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pipe: Fix missing mask update after pipe_wait() 

Fix pipe_write() to not cache the ring index mask and max_usage as their
values are invalidated by calling pipe_wait() because the latter
function drops the pipe lock, thereby allowing F_SETPIPE_SZ change them.
Without this, pipe_write() may subsequently miscalculate the array
indices and pipe fullness, leading to an oops like the following:

  BUG: KASAN: slab-out-of-bounds in pipe_write+0xc25/0xe10 fs/pipe.c:481
  Write of size 8 at addr ffff8880771167a8 by task syz-executor.3/7987
  ...
  CPU: 1 PID: 7987 Comm: syz-executor.3 Not tainted 5.4.0-rc2-syzkaller #0
  ...
  Call Trace:
    pipe_write+0xc25/0xe10 fs/pipe.c:481
    call_write_iter include/linux/fs.h:1895 [inline]
    new_sync_write+0x3fd/0x7e0 fs/read_write.c:483
    __vfs_write+0x94/0x110 fs/read_write.c:496
    vfs_write+0x18a/0x520 fs/read_write.c:558
    ksys_write+0x105/0x220 fs/read_write.c:611
    __do_sys_write fs/read_write.c:623 [inline]
    __se_sys_write fs/read_write.c:620 [inline]
    __x64_sys_write+0x6e/0xb0 fs/read_write.c:620
    do_syscall_64+0xca/0x5d0 arch/x86/entry/common.c:290
    entry_SYSCALL_64_after_hwframe+0x49/0xbe

This is not a problem for pipe_read() as the mask is recalculated on
each pass of the loop, after pipe_wait() has been called.

Fixes: 8cefc107ca ("pipe: Use head and tail pointers for the ring, not cursor and length")
Reported-by: syzbot+838eb0878ffd51f27c41@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Eric Biggers <ebiggers@kernel.org>
[ Changed it to use a temporary variable 'mask' to avoid long lines -Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Howells 2019-12-05 22:30:37 +00:00 committed by Linus Torvalds
parent 8c7b8c34ae
commit 8f868d68d3
1 changed files with 6 additions and 6 deletions
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12
fs/pipe.c
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@ -389,7 +389,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
{ {
struct file *filp = iocb->ki_filp; struct file *filp = iocb->ki_filp;
struct pipe_inode_info *pipe = filp->private_data; struct pipe_inode_info *pipe = filp->private_data;
unsigned int head, max_usage, mask; unsigned int head;
ssize_t ret = 0; ssize_t ret = 0;
int do_wakeup = 0; int do_wakeup = 0;
size_t total_len = iov_iter_count(from); size_t total_len = iov_iter_count(from);
@ -408,12 +408,11 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
} }
head = pipe->head; head = pipe->head;
max_usage = pipe->max_usage;
mask = pipe->ring_size - 1;
/* We try to merge small writes */ /* We try to merge small writes */
chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */ chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
if (!pipe_empty(head, pipe->tail) && chars != 0) { if (!pipe_empty(head, pipe->tail) && chars != 0) {
unsigned int mask = pipe->ring_size - 1;
struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask]; struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];
int offset = buf->offset + buf->len; int offset = buf->offset + buf->len;
@ -443,7 +442,8 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
} }
head = pipe->head; head = pipe->head;
if (!pipe_full(head, pipe->tail, max_usage)) { 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 pipe_buffer *buf = &pipe->bufs[head & mask];
struct page *page = pipe->tmp_page; struct page *page = pipe->tmp_page;
int copied; int copied;
@ -465,7 +465,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
spin_lock_irq(&pipe->wait.lock); spin_lock_irq(&pipe->wait.lock);
head = pipe->head; head = pipe->head;
if (pipe_full(head, pipe->tail, max_usage)) { if (pipe_full(head, pipe->tail, pipe->max_usage)) {
spin_unlock_irq(&pipe->wait.lock); spin_unlock_irq(&pipe->wait.lock);
continue; continue;
} }
@ -510,7 +510,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
break; break;
} }
if (!pipe_full(head, pipe->tail, max_usage)) if (!pipe_full(head, pipe->tail, pipe->max_usage))
continue; continue;
/* Wait for buffer space to become available. */ /* Wait for buffer space to become available. */