[PATCH AUTOSEL 5.10 15/37] watchdog: sc520_wdt: Fix possible use-after-free in wdt_turnoff()

From: Sasha Levin
Date: Sat Jul 10 2021 - 19:52:00 EST

From: Zou Wei <zou_wei@xxxxxxxxxx>

[ Upstream commit 90b7c141132244e8e49a34a4c1e445cce33e07f4 ]

This module's remove path calls del_timer(). However, that function
does not wait until the timer handler finishes. This means that the
timer handler may still be running after the driver's remove function
has finished, which would result in a use-after-free.

Fix by calling del_timer_sync(), which makes sure the timer handler
has finished, and unable to re-schedule itself.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Zou Wei <zou_wei@xxxxxxxxxx>
Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1620716691-108460-1-git-send-email-zou_wei@xxxxxxxxxx
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Wim Van Sebroeck <wim@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
drivers/watchdog/sc520_wdt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/watchdog/sc520_wdt.c b/drivers/watchdog/sc520_wdt.c
index e66e6b905964..ca65468f4b9c 100644
--- a/drivers/watchdog/sc520_wdt.c
+++ b/drivers/watchdog/sc520_wdt.c
@@ -186,7 +186,7 @@ static int wdt_startup(void)
static int wdt_turnoff(void)
/* Stop the timer */
- del_timer(&timer);
+ del_timer_sync(&timer);

/* Stop the watchdog */