linux/net/ipv4/tcp_minisocks.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   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#include <linux/mm.h>
  23#include <linux/module.h>
  24#include <linux/slab.h>
  25#include <linux/sysctl.h>
  26#include <linux/workqueue.h>
  27#include <linux/static_key.h>
  28#include <net/tcp.h>
  29#include <net/inet_common.h>
  30#include <net/xfrm.h>
  31#include <net/busy_poll.h>
  32
  33static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
  34{
  35        if (seq == s_win)
  36                return true;
  37        if (after(end_seq, s_win) && before(seq, e_win))
  38                return true;
  39        return seq == e_win && seq == end_seq;
  40}
  41
  42static enum tcp_tw_status
  43tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
  44                                  const struct sk_buff *skb, int mib_idx)
  45{
  46        struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
  47
  48        if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx,
  49                                  &tcptw->tw_last_oow_ack_time)) {
  50                /* Send ACK. Note, we do not put the bucket,
  51                 * it will be released by caller.
  52                 */
  53                return TCP_TW_ACK;
  54        }
  55
  56        /* We are rate-limiting, so just release the tw sock and drop skb. */
  57        inet_twsk_put(tw);
  58        return TCP_TW_SUCCESS;
  59}
  60
  61/*
  62 * * Main purpose of TIME-WAIT state is to close connection gracefully,
  63 *   when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
  64 *   (and, probably, tail of data) and one or more our ACKs are lost.
  65 * * What is TIME-WAIT timeout? It is associated with maximal packet
  66 *   lifetime in the internet, which results in wrong conclusion, that
  67 *   it is set to catch "old duplicate segments" wandering out of their path.
  68 *   It is not quite correct. This timeout is calculated so that it exceeds
  69 *   maximal retransmission timeout enough to allow to lose one (or more)
  70 *   segments sent by peer and our ACKs. This time may be calculated from RTO.
  71 * * When TIME-WAIT socket receives RST, it means that another end
  72 *   finally closed and we are allowed to kill TIME-WAIT too.
  73 * * Second purpose of TIME-WAIT is catching old duplicate segments.
  74 *   Well, certainly it is pure paranoia, but if we load TIME-WAIT
  75 *   with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
  76 * * If we invented some more clever way to catch duplicates
  77 *   (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
  78 *
  79 * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
  80 * When you compare it to RFCs, please, read section SEGMENT ARRIVES
  81 * from the very beginning.
  82 *
  83 * NOTE. With recycling (and later with fin-wait-2) TW bucket
  84 * is _not_ stateless. It means, that strictly speaking we must
  85 * spinlock it. I do not want! Well, probability of misbehaviour
  86 * is ridiculously low and, seems, we could use some mb() tricks
  87 * to avoid misread sequence numbers, states etc.  --ANK
  88 *
  89 * We don't need to initialize tmp_out.sack_ok as we don't use the results
  90 */
  91enum tcp_tw_status
  92tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
  93                           const struct tcphdr *th)
  94{
  95        struct tcp_options_received tmp_opt;
  96        struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
  97        bool paws_reject = false;
  98
  99        tmp_opt.saw_tstamp = 0;
 100        if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
 101                tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL);
 102
 103                if (tmp_opt.saw_tstamp) {
 104                        if (tmp_opt.rcv_tsecr)
 105                                tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset;
 106                        tmp_opt.ts_recent       = tcptw->tw_ts_recent;
 107                        tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
 108                        paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
 109                }
 110        }
 111
 112        if (tw->tw_substate == TCP_FIN_WAIT2) {
 113                /* Just repeat all the checks of tcp_rcv_state_process() */
 114
 115                /* Out of window, send ACK */
 116                if (paws_reject ||
 117                    !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
 118                                   tcptw->tw_rcv_nxt,
 119                                   tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
 120                        return tcp_timewait_check_oow_rate_limit(
 121                                tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);
 122
 123                if (th->rst)
 124                        goto kill;
 125
 126                if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
 127                        return TCP_TW_RST;
 128
 129                /* Dup ACK? */
 130                if (!th->ack ||
 131                    !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
 132                    TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
 133                        inet_twsk_put(tw);
 134                        return TCP_TW_SUCCESS;
 135                }
 136
 137                /* New data or FIN. If new data arrive after half-duplex close,
 138                 * reset.
 139                 */
 140                if (!th->fin ||
 141                    TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1)
 142                        return TCP_TW_RST;
 143
 144                /* FIN arrived, enter true time-wait state. */
 145                tw->tw_substate   = TCP_TIME_WAIT;
 146                tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
 147                if (tmp_opt.saw_tstamp) {
 148                        tcptw->tw_ts_recent_stamp = ktime_get_seconds();
 149                        tcptw->tw_ts_recent       = tmp_opt.rcv_tsval;
 150                }
 151
 152                inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
 153                return TCP_TW_ACK;
 154        }
 155
 156        /*
 157         *      Now real TIME-WAIT state.
 158         *
 159         *      RFC 1122:
 160         *      "When a connection is [...] on TIME-WAIT state [...]
 161         *      [a TCP] MAY accept a new SYN from the remote TCP to
 162         *      reopen the connection directly, if it:
 163         *
 164         *      (1)  assigns its initial sequence number for the new
 165         *      connection to be larger than the largest sequence
 166         *      number it used on the previous connection incarnation,
 167         *      and
 168         *
 169         *      (2)  returns to TIME-WAIT state if the SYN turns out
 170         *      to be an old duplicate".
 171         */
 172
 173        if (!paws_reject &&
 174            (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
 175             (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
 176                /* In window segment, it may be only reset or bare ack. */
 177
 178                if (th->rst) {
 179                        /* This is TIME_WAIT assassination, in two flavors.
 180                         * Oh well... nobody has a sufficient solution to this
 181                         * protocol bug yet.
 182                         */
 183                        if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) {
 184kill:
 185                                inet_twsk_deschedule_put(tw);
 186                                return TCP_TW_SUCCESS;
 187                        }
 188                } else {
 189                        inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
 190                }
 191
 192                if (tmp_opt.saw_tstamp) {
 193                        tcptw->tw_ts_recent       = tmp_opt.rcv_tsval;
 194                        tcptw->tw_ts_recent_stamp = ktime_get_seconds();
 195                }
 196
 197                inet_twsk_put(tw);
 198                return TCP_TW_SUCCESS;
 199        }
 200
 201        /* Out of window segment.
 202
 203           All the segments are ACKed immediately.
 204
 205           The only exception is new SYN. We accept it, if it is
 206           not old duplicate and we are not in danger to be killed
 207           by delayed old duplicates. RFC check is that it has
 208           newer sequence number works at rates <40Mbit/sec.
 209           However, if paws works, it is reliable AND even more,
 210           we even may relax silly seq space cutoff.
 211
 212           RED-PEN: we violate main RFC requirement, if this SYN will appear
 213           old duplicate (i.e. we receive RST in reply to SYN-ACK),
 214           we must return socket to time-wait state. It is not good,
 215           but not fatal yet.
 216         */
 217
 218        if (th->syn && !th->rst && !th->ack && !paws_reject &&
 219            (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
 220             (tmp_opt.saw_tstamp &&
 221              (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
 222                u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
 223                if (isn == 0)
 224                        isn++;
 225                TCP_SKB_CB(skb)->tcp_tw_isn = isn;
 226                return TCP_TW_SYN;
 227        }
 228
 229        if (paws_reject)
 230                __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
 231
 232        if (!th->rst) {
 233                /* In this case we must reset the TIMEWAIT timer.
 234                 *
 235                 * If it is ACKless SYN it may be both old duplicate
 236                 * and new good SYN with random sequence number <rcv_nxt.
 237                 * Do not reschedule in the last case.
 238                 */
 239                if (paws_reject || th->ack)
 240                        inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
 241
 242                return tcp_timewait_check_oow_rate_limit(
 243                        tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
 244        }
 245        inet_twsk_put(tw);
 246        return TCP_TW_SUCCESS;
 247}
 248EXPORT_SYMBOL(tcp_timewait_state_process);
 249
 250/*
 251 * Move a socket to time-wait or dead fin-wait-2 state.
 252 */
 253void tcp_time_wait(struct sock *sk, int state, int timeo)
 254{
 255        const struct inet_connection_sock *icsk = inet_csk(sk);
 256        const struct tcp_sock *tp = tcp_sk(sk);
 257        struct inet_timewait_sock *tw;
 258        struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;
 259
 260        tw = inet_twsk_alloc(sk, tcp_death_row, state);
 261
 262        if (tw) {
 263                struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
 264                const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
 265                struct inet_sock *inet = inet_sk(sk);
 266
 267                tw->tw_transparent      = inet->transparent;
 268                tw->tw_mark             = sk->sk_mark;
 269                tw->tw_priority         = sk->sk_priority;
 270                tw->tw_rcv_wscale       = tp->rx_opt.rcv_wscale;
 271                tcptw->tw_rcv_nxt       = tp->rcv_nxt;
 272                tcptw->tw_snd_nxt       = tp->snd_nxt;
 273                tcptw->tw_rcv_wnd       = tcp_receive_window(tp);
 274                tcptw->tw_ts_recent     = tp->rx_opt.ts_recent;
 275                tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
 276                tcptw->tw_ts_offset     = tp->tsoffset;
 277                tcptw->tw_last_oow_ack_time = 0;
 278                tcptw->tw_tx_delay      = tp->tcp_tx_delay;
 279#if IS_ENABLED(CONFIG_IPV6)
 280                if (tw->tw_family == PF_INET6) {
 281                        struct ipv6_pinfo *np = inet6_sk(sk);
 282
 283                        tw->tw_v6_daddr = sk->sk_v6_daddr;
 284                        tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
 285                        tw->tw_tclass = np->tclass;
 286                        tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK);
 287                        tw->tw_txhash = sk->sk_txhash;
 288                        tw->tw_ipv6only = sk->sk_ipv6only;
 289                }
 290#endif
 291
 292#ifdef CONFIG_TCP_MD5SIG
 293                /*
 294                 * The timewait bucket does not have the key DB from the
 295                 * sock structure. We just make a quick copy of the
 296                 * md5 key being used (if indeed we are using one)
 297                 * so the timewait ack generating code has the key.
 298                 */
 299                do {
 300                        tcptw->tw_md5_key = NULL;
 301                        if (static_branch_unlikely(&tcp_md5_needed)) {
 302                                struct tcp_md5sig_key *key;
 303
 304                                key = tp->af_specific->md5_lookup(sk, sk);
 305                                if (key) {
 306                                        tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
 307                                        BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool());
 308                                }
 309                        }
 310                } while (0);
 311#endif
 312
 313                /* Get the TIME_WAIT timeout firing. */
 314                if (timeo < rto)
 315                        timeo = rto;
 316
 317                if (state == TCP_TIME_WAIT)
 318                        timeo = TCP_TIMEWAIT_LEN;
 319
 320                /* tw_timer is pinned, so we need to make sure BH are disabled
 321                 * in following section, otherwise timer handler could run before
 322                 * we complete the initialization.
 323                 */
 324                local_bh_disable();
 325                inet_twsk_schedule(tw, timeo);
 326                /* Linkage updates.
 327                 * Note that access to tw after this point is illegal.
 328                 */
 329                inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
 330                local_bh_enable();
 331        } else {
 332                /* Sorry, if we're out of memory, just CLOSE this
 333                 * socket up.  We've got bigger problems than
 334                 * non-graceful socket closings.
 335                 */
 336                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
 337        }
 338
 339        tcp_update_metrics(sk);
 340        tcp_done(sk);
 341}
 342EXPORT_SYMBOL(tcp_time_wait);
 343
 344void tcp_twsk_destructor(struct sock *sk)
 345{
 346#ifdef CONFIG_TCP_MD5SIG
 347        if (static_branch_unlikely(&tcp_md5_needed)) {
 348                struct tcp_timewait_sock *twsk = tcp_twsk(sk);
 349
 350                if (twsk->tw_md5_key)
 351                        kfree_rcu(twsk->tw_md5_key, rcu);
 352        }
 353#endif
 354}
 355EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
 356
 357/* Warning : This function is called without sk_listener being locked.
 358 * Be sure to read socket fields once, as their value could change under us.
 359 */
 360void tcp_openreq_init_rwin(struct request_sock *req,
 361                           const struct sock *sk_listener,
 362                           const struct dst_entry *dst)
 363{
 364        struct inet_request_sock *ireq = inet_rsk(req);
 365        const struct tcp_sock *tp = tcp_sk(sk_listener);
 366        int full_space = tcp_full_space(sk_listener);
 367        u32 window_clamp;
 368        __u8 rcv_wscale;
 369        u32 rcv_wnd;
 370        int mss;
 371
 372        mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
 373        window_clamp = READ_ONCE(tp->window_clamp);
 374        /* Set this up on the first call only */
 375        req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
 376
 377        /* limit the window selection if the user enforce a smaller rx buffer */
 378        if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
 379            (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
 380                req->rsk_window_clamp = full_space;
 381
 382        rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req);
 383        if (rcv_wnd == 0)
 384                rcv_wnd = dst_metric(dst, RTAX_INITRWND);
 385        else if (full_space < rcv_wnd * mss)
 386                full_space = rcv_wnd * mss;
 387
 388        /* tcp_full_space because it is guaranteed to be the first packet */
 389        tcp_select_initial_window(sk_listener, full_space,
 390                mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
 391                &req->rsk_rcv_wnd,
 392                &req->rsk_window_clamp,
 393                ireq->wscale_ok,
 394                &rcv_wscale,
 395                rcv_wnd);
 396        ireq->rcv_wscale = rcv_wscale;
 397}
 398EXPORT_SYMBOL(tcp_openreq_init_rwin);
 399
 400static void tcp_ecn_openreq_child(struct tcp_sock *tp,
 401                                  const struct request_sock *req)
 402{
 403        tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
 404}
 405
 406void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
 407{
 408        struct inet_connection_sock *icsk = inet_csk(sk);
 409        u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
 410        bool ca_got_dst = false;
 411
 412        if (ca_key != TCP_CA_UNSPEC) {
 413                const struct tcp_congestion_ops *ca;
 414
 415                rcu_read_lock();
 416                ca = tcp_ca_find_key(ca_key);
 417                if (likely(ca && try_module_get(ca->owner))) {
 418                        icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
 419                        icsk->icsk_ca_ops = ca;
 420                        ca_got_dst = true;
 421                }
 422                rcu_read_unlock();
 423        }
 424
 425        /* If no valid choice made yet, assign current system default ca. */
 426        if (!ca_got_dst &&
 427            (!icsk->icsk_ca_setsockopt ||
 428             !try_module_get(icsk->icsk_ca_ops->owner)))
 429                tcp_assign_congestion_control(sk);
 430
 431        tcp_set_ca_state(sk, TCP_CA_Open);
 432}
 433EXPORT_SYMBOL_GPL(tcp_ca_openreq_child);
 434
 435static void smc_check_reset_syn_req(struct tcp_sock *oldtp,
 436                                    struct request_sock *req,
 437                                    struct tcp_sock *newtp)
 438{
 439#if IS_ENABLED(CONFIG_SMC)
 440        struct inet_request_sock *ireq;
 441
 442        if (static_branch_unlikely(&tcp_have_smc)) {
 443                ireq = inet_rsk(req);
 444                if (oldtp->syn_smc && !ireq->smc_ok)
 445                        newtp->syn_smc = 0;
 446        }
 447#endif
 448}
 449
 450/* This is not only more efficient than what we used to do, it eliminates
 451 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
 452 *
 453 * Actually, we could lots of memory writes here. tp of listening
 454 * socket contains all necessary default parameters.
 455 */
 456struct sock *tcp_create_openreq_child(const struct sock *sk,
 457                                      struct request_sock *req,
 458                                      struct sk_buff *skb)
 459{
 460        struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
 461        const struct inet_request_sock *ireq = inet_rsk(req);
 462        struct tcp_request_sock *treq = tcp_rsk(req);
 463        struct inet_connection_sock *newicsk;
 464        struct tcp_sock *oldtp, *newtp;
 465        u32 seq;
 466
 467        if (!newsk)
 468                return NULL;
 469
 470        newicsk = inet_csk(newsk);
 471        newtp = tcp_sk(newsk);
 472        oldtp = tcp_sk(sk);
 473
 474        smc_check_reset_syn_req(oldtp, req, newtp);
 475
 476        /* Now setup tcp_sock */
 477        newtp->pred_flags = 0;
 478
 479        seq = treq->rcv_isn + 1;
 480        newtp->rcv_wup = seq;
 481        WRITE_ONCE(newtp->copied_seq, seq);
 482        WRITE_ONCE(newtp->rcv_nxt, seq);
 483        newtp->segs_in = 1;
 484
 485        seq = treq->snt_isn + 1;
 486        newtp->snd_sml = newtp->snd_una = seq;
 487        WRITE_ONCE(newtp->snd_nxt, seq);
 488        newtp->snd_up = seq;
 489
 490        INIT_LIST_HEAD(&newtp->tsq_node);
 491        INIT_LIST_HEAD(&newtp->tsorted_sent_queue);
 492
 493        tcp_init_wl(newtp, treq->rcv_isn);
 494
 495        minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U);
 496        newicsk->icsk_ack.lrcvtime = tcp_jiffies32;
 497
 498        newtp->lsndtime = tcp_jiffies32;
 499        newsk->sk_txhash = treq->txhash;
 500        newtp->total_retrans = req->num_retrans;
 501
 502        tcp_init_xmit_timers(newsk);
 503        WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1);
 504
 505        if (sock_flag(newsk, SOCK_KEEPOPEN))
 506                inet_csk_reset_keepalive_timer(newsk,
 507                                               keepalive_time_when(newtp));
 508
 509        newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
 510        newtp->rx_opt.sack_ok = ireq->sack_ok;
 511        newtp->window_clamp = req->rsk_window_clamp;
 512        newtp->rcv_ssthresh = req->rsk_rcv_wnd;
 513        newtp->rcv_wnd = req->rsk_rcv_wnd;
 514        newtp->rx_opt.wscale_ok = ireq->wscale_ok;
 515        if (newtp->rx_opt.wscale_ok) {
 516                newtp->rx_opt.snd_wscale = ireq->snd_wscale;
 517                newtp->rx_opt.rcv_wscale = ireq->rcv_wscale;
 518        } else {
 519                newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
 520                newtp->window_clamp = min(newtp->window_clamp, 65535U);
 521        }
 522        newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale;
 523        newtp->max_window = newtp->snd_wnd;
 524
 525        if (newtp->rx_opt.tstamp_ok) {
 526                newtp->rx_opt.ts_recent = req->ts_recent;
 527                newtp->rx_opt.ts_recent_stamp = ktime_get_seconds();
 528                newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
 529        } else {
 530                newtp->rx_opt.ts_recent_stamp = 0;
 531                newtp->tcp_header_len = sizeof(struct tcphdr);
 532        }
 533        if (req->num_timeout) {
 534                newtp->undo_marker = treq->snt_isn;
 535                newtp->retrans_stamp = div_u64(treq->snt_synack,
 536                                               USEC_PER_SEC / TCP_TS_HZ);
 537        }
 538        newtp->tsoffset = treq->ts_off;
 539#ifdef CONFIG_TCP_MD5SIG
 540        newtp->md5sig_info = NULL;      /*XXX*/
 541        if (newtp->af_specific->md5_lookup(sk, newsk))
 542                newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
 543#endif
 544        if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len)
 545                newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len;
 546        newtp->rx_opt.mss_clamp = req->mss;
 547        tcp_ecn_openreq_child(newtp, req);
 548        newtp->fastopen_req = NULL;
 549        RCU_INIT_POINTER(newtp->fastopen_rsk, NULL);
 550
 551        __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
 552
 553        return newsk;
 554}
 555EXPORT_SYMBOL(tcp_create_openreq_child);
 556
 557/*
 558 * Process an incoming packet for SYN_RECV sockets represented as a
 559 * request_sock. Normally sk is the listener socket but for TFO it
 560 * points to the child socket.
 561 *
 562 * XXX (TFO) - The current impl contains a special check for ack
 563 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better?
 564 *
 565 * We don't need to initialize tmp_opt.sack_ok as we don't use the results
 566 */
 567
 568struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 569                           struct request_sock *req,
 570                           bool fastopen, bool *req_stolen)
 571{
 572        struct tcp_options_received tmp_opt;
 573        struct sock *child;
 574        const struct tcphdr *th = tcp_hdr(skb);
 575        __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
 576        bool paws_reject = false;
 577        bool own_req;
 578
 579        tmp_opt.saw_tstamp = 0;
 580        if (th->doff > (sizeof(struct tcphdr)>>2)) {
 581                tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL);
 582
 583                if (tmp_opt.saw_tstamp) {
 584                        tmp_opt.ts_recent = req->ts_recent;
 585                        if (tmp_opt.rcv_tsecr)
 586                                tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off;
 587                        /* We do not store true stamp, but it is not required,
 588                         * it can be estimated (approximately)
 589                         * from another data.
 590                         */
 591                        tmp_opt.ts_recent_stamp = ktime_get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
 592                        paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
 593                }
 594        }
 595
 596        /* Check for pure retransmitted SYN. */
 597        if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn &&
 598            flg == TCP_FLAG_SYN &&
 599            !paws_reject) {
 600                /*
 601                 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
 602                 * this case on figure 6 and figure 8, but formal
 603                 * protocol description says NOTHING.
 604                 * To be more exact, it says that we should send ACK,
 605                 * because this segment (at least, if it has no data)
 606                 * is out of window.
 607                 *
 608                 *  CONCLUSION: RFC793 (even with RFC1122) DOES NOT
 609                 *  describe SYN-RECV state. All the description
 610                 *  is wrong, we cannot believe to it and should
 611                 *  rely only on common sense and implementation
 612                 *  experience.
 613                 *
 614                 * Enforce "SYN-ACK" according to figure 8, figure 6
 615                 * of RFC793, fixed by RFC1122.
 616                 *
 617                 * Note that even if there is new data in the SYN packet
 618                 * they will be thrown away too.
 619                 *
 620                 * Reset timer after retransmitting SYNACK, similar to
 621                 * the idea of fast retransmit in recovery.
 622                 */
 623                if (!tcp_oow_rate_limited(sock_net(sk), skb,
 624                                          LINUX_MIB_TCPACKSKIPPEDSYNRECV,
 625                                          &tcp_rsk(req)->last_oow_ack_time) &&
 626
 627                    !inet_rtx_syn_ack(sk, req)) {
 628                        unsigned long expires = jiffies;
 629
 630                        expires += min(TCP_TIMEOUT_INIT << req->num_timeout,
 631                                       TCP_RTO_MAX);
 632                        if (!fastopen)
 633                                mod_timer_pending(&req->rsk_timer, expires);
 634                        else
 635                                req->rsk_timer.expires = expires;
 636                }
 637                return NULL;
 638        }
 639
 640        /* Further reproduces section "SEGMENT ARRIVES"
 641           for state SYN-RECEIVED of RFC793.
 642           It is broken, however, it does not work only
 643           when SYNs are crossed.
 644
 645           You would think that SYN crossing is impossible here, since
 646           we should have a SYN_SENT socket (from connect()) on our end,
 647           but this is not true if the crossed SYNs were sent to both
 648           ends by a malicious third party.  We must defend against this,
 649           and to do that we first verify the ACK (as per RFC793, page
 650           36) and reset if it is invalid.  Is this a true full defense?
 651           To convince ourselves, let us consider a way in which the ACK
 652           test can still pass in this 'malicious crossed SYNs' case.
 653           Malicious sender sends identical SYNs (and thus identical sequence
 654           numbers) to both A and B:
 655
 656                A: gets SYN, seq=7
 657                B: gets SYN, seq=7
 658
 659           By our good fortune, both A and B select the same initial
 660           send sequence number of seven :-)
 661
 662                A: sends SYN|ACK, seq=7, ack_seq=8
 663                B: sends SYN|ACK, seq=7, ack_seq=8
 664
 665           So we are now A eating this SYN|ACK, ACK test passes.  So
 666           does sequence test, SYN is truncated, and thus we consider
 667           it a bare ACK.
 668
 669           If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
 670           bare ACK.  Otherwise, we create an established connection.  Both
 671           ends (listening sockets) accept the new incoming connection and try
 672           to talk to each other. 8-)
 673
 674           Note: This case is both harmless, and rare.  Possibility is about the
 675           same as us discovering intelligent life on another plant tomorrow.
 676
 677           But generally, we should (RFC lies!) to accept ACK
 678           from SYNACK both here and in tcp_rcv_state_process().
 679           tcp_rcv_state_process() does not, hence, we do not too.
 680
 681           Note that the case is absolutely generic:
 682           we cannot optimize anything here without
 683           violating protocol. All the checks must be made
 684           before attempt to create socket.
 685         */
 686
 687        /* RFC793 page 36: "If the connection is in any non-synchronized state ...
 688         *                  and the incoming segment acknowledges something not yet
 689         *                  sent (the segment carries an unacceptable ACK) ...
 690         *                  a reset is sent."
 691         *
 692         * Invalid ACK: reset will be sent by listening socket.
 693         * Note that the ACK validity check for a Fast Open socket is done
 694         * elsewhere and is checked directly against the child socket rather
 695         * than req because user data may have been sent out.
 696         */
 697        if ((flg & TCP_FLAG_ACK) && !fastopen &&
 698            (TCP_SKB_CB(skb)->ack_seq !=
 699             tcp_rsk(req)->snt_isn + 1))
 700                return sk;
 701
 702        /* Also, it would be not so bad idea to check rcv_tsecr, which
 703         * is essentially ACK extension and too early or too late values
 704         * should cause reset in unsynchronized states.
 705         */
 706
 707        /* RFC793: "first check sequence number". */
 708
 709        if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
 710                                          tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) {
 711                /* Out of window: send ACK and drop. */
 712                if (!(flg & TCP_FLAG_RST) &&
 713                    !tcp_oow_rate_limited(sock_net(sk), skb,
 714                                          LINUX_MIB_TCPACKSKIPPEDSYNRECV,
 715                                          &tcp_rsk(req)->last_oow_ack_time))
 716                        req->rsk_ops->send_ack(sk, skb, req);
 717                if (paws_reject)
 718                        __NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
 719                return NULL;
 720        }
 721
 722        /* In sequence, PAWS is OK. */
 723
 724        if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
 725                req->ts_recent = tmp_opt.rcv_tsval;
 726
 727        if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
 728                /* Truncate SYN, it is out of window starting
 729                   at tcp_rsk(req)->rcv_isn + 1. */
 730                flg &= ~TCP_FLAG_SYN;
 731        }
 732
 733        /* RFC793: "second check the RST bit" and
 734         *         "fourth, check the SYN bit"
 735         */
 736        if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
 737                __TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
 738                goto embryonic_reset;
 739        }
 740
 741        /* ACK sequence verified above, just make sure ACK is
 742         * set.  If ACK not set, just silently drop the packet.
 743         *
 744         * XXX (TFO) - if we ever allow "data after SYN", the
 745         * following check needs to be removed.
 746         */
 747        if (!(flg & TCP_FLAG_ACK))
 748                return NULL;
 749
 750        /* For Fast Open no more processing is needed (sk is the
 751         * child socket).
 752         */
 753        if (fastopen)
 754                return sk;
 755
 756        /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
 757        if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
 758            TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
 759                inet_rsk(req)->acked = 1;
 760                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
 761                return NULL;
 762        }
 763
 764        /* OK, ACK is valid, create big socket and
 765         * feed this segment to it. It will repeat all
 766         * the tests. THIS SEGMENT MUST MOVE SOCKET TO
 767         * ESTABLISHED STATE. If it will be dropped after
 768         * socket is created, wait for troubles.
 769         */
 770        child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
 771                                                         req, &own_req);
 772        if (!child)
 773                goto listen_overflow;
 774
 775        sock_rps_save_rxhash(child, skb);
 776        tcp_synack_rtt_meas(child, req);
 777        *req_stolen = !own_req;
 778        return inet_csk_complete_hashdance(sk, child, req, own_req);
 779
 780listen_overflow:
 781        if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) {
 782                inet_rsk(req)->acked = 1;
 783                return NULL;
 784        }
 785
 786embryonic_reset:
 787        if (!(flg & TCP_FLAG_RST)) {
 788                /* Received a bad SYN pkt - for TFO We try not to reset
 789                 * the local connection unless it's really necessary to
 790                 * avoid becoming vulnerable to outside attack aiming at
 791                 * resetting legit local connections.
 792                 */
 793                req->rsk_ops->send_reset(sk, skb);
 794        } else if (fastopen) { /* received a valid RST pkt */
 795                reqsk_fastopen_remove(sk, req, true);
 796                tcp_reset(sk);
 797        }
 798        if (!fastopen) {
 799                inet_csk_reqsk_queue_drop(sk, req);
 800                __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
 801        }
 802        return NULL;
 803}
 804EXPORT_SYMBOL(tcp_check_req);
 805
 806/*
 807 * Queue segment on the new socket if the new socket is active,
 808 * otherwise we just shortcircuit this and continue with
 809 * the new socket.
 810 *
 811 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV
 812 * when entering. But other states are possible due to a race condition
 813 * where after __inet_lookup_established() fails but before the listener
 814 * locked is obtained, other packets cause the same connection to
 815 * be created.
 816 */
 817
 818int tcp_child_process(struct sock *parent, struct sock *child,
 819                      struct sk_buff *skb)
 820{
 821        int ret = 0;
 822        int state = child->sk_state;
 823
 824        /* record NAPI ID of child */
 825        sk_mark_napi_id(child, skb);
 826
 827        tcp_segs_in(tcp_sk(child), skb);
 828        if (!sock_owned_by_user(child)) {
 829                ret = tcp_rcv_state_process(child, skb);
 830                /* Wakeup parent, send SIGIO */
 831                if (state == TCP_SYN_RECV && child->sk_state != state)
 832                        parent->sk_data_ready(parent);
 833        } else {
 834                /* Alas, it is possible again, because we do lookup
 835                 * in main socket hash table and lock on listening
 836                 * socket does not protect us more.
 837                 */
 838                __sk_add_backlog(child, skb);
 839        }
 840
 841        bh_unlock_sock(child);
 842        sock_put(child);
 843        return ret;
 844}
 845EXPORT_SYMBOL(tcp_child_process);
 846