linux-stable/fs/pipe.c
David Howells 2ed147f015 watch_queue: Fix lack of barrier/sync/lock between post and read
There's nothing to synchronise post_one_notification() versus
pipe_read().  Whilst posting is done under pipe->rd_wait.lock, the
reader only takes pipe->mutex which cannot bar notification posting as
that may need to be made from contexts that cannot sleep.

Fix this by setting pipe->head with a barrier in post_one_notification()
and reading pipe->head with a barrier in pipe_read().

If that's not sufficient, the rd_wait.lock will need to be taken,
possibly in a ->confirm() op so that it only applies to notifications.
The lock would, however, have to be dropped before copy_page_to_iter()
is invoked.

Fixes: c73be61ced ("pipe: Add general notification queue support")
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-03-11 10:17:13 -08:00

1506 lines
36 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* linux/fs/pipe.c
*
* Copyright (C) 1991, 1992, 1999 Linus Torvalds
*/
#include <linux/mm.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/log2.h>
#include <linux/mount.h>
#include <linux/pseudo_fs.h>
#include <linux/magic.h>
#include <linux/pipe_fs_i.h>
#include <linux/uio.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/audit.h>
#include <linux/syscalls.h>
#include <linux/fcntl.h>
#include <linux/memcontrol.h>
#include <linux/watch_queue.h>
#include <linux/sysctl.h>
#include <linux/uaccess.h>
#include <asm/ioctls.h>
#include "internal.h"
/*
* New pipe buffers will be restricted to this size while the user is exceeding
* their pipe buffer quota. The general pipe use case needs at least two
* buffers: one for data yet to be read, and one for new data. If this is less
* than two, then a write to a non-empty pipe may block even if the pipe is not
* full. This can occur with GNU make jobserver or similar uses of pipes as
* semaphores: multiple processes may be waiting to write tokens back to the
* pipe before reading tokens: https://lore.kernel.org/lkml/1628086770.5rn8p04n6j.none@localhost/.
*
* Users can reduce their pipe buffers with F_SETPIPE_SZ below this at their
* own risk, namely: pipe writes to non-full pipes may block until the pipe is
* emptied.
*/
#define PIPE_MIN_DEF_BUFFERS 2
/*
* The max size that a non-root user is allowed to grow the pipe. Can
* be set by root in /proc/sys/fs/pipe-max-size
*/
static unsigned int pipe_max_size = 1048576;
/* Maximum allocatable pages per user. Hard limit is unset by default, soft
* matches default values.
*/
static unsigned long pipe_user_pages_hard;
static unsigned long pipe_user_pages_soft = PIPE_DEF_BUFFERS * INR_OPEN_CUR;
/*
* We use head and tail indices that aren't masked off, except at the point of
* dereference, but rather they're allowed to wrap naturally. This means there
* isn't a dead spot in the buffer, but the ring has to be a power of two and
* <= 2^31.
* -- David Howells 2019-09-23.
*
* Reads with count = 0 should always return 0.
* -- Julian Bradfield 1999-06-07.
*
* FIFOs and Pipes now generate SIGIO for both readers and writers.
* -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
*
* pipe_read & write cleanup
* -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
*/
static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
{
if (pipe->files)
mutex_lock_nested(&pipe->mutex, subclass);
}
void pipe_lock(struct pipe_inode_info *pipe)
{
/*
* pipe_lock() nests non-pipe inode locks (for writing to a file)
*/
pipe_lock_nested(pipe, I_MUTEX_PARENT);
}
EXPORT_SYMBOL(pipe_lock);
void pipe_unlock(struct pipe_inode_info *pipe)
{
if (pipe->files)
mutex_unlock(&pipe->mutex);
}
EXPORT_SYMBOL(pipe_unlock);
static inline void __pipe_lock(struct pipe_inode_info *pipe)
{
mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
}
static inline void __pipe_unlock(struct pipe_inode_info *pipe)
{
mutex_unlock(&pipe->mutex);
}
void pipe_double_lock(struct pipe_inode_info *pipe1,
struct pipe_inode_info *pipe2)
{
BUG_ON(pipe1 == pipe2);
if (pipe1 < pipe2) {
pipe_lock_nested(pipe1, I_MUTEX_PARENT);
pipe_lock_nested(pipe2, I_MUTEX_CHILD);
} else {
pipe_lock_nested(pipe2, I_MUTEX_PARENT);
pipe_lock_nested(pipe1, I_MUTEX_CHILD);
}
}
static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
struct page *page = buf->page;
/*
* If nobody else uses this page, and we don't already have a
* temporary page, let's keep track of it as a one-deep
* allocation cache. (Otherwise just release our reference to it)
*/
if (page_count(page) == 1 && !pipe->tmp_page)
pipe->tmp_page = page;
else
put_page(page);
}
static bool anon_pipe_buf_try_steal(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
struct page *page = buf->page;
if (page_count(page) != 1)
return false;
memcg_kmem_uncharge_page(page, 0);
__SetPageLocked(page);
return true;
}
/**
* generic_pipe_buf_try_steal - attempt to take ownership of a &pipe_buffer
* @pipe: the pipe that the buffer belongs to
* @buf: the buffer to attempt to steal
*
* Description:
* This function attempts to steal the &struct page attached to
* @buf. If successful, this function returns 0 and returns with
* the page locked. The caller may then reuse the page for whatever
* he wishes; the typical use is insertion into a different file
* page cache.
*/
bool generic_pipe_buf_try_steal(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
struct page *page = buf->page;
/*
* A reference of one is golden, that means that the owner of this
* page is the only one holding a reference to it. lock the page
* and return OK.
*/
if (page_count(page) == 1) {
lock_page(page);
return true;
}
return false;
}
EXPORT_SYMBOL(generic_pipe_buf_try_steal);
/**
* generic_pipe_buf_get - get a reference to a &struct pipe_buffer
* @pipe: the pipe that the buffer belongs to
* @buf: the buffer to get a reference to
*
* Description:
* This function grabs an extra reference to @buf. It's used in
* the tee() system call, when we duplicate the buffers in one
* pipe into another.
*/
bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
{
return try_get_page(buf->page);
}
EXPORT_SYMBOL(generic_pipe_buf_get);
/**
* generic_pipe_buf_release - put a reference to a &struct pipe_buffer
* @pipe: the pipe that the buffer belongs to
* @buf: the buffer to put a reference to
*
* Description:
* This function releases a reference to @buf.
*/
void generic_pipe_buf_release(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
put_page(buf->page);
}
EXPORT_SYMBOL(generic_pipe_buf_release);
static const struct pipe_buf_operations anon_pipe_buf_ops = {
.release = anon_pipe_buf_release,
.try_steal = anon_pipe_buf_try_steal,
.get = generic_pipe_buf_get,
};
/* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
static inline bool pipe_readable(const struct pipe_inode_info *pipe)
{
unsigned int head = READ_ONCE(pipe->head);
unsigned int tail = READ_ONCE(pipe->tail);
unsigned int writers = READ_ONCE(pipe->writers);
return !pipe_empty(head, tail) || !writers;
}
static ssize_t
pipe_read(struct kiocb *iocb, struct iov_iter *to)
{
size_t total_len = iov_iter_count(to);
struct file *filp = iocb->ki_filp;
struct pipe_inode_info *pipe = filp->private_data;
bool was_full, wake_next_reader = false;
ssize_t ret;
/* Null read succeeds. */
if (unlikely(total_len == 0))
return 0;
ret = 0;
__pipe_lock(pipe);
/*
* We only wake up writers if the pipe was full when we started
* reading in order to avoid unnecessary wakeups.
*
* But when we do wake up writers, we do so using a sync wakeup
* (WF_SYNC), because we want them to get going and generate more
* data for us.
*/
was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
for (;;) {
/* Read ->head with a barrier vs post_one_notification() */
unsigned int head = smp_load_acquire(&pipe->head);
unsigned int tail = pipe->tail;
unsigned int mask = pipe->ring_size - 1;
#ifdef CONFIG_WATCH_QUEUE
if (pipe->note_loss) {
struct watch_notification n;
if (total_len < 8) {
if (ret == 0)
ret = -ENOBUFS;
break;
}
n.type = WATCH_TYPE_META;
n.subtype = WATCH_META_LOSS_NOTIFICATION;
n.info = watch_sizeof(n);
if (copy_to_iter(&n, sizeof(n), to) != sizeof(n)) {
if (ret == 0)
ret = -EFAULT;
break;
}
ret += sizeof(n);
total_len -= sizeof(n);
pipe->note_loss = false;
}
#endif
if (!pipe_empty(head, tail)) {
struct pipe_buffer *buf = &pipe->bufs[tail & mask];
size_t chars = buf->len;
size_t written;
int error;
if (chars > total_len) {
if (buf->flags & PIPE_BUF_FLAG_WHOLE) {
if (ret == 0)
ret = -ENOBUFS;
break;
}
chars = total_len;
}
error = pipe_buf_confirm(pipe, buf);
if (error) {
if (!ret)
ret = error;
break;
}
written = copy_page_to_iter(buf->page, buf->offset, chars, to);
if (unlikely(written < chars)) {
if (!ret)
ret = -EFAULT;
break;
}
ret += chars;
buf->offset += chars;
buf->len -= chars;
/* Was it a packet buffer? Clean up and exit */
if (buf->flags & PIPE_BUF_FLAG_PACKET) {
total_len = chars;
buf->len = 0;
}
if (!buf->len) {
pipe_buf_release(pipe, buf);
spin_lock_irq(&pipe->rd_wait.lock);
#ifdef CONFIG_WATCH_QUEUE
if (buf->flags & PIPE_BUF_FLAG_LOSS)
pipe->note_loss = true;
#endif
tail++;
pipe->tail = tail;
spin_unlock_irq(&pipe->rd_wait.lock);
}
total_len -= chars;
if (!total_len)
break; /* common path: read succeeded */
if (!pipe_empty(head, tail)) /* More to do? */
continue;
}
if (!pipe->writers)
break;
if (ret)
break;
if (filp->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
break;
}
__pipe_unlock(pipe);
/*
* We only get here if we didn't actually read anything.
*
* However, we could have seen (and removed) a zero-sized
* pipe buffer, and might have made space in the buffers
* that way.
*
* You can't make zero-sized pipe buffers by doing an empty
* write (not even in packet mode), but they can happen if
* the writer gets an EFAULT when trying to fill a buffer
* that already got allocated and inserted in the buffer
* array.
*
* So we still need to wake up any pending writers in the
* _very_ unlikely case that the pipe was full, but we got
* no data.
*/
if (unlikely(was_full))
wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
/*
* But because we didn't read anything, at this point we can
* just return directly with -ERESTARTSYS if we're interrupted,
* since we've done any required wakeups and there's no need
* to mark anything accessed. And we've dropped the lock.
*/
if (wait_event_interruptible_exclusive(pipe->rd_wait, pipe_readable(pipe)) < 0)
return -ERESTARTSYS;
__pipe_lock(pipe);
was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
wake_next_reader = true;
}
if (pipe_empty(pipe->head, pipe->tail))
wake_next_reader = false;
__pipe_unlock(pipe);
if (was_full)
wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
if (wake_next_reader)
wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
if (ret > 0)
file_accessed(filp);
return ret;
}
static inline int is_packetized(struct file *file)
{
return (file->f_flags & O_DIRECT) != 0;
}
/* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
static inline bool pipe_writable(const struct pipe_inode_info *pipe)
{
unsigned int head = READ_ONCE(pipe->head);
unsigned int tail = READ_ONCE(pipe->tail);
unsigned int max_usage = READ_ONCE(pipe->max_usage);
return !pipe_full(head, tail, max_usage) ||
!READ_ONCE(pipe->readers);
}
static ssize_t
pipe_write(struct kiocb *iocb, struct iov_iter *from)
{
struct file *filp = iocb->ki_filp;
struct pipe_inode_info *pipe = filp->private_data;
unsigned int head;
ssize_t ret = 0;
size_t total_len = iov_iter_count(from);
ssize_t chars;
bool was_empty = false;
bool wake_next_writer = false;
/* Null write succeeds. */
if (unlikely(total_len == 0))
return 0;
__pipe_lock(pipe);
if (!pipe->readers) {
send_sig(SIGPIPE, current, 0);
ret = -EPIPE;
goto out;
}
#ifdef CONFIG_WATCH_QUEUE
if (pipe->watch_queue) {
ret = -EXDEV;
goto out;
}
#endif
/*
* If it wasn't empty we try to merge new data into
* the last buffer.
*
* That naturally merges small writes, but it also
* page-aligns the rest of the writes for large writes
* spanning multiple pages.
*/
head = pipe->head;
was_empty = pipe_empty(head, pipe->tail);
chars = total_len & (PAGE_SIZE-1);
if (chars && !was_empty) {
unsigned int mask = pipe->ring_size - 1;
struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];
int offset = buf->offset + buf->len;
if ((buf->flags & PIPE_BUF_FLAG_CAN_MERGE) &&
offset + chars <= PAGE_SIZE) {
ret = pipe_buf_confirm(pipe, buf);
if (ret)
goto out;
ret = copy_page_from_iter(buf->page, offset, chars, from);
if (unlikely(ret < chars)) {
ret = -EFAULT;
goto out;
}
buf->len += ret;
if (!iov_iter_count(from))
goto out;
}
}
for (;;) {
if (!pipe->readers) {
send_sig(SIGPIPE, current, 0);
if (!ret)
ret = -EPIPE;
break;
}
head = pipe->head;
if (!pipe_full(head, pipe->tail, pipe->max_usage)) {
unsigned int mask = pipe->ring_size - 1;
struct pipe_buffer *buf = &pipe->bufs[head & mask];
struct page *page = pipe->tmp_page;
int copied;
if (!page) {
page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);
if (unlikely(!page)) {
ret = ret ? : -ENOMEM;
break;
}
pipe->tmp_page = page;
}
/* Allocate a slot in the ring in advance and attach an
* empty buffer. If we fault or otherwise fail to use
* it, either the reader will consume it or it'll still
* be there for the next write.
*/
spin_lock_irq(&pipe->rd_wait.lock);
head = pipe->head;
if (pipe_full(head, pipe->tail, pipe->max_usage)) {
spin_unlock_irq(&pipe->rd_wait.lock);
continue;
}
pipe->head = head + 1;
spin_unlock_irq(&pipe->rd_wait.lock);
/* Insert it into the buffer array */
buf = &pipe->bufs[head & mask];
buf->page = page;
buf->ops = &anon_pipe_buf_ops;
buf->offset = 0;
buf->len = 0;
if (is_packetized(filp))
buf->flags = PIPE_BUF_FLAG_PACKET;
else
buf->flags = PIPE_BUF_FLAG_CAN_MERGE;
pipe->tmp_page = NULL;
copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);
if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {
if (!ret)
ret = -EFAULT;
break;
}
ret += copied;
buf->offset = 0;
buf->len = copied;
if (!iov_iter_count(from))
break;
}
if (!pipe_full(head, pipe->tail, pipe->max_usage))
continue;
/* Wait for buffer space to become available. */
if (filp->f_flags & O_NONBLOCK) {
if (!ret)
ret = -EAGAIN;
break;
}
if (signal_pending(current)) {
if (!ret)
ret = -ERESTARTSYS;
break;
}
/*
* We're going to release the pipe lock and wait for more
* space. We wake up any readers if necessary, and then
* after waiting we need to re-check whether the pipe
* become empty while we dropped the lock.
*/
__pipe_unlock(pipe);
if (was_empty)
wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
wait_event_interruptible_exclusive(pipe->wr_wait, pipe_writable(pipe));
__pipe_lock(pipe);
was_empty = pipe_empty(pipe->head, pipe->tail);
wake_next_writer = true;
}
out:
if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
wake_next_writer = false;
__pipe_unlock(pipe);
/*
* If we do do a wakeup event, we do a 'sync' wakeup, because we
* want the reader to start processing things asap, rather than
* leave the data pending.
*
* This is particularly important for small writes, because of
* how (for example) the GNU make jobserver uses small writes to
* wake up pending jobs
*
* Epoll nonsensically wants a wakeup whether the pipe
* was already empty or not.
*/
if (was_empty || pipe->poll_usage)
wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
if (wake_next_writer)
wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {
int err = file_update_time(filp);
if (err)
ret = err;
sb_end_write(file_inode(filp)->i_sb);
}
return ret;
}
static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
struct pipe_inode_info *pipe = filp->private_data;
int count, head, tail, mask;
switch (cmd) {
case FIONREAD:
__pipe_lock(pipe);
count = 0;
head = pipe->head;
tail = pipe->tail;
mask = pipe->ring_size - 1;
while (tail != head) {
count += pipe->bufs[tail & mask].len;
tail++;
}
__pipe_unlock(pipe);
return put_user(count, (int __user *)arg);
#ifdef CONFIG_WATCH_QUEUE
case IOC_WATCH_QUEUE_SET_SIZE: {
int ret;
__pipe_lock(pipe);
ret = watch_queue_set_size(pipe, arg);
__pipe_unlock(pipe);
return ret;
}
case IOC_WATCH_QUEUE_SET_FILTER:
return watch_queue_set_filter(
pipe, (struct watch_notification_filter __user *)arg);
#endif
default:
return -ENOIOCTLCMD;
}
}
/* No kernel lock held - fine */
static __poll_t
pipe_poll(struct file *filp, poll_table *wait)
{
__poll_t mask;
struct pipe_inode_info *pipe = filp->private_data;
unsigned int head, tail;
/* Epoll has some historical nasty semantics, this enables them */
pipe->poll_usage = 1;
/*
* Reading pipe state only -- no need for acquiring the semaphore.
*
* But because this is racy, the code has to add the
* entry to the poll table _first_ ..
*/
if (filp->f_mode & FMODE_READ)
poll_wait(filp, &pipe->rd_wait, wait);
if (filp->f_mode & FMODE_WRITE)
poll_wait(filp, &pipe->wr_wait, wait);
/*
* .. and only then can you do the racy tests. That way,
* if something changes and you got it wrong, the poll
* table entry will wake you up and fix it.
*/
head = READ_ONCE(pipe->head);
tail = READ_ONCE(pipe->tail);
mask = 0;
if (filp->f_mode & FMODE_READ) {
if (!pipe_empty(head, tail))
mask |= EPOLLIN | EPOLLRDNORM;
if (!pipe->writers && filp->f_version != pipe->w_counter)
mask |= EPOLLHUP;
}
if (filp->f_mode & FMODE_WRITE) {
if (!pipe_full(head, tail, pipe->max_usage))
mask |= EPOLLOUT | EPOLLWRNORM;
/*
* Most Unices do not set EPOLLERR for FIFOs but on Linux they
* behave exactly like pipes for poll().
*/
if (!pipe->readers)
mask |= EPOLLERR;
}
return mask;
}
static void put_pipe_info(struct inode *inode, struct pipe_inode_info *pipe)
{
int kill = 0;
spin_lock(&inode->i_lock);
if (!--pipe->files) {
inode->i_pipe = NULL;
kill = 1;
}
spin_unlock(&inode->i_lock);
if (kill)
free_pipe_info(pipe);
}
static int
pipe_release(struct inode *inode, struct file *file)
{
struct pipe_inode_info *pipe = file->private_data;
__pipe_lock(pipe);
if (file->f_mode & FMODE_READ)
pipe->readers--;
if (file->f_mode & FMODE_WRITE)
pipe->writers--;
/* Was that the last reader or writer, but not the other side? */
if (!pipe->readers != !pipe->writers) {
wake_up_interruptible_all(&pipe->rd_wait);
wake_up_interruptible_all(&pipe->wr_wait);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
}
__pipe_unlock(pipe);
put_pipe_info(inode, pipe);
return 0;
}
static int
pipe_fasync(int fd, struct file *filp, int on)
{
struct pipe_inode_info *pipe = filp->private_data;
int retval = 0;
__pipe_lock(pipe);
if (filp->f_mode & FMODE_READ)
retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
if ((filp->f_mode & FMODE_WRITE) && retval >= 0) {
retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
if (retval < 0 && (filp->f_mode & FMODE_READ))
/* this can happen only if on == T */
fasync_helper(-1, filp, 0, &pipe->fasync_readers);
}
__pipe_unlock(pipe);
return retval;
}
unsigned long account_pipe_buffers(struct user_struct *user,
unsigned long old, unsigned long new)
{
return atomic_long_add_return(new - old, &user->pipe_bufs);
}
bool too_many_pipe_buffers_soft(unsigned long user_bufs)
{
unsigned long soft_limit = READ_ONCE(pipe_user_pages_soft);
return soft_limit && user_bufs > soft_limit;
}
bool too_many_pipe_buffers_hard(unsigned long user_bufs)
{
unsigned long hard_limit = READ_ONCE(pipe_user_pages_hard);
return hard_limit && user_bufs > hard_limit;
}
bool pipe_is_unprivileged_user(void)
{
return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
}
struct pipe_inode_info *alloc_pipe_info(void)
{
struct pipe_inode_info *pipe;
unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
struct user_struct *user = get_current_user();
unsigned long user_bufs;
unsigned int max_size = READ_ONCE(pipe_max_size);
pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL_ACCOUNT);
if (pipe == NULL)
goto out_free_uid;
if (pipe_bufs * PAGE_SIZE > max_size && !capable(CAP_SYS_RESOURCE))
pipe_bufs = max_size >> PAGE_SHIFT;
user_bufs = account_pipe_buffers(user, 0, pipe_bufs);
if (too_many_pipe_buffers_soft(user_bufs) && pipe_is_unprivileged_user()) {
user_bufs = account_pipe_buffers(user, pipe_bufs, PIPE_MIN_DEF_BUFFERS);
pipe_bufs = PIPE_MIN_DEF_BUFFERS;
}
if (too_many_pipe_buffers_hard(user_bufs) && pipe_is_unprivileged_user())
goto out_revert_acct;
pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
GFP_KERNEL_ACCOUNT);
if (pipe->bufs) {
init_waitqueue_head(&pipe->rd_wait);
init_waitqueue_head(&pipe->wr_wait);
pipe->r_counter = pipe->w_counter = 1;
pipe->max_usage = pipe_bufs;
pipe->ring_size = pipe_bufs;
pipe->nr_accounted = pipe_bufs;
pipe->user = user;
mutex_init(&pipe->mutex);
return pipe;
}
out_revert_acct:
(void) account_pipe_buffers(user, pipe_bufs, 0);
kfree(pipe);
out_free_uid:
free_uid(user);
return NULL;
}
void free_pipe_info(struct pipe_inode_info *pipe)
{
int i;
#ifdef CONFIG_WATCH_QUEUE
if (pipe->watch_queue)
watch_queue_clear(pipe->watch_queue);
#endif
(void) account_pipe_buffers(pipe->user, pipe->nr_accounted, 0);
free_uid(pipe->user);
for (i = 0; i < pipe->ring_size; i++) {
struct pipe_buffer *buf = pipe->bufs + i;
if (buf->ops)
pipe_buf_release(pipe, buf);
}
#ifdef CONFIG_WATCH_QUEUE
if (pipe->watch_queue)
put_watch_queue(pipe->watch_queue);
#endif
if (pipe->tmp_page)
__free_page(pipe->tmp_page);
kfree(pipe->bufs);
kfree(pipe);
}
static struct vfsmount *pipe_mnt __read_mostly;
/*
* pipefs_dname() is called from d_path().
*/
static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
{
return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
d_inode(dentry)->i_ino);
}
static const struct dentry_operations pipefs_dentry_operations = {
.d_dname = pipefs_dname,
};
static struct inode * get_pipe_inode(void)
{
struct inode *inode = new_inode_pseudo(pipe_mnt->mnt_sb);
struct pipe_inode_info *pipe;
if (!inode)
goto fail_inode;
inode->i_ino = get_next_ino();
pipe = alloc_pipe_info();
if (!pipe)
goto fail_iput;
inode->i_pipe = pipe;
pipe->files = 2;
pipe->readers = pipe->writers = 1;
inode->i_fop = &pipefifo_fops;
/*
* Mark the inode dirty from the very beginning,
* that way it will never be moved to the dirty
* list because "mark_inode_dirty()" will think
* that it already _is_ on the dirty list.
*/
inode->i_state = I_DIRTY;
inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
inode->i_uid = current_fsuid();
inode->i_gid = current_fsgid();
inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
return inode;
fail_iput:
iput(inode);
fail_inode:
return NULL;
}
int create_pipe_files(struct file **res, int flags)
{
struct inode *inode = get_pipe_inode();
struct file *f;
int error;
if (!inode)
return -ENFILE;
if (flags & O_NOTIFICATION_PIPE) {
error = watch_queue_init(inode->i_pipe);
if (error) {
free_pipe_info(inode->i_pipe);
iput(inode);
return error;
}
}
f = alloc_file_pseudo(inode, pipe_mnt, "",
O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT)),
&pipefifo_fops);
if (IS_ERR(f)) {
free_pipe_info(inode->i_pipe);
iput(inode);
return PTR_ERR(f);
}
f->private_data = inode->i_pipe;
res[0] = alloc_file_clone(f, O_RDONLY | (flags & O_NONBLOCK),
&pipefifo_fops);
if (IS_ERR(res[0])) {
put_pipe_info(inode, inode->i_pipe);
fput(f);
return PTR_ERR(res[0]);
}
res[0]->private_data = inode->i_pipe;
res[1] = f;
stream_open(inode, res[0]);
stream_open(inode, res[1]);
return 0;
}
static int __do_pipe_flags(int *fd, struct file **files, int flags)
{
int error;
int fdw, fdr;
if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT | O_NOTIFICATION_PIPE))
return -EINVAL;
error = create_pipe_files(files, flags);
if (error)
return error;
error = get_unused_fd_flags(flags);
if (error < 0)
goto err_read_pipe;
fdr = error;
error = get_unused_fd_flags(flags);
if (error < 0)
goto err_fdr;
fdw = error;
audit_fd_pair(fdr, fdw);
fd[0] = fdr;
fd[1] = fdw;
return 0;
err_fdr:
put_unused_fd(fdr);
err_read_pipe:
fput(files[0]);
fput(files[1]);
return error;
}
int do_pipe_flags(int *fd, int flags)
{
struct file *files[2];
int error = __do_pipe_flags(fd, files, flags);
if (!error) {
fd_install(fd[0], files[0]);
fd_install(fd[1], files[1]);
}
return error;
}
/*
* sys_pipe() is the normal C calling standard for creating
* a pipe. It's not the way Unix traditionally does this, though.
*/
static int do_pipe2(int __user *fildes, int flags)
{
struct file *files[2];
int fd[2];
int error;
error = __do_pipe_flags(fd, files, flags);
if (!error) {
if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
fput(files[0]);
fput(files[1]);
put_unused_fd(fd[0]);
put_unused_fd(fd[1]);
error = -EFAULT;
} else {
fd_install(fd[0], files[0]);
fd_install(fd[1], files[1]);
}
}
return error;
}
SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)
{
return do_pipe2(fildes, flags);
}
SYSCALL_DEFINE1(pipe, int __user *, fildes)
{
return do_pipe2(fildes, 0);
}
/*
* This is the stupid "wait for pipe to be readable or writable"
* model.
*
* See pipe_read/write() for the proper kind of exclusive wait,
* but that requires that we wake up any other readers/writers
* if we then do not end up reading everything (ie the whole
* "wake_next_reader/writer" logic in pipe_read/write()).
*/
void pipe_wait_readable(struct pipe_inode_info *pipe)
{
pipe_unlock(pipe);
wait_event_interruptible(pipe->rd_wait, pipe_readable(pipe));
pipe_lock(pipe);
}
void pipe_wait_writable(struct pipe_inode_info *pipe)
{
pipe_unlock(pipe);
wait_event_interruptible(pipe->wr_wait, pipe_writable(pipe));
pipe_lock(pipe);
}
/*
* This depends on both the wait (here) and the wakeup (wake_up_partner)
* holding the pipe lock, so "*cnt" is stable and we know a wakeup cannot
* race with the count check and waitqueue prep.
*
* Normally in order to avoid races, you'd do the prepare_to_wait() first,
* then check the condition you're waiting for, and only then sleep. But
* because of the pipe lock, we can check the condition before being on
* the wait queue.
*
* We use the 'rd_wait' waitqueue for pipe partner waiting.
*/
static int wait_for_partner(struct pipe_inode_info *pipe, unsigned int *cnt)
{
DEFINE_WAIT(rdwait);
int cur = *cnt;
while (cur == *cnt) {
prepare_to_wait(&pipe->rd_wait, &rdwait, TASK_INTERRUPTIBLE);
pipe_unlock(pipe);
schedule();
finish_wait(&pipe->rd_wait, &rdwait);
pipe_lock(pipe);
if (signal_pending(current))
break;
}
return cur == *cnt ? -ERESTARTSYS : 0;
}
static void wake_up_partner(struct pipe_inode_info *pipe)
{
wake_up_interruptible_all(&pipe->rd_wait);
}
static int fifo_open(struct inode *inode, struct file *filp)
{
struct pipe_inode_info *pipe;
bool is_pipe = inode->i_sb->s_magic == PIPEFS_MAGIC;
int ret;
filp->f_version = 0;
spin_lock(&inode->i_lock);
if (inode->i_pipe) {
pipe = inode->i_pipe;
pipe->files++;
spin_unlock(&inode->i_lock);
} else {
spin_unlock(&inode->i_lock);
pipe = alloc_pipe_info();
if (!pipe)
return -ENOMEM;
pipe->files = 1;
spin_lock(&inode->i_lock);
if (unlikely(inode->i_pipe)) {
inode->i_pipe->files++;
spin_unlock(&inode->i_lock);
free_pipe_info(pipe);
pipe = inode->i_pipe;
} else {
inode->i_pipe = pipe;
spin_unlock(&inode->i_lock);
}
}
filp->private_data = pipe;
/* OK, we have a pipe and it's pinned down */
__pipe_lock(pipe);
/* We can only do regular read/write on fifos */
stream_open(inode, filp);
switch (filp->f_mode & (FMODE_READ | FMODE_WRITE)) {
case FMODE_READ:
/*
* O_RDONLY
* POSIX.1 says that O_NONBLOCK means return with the FIFO
* opened, even when there is no process writing the FIFO.
*/
pipe->r_counter++;
if (pipe->readers++ == 0)
wake_up_partner(pipe);
if (!is_pipe && !pipe->writers) {
if ((filp->f_flags & O_NONBLOCK)) {
/* suppress EPOLLHUP until we have
* seen a writer */
filp->f_version = pipe->w_counter;
} else {
if (wait_for_partner(pipe, &pipe->w_counter))
goto err_rd;
}
}
break;
case FMODE_WRITE:
/*
* O_WRONLY
* POSIX.1 says that O_NONBLOCK means return -1 with
* errno=ENXIO when there is no process reading the FIFO.
*/
ret = -ENXIO;
if (!is_pipe && (filp->f_flags & O_NONBLOCK) && !pipe->readers)
goto err;
pipe->w_counter++;
if (!pipe->writers++)
wake_up_partner(pipe);
if (!is_pipe && !pipe->readers) {
if (wait_for_partner(pipe, &pipe->r_counter))
goto err_wr;
}
break;
case FMODE_READ | FMODE_WRITE:
/*
* O_RDWR
* POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
* This implementation will NEVER block on a O_RDWR open, since
* the process can at least talk to itself.
*/
pipe->readers++;
pipe->writers++;
pipe->r_counter++;
pipe->w_counter++;
if (pipe->readers == 1 || pipe->writers == 1)
wake_up_partner(pipe);
break;
default:
ret = -EINVAL;
goto err;
}
/* Ok! */
__pipe_unlock(pipe);
return 0;
err_rd:
if (!--pipe->readers)
wake_up_interruptible(&pipe->wr_wait);
ret = -ERESTARTSYS;
goto err;
err_wr:
if (!--pipe->writers)
wake_up_interruptible_all(&pipe->rd_wait);
ret = -ERESTARTSYS;
goto err;
err:
__pipe_unlock(pipe);
put_pipe_info(inode, pipe);
return ret;
}
const struct file_operations pipefifo_fops = {
.open = fifo_open,
.llseek = no_llseek,
.read_iter = pipe_read,
.write_iter = pipe_write,
.poll = pipe_poll,
.unlocked_ioctl = pipe_ioctl,
.release = pipe_release,
.fasync = pipe_fasync,
.splice_write = iter_file_splice_write,
};
/*
* Currently we rely on the pipe array holding a power-of-2 number
* of pages. Returns 0 on error.
*/
unsigned int round_pipe_size(unsigned long size)
{
if (size > (1U << 31))
return 0;
/* Minimum pipe size, as required by POSIX */
if (size < PAGE_SIZE)
return PAGE_SIZE;
return roundup_pow_of_two(size);
}
/*
* Resize the pipe ring to a number of slots.
*/
int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
{
struct pipe_buffer *bufs;
unsigned int head, tail, mask, n;
/*
* We can shrink the pipe, if arg is greater than the ring occupancy.
* Since we don't expect a lot of shrink+grow operations, just free and
* allocate again like we would do for growing. If the pipe currently
* contains more buffers than arg, then return busy.
*/
mask = pipe->ring_size - 1;
head = pipe->head;
tail = pipe->tail;
n = pipe_occupancy(pipe->head, pipe->tail);
if (nr_slots < n)
return -EBUSY;
bufs = kcalloc(nr_slots, sizeof(*bufs),
GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
if (unlikely(!bufs))
return -ENOMEM;
/*
* The pipe array wraps around, so just start the new one at zero
* and adjust the indices.
*/
if (n > 0) {
unsigned int h = head & mask;
unsigned int t = tail & mask;
if (h > t) {
memcpy(bufs, pipe->bufs + t,
n * sizeof(struct pipe_buffer));
} else {
unsigned int tsize = pipe->ring_size - t;
if (h > 0)
memcpy(bufs + tsize, pipe->bufs,
h * sizeof(struct pipe_buffer));
memcpy(bufs, pipe->bufs + t,
tsize * sizeof(struct pipe_buffer));
}
}
head = n;
tail = 0;
kfree(pipe->bufs);
pipe->bufs = bufs;
pipe->ring_size = nr_slots;
if (pipe->max_usage > nr_slots)
pipe->max_usage = nr_slots;
pipe->tail = tail;
pipe->head = head;
/* This might have made more room for writers */
wake_up_interruptible(&pipe->wr_wait);
return 0;
}
/*
* Allocate a new array of pipe buffers and copy the info over. Returns the
* pipe size if successful, or return -ERROR on error.
*/
static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
{
unsigned long user_bufs;
unsigned int nr_slots, size;
long ret = 0;
#ifdef CONFIG_WATCH_QUEUE
if (pipe->watch_queue)
return -EBUSY;
#endif
size = round_pipe_size(arg);
nr_slots = size >> PAGE_SHIFT;
if (!nr_slots)
return -EINVAL;
/*
* If trying to increase the pipe capacity, check that an
* unprivileged user is not trying to exceed various limits
* (soft limit check here, hard limit check just below).
* Decreasing the pipe capacity is always permitted, even
* if the user is currently over a limit.
*/
if (nr_slots > pipe->max_usage &&
size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
return -EPERM;
user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_slots);
if (nr_slots > pipe->max_usage &&
(too_many_pipe_buffers_hard(user_bufs) ||
too_many_pipe_buffers_soft(user_bufs)) &&
pipe_is_unprivileged_user()) {
ret = -EPERM;
goto out_revert_acct;
}
ret = pipe_resize_ring(pipe, nr_slots);
if (ret < 0)
goto out_revert_acct;
pipe->max_usage = nr_slots;
pipe->nr_accounted = nr_slots;
return pipe->max_usage * PAGE_SIZE;
out_revert_acct:
(void) account_pipe_buffers(pipe->user, nr_slots, pipe->nr_accounted);
return ret;
}
/*
* Note that i_pipe and i_cdev share the same location, so checking ->i_pipe is
* not enough to verify that this is a pipe.
*/
struct pipe_inode_info *get_pipe_info(struct file *file, bool for_splice)
{
struct pipe_inode_info *pipe = file->private_data;
if (file->f_op != &pipefifo_fops || !pipe)
return NULL;
#ifdef CONFIG_WATCH_QUEUE
if (for_splice && pipe->watch_queue)
return NULL;
#endif
return pipe;
}
long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct pipe_inode_info *pipe;
long ret;
pipe = get_pipe_info(file, false);
if (!pipe)
return -EBADF;
__pipe_lock(pipe);
switch (cmd) {
case F_SETPIPE_SZ:
ret = pipe_set_size(pipe, arg);
break;
case F_GETPIPE_SZ:
ret = pipe->max_usage * PAGE_SIZE;
break;
default:
ret = -EINVAL;
break;
}
__pipe_unlock(pipe);
return ret;
}
static const struct super_operations pipefs_ops = {
.destroy_inode = free_inode_nonrcu,
.statfs = simple_statfs,
};
/*
* pipefs should _never_ be mounted by userland - too much of security hassle,
* no real gain from having the whole whorehouse mounted. So we don't need
* any operations on the root directory. However, we need a non-trivial
* d_name - pipe: will go nicely and kill the special-casing in procfs.
*/
static int pipefs_init_fs_context(struct fs_context *fc)
{
struct pseudo_fs_context *ctx = init_pseudo(fc, PIPEFS_MAGIC);
if (!ctx)
return -ENOMEM;
ctx->ops = &pipefs_ops;
ctx->dops = &pipefs_dentry_operations;
return 0;
}
static struct file_system_type pipe_fs_type = {
.name = "pipefs",
.init_fs_context = pipefs_init_fs_context,
.kill_sb = kill_anon_super,
};
#ifdef CONFIG_SYSCTL
static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
unsigned int *valp,
int write, void *data)
{
if (write) {
unsigned int val;
val = round_pipe_size(*lvalp);
if (val == 0)
return -EINVAL;
*valp = val;
} else {
unsigned int val = *valp;
*lvalp = (unsigned long) val;
}
return 0;
}
static int proc_dopipe_max_size(struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
return do_proc_douintvec(table, write, buffer, lenp, ppos,
do_proc_dopipe_max_size_conv, NULL);
}
static struct ctl_table fs_pipe_sysctls[] = {
{
.procname = "pipe-max-size",
.data = &pipe_max_size,
.maxlen = sizeof(pipe_max_size),
.mode = 0644,
.proc_handler = proc_dopipe_max_size,
},
{
.procname = "pipe-user-pages-hard",
.data = &pipe_user_pages_hard,
.maxlen = sizeof(pipe_user_pages_hard),
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
},
{
.procname = "pipe-user-pages-soft",
.data = &pipe_user_pages_soft,
.maxlen = sizeof(pipe_user_pages_soft),
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
},
{ }
};
#endif
static int __init init_pipe_fs(void)
{
int err = register_filesystem(&pipe_fs_type);
if (!err) {
pipe_mnt = kern_mount(&pipe_fs_type);
if (IS_ERR(pipe_mnt)) {
err = PTR_ERR(pipe_mnt);
unregister_filesystem(&pipe_fs_type);
}
}
#ifdef CONFIG_SYSCTL
register_sysctl_init("fs", fs_pipe_sysctls);
#endif
return err;
}
fs_initcall(init_pipe_fs);