watch_queue: Fix missing locking in add_watch_to_object()
If a watch is being added to a queue, it needs to guard against interference from addition of a new watch, manual removal of a watch and removal of a watch due to some other queue being destroyed. KEYCTL_WATCH_KEY guards against this for the same {key,queue} pair by holding the key->sem writelocked and by holding refs on both the key and the queue - but that doesn't prevent interaction from other {key,queue} pairs. While add_watch_to_object() does take the spinlock on the event queue, it doesn't take the lock on the source's watch list. The assumption was that the caller would prevent that (say by taking key->sem) - but that doesn't prevent interference from the destruction of another queue. Fix this by locking the watcher list in add_watch_to_object(). Fixes: c73be61c ("pipe: Add general notification queue support") Reported-by: syzbot+03d7b43290037d1f87ca@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: keyrings@vger.kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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