linux/net/core/datagram.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 *      SUCS NET3:
   4 *
   5 *      Generic datagram handling routines. These are generic for all
   6 *      protocols. Possibly a generic IP version on top of these would
   7 *      make sense. Not tonight however 8-).
   8 *      This is used because UDP, RAW, PACKET, DDP, IPX, AX.25 and
   9 *      NetROM layer all have identical poll code and mostly
  10 *      identical recvmsg() code. So we share it here. The poll was
  11 *      shared before but buried in udp.c so I moved it.
  12 *
  13 *      Authors:        Alan Cox <alan@lxorguk.ukuu.org.uk>. (datagram_poll() from old
  14 *                                                   udp.c code)
  15 *
  16 *      Fixes:
  17 *              Alan Cox        :       NULL return from skb_peek_copy()
  18 *                                      understood
  19 *              Alan Cox        :       Rewrote skb_read_datagram to avoid the
  20 *                                      skb_peek_copy stuff.
  21 *              Alan Cox        :       Added support for SOCK_SEQPACKET.
  22 *                                      IPX can no longer use the SO_TYPE hack
  23 *                                      but AX.25 now works right, and SPX is
  24 *                                      feasible.
  25 *              Alan Cox        :       Fixed write poll of non IP protocol
  26 *                                      crash.
  27 *              Florian  La Roche:      Changed for my new skbuff handling.
  28 *              Darryl Miles    :       Fixed non-blocking SOCK_SEQPACKET.
  29 *              Linus Torvalds  :       BSD semantic fixes.
  30 *              Alan Cox        :       Datagram iovec handling
  31 *              Darryl Miles    :       Fixed non-blocking SOCK_STREAM.
  32 *              Alan Cox        :       POSIXisms
  33 *              Pete Wyckoff    :       Unconnected accept() fix.
  34 *
  35 */
  36
  37#include <linux/module.h>
  38#include <linux/types.h>
  39#include <linux/kernel.h>
  40#include <linux/uaccess.h>
  41#include <linux/mm.h>
  42#include <linux/interrupt.h>
  43#include <linux/errno.h>
  44#include <linux/sched.h>
  45#include <linux/inet.h>
  46#include <linux/netdevice.h>
  47#include <linux/rtnetlink.h>
  48#include <linux/poll.h>
  49#include <linux/highmem.h>
  50#include <linux/spinlock.h>
  51#include <linux/slab.h>
  52#include <linux/pagemap.h>
  53#include <linux/uio.h>
  54#include <linux/indirect_call_wrapper.h>
  55
  56#include <net/protocol.h>
  57#include <linux/skbuff.h>
  58
  59#include <net/checksum.h>
  60#include <net/sock.h>
  61#include <net/tcp_states.h>
  62#include <trace/events/skb.h>
  63#include <net/busy_poll.h>
  64
  65#include "datagram.h"
  66
  67/*
  68 *      Is a socket 'connection oriented' ?
  69 */
  70static inline int connection_based(struct sock *sk)
  71{
  72        return sk->sk_type == SOCK_SEQPACKET || sk->sk_type == SOCK_STREAM;
  73}
  74
  75static int receiver_wake_function(wait_queue_entry_t *wait, unsigned int mode, int sync,
  76                                  void *key)
  77{
  78        /*
  79         * Avoid a wakeup if event not interesting for us
  80         */
  81        if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR)))
  82                return 0;
  83        return autoremove_wake_function(wait, mode, sync, key);
  84}
  85/*
  86 * Wait for the last received packet to be different from skb
  87 */
  88int __skb_wait_for_more_packets(struct sock *sk, struct sk_buff_head *queue,
  89                                int *err, long *timeo_p,
  90                                const struct sk_buff *skb)
  91{
  92        int error;
  93        DEFINE_WAIT_FUNC(wait, receiver_wake_function);
  94
  95        prepare_to_wait_exclusive(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
  96
  97        /* Socket errors? */
  98        error = sock_error(sk);
  99        if (error)
 100                goto out_err;
 101
 102        if (READ_ONCE(queue->prev) != skb)
 103                goto out;
 104
 105        /* Socket shut down? */
 106        if (sk->sk_shutdown & RCV_SHUTDOWN)
 107                goto out_noerr;
 108
 109        /* Sequenced packets can come disconnected.
 110         * If so we report the problem
 111         */
 112        error = -ENOTCONN;
 113        if (connection_based(sk) &&
 114            !(sk->sk_state == TCP_ESTABLISHED || sk->sk_state == TCP_LISTEN))
 115                goto out_err;
 116
 117        /* handle signals */
 118        if (signal_pending(current))
 119                goto interrupted;
 120
 121        error = 0;
 122        *timeo_p = schedule_timeout(*timeo_p);
 123out:
 124        finish_wait(sk_sleep(sk), &wait);
 125        return error;
 126interrupted:
 127        error = sock_intr_errno(*timeo_p);
 128out_err:
 129        *err = error;
 130        goto out;
 131out_noerr:
 132        *err = 0;
 133        error = 1;
 134        goto out;
 135}
 136EXPORT_SYMBOL(__skb_wait_for_more_packets);
 137
 138static struct sk_buff *skb_set_peeked(struct sk_buff *skb)
 139{
 140        struct sk_buff *nskb;
 141
 142        if (skb->peeked)
 143                return skb;
 144
 145        /* We have to unshare an skb before modifying it. */
 146        if (!skb_shared(skb))
 147                goto done;
 148
 149        nskb = skb_clone(skb, GFP_ATOMIC);
 150        if (!nskb)
 151                return ERR_PTR(-ENOMEM);
 152
 153        skb->prev->next = nskb;
 154        skb->next->prev = nskb;
 155        nskb->prev = skb->prev;
 156        nskb->next = skb->next;
 157
 158        consume_skb(skb);
 159        skb = nskb;
 160
 161done:
 162        skb->peeked = 1;
 163
 164        return skb;
 165}
 166
 167struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
 168                                          struct sk_buff_head *queue,
 169                                          unsigned int flags,
 170                                          int *off, int *err,
 171                                          struct sk_buff **last)
 172{
 173        bool peek_at_off = false;
 174        struct sk_buff *skb;
 175        int _off = 0;
 176
 177        if (unlikely(flags & MSG_PEEK && *off >= 0)) {
 178                peek_at_off = true;
 179                _off = *off;
 180        }
 181
 182        *last = queue->prev;
 183        skb_queue_walk(queue, skb) {
 184                if (flags & MSG_PEEK) {
 185                        if (peek_at_off && _off >= skb->len &&
 186                            (_off || skb->peeked)) {
 187                                _off -= skb->len;
 188                                continue;
 189                        }
 190                        if (!skb->len) {
 191                                skb = skb_set_peeked(skb);
 192                                if (IS_ERR(skb)) {
 193                                        *err = PTR_ERR(skb);
 194                                        return NULL;
 195                                }
 196                        }
 197                        refcount_inc(&skb->users);
 198                } else {
 199                        __skb_unlink(skb, queue);
 200                }
 201                *off = _off;
 202                return skb;
 203        }
 204        return NULL;
 205}
 206
 207/**
 208 *      __skb_try_recv_datagram - Receive a datagram skbuff
 209 *      @sk: socket
 210 *      @queue: socket queue from which to receive
 211 *      @flags: MSG\_ flags
 212 *      @off: an offset in bytes to peek skb from. Returns an offset
 213 *            within an skb where data actually starts
 214 *      @err: error code returned
 215 *      @last: set to last peeked message to inform the wait function
 216 *             what to look for when peeking
 217 *
 218 *      Get a datagram skbuff, understands the peeking, nonblocking wakeups
 219 *      and possible races. This replaces identical code in packet, raw and
 220 *      udp, as well as the IPX AX.25 and Appletalk. It also finally fixes
 221 *      the long standing peek and read race for datagram sockets. If you
 222 *      alter this routine remember it must be re-entrant.
 223 *
 224 *      This function will lock the socket if a skb is returned, so
 225 *      the caller needs to unlock the socket in that case (usually by
 226 *      calling skb_free_datagram). Returns NULL with @err set to
 227 *      -EAGAIN if no data was available or to some other value if an
 228 *      error was detected.
 229 *
 230 *      * It does not lock socket since today. This function is
 231 *      * free of race conditions. This measure should/can improve
 232 *      * significantly datagram socket latencies at high loads,
 233 *      * when data copying to user space takes lots of time.
 234 *      * (BTW I've just killed the last cli() in IP/IPv6/core/netlink/packet
 235 *      *  8) Great win.)
 236 *      *                                           --ANK (980729)
 237 *
 238 *      The order of the tests when we find no data waiting are specified
 239 *      quite explicitly by POSIX 1003.1g, don't change them without having
 240 *      the standard around please.
 241 */
 242struct sk_buff *__skb_try_recv_datagram(struct sock *sk,
 243                                        struct sk_buff_head *queue,
 244                                        unsigned int flags, int *off, int *err,
 245                                        struct sk_buff **last)
 246{
 247        struct sk_buff *skb;
 248        unsigned long cpu_flags;
 249        /*
 250         * Caller is allowed not to check sk->sk_err before skb_recv_datagram()
 251         */
 252        int error = sock_error(sk);
 253
 254        if (error)
 255                goto no_packet;
 256
 257        do {
 258                /* Again only user level code calls this function, so nothing
 259                 * interrupt level will suddenly eat the receive_queue.
 260                 *
 261                 * Look at current nfs client by the way...
 262                 * However, this function was correct in any case. 8)
 263                 */
 264                spin_lock_irqsave(&queue->lock, cpu_flags);
 265                skb = __skb_try_recv_from_queue(sk, queue, flags, off, &error,
 266                                                last);
 267                spin_unlock_irqrestore(&queue->lock, cpu_flags);
 268                if (error)
 269                        goto no_packet;
 270                if (skb)
 271                        return skb;
 272
 273                if (!sk_can_busy_loop(sk))
 274                        break;
 275
 276                sk_busy_loop(sk, flags & MSG_DONTWAIT);
 277        } while (READ_ONCE(queue->prev) != *last);
 278
 279        error = -EAGAIN;
 280
 281no_packet:
 282        *err = error;
 283        return NULL;
 284}
 285EXPORT_SYMBOL(__skb_try_recv_datagram);
 286
 287struct sk_buff *__skb_recv_datagram(struct sock *sk,
 288                                    struct sk_buff_head *sk_queue,
 289                                    unsigned int flags, int *off, int *err)
 290{
 291        struct sk_buff *skb, *last;
 292        long timeo;
 293
 294        timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
 295
 296        do {
 297                skb = __skb_try_recv_datagram(sk, sk_queue, flags, off, err,
 298                                              &last);
 299                if (skb)
 300                        return skb;
 301
 302                if (*err != -EAGAIN)
 303                        break;
 304        } while (timeo &&
 305                 !__skb_wait_for_more_packets(sk, sk_queue, err,
 306                                              &timeo, last));
 307
 308        return NULL;
 309}
 310EXPORT_SYMBOL(__skb_recv_datagram);
 311
 312struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned int flags,
 313                                  int noblock, int *err)
 314{
 315        int off = 0;
 316
 317        return __skb_recv_datagram(sk, &sk->sk_receive_queue,
 318                                   flags | (noblock ? MSG_DONTWAIT : 0),
 319                                   &off, err);
 320}
 321EXPORT_SYMBOL(skb_recv_datagram);
 322
 323void skb_free_datagram(struct sock *sk, struct sk_buff *skb)
 324{
 325        consume_skb(skb);
 326        sk_mem_reclaim_partial(sk);
 327}
 328EXPORT_SYMBOL(skb_free_datagram);
 329
 330void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len)
 331{
 332        bool slow;
 333
 334        if (!skb_unref(skb)) {
 335                sk_peek_offset_bwd(sk, len);
 336                return;
 337        }
 338
 339        slow = lock_sock_fast(sk);
 340        sk_peek_offset_bwd(sk, len);
 341        skb_orphan(skb);
 342        sk_mem_reclaim_partial(sk);
 343        unlock_sock_fast(sk, slow);
 344
 345        /* skb is now orphaned, can be freed outside of locked section */
 346        __kfree_skb(skb);
 347}
 348EXPORT_SYMBOL(__skb_free_datagram_locked);
 349
 350int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
 351                        struct sk_buff *skb, unsigned int flags,
 352                        void (*destructor)(struct sock *sk,
 353                                           struct sk_buff *skb))
 354{
 355        int err = 0;
 356
 357        if (flags & MSG_PEEK) {
 358                err = -ENOENT;
 359                spin_lock_bh(&sk_queue->lock);
 360                if (skb->next) {
 361                        __skb_unlink(skb, sk_queue);
 362                        refcount_dec(&skb->users);
 363                        if (destructor)
 364                                destructor(sk, skb);
 365                        err = 0;
 366                }
 367                spin_unlock_bh(&sk_queue->lock);
 368        }
 369
 370        atomic_inc(&sk->sk_drops);
 371        return err;
 372}
 373EXPORT_SYMBOL(__sk_queue_drop_skb);
 374
 375/**
 376 *      skb_kill_datagram - Free a datagram skbuff forcibly
 377 *      @sk: socket
 378 *      @skb: datagram skbuff
 379 *      @flags: MSG\_ flags
 380 *
 381 *      This function frees a datagram skbuff that was received by
 382 *      skb_recv_datagram.  The flags argument must match the one
 383 *      used for skb_recv_datagram.
 384 *
 385 *      If the MSG_PEEK flag is set, and the packet is still on the
 386 *      receive queue of the socket, it will be taken off the queue
 387 *      before it is freed.
 388 *
 389 *      This function currently only disables BH when acquiring the
 390 *      sk_receive_queue lock.  Therefore it must not be used in a
 391 *      context where that lock is acquired in an IRQ context.
 392 *
 393 *      It returns 0 if the packet was removed by us.
 394 */
 395
 396int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
 397{
 398        int err = __sk_queue_drop_skb(sk, &sk->sk_receive_queue, skb, flags,
 399                                      NULL);
 400
 401        kfree_skb(skb);
 402        sk_mem_reclaim_partial(sk);
 403        return err;
 404}
 405EXPORT_SYMBOL(skb_kill_datagram);
 406
 407INDIRECT_CALLABLE_DECLARE(static size_t simple_copy_to_iter(const void *addr,
 408                                                size_t bytes,
 409                                                void *data __always_unused,
 410                                                struct iov_iter *i));
 411
 412static int __skb_datagram_iter(const struct sk_buff *skb, int offset,
 413                               struct iov_iter *to, int len, bool fault_short,
 414                               size_t (*cb)(const void *, size_t, void *,
 415                                            struct iov_iter *), void *data)
 416{
 417        int start = skb_headlen(skb);
 418        int i, copy = start - offset, start_off = offset, n;
 419        struct sk_buff *frag_iter;
 420
 421        /* Copy header. */
 422        if (copy > 0) {
 423                if (copy > len)
 424                        copy = len;
 425                n = INDIRECT_CALL_1(cb, simple_copy_to_iter,
 426                                    skb->data + offset, copy, data, to);
 427                offset += n;
 428                if (n != copy)
 429                        goto short_copy;
 430                if ((len -= copy) == 0)
 431                        return 0;
 432        }
 433
 434        /* Copy paged appendix. Hmm... why does this look so complicated? */
 435        for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
 436                int end;
 437                const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 438
 439                WARN_ON(start > offset + len);
 440
 441                end = start + skb_frag_size(frag);
 442                if ((copy = end - offset) > 0) {
 443                        struct page *page = skb_frag_page(frag);
 444                        u8 *vaddr = kmap(page);
 445
 446                        if (copy > len)
 447                                copy = len;
 448                        n = INDIRECT_CALL_1(cb, simple_copy_to_iter,
 449                                        vaddr + skb_frag_off(frag) + offset - start,
 450                                        copy, data, to);
 451                        kunmap(page);
 452                        offset += n;
 453                        if (n != copy)
 454                                goto short_copy;
 455                        if (!(len -= copy))
 456                                return 0;
 457                }
 458                start = end;
 459        }
 460
 461        skb_walk_frags(skb, frag_iter) {
 462                int end;
 463
 464                WARN_ON(start > offset + len);
 465
 466                end = start + frag_iter->len;
 467                if ((copy = end - offset) > 0) {
 468                        if (copy > len)
 469                                copy = len;
 470                        if (__skb_datagram_iter(frag_iter, offset - start,
 471                                                to, copy, fault_short, cb, data))
 472                                goto fault;
 473                        if ((len -= copy) == 0)
 474                                return 0;
 475                        offset += copy;
 476                }
 477                start = end;
 478        }
 479        if (!len)
 480                return 0;
 481
 482        /* This is not really a user copy fault, but rather someone
 483         * gave us a bogus length on the skb.  We should probably
 484         * print a warning here as it may indicate a kernel bug.
 485         */
 486
 487fault:
 488        iov_iter_revert(to, offset - start_off);
 489        return -EFAULT;
 490
 491short_copy:
 492        if (fault_short || iov_iter_count(to))
 493                goto fault;
 494
 495        return 0;
 496}
 497
 498/**
 499 *      skb_copy_and_hash_datagram_iter - Copy datagram to an iovec iterator
 500 *          and update a hash.
 501 *      @skb: buffer to copy
 502 *      @offset: offset in the buffer to start copying from
 503 *      @to: iovec iterator to copy to
 504 *      @len: amount of data to copy from buffer to iovec
 505 *      @hash: hash request to update
 506 */
 507int skb_copy_and_hash_datagram_iter(const struct sk_buff *skb, int offset,
 508                           struct iov_iter *to, int len,
 509                           struct ahash_request *hash)
 510{
 511        return __skb_datagram_iter(skb, offset, to, len, true,
 512                        hash_and_copy_to_iter, hash);
 513}
 514EXPORT_SYMBOL(skb_copy_and_hash_datagram_iter);
 515
 516static size_t simple_copy_to_iter(const void *addr, size_t bytes,
 517                void *data __always_unused, struct iov_iter *i)
 518{
 519        return copy_to_iter(addr, bytes, i);
 520}
 521
 522/**
 523 *      skb_copy_datagram_iter - Copy a datagram to an iovec iterator.
 524 *      @skb: buffer to copy
 525 *      @offset: offset in the buffer to start copying from
 526 *      @to: iovec iterator to copy to
 527 *      @len: amount of data to copy from buffer to iovec
 528 */
 529int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
 530                           struct iov_iter *to, int len)
 531{
 532        trace_skb_copy_datagram_iovec(skb, len);
 533        return __skb_datagram_iter(skb, offset, to, len, false,
 534                        simple_copy_to_iter, NULL);
 535}
 536EXPORT_SYMBOL(skb_copy_datagram_iter);
 537
 538/**
 539 *      skb_copy_datagram_from_iter - Copy a datagram from an iov_iter.
 540 *      @skb: buffer to copy
 541 *      @offset: offset in the buffer to start copying to
 542 *      @from: the copy source
 543 *      @len: amount of data to copy to buffer from iovec
 544 *
 545 *      Returns 0 or -EFAULT.
 546 */
 547int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
 548                                 struct iov_iter *from,
 549                                 int len)
 550{
 551        int start = skb_headlen(skb);
 552        int i, copy = start - offset;
 553        struct sk_buff *frag_iter;
 554
 555        /* Copy header. */
 556        if (copy > 0) {
 557                if (copy > len)
 558                        copy = len;
 559                if (copy_from_iter(skb->data + offset, copy, from) != copy)
 560                        goto fault;
 561                if ((len -= copy) == 0)
 562                        return 0;
 563                offset += copy;
 564        }
 565
 566        /* Copy paged appendix. Hmm... why does this look so complicated? */
 567        for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
 568                int end;
 569                const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 570
 571                WARN_ON(start > offset + len);
 572
 573                end = start + skb_frag_size(frag);
 574                if ((copy = end - offset) > 0) {
 575                        size_t copied;
 576
 577                        if (copy > len)
 578                                copy = len;
 579                        copied = copy_page_from_iter(skb_frag_page(frag),
 580                                          skb_frag_off(frag) + offset - start,
 581                                          copy, from);
 582                        if (copied != copy)
 583                                goto fault;
 584
 585                        if (!(len -= copy))
 586                                return 0;
 587                        offset += copy;
 588                }
 589                start = end;
 590        }
 591
 592        skb_walk_frags(skb, frag_iter) {
 593                int end;
 594
 595                WARN_ON(start > offset + len);
 596
 597                end = start + frag_iter->len;
 598                if ((copy = end - offset) > 0) {
 599                        if (copy > len)
 600                                copy = len;
 601                        if (skb_copy_datagram_from_iter(frag_iter,
 602                                                        offset - start,
 603                                                        from, copy))
 604                                goto fault;
 605                        if ((len -= copy) == 0)
 606                                return 0;
 607                        offset += copy;
 608                }
 609                start = end;
 610        }
 611        if (!len)
 612                return 0;
 613
 614fault:
 615        return -EFAULT;
 616}
 617EXPORT_SYMBOL(skb_copy_datagram_from_iter);
 618
 619int __zerocopy_sg_from_iter(struct sock *sk, struct sk_buff *skb,
 620                            struct iov_iter *from, size_t length)
 621{
 622        int frag = skb_shinfo(skb)->nr_frags;
 623
 624        while (length && iov_iter_count(from)) {
 625                struct page *pages[MAX_SKB_FRAGS];
 626                struct page *last_head = NULL;
 627                size_t start;
 628                ssize_t copied;
 629                unsigned long truesize;
 630                int refs, n = 0;
 631
 632                if (frag == MAX_SKB_FRAGS)
 633                        return -EMSGSIZE;
 634
 635                copied = iov_iter_get_pages(from, pages, length,
 636                                            MAX_SKB_FRAGS - frag, &start);
 637                if (copied < 0)
 638                        return -EFAULT;
 639
 640                iov_iter_advance(from, copied);
 641                length -= copied;
 642
 643                truesize = PAGE_ALIGN(copied + start);
 644                skb->data_len += copied;
 645                skb->len += copied;
 646                skb->truesize += truesize;
 647                if (sk && sk->sk_type == SOCK_STREAM) {
 648                        sk_wmem_queued_add(sk, truesize);
 649                        sk_mem_charge(sk, truesize);
 650                } else {
 651                        refcount_add(truesize, &skb->sk->sk_wmem_alloc);
 652                }
 653                for (refs = 0; copied != 0; start = 0) {
 654                        int size = min_t(int, copied, PAGE_SIZE - start);
 655                        struct page *head = compound_head(pages[n]);
 656
 657                        start += (pages[n] - head) << PAGE_SHIFT;
 658                        copied -= size;
 659                        n++;
 660                        if (frag) {
 661                                skb_frag_t *last = &skb_shinfo(skb)->frags[frag - 1];
 662
 663                                if (head == skb_frag_page(last) &&
 664                                    start == skb_frag_off(last) + skb_frag_size(last)) {
 665                                        skb_frag_size_add(last, size);
 666                                        /* We combined this page, we need to release
 667                                         * a reference. Since compound pages refcount
 668                                         * is shared among many pages, batch the refcount
 669                                         * adjustments to limit false sharing.
 670                                         */
 671                                        last_head = head;
 672                                        refs++;
 673                                        continue;
 674                                }
 675                        }
 676                        if (refs) {
 677                                page_ref_sub(last_head, refs);
 678                                refs = 0;
 679                        }
 680                        skb_fill_page_desc(skb, frag++, head, start, size);
 681                }
 682                if (refs)
 683                        page_ref_sub(last_head, refs);
 684        }
 685        return 0;
 686}
 687EXPORT_SYMBOL(__zerocopy_sg_from_iter);
 688
 689/**
 690 *      zerocopy_sg_from_iter - Build a zerocopy datagram from an iov_iter
 691 *      @skb: buffer to copy
 692 *      @from: the source to copy from
 693 *
 694 *      The function will first copy up to headlen, and then pin the userspace
 695 *      pages and build frags through them.
 696 *
 697 *      Returns 0, -EFAULT or -EMSGSIZE.
 698 */
 699int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *from)
 700{
 701        int copy = min_t(int, skb_headlen(skb), iov_iter_count(from));
 702
 703        /* copy up to skb headlen */
 704        if (skb_copy_datagram_from_iter(skb, 0, from, copy))
 705                return -EFAULT;
 706
 707        return __zerocopy_sg_from_iter(NULL, skb, from, ~0U);
 708}
 709EXPORT_SYMBOL(zerocopy_sg_from_iter);
 710
 711/**
 712 *      skb_copy_and_csum_datagram_iter - Copy datagram to an iovec iterator
 713 *          and update a checksum.
 714 *      @skb: buffer to copy
 715 *      @offset: offset in the buffer to start copying from
 716 *      @to: iovec iterator to copy to
 717 *      @len: amount of data to copy from buffer to iovec
 718 *      @csump: checksum pointer
 719 */
 720static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
 721                                      struct iov_iter *to, int len,
 722                                      __wsum *csump)
 723{
 724        return __skb_datagram_iter(skb, offset, to, len, true,
 725                        csum_and_copy_to_iter, csump);
 726}
 727
 728/**
 729 *      skb_copy_and_csum_datagram_msg - Copy and checksum skb to user iovec.
 730 *      @skb: skbuff
 731 *      @hlen: hardware length
 732 *      @msg: destination
 733 *
 734 *      Caller _must_ check that skb will fit to this iovec.
 735 *
 736 *      Returns: 0       - success.
 737 *               -EINVAL - checksum failure.
 738 *               -EFAULT - fault during copy.
 739 */
 740int skb_copy_and_csum_datagram_msg(struct sk_buff *skb,
 741                                   int hlen, struct msghdr *msg)
 742{
 743        __wsum csum;
 744        int chunk = skb->len - hlen;
 745
 746        if (!chunk)
 747                return 0;
 748
 749        if (msg_data_left(msg) < chunk) {
 750                if (__skb_checksum_complete(skb))
 751                        return -EINVAL;
 752                if (skb_copy_datagram_msg(skb, hlen, msg, chunk))
 753                        goto fault;
 754        } else {
 755                csum = csum_partial(skb->data, hlen, skb->csum);
 756                if (skb_copy_and_csum_datagram(skb, hlen, &msg->msg_iter,
 757                                               chunk, &csum))
 758                        goto fault;
 759
 760                if (csum_fold(csum)) {
 761                        iov_iter_revert(&msg->msg_iter, chunk);
 762                        return -EINVAL;
 763                }
 764
 765                if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
 766                    !skb->csum_complete_sw)
 767                        netdev_rx_csum_fault(NULL, skb);
 768        }
 769        return 0;
 770fault:
 771        return -EFAULT;
 772}
 773EXPORT_SYMBOL(skb_copy_and_csum_datagram_msg);
 774
 775/**
 776 *      datagram_poll - generic datagram poll
 777 *      @file: file struct
 778 *      @sock: socket
 779 *      @wait: poll table
 780 *
 781 *      Datagram poll: Again totally generic. This also handles
 782 *      sequenced packet sockets providing the socket receive queue
 783 *      is only ever holding data ready to receive.
 784 *
 785 *      Note: when you *don't* use this routine for this protocol,
 786 *      and you use a different write policy from sock_writeable()
 787 *      then please supply your own write_space callback.
 788 */
 789__poll_t datagram_poll(struct file *file, struct socket *sock,
 790                           poll_table *wait)
 791{
 792        struct sock *sk = sock->sk;
 793        __poll_t mask;
 794
 795        sock_poll_wait(file, sock, wait);
 796        mask = 0;
 797
 798        /* exceptional events? */
 799        if (sk->sk_err || !skb_queue_empty_lockless(&sk->sk_error_queue))
 800                mask |= EPOLLERR |
 801                        (sock_flag(sk, SOCK_SELECT_ERR_QUEUE) ? EPOLLPRI : 0);
 802
 803        if (sk->sk_shutdown & RCV_SHUTDOWN)
 804                mask |= EPOLLRDHUP | EPOLLIN | EPOLLRDNORM;
 805        if (sk->sk_shutdown == SHUTDOWN_MASK)
 806                mask |= EPOLLHUP;
 807
 808        /* readable? */
 809        if (!skb_queue_empty_lockless(&sk->sk_receive_queue))
 810                mask |= EPOLLIN | EPOLLRDNORM;
 811
 812        /* Connection-based need to check for termination and startup */
 813        if (connection_based(sk)) {
 814                if (sk->sk_state == TCP_CLOSE)
 815                        mask |= EPOLLHUP;
 816                /* connection hasn't started yet? */
 817                if (sk->sk_state == TCP_SYN_SENT)
 818                        return mask;
 819        }
 820
 821        /* writable? */
 822        if (sock_writeable(sk))
 823                mask |= EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND;
 824        else
 825                sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
 826
 827        return mask;
 828}
 829EXPORT_SYMBOL(datagram_poll);
 830