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TOMOYO Linux Cross Reference
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 
 55 #include <net/protocol.h>
 56 #include <linux/skbuff.h>
 57 
 58 #include <net/checksum.h>
 59 #include <net/sock.h>
 60 #include <net/tcp_states.h>
 61 #include <trace/events/skb.h>
 62 #include <net/busy_poll.h>
 63 
 64 /*
 65  *      Is a socket 'connection oriented' ?
 66  */
 67 static inline int connection_based(struct sock *sk)
 68 {
 69         return sk->sk_type == SOCK_SEQPACKET || sk->sk_type == SOCK_STREAM;
 70 }
 71 
 72 static int receiver_wake_function(wait_queue_entry_t *wait, unsigned int mode, int sync,
 73                                   void *key)
 74 {
 75         unsigned long bits = (unsigned long)key;
 76 
 77         /*
 78          * Avoid a wakeup if event not interesting for us
 79          */
 80         if (bits && !(bits & (POLLIN | POLLERR)))
 81                 return 0;
 82         return autoremove_wake_function(wait, mode, sync, key);
 83 }
 84 /*
 85  * Wait for the last received packet to be different from skb
 86  */
 87 int __skb_wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
 88                                 const struct sk_buff *skb)
 89 {
 90         int error;
 91         DEFINE_WAIT_FUNC(wait, receiver_wake_function);
 92 
 93         prepare_to_wait_exclusive(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
 94 
 95         /* Socket errors? */
 96         error = sock_error(sk);
 97         if (error)
 98                 goto out_err;
 99 
100         if (sk->sk_receive_queue.prev != skb)
101                 goto out;
102 
103         /* Socket shut down? */
104         if (sk->sk_shutdown & RCV_SHUTDOWN)
105                 goto out_noerr;
106 
107         /* Sequenced packets can come disconnected.
108          * If so we report the problem
109          */
110         error = -ENOTCONN;
111         if (connection_based(sk) &&
112             !(sk->sk_state == TCP_ESTABLISHED || sk->sk_state == TCP_LISTEN))
113                 goto out_err;
114 
115         /* handle signals */
116         if (signal_pending(current))
117                 goto interrupted;
118 
119         error = 0;
120         *timeo_p = schedule_timeout(*timeo_p);
121 out:
122         finish_wait(sk_sleep(sk), &wait);
123         return error;
124 interrupted:
125         error = sock_intr_errno(*timeo_p);
126 out_err:
127         *err = error;
128         goto out;
129 out_noerr:
130         *err = 0;
131         error = 1;
132         goto out;
133 }
134 EXPORT_SYMBOL(__skb_wait_for_more_packets);
135 
136 static struct sk_buff *skb_set_peeked(struct sk_buff *skb)
137 {
138         struct sk_buff *nskb;
139 
140         if (skb->peeked)
141                 return skb;
142 
143         /* We have to unshare an skb before modifying it. */
144         if (!skb_shared(skb))
145                 goto done;
146 
147         nskb = skb_clone(skb, GFP_ATOMIC);
148         if (!nskb)
149                 return ERR_PTR(-ENOMEM);
150 
151         skb->prev->next = nskb;
152         skb->next->prev = nskb;
153         nskb->prev = skb->prev;
154         nskb->next = skb->next;
155 
156         consume_skb(skb);
157         skb = nskb;
158 
159 done:
160         skb->peeked = 1;
161 
162         return skb;
163 }
164 
165 struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
166                                           struct sk_buff_head *queue,
167                                           unsigned int flags,
168                                           void (*destructor)(struct sock *sk,
169                                                            struct sk_buff *skb),
170                                           int *peeked, 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                         *peeked = 1;
198                         refcount_inc(&skb->users);
199                 } else {
200                         __skb_unlink(skb, queue);
201                         if (destructor)
202                                 destructor(sk, skb);
203                 }
204                 *off = _off;
205                 return skb;
206         }
207         return NULL;
208 }
209 
210 /**
211  *      __skb_try_recv_datagram - Receive a datagram skbuff
212  *      @sk: socket
213  *      @flags: MSG\_ flags
214  *      @destructor: invoked under the receive lock on successful dequeue
215  *      @peeked: returns non-zero if this packet has been seen before
216  *      @off: an offset in bytes to peek skb from. Returns an offset
217  *            within an skb where data actually starts
218  *      @err: error code returned
219  *      @last: set to last peeked message to inform the wait function
220  *             what to look for when peeking
221  *
222  *      Get a datagram skbuff, understands the peeking, nonblocking wakeups
223  *      and possible races. This replaces identical code in packet, raw and
224  *      udp, as well as the IPX AX.25 and Appletalk. It also finally fixes
225  *      the long standing peek and read race for datagram sockets. If you
226  *      alter this routine remember it must be re-entrant.
227  *
228  *      This function will lock the socket if a skb is returned, so
229  *      the caller needs to unlock the socket in that case (usually by
230  *      calling skb_free_datagram). Returns NULL with @err set to
231  *      -EAGAIN if no data was available or to some other value if an
232  *      error was detected.
233  *
234  *      * It does not lock socket since today. This function is
235  *      * free of race conditions. This measure should/can improve
236  *      * significantly datagram socket latencies at high loads,
237  *      * when data copying to user space takes lots of time.
238  *      * (BTW I've just killed the last cli() in IP/IPv6/core/netlink/packet
239  *      *  8) Great win.)
240  *      *                                           --ANK (980729)
241  *
242  *      The order of the tests when we find no data waiting are specified
243  *      quite explicitly by POSIX 1003.1g, don't change them without having
244  *      the standard around please.
245  */
246 struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned int flags,
247                                         void (*destructor)(struct sock *sk,
248                                                            struct sk_buff *skb),
249                                         int *peeked, int *off, int *err,
250                                         struct sk_buff **last)
251 {
252         struct sk_buff_head *queue = &sk->sk_receive_queue;
253         struct sk_buff *skb;
254         unsigned long cpu_flags;
255         /*
256          * Caller is allowed not to check sk->sk_err before skb_recv_datagram()
257          */
258         int error = sock_error(sk);
259 
260         if (error)
261                 goto no_packet;
262 
263         *peeked = 0;
264         do {
265                 /* Again only user level code calls this function, so nothing
266                  * interrupt level will suddenly eat the receive_queue.
267                  *
268                  * Look at current nfs client by the way...
269                  * However, this function was correct in any case. 8)
270                  */
271                 spin_lock_irqsave(&queue->lock, cpu_flags);
272                 skb = __skb_try_recv_from_queue(sk, queue, flags, destructor,
273                                                 peeked, off, &error, last);
274                 spin_unlock_irqrestore(&queue->lock, cpu_flags);
275                 if (error)
276                         goto no_packet;
277                 if (skb)
278                         return skb;
279 
280                 if (!sk_can_busy_loop(sk))
281                         break;
282 
283                 sk_busy_loop(sk, flags & MSG_DONTWAIT);
284         } while (!skb_queue_empty(&sk->sk_receive_queue));
285 
286         error = -EAGAIN;
287 
288 no_packet:
289         *err = error;
290         return NULL;
291 }
292 EXPORT_SYMBOL(__skb_try_recv_datagram);
293 
294 struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
295                                     void (*destructor)(struct sock *sk,
296                                                        struct sk_buff *skb),
297                                     int *peeked, int *off, int *err)
298 {
299         struct sk_buff *skb, *last;
300         long timeo;
301 
302         timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
303 
304         do {
305                 skb = __skb_try_recv_datagram(sk, flags, destructor, peeked,
306                                               off, err, &last);
307                 if (skb)
308                         return skb;
309 
310                 if (*err != -EAGAIN)
311                         break;
312         } while (timeo &&
313                 !__skb_wait_for_more_packets(sk, err, &timeo, last));
314 
315         return NULL;
316 }
317 EXPORT_SYMBOL(__skb_recv_datagram);
318 
319 struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned int flags,
320                                   int noblock, int *err)
321 {
322         int peeked, off = 0;
323 
324         return __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0),
325                                    NULL, &peeked, &off, err);
326 }
327 EXPORT_SYMBOL(skb_recv_datagram);
328 
329 void skb_free_datagram(struct sock *sk, struct sk_buff *skb)
330 {
331         consume_skb(skb);
332         sk_mem_reclaim_partial(sk);
333 }
334 EXPORT_SYMBOL(skb_free_datagram);
335 
336 void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len)
337 {
338         bool slow;
339 
340         if (!skb_unref(skb)) {
341                 sk_peek_offset_bwd(sk, len);
342                 return;
343         }
344 
345         slow = lock_sock_fast(sk);
346         sk_peek_offset_bwd(sk, len);
347         skb_orphan(skb);
348         sk_mem_reclaim_partial(sk);
349         unlock_sock_fast(sk, slow);
350 
351         /* skb is now orphaned, can be freed outside of locked section */
352         __kfree_skb(skb);
353 }
354 EXPORT_SYMBOL(__skb_free_datagram_locked);
355 
356 int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
357                         struct sk_buff *skb, unsigned int flags,
358                         void (*destructor)(struct sock *sk,
359                                            struct sk_buff *skb))
360 {
361         int err = 0;
362 
363         if (flags & MSG_PEEK) {
364                 err = -ENOENT;
365                 spin_lock_bh(&sk_queue->lock);
366                 if (skb->next) {
367                         __skb_unlink(skb, sk_queue);
368                         refcount_dec(&skb->users);
369                         if (destructor)
370                                 destructor(sk, skb);
371                         err = 0;
372                 }
373                 spin_unlock_bh(&sk_queue->lock);
374         }
375 
376         atomic_inc(&sk->sk_drops);
377         return err;
378 }
379 EXPORT_SYMBOL(__sk_queue_drop_skb);
380 
381 /**
382  *      skb_kill_datagram - Free a datagram skbuff forcibly
383  *      @sk: socket
384  *      @skb: datagram skbuff
385  *      @flags: MSG\_ flags
386  *
387  *      This function frees a datagram skbuff that was received by
388  *      skb_recv_datagram.  The flags argument must match the one
389  *      used for skb_recv_datagram.
390  *
391  *      If the MSG_PEEK flag is set, and the packet is still on the
392  *      receive queue of the socket, it will be taken off the queue
393  *      before it is freed.
394  *
395  *      This function currently only disables BH when acquiring the
396  *      sk_receive_queue lock.  Therefore it must not be used in a
397  *      context where that lock is acquired in an IRQ context.
398  *
399  *      It returns 0 if the packet was removed by us.
400  */
401 
402 int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
403 {
404         int err = __sk_queue_drop_skb(sk, &sk->sk_receive_queue, skb, flags,
405                                       NULL);
406 
407         kfree_skb(skb);
408         sk_mem_reclaim_partial(sk);
409         return err;
410 }
411 EXPORT_SYMBOL(skb_kill_datagram);
412 
413 /**
414  *      skb_copy_datagram_iter - Copy a datagram to an iovec iterator.
415  *      @skb: buffer to copy
416  *      @offset: offset in the buffer to start copying from
417  *      @to: iovec iterator to copy to
418  *      @len: amount of data to copy from buffer to iovec
419  */
420 int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
421                            struct iov_iter *to, int len)
422 {
423         int start = skb_headlen(skb);
424         int i, copy = start - offset, start_off = offset, n;
425         struct sk_buff *frag_iter;
426 
427         trace_skb_copy_datagram_iovec(skb, len);
428 
429         /* Copy header. */
430         if (copy > 0) {
431                 if (copy > len)
432                         copy = len;
433                 n = copy_to_iter(skb->data + offset, copy, to);
434                 offset += n;
435                 if (n != copy)
436                         goto short_copy;
437                 if ((len -= copy) == 0)
438                         return 0;
439         }
440 
441         /* Copy paged appendix. Hmm... why does this look so complicated? */
442         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
443                 int end;
444                 const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
445 
446                 WARN_ON(start > offset + len);
447 
448                 end = start + skb_frag_size(frag);
449                 if ((copy = end - offset) > 0) {
450                         if (copy > len)
451                                 copy = len;
452                         n = copy_page_to_iter(skb_frag_page(frag),
453                                               frag->page_offset + offset -
454                                               start, copy, to);
455                         offset += n;
456                         if (n != copy)
457                                 goto short_copy;
458                         if (!(len -= copy))
459                                 return 0;
460                 }
461                 start = end;
462         }
463 
464         skb_walk_frags(skb, frag_iter) {
465                 int end;
466 
467                 WARN_ON(start > offset + len);
468 
469                 end = start + frag_iter->len;
470                 if ((copy = end - offset) > 0) {
471                         if (copy > len)
472                                 copy = len;
473                         if (skb_copy_datagram_iter(frag_iter, offset - start,
474                                                    to, copy))
475                                 goto fault;
476                         if ((len -= copy) == 0)
477                                 return 0;
478                         offset += copy;
479                 }
480                 start = end;
481         }
482         if (!len)
483                 return 0;
484 
485         /* This is not really a user copy fault, but rather someone
486          * gave us a bogus length on the skb.  We should probably
487          * print a warning here as it may indicate a kernel bug.
488          */
489 
490 fault:
491         iov_iter_revert(to, offset - start_off);
492         return -EFAULT;
493 
494 short_copy:
495         if (iov_iter_count(to))
496                 goto fault;
497 
498         return 0;
499 }
500 EXPORT_SYMBOL(skb_copy_datagram_iter);
501 
502 /**
503  *      skb_copy_datagram_from_iter - Copy a datagram from an iov_iter.
504  *      @skb: buffer to copy
505  *      @offset: offset in the buffer to start copying to
506  *      @from: the copy source
507  *      @len: amount of data to copy to buffer from iovec
508  *
509  *      Returns 0 or -EFAULT.
510  */
511 int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
512                                  struct iov_iter *from,
513                                  int len)
514 {
515         int start = skb_headlen(skb);
516         int i, copy = start - offset;
517         struct sk_buff *frag_iter;
518 
519         /* Copy header. */
520         if (copy > 0) {
521                 if (copy > len)
522                         copy = len;
523                 if (copy_from_iter(skb->data + offset, copy, from) != copy)
524                         goto fault;
525                 if ((len -= copy) == 0)
526                         return 0;
527                 offset += copy;
528         }
529 
530         /* Copy paged appendix. Hmm... why does this look so complicated? */
531         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
532                 int end;
533                 const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
534 
535                 WARN_ON(start > offset + len);
536 
537                 end = start + skb_frag_size(frag);
538                 if ((copy = end - offset) > 0) {
539                         size_t copied;
540 
541                         if (copy > len)
542                                 copy = len;
543                         copied = copy_page_from_iter(skb_frag_page(frag),
544                                           frag->page_offset + offset - start,
545                                           copy, from);
546                         if (copied != copy)
547                                 goto fault;
548 
549                         if (!(len -= copy))
550                                 return 0;
551                         offset += copy;
552                 }
553                 start = end;
554         }
555 
556         skb_walk_frags(skb, frag_iter) {
557                 int end;
558 
559                 WARN_ON(start > offset + len);
560 
561                 end = start + frag_iter->len;
562                 if ((copy = end - offset) > 0) {
563                         if (copy > len)
564                                 copy = len;
565                         if (skb_copy_datagram_from_iter(frag_iter,
566                                                         offset - start,
567                                                         from, copy))
568                                 goto fault;
569                         if ((len -= copy) == 0)
570                                 return 0;
571                         offset += copy;
572                 }
573                 start = end;
574         }
575         if (!len)
576                 return 0;
577 
578 fault:
579         return -EFAULT;
580 }
581 EXPORT_SYMBOL(skb_copy_datagram_from_iter);
582 
583 int __zerocopy_sg_from_iter(struct sock *sk, struct sk_buff *skb,
584                             struct iov_iter *from, size_t length)
585 {
586         int frag = skb_shinfo(skb)->nr_frags;
587 
588         while (length && iov_iter_count(from)) {
589                 struct page *pages[MAX_SKB_FRAGS];
590                 size_t start;
591                 ssize_t copied;
592                 unsigned long truesize;
593                 int n = 0;
594 
595                 if (frag == MAX_SKB_FRAGS)
596                         return -EMSGSIZE;
597 
598                 copied = iov_iter_get_pages(from, pages, length,
599                                             MAX_SKB_FRAGS - frag, &start);
600                 if (copied < 0)
601                         return -EFAULT;
602 
603                 iov_iter_advance(from, copied);
604                 length -= copied;
605 
606                 truesize = PAGE_ALIGN(copied + start);
607                 skb->data_len += copied;
608                 skb->len += copied;
609                 skb->truesize += truesize;
610                 if (sk && sk->sk_type == SOCK_STREAM) {
611                         sk->sk_wmem_queued += truesize;
612                         sk_mem_charge(sk, truesize);
613                 } else {
614                         refcount_add(truesize, &skb->sk->sk_wmem_alloc);
615                 }
616                 while (copied) {
617                         int size = min_t(int, copied, PAGE_SIZE - start);
618                         skb_fill_page_desc(skb, frag++, pages[n], start, size);
619                         start = 0;
620                         copied -= size;
621                         n++;
622                 }
623         }
624         return 0;
625 }
626 EXPORT_SYMBOL(__zerocopy_sg_from_iter);
627 
628 /**
629  *      zerocopy_sg_from_iter - Build a zerocopy datagram from an iov_iter
630  *      @skb: buffer to copy
631  *      @from: the source to copy from
632  *
633  *      The function will first copy up to headlen, and then pin the userspace
634  *      pages and build frags through them.
635  *
636  *      Returns 0, -EFAULT or -EMSGSIZE.
637  */
638 int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *from)
639 {
640         int copy = min_t(int, skb_headlen(skb), iov_iter_count(from));
641 
642         /* copy up to skb headlen */
643         if (skb_copy_datagram_from_iter(skb, 0, from, copy))
644                 return -EFAULT;
645 
646         return __zerocopy_sg_from_iter(NULL, skb, from, ~0U);
647 }
648 EXPORT_SYMBOL(zerocopy_sg_from_iter);
649 
650 static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
651                                       struct iov_iter *to, int len,
652                                       __wsum *csump)
653 {
654         int start = skb_headlen(skb);
655         int i, copy = start - offset, start_off = offset;
656         struct sk_buff *frag_iter;
657         int pos = 0;
658         int n;
659 
660         /* Copy header. */
661         if (copy > 0) {
662                 if (copy > len)
663                         copy = len;
664                 n = csum_and_copy_to_iter(skb->data + offset, copy, csump, to);
665                 offset += n;
666                 if (n != copy)
667                         goto fault;
668                 if ((len -= copy) == 0)
669                         return 0;
670                 pos = copy;
671         }
672 
673         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
674                 int end;
675                 const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
676 
677                 WARN_ON(start > offset + len);
678 
679                 end = start + skb_frag_size(frag);
680                 if ((copy = end - offset) > 0) {
681                         __wsum csum2 = 0;
682                         struct page *page = skb_frag_page(frag);
683                         u8  *vaddr = kmap(page);
684 
685                         if (copy > len)
686                                 copy = len;
687                         n = csum_and_copy_to_iter(vaddr + frag->page_offset +
688                                                   offset - start, copy,
689                                                   &csum2, to);
690                         kunmap(page);
691                         offset += n;
692                         if (n != copy)
693                                 goto fault;
694                         *csump = csum_block_add(*csump, csum2, pos);
695                         if (!(len -= copy))
696                                 return 0;
697                         pos += copy;
698                 }
699                 start = end;
700         }
701 
702         skb_walk_frags(skb, frag_iter) {
703                 int end;
704 
705                 WARN_ON(start > offset + len);
706 
707                 end = start + frag_iter->len;
708                 if ((copy = end - offset) > 0) {
709                         __wsum csum2 = 0;
710                         if (copy > len)
711                                 copy = len;
712                         if (skb_copy_and_csum_datagram(frag_iter,
713                                                        offset - start,
714                                                        to, copy,
715                                                        &csum2))
716                                 goto fault;
717                         *csump = csum_block_add(*csump, csum2, pos);
718                         if ((len -= copy) == 0)
719                                 return 0;
720                         offset += copy;
721                         pos += copy;
722                 }
723                 start = end;
724         }
725         if (!len)
726                 return 0;
727 
728 fault:
729         iov_iter_revert(to, offset - start_off);
730         return -EFAULT;
731 }
732 
733 __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len)
734 {
735         __sum16 sum;
736 
737         sum = csum_fold(skb_checksum(skb, 0, len, skb->csum));
738         if (likely(!sum)) {
739                 if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
740                     !skb->csum_complete_sw)
741                         netdev_rx_csum_fault(skb->dev);
742         }
743         if (!skb_shared(skb))
744                 skb->csum_valid = !sum;
745         return sum;
746 }
747 EXPORT_SYMBOL(__skb_checksum_complete_head);
748 
749 __sum16 __skb_checksum_complete(struct sk_buff *skb)
750 {
751         __wsum csum;
752         __sum16 sum;
753 
754         csum = skb_checksum(skb, 0, skb->len, 0);
755 
756         /* skb->csum holds pseudo checksum */
757         sum = csum_fold(csum_add(skb->csum, csum));
758         if (likely(!sum)) {
759                 if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
760                     !skb->csum_complete_sw)
761                         netdev_rx_csum_fault(skb->dev);
762         }
763 
764         if (!skb_shared(skb)) {
765                 /* Save full packet checksum */
766                 skb->csum = csum;
767                 skb->ip_summed = CHECKSUM_COMPLETE;
768                 skb->csum_complete_sw = 1;
769                 skb->csum_valid = !sum;
770         }
771 
772         return sum;
773 }
774 EXPORT_SYMBOL(__skb_checksum_complete);
775 
776 /**
777  *      skb_copy_and_csum_datagram_msg - Copy and checksum skb to user iovec.
778  *      @skb: skbuff
779  *      @hlen: hardware length
780  *      @msg: destination
781  *
782  *      Caller _must_ check that skb will fit to this iovec.
783  *
784  *      Returns: 0       - success.
785  *               -EINVAL - checksum failure.
786  *               -EFAULT - fault during copy.
787  */
788 int skb_copy_and_csum_datagram_msg(struct sk_buff *skb,
789                                    int hlen, struct msghdr *msg)
790 {
791         __wsum csum;
792         int chunk = skb->len - hlen;
793 
794         if (!chunk)
795                 return 0;
796 
797         if (msg_data_left(msg) < chunk) {
798                 if (__skb_checksum_complete(skb))
799                         return -EINVAL;
800                 if (skb_copy_datagram_msg(skb, hlen, msg, chunk))
801                         goto fault;
802         } else {
803                 csum = csum_partial(skb->data, hlen, skb->csum);
804                 if (skb_copy_and_csum_datagram(skb, hlen, &msg->msg_iter,
805                                                chunk, &csum))
806                         goto fault;
807 
808                 if (csum_fold(csum)) {
809                         iov_iter_revert(&msg->msg_iter, chunk);
810                         return -EINVAL;
811                 }
812 
813                 if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE))
814                         netdev_rx_csum_fault(skb->dev);
815         }
816         return 0;
817 fault:
818         return -EFAULT;
819 }
820 EXPORT_SYMBOL(skb_copy_and_csum_datagram_msg);
821 
822 /**
823  *      datagram_poll - generic datagram poll
824  *      @file: file struct
825  *      @sock: socket
826  *      @wait: poll table
827  *
828  *      Datagram poll: Again totally generic. This also handles
829  *      sequenced packet sockets providing the socket receive queue
830  *      is only ever holding data ready to receive.
831  *
832  *      Note: when you *don't* use this routine for this protocol,
833  *      and you use a different write policy from sock_writeable()
834  *      then please supply your own write_space callback.
835  */
836 unsigned int datagram_poll(struct file *file, struct socket *sock,
837                            poll_table *wait)
838 {
839         struct sock *sk = sock->sk;
840         unsigned int mask;
841 
842         sock_poll_wait(file, sk_sleep(sk), wait);
843         mask = 0;
844 
845         /* exceptional events? */
846         if (sk->sk_err || !skb_queue_empty(&sk->sk_error_queue))
847                 mask |= POLLERR |
848                         (sock_flag(sk, SOCK_SELECT_ERR_QUEUE) ? POLLPRI : 0);
849 
850         if (sk->sk_shutdown & RCV_SHUTDOWN)
851                 mask |= POLLRDHUP | POLLIN | POLLRDNORM;
852         if (sk->sk_shutdown == SHUTDOWN_MASK)
853                 mask |= POLLHUP;
854 
855         /* readable? */
856         if (!skb_queue_empty(&sk->sk_receive_queue))
857                 mask |= POLLIN | POLLRDNORM;
858 
859         /* Connection-based need to check for termination and startup */
860         if (connection_based(sk)) {
861                 if (sk->sk_state == TCP_CLOSE)
862                         mask |= POLLHUP;
863                 /* connection hasn't started yet? */
864                 if (sk->sk_state == TCP_SYN_SENT)
865                         return mask;
866         }
867 
868         /* writable? */
869         if (sock_writeable(sk))
870                 mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
871         else
872                 sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
873 
874         return mask;
875 }
876 EXPORT_SYMBOL(datagram_poll);
877 

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