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

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>

diff --git a/drivers/watchdog/sbc60xxwdt.c b/drivers/watchdog/sbc60xxwdt.c
index a947a63fb44ae9c082c5f395d69811af1bc038be..7b974802dfc7cf25337d76b4e4ea0a8f2a12c99c 100644 (file)
--- a/drivers/watchdog/sbc60xxwdt.c
+++ b/drivers/watchdog/sbc60xxwdt.c
@@ -146,7 +146,7 @@ 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");
 }