From 447c19f3b5074409c794b350b10306e1da1ef4ba Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Fri, 14 May 2021 12:02:50 +0100
Subject: [PATCH] io_uring: fix ltout double free on completion race
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: 90cd7e424969d ("io_uring: track link timeout's master explicitly")
Reported-and-tested-by: syzbot+5a864149dd970b546223@syzkaller.appspotmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/69c46bf6ce37fec4fdcd98f0882e18eb07ce693a.1620990121.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
fs/io_uring.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 9ac5e278a91e6..599102cc6dfc2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6354,10 +6354,11 @@ static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer)
* We don't expect the list to be empty, that will only happen if we
* race with the completion of the linked work.
*/
- if (prev && req_ref_inc_not_zero(prev))
+ if (prev) {
io_remove_next_linked(prev);
- else
- prev = NULL;
+ if (!req_ref_inc_not_zero(prev))
+ prev = NULL;
+ }
spin_unlock_irqrestore(&ctx->completion_lock, flags);
if (prev) {
--
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