fs/pipe: Fix lockdep false-positive in watchqueue pipe_write()

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[ Upstream commit 055ca83559 ]

When you try to splice between a normal pipe and a notification pipe,
get_pipe_info(..., true) fails, so splice() falls back to treating the
notification pipe like a normal pipe - so we end up in
iter_file_splice_write(), which first locks the input pipe, then calls
vfs_iter_write(), which locks the output pipe.

Lockdep complains about that, because we're taking a pipe lock while
already holding another pipe lock.

I think this probably (?) can't actually lead to deadlocks, since you'd
need another way to nest locking a normal pipe into locking a
watch_queue pipe, but the lockdep annotations don't make that clear.

Bail out earlier in pipe_write() for notification pipes, before taking
the pipe lock.

Reported-and-tested-by: <syzbot+011e4ea1da6692cf881c@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=011e4ea1da6692cf881c
Fixes: c73be61ced ("pipe: Add general notification queue support")
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/r/20231124150822.2121798-1-jannh@google.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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Jann Horn 2023-11-24 16:08:22 +01:00 • committed by Greg Kroah-Hartman

parent 92d79ca28d

commit cdd8fc7dc4

1 changed files with 12 additions and 5 deletions

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fs/pipe.c

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