io_uring: fix double poll leak on repolling

commit c0737fa upstream.

We have re-polling for partial IO, so a request can be polled twice. If
it used two poll entries the first time then on the second
io_arm_poll_handler() it will find the old apoll entry and NULL
kmalloc()'ed second entry, i.e. apoll->double_poll, so leaking it.

Fixes: 10c8733 ("io_uring: allow re-poll if we made progress")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/fee2452494222ecc7f1f88c8fb659baef971414a.1655852245.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

io_uring/io_uring.c

@@ -5751,10 +5751,12 @@ static int io_arm_poll_handler(struct io_kiocb *req)
 		mask |= POLLOUT | POLLWRNORM;
 	}
 
-	if (req->flags & REQ_F_POLLED)
+	if (req->flags & REQ_F_POLLED) {
 		apoll = req->apoll;
-	else
+		kfree(apoll->double_poll);
+	} else {
 		apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC);
+	}
 	if (unlikely(!apoll))
 		return IO_APOLL_ABORTED;
 	apoll->double_poll = NULL;