xref: /openbmc/linux/fs/pipe.c (revision 8dd99871)
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/magic.h>
18 #include <linux/pipe_fs_i.h>
19 #include <linux/uio.h>
20 #include <linux/highmem.h>
21 #include <linux/pagemap.h>
22 #include <linux/audit.h>
23 #include <linux/syscalls.h>
24 #include <linux/fcntl.h>
25 #include <linux/memcontrol.h>
26 
27 #include <linux/uaccess.h>
28 #include <asm/ioctls.h>
29 
30 #include "internal.h"
31 
32 /*
33  * The max size that a non-root user is allowed to grow the pipe. Can
34  * be set by root in /proc/sys/fs/pipe-max-size
35  */
36 unsigned int pipe_max_size = 1048576;
37 
38 /* Maximum allocatable pages per user. Hard limit is unset by default, soft
39  * matches default values.
40  */
41 unsigned long pipe_user_pages_hard;
42 unsigned long pipe_user_pages_soft = PIPE_DEF_BUFFERS * INR_OPEN_CUR;
43 
44 /*
45  * We use a start+len construction, which provides full use of the
46  * allocated memory.
47  * -- Florian Coosmann (FGC)
48  *
49  * Reads with count = 0 should always return 0.
50  * -- Julian Bradfield 1999-06-07.
51  *
52  * FIFOs and Pipes now generate SIGIO for both readers and writers.
53  * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
54  *
55  * pipe_read & write cleanup
56  * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
57  */
58 
59 static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
60 {
61 	if (pipe->files)
62 		mutex_lock_nested(&pipe->mutex, subclass);
63 }
64 
65 void pipe_lock(struct pipe_inode_info *pipe)
66 {
67 	/*
68 	 * pipe_lock() nests non-pipe inode locks (for writing to a file)
69 	 */
70 	pipe_lock_nested(pipe, I_MUTEX_PARENT);
71 }
72 EXPORT_SYMBOL(pipe_lock);
73 
74 void pipe_unlock(struct pipe_inode_info *pipe)
75 {
76 	if (pipe->files)
77 		mutex_unlock(&pipe->mutex);
78 }
79 EXPORT_SYMBOL(pipe_unlock);
80 
81 static inline void __pipe_lock(struct pipe_inode_info *pipe)
82 {
83 	mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
84 }
85 
86 static inline void __pipe_unlock(struct pipe_inode_info *pipe)
87 {
88 	mutex_unlock(&pipe->mutex);
89 }
90 
91 void pipe_double_lock(struct pipe_inode_info *pipe1,
92 		      struct pipe_inode_info *pipe2)
93 {
94 	BUG_ON(pipe1 == pipe2);
95 
96 	if (pipe1 < pipe2) {
97 		pipe_lock_nested(pipe1, I_MUTEX_PARENT);
98 		pipe_lock_nested(pipe2, I_MUTEX_CHILD);
99 	} else {
100 		pipe_lock_nested(pipe2, I_MUTEX_PARENT);
101 		pipe_lock_nested(pipe1, I_MUTEX_CHILD);
102 	}
103 }
104 
105 /* Drop the inode semaphore and wait for a pipe event, atomically */
106 void pipe_wait(struct pipe_inode_info *pipe)
107 {
108 	DEFINE_WAIT(wait);
109 
110 	/*
111 	 * Pipes are system-local resources, so sleeping on them
112 	 * is considered a noninteractive wait:
113 	 */
114 	prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
115 	pipe_unlock(pipe);
116 	schedule();
117 	finish_wait(&pipe->wait, &wait);
118 	pipe_lock(pipe);
119 }
120 
121 static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
122 				  struct pipe_buffer *buf)
123 {
124 	struct page *page = buf->page;
125 
126 	/*
127 	 * If nobody else uses this page, and we don't already have a
128 	 * temporary page, let's keep track of it as a one-deep
129 	 * allocation cache. (Otherwise just release our reference to it)
130 	 */
131 	if (page_count(page) == 1 && !pipe->tmp_page)
132 		pipe->tmp_page = page;
133 	else
134 		put_page(page);
135 }
136 
137 static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
138 			       struct pipe_buffer *buf)
139 {
140 	struct page *page = buf->page;
141 
142 	if (page_count(page) == 1) {
143 		if (memcg_kmem_enabled())
144 			memcg_kmem_uncharge(page, 0);
145 		__SetPageLocked(page);
146 		return 0;
147 	}
148 	return 1;
149 }
150 
151 /**
152  * generic_pipe_buf_steal - attempt to take ownership of a &pipe_buffer
153  * @pipe:	the pipe that the buffer belongs to
154  * @buf:	the buffer to attempt to steal
155  *
156  * Description:
157  *	This function attempts to steal the &struct page attached to
158  *	@buf. If successful, this function returns 0 and returns with
159  *	the page locked. The caller may then reuse the page for whatever
160  *	he wishes; the typical use is insertion into a different file
161  *	page cache.
162  */
163 int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
164 			   struct pipe_buffer *buf)
165 {
166 	struct page *page = buf->page;
167 
168 	/*
169 	 * A reference of one is golden, that means that the owner of this
170 	 * page is the only one holding a reference to it. lock the page
171 	 * and return OK.
172 	 */
173 	if (page_count(page) == 1) {
174 		lock_page(page);
175 		return 0;
176 	}
177 
178 	return 1;
179 }
180 EXPORT_SYMBOL(generic_pipe_buf_steal);
181 
182 /**
183  * generic_pipe_buf_get - get a reference to a &struct pipe_buffer
184  * @pipe:	the pipe that the buffer belongs to
185  * @buf:	the buffer to get a reference to
186  *
187  * Description:
188  *	This function grabs an extra reference to @buf. It's used in
189  *	in the tee() system call, when we duplicate the buffers in one
190  *	pipe into another.
191  */
192 void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
193 {
194 	get_page(buf->page);
195 }
196 EXPORT_SYMBOL(generic_pipe_buf_get);
197 
198 /**
199  * generic_pipe_buf_confirm - verify contents of the pipe buffer
200  * @info:	the pipe that the buffer belongs to
201  * @buf:	the buffer to confirm
202  *
203  * Description:
204  *	This function does nothing, because the generic pipe code uses
205  *	pages that are always good when inserted into the pipe.
206  */
207 int generic_pipe_buf_confirm(struct pipe_inode_info *info,
208 			     struct pipe_buffer *buf)
209 {
210 	return 0;
211 }
212 EXPORT_SYMBOL(generic_pipe_buf_confirm);
213 
214 /**
215  * generic_pipe_buf_release - put a reference to a &struct pipe_buffer
216  * @pipe:	the pipe that the buffer belongs to
217  * @buf:	the buffer to put a reference to
218  *
219  * Description:
220  *	This function releases a reference to @buf.
221  */
222 void generic_pipe_buf_release(struct pipe_inode_info *pipe,
223 			      struct pipe_buffer *buf)
224 {
225 	put_page(buf->page);
226 }
227 EXPORT_SYMBOL(generic_pipe_buf_release);
228 
229 static const struct pipe_buf_operations anon_pipe_buf_ops = {
230 	.can_merge = 1,
231 	.confirm = generic_pipe_buf_confirm,
232 	.release = anon_pipe_buf_release,
233 	.steal = anon_pipe_buf_steal,
234 	.get = generic_pipe_buf_get,
235 };
236 
237 static const struct pipe_buf_operations packet_pipe_buf_ops = {
238 	.can_merge = 0,
239 	.confirm = generic_pipe_buf_confirm,
240 	.release = anon_pipe_buf_release,
241 	.steal = anon_pipe_buf_steal,
242 	.get = generic_pipe_buf_get,
243 };
244 
245 static ssize_t
246 pipe_read(struct kiocb *iocb, struct iov_iter *to)
247 {
248 	size_t total_len = iov_iter_count(to);
249 	struct file *filp = iocb->ki_filp;
250 	struct pipe_inode_info *pipe = filp->private_data;
251 	int do_wakeup;
252 	ssize_t ret;
253 
254 	/* Null read succeeds. */
255 	if (unlikely(total_len == 0))
256 		return 0;
257 
258 	do_wakeup = 0;
259 	ret = 0;
260 	__pipe_lock(pipe);
261 	for (;;) {
262 		int bufs = pipe->nrbufs;
263 		if (bufs) {
264 			int curbuf = pipe->curbuf;
265 			struct pipe_buffer *buf = pipe->bufs + curbuf;
266 			size_t chars = buf->len;
267 			size_t written;
268 			int error;
269 
270 			if (chars > total_len)
271 				chars = total_len;
272 
273 			error = pipe_buf_confirm(pipe, buf);
274 			if (error) {
275 				if (!ret)
276 					ret = error;
277 				break;
278 			}
279 
280 			written = copy_page_to_iter(buf->page, buf->offset, chars, to);
281 			if (unlikely(written < chars)) {
282 				if (!ret)
283 					ret = -EFAULT;
284 				break;
285 			}
286 			ret += chars;
287 			buf->offset += chars;
288 			buf->len -= chars;
289 
290 			/* Was it a packet buffer? Clean up and exit */
291 			if (buf->flags & PIPE_BUF_FLAG_PACKET) {
292 				total_len = chars;
293 				buf->len = 0;
294 			}
295 
296 			if (!buf->len) {
297 				pipe_buf_release(pipe, buf);
298 				curbuf = (curbuf + 1) & (pipe->buffers - 1);
299 				pipe->curbuf = curbuf;
300 				pipe->nrbufs = --bufs;
301 				do_wakeup = 1;
302 			}
303 			total_len -= chars;
304 			if (!total_len)
305 				break;	/* common path: read succeeded */
306 		}
307 		if (bufs)	/* More to do? */
308 			continue;
309 		if (!pipe->writers)
310 			break;
311 		if (!pipe->waiting_writers) {
312 			/* syscall merging: Usually we must not sleep
313 			 * if O_NONBLOCK is set, or if we got some data.
314 			 * But if a writer sleeps in kernel space, then
315 			 * we can wait for that data without violating POSIX.
316 			 */
317 			if (ret)
318 				break;
319 			if (filp->f_flags & O_NONBLOCK) {
320 				ret = -EAGAIN;
321 				break;
322 			}
323 		}
324 		if (signal_pending(current)) {
325 			if (!ret)
326 				ret = -ERESTARTSYS;
327 			break;
328 		}
329 		if (do_wakeup) {
330 			wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM);
331  			kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
332 		}
333 		pipe_wait(pipe);
334 	}
335 	__pipe_unlock(pipe);
336 
337 	/* Signal writers asynchronously that there is more room. */
338 	if (do_wakeup) {
339 		wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM);
340 		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
341 	}
342 	if (ret > 0)
343 		file_accessed(filp);
344 	return ret;
345 }
346 
347 static inline int is_packetized(struct file *file)
348 {
349 	return (file->f_flags & O_DIRECT) != 0;
350 }
351 
352 static ssize_t
353 pipe_write(struct kiocb *iocb, struct iov_iter *from)
354 {
355 	struct file *filp = iocb->ki_filp;
356 	struct pipe_inode_info *pipe = filp->private_data;
357 	ssize_t ret = 0;
358 	int do_wakeup = 0;
359 	size_t total_len = iov_iter_count(from);
360 	ssize_t chars;
361 
362 	/* Null write succeeds. */
363 	if (unlikely(total_len == 0))
364 		return 0;
365 
366 	__pipe_lock(pipe);
367 
368 	if (!pipe->readers) {
369 		send_sig(SIGPIPE, current, 0);
370 		ret = -EPIPE;
371 		goto out;
372 	}
373 
374 	/* We try to merge small writes */
375 	chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
376 	if (pipe->nrbufs && chars != 0) {
377 		int lastbuf = (pipe->curbuf + pipe->nrbufs - 1) &
378 							(pipe->buffers - 1);
379 		struct pipe_buffer *buf = pipe->bufs + lastbuf;
380 		int offset = buf->offset + buf->len;
381 
382 		if (buf->ops->can_merge && offset + chars <= PAGE_SIZE) {
383 			ret = pipe_buf_confirm(pipe, buf);
384 			if (ret)
385 				goto out;
386 
387 			ret = copy_page_from_iter(buf->page, offset, chars, from);
388 			if (unlikely(ret < chars)) {
389 				ret = -EFAULT;
390 				goto out;
391 			}
392 			do_wakeup = 1;
393 			buf->len += ret;
394 			if (!iov_iter_count(from))
395 				goto out;
396 		}
397 	}
398 
399 	for (;;) {
400 		int bufs;
401 
402 		if (!pipe->readers) {
403 			send_sig(SIGPIPE, current, 0);
404 			if (!ret)
405 				ret = -EPIPE;
406 			break;
407 		}
408 		bufs = pipe->nrbufs;
409 		if (bufs < pipe->buffers) {
410 			int newbuf = (pipe->curbuf + bufs) & (pipe->buffers-1);
411 			struct pipe_buffer *buf = pipe->bufs + newbuf;
412 			struct page *page = pipe->tmp_page;
413 			int copied;
414 
415 			if (!page) {
416 				page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);
417 				if (unlikely(!page)) {
418 					ret = ret ? : -ENOMEM;
419 					break;
420 				}
421 				pipe->tmp_page = page;
422 			}
423 			/* Always wake up, even if the copy fails. Otherwise
424 			 * we lock up (O_NONBLOCK-)readers that sleep due to
425 			 * syscall merging.
426 			 * FIXME! Is this really true?
427 			 */
428 			do_wakeup = 1;
429 			copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);
430 			if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {
431 				if (!ret)
432 					ret = -EFAULT;
433 				break;
434 			}
435 			ret += copied;
436 
437 			/* Insert it into the buffer array */
438 			buf->page = page;
439 			buf->ops = &anon_pipe_buf_ops;
440 			buf->offset = 0;
441 			buf->len = copied;
442 			buf->flags = 0;
443 			if (is_packetized(filp)) {
444 				buf->ops = &packet_pipe_buf_ops;
445 				buf->flags = PIPE_BUF_FLAG_PACKET;
446 			}
447 			pipe->nrbufs = ++bufs;
448 			pipe->tmp_page = NULL;
449 
450 			if (!iov_iter_count(from))
451 				break;
452 		}
453 		if (bufs < pipe->buffers)
454 			continue;
455 		if (filp->f_flags & O_NONBLOCK) {
456 			if (!ret)
457 				ret = -EAGAIN;
458 			break;
459 		}
460 		if (signal_pending(current)) {
461 			if (!ret)
462 				ret = -ERESTARTSYS;
463 			break;
464 		}
465 		if (do_wakeup) {
466 			wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLRDNORM);
467 			kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
468 			do_wakeup = 0;
469 		}
470 		pipe->waiting_writers++;
471 		pipe_wait(pipe);
472 		pipe->waiting_writers--;
473 	}
474 out:
475 	__pipe_unlock(pipe);
476 	if (do_wakeup) {
477 		wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLRDNORM);
478 		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
479 	}
480 	if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {
481 		int err = file_update_time(filp);
482 		if (err)
483 			ret = err;
484 		sb_end_write(file_inode(filp)->i_sb);
485 	}
486 	return ret;
487 }
488 
489 static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
490 {
491 	struct pipe_inode_info *pipe = filp->private_data;
492 	int count, buf, nrbufs;
493 
494 	switch (cmd) {
495 		case FIONREAD:
496 			__pipe_lock(pipe);
497 			count = 0;
498 			buf = pipe->curbuf;
499 			nrbufs = pipe->nrbufs;
500 			while (--nrbufs >= 0) {
501 				count += pipe->bufs[buf].len;
502 				buf = (buf+1) & (pipe->buffers - 1);
503 			}
504 			__pipe_unlock(pipe);
505 
506 			return put_user(count, (int __user *)arg);
507 		default:
508 			return -ENOIOCTLCMD;
509 	}
510 }
511 
512 /* No kernel lock held - fine */
513 static __poll_t
514 pipe_poll(struct file *filp, poll_table *wait)
515 {
516 	__poll_t mask;
517 	struct pipe_inode_info *pipe = filp->private_data;
518 	int nrbufs;
519 
520 	poll_wait(filp, &pipe->wait, wait);
521 
522 	/* Reading only -- no need for acquiring the semaphore.  */
523 	nrbufs = pipe->nrbufs;
524 	mask = 0;
525 	if (filp->f_mode & FMODE_READ) {
526 		mask = (nrbufs > 0) ? EPOLLIN | EPOLLRDNORM : 0;
527 		if (!pipe->writers && filp->f_version != pipe->w_counter)
528 			mask |= EPOLLHUP;
529 	}
530 
531 	if (filp->f_mode & FMODE_WRITE) {
532 		mask |= (nrbufs < pipe->buffers) ? EPOLLOUT | EPOLLWRNORM : 0;
533 		/*
534 		 * Most Unices do not set EPOLLERR for FIFOs but on Linux they
535 		 * behave exactly like pipes for poll().
536 		 */
537 		if (!pipe->readers)
538 			mask |= EPOLLERR;
539 	}
540 
541 	return mask;
542 }
543 
544 static void put_pipe_info(struct inode *inode, struct pipe_inode_info *pipe)
545 {
546 	int kill = 0;
547 
548 	spin_lock(&inode->i_lock);
549 	if (!--pipe->files) {
550 		inode->i_pipe = NULL;
551 		kill = 1;
552 	}
553 	spin_unlock(&inode->i_lock);
554 
555 	if (kill)
556 		free_pipe_info(pipe);
557 }
558 
559 static int
560 pipe_release(struct inode *inode, struct file *file)
561 {
562 	struct pipe_inode_info *pipe = file->private_data;
563 
564 	__pipe_lock(pipe);
565 	if (file->f_mode & FMODE_READ)
566 		pipe->readers--;
567 	if (file->f_mode & FMODE_WRITE)
568 		pipe->writers--;
569 
570 	if (pipe->readers || pipe->writers) {
571 		wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLOUT | EPOLLRDNORM | EPOLLWRNORM | EPOLLERR | EPOLLHUP);
572 		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
573 		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
574 	}
575 	__pipe_unlock(pipe);
576 
577 	put_pipe_info(inode, pipe);
578 	return 0;
579 }
580 
581 static int
582 pipe_fasync(int fd, struct file *filp, int on)
583 {
584 	struct pipe_inode_info *pipe = filp->private_data;
585 	int retval = 0;
586 
587 	__pipe_lock(pipe);
588 	if (filp->f_mode & FMODE_READ)
589 		retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
590 	if ((filp->f_mode & FMODE_WRITE) && retval >= 0) {
591 		retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
592 		if (retval < 0 && (filp->f_mode & FMODE_READ))
593 			/* this can happen only if on == T */
594 			fasync_helper(-1, filp, 0, &pipe->fasync_readers);
595 	}
596 	__pipe_unlock(pipe);
597 	return retval;
598 }
599 
600 static unsigned long account_pipe_buffers(struct user_struct *user,
601                                  unsigned long old, unsigned long new)
602 {
603 	return atomic_long_add_return(new - old, &user->pipe_bufs);
604 }
605 
606 static bool too_many_pipe_buffers_soft(unsigned long user_bufs)
607 {
608 	unsigned long soft_limit = READ_ONCE(pipe_user_pages_soft);
609 
610 	return soft_limit && user_bufs > soft_limit;
611 }
612 
613 static bool too_many_pipe_buffers_hard(unsigned long user_bufs)
614 {
615 	unsigned long hard_limit = READ_ONCE(pipe_user_pages_hard);
616 
617 	return hard_limit && user_bufs > hard_limit;
618 }
619 
620 static bool is_unprivileged_user(void)
621 {
622 	return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
623 }
624 
625 struct pipe_inode_info *alloc_pipe_info(void)
626 {
627 	struct pipe_inode_info *pipe;
628 	unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
629 	struct user_struct *user = get_current_user();
630 	unsigned long user_bufs;
631 	unsigned int max_size = READ_ONCE(pipe_max_size);
632 
633 	pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL_ACCOUNT);
634 	if (pipe == NULL)
635 		goto out_free_uid;
636 
637 	if (pipe_bufs * PAGE_SIZE > max_size && !capable(CAP_SYS_RESOURCE))
638 		pipe_bufs = max_size >> PAGE_SHIFT;
639 
640 	user_bufs = account_pipe_buffers(user, 0, pipe_bufs);
641 
642 	if (too_many_pipe_buffers_soft(user_bufs) && is_unprivileged_user()) {
643 		user_bufs = account_pipe_buffers(user, pipe_bufs, 1);
644 		pipe_bufs = 1;
645 	}
646 
647 	if (too_many_pipe_buffers_hard(user_bufs) && is_unprivileged_user())
648 		goto out_revert_acct;
649 
650 	pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
651 			     GFP_KERNEL_ACCOUNT);
652 
653 	if (pipe->bufs) {
654 		init_waitqueue_head(&pipe->wait);
655 		pipe->r_counter = pipe->w_counter = 1;
656 		pipe->buffers = pipe_bufs;
657 		pipe->user = user;
658 		mutex_init(&pipe->mutex);
659 		return pipe;
660 	}
661 
662 out_revert_acct:
663 	(void) account_pipe_buffers(user, pipe_bufs, 0);
664 	kfree(pipe);
665 out_free_uid:
666 	free_uid(user);
667 	return NULL;
668 }
669 
670 void free_pipe_info(struct pipe_inode_info *pipe)
671 {
672 	int i;
673 
674 	(void) account_pipe_buffers(pipe->user, pipe->buffers, 0);
675 	free_uid(pipe->user);
676 	for (i = 0; i < pipe->buffers; i++) {
677 		struct pipe_buffer *buf = pipe->bufs + i;
678 		if (buf->ops)
679 			pipe_buf_release(pipe, buf);
680 	}
681 	if (pipe->tmp_page)
682 		__free_page(pipe->tmp_page);
683 	kfree(pipe->bufs);
684 	kfree(pipe);
685 }
686 
687 static struct vfsmount *pipe_mnt __read_mostly;
688 
689 /*
690  * pipefs_dname() is called from d_path().
691  */
692 static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
693 {
694 	return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
695 				d_inode(dentry)->i_ino);
696 }
697 
698 static const struct dentry_operations pipefs_dentry_operations = {
699 	.d_dname	= pipefs_dname,
700 };
701 
702 static struct inode * get_pipe_inode(void)
703 {
704 	struct inode *inode = new_inode_pseudo(pipe_mnt->mnt_sb);
705 	struct pipe_inode_info *pipe;
706 
707 	if (!inode)
708 		goto fail_inode;
709 
710 	inode->i_ino = get_next_ino();
711 
712 	pipe = alloc_pipe_info();
713 	if (!pipe)
714 		goto fail_iput;
715 
716 	inode->i_pipe = pipe;
717 	pipe->files = 2;
718 	pipe->readers = pipe->writers = 1;
719 	inode->i_fop = &pipefifo_fops;
720 
721 	/*
722 	 * Mark the inode dirty from the very beginning,
723 	 * that way it will never be moved to the dirty
724 	 * list because "mark_inode_dirty()" will think
725 	 * that it already _is_ on the dirty list.
726 	 */
727 	inode->i_state = I_DIRTY;
728 	inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
729 	inode->i_uid = current_fsuid();
730 	inode->i_gid = current_fsgid();
731 	inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
732 
733 	return inode;
734 
735 fail_iput:
736 	iput(inode);
737 
738 fail_inode:
739 	return NULL;
740 }
741 
742 int create_pipe_files(struct file **res, int flags)
743 {
744 	int err;
745 	struct inode *inode = get_pipe_inode();
746 	struct file *f;
747 	struct path path;
748 
749 	if (!inode)
750 		return -ENFILE;
751 
752 	err = -ENOMEM;
753 	path.dentry = d_alloc_pseudo(pipe_mnt->mnt_sb, &empty_name);
754 	if (!path.dentry)
755 		goto err_inode;
756 	path.mnt = mntget(pipe_mnt);
757 
758 	d_instantiate(path.dentry, inode);
759 
760 	f = alloc_file(&path, FMODE_WRITE, &pipefifo_fops);
761 	if (IS_ERR(f)) {
762 		err = PTR_ERR(f);
763 		goto err_dentry;
764 	}
765 
766 	f->f_flags = O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT));
767 	f->private_data = inode->i_pipe;
768 
769 	res[0] = alloc_file(&path, FMODE_READ, &pipefifo_fops);
770 	if (IS_ERR(res[0])) {
771 		err = PTR_ERR(res[0]);
772 		goto err_file;
773 	}
774 
775 	path_get(&path);
776 	res[0]->private_data = inode->i_pipe;
777 	res[0]->f_flags = O_RDONLY | (flags & O_NONBLOCK);
778 	res[1] = f;
779 	return 0;
780 
781 err_file:
782 	put_filp(f);
783 err_dentry:
784 	free_pipe_info(inode->i_pipe);
785 	path_put(&path);
786 	return err;
787 
788 err_inode:
789 	free_pipe_info(inode->i_pipe);
790 	iput(inode);
791 	return err;
792 }
793 
794 static int __do_pipe_flags(int *fd, struct file **files, int flags)
795 {
796 	int error;
797 	int fdw, fdr;
798 
799 	if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT))
800 		return -EINVAL;
801 
802 	error = create_pipe_files(files, flags);
803 	if (error)
804 		return error;
805 
806 	error = get_unused_fd_flags(flags);
807 	if (error < 0)
808 		goto err_read_pipe;
809 	fdr = error;
810 
811 	error = get_unused_fd_flags(flags);
812 	if (error < 0)
813 		goto err_fdr;
814 	fdw = error;
815 
816 	audit_fd_pair(fdr, fdw);
817 	fd[0] = fdr;
818 	fd[1] = fdw;
819 	return 0;
820 
821  err_fdr:
822 	put_unused_fd(fdr);
823  err_read_pipe:
824 	fput(files[0]);
825 	fput(files[1]);
826 	return error;
827 }
828 
829 int do_pipe_flags(int *fd, int flags)
830 {
831 	struct file *files[2];
832 	int error = __do_pipe_flags(fd, files, flags);
833 	if (!error) {
834 		fd_install(fd[0], files[0]);
835 		fd_install(fd[1], files[1]);
836 	}
837 	return error;
838 }
839 
840 /*
841  * sys_pipe() is the normal C calling standard for creating
842  * a pipe. It's not the way Unix traditionally does this, though.
843  */
844 static int do_pipe2(int __user *fildes, int flags)
845 {
846 	struct file *files[2];
847 	int fd[2];
848 	int error;
849 
850 	error = __do_pipe_flags(fd, files, flags);
851 	if (!error) {
852 		if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
853 			fput(files[0]);
854 			fput(files[1]);
855 			put_unused_fd(fd[0]);
856 			put_unused_fd(fd[1]);
857 			error = -EFAULT;
858 		} else {
859 			fd_install(fd[0], files[0]);
860 			fd_install(fd[1], files[1]);
861 		}
862 	}
863 	return error;
864 }
865 
866 SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)
867 {
868 	return do_pipe2(fildes, flags);
869 }
870 
871 SYSCALL_DEFINE1(pipe, int __user *, fildes)
872 {
873 	return do_pipe2(fildes, 0);
874 }
875 
876 static int wait_for_partner(struct pipe_inode_info *pipe, unsigned int *cnt)
877 {
878 	int cur = *cnt;
879 
880 	while (cur == *cnt) {
881 		pipe_wait(pipe);
882 		if (signal_pending(current))
883 			break;
884 	}
885 	return cur == *cnt ? -ERESTARTSYS : 0;
886 }
887 
888 static void wake_up_partner(struct pipe_inode_info *pipe)
889 {
890 	wake_up_interruptible(&pipe->wait);
891 }
892 
893 static int fifo_open(struct inode *inode, struct file *filp)
894 {
895 	struct pipe_inode_info *pipe;
896 	bool is_pipe = inode->i_sb->s_magic == PIPEFS_MAGIC;
897 	int ret;
898 
899 	filp->f_version = 0;
900 
901 	spin_lock(&inode->i_lock);
902 	if (inode->i_pipe) {
903 		pipe = inode->i_pipe;
904 		pipe->files++;
905 		spin_unlock(&inode->i_lock);
906 	} else {
907 		spin_unlock(&inode->i_lock);
908 		pipe = alloc_pipe_info();
909 		if (!pipe)
910 			return -ENOMEM;
911 		pipe->files = 1;
912 		spin_lock(&inode->i_lock);
913 		if (unlikely(inode->i_pipe)) {
914 			inode->i_pipe->files++;
915 			spin_unlock(&inode->i_lock);
916 			free_pipe_info(pipe);
917 			pipe = inode->i_pipe;
918 		} else {
919 			inode->i_pipe = pipe;
920 			spin_unlock(&inode->i_lock);
921 		}
922 	}
923 	filp->private_data = pipe;
924 	/* OK, we have a pipe and it's pinned down */
925 
926 	__pipe_lock(pipe);
927 
928 	/* We can only do regular read/write on fifos */
929 	filp->f_mode &= (FMODE_READ | FMODE_WRITE);
930 
931 	switch (filp->f_mode) {
932 	case FMODE_READ:
933 	/*
934 	 *  O_RDONLY
935 	 *  POSIX.1 says that O_NONBLOCK means return with the FIFO
936 	 *  opened, even when there is no process writing the FIFO.
937 	 */
938 		pipe->r_counter++;
939 		if (pipe->readers++ == 0)
940 			wake_up_partner(pipe);
941 
942 		if (!is_pipe && !pipe->writers) {
943 			if ((filp->f_flags & O_NONBLOCK)) {
944 				/* suppress EPOLLHUP until we have
945 				 * seen a writer */
946 				filp->f_version = pipe->w_counter;
947 			} else {
948 				if (wait_for_partner(pipe, &pipe->w_counter))
949 					goto err_rd;
950 			}
951 		}
952 		break;
953 
954 	case FMODE_WRITE:
955 	/*
956 	 *  O_WRONLY
957 	 *  POSIX.1 says that O_NONBLOCK means return -1 with
958 	 *  errno=ENXIO when there is no process reading the FIFO.
959 	 */
960 		ret = -ENXIO;
961 		if (!is_pipe && (filp->f_flags & O_NONBLOCK) && !pipe->readers)
962 			goto err;
963 
964 		pipe->w_counter++;
965 		if (!pipe->writers++)
966 			wake_up_partner(pipe);
967 
968 		if (!is_pipe && !pipe->readers) {
969 			if (wait_for_partner(pipe, &pipe->r_counter))
970 				goto err_wr;
971 		}
972 		break;
973 
974 	case FMODE_READ | FMODE_WRITE:
975 	/*
976 	 *  O_RDWR
977 	 *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
978 	 *  This implementation will NEVER block on a O_RDWR open, since
979 	 *  the process can at least talk to itself.
980 	 */
981 
982 		pipe->readers++;
983 		pipe->writers++;
984 		pipe->r_counter++;
985 		pipe->w_counter++;
986 		if (pipe->readers == 1 || pipe->writers == 1)
987 			wake_up_partner(pipe);
988 		break;
989 
990 	default:
991 		ret = -EINVAL;
992 		goto err;
993 	}
994 
995 	/* Ok! */
996 	__pipe_unlock(pipe);
997 	return 0;
998 
999 err_rd:
1000 	if (!--pipe->readers)
1001 		wake_up_interruptible(&pipe->wait);
1002 	ret = -ERESTARTSYS;
1003 	goto err;
1004 
1005 err_wr:
1006 	if (!--pipe->writers)
1007 		wake_up_interruptible(&pipe->wait);
1008 	ret = -ERESTARTSYS;
1009 	goto err;
1010 
1011 err:
1012 	__pipe_unlock(pipe);
1013 
1014 	put_pipe_info(inode, pipe);
1015 	return ret;
1016 }
1017 
1018 const struct file_operations pipefifo_fops = {
1019 	.open		= fifo_open,
1020 	.llseek		= no_llseek,
1021 	.read_iter	= pipe_read,
1022 	.write_iter	= pipe_write,
1023 	.poll		= pipe_poll,
1024 	.unlocked_ioctl	= pipe_ioctl,
1025 	.release	= pipe_release,
1026 	.fasync		= pipe_fasync,
1027 };
1028 
1029 /*
1030  * Currently we rely on the pipe array holding a power-of-2 number
1031  * of pages. Returns 0 on error.
1032  */
1033 unsigned int round_pipe_size(unsigned long size)
1034 {
1035 	if (size > (1U << 31))
1036 		return 0;
1037 
1038 	/* Minimum pipe size, as required by POSIX */
1039 	if (size < PAGE_SIZE)
1040 		return PAGE_SIZE;
1041 
1042 	return roundup_pow_of_two(size);
1043 }
1044 
1045 /*
1046  * Allocate a new array of pipe buffers and copy the info over. Returns the
1047  * pipe size if successful, or return -ERROR on error.
1048  */
1049 static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
1050 {
1051 	struct pipe_buffer *bufs;
1052 	unsigned int size, nr_pages;
1053 	unsigned long user_bufs;
1054 	long ret = 0;
1055 
1056 	size = round_pipe_size(arg);
1057 	nr_pages = size >> PAGE_SHIFT;
1058 
1059 	if (!nr_pages)
1060 		return -EINVAL;
1061 
1062 	/*
1063 	 * If trying to increase the pipe capacity, check that an
1064 	 * unprivileged user is not trying to exceed various limits
1065 	 * (soft limit check here, hard limit check just below).
1066 	 * Decreasing the pipe capacity is always permitted, even
1067 	 * if the user is currently over a limit.
1068 	 */
1069 	if (nr_pages > pipe->buffers &&
1070 			size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
1071 		return -EPERM;
1072 
1073 	user_bufs = account_pipe_buffers(pipe->user, pipe->buffers, nr_pages);
1074 
1075 	if (nr_pages > pipe->buffers &&
1076 			(too_many_pipe_buffers_hard(user_bufs) ||
1077 			 too_many_pipe_buffers_soft(user_bufs)) &&
1078 			is_unprivileged_user()) {
1079 		ret = -EPERM;
1080 		goto out_revert_acct;
1081 	}
1082 
1083 	/*
1084 	 * We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
1085 	 * expect a lot of shrink+grow operations, just free and allocate
1086 	 * again like we would do for growing. If the pipe currently
1087 	 * contains more buffers than arg, then return busy.
1088 	 */
1089 	if (nr_pages < pipe->nrbufs) {
1090 		ret = -EBUSY;
1091 		goto out_revert_acct;
1092 	}
1093 
1094 	bufs = kcalloc(nr_pages, sizeof(*bufs),
1095 		       GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
1096 	if (unlikely(!bufs)) {
1097 		ret = -ENOMEM;
1098 		goto out_revert_acct;
1099 	}
1100 
1101 	/*
1102 	 * The pipe array wraps around, so just start the new one at zero
1103 	 * and adjust the indexes.
1104 	 */
1105 	if (pipe->nrbufs) {
1106 		unsigned int tail;
1107 		unsigned int head;
1108 
1109 		tail = pipe->curbuf + pipe->nrbufs;
1110 		if (tail < pipe->buffers)
1111 			tail = 0;
1112 		else
1113 			tail &= (pipe->buffers - 1);
1114 
1115 		head = pipe->nrbufs - tail;
1116 		if (head)
1117 			memcpy(bufs, pipe->bufs + pipe->curbuf, head * sizeof(struct pipe_buffer));
1118 		if (tail)
1119 			memcpy(bufs + head, pipe->bufs, tail * sizeof(struct pipe_buffer));
1120 	}
1121 
1122 	pipe->curbuf = 0;
1123 	kfree(pipe->bufs);
1124 	pipe->bufs = bufs;
1125 	pipe->buffers = nr_pages;
1126 	return nr_pages * PAGE_SIZE;
1127 
1128 out_revert_acct:
1129 	(void) account_pipe_buffers(pipe->user, nr_pages, pipe->buffers);
1130 	return ret;
1131 }
1132 
1133 /*
1134  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1135  * location, so checking ->i_pipe is not enough to verify that this is a
1136  * pipe.
1137  */
1138 struct pipe_inode_info *get_pipe_info(struct file *file)
1139 {
1140 	return file->f_op == &pipefifo_fops ? file->private_data : NULL;
1141 }
1142 
1143 long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
1144 {
1145 	struct pipe_inode_info *pipe;
1146 	long ret;
1147 
1148 	pipe = get_pipe_info(file);
1149 	if (!pipe)
1150 		return -EBADF;
1151 
1152 	__pipe_lock(pipe);
1153 
1154 	switch (cmd) {
1155 	case F_SETPIPE_SZ:
1156 		ret = pipe_set_size(pipe, arg);
1157 		break;
1158 	case F_GETPIPE_SZ:
1159 		ret = pipe->buffers * PAGE_SIZE;
1160 		break;
1161 	default:
1162 		ret = -EINVAL;
1163 		break;
1164 	}
1165 
1166 	__pipe_unlock(pipe);
1167 	return ret;
1168 }
1169 
1170 static const struct super_operations pipefs_ops = {
1171 	.destroy_inode = free_inode_nonrcu,
1172 	.statfs = simple_statfs,
1173 };
1174 
1175 /*
1176  * pipefs should _never_ be mounted by userland - too much of security hassle,
1177  * no real gain from having the whole whorehouse mounted. So we don't need
1178  * any operations on the root directory. However, we need a non-trivial
1179  * d_name - pipe: will go nicely and kill the special-casing in procfs.
1180  */
1181 static struct dentry *pipefs_mount(struct file_system_type *fs_type,
1182 			 int flags, const char *dev_name, void *data)
1183 {
1184 	return mount_pseudo(fs_type, "pipe:", &pipefs_ops,
1185 			&pipefs_dentry_operations, PIPEFS_MAGIC);
1186 }
1187 
1188 static struct file_system_type pipe_fs_type = {
1189 	.name		= "pipefs",
1190 	.mount		= pipefs_mount,
1191 	.kill_sb	= kill_anon_super,
1192 };
1193 
1194 static int __init init_pipe_fs(void)
1195 {
1196 	int err = register_filesystem(&pipe_fs_type);
1197 
1198 	if (!err) {
1199 		pipe_mnt = kern_mount(&pipe_fs_type);
1200 		if (IS_ERR(pipe_mnt)) {
1201 			err = PTR_ERR(pipe_mnt);
1202 			unregister_filesystem(&pipe_fs_type);
1203 		}
1204 	}
1205 	return err;
1206 }
1207 
1208 fs_initcall(init_pipe_fs);
1209