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TOMOYO Linux Cross Reference
Linux/fs/pipe.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *  linux/fs/pipe.c
  4  *
  5  *  Copyright (C) 1991, 1992, 1999  Linus Torvalds
  6  */
  7 
  8 #include <linux/mm.h>
  9 #include <linux/file.h>
 10 #include <linux/poll.h>
 11 #include <linux/slab.h>
 12 #include <linux/module.h>
 13 #include <linux/init.h>
 14 #include <linux/fs.h>
 15 #include <linux/log2.h>
 16 #include <linux/mount.h>
 17 #include <linux/pseudo_fs.h>
 18 #include <linux/magic.h>
 19 #include <linux/pipe_fs_i.h>
 20 #include <linux/uio.h>
 21 #include <linux/highmem.h>
 22 #include <linux/pagemap.h>
 23 #include <linux/audit.h>
 24 #include <linux/syscalls.h>
 25 #include <linux/fcntl.h>
 26 #include <linux/memcontrol.h>
 27 
 28 #include <linux/uaccess.h>
 29 #include <asm/ioctls.h>
 30 
 31 #include "internal.h"
 32 
 33 /*
 34  * The max size that a non-root user is allowed to grow the pipe. Can
 35  * be set by root in /proc/sys/fs/pipe-max-size
 36  */
 37 unsigned int pipe_max_size = 1048576;
 38 
 39 /* Maximum allocatable pages per user. Hard limit is unset by default, soft
 40  * matches default values.
 41  */
 42 unsigned long pipe_user_pages_hard;
 43 unsigned long pipe_user_pages_soft = PIPE_DEF_BUFFERS * INR_OPEN_CUR;
 44 
 45 /*
 46  * We use head and tail indices that aren't masked off, except at the point of
 47  * dereference, but rather they're allowed to wrap naturally.  This means there
 48  * isn't a dead spot in the buffer, but the ring has to be a power of two and
 49  * <= 2^31.
 50  * -- David Howells 2019-09-23.
 51  *
 52  * Reads with count = 0 should always return 0.
 53  * -- Julian Bradfield 1999-06-07.
 54  *
 55  * FIFOs and Pipes now generate SIGIO for both readers and writers.
 56  * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
 57  *
 58  * pipe_read & write cleanup
 59  * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
 60  */
 61 
 62 static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
 63 {
 64         if (pipe->files)
 65                 mutex_lock_nested(&pipe->mutex, subclass);
 66 }
 67 
 68 void pipe_lock(struct pipe_inode_info *pipe)
 69 {
 70         /*
 71          * pipe_lock() nests non-pipe inode locks (for writing to a file)
 72          */
 73         pipe_lock_nested(pipe, I_MUTEX_PARENT);
 74 }
 75 EXPORT_SYMBOL(pipe_lock);
 76 
 77 void pipe_unlock(struct pipe_inode_info *pipe)
 78 {
 79         if (pipe->files)
 80                 mutex_unlock(&pipe->mutex);
 81 }
 82 EXPORT_SYMBOL(pipe_unlock);
 83 
 84 static inline void __pipe_lock(struct pipe_inode_info *pipe)
 85 {
 86         mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
 87 }
 88 
 89 static inline void __pipe_unlock(struct pipe_inode_info *pipe)
 90 {
 91         mutex_unlock(&pipe->mutex);
 92 }
 93 
 94 void pipe_double_lock(struct pipe_inode_info *pipe1,
 95                       struct pipe_inode_info *pipe2)
 96 {
 97         BUG_ON(pipe1 == pipe2);
 98 
 99         if (pipe1 < pipe2) {
100                 pipe_lock_nested(pipe1, I_MUTEX_PARENT);
101                 pipe_lock_nested(pipe2, I_MUTEX_CHILD);
102         } else {
103                 pipe_lock_nested(pipe2, I_MUTEX_PARENT);
104                 pipe_lock_nested(pipe1, I_MUTEX_CHILD);
105         }
106 }
107 
108 /* Drop the inode semaphore and wait for a pipe event, atomically */
109 void pipe_wait(struct pipe_inode_info *pipe)
110 {
111         DEFINE_WAIT(wait);
112 
113         /*
114          * Pipes are system-local resources, so sleeping on them
115          * is considered a noninteractive wait:
116          */
117         prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
118         pipe_unlock(pipe);
119         schedule();
120         finish_wait(&pipe->wait, &wait);
121         pipe_lock(pipe);
122 }
123 
124 static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
125                                   struct pipe_buffer *buf)
126 {
127         struct page *page = buf->page;
128 
129         /*
130          * If nobody else uses this page, and we don't already have a
131          * temporary page, let's keep track of it as a one-deep
132          * allocation cache. (Otherwise just release our reference to it)
133          */
134         if (page_count(page) == 1 && !pipe->tmp_page)
135                 pipe->tmp_page = page;
136         else
137                 put_page(page);
138 }
139 
140 static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
141                                struct pipe_buffer *buf)
142 {
143         struct page *page = buf->page;
144 
145         if (page_count(page) == 1) {
146                 memcg_kmem_uncharge(page, 0);
147                 __SetPageLocked(page);
148                 return 0;
149         }
150         return 1;
151 }
152 
153 /**
154  * generic_pipe_buf_steal - attempt to take ownership of a &pipe_buffer
155  * @pipe:       the pipe that the buffer belongs to
156  * @buf:        the buffer to attempt to steal
157  *
158  * Description:
159  *      This function attempts to steal the &struct page attached to
160  *      @buf. If successful, this function returns 0 and returns with
161  *      the page locked. The caller may then reuse the page for whatever
162  *      he wishes; the typical use is insertion into a different file
163  *      page cache.
164  */
165 int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
166                            struct pipe_buffer *buf)
167 {
168         struct page *page = buf->page;
169 
170         /*
171          * A reference of one is golden, that means that the owner of this
172          * page is the only one holding a reference to it. lock the page
173          * and return OK.
174          */
175         if (page_count(page) == 1) {
176                 lock_page(page);
177                 return 0;
178         }
179 
180         return 1;
181 }
182 EXPORT_SYMBOL(generic_pipe_buf_steal);
183 
184 /**
185  * generic_pipe_buf_get - get a reference to a &struct pipe_buffer
186  * @pipe:       the pipe that the buffer belongs to
187  * @buf:        the buffer to get a reference to
188  *
189  * Description:
190  *      This function grabs an extra reference to @buf. It's used in
191  *      in the tee() system call, when we duplicate the buffers in one
192  *      pipe into another.
193  */
194 bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
195 {
196         return try_get_page(buf->page);
197 }
198 EXPORT_SYMBOL(generic_pipe_buf_get);
199 
200 /**
201  * generic_pipe_buf_confirm - verify contents of the pipe buffer
202  * @info:       the pipe that the buffer belongs to
203  * @buf:        the buffer to confirm
204  *
205  * Description:
206  *      This function does nothing, because the generic pipe code uses
207  *      pages that are always good when inserted into the pipe.
208  */
209 int generic_pipe_buf_confirm(struct pipe_inode_info *info,
210                              struct pipe_buffer *buf)
211 {
212         return 0;
213 }
214 EXPORT_SYMBOL(generic_pipe_buf_confirm);
215 
216 /**
217  * generic_pipe_buf_release - put a reference to a &struct pipe_buffer
218  * @pipe:       the pipe that the buffer belongs to
219  * @buf:        the buffer to put a reference to
220  *
221  * Description:
222  *      This function releases a reference to @buf.
223  */
224 void generic_pipe_buf_release(struct pipe_inode_info *pipe,
225                               struct pipe_buffer *buf)
226 {
227         put_page(buf->page);
228 }
229 EXPORT_SYMBOL(generic_pipe_buf_release);
230 
231 /* New data written to a pipe may be appended to a buffer with this type. */
232 static const struct pipe_buf_operations anon_pipe_buf_ops = {
233         .confirm = generic_pipe_buf_confirm,
234         .release = anon_pipe_buf_release,
235         .steal = anon_pipe_buf_steal,
236         .get = generic_pipe_buf_get,
237 };
238 
239 static const struct pipe_buf_operations anon_pipe_buf_nomerge_ops = {
240         .confirm = generic_pipe_buf_confirm,
241         .release = anon_pipe_buf_release,
242         .steal = anon_pipe_buf_steal,
243         .get = generic_pipe_buf_get,
244 };
245 
246 static const struct pipe_buf_operations packet_pipe_buf_ops = {
247         .confirm = generic_pipe_buf_confirm,
248         .release = anon_pipe_buf_release,
249         .steal = anon_pipe_buf_steal,
250         .get = generic_pipe_buf_get,
251 };
252 
253 /**
254  * pipe_buf_mark_unmergeable - mark a &struct pipe_buffer as unmergeable
255  * @buf:        the buffer to mark
256  *
257  * Description:
258  *      This function ensures that no future writes will be merged into the
259  *      given &struct pipe_buffer. This is necessary when multiple pipe buffers
260  *      share the same backing page.
261  */
262 void pipe_buf_mark_unmergeable(struct pipe_buffer *buf)
263 {
264         if (buf->ops == &anon_pipe_buf_ops)
265                 buf->ops = &anon_pipe_buf_nomerge_ops;
266 }
267 
268 static bool pipe_buf_can_merge(struct pipe_buffer *buf)
269 {
270         return buf->ops == &anon_pipe_buf_ops;
271 }
272 
273 /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
274 static inline bool pipe_readable(const struct pipe_inode_info *pipe)
275 {
276         unsigned int head = READ_ONCE(pipe->head);
277         unsigned int tail = READ_ONCE(pipe->tail);
278         unsigned int writers = READ_ONCE(pipe->writers);
279 
280         return !pipe_empty(head, tail) || !writers;
281 }
282 
283 static ssize_t
284 pipe_read(struct kiocb *iocb, struct iov_iter *to)
285 {
286         size_t total_len = iov_iter_count(to);
287         struct file *filp = iocb->ki_filp;
288         struct pipe_inode_info *pipe = filp->private_data;
289         bool was_full;
290         ssize_t ret;
291 
292         /* Null read succeeds. */
293         if (unlikely(total_len == 0))
294                 return 0;
295 
296         ret = 0;
297         __pipe_lock(pipe);
298 
299         /*
300          * We only wake up writers if the pipe was full when we started
301          * reading in order to avoid unnecessary wakeups.
302          *
303          * But when we do wake up writers, we do so using a sync wakeup
304          * (WF_SYNC), because we want them to get going and generate more
305          * data for us.
306          */
307         was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
308         for (;;) {
309                 unsigned int head = pipe->head;
310                 unsigned int tail = pipe->tail;
311                 unsigned int mask = pipe->ring_size - 1;
312 
313                 if (!pipe_empty(head, tail)) {
314                         struct pipe_buffer *buf = &pipe->bufs[tail & mask];
315                         size_t chars = buf->len;
316                         size_t written;
317                         int error;
318 
319                         if (chars > total_len)
320                                 chars = total_len;
321 
322                         error = pipe_buf_confirm(pipe, buf);
323                         if (error) {
324                                 if (!ret)
325                                         ret = error;
326                                 break;
327                         }
328 
329                         written = copy_page_to_iter(buf->page, buf->offset, chars, to);
330                         if (unlikely(written < chars)) {
331                                 if (!ret)
332                                         ret = -EFAULT;
333                                 break;
334                         }
335                         ret += chars;
336                         buf->offset += chars;
337                         buf->len -= chars;
338 
339                         /* Was it a packet buffer? Clean up and exit */
340                         if (buf->flags & PIPE_BUF_FLAG_PACKET) {
341                                 total_len = chars;
342                                 buf->len = 0;
343                         }
344 
345                         if (!buf->len) {
346                                 pipe_buf_release(pipe, buf);
347                                 spin_lock_irq(&pipe->wait.lock);
348                                 tail++;
349                                 pipe->tail = tail;
350                                 spin_unlock_irq(&pipe->wait.lock);
351                         }
352                         total_len -= chars;
353                         if (!total_len)
354                                 break;  /* common path: read succeeded */
355                         if (!pipe_empty(head, tail))    /* More to do? */
356                                 continue;
357                 }
358 
359                 if (!pipe->writers)
360                         break;
361                 if (ret)
362                         break;
363                 if (filp->f_flags & O_NONBLOCK) {
364                         ret = -EAGAIN;
365                         break;
366                 }
367                 __pipe_unlock(pipe);
368 
369                 /*
370                  * We only get here if we didn't actually read anything.
371                  *
372                  * However, we could have seen (and removed) a zero-sized
373                  * pipe buffer, and might have made space in the buffers
374                  * that way.
375                  *
376                  * You can't make zero-sized pipe buffers by doing an empty
377                  * write (not even in packet mode), but they can happen if
378                  * the writer gets an EFAULT when trying to fill a buffer
379                  * that already got allocated and inserted in the buffer
380                  * array.
381                  *
382                  * So we still need to wake up any pending writers in the
383                  * _very_ unlikely case that the pipe was full, but we got
384                  * no data.
385                  */
386                 if (unlikely(was_full)) {
387                         wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM);
388                         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
389                 }
390 
391                 /*
392                  * But because we didn't read anything, at this point we can
393                  * just return directly with -ERESTARTSYS if we're interrupted,
394                  * since we've done any required wakeups and there's no need
395                  * to mark anything accessed. And we've dropped the lock.
396                  */
397                 if (wait_event_interruptible(pipe->wait, pipe_readable(pipe)) < 0)
398                         return -ERESTARTSYS;
399 
400                 __pipe_lock(pipe);
401                 was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
402         }
403         __pipe_unlock(pipe);
404 
405         if (was_full) {
406                 wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM);
407                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
408         }
409         if (ret > 0)
410                 file_accessed(filp);
411         return ret;
412 }
413 
414 static inline int is_packetized(struct file *file)
415 {
416         return (file->f_flags & O_DIRECT) != 0;
417 }
418 
419 /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
420 static inline bool pipe_writable(const struct pipe_inode_info *pipe)
421 {
422         unsigned int head = READ_ONCE(pipe->head);
423         unsigned int tail = READ_ONCE(pipe->tail);
424         unsigned int max_usage = READ_ONCE(pipe->max_usage);
425 
426         return !pipe_full(head, tail, max_usage) ||
427                 !READ_ONCE(pipe->readers);
428 }
429 
430 static ssize_t
431 pipe_write(struct kiocb *iocb, struct iov_iter *from)
432 {
433         struct file *filp = iocb->ki_filp;
434         struct pipe_inode_info *pipe = filp->private_data;
435         unsigned int head;
436         ssize_t ret = 0;
437         size_t total_len = iov_iter_count(from);
438         ssize_t chars;
439         bool was_empty = false;
440 
441         /* Null write succeeds. */
442         if (unlikely(total_len == 0))
443                 return 0;
444 
445         __pipe_lock(pipe);
446 
447         if (!pipe->readers) {
448                 send_sig(SIGPIPE, current, 0);
449                 ret = -EPIPE;
450                 goto out;
451         }
452 
453         /*
454          * Only wake up if the pipe started out empty, since
455          * otherwise there should be no readers waiting.
456          *
457          * If it wasn't empty we try to merge new data into
458          * the last buffer.
459          *
460          * That naturally merges small writes, but it also
461          * page-aligs the rest of the writes for large writes
462          * spanning multiple pages.
463          */
464         head = pipe->head;
465         was_empty = pipe_empty(head, pipe->tail);
466         chars = total_len & (PAGE_SIZE-1);
467         if (chars && !was_empty) {
468                 unsigned int mask = pipe->ring_size - 1;
469                 struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];
470                 int offset = buf->offset + buf->len;
471 
472                 if (pipe_buf_can_merge(buf) && offset + chars <= PAGE_SIZE) {
473                         ret = pipe_buf_confirm(pipe, buf);
474                         if (ret)
475                                 goto out;
476 
477                         ret = copy_page_from_iter(buf->page, offset, chars, from);
478                         if (unlikely(ret < chars)) {
479                                 ret = -EFAULT;
480                                 goto out;
481                         }
482 
483                         buf->len += ret;
484                         if (!iov_iter_count(from))
485                                 goto out;
486                 }
487         }
488 
489         for (;;) {
490                 if (!pipe->readers) {
491                         send_sig(SIGPIPE, current, 0);
492                         if (!ret)
493                                 ret = -EPIPE;
494                         break;
495                 }
496 
497                 head = pipe->head;
498                 if (!pipe_full(head, pipe->tail, pipe->max_usage)) {
499                         unsigned int mask = pipe->ring_size - 1;
500                         struct pipe_buffer *buf = &pipe->bufs[head & mask];
501                         struct page *page = pipe->tmp_page;
502                         int copied;
503 
504                         if (!page) {
505                                 page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);
506                                 if (unlikely(!page)) {
507                                         ret = ret ? : -ENOMEM;
508                                         break;
509                                 }
510                                 pipe->tmp_page = page;
511                         }
512 
513                         /* Allocate a slot in the ring in advance and attach an
514                          * empty buffer.  If we fault or otherwise fail to use
515                          * it, either the reader will consume it or it'll still
516                          * be there for the next write.
517                          */
518                         spin_lock_irq(&pipe->wait.lock);
519 
520                         head = pipe->head;
521                         if (pipe_full(head, pipe->tail, pipe->max_usage)) {
522                                 spin_unlock_irq(&pipe->wait.lock);
523                                 continue;
524                         }
525 
526                         pipe->head = head + 1;
527                         spin_unlock_irq(&pipe->wait.lock);
528 
529                         /* Insert it into the buffer array */
530                         buf = &pipe->bufs[head & mask];
531                         buf->page = page;
532                         buf->ops = &anon_pipe_buf_ops;
533                         buf->offset = 0;
534                         buf->len = 0;
535                         buf->flags = 0;
536                         if (is_packetized(filp)) {
537                                 buf->ops = &packet_pipe_buf_ops;
538                                 buf->flags = PIPE_BUF_FLAG_PACKET;
539                         }
540                         pipe->tmp_page = NULL;
541 
542                         copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);
543                         if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {
544                                 if (!ret)
545                                         ret = -EFAULT;
546                                 break;
547                         }
548                         ret += copied;
549                         buf->offset = 0;
550                         buf->len = copied;
551 
552                         if (!iov_iter_count(from))
553                                 break;
554                 }
555 
556                 if (!pipe_full(head, pipe->tail, pipe->max_usage))
557                         continue;
558 
559                 /* Wait for buffer space to become available. */
560                 if (filp->f_flags & O_NONBLOCK) {
561                         if (!ret)
562                                 ret = -EAGAIN;
563                         break;
564                 }
565                 if (signal_pending(current)) {
566                         if (!ret)
567                                 ret = -ERESTARTSYS;
568                         break;
569                 }
570 
571                 /*
572                  * We're going to release the pipe lock and wait for more
573                  * space. We wake up any readers if necessary, and then
574                  * after waiting we need to re-check whether the pipe
575                  * become empty while we dropped the lock.
576                  */
577                 __pipe_unlock(pipe);
578                 if (was_empty) {
579                         wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLRDNORM);
580                         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
581                 }
582                 wait_event_interruptible(pipe->wait, pipe_writable(pipe));
583                 __pipe_lock(pipe);
584                 was_empty = pipe_empty(pipe->head, pipe->tail);
585         }
586 out:
587         __pipe_unlock(pipe);
588 
589         /*
590          * If we do do a wakeup event, we do a 'sync' wakeup, because we
591          * want the reader to start processing things asap, rather than
592          * leave the data pending.
593          *
594          * This is particularly important for small writes, because of
595          * how (for example) the GNU make jobserver uses small writes to
596          * wake up pending jobs
597          */
598         if (was_empty) {
599                 wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLRDNORM);
600                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
601         }
602         if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {
603                 int err = file_update_time(filp);
604                 if (err)
605                         ret = err;
606                 sb_end_write(file_inode(filp)->i_sb);
607         }
608         return ret;
609 }
610 
611 static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
612 {
613         struct pipe_inode_info *pipe = filp->private_data;
614         int count, head, tail, mask;
615 
616         switch (cmd) {
617                 case FIONREAD:
618                         __pipe_lock(pipe);
619                         count = 0;
620                         head = pipe->head;
621                         tail = pipe->tail;
622                         mask = pipe->ring_size - 1;
623 
624                         while (tail != head) {
625                                 count += pipe->bufs[tail & mask].len;
626                                 tail++;
627                         }
628                         __pipe_unlock(pipe);
629 
630                         return put_user(count, (int __user *)arg);
631                 default:
632                         return -ENOIOCTLCMD;
633         }
634 }
635 
636 /* No kernel lock held - fine */
637 static __poll_t
638 pipe_poll(struct file *filp, poll_table *wait)
639 {
640         __poll_t mask;
641         struct pipe_inode_info *pipe = filp->private_data;
642         unsigned int head, tail;
643 
644         /*
645          * Reading only -- no need for acquiring the semaphore.
646          *
647          * But because this is racy, the code has to add the
648          * entry to the poll table _first_ ..
649          */
650         poll_wait(filp, &pipe->wait, wait);
651 
652         /*
653          * .. and only then can you do the racy tests. That way,
654          * if something changes and you got it wrong, the poll
655          * table entry will wake you up and fix it.
656          */
657         head = READ_ONCE(pipe->head);
658         tail = READ_ONCE(pipe->tail);
659 
660         mask = 0;
661         if (filp->f_mode & FMODE_READ) {
662                 if (!pipe_empty(head, tail))
663                         mask |= EPOLLIN | EPOLLRDNORM;
664                 if (!pipe->writers && filp->f_version != pipe->w_counter)
665                         mask |= EPOLLHUP;
666         }
667 
668         if (filp->f_mode & FMODE_WRITE) {
669                 if (!pipe_full(head, tail, pipe->max_usage))
670                         mask |= EPOLLOUT | EPOLLWRNORM;
671                 /*
672                  * Most Unices do not set EPOLLERR for FIFOs but on Linux they
673                  * behave exactly like pipes for poll().
674                  */
675                 if (!pipe->readers)
676                         mask |= EPOLLERR;
677         }
678 
679         return mask;
680 }
681 
682 static void put_pipe_info(struct inode *inode, struct pipe_inode_info *pipe)
683 {
684         int kill = 0;
685 
686         spin_lock(&inode->i_lock);
687         if (!--pipe->files) {
688                 inode->i_pipe = NULL;
689                 kill = 1;
690         }
691         spin_unlock(&inode->i_lock);
692 
693         if (kill)
694                 free_pipe_info(pipe);
695 }
696 
697 static int
698 pipe_release(struct inode *inode, struct file *file)
699 {
700         struct pipe_inode_info *pipe = file->private_data;
701 
702         __pipe_lock(pipe);
703         if (file->f_mode & FMODE_READ)
704                 pipe->readers--;
705         if (file->f_mode & FMODE_WRITE)
706                 pipe->writers--;
707 
708         if (pipe->readers || pipe->writers) {
709                 wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLOUT | EPOLLRDNORM | EPOLLWRNORM | EPOLLERR | EPOLLHUP);
710                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
711                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
712         }
713         __pipe_unlock(pipe);
714 
715         put_pipe_info(inode, pipe);
716         return 0;
717 }
718 
719 static int
720 pipe_fasync(int fd, struct file *filp, int on)
721 {
722         struct pipe_inode_info *pipe = filp->private_data;
723         int retval = 0;
724 
725         __pipe_lock(pipe);
726         if (filp->f_mode & FMODE_READ)
727                 retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
728         if ((filp->f_mode & FMODE_WRITE) && retval >= 0) {
729                 retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
730                 if (retval < 0 && (filp->f_mode & FMODE_READ))
731                         /* this can happen only if on == T */
732                         fasync_helper(-1, filp, 0, &pipe->fasync_readers);
733         }
734         __pipe_unlock(pipe);
735         return retval;
736 }
737 
738 static unsigned long account_pipe_buffers(struct user_struct *user,
739                                  unsigned long old, unsigned long new)
740 {
741         return atomic_long_add_return(new - old, &user->pipe_bufs);
742 }
743 
744 static bool too_many_pipe_buffers_soft(unsigned long user_bufs)
745 {
746         unsigned long soft_limit = READ_ONCE(pipe_user_pages_soft);
747 
748         return soft_limit && user_bufs > soft_limit;
749 }
750 
751 static bool too_many_pipe_buffers_hard(unsigned long user_bufs)
752 {
753         unsigned long hard_limit = READ_ONCE(pipe_user_pages_hard);
754 
755         return hard_limit && user_bufs > hard_limit;
756 }
757 
758 static bool is_unprivileged_user(void)
759 {
760         return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
761 }
762 
763 struct pipe_inode_info *alloc_pipe_info(void)
764 {
765         struct pipe_inode_info *pipe;
766         unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
767         struct user_struct *user = get_current_user();
768         unsigned long user_bufs;
769         unsigned int max_size = READ_ONCE(pipe_max_size);
770 
771         pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL_ACCOUNT);
772         if (pipe == NULL)
773                 goto out_free_uid;
774 
775         if (pipe_bufs * PAGE_SIZE > max_size && !capable(CAP_SYS_RESOURCE))
776                 pipe_bufs = max_size >> PAGE_SHIFT;
777 
778         user_bufs = account_pipe_buffers(user, 0, pipe_bufs);
779 
780         if (too_many_pipe_buffers_soft(user_bufs) && is_unprivileged_user()) {
781                 user_bufs = account_pipe_buffers(user, pipe_bufs, 1);
782                 pipe_bufs = 1;
783         }
784 
785         if (too_many_pipe_buffers_hard(user_bufs) && is_unprivileged_user())
786                 goto out_revert_acct;
787 
788         pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
789                              GFP_KERNEL_ACCOUNT);
790 
791         if (pipe->bufs) {
792                 init_waitqueue_head(&pipe->wait);
793                 pipe->r_counter = pipe->w_counter = 1;
794                 pipe->max_usage = pipe_bufs;
795                 pipe->ring_size = pipe_bufs;
796                 pipe->user = user;
797                 mutex_init(&pipe->mutex);
798                 return pipe;
799         }
800 
801 out_revert_acct:
802         (void) account_pipe_buffers(user, pipe_bufs, 0);
803         kfree(pipe);
804 out_free_uid:
805         free_uid(user);
806         return NULL;
807 }
808 
809 void free_pipe_info(struct pipe_inode_info *pipe)
810 {
811         int i;
812 
813         (void) account_pipe_buffers(pipe->user, pipe->ring_size, 0);
814         free_uid(pipe->user);
815         for (i = 0; i < pipe->ring_size; i++) {
816                 struct pipe_buffer *buf = pipe->bufs + i;
817                 if (buf->ops)
818                         pipe_buf_release(pipe, buf);
819         }
820         if (pipe->tmp_page)
821                 __free_page(pipe->tmp_page);
822         kfree(pipe->bufs);
823         kfree(pipe);
824 }
825 
826 static struct vfsmount *pipe_mnt __read_mostly;
827 
828 /*
829  * pipefs_dname() is called from d_path().
830  */
831 static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
832 {
833         return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
834                                 d_inode(dentry)->i_ino);
835 }
836 
837 static const struct dentry_operations pipefs_dentry_operations = {
838         .d_dname        = pipefs_dname,
839 };
840 
841 static struct inode * get_pipe_inode(void)
842 {
843         struct inode *inode = new_inode_pseudo(pipe_mnt->mnt_sb);
844         struct pipe_inode_info *pipe;
845 
846         if (!inode)
847                 goto fail_inode;
848 
849         inode->i_ino = get_next_ino();
850 
851         pipe = alloc_pipe_info();
852         if (!pipe)
853                 goto fail_iput;
854 
855         inode->i_pipe = pipe;
856         pipe->files = 2;
857         pipe->readers = pipe->writers = 1;
858         inode->i_fop = &pipefifo_fops;
859 
860         /*
861          * Mark the inode dirty from the very beginning,
862          * that way it will never be moved to the dirty
863          * list because "mark_inode_dirty()" will think
864          * that it already _is_ on the dirty list.
865          */
866         inode->i_state = I_DIRTY;
867         inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
868         inode->i_uid = current_fsuid();
869         inode->i_gid = current_fsgid();
870         inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
871 
872         return inode;
873 
874 fail_iput:
875         iput(inode);
876 
877 fail_inode:
878         return NULL;
879 }
880 
881 int create_pipe_files(struct file **res, int flags)
882 {
883         struct inode *inode = get_pipe_inode();
884         struct file *f;
885 
886         if (!inode)
887                 return -ENFILE;
888 
889         f = alloc_file_pseudo(inode, pipe_mnt, "",
890                                 O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT)),
891                                 &pipefifo_fops);
892         if (IS_ERR(f)) {
893                 free_pipe_info(inode->i_pipe);
894                 iput(inode);
895                 return PTR_ERR(f);
896         }
897 
898         f->private_data = inode->i_pipe;
899 
900         res[0] = alloc_file_clone(f, O_RDONLY | (flags & O_NONBLOCK),
901                                   &pipefifo_fops);
902         if (IS_ERR(res[0])) {
903                 put_pipe_info(inode, inode->i_pipe);
904                 fput(f);
905                 return PTR_ERR(res[0]);
906         }
907         res[0]->private_data = inode->i_pipe;
908         res[1] = f;
909         stream_open(inode, res[0]);
910         stream_open(inode, res[1]);
911         return 0;
912 }
913 
914 static int __do_pipe_flags(int *fd, struct file **files, int flags)
915 {
916         int error;
917         int fdw, fdr;
918 
919         if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT))
920                 return -EINVAL;
921 
922         error = create_pipe_files(files, flags);
923         if (error)
924                 return error;
925 
926         error = get_unused_fd_flags(flags);
927         if (error < 0)
928                 goto err_read_pipe;
929         fdr = error;
930 
931         error = get_unused_fd_flags(flags);
932         if (error < 0)
933                 goto err_fdr;
934         fdw = error;
935 
936         audit_fd_pair(fdr, fdw);
937         fd[0] = fdr;
938         fd[1] = fdw;
939         return 0;
940 
941  err_fdr:
942         put_unused_fd(fdr);
943  err_read_pipe:
944         fput(files[0]);
945         fput(files[1]);
946         return error;
947 }
948 
949 int do_pipe_flags(int *fd, int flags)
950 {
951         struct file *files[2];
952         int error = __do_pipe_flags(fd, files, flags);
953         if (!error) {
954                 fd_install(fd[0], files[0]);
955                 fd_install(fd[1], files[1]);
956         }
957         return error;
958 }
959 
960 /*
961  * sys_pipe() is the normal C calling standard for creating
962  * a pipe. It's not the way Unix traditionally does this, though.
963  */
964 static int do_pipe2(int __user *fildes, int flags)
965 {
966         struct file *files[2];
967         int fd[2];
968         int error;
969 
970         error = __do_pipe_flags(fd, files, flags);
971         if (!error) {
972                 if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
973                         fput(files[0]);
974                         fput(files[1]);
975                         put_unused_fd(fd[0]);
976                         put_unused_fd(fd[1]);
977                         error = -EFAULT;
978                 } else {
979                         fd_install(fd[0], files[0]);
980                         fd_install(fd[1], files[1]);
981                 }
982         }
983         return error;
984 }
985 
986 SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)
987 {
988         return do_pipe2(fildes, flags);
989 }
990 
991 SYSCALL_DEFINE1(pipe, int __user *, fildes)
992 {
993         return do_pipe2(fildes, 0);
994 }
995 
996 static int wait_for_partner(struct pipe_inode_info *pipe, unsigned int *cnt)
997 {
998         int cur = *cnt;
999 
1000         while (cur == *cnt) {
1001                 pipe_wait(pipe);
1002                 if (signal_pending(current))
1003                         break;
1004         }
1005         return cur == *cnt ? -ERESTARTSYS : 0;
1006 }
1007 
1008 static void wake_up_partner(struct pipe_inode_info *pipe)
1009 {
1010         wake_up_interruptible(&pipe->wait);
1011 }
1012 
1013 static int fifo_open(struct inode *inode, struct file *filp)
1014 {
1015         struct pipe_inode_info *pipe;
1016         bool is_pipe = inode->i_sb->s_magic == PIPEFS_MAGIC;
1017         int ret;
1018 
1019         filp->f_version = 0;
1020 
1021         spin_lock(&inode->i_lock);
1022         if (inode->i_pipe) {
1023                 pipe = inode->i_pipe;
1024                 pipe->files++;
1025                 spin_unlock(&inode->i_lock);
1026         } else {
1027                 spin_unlock(&inode->i_lock);
1028                 pipe = alloc_pipe_info();
1029                 if (!pipe)
1030                         return -ENOMEM;
1031                 pipe->files = 1;
1032                 spin_lock(&inode->i_lock);
1033                 if (unlikely(inode->i_pipe)) {
1034                         inode->i_pipe->files++;
1035                         spin_unlock(&inode->i_lock);
1036                         free_pipe_info(pipe);
1037                         pipe = inode->i_pipe;
1038                 } else {
1039                         inode->i_pipe = pipe;
1040                         spin_unlock(&inode->i_lock);
1041                 }
1042         }
1043         filp->private_data = pipe;
1044         /* OK, we have a pipe and it's pinned down */
1045 
1046         __pipe_lock(pipe);
1047 
1048         /* We can only do regular read/write on fifos */
1049         stream_open(inode, filp);
1050 
1051         switch (filp->f_mode & (FMODE_READ | FMODE_WRITE)) {
1052         case FMODE_READ:
1053         /*
1054          *  O_RDONLY
1055          *  POSIX.1 says that O_NONBLOCK means return with the FIFO
1056          *  opened, even when there is no process writing the FIFO.
1057          */
1058                 pipe->r_counter++;
1059                 if (pipe->readers++ == 0)
1060                         wake_up_partner(pipe);
1061 
1062                 if (!is_pipe && !pipe->writers) {
1063                         if ((filp->f_flags & O_NONBLOCK)) {
1064                                 /* suppress EPOLLHUP until we have
1065                                  * seen a writer */
1066                                 filp->f_version = pipe->w_counter;
1067                         } else {
1068                                 if (wait_for_partner(pipe, &pipe->w_counter))
1069                                         goto err_rd;
1070                         }
1071                 }
1072                 break;
1073 
1074         case FMODE_WRITE:
1075         /*
1076          *  O_WRONLY
1077          *  POSIX.1 says that O_NONBLOCK means return -1 with
1078          *  errno=ENXIO when there is no process reading the FIFO.
1079          */
1080                 ret = -ENXIO;
1081                 if (!is_pipe && (filp->f_flags & O_NONBLOCK) && !pipe->readers)
1082                         goto err;
1083 
1084                 pipe->w_counter++;
1085                 if (!pipe->writers++)
1086                         wake_up_partner(pipe);
1087 
1088                 if (!is_pipe && !pipe->readers) {
1089                         if (wait_for_partner(pipe, &pipe->r_counter))
1090                                 goto err_wr;
1091                 }
1092                 break;
1093 
1094         case FMODE_READ | FMODE_WRITE:
1095         /*
1096          *  O_RDWR
1097          *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
1098          *  This implementation will NEVER block on a O_RDWR open, since
1099          *  the process can at least talk to itself.
1100          */
1101 
1102                 pipe->readers++;
1103                 pipe->writers++;
1104                 pipe->r_counter++;
1105                 pipe->w_counter++;
1106                 if (pipe->readers == 1 || pipe->writers == 1)
1107                         wake_up_partner(pipe);
1108                 break;
1109 
1110         default:
1111                 ret = -EINVAL;
1112                 goto err;
1113         }
1114 
1115         /* Ok! */
1116         __pipe_unlock(pipe);
1117         return 0;
1118 
1119 err_rd:
1120         if (!--pipe->readers)
1121                 wake_up_interruptible(&pipe->wait);
1122         ret = -ERESTARTSYS;
1123         goto err;
1124 
1125 err_wr:
1126         if (!--pipe->writers)
1127                 wake_up_interruptible(&pipe->wait);
1128         ret = -ERESTARTSYS;
1129         goto err;
1130 
1131 err:
1132         __pipe_unlock(pipe);
1133 
1134         put_pipe_info(inode, pipe);
1135         return ret;
1136 }
1137 
1138 const struct file_operations pipefifo_fops = {
1139         .open           = fifo_open,
1140         .llseek         = no_llseek,
1141         .read_iter      = pipe_read,
1142         .write_iter     = pipe_write,
1143         .poll           = pipe_poll,
1144         .unlocked_ioctl = pipe_ioctl,
1145         .release        = pipe_release,
1146         .fasync         = pipe_fasync,
1147 };
1148 
1149 /*
1150  * Currently we rely on the pipe array holding a power-of-2 number
1151  * of pages. Returns 0 on error.
1152  */
1153 unsigned int round_pipe_size(unsigned long size)
1154 {
1155         if (size > (1U << 31))
1156                 return 0;
1157 
1158         /* Minimum pipe size, as required by POSIX */
1159         if (size < PAGE_SIZE)
1160                 return PAGE_SIZE;
1161 
1162         return roundup_pow_of_two(size);
1163 }
1164 
1165 /*
1166  * Allocate a new array of pipe buffers and copy the info over. Returns the
1167  * pipe size if successful, or return -ERROR on error.
1168  */
1169 static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
1170 {
1171         struct pipe_buffer *bufs;
1172         unsigned int size, nr_slots, head, tail, mask, n;
1173         unsigned long user_bufs;
1174         long ret = 0;
1175 
1176         size = round_pipe_size(arg);
1177         nr_slots = size >> PAGE_SHIFT;
1178 
1179         if (!nr_slots)
1180                 return -EINVAL;
1181 
1182         /*
1183          * If trying to increase the pipe capacity, check that an
1184          * unprivileged user is not trying to exceed various limits
1185          * (soft limit check here, hard limit check just below).
1186          * Decreasing the pipe capacity is always permitted, even
1187          * if the user is currently over a limit.
1188          */
1189         if (nr_slots > pipe->ring_size &&
1190                         size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
1191                 return -EPERM;
1192 
1193         user_bufs = account_pipe_buffers(pipe->user, pipe->ring_size, nr_slots);
1194 
1195         if (nr_slots > pipe->ring_size &&
1196                         (too_many_pipe_buffers_hard(user_bufs) ||
1197                          too_many_pipe_buffers_soft(user_bufs)) &&
1198                         is_unprivileged_user()) {
1199                 ret = -EPERM;
1200                 goto out_revert_acct;
1201         }
1202 
1203         /*
1204          * We can shrink the pipe, if arg is greater than the ring occupancy.
1205          * Since we don't expect a lot of shrink+grow operations, just free and
1206          * allocate again like we would do for growing.  If the pipe currently
1207          * contains more buffers than arg, then return busy.
1208          */
1209         mask = pipe->ring_size - 1;
1210         head = pipe->head;
1211         tail = pipe->tail;
1212         n = pipe_occupancy(pipe->head, pipe->tail);
1213         if (nr_slots < n) {
1214                 ret = -EBUSY;
1215                 goto out_revert_acct;
1216         }
1217 
1218         bufs = kcalloc(nr_slots, sizeof(*bufs),
1219                        GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
1220         if (unlikely(!bufs)) {
1221                 ret = -ENOMEM;
1222                 goto out_revert_acct;
1223         }
1224 
1225         /*
1226          * The pipe array wraps around, so just start the new one at zero
1227          * and adjust the indices.
1228          */
1229         if (n > 0) {
1230                 unsigned int h = head & mask;
1231                 unsigned int t = tail & mask;
1232                 if (h > t) {
1233                         memcpy(bufs, pipe->bufs + t,
1234                                n * sizeof(struct pipe_buffer));
1235                 } else {
1236                         unsigned int tsize = pipe->ring_size - t;
1237                         if (h > 0)
1238                                 memcpy(bufs + tsize, pipe->bufs,
1239                                        h * sizeof(struct pipe_buffer));
1240                         memcpy(bufs, pipe->bufs + t,
1241                                tsize * sizeof(struct pipe_buffer));
1242                 }
1243         }
1244 
1245         head = n;
1246         tail = 0;
1247 
1248         kfree(pipe->bufs);
1249         pipe->bufs = bufs;
1250         pipe->ring_size = nr_slots;
1251         pipe->max_usage = nr_slots;
1252         pipe->tail = tail;
1253         pipe->head = head;
1254         wake_up_interruptible_all(&pipe->wait);
1255         return pipe->max_usage * PAGE_SIZE;
1256 
1257 out_revert_acct:
1258         (void) account_pipe_buffers(pipe->user, nr_slots, pipe->ring_size);
1259         return ret;
1260 }
1261 
1262 /*
1263  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1264  * location, so checking ->i_pipe is not enough to verify that this is a
1265  * pipe.
1266  */
1267 struct pipe_inode_info *get_pipe_info(struct file *file)
1268 {
1269         return file->f_op == &pipefifo_fops ? file->private_data : NULL;
1270 }
1271 
1272 long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
1273 {
1274         struct pipe_inode_info *pipe;
1275         long ret;
1276 
1277         pipe = get_pipe_info(file);
1278         if (!pipe)
1279                 return -EBADF;
1280 
1281         __pipe_lock(pipe);
1282 
1283         switch (cmd) {
1284         case F_SETPIPE_SZ:
1285                 ret = pipe_set_size(pipe, arg);
1286                 break;
1287         case F_GETPIPE_SZ:
1288                 ret = pipe->max_usage * PAGE_SIZE;
1289                 break;
1290         default:
1291                 ret = -EINVAL;
1292                 break;
1293         }
1294 
1295         __pipe_unlock(pipe);
1296         return ret;
1297 }
1298 
1299 static const struct super_operations pipefs_ops = {
1300         .destroy_inode = free_inode_nonrcu,
1301         .statfs = simple_statfs,
1302 };
1303 
1304 /*
1305  * pipefs should _never_ be mounted by userland - too much of security hassle,
1306  * no real gain from having the whole whorehouse mounted. So we don't need
1307  * any operations on the root directory. However, we need a non-trivial
1308  * d_name - pipe: will go nicely and kill the special-casing in procfs.
1309  */
1310 
1311 static int pipefs_init_fs_context(struct fs_context *fc)
1312 {
1313         struct pseudo_fs_context *ctx = init_pseudo(fc, PIPEFS_MAGIC);
1314         if (!ctx)
1315                 return -ENOMEM;
1316         ctx->ops = &pipefs_ops;
1317         ctx->dops = &pipefs_dentry_operations;
1318         return 0;
1319 }
1320 
1321 static struct file_system_type pipe_fs_type = {
1322         .name           = "pipefs",
1323         .init_fs_context = pipefs_init_fs_context,
1324         .kill_sb        = kill_anon_super,
1325 };
1326 
1327 static int __init init_pipe_fs(void)
1328 {
1329         int err = register_filesystem(&pipe_fs_type);
1330 
1331         if (!err) {
1332                 pipe_mnt = kern_mount(&pipe_fs_type);
1333                 if (IS_ERR(pipe_mnt)) {
1334                         err = PTR_ERR(pipe_mnt);
1335                         unregister_filesystem(&pipe_fs_type);
1336                 }
1337         }
1338         return err;
1339 }
1340 
1341 fs_initcall(init_pipe_fs);
1342 

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