[PATCH] io_uring: fix list corruption race in io_pollfree_wake()

[Soham Kute <officialsohamkute@gmail.com>]

io_pollfree_wake() removes the poll wait entry without holding
the waitqueue head lock. Other removal paths take the head lock,
so this can race and lead to list corruption detected by list_debug.

Acquire the waitqueue lock before calling io_poll_remove_waitq(),
matching the locking used in io_poll_remove_entry().

Reported-by: syzbot+ab12f0c08dd7ab8d057c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ab12f0c08dd7ab8d057c
Signed-off-by: Soham Kute <officialsohamkute@gmail.com>
---
 io_uring/poll.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/io_uring/poll.c b/io_uring/poll.c
index aac4b3b88..006154355 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -383,10 +383,17 @@ static void io_poll_cancel_req(struct io_kiocb *req)
 
 static __cold int io_pollfree_wake(struct io_kiocb *req, struct io_poll *poll)
 {
+	struct wait_queue_head *head;
 	io_poll_mark_cancelled(req);
 	/* we have to kick tw in case it's not already */
 	io_poll_execute(req, 0);
-	io_poll_remove_waitq(poll);
+	/* Pairs with smp_store_release() in io_poll_remove_waitq() */
+	head = smp_load_acquire(&poll->head);
+	if (head) {
+		spin_lock_irq(&head->lock);
+		io_poll_remove_waitq(poll);
+		spin_unlock_irq(&head->lock);
+	}
 	return 1;
 }
 
-- 
2.34.1