[PATCH] watchdog: cpu5wdt.c: Fix use-after-free bug caused by cpu5wdt_trigger

[Duoming Zhou]

When the cpu5wdt module is removing, the origin code uses del_timer() to
de-activate the timer. If the timer handler is running, del_timer() could
not stop it and will return directly. If the port region is released by
release_region() and then the timer handler cpu5wdt_trigger() calls outb()
to write into the region that is released, the use-after-free bug will
happen.

Change del_timer() to timer_shutdown_sync() in order that the timer handler
could be finished before the port region is released.

Fixes: e09d9c3e9f85 ("watchdog: cpu5wdt.c: add missing del_timer call")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
 drivers/watchdog/cpu5wdt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/watchdog/cpu5wdt.c b/drivers/watchdog/cpu5wdt.c
index 688b112e712..9f279c0e13a 100644
--- a/drivers/watchdog/cpu5wdt.c
+++ b/drivers/watchdog/cpu5wdt.c
@@ -252,7 +252,7 @@ static void cpu5wdt_exit(void)
 	if (cpu5wdt_device.queue) {
 		cpu5wdt_device.queue = 0;
 		wait_for_completion(&cpu5wdt_device.stop);
-		del_timer(&cpu5wdt_device.timer);
+		timer_shutdown_sync(&cpu5wdt_device.timer);
 	}
 
 	misc_deregister(&cpu5wdt_misc);
-- 
2.17.1