io_uring: fix ltout double free on completion race

mainline inclusion
from mainline-v5.13-rc2
commit 447c19f3
category: bugfix
bugzilla: 185736
CVE: NA

-----------------------------------------------

Always remove linked timeout on io_link_timeout_fn() from the master
request link list, otherwise we may get use-after-free when first
io_link_timeout_fn() puts linked timeout in the fail path, and then
will be found and put on master's free.

Cc: stable@vger.kernel.org # 5.10+
Fixes: 90cd7e42 ("io_uring: track link timeout's master explicitly")
Reported-and-tested-by: syzbot+5a864149dd970b546223@syzkaller.appspotmail.com
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/69c46bf6ce37fec4fdcd98f0882e18eb07ce693a.1620990121.git.asml.silence@gmail.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

conflicts:
fs/io_uring.c
Signed-off-by: NYe Bin <yebin10@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/io_uring.c

@@ -5925,8 +5925,8 @@ static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer)
 	if (!list_empty(&req->link_list)) {
 		prev = list_entry(req->link_list.prev, struct io_kiocb,
 				  link_list);
-		if (refcount_inc_not_zero(&prev->refs)) {
 		list_del_init(&req->link_list);
+		if (refcount_inc_not_zero(&prev->refs)) {
 			prev->flags &= ~REQ_F_LINK_TIMEOUT;
 		} else
 			prev = NULL;