watchdog: Fix possible use-after-free in wdt_startup()

[ Upstream commit c08a6b31e4917034f0ed0cb457c3bb209576f542 ]

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@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1620716495-108352-1-git-send-email-zou_wei@huawei.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/watchdog/sbc60xxwdt.c b/drivers/watchdog/sbc60xxwdt.c
index 2eef58a0cf059837c5055d386bede89e21247c7f..152db059d5aa15a34038f4d809ccd55abd0588a5 100644 (file)
--- a/drivers/watchdog/sbc60xxwdt.c
+++ b/drivers/watchdog/sbc60xxwdt.c
@@ -152,7 +152,7 @@ static void wdt_startup(void)
 static void wdt_turnoff(void)
 {
        /* Stop the timer */
-       del_timer(&timer);
+       del_timer_sync(&timer);
        inb_p(wdt_stop);
        pr_info("Watchdog timer is now disabled...\n");
 }