[PATCH] drivers:md:fix a potential use-after-free bug

[Wentao_Liang]

In line 2884, "raid5_release_stripe(sh);" drops the reference to sh and
may cause sh to be released. However, sh is subsequently used in lines
2886 "if (sh->batch_head && sh != sh->batch_head)". This may result in an
use-after-free bug.

It can be fixed by moving "raid5_release_stripe(sh);" to the bottom of
the function.

The bug has been confirmed by Song on 2021-08-14. Now, I resend this
patch with my real name. I hope the patch can be updated in a near
future.

Signed-off-by: Wentao_Liang <Wentao_Liang_g@xxxxxxx>
---
 drivers/md/raid5.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 5d09256d7f81..93fcbeac5096 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2881,10 +2881,10 @@ static void raid5_end_write_request(struct bio *bi)
 	if (!test_and_clear_bit(R5_DOUBLE_LOCKED, &sh->dev[i].flags))
 		clear_bit(R5_LOCKED, &sh->dev[i].flags);
 	set_bit(STRIPE_HANDLE, &sh->state);
-	raid5_release_stripe(sh);
 
 	if (sh->batch_head && sh != sh->batch_head)
 		raid5_release_stripe(sh->batch_head);
+	raid5_release_stripe(sh);
 }
 
 static void raid5_error(struct mddev *mddev, struct md_rdev *rdev)
-- 
2.25.1