451/* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2452 * It computes the number of packets to send (sndcnt) based on packets newly
2453 * delivered:
2454 *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2455 *      cwnd reductions across a full RTT.
2456 *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2457 *      But when the retransmits are acked without further losses, PRR
2458 *      slow starts cwnd up to ssthresh to speed up the recovery.
2459 */
2460static void tcp_init_cwnd_reduction(struct sock *sk)
2461{
2462        struct tcp_sock *tp = tcp_sk(sk);
2463
2464        tp->high_seq = tp->snd_nxt;
2465        tp->tlp_high_seq = 0;
2466        tp->snd_cwnd_cnt = 0;
2467        tp->prior_cwnd = tp->snd_cwnd;
2468        tp->prr_delivered = 0;
2469        tp->prr_out = 0;
2470        tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2471        tcp_ecn_queue_cwr(tp);
2472}
2473
2474void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int flag)
2475{
2476        struct tcp_sock *tp = tcp_sk(sk);
2477        int sndcnt = 0;
2478        int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2479
2480        if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2481                return;
2482
2483        tp->prr_delivered += newly_acked_sacked;
2484        if (delta < 0) {
2485                u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2486                               tp->prior_cwnd - 1;
2487                sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2488        } else if ((flag & (FLAG_RETRANS_DATA_ACKED | FLAG_LOST_RETRANS)) ==
2489                   FLAG_RETRANS_DATA_ACKED) {
2490                sndcnt = min_t(int, delta,
2491                               max_t(int, tp->prr_delivered - tp->prr_out,
2492                                     newly_acked_sacked) + 1);
2493        } else {
2494                sndcnt = min(delta, newly_acked_sacked);
2495        }
2496        /* Force a fast retransmit upon entering fast recovery */
2497        sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2498        tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2499}
2500
2501static inline void tcp_end_cwnd_reduction(struct sock *sk)
2502{
2503        struct tcp_sock *tp = tcp_sk(sk);
2504
2505        if (inet_csk(sk)->icsk_ca_ops->cong_control)
2506                return;
2507
2508        /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2509        if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
2510            (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
2511                tp->snd_cwnd = tp->snd_ssthresh;
2512                tp->snd_cwnd_stamp = tcp_jiffies32;
2513        }
2514        tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2515}
2516
2517/* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2518void tcp_enter_cwr(struct sock *sk)
2519{
2520        struct tcp_sock *tp = tcp_sk(sk);
2521
2522        tp->prior_ssthresh = 0;
2523        if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2524                tp->undo_marker = 0;
2525                tcp_init_cwnd_reduction(sk);
2526                tcp_set_ca_state(sk, TCP_CA_CWR);
2527        }
2528}
2529EXPORT_SYMBOL(tcp_enter_cwr);
2530
2531static void tcp_try_keep_open(struct sock *sk)
2532{
2533        struct tcp_sock *tp = tcp_sk(sk);
2534        int state = TCP_CA_Open;
2535
2536        if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2537                state = TCP_CA_Disorder;
2538
2539        if (inet_csk(sk)->icsk_ca_state != state) {
2540                tcp_set_ca_state(sk, state);
2541                tp->high_seq = tp->snd_nxt;
2542        }
2543}
2544
2545static void tcp_try_to_open(struct sock *sk, int flag)
2546{
2547        struct tcp_sock *tp = tcp_sk(sk);
2548
2549        tcp_verify_left_out(tp);
2550
2551        if (!tcp_any_retrans_done(sk))
2552                tp->retrans_stamp = 0;
2553
2554        if (flag & FLAG_ECE)
2555                tcp_enter_cwr(sk);
2556
2557        if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2558                tcp_try_keep_open(sk);
2559        }
2560}
2561
2562static void tcp_mtup_probe_failed(struct sock *sk)
2563{
2564        struct inet_connection_sock *icsk = inet_csk(sk);
2565
2566        icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2567        icsk->icsk_mtup.probe_size = 0;
2568        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2569}
2570
2571static void tcp_mtup_probe_success(struct sock *sk)
2572{
2573        struct tcp_sock *tp = tcp_sk(sk);
2574        struct inet_connection_sock *icsk = inet_csk(sk);
2575
2576        /* FIXME: breaks with very large cwnd */
2577        tp->prior_ssthresh = tcp_current_ssthresh(sk);
2578        tp->snd_cwnd = tp->snd_cwnd *
2579                       tcp_mss_to_mtu(sk, tp->mss_cache) /
2580                       icsk->icsk_mtup.probe_size;
2581        tp->snd_cwnd_cnt = 0;
2582        tp->snd_cwnd_stamp = tcp_jiffies32;
2583        tp->snd_ssthresh = tcp_current_ssthresh(sk);
2584
2585        icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2586        icsk->icsk_mtup.probe_size = 0;
2587        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2588        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2589}
2590
2591/* Do a simple retransmit without using the backoff mechanisms in
2592 * tcp_timer. This is used for path mtu discovery.
2593 * The socket is already locked here.
2594 */
2595void tcp_simple_retransmit(struct sock *sk)
2596{
2597        const struct inet_connection_sock *icsk = inet_csk(sk);
2598        struct tcp_sock *tp = tcp_sk(sk);
2599        struct sk_buff *skb;
2600        unsigned int mss = tcp_current_mss(sk);
2601
2602        skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2603                if (tcp_skb_seglen(skb) > mss &&
2604                    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2605                        if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2606                                TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2607                                tp->retrans_out -= tcp_skb_pcount(skb);
2608                        }
2609                        tcp_skb_mark_lost_uncond_verify(tp, skb);
2610                }
2611        }
2612
2613        tcp_clear_retrans_hints_partial(tp);
2614
2615        if (!tp->lost_out)
2616                return;
2617
2618        if (tcp_is_reno(tp))
2619                tcp_limit_reno_sacked(tp);
2620
2621        tcp_verify_left_out(tp);
2622
2623        /* Don't muck with the congestion window here.
2624         * Reason is that we do not increase amount of _data_
2625         * in network, but units changed and effective
2626         * cwnd/ssthresh really reduced now.
2627         */
2628        if (icsk->icsk_ca_state != TCP_CA_Loss) {
2629                tp->high_seq = tp->snd_nxt;
2630                tp->snd_ssthresh = tcp_current_ssthresh(sk);
2631                tp->prior_ssthresh = 0;
2632                tp->undo_marker = 0;
2633                tcp_set_ca_state(sk, TCP_CA_Loss);
2634        }
2635        tcp_xmit_retransmit_queue(sk);
2636}
2637EXPORT_SYMBOL(tcp_simple_retransmit);
2638
2639void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2640{
2641        struct tcp_sock *tp = tcp_sk(sk);
2642        int mib_idx;
2643
2644        if (tcp_is_reno(tp))
2645                mib_idx = LINUX_MIB_TCPRENORECOVERY;
2646        else
2647                mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2648
2649        NET_INC_STATS(sock_net(sk), mib_idx);
2650
2651        tp->prior_ssthresh = 0;
2652        tcp_init_undo(tp);
2653
2654        if (!tcp_in_cwnd_reduction(sk)) {
2655                if (!ece_ack)
2656                        tp->prior_ssthresh = tcp_current_ssthresh(sk);
2657                tcp_init_cwnd_reduction(sk);
2658        }
2659        tcp_set_ca_state(sk, TCP_CA_Recovery);
2660}
2661
2662/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2663 * recovered or spurious. Otherwise retransmits more on partial ACKs.
2664 */
2665static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
2666                             int *rexmit)
2667{
2668        struct tcp_sock *tp = tcp_sk(sk);
2669        bool recovered = !before(tp->snd_una, tp->high_seq);
2670
2671        if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) &&
2672            tcp_try_undo_loss(sk, false))
2673                return;
2674
2675        if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2676                /* Step 3.b. A timeout is spurious if not all data are
2677                 * lost, i.e., never-retransmitted data are (s)acked.
2678                 */
2679                if ((flag & FLAG_ORIG_SACK_ACKED) &&
2680                    tcp_try_undo_loss(sk, true))
2681                        return;
2682
2683                if (after(tp->snd_nxt, tp->high_seq)) {
2684                        if (flag & FLAG_DATA_SACKED || num_dupack)
2685                                tp->frto = 0; /* Step 3.a. loss was real */
2686                } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2687                        tp->high_seq = tp->snd_nxt;
2688                        /* Step 2.b. Try send new data (but deferred until cwnd
2689                         * is updated in tcp_ack()). Otherwise fall back to
2690                         * the conventional recovery.
2691                         */
2692                        if (!tcp_write_queue_empty(sk) &&
2693                            after(tcp_wnd_end(tp), tp->snd_nxt)) {
2694                                *rexmit = REXMIT_NEW;
2695                                return;
2696                        }
2697                        tp->frto = 0;
2698                }
2699        }
2700
2701        if (recovered) {
2702                /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2703                tcp_try_undo_recovery(sk);
2704                return;
2705        }
2706        if (tcp_is_reno(tp)) {
2707                /* A Reno DUPACK means new data in F-RTO step 2.b above are
2708                 * delivered. Lower inflight to clock out (re)tranmissions.
2709                 */
2710                if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
2711                        tcp_add_reno_sack(sk, num_dupack);
2712                else if (flag & FLAG_SND_UNA_ADVANCED)
2713                        tcp_reset_reno_sack(tp);
2714        }
2715        *rexmit = REXMIT_LOST;
2716}
2717
2718/* Undo during fast recovery after partial ACK. */
2719static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una)
2720{
2721        struct tcp_sock *tp = tcp_sk(sk);
2722
2723        if (tp->undo_marker && tcp_packet_delayed(tp)) {
2724                /* Plain luck! Hole if filled with delayed
2725                 * packet, rather than with a retransmit. Check reordering.
2726                 */
2727                tcp_check_sack_reordering(sk, prior_snd_una, 1);
2728
2729                /* We are getting evidence that the reordering degree is higher
2730                 * than we realized. If there are no retransmits out then we
2731                 * can undo. Otherwise we clock out new packets but do not
2732                 * mark more packets lost or retransmit more.
2733                 */
2734                if (tp->retrans_out)
2735                        return true;
2736
2737                if (!tcp_any_retrans_done(sk))
2738                        tp->retrans_stamp = 0;
2739
2740                DBGUNDO(sk, "partial recovery");
2741                tcp_undo_cwnd_reduction(sk, true);
2742                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2743                tcp_try_keep_open(sk);
2744                return true;
2745        }
2746        return false;
2747}
2748
2749static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
2750{
2751        struct tcp_sock *tp = tcp_sk(sk);
2752
2753        if (tcp_rtx_queue_empty(sk))
2754                return;
2755
2756        if (unlikely(tcp_is_reno(tp))) {
2757                tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
2758        } else if (tcp_is_rack(sk)) {
2759                u32 prior_retrans = tp->retrans_out;
2760
2761                tcp_rack_mark_lost(sk);
2762                if (prior_retrans > tp->retrans_out)
2763                        *ack_flag |= FLAG_LOST_RETRANS;
2764        }
2765}
2766
2767static bool tcp_force_fast_retransmit(struct sock *sk)
2768{
2769        struct tcp_sock *tp = tcp_sk(sk);
2770
2771        return after(tcp_highest_sack_seq(tp),
2772                     tp->snd_una + tp->reordering * tp->mss_cache);
2773}
2774
2775/* Process an event, which can update packets-in-flight not trivially.
2776 * Main goal of this function is to calculate new estimate for left_out,
2777 * taking into account both packets sitting in receiver's buffer and
2778 * packets lost by network.
2779 *
2780 * Besides that it updates the congestion state when packet loss or ECN
2781 * is detected. But it does not reduce the cwnd, it is done by the
2782 * congestion control later.
2783 *
2784 * It does _not_ decide what to send, it is made in function
2785 * tcp_xmit_retransmit_queue().
2786 */
2787static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
2788                                  int num_dupack, int *ack_flag, int *rexmit)
2789{
2790        struct inet_connection_sock *icsk = inet_csk(sk);
2791        struct tcp_sock *tp = tcp_sk(sk);
2792        int fast_rexmit = 0, flag = *ack_flag;
2793        bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
2794                                      tcp_force_fast_retransmit(sk));
2795
2796        if (!tp->packets_out && tp->sacked_out)
2797                tp->sacked_out = 0;
2798
2799        /* Now state machine starts.
2800         * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2801        if (flag & FLAG_ECE)
2802                tp->prior_ssthresh = 0;
2803
2804        /* B. In all the states check for reneging SACKs. */
2805        if (tcp_check_sack_reneging(sk, flag))
2806                return;
2807
2808        /* C. Check consistency of the current state. */
2809        tcp_verify_left_out(tp);
2810
2811        /* D. Check state exit conditions. State can be terminated
2812         *    when high_seq is ACKed. */
2813        if (icsk->icsk_ca_state == TCP_CA_Open) {
2814                WARN_ON(tp->retrans_out != 0);
2815                tp->retrans_stamp = 0;
2816        } else if (!before(tp->snd_una, tp->high_seq)) {
2817                switch (icsk->icsk_ca_state) {
2818                case TCP_CA_CWR:
2819                        /* CWR is to be held something *above* high_seq
2820                         * is ACKed for CWR bit to reach receiver. */
2821                        if (tp->snd_una != tp->high_seq) {
2822                                tcp_end_cwnd_reduction(sk);
2823                                tcp_set_ca_state(sk, TCP_CA_Open);
2824                        }
2825                        break;
2826
2827                case TCP_CA_Recovery:
2828                        if (tcp_is_reno(tp))
2829                                tcp_reset_reno_sack(tp);
2830                        if (tcp_try_undo_recovery(sk))
2831                                return;
2832                        tcp_end_cwnd_reduction(sk);
2833                        break;
2834                }
2835        }
2836
2837        /* E. Process state. */
2838        switch (icsk->icsk_ca_state) {
2839        case TCP_CA_Recovery:
2840                if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2841                        if (tcp_is_reno(tp))
2842                                tcp_add_reno_sack(sk, num_dupack);
2843                } else {
2844                        if (tcp_try_undo_partial(sk, prior_snd_una))
2845                                return;
2846                        /* Partial ACK arrived. Force fast retransmit. */
2847                        do_lost = tcp_is_reno(tp) ||
2848                                  tcp_force_fast_retransmit(sk);
2849                }
2850                if (tcp_try_undo_dsack(sk)) {
2851                        tcp_try_keep_open(sk);
2852                        return;
2853                }
2854                tcp_identify_packet_loss(sk, ack_flag);
2855                break;
2856        case TCP_CA_Loss:
2857                tcp_process_loss(sk, flag, num_dupack, rexmit);
2858                tcp_identify_packet_loss(sk, ack_flag);
2859                if (!(icsk->icsk_ca_state == TCP_CA_Open ||
2860                      (*ack_flag & FLAG_LOST_RETRANS)))
2861                        return;
2862                /* Change state if cwnd is undone or retransmits are lost */
2863                /* fall through */
2864        default:
2865                if (tcp_is_reno(tp)) {
2866                        if (flag & FLAG_SND_UNA_ADVANCED)
2867                                tcp_reset_reno_sack(tp);
2868                        tcp_add_reno_sack(sk, num_dupack);
2869                }
2870
2871                if (icsk->icsk_ca_state <= TCP_CA_Disorder)
2872                        tcp_try_undo_dsack(sk);
2873
2874                tcp_identify_packet_loss(sk, ack_flag);
2875                if (!tcp_time_to_recover(sk, flag)) {
2876                        tcp_try_to_open(sk, flag);
2877                        return;
2878                }
2879
2880                /* MTU probe failure: don't reduce cwnd */
2881                if (icsk->icsk_ca_state < TCP_CA_CWR &&
2882                    icsk->icsk_mtup.probe_size &&
2883                    tp->snd_una == tp->mtu_probe.probe_seq_start) {
2884                        tcp_mtup_probe_failed(sk);
2885                        /* Restores the reduction we did in tcp_mtup_probe() */
2886                        tp->snd_cwnd++;
2887                        tcp_simple_retransmit(sk);
2888                        return;
2889                }
2890
2891                /* Otherwise enter Recovery state */
2892                tcp_enter_recovery(sk, (flag & FLAG_ECE));
2893                fast_rexmit = 1;
2894        }
2895
2896        if (!tcp_is_rack(sk) && do_lost)
2897                tcp_update_scoreboard(sk, fast_rexmit);
2898        *rexmit = REXMIT_LOST;
2899}
2900
2901static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
2902{
2903        u32 wlen = sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen * HZ;
2904        struct tcp_sock *tp = tcp_sk(sk);
2905
2906        if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
2907                /* If the remote keeps returning delayed ACKs, eventually
2908                 * the min filter would pick it up and overestimate the
2909                 * prop. delay when it expires. Skip suspected delayed ACKs.
2910                 */
2911                return;
2912        }
2913        minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
2914                           rtt_us ? : jiffies_to_usecs(1));
2915}
2916
2917static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
2918                               long seq_rtt_us, long sack_rtt_us,
2919                               long ca_rtt_us, struct rate_sample *rs)
2920{
2921        const struct tcp_sock *tp = tcp_sk(sk);
2922
2923        /* Prefer RTT measured from ACK's timing to TS-ECR. This is because
2924         * broken middle-boxes or peers may corrupt TS-ECR fields. But
2925         * Karn's algorithm forbids taking RTT if some retransmitted data
2926         * is acked (RFC6298).
2927         */
2928        if (seq_rtt_us < 0)
2929                seq_rtt_us = sack_rtt_us;
2930
2931        /* RTTM Rule: A TSecr value received in a segment is used to
2932         * update the averaged RTT measurement only if the segment
2933         * acknowledges some new data, i.e., only if it advances the
2934         * left edge of the send window.
2935         * See draft-ietf-tcplw-high-performance-00, section 3.3.
2936         */
2937        if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2938            flag & FLAG_ACKED) {
2939                u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
2940
2941                if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
2942                        seq_rtt_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
2943                        ca_rtt_us = seq_rtt_us;
2944                }
2945        }
2946        rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
2947        if (seq_rtt_us < 0)
2948                return false;
2949
2950        /* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
2951         * always taken together with ACK, SACK, or TS-opts. Any negative
2952         * values will be skipped with the seq_rtt_us < 0 check above.
2953         */
2954        tcp_update_rtt_min(sk, ca_rtt_us, flag);
2955        tcp_rtt_estimator(sk, seq_rtt_us);
2956        tcp_set_rto(sk);
2957
2958        /* RFC6298: only reset backoff on valid RTT measurement. */
2959        inet_csk(sk)->icsk_backoff = 0;
2960        return true;
2961}
2962
2963/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
2964void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
2965{
2966        struct rate_sample rs;
2967        long rtt_us = -1L;
2968
2969        if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
2970                rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
2971
2972        tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
2973}
2974
2975
2976static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
2977{
2978        const struct inet_connection_sock *icsk = inet_csk(sk);
2979
2980        icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
2981        tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
2982}
2983
2984/* Restart timer after forward progress on connection.
2985 * RFC2988 recommends to restart timer to now+rto.
2986 */
2987void tcp_rearm_rto(struct sock *sk)
2988{
2989        const struct inet_connection_sock *icsk = inet_csk(sk);
2990        struct tcp_sock *tp = tcp_sk(sk);
2991
2992        /* If the retrans timer is currently being used by Fast Open
2993         * for SYN-ACK retrans purpose, stay put.
2994         */
2995        if (rcu_access_pointer(tp->fastopen_rsk))
2996                return;
2997
2998        if (!tp->packets_out) {
2999                inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3000        } else {
3001                u32 rto = inet_csk(sk)->icsk_rto;
3002                /* Offset the time elapsed after installing regular RTO */
3003                if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
3004                    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3005                        s64 delta_us = tcp_rto_delta_us(sk);
3006                        /* delta_us may not be positive if the socket is locked
3007                         * when the retrans timer fires and is rescheduled.
3008                         */
3009                        rto = usecs_to_jiffies(max_t(int, delta_us, 1));
3010                }
3011                tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3012                                     TCP_RTO_MAX, tcp_rtx_queue_head(sk));
3013        }
3014}
3015
3016/* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
3017static void tcp_set_xmit_timer(struct sock *sk)
3018{
3019        if (!tcp_schedule_loss_probe(sk, true))
3020                tcp_rearm_rto(sk);
3021}
3022
3023/* If we get here, the whole TSO packet has not been acked. */
3024static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3025{
3026        struct tcp_sock *tp = tcp_sk(sk);
3027        u32 packets_acked;
3028
3029        BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3030
3031        packets_acked = tcp_skb_pcount(skb);
3032        if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3033                return 0;
3034        packets_acked -= tcp_skb_pcount(skb);
3035
3036        if (packets_acked) {
3037                BUG_ON(tcp_skb_pcount(skb) == 0);
3038                BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3039        }
3040
3041        return packets_acked;
3042}
3043
3044static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3045                           u32 prior_snd_una)
3046{
3047        const struct skb_shared_info *shinfo;
3048
3049        /* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3050        if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
3051                return;
3052
3053        shinfo = skb_shinfo(skb);
3054        if (!before(shinfo->tskey, prior_snd_una) &&
3055            before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
3056                tcp_skb_tsorted_save(skb) {
3057                        __skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
3058                } tcp_skb_tsorted_restore(skb);
3059        }
3060}
3061
3062/* Remove acknowledged frames from the retransmission queue. If our packet
3063 * is before the ack sequence we can discard it as it's confirmed to have
3064 * arrived at the other end.
3065 */
3066static int tcp_clean_rtx_queue(struct sock *sk, u32 prior_fack,
3067                               u32 prior_snd_una,
3068                               struct tcp_sacktag_state *sack)
3069{
3070        const struct inet_connection_sock *icsk = inet_csk(sk);
3071        u64 first_ackt, last_ackt;
3072        struct tcp_sock *tp = tcp_sk(sk);
3073        u32 prior_sacked = tp->sacked_out;
3074        u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
3075        struct sk_buff *skb, *next;
3076        bool fully_acked = true;
3077        long sack_rtt_us = -1L;
3078        long seq_rtt_us = -1L;
3079        long ca_rtt_us = -1L;
3080        u32 pkts_acked = 0;
3081        u32 last_in_flight = 0;
3082        bool rtt_update;
3083        int flag = 0;
3084
3085        first_ackt = 0;
3086
3087        for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
3088                struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3089                const u32 start_seq = scb->seq;
3090                u8 sacked = scb->sacked;
3091                u32 acked_pcount;
3092
3093                tcp_ack_tstamp(sk, skb, prior_snd_una);
3094
3095                /* Determine how many packets and what bytes were acked, tso and else */
3096                if (after(scb->end_seq, tp->snd_una)) {
3097                        if (tcp_skb_pcount(skb) == 1 ||
3098                            !after(tp->snd_una, scb->seq))
3099                                break;
3100
3101                        acked_pcount = tcp_tso_acked(sk, skb);
3102                        if (!acked_pcount)
3103                                break;
3104                        fully_acked = false;
3105                } else {
3106                        acked_pcount = tcp_skb_pcount(skb);
3107                }
3108
3109                if (unlikely(sacked & TCPCB_RETRANS)) {
3110                        if (sacked & TCPCB_SACKED_RETRANS)
3111                                tp->retrans_out -= acked_pcount;
3112                        flag |= FLAG_RETRANS_DATA_ACKED;
3113                } else if (!(sacked & TCPCB_SACKED_ACKED)) {
3114                        last_ackt = tcp_skb_timestamp_us(skb);
3115                        WARN_ON_ONCE(last_ackt == 0);
3116                        if (!first_ackt)
3117                                first_ackt = last_ackt;
3118
3119                        last_in_flight = TCP_SKB_CB(skb)->tx.in_flight;
3120                        if (before(start_seq, reord))
3121                                reord = start_seq;
3122                        if (!after(scb->end_seq, tp->high_seq))
3123                                flag |= FLAG_ORIG_SACK_ACKED;
3124                }
3125
3126                if (sacked & TCPCB_SACKED_ACKED) {
3127                        tp->sacked_out -= acked_pcount;
3128                } else if (tcp_is_sack(tp)) {
3129                        tp->delivered += acked_pcount;
3130                        if (!tcp_skb_spurious_retrans(tp, skb))
3131                                tcp_rack_advance(tp, sacked, scb->end_seq,
3132                                                 tcp_skb_timestamp_us(skb));
3133                }
3134                if (sacked & TCPCB_LOST)
3135                        tp->lost_out -= acked_pcount;
3136
3137                tp->packets_out -= acked_pcount;
3138                pkts_acked += acked_pcount;
3139                tcp_rate_skb_delivered(sk, skb, sack->rate);
3140
3141                /* Initial outgoing SYN's get put onto the write_queue
3142                 * just like anything else we transmit.  It is not
3143                 * true data, and if we misinform our callers that
3144                 * this ACK acks real data, we will erroneously exit
3145                 * connection startup slow start one packet too
3146                 * quickly.  This is severely frowned upon behavior.
3147                 */
3148                if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3149                        flag |= FLAG_DATA_ACKED;
3150                } else {
3151                        flag |= FLAG_SYN_ACKED;
3152                        tp->retrans_stamp = 0;
3153                }
3154
3155                if (!fully_acked)
3156                        break;
3157
3158                next = skb_rb_next(skb);
3159                if (unlikely(skb == tp->retransmit_skb_hint))
3160                        tp->retransmit_skb_hint = NULL;
3161                if (unlikely(skb == tp->lost_skb_hint))
3162                        tp->lost_skb_hint = NULL;
3163                tcp_rtx_queue_unlink_and_free(skb, sk);
3164        }
3165
3166        if (!skb)
3167                tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
3168
3169        if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3170                tp->snd_up = tp->snd_una;
3171
3172        if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3173                flag |= FLAG_SACK_RENEGING;
3174
3175        if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3176                seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
3177                ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
3178
3179                if (pkts_acked == 1 && last_in_flight < tp->mss_cache &&
3180                    last_in_flight && !prior_sacked && fully_acked &&
3181                    sack->rate->prior_delivered + 1 == tp->delivered &&
3182                    !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
3183                        /* Conservatively mark a delayed ACK. It's typically
3184                         * from a lone runt packet over the round trip to
3185                         * a receiver w/o out-of-order or CE events.
3186                         */
3187                        flag |= FLAG_ACK_MAYBE_DELAYED;
3188                }
3189        }
3190        if (sack->first_sackt) {
3191                sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
3192                ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
3193        }
3194        rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3195                                        ca_rtt_us, sack->rate);
3196
3197        if (flag & FLAG_ACKED) {
3198                flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3199                if (unlikely(icsk->icsk_mtup.probe_size &&
3200                             !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3201                        tcp_mtup_probe_success(sk);
3202                }
3203
3204                if (tcp_is_reno(tp)) {
3205                        tcp_remove_reno_sacks(sk, pkts_acked);
3206
3207                        /* If any of the cumulatively ACKed segments was
3208                         * retransmitted, non-SACK case cannot confirm that
3209                         * progress was due to original transmission due to
3210                         * lack of TCPCB_SACKED_ACKED bits even if some of
3211                         * the packets may have been never retransmitted.
3212                         */
3213                        if (flag & FLAG_RETRANS_DATA_ACKED)
3214                                flag &= ~FLAG_ORIG_SACK_ACKED;
3215                } else {
3216                        int delta;
3217
3218                        /* Non-retransmitted hole got filled? That's reordering */
3219                        if (before(reord, prior_fack))
3220                                tcp_check_sack_reordering(sk, reord, 0);
3221
3222                        delta = prior_sacked - tp->sacked_out;
3223                        tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3224                }
3225        } else if (skb && rtt_update && sack_rtt_us >= 0 &&
3226                   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
3227                                                    tcp_skb_timestamp_us(skb))) {
3228                /* Do not re-arm RTO if the sack RTT is measured from data sent
3229                 * after when the head was last (re)transmitted. Otherwise the
3230                 * timeout may continue to extend in loss recovery.
3231                 */
3232                flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3233        }
3234
3235        if (icsk->icsk_ca_ops->pkts_acked) {
3236                struct ack_sample sample = { .pkts_acked = pkts_acked,
3237                                             .rtt_us = sack->rate->rtt_us,
3238                                             .in_flight = last_in_flight };
3239
3240                icsk->icsk_ca_ops->pkts_acked(sk, &sample);
3241        }
3242
3243#if FASTRETRANS_DEBUG > 0
3244        WARN_ON((int)tp->sacked_out < 0);
3245        WARN_ON((int)tp->lost_out < 0);
3246        WARN_ON((int)tp->retrans_out < 0);
3247        if (!tp->packets_out && tcp_is_sack(tp)) {
3248                icsk = inet_csk(sk);
3249                if (tp->lost_out) {
3250                        pr_debug("Leak l=%u %d\n",
3251                                 tp->lost_out, icsk->icsk_ca_state);
3252                        tp->lost_out = 0;
3253                }
3254                if (tp->sacked_out) {
3255                        pr_debug("Leak s=%u %d\n",
3256                                 tp->sacked_out, icsk->icsk_ca_state);
3257                        tp->sacked_out = 0;
3258                }
3259                if (tp->retrans_out) {
3260                        pr_debug("Leak r=%u %d\n",
3261                                 tp->retrans_out, icsk->icsk_ca_state);
3262                        tp->retrans_out = 0;
3263                }
3264        }
3265#endif
3266        return flag;
3267}
3268
3269static void tcp_ack_probe(struct sock *sk)
3270{
3271        struct inet_connection_sock *icsk = inet_csk(sk);
3272        struct sk_buff *head = tcp_send_head(sk);
3273        const struct tcp_sock *tp = tcp_sk(sk);
3274
3275        /* Was it a usable window open? */
3276        if (!head)
3277                return;
3278        if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
3279                icsk->icsk_backoff = 0;
3280                inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3281                /* Socket must be waked up by subsequent tcp_data_snd_check().
3282                 * This function is not for random using!
3283                 */
3284        } else {
3285                unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3286
3287                tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3288                                     when, TCP_RTO_MAX, NULL);
3289        }
3290}
3291
3292static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3293{
3294        return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3295                inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3296}
3297
3298/* Decide wheather to run the increase function of congestion control. */
3299static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3300{
3301        /* If reordering is high then always grow cwnd whenever data is
3302         * delivered regardless of its ordering. Otherwise stay conservative
3303         * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3304         * new SACK or ECE mark may first advance cwnd here and later reduce
3305         * cwnd in tcp_fastretrans_alert() based on more states.
3306         */
3307        if (tcp_sk(sk)->reordering > sock_net(sk)->ipv4.sysctl_tcp_reordering)
3308                return flag & FLAG_FORWARD_PROGRESS;
3309
3310        return flag & FLAG_DATA_ACKED;
3311}
3312
3313/* The "ultimate" congestion control function that aims to replace the rigid
3314 * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3315 * It's called toward the end of processing an ACK with precise rate
3316 * information. All transmission or retransmission are delayed afterwards.
3317 */
3318static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3319                             int flag, const struct rate_sample *rs)
3320{
3321        const struct inet_connection_sock *icsk = inet_csk(sk);
3322
3323        if (icsk->icsk_ca_ops->cong_control) {
3324                icsk->icsk_ca_ops->cong_control(sk, rs);
3325                return;
3326        }
3327
3328        if (tcp_in_cwnd_reduction(sk)) {
3329                /* Reduce cwnd if state mandates */
3330                tcp_cwnd_reduction(sk, acked_sacked, flag);
3331        } else if (tcp_may_raise_cwnd(sk, flag)) {
3332                /* Advance cwnd if state allows */
3333                tcp_cong_avoid(sk, ack, acked_sacked);
3334        }
3335        tcp_update_pacing_rate(sk);
3336}
3337
3338/* Check that window update is acceptable.
3339 * The function assumes that snd_una<=ack<=snd_next.
3340 */
3341static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3342                                        const u32 ack, const u32 ack_seq,
3343                                        const u32 nwin)
3344{
3345        return  after(ack, tp->snd_una) ||
3346                after(ack_seq, tp->snd_wl1) ||
3347                (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3348}
3349
3350/* If we update tp->snd_una, also update tp->bytes_acked */
3351static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3352{
3353        u32 delta = ack - tp->snd_una;
3354
3355        sock_owned_by_me((struct sock *)tp);
3356        tp->bytes_acked += delta;
3357        tp->snd_una = ack;
3358}
3359
3360/* If we update tp->rcv_nxt, also update tp->bytes_received */
3361static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3362{
3363        u32 delta = seq - tp->rcv_nxt;
3364
3365        sock_owned_by_me((struct sock *)tp);
3366        tp->bytes_received += delta;
3367        WRITE_ONCE(tp->rcv_nxt, seq);
3368}
3369
3370/* Update our send window.
3371 *
3372 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3373 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3374 */
3375static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3376                                 u32 ack_seq)
3377{
3378        struct tcp_sock *tp = tcp_sk(sk);
3379        int flag = 0;
3380        u32 nwin = ntohs(tcp_hdr(skb)->window);
3381
3382        if (likely(!tcp_hdr(skb)->syn))
3383                nwin <<= tp->rx_opt.snd_wscale;
3384
3385        if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3386                flag |= FLAG_WIN_UPDATE;
3387                tcp_update_wl(tp, ack_seq);
3388
3389                if (tp->snd_wnd != nwin) {
3390                        tp->snd_wnd = nwin;
3391
3392                        /* Note, it is the only place, where
3393                         * fast path is recovered for sending TCP.
3394                         */
3395                        tp->pred_flags = 0;
3396                        tcp_fast_path_check(sk);
3397
3398                        if (!tcp_write_queue_empty(sk))
3399                                tcp_slow_start_after_idle_check(sk);
3400
3401                        if (nwin > tp->max_window) {
3402                                tp->max_window = nwin;
3403                                tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3404                        }
3405                }
3406        }
3407
3408        tcp_snd_una_update(tp, ack);
3409
3410        return flag;
3411}
3412
3413static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
3414                                   u32 *last_oow_ack_time)
3415{
3416        if (*last_oow_ack_time) {
3417                s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
3418
3419                if (0 <= elapsed && elapsed < net->ipv4.sysctl_tcp_invalid_ratelimit) {
3420                        NET_INC_STATS(net, mib_idx);
3421                        return true;    /* rate-limited: don't send yet! */
3422                }
3423        }
3424
3425        *last_oow_ack_time = tcp_jiffies32;
3426
3427        return false;   /* not rate-limited: go ahead, send dupack now! */
3428}
3429
3430/* Return true if we're currently rate-limiting out-of-window ACKs and
3431 * thus shouldn't send a dupack right now. We rate-limit dupacks in
3432 * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3433 * attacks that send repeated SYNs or ACKs for the same connection. To
3434 * do this, we do not send a duplicate SYNACK or ACK if the remote
3435 * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3436 */
3437bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3438                          int mib_idx, u32 *last_oow_ack_time)
3439{
3440        /* Data packets without SYNs are not likely part of an ACK loop. */
3441        if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3442            !tcp_hdr(skb)->syn)
3443                return false;
3444
3445        return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
3446}
3447
3448/* RFC 5961 7 [ACK Throttling] */
3449static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
3450{
3451        /* unprotected vars, we dont care of overwrites */
3452        static u32 challenge_timestamp;
3453        static unsigned int challenge_count;
3454        struct tcp_sock *tp = tcp_sk(sk);
3455        struct net *net = sock_net(sk);
3456        u32 count, now;
3457
3458        /* First check our per-socket dupack rate limit. */
3459        if (__tcp_oow_rate_limited(net,
3460                                   LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3461                                   &tp->last_oow_ack_time))
3462                return;
3463
3464        /* Then check host-wide RFC 5961 rate limit. */
3465        now = jiffies / HZ;
3466        if (now != challenge_timestamp) {
3467                u32 ack_limit = net->ipv4.sysctl_tcp_challenge_ack_limit;
3468                u32 half = (ack_limit + 1) >> 1;
3469
3470                challenge_timestamp = now;
3471                WRITE_ONCE(challenge_count, half + prandom_u32_max(ack_limit));
3472        }
3473        count = READ_ONCE(challenge_count);
3474        if (count > 0) {
3475                WRITE_ONCE(challenge_count, count - 1);
3476                NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
3477                tcp_send_ack(sk);
3478        }
3479}
3480
3481static void tcp_store_ts_recent(struct tcp_sock *tp)
3482{
3483        tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3484        tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
3485}
3486
3487static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3488{
3489        if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3490                /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3491                 * extra check below makes sure this can only happen
3492                 * for pure ACK frames.  -DaveM
3493                 *
3494                 * Not only, also it occurs for expired timestamps.
3495                 */
3496
3497                if (tcp_paws_check(&tp->rx_opt, 0))
3498                        tcp_store_ts_recent(tp);
3499        }
3500}
3501
3502/* This routine deals with acks during a TLP episode.
3503 * We mark the end of a TLP episode on receiving TLP dupack or when
3504 * ack is after tlp_high_seq.
3505 * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
3506 */
3507static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3508{
3509        struct tcp_sock *tp = tcp_sk(sk);
3510
3511        if (before(ack, tp->tlp_high_seq))
3512                return;
3513
3514        if (flag & FLAG_DSACKING_ACK) {
3515                /* This DSACK means original and TLP probe arrived; no loss */
3516                tp->tlp_high_seq = 0;
3517        } else if (after(ack, tp->tlp_high_seq)) {
3518                /* ACK advances: there was a loss, so reduce cwnd. Reset
3519                 * tlp_high_seq in tcp_init_cwnd_reduction()
3520                 */
3521                tcp_init_cwnd_reduction(sk);
3522                tcp_set_ca_state(sk, TCP_CA_CWR);
3523                tcp_end_cwnd_reduction(sk);
3524                tcp_try_keep_open(sk);
3525                NET_INC_STATS(sock_net(sk),
3526                                LINUX_MIB_TCPLOSSPROBERECOVERY);
3527        } else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3528                             FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3529                /* Pure dupack: original and TLP probe arrived; no loss */
3530                tp->tlp_high_seq = 0;
3531        }
3532}
3533
3534static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3535{
3536        const struct inet_connection_sock *icsk = inet_csk(sk);
3537
3538        if (icsk->icsk_ca_ops->in_ack_event)
3539                icsk->icsk_ca_ops->in_ack_event(sk, flags);
3540}
3541
3542/* Congestion control has updated the cwnd already. So if we're in
3543 * loss recovery then now we do any new sends (for FRTO) or
3544 * retransmits (for CA_Loss or CA_recovery) that make sense.
3545 */
3546static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3547{
3548        struct tcp_sock *tp = tcp_sk(sk);
3549
3550        if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
3551                return;
3552
3553        if (unlikely(rexmit == 2)) {
3554                __tcp_push_pending_frames(sk, tcp_current_mss(sk),
3555                                          TCP_NAGLE_OFF);
3556                if (after(tp->snd_nxt, tp->high_seq))
3557                        return;
3558                tp->frto = 0;
3559        }
3560        tcp_xmit_retransmit_queue(sk);
3561}
3562
3563/* Returns the number of packets newly acked or sacked by the current ACK */
3564static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
3565{
3566        const struct net *net = sock_net(sk);
3567        struct tcp_sock *tp = tcp_sk(sk);
3568        u32 delivered;
3569
3570        delivered = tp->delivered - prior_delivered;
3571        NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
3572        if (flag & FLAG_ECE) {
3573                tp->delivered_ce += delivered;
3574                NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered);
3575        }
3576        return delivered;
3577}
3578
3579/* This routine deals with incoming acks, but not outgoing ones. */
3580static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3581{
3582        struct inet_connection_sock *icsk = inet_csk(sk);
3583        struct tcp_sock *tp = tcp_sk(sk);
3584        struct tcp_sacktag_state sack_state;
3585        struct rate_sample rs = { .prior_delivered = 0 };
3586        u32 prior_snd_una = tp->snd_una;
3587        bool is_sack_reneg = tp->is_sack_reneg;
3588        u32 ack_seq = TCP_SKB_CB(skb)->seq;
3589        u32 ack = TCP_SKB_CB(skb)->ack_seq;
3590        int num_dupack = 0;
3591        int prior_packets = tp->packets_out;
3592        u32 delivered = tp->delivered;
3593        u32 lost = tp->lost;
3594        int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3595        u32 prior_fack;
3596
3597        sack_state.first_sackt = 0;
3598        sack_state.rate = &rs;
3599
3600        /* We very likely will need to access rtx queue. */
3601        prefetch(sk->tcp_rtx_queue.rb_node);
3602
3603        /* If the ack is older than previous acks
3604         * then we can probably ignore it.
3605         */
3606        if (before(ack, prior_snd_una)) {
3607                /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3608                if (before(ack, prior_snd_una - tp->max_window)) {
3609                        if (!(flag & FLAG_NO_CHALLENGE_ACK))
3610                                tcp_send_challenge_ack(sk, skb);
3611                        return -1;
3612                }
3613                goto old_ack;
3614        }
3615
3616        /* If the ack includes data we haven't sent yet, discard
3617         * this segment (RFC793 Section 3.9).
3618         */
3619        if (after(ack, tp->snd_nxt))
3620                return -1;
3621
3622        if (after(ack, prior_snd_una)) {
3623                flag |= FLAG_SND_UNA_ADVANCED;
3624                icsk->icsk_retransmits = 0;
3625
3626#if IS_ENABLED(CONFIG_TLS_DEVICE)
3627                if (static_branch_unlikely(&clean_acked_data_enabled.key))
3628                        if (icsk->icsk_clean_acked)
3629                                icsk->icsk_clean_acked(sk, ack);
3630#endif
3631        }
3632
3633        prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
3634        rs.prior_in_flight = tcp_packets_in_flight(tp);
3635
3636        /* ts_recent update must be made after we are sure that the packet
3637         * is in window.
3638         */
3639        if (flag & FLAG_UPDATE_TS_RECENT)
3640                tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3641
3642        if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) ==
3643            FLAG_SND_UNA_ADVANCED) {
3644                /* Window is constant, pure forward advance.
3645                 * No more checks are required.
3646                 * Note, we use the fact that SND.UNA>=SND.WL2.
3647                 */
3648                tcp_update_wl(tp, ack_seq);
3649                tcp_snd_una_update(tp, ack);
3650                flag |= FLAG_WIN_UPDATE;
3651
3652                tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3653
3654                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
3655        } else {
3656                u32 ack_ev_flags = CA_ACK_SLOWPATH;
3657
3658                if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3659                        flag |= FLAG_DATA;
3660                else
3661                        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3662
3663                flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3664
3665                if (TCP_SKB_CB(skb)->sacked)
3666                        flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3667                                                        &sack_state);
3668
3669                if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3670                        flag |= FLAG_ECE;
3671                        ack_ev_flags |= CA_ACK_ECE;
3672                }
3673
3674                if (flag & FLAG_WIN_UPDATE)
3675                        ack_ev_flags |= CA_ACK_WIN_UPDATE;
3676
3677                tcp_in_ack_event(sk, ack_ev_flags);
3678        }
3679
3680        /* We passed data and got it acked, remove any soft error
3681         * log. Something worked...
3682         */
3683        sk->sk_err_soft = 0;
3684        icsk->icsk_probes_out = 0;
3685        tp->rcv_tstamp = tcp_jiffies32;
3686        if (!prior_packets)
3687                goto no_queue;
3688
3689        /* See if we can take anything off of the retransmit queue. */
3690        flag |= tcp_clean_rtx_queue(sk, prior_fack, prior_snd_una, &sack_state);
3691
3692        tcp_rack_update_reo_wnd(sk, &rs);
3693
3694        if (tp->tlp_high_seq)
3695                tcp_process_tlp_ack(sk, ack, flag);
3696        /* If needed, reset TLP/RTO timer; RACK may later override this. */
3697        if (flag & FLAG_SET_XMIT_TIMER)
3698                tcp_set_xmit_timer(sk);
3699
3700        if (tcp_ack_is_dubious(sk, flag)) {
3701                if (!(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP))) {
3702                        num_dupack = 1;
3703                        /* Consider if pure acks were aggregated in tcp_add_backlog() */
3704                        if (!(flag & FLAG_DATA))
3705                                num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
3706                }
3707                tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3708                                      &rexmit);
3709        }
3710
3711        if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3712                sk_dst_confirm(sk);
3713
3714        delivered = tcp_newly_delivered(sk, delivered, flag);
3715        lost = tp->lost - lost;                 /* freshly marked lost */
3716        rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
3717        tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
3718        tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
3719        tcp_xmit_recovery(sk, rexmit);
3720        return 1;
3721
3722no_queue:
3723        /* If data was DSACKed, see if we can undo a cwnd reduction. */
3724        if (flag & FLAG_DSACKING_ACK) {
3725                tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3726                                      &rexmit);
3727                tcp_newly_delivered(sk, delivered, flag);
3728        }
3729        /* If this ack opens up a zero window, clear backoff.  It was
3730         * being used to time the probes, and is probably far higher than
3731         * it needs to be for normal retransmission.
3732         */
3733        tcp_ack_probe(sk);
3734
3735        if (tp->tlp_high_seq)
3736                tcp_process_tlp_ack(sk, ack, flag);
3737        return 1;
3738
3739old_ack:
3740        /* If data was SACKed, tag it and see if we should send more data.
3741         * If data was DSACKed, see if we can undo a cwnd reduction.
3742         */
3743        if (TCP_SKB_CB(skb)->sacked) {
3744                flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3745                                                &sack_state);
3746                tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3747                                      &rexmit);
3748                tcp_newly_delivered(sk, delivered, flag);
3749                tcp_xmit_recovery(sk, rexmit);
3750        }
3751
3752        return 0;
3753}
3754
3755static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3756                                      bool syn, struct tcp_fastopen_cookie *foc,
3757                                      bool exp_opt)
3758{
3759        /* Valid only in SYN or SYN-ACK with an even length.  */
3760        if (!foc || !syn || len < 0 || (len & 1))
3761                return;
3762
3763        if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3764            len <= TCP_FASTOPEN_COOKIE_MAX)
3765                memcpy(foc->val, cookie, len);
3766        else if (len != 0)
3767                len = -1;
3768        foc->len = len;
3769        foc->exp = exp_opt;
3770}
3771
3772static void smc_parse_options(const struct tcphdr *th,
3773                              struct tcp_options_received *opt_rx,
3774                              const unsigned char *ptr,
3775                              int opsize)
3776{
3777#if IS_ENABLED(CONFIG_SMC)
3778        if (static_branch_unlikely(&tcp_have_smc)) {
3779                if (th->syn && !(opsize & 1) &&
3780                    opsize >= TCPOLEN_EXP_SMC_BASE &&
3781                    get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC)
3782                        opt_rx->smc_ok = 1;
3783        }
3784#endif
3785}
3786
3787/* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
3788 * value on success.
3789 */
3790static u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
3791{
3792        const unsigned char *ptr = (const unsigned char *)(th + 1);
3793        int length = (th->doff * 4) - sizeof(struct tcphdr);
3794        u16 mss = 0;
3795
3796        while (length > 0) {
3797                int opcode = *ptr++;
3798                int opsize;
3799
3800                switch (opcode) {
3801                case TCPOPT_EOL:
3802                        return mss;
3803                case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3804                        length--;
3805                        continue;
3806                default:
3807                        if (length < 2)
3808                                return mss;
3809                        opsize = *ptr++;
3810                        if (opsize < 2) /* "silly options" */
3811                                return mss;
3812                        if (opsize > length)
3813                                return mss;     /* fail on partial options */
3814                        if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
3815                                u16 in_mss = get_unaligned_be16(ptr);
3816
3817                                if (in_mss) {
3818                                        if (user_mss && user_mss < in_mss)
3819                                                in_mss = user_mss;
3820                                        mss = in_mss;
3821                                }
3822                        }
3823                        ptr += opsize - 2;
3824                        length -= opsize;
3825                }
3826        }
3827        return mss;
3828}
3829
3830/* Look for tcp options. Normally only called on SYN and SYNACK packets.
3831 * But, this can also be called on packets in the established flow when
3832 * the fast version below fails.
3833 */
3834void tcp_parse_options(const struct net *net,
3835                       const struct sk_buff *skb,
3836                       struct tcp_options_received *opt_rx, int estab,
3837                       struct tcp_fastopen_cookie *foc)
3838{
3839        const unsigned char *ptr;
3840        const struct tcphdr *th = tcp_hdr(skb);
3841        int length = (th->doff * 4) - sizeof(struct tcphdr);
3842
3843        ptr = (const unsigned char *)(th + 1);
3844        opt_rx->saw_tstamp = 0;
3845
3846        while (length > 0) {
3847                int opcode = *ptr++;
3848                int opsize;
3849
3850                switch (opcode) {
3851                case TCPOPT_EOL:
3852                        return;
3853                case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3854                        length--;
3855                        continue;
3856                default:
3857                        if (length < 2)
3858                                return;
3859                        opsize = *ptr++;
3860                        if (opsize < 2) /* "silly options" */
3861                                return;
3862                        if (opsize > length)
3863                                return; /* don't parse partial options */
3864                        switch (opcode) {
3865                        case TCPOPT_MSS:
3866                                if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3867                                        u16 in_mss = get_unaligned_be16(ptr);
3868                                        if (in_mss) {
3869                                                if (opt_rx->user_mss &&
3870                                                    opt_rx->user_mss < in_mss)
3871                                                        in_mss = opt_rx->user_mss;
3872                                                opt_rx->mss_clamp = in_mss;
3873                                        }
3874                                }
3875                                break;
3876                        case TCPOPT_WINDOW:
3877                                if (opsize == TCPOLEN_WINDOW && th->syn &&
3878                                    !estab && net->ipv4.sysctl_tcp_window_scaling) {
3879                                        __u8 snd_wscale = *(__u8 *)ptr;
3880                                        opt_rx->wscale_ok = 1;
3881                                        if (snd_wscale > TCP_MAX_WSCALE) {
3882                                                net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
3883                                                                     __func__,
3884                                                                     snd_wscale,
3885                                                                     TCP_MAX_WSCALE);
3886                                                snd_wscale = TCP_MAX_WSCALE;
3887                                        }
3888                                        opt_rx->snd_wscale = snd_wscale;
3889                                }
3890                                break;
3891                        case TCPOPT_TIMESTAMP:
3892                                if ((opsize == TCPOLEN_TIMESTAMP) &&
3893                                    ((estab && opt_rx->tstamp_ok) ||
3894                                     (!estab && net->ipv4.sysctl_tcp_timestamps))) {
3895                                        opt_rx->saw_tstamp = 1;
3896                                        opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3897                                        opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3898                                }
3899                                break;
3900                        case TCPOPT_SACK_PERM:
3901                                if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3902                                    !estab && net->ipv4.sysctl_tcp_sack) {
3903                                        opt_rx->sack_ok = TCP_SACK_SEEN;
3904                                        tcp_sack_reset(opt_rx);
3905                                }
3906                                break;
3907
3908                        case TCPOPT_SACK:
3909                                if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3910                                   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3911                                   opt_rx->sack_ok) {
3912                                        TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3913                                }
3914                                break;
3915#ifdef CONFIG_TCP_MD5SIG
3916                        case TCPOPT_MD5SIG:
3917                                /*
3918                                 * The MD5 Hash has already been
3919                                 * checked (see tcp_v{4,6}_do_rcv()).
3920                                 */
3921                                break;
3922#endif
3923                        case TCPOPT_FASTOPEN:
3924                                tcp_parse_fastopen_option(
3925                                        opsize - TCPOLEN_FASTOPEN_BASE,
3926                                        ptr, th->syn, foc, false);
3927                                break;
3928
3929                        case TCPOPT_EXP:
3930                                /* Fast Open option shares code 254 using a
3931                                 * 16 bits magic number.
3932                                 */
3933                                if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
3934                                    get_unaligned_be16(ptr) ==
3935                                    TCPOPT_FASTOPEN_MAGIC)
3936                                        tcp_parse_fastopen_option(opsize -
3937                                                TCPOLEN_EXP_FASTOPEN_BASE,
3938                                                ptr + 2, th->syn, foc, true);
3939                                else
3940                                        smc_parse_options(th, opt_rx, ptr,
3941                                                          opsize);
3942                                break;
3943
3944                        }
3945                        ptr += opsize-2;
3946                        length -= opsize;
3947                }
3948        }
3949}
3950EXPORT_SYMBOL(tcp_parse_options);
3951
3952static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3953{
3954        const __be32 *ptr = (const __be32 *)(th + 1);
3955
3956        if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3957                          | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3958                tp->rx_opt.saw_tstamp = 1;
3959                ++ptr;
3960                tp->rx_opt.rcv_tsval = ntohl(*ptr);
3961                ++ptr;
3962                if (*ptr)
3963                        tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
3964                else
3965                        tp->rx_opt.rcv_tsecr = 0;
3966                return true;
3967        }
3968        return false;
3969}
3970
3971/* Fast parse options. This hopes to only see timestamps.
3972 * If it is wrong it falls back on tcp_parse_options().
3973 */
3974static bool tcp_fast_parse_options(const struct net *net,
3975                                   const struct sk_buff *skb,
3976                                   const struct tcphdr *th, struct tcp_sock *tp)
3977{
3978        /* In the spirit of fast parsing, compare doff directly to constant
3979         * values.  Because equality is used, short doff can be ignored here.
3980         */
3981        if (th->doff == (sizeof(*th) / 4)) {
3982                tp->rx_opt.saw_tstamp = 0;
3983                return false;
3984        } else if (tp->rx_opt.tstamp_ok &&
3985                   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3986                if (tcp_parse_aligned_timestamp(tp, th))
3987                        return true;
3988        }
3989
3990        tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
3991        if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3992                tp->rx_opt.rcv_tsecr -= tp->tsoffset;
3993
3994        return true;
3995}
3996
3997#ifdef CONFIG_TCP_MD5SIG
3998/*
3999 * Parse MD5 Signature option
4000 */
4001const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
4002{
4003        int length = (th->doff << 2) - sizeof(*th);
4004        const u8 *ptr = (const u8 *)(th + 1);
4005
4006        /* If not enough data remaining, we can short cut */
4007        while (length >= TCPOLEN_MD5SIG) {
4008                int opcode = *ptr++;
4009                int opsize;
4010
4011                switch (opcode) {
4012                case TCPOPT_EOL:
4013                        return NULL;
4014                case TCPOPT_NOP:
4015                        length--;
4016                        continue;
4017                default:
4018                        opsize = *ptr++;
4019                        if (opsize < 2 || opsize > length)
4020                                return NULL;
4021                        if (opcode == TCPOPT_MD5SIG)
4022                                return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
4023                }
4024                ptr += opsize - 2;
4025                length -= opsize;
4026        }
4027        return NULL;
4028}
4029EXPORT_SYMBOL(tcp_parse_md5sig_option);
4030#endif
4031
4032/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4033 *
4034 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4035 * it can pass through stack. So, the following predicate verifies that
4036 * this segment is not used for anything but congestion avoidance or
4037 * fast retransmit. Moreover, we even are able to eliminate most of such
4038 * second order effects, if we apply some small "replay" window (~RTO)
4039 * to timestamp space.
4040 *
4041 * All these measures still do not guarantee that we reject wrapped ACKs
4042 * on networks with high bandwidth, when sequence space is recycled fastly,
4043 * but it guarantees that such events will be very rare and do not affect
4044 * connection seriously. This doesn't look nice, but alas, PAWS is really
4045 * buggy extension.
4046 *
4047 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4048 * states that events when retransmit arrives after original data are rare.
4049 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4050 * the biggest problem on large power networks even with minor reordering.
4051 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4052 * up to bandwidth of 18Gigabit/sec. 8) ]
4053 */
4054
4055static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
4056{
4057        const struct tcp_sock *tp = tcp_sk(sk);
4058        const struct tcphdr *th = tcp_hdr(skb);
4059        u32 seq = TCP_SKB_CB(skb)->seq;
4060        u32 ack = TCP_SKB_CB(skb)->ack_seq;
4061
4062        return (/* 1. Pure ACK with correct sequence number. */
4063                (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4064
4065                /* 2. ... and duplicate ACK. */
4066                ack == tp->snd_una &&
4067
4068                /* 3. ... and does not update window. */
4069                !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4070
4071                /* 4. ... and sits in replay window. */
4072                (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4073}
4074
4075static inline bool tcp_paws_discard(const struct sock *sk,
4076                                   const struct sk_buff *skb)
4077{
4078        const struct tcp_sock *tp = tcp_sk(sk);
4079
4080        return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4081               !tcp_disordered_ack(sk, skb);
4082}
4083
4084/* Check segment sequence number for validity.
4085 *
4086 * Segment controls are considered valid, if the segment
4087 * fits to the window after truncation to the window. Acceptability
4088 * of data (and SYN, FIN, of course) is checked separately.
4089 * See tcp_data_queue(), for example.
4090 *
4091 * Also, controls (RST is main one) are accepted using RCV.WUP instead
4092 * of RCV.NXT. Peer still did not advance his SND.UNA when we
4093 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4094 * (borrowed from freebsd)
4095 */
4096
4097static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
4098{
4099        return  !before(end_seq, tp->rcv_wup) &&
4100                !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4101}
4102
4103/* When we get a reset we do this. */
4104void tcp_reset(struct sock *sk)
4105{
4106        trace_tcp_receive_reset(sk);
4107
4108        /* We want the right error as BSD sees it (and indeed as we do). */
4109        switch (sk->sk_state) {
4110        case TCP_SYN_SENT:
4111                sk->sk_err = ECONNREFUSED;
4112                break;
4113        case TCP_CLOSE_WAIT:
4114                sk->sk_err = EPIPE;
4115                break;
4116        case TCP_CLOSE:
4117                return;
4118        default:
4119                sk->sk_err = ECONNRESET;
4120        }
4121        /* This barrier is coupled with smp_rmb() in tcp_poll() */
4122        smp_wmb();
4123
4124        tcp_write_queue_purge(sk);
4125        tcp_done(sk);
4126
4127        if (!sock_flag(sk, SOCK_DEAD))
4128                sk->sk_error_report(sk);
4129}
4130
4131/*
4132 *      Process the FIN bit. This now behaves as it is supposed to work
4133 *      and the FIN takes effect when it is validly part of sequence
4134 *      space. Not before when we get holes.
4135 *
4136 *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4137 *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
4138 *      TIME-WAIT)
4139 *
4140 *      If we are in FINWAIT-1, a received FIN indicates simultaneous
4141 *      close and we go into CLOSING (and later onto TIME-WAIT)
4142 *
4143 *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4144 */
4145void tcp_fin(struct sock *sk)
4146{
4147        struct tcp_sock *tp = tcp_sk(sk);
4148
4149        inet_csk_schedule_ack(sk);
4150
4151        sk->sk_shutdown |= RCV_SHUTDOWN;
4152        sock_set_flag(sk, SOCK_DONE);
4153
4154        switch (sk->sk_state) {
4155        case TCP_SYN_RECV:
4156        case TCP_ESTABLISHED:
4157                /* Move to CLOSE_WAIT */
4158                tcp_set_state(sk, TCP_CLOSE_WAIT);
4159                inet_csk_enter_pingpong_mode(sk);
4160                break;
4161
4162        case TCP_CLOSE_WAIT:
4163        case TCP_CLOSING:
4164                /* Received a retransmission of the FIN, do
4165                 * nothing.
4166                 */
4167                break;
4168        case TCP_LAST_ACK:
4169                /* RFC793: Remain in the LAST-ACK state. */
4170                break;
4171
4172        case TCP_FIN_WAIT1:
4173                /* This case occurs when a simultaneous close
4174                 * happens, we must ack the received FIN and
4175                 * enter the CLOSING state.
4176                 */
4177                tcp_send_ack(sk);
4178                tcp_set_state(sk, TCP_CLOSING);
4179                break;
4180        case TCP_FIN_WAIT2:
4181                /* Received a FIN -- send ACK and enter TIME_WAIT. */
4182                tcp_send_ack(sk);
4183                tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4184                break;
4185        default:
4186                /* Only TCP_LISTEN and TCP_CLOSE are left, in these
4187                 * cases we should never reach this piece of code.
4188                 */
4189                pr_err("%s: Impossible, sk->sk_state=%d\n",
4190                       __func__, sk->sk_state);
4191                break;
4192        }
4193
4194        /* It _is_ possible, that we have something out-of-order _after_ FIN.
4195         * Probably, we should reset in this case. For now drop them.
4196         */
4197        skb_rbtree_purge(&tp->out_of_order_queue);
4198        if (tcp_is_sack(tp))
4199                tcp_sack_reset(&tp->rx_opt);
4200        sk_mem_reclaim(sk);
4201
4202        if (!sock_flag(sk, SOCK_DEAD)) {
4203                sk->sk_state_change(sk);
4204
4205                /* Do not send POLL_HUP for half duplex close. */
4206                if (sk->sk_shutdown == SHUTDOWN_MASK ||
4207                    sk->sk_state == TCP_CLOSE)
4208                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4209                else
4210                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4211        }
4212}
4213
4214static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4215                                  u32 end_seq)
4216{
4217        if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4218                if (before(seq, sp->start_seq))
4219                        sp->start_seq = seq;
4220                if (after(end_seq, sp->end_seq))
4221                        sp->end_seq = end_seq;
4222                return true;
4223        }
4224        return false;
4225}
4226
4227static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4228{
4229        struct tcp_sock *tp = tcp_sk(sk);
4230
4231        if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
4232                int mib_idx;
4233
4234                if (before(seq, tp->rcv_nxt))
4235                        mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4236                else
4237                        mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4238
4239                NET_INC_STATS(sock_net(sk), mib_idx);
4240
4241                tp->rx_opt.dsack = 1;
4242                tp->duplicate_sack[0].start_seq = seq;
4243                tp->duplicate_sack[0].end_seq = end_seq;
4244        }
4245}
4246
4247static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4248{
4249        struct tcp_sock *tp = tcp_sk(sk);
4250
4251        if (!tp->rx_opt.dsack)
4252                tcp_dsack_set(sk, seq, end_seq);
4253        else
4254                tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4255}
4256
4257static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
4258{
4259        /* When the ACK path fails or drops most ACKs, the sender would
4260         * timeout and spuriously retransmit the same segment repeatedly.
4261         * The receiver remembers and reflects via DSACKs. Leverage the
4262         * DSACK state and change the txhash to re-route speculatively.
4263         */
4264        if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq)
4265                sk_rethink_txhash(sk);
4266}
4267
4268static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4269{
4270        struct tcp_sock *tp = tcp_sk(sk);
4271
4272        if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4273            before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4274                NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4275                tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4276
4277                if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
4278                        u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4279
4280                        tcp_rcv_spurious_retrans(sk, skb);
4281                        if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4282                                end_seq = tp->rcv_nxt;
4283                        tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4284                }
4285        }
4286
4287        tcp_send_ack(sk);
4288}
4289
4290/* These routines update the SACK block as out-of-order packets arrive or
4291 * in-order packets close up the sequence space.
4292 */
4293static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4294{
4295        int this_sack;
4296        struct tcp_sack_block *sp = &tp->selective_acks[0];
4297        struct tcp_sack_block *swalk = sp + 1;
4298
4299        /* See if the recent change to the first SACK eats into
4300         * or hits the sequence space of other SACK blocks, if so coalesce.
4301         */
4302        for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4303                if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4304                        int i;
4305
4306                        /* Zap SWALK, by moving every further SACK up by one slot.
4307                         * Decrease num_sacks.
4308                         */
4309                        tp->rx_opt.num_sacks--;
4310                        for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4311                                sp[i] = sp[i + 1];
4312                        continue;
4313                }
4314                this_sack++, swalk++;
4315        }
4316}
4317
4318static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4319{
4320        struct tcp_sock *tp = tcp_sk(sk);
4321        struct tcp_sack_block *sp = &tp->selective_acks[0];
4322        int cur_sacks = tp->rx_opt.num_sacks;
4323        int this_sack;
4324
4325        if (!cur_sacks)
4326                goto new_sack;
4327
4328        for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4329                if (tcp_sack_extend(sp, seq, end_seq)) {
4330                        /* Rotate this_sack to the first one. */
4331                        for (; this_sack > 0; this_sack--, sp--)
4332                                swap(*sp, *(sp - 1));
4333                        if (cur_sacks > 1)
4334                                tcp_sack_maybe_coalesce(tp);
4335                        return;
4336                }
4337        }
4338
4339        /* Could not find an adjacent existing SACK, build a new one,
4340         * put it at the front, and shift everyone else down.  We
4341         * always know there is at least one SACK present already here.
4342         *
4343         * If the sack array is full, forget about the last one.
4344         */
4345        if (this_sack >= TCP_NUM_SACKS) {
4346                if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)
4347                        tcp_send_ack(sk);
4348                this_sack--;
4349                tp->rx_opt.num_sacks--;
4350                sp--;
4351        }
4352        for (; this_sack > 0; this_sack--, sp--)
4353                *sp = *(sp - 1);
4354
4355new_sack:
4356        /* Build the new head SACK, and we're done. */
4357        sp->start_seq = seq;
4358        sp->end_seq = end_seq;
4359        tp->rx_opt.num_sacks++;
4360}
4361
4362/* RCV.NXT advances, some SACKs should be eaten. */
4363
4364static void tcp_sack_remove(struct tcp_sock *tp)
4365{
4366        struct tcp_sack_block *sp = &tp->selective_acks[0];
4367        int num_sacks = tp->rx_opt.num_sacks;
4368        int this_sack;
4369
4370        /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4371        if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4372                tp->rx_opt.num_sacks = 0;
4373                return;
4374        }
4375
4376        for (this_sack = 0; this_sack < num_sacks;) {
4377                /* Check if the start of the sack is covered by RCV.NXT. */
4378                if (!before(tp->rcv_nxt, sp->start_seq)) {
4379                        int i;
4380
4381                        /* RCV.NXT must cover all the block! */
4382                        WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4383
4384                        /* Zap this SACK, by moving forward any other SACKS. */
4385                        for (i = this_sack+1; i < num_sacks; i++)
4386                                tp->selective_acks[i-1] = tp->selective_acks[i];
4387                        num_sacks--;
4388                        continue;
4389                }
4390                this_sack++;
4391                sp++;
4392        }
4393        tp->rx_opt.num_sacks = num_sacks;
4394}
4395
4396/**
4397 * tcp_try_coalesce - try to merge skb to prior one
4398 * @sk: socket
4399 * @dest: destination queue
4400 * @to: prior buffer
4401 * @from: buffer to add in queue
4402 * @fragstolen: pointer to boolean
4403 *
4404 * Before queueing skb @from after @to, try to merge them
4405 * to reduce overall memory use and queue lengths, if cost is small.
4406 * Packets in ofo or receive queues can stay a long time.
4407 * Better try to coalesce them right now to avoid future collapses.
4408 * Returns true if caller should free @from instead of queueing it
4409 */
4410static bool tcp_try_coalesce(struct sock *sk,
4411                             struct sk_buff *to,
4412                             struct sk_buff *from,
4413                             bool *fragstolen)
4414{
4415        int delta;
4416
4417        *fragstolen = false;
4418
4419        /* Its possible this segment overlaps with prior segment in queue */
4420        if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4421                return false;
4422
4423#ifdef CONFIG_TLS_DEVICE
4424        if (from->decrypted != to->decrypted)
4425                return false;
4426#endif
4427
4428        if (!skb_try_coalesce(to, from, fragstolen, &delta))
4429                return false;
4430
4431        atomic_add(delta, &sk->sk_rmem_alloc);
4432        sk_mem_charge(sk, delta);
4433        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4434        TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4435        TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4436        TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4437
4438        if (TCP_SKB_CB(from)->has_rxtstamp) {
4439                TCP_SKB_CB(to)->has_rxtstamp = true;
4440                to->tstamp = from->tstamp;
4441                skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
4442        }
4443
4444        return true;
4445}
4446
4447static bool tcp_ooo_try_coalesce(struct sock *sk,
4448                             struct sk_buff *to,
4449                             struct sk_buff *from,
4450                             bool *fragstolen)
4451{
4452        bool res = tcp_try_coalesce(sk, to, from, fragstolen);
4453
4454        /* In case tcp_drop() is called later, update to->gso_segs */
4455        if (res) {
4456                u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
4457                               max_t(u16, 1, skb_shinfo(from)->gso_segs);
4458
4459                skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
4460        }
4461        return res;
4462}
4463
4464static void tcp_drop(struct sock *sk, struct sk_buff *skb)
4465{
4466        sk_drops_add(sk, skb);
4467        __kfree_skb(skb);
4468}
4469
4470/* This one checks to see if we can put data from the
4471 * out_of_order queue into the receive_queue.
4472 */
4473static void tcp_ofo_queue(struct sock *sk)
4474{
4475        struct tcp_sock *tp = tcp_sk(sk);
4476        __u32 dsack_high = tp->rcv_nxt;
4477        bool fin, fragstolen, eaten;
4478        struct sk_buff *skb, *tail;
4479        struct rb_node *p;
4480
4481        p = rb_first(&tp->out_of_order_queue);
4482        while (p) {
4483                skb = rb_to_skb(p);
4484                if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4485                        break;
4486
4487                if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4488                        __u32 dsack = dsack_high;
4489                        if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4490                                dsack_high = TCP_SKB_CB(skb)->end_seq;
4491                        tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4492                }
4493                p = rb_next(p);
4494                rb_erase(&skb->rbnode, &tp->out_of_order_queue);
4495
4496                if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
4497                        tcp_drop(sk, skb);
4498                        continue;
4499                }
4500
4501                tail = skb_peek_tail(&sk->sk_receive_queue);
4502                eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4503                tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4504                fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
4505                if (!eaten)
4506                        __skb_queue_tail(&sk->sk_receive_queue, skb);
4507                else
4508                        kfree_skb_partial(skb, fragstolen);
4509
4510                if (unlikely(fin)) {
4511                        tcp_fin(sk);
4512                        /* tcp_fin() purges tp->out_of_order_queue,
4513                         * so we must end this loop right now.
4514                         */
4515                        break;
4516                }
4517        }
4518}
4519
4520static bool tcp_prune_ofo_queue(struct sock *sk);
4521static int tcp_prune_queue(struct sock *sk);
4522
4523static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4524                                 unsigned int size)
4525{
4526        if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4527            !sk_rmem_schedule(sk, skb, size)) {
4528
4529                if (tcp_prune_queue(sk) < 0)
4530                        return -1;
4531
4532                while (!sk_rmem_schedule(sk, skb, size)) {
4533                        if (!tcp_prune_ofo_queue(sk))
4534                                return -1;
4535                }
4536        }
4537        return 0;
4538}
4539
4540static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4541{
4542        struct tcp_sock *tp = tcp_sk(sk);
4543        struct rb_node **p, *parent;
4544        struct sk_buff *skb1;
4545        u32 seq, end_seq;
4546        bool fragstolen;
4547
4548        tcp_ecn_check_ce(sk, skb);
4549
4550        if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4551                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
4552                tcp_drop(sk, skb);
4553                return;
4554        }
4555
4556        /* Disable header prediction. */
4557        tp->pred_flags = 0;
4558        inet_csk_schedule_ack(sk);
4559
4560        tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
4561        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4562        seq = TCP_SKB_CB(skb)->seq;
4563        end_seq = TCP_SKB_CB(skb)->end_seq;
4564
4565        p = &tp->out_of_order_queue.rb_node;
4566        if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4567                /* Initial out of order segment, build 1 SACK. */
4568                if (tcp_is_sack(tp)) {
4569                        tp->rx_opt.num_sacks = 1;
4570                        tp->selective_acks[0].start_seq = seq;
4571                        tp->selective_acks[0].end_seq = end_seq;
4572                }
4573                rb_link_node(&skb->rbnode, NULL, p);
4574                rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4575                tp->ooo_last_skb = skb;
4576                goto end;
4577        }
4578
4579        /* In the typical case, we are adding an skb to the end of the list.
4580         * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
4581         */
4582        if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
4583                                 skb, &fragstolen)) {
4584coalesce_done:
4585                tcp_grow_window(sk, skb);
4586                kfree_skb_partial(skb, fragstolen);
4587                skb = NULL;
4588                goto add_sack;
4589        }
4590        /* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
4591        if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
4592                parent = &tp->ooo_last_skb->rbnode;
4593                p = &parent->rb_right;
4594                goto insert;
4595        }
4596
4597        /* Find place to insert this segment. Handle overlaps on the way. */
4598        parent = NULL;
4599        while (*p) {
4600                parent = *p;
4601                skb1 = rb_to_skb(parent);
4602                if (before(seq, TCP_SKB_CB(skb1)->seq)) {
4603                        p = &parent->rb_left;
4604                        continue;
4605                }
4606                if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4607                        if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4608                                /* All the bits are present. Drop. */
4609                                NET_INC_STATS(sock_net(sk),
4610                                              LINUX_MIB_TCPOFOMERGE);
4611                                tcp_drop(sk, skb);
4612                                skb = NULL;
4613                                tcp_dsack_set(sk, seq, end_seq);
4614                                goto add_sack;
4615                        }
4616                        if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4617                                /* Partial overlap. */
4618                                tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
4619                        } else {
4620                                /* skb's seq == skb1's seq and skb covers skb1.
4621                                 * Replace skb1 with skb.
4622                                 */
4623                                rb_replace_node(&skb1->rbnode, &skb->rbnode,
4624                                                &tp->out_of_order_queue);
4625                                tcp_dsack_extend(sk,
4626                                                 TCP_SKB_CB(skb1)->seq,
4627                                                 TCP_SKB_CB(skb1)->end_seq);
4628                                NET_INC_STATS(sock_net(sk),
4629                                              LINUX_MIB_TCPOFOMERGE);
4630                                tcp_drop(sk, skb1);
4631                                goto merge_right;
4632                        }
4633                } else if (tcp_ooo_try_coalesce(sk, skb1,
4634                                                skb, &fragstolen)) {
4635                        goto coalesce_done;
4636                }
4637                p = &parent->rb_right;
4638        }
4639insert:
4640        /* Insert segment into RB tree. */
4641        rb_link_node(&skb->rbnode, parent, p);
4642        rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4643
4644merge_right:
4645        /* Remove other segments covered by skb. */
4646        while ((skb1 = skb_rb_next(skb)) != NULL) {
4647                if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4648                        break;
4649                if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4650                        tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4651                                         end_seq);
4652                        break;
4653                }
4654                rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
4655                tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4656                                 TCP_SKB_CB(skb1)->end_seq);
4657                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4658                tcp_drop(sk, skb1);
4659        }
4660        /* If there is no skb after us, we are the last_skb ! */
4661        if (!skb1)
4662                tp->ooo_last_skb = skb;
4663
4664add_sack:
4665        if (tcp_is_sack(tp))
4666                tcp_sack_new_ofo_skb(sk, seq, end_seq);
4667end:
4668        if (skb) {
4669                tcp_grow_window(sk, skb);
4670                skb_condense(skb);
4671                skb_set_owner_r(skb, sk);
4672        }
4673}
4674
4675static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
4676                                      bool *fragstolen)
4677{
4678        int eaten;
4679        struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4680
4681        eaten = (tail &&
4682                 tcp_try_coalesce(sk, tail,
4683                                  skb, fragstolen)) ? 1 : 0;
4684        tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4685        if (!eaten) {
4686                __skb_queue_tail(&sk->sk_receive_queue, skb);
4687                skb_set_owner_r(skb, sk);
4688        }
4689        return eaten;
4690}
4691
4692int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4693{
4694        struct sk_buff *skb;
4695        int err = -ENOMEM;
4696        int data_len = 0;
4697        bool fragstolen;
4698
4699        if (size == 0)
4700                return 0;
4701
4702        if (size > PAGE_SIZE) {
4703                int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
4704
4705                data_len = npages << PAGE_SHIFT;
4706                size = data_len + (size & ~PAGE_MASK);
4707        }
4708        skb = alloc_skb_with_frags(size - data_len, data_len,
4709                                   PAGE_ALLOC_COSTLY_ORDER,
4710                                   &err, sk->sk_allocation);
4711        if (!skb)
4712                goto err;
4713
4714        skb_put(skb, size - data_len);
4715        skb->data_len = data_len;
4716        skb->len = size;
4717
4718        if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
4719                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
4720                goto err_free;
4721        }
4722
4723        err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
4724        if (err)
4725                goto err_free;
4726
4727        TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4728        TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4729        TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4730
4731        if (tcp_queue_rcv(sk, skb, &fragstolen)) {
4732                WARN_ON_ONCE(fragstolen); /* should not happen */
4733                __kfree_skb(skb);
4734        }
4735        return size;
4736
4737err_free:
4738        kfree_skb(skb);
4739err:
4740        return err;
4741
4742}
4743
4744void tcp_data_ready(struct sock *sk)
4745{
4746        const struct tcp_sock *tp = tcp_sk(sk);
4747        int avail = tp->rcv_nxt - tp->copied_seq;
4748
4749        if (avail < sk->sk_rcvlowat && !sock_flag(sk, SOCK_DONE))
4750                return;
4751
4752        sk->sk_data_ready(sk);
4753}
4754
4755static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4756{
4757        struct tcp_sock *tp = tcp_sk(sk);
4758        bool fragstolen;
4759        int eaten;
4760
4761        if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
4762                __kfree_skb(skb);
4763                return;
4764        }
4765        skb_dst_drop(skb);
4766        __skb_pull(skb, tcp_hdr(skb)->doff * 4);
4767
4768        tcp_ecn_accept_cwr(sk, skb);
4769
4770        tp->rx_opt.dsack = 0;
4771
4772        /*  Queue data for delivery to the user.
4773         *  Packets in sequence go to the receive queue.
4774         *  Out of sequence packets to the out_of_order_queue.
4775         */
4776        if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4777                if (tcp_receive_window(tp) == 0) {
4778                        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
4779                        goto out_of_window;
4780                }
4781
4782                /* Ok. In sequence. In window. */
4783queue_and_out:
4784                if (skb_queue_len(&sk->sk_receive_queue) == 0)
4785                        sk_forced_mem_schedule(sk, skb->truesize);
4786                else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
4787                        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
4788                        goto drop;
4789                }
4790
4791                eaten = tcp_queue_rcv(sk, skb, &fragstolen);
4792                if (skb->len)
4793                        tcp_event_data_recv(sk, skb);
4794                if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4795                        tcp_fin(sk);
4796
4797                if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4798                        tcp_ofo_queue(sk);
4799
4800                        /* RFC5681. 4.2. SHOULD send immediate ACK, when
4801                         * gap in queue is filled.
4802                         */
4803                        if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
4804                                inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
4805                }
4806
4807                if (tp->rx_opt.num_sacks)
4808                        tcp_sack_remove(tp);
4809
4810                tcp_fast_path_check(sk);
4811
4812                if (eaten > 0)
4813                        kfree_skb_partial(skb, fragstolen);
4814                if (!sock_flag(sk, SOCK_DEAD))
4815                        tcp_data_ready(sk);
4816                return;
4817        }
4818
4819        if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4820                tcp_rcv_spurious_retrans(sk, skb);
4821                /* A retransmit, 2nd most common case.  Force an immediate ack. */
4822                NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4823                tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4824
4825out_of_window:
4826                tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4827                inet_csk_schedule_ack(sk);
4828drop:
4829                tcp_drop(sk, skb);
4830                return;
4831        }
4832
4833        /* Out of window. F.e. zero window probe. */
4834        if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4835                goto out_of_window;
4836
4837        if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4838                /* Partial packet, seq < rcv_next < end_seq */
4839                tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4840
4841                /* If window is closed, drop tail of packet. But after
4842                 * remembering D-SACK for its head made in previous line.
4843                 */
4844                if (!tcp_receive_window(tp)) {
4845                        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
4846                        goto out_of_window;
4847                }
4848                goto queue_and_out;
4849        }
4850
4851        tcp_data_queue_ofo(sk, skb);
4852}
4853
4854static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
4855{
4856        if (list)
4857                return !skb_queue_is_last(list, skb) ? skb->next : NULL;
4858
4859        return skb_rb_next(skb);
4860}
4861
4862static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4863                                        struct sk_buff_head *list,
4864                                        struct rb_root *root)
4865{
4866        struct sk_buff *next = tcp_skb_next(skb, list);
4867
4868        if (list)
4869                __skb_unlink(skb, list);
4870        else
4871                rb_erase(&skb->rbnode, root);
4872
4873        __kfree_skb(skb);
4874        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4875
4876        return next;
4877}
4878
4879/* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
4880void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
4881{
4882        struct rb_node **p = &root->rb_node;
4883        struct rb_node *parent = NULL;
4884        struct sk_buff *skb1;
4885
4886        while (*p) {
4887                parent = *p;
4888                skb1 = rb_to_skb(parent);
4889                if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
4890                        p = &parent->rb_left;
4891                else
4892                        p = &parent->rb_right;
4893        }
4894        rb_link_node(&skb->rbnode, parent, p);
4895        rb_insert_color(&skb->rbnode, root);
4896}
4897
4898/* Collapse contiguous sequence of skbs head..tail with
4899 * sequence numbers start..end.
4900 *
4901 * If tail is NULL, this means until the end of the queue.
4902 *
4903 * Segments with FIN/SYN are not collapsed (only because this
4904 * simplifies code)
4905 */
4906static void
4907tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
4908             struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
4909{
4910        struct sk_buff *skb = head, *n;
4911        struct sk_buff_head tmp;
4912        bool end_of_skbs;
4913
4914        /* First, check that queue is collapsible and find
4915         * the point where collapsing can be useful.
4916         */
4917restart:
4918        for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
4919                n = tcp_skb_next(skb, list);
4920
4921                /* No new bits? It is possible on ofo queue. */
4922                if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4923                        skb = tcp_collapse_one(sk, skb, list, root);
4924                        if (!skb)
4925                                break;
4926                        goto restart;
4927                }
4928
4929                /* The first skb to collapse is:
4930                 * - not SYN/FIN and
4931                 * - bloated or contains data before "start" or
4932                 *   overlaps to the next one.
4933                 */
4934                if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
4935                    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
4936                     before(TCP_SKB_CB(skb)->seq, start))) {
4937                        end_of_skbs = false;
4938                        break;
4939                }
4940
4941                if (n && n != tail &&
4942                    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
4943                        end_of_skbs = false;
4944                        break;
4945                }
4946
4947                /* Decided to skip this, advance start seq. */
4948                start = TCP_SKB_CB(skb)->end_seq;
4949        }
4950        if (end_of_skbs ||
4951            (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4952                return;
4953
4954        __skb_queue_head_init(&tmp);
4955
4956        while (before(start, end)) {
4957                int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
4958                struct sk_buff *nskb;
4959
4960                nskb = alloc_skb(copy, GFP_ATOMIC);
4961                if (!nskb)
4962                        break;
4963
4964                memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4965#ifdef CONFIG_TLS_DEVICE
4966                nskb->decrypted = skb->decrypted;
4967#endif
4968                TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4969                if (list)
4970                        __skb_queue_before(list, skb, nskb);
4971                else
4972                        __skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
4973                skb_set_owner_r(nskb, sk);
4974
4975                /* Copy data, releasing collapsed skbs. */
4976                while (copy > 0) {
4977                        int offset = start - TCP_SKB_CB(skb)->seq;
4978                        int size = TCP_SKB_CB(skb)->end_seq - start;
4979
4980                        BUG_ON(offset < 0);
4981                        if (size > 0) {
4982                                size = min(copy, size);
4983                                if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4984                                        BUG();
4985                                TCP_SKB_CB(nskb)->end_seq += size;
4986                                copy -= size;
4987                                start += size;
4988                        }
4989                        if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4990                                skb = tcp_collapse_one(sk, skb, list, root);
4991                                if (!skb ||
4992                                    skb == tail ||
4993                                    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4994                                        goto end;
4995#ifdef CONFIG_TLS_DEVICE
4996                                if (skb->decrypted != nskb->decrypted)
4997                                        goto end;
4998#endif
4999                        }
5000                }
5001        }
5002end:
5003        skb_queue_walk_safe(&tmp, skb, n)
5004                tcp_rbtree_insert(root, skb);
5005}
5006
5007/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
5008 * and tcp_collapse() them until all the queue is collapsed.
5009 */
5010static void tcp_collapse_ofo_queue(struct sock *sk)
5011{
5012        struct tcp_sock *tp = tcp_sk(sk);
5013        u32 range_truesize, sum_tiny = 0;
5014        struct sk_buff *skb, *head;
5015        u32 start, end;
5016
5017        skb = skb_rb_first(&tp->out_of_order_queue);
5018new_range:
5019        if (!skb) {
5020                tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
5021                return;
5022        }
5023        start = TCP_SKB_CB(skb)->seq;
5024        end = TCP_SKB_CB(skb)->end_seq;
5025        range_truesize = skb->truesize;
5026
5027        for (head = skb;;) {
5028                skb = skb_rb_next(skb);
5029
5030                /* Range is terminated when we see a gap or when
5031                 * we are at the queue end.
5032                 */
5033                if (!skb ||
5034                    after(TCP_SKB_CB(skb)->seq, end) ||
5035                    before(TCP_SKB_CB(skb)->end_seq, start)) {
5036                        /* Do not attempt collapsing tiny skbs */
5037                        if (range_truesize != head->truesize ||
5038                            end - start >= SKB_WITH_OVERHEAD(SK_MEM_QUANTUM)) {
5039                                tcp_collapse(sk, NULL, &tp->out_of_order_queue,
5040                                             head, skb, start, end);
5041                        } else {
5042                                sum_tiny += range_truesize;
5043                                if (sum_tiny > sk->sk_rcvbuf >> 3)
5044                                        return;
5045                        }
5046                        goto new_range;
5047                }
5048
5049                range_truesize += skb->truesize;
5050                if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
5051                        start = TCP_SKB_CB(skb)->seq;
5052                if (after(TCP_SKB_CB(skb)->end_seq, end))
5053                        end = TCP_SKB_CB(skb)->end_seq;
5054        }
5055}
5056
5057/*
5058 * Clean the out-of-order queue to make room.
5059 * We drop high sequences packets to :
5060 * 1) Let a chance for holes to be filled.
5061 * 2) not add too big latencies if thousands of packets sit there.
5062 *    (But if application shrinks SO_RCVBUF, we could still end up
5063 *     freeing whole queue here)
5064 * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
5065 *
5066 * Return true if queue has shrunk.
5067 */
5068static bool tcp_prune_ofo_queue(struct sock *sk)
5069{
5070        struct tcp_sock *tp = tcp_sk(sk);
5071        struct rb_node *node, *prev;
5072        int goal;
5073
5074        if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5075                return false;
5076
5077        NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
5078        goal = sk->sk_rcvbuf >> 3;
5079        node = &tp->ooo_last_skb->rbnode;
5080        do {
5081                prev = rb_prev(node);
5082                rb_erase(node, &tp->out_of_order_queue);
5083                goal -= rb_to_skb(node)->truesize;
5084                tcp_drop(sk, rb_to_skb(node));
5085                if (!prev || goal <= 0) {
5086                        sk_mem_reclaim(sk);
5087                        if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
5088                            !tcp_under_memory_pressure(sk))
5089                                break;
5090                        goal = sk->sk_rcvbuf >> 3;
5091                }
5092                node = prev;
5093        } while (node);
5094        tp->ooo_last_skb = rb_to_skb(prev);
5095
5096        /* Reset SACK state.  A conforming SACK implementation will
5097         * do the same at a timeout based retransmit.  When a connection
5098         * is in a sad state like this, we care only about integrity
5099         * of the connection not performance.
5100         */
5101        if (tp->rx_opt.sack_ok)
5102                tcp_sack_reset(&tp->rx_opt);
5103        return true;
5104}
5105
5106/* Reduce allocated memory if we can, trying to get
5107 * the socket within its memory limits again.
5108 *
5109 * Return less than zero if we should start dropping frames
5110 * until the socket owning process reads some of the data
5111 * to stabilize the situation.
5112 */
5113static int tcp_prune_queue(struct sock *sk)
5114{
5115        struct tcp_sock *tp = tcp_sk(sk);
5116
5117        NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
5118
5119        if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
5120                tcp_clamp_window(sk);
5121        else if (tcp_under_memory_pressure(sk))
5122                tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
5123
5124        if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5125                return 0;
5126
5127        tcp_collapse_ofo_queue(sk);
5128        if (!skb_queue_empty(&sk->sk_receive_queue))
5129                tcp_collapse(sk, &sk->sk_receive_queue, NULL,
5130                             skb_peek(&sk->sk_receive_queue),
5131                             NULL,
5132                             tp->copied_seq, tp->rcv_nxt);
5133        sk_mem_reclaim(sk);
5134
5135        if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5136                return 0;
5137
5138        /* Collapsing did not help, destructive actions follow.
5139         * This must not ever occur. */
5140
5141        tcp_prune_ofo_queue(sk);
5142
5143        if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5144                return 0;
5145
5146        /* If we are really being abused, tell the caller to silently
5147         * drop receive data on the floor.  It will get retransmitted
5148         * and hopefully then we'll have sufficient space.
5149         */
5150        NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
5151
5152        /* Massive buffer overcommit. */
5153        tp->pred_flags = 0;
5154        return -1;
5155}
5156
5157static bool tcp_should_expand_sndbuf(const struct sock *sk)
5158{
5159        const struct tcp_sock *tp = tcp_sk(sk);
5160
5161        /* If the user specified a specific send buffer setting, do
5162         * not modify it.
5163         */
5164        if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5165                return false;
5166
5167        /* If we are under global TCP memory pressure, do not expand.  */
5168        if (tcp_under_memory_pressure(sk))
5169                return false;
5170
5171        /* If we are under soft global TCP memory pressure, do not expand.  */
5172        if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5173                return false;
5174
5175        /* If we filled the congestion window, do not expand.  */
5176        if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
5177                return false;
5178
5179        return true;
5180}
5181
5182/* When incoming ACK allowed to free some skb from write_queue,
5183 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
5184 * on the exit from tcp input handler.
5185 *
5186 * PROBLEM: sndbuf expansion does not work well with largesend.
5187 */
5188static void tcp_new_space(struct sock *sk)
5189{
5190        struct tcp_sock *tp = tcp_sk(sk);
5191
5192        if (tcp_should_expand_sndbuf(sk)) {
5193                tcp_sndbuf_expand(sk);
5194                tp->snd_cwnd_stamp = tcp_jiffies32;
5195        }
5196
5197        sk->sk_write_space(sk);
5198}
5199
5200static void tcp_check_space(struct sock *sk)
5201{
5202        if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
5203                sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
5204                /* pairs with tcp_poll() */
5205                smp_mb();
5206                if (sk->sk_socket &&
5207                    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5208                        tcp_new_space(sk);
5209                        if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5210                                tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
5211                }
5212        }
5213}
5214
5215static inline void tcp_data_snd_check(struct sock *sk)
5216{
5217        tcp_push_pending_frames(sk);
5218        tcp_check_space(sk);
5219}
5220
5221/*
5222 * Check if sending an ack is needed.
5223 */
5224static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5225{
5226        struct tcp_sock *tp = tcp_sk(sk);
5227        unsigned long rtt, delay;
5228
5229            /* More than one full frame received... */
5230        if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5231             /* ... and right edge of window advances far enough.
5232              * (tcp_recvmsg() will send ACK otherwise).
5233              * If application uses SO_RCVLOWAT, we want send ack now if
5234              * we have not received enough bytes to satisfy the condition.
5235              */
5236            (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
5237             __tcp_select_window(sk) >= tp->rcv_wnd)) ||
5238            /* We ACK each frame or... */
5239            tcp_in_quickack_mode(sk) ||
5240            /* Protocol state mandates a one-time immediate ACK */
5241            inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
5242send_now:
5243                tcp_send_ack(sk);
5244                return;
5245        }
5246
5247        if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5248                tcp_send_delayed_ack(sk);
5249                return;
5250        }
5251
5252        if (!tcp_is_sack(tp) ||
5253            tp->compressed_ack >= sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr)
5254                goto send_now;
5255
5256        if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
5257                tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
5258                if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)
5259                        NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
5260                                      tp->compressed_ack - TCP_FASTRETRANS_THRESH);
5261                tp->compressed_ack = 0;
5262        }
5263
5264        if (++tp->compressed_ack <= TCP_FASTRETRANS_THRESH)
5265                goto send_now;
5266
5267        if (hrtimer_is_queued(&tp->compressed_ack_timer))
5268                return;
5269
5270        /* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
5271
5272        rtt = tp->rcv_rtt_est.rtt_us;
5273        if (tp->srtt_us && tp->srtt_us < rtt)
5274                rtt = tp->srtt_us;
5275
5276        delay = min_t(unsigned long, sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns,
5277                      rtt * (NSEC_PER_USEC >> 3)/20);
5278        sock_hold(sk);
5279        hrtimer_start(&tp->compressed_ack_timer, ns_to_ktime(delay),
5280                      HRTIMER_MODE_REL_PINNED_SOFT);
5281}
5282
5283static inline void tcp_ack_snd_check(struct sock *sk)
5284{
5285        if (!inet_csk_ack_scheduled(sk)) {
5286                /* We sent a data segment already. */
5287                return;
5288        }
5289        __tcp_ack_snd_check(sk, 1);
5290}
5291
5292/*
5293 *      This routine is only called when we have urgent data
5294 *      signaled. Its the 'slow' part of tcp_urg. It could be
5295 *      moved inline now as tcp_urg is only called from one
5296 *      place. We handle URGent data wrong. We have to - as
5297 *      BSD still doesn't use the correction from RFC961.
5298 *      For 1003.1g we should support a new option TCP_STDURG to permit
5299 *      either form (or just set the sysctl tcp_stdurg).
5300 */
5301
5302static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5303{
5304        struct tcp_sock *tp = tcp_sk(sk);
5305        u32 ptr = ntohs(th->urg_ptr);
5306
5307        if (ptr && !sock_net(sk)->ipv4.sysctl_tcp_stdurg)
5308                ptr--;
5309        ptr += ntohl(th->seq);
5310
5311        /* Ignore urgent data that we've already seen and read. */
5312        if (after(tp->copied_seq, ptr))
5313                return;
5314
5315        /* Do not replay urg ptr.
5316         *
5317         * NOTE: interesting situation not covered by specs.
5318         * Misbehaving sender may send urg ptr, pointing to segment,
5319         * which we already have in ofo queue. We are not able to fetch
5320         * such data and will stay in TCP_URG_NOTYET until will be eaten
5321         * by recvmsg(). Seems, we are not obliged to handle such wicked
5322         * situations. But it is worth to think about possibility of some
5323         * DoSes using some hypothetical application level deadlock.
5324         */
5325        if (before(ptr, tp->rcv_nxt))
5326                return;
5327
5328        /* Do we already have a newer (or duplicate) urgent pointer? */
5329        if (tp->urg_data && !after(ptr, tp->urg_seq))
5330                return;
5331
5332        /* Tell the world about our new urgent pointer. */
5333        sk_send_sigurg(sk);
5334
5335        /* We may be adding urgent data when the last byte read was
5336         * urgent. To do this requires some care. We cannot just ignore
5337         * tp->copied_seq since we would read the last urgent byte again
5338         * as data, nor can we alter copied_seq until this data arrives
5339         * or we break the semantics of SIOCATMARK (and thus sockatmark())
5340         *
5341         * NOTE. Double Dutch. Rendering to plain English: author of comment
5342         * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
5343         * and expect that both A and B disappear from stream. This is _wrong_.
5344         * Though this happens in BSD with high probability, this is occasional.
5345         * Any application relying on this is buggy. Note also, that fix "works"
5346         * only in this artificial test. Insert some normal data between A and B and we will
5347         * decline of BSD again. Verdict: it is better to remove to trap
5348         * buggy users.
5349         */
5350        if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5351            !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5352                struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5353                tp->copied_seq++;
5354                if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5355                        __skb_unlink(skb, &sk->sk_receive_queue);
5356                        __kfree_skb(skb);
5357                }
5358        }
5359
5360        tp->urg_data = TCP_URG_NOTYET;
5361        WRITE_ONCE(tp->urg_seq, ptr);
5362
5363        /* Disable header prediction. */
5364        tp->pred_flags = 0;
5365}
5366
5367/* This is the 'fast' part of urgent handling. */
5368static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5369{
5370        struct tcp_sock *tp = tcp_sk(sk);
5371
5372        /* Check if we get a new urgent pointer - normally not. */
5373        if (th->urg)
5374                tcp_check_urg(sk, th);
5375
5376        /* Do we wait for any urgent data? - normally not... */
5377        if (tp->urg_data == TCP_URG_NOTYET) {
5378                u32