6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jann Horn jannh@google.com
[ Upstream commit 055ca83559912f2cfd91c9441427bac4caf3c74e ]
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: c73be61cede5 ("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 --- fs/pipe.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/fs/pipe.c b/fs/pipe.c index a234035cc375d..ba4376341ddd2 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -425,6 +425,18 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) bool was_empty = false; bool wake_next_writer = false;
+ /* + * Reject writing to watch queue pipes before the point where we lock + * the pipe. + * Otherwise, lockdep would be unhappy if the caller already has another + * pipe locked. + * If we had to support locking a normal pipe and a notification pipe at + * the same time, we could set up lockdep annotations for that, but + * since we don't actually need that, it's simpler to just bail here. + */ + if (pipe_has_watch_queue(pipe)) + return -EXDEV; + /* Null write succeeds. */ if (unlikely(total_len == 0)) return 0; @@ -437,11 +449,6 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) goto out; }
- if (pipe_has_watch_queue(pipe)) { - ret = -EXDEV; - goto out; - } - /* * If it wasn't empty we try to merge new data into * the last buffer.