[PATCH -next] watchdog: sc520_wdt: Fix possible use-after-free in wdt_turnoff()

[PATCH -next] watchdog: sc520_wdt: Fix possible use-after-free in wdt_turnoff()

[Zou Wei]

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>
---
 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 e66e6b9..ca65468 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 */
 	wdt_config(0);
-- 
2.6.2

Re: [PATCH -next] watchdog: sc520_wdt: Fix possible use-after-free in wdt_turnoff()

[Guenter Roeck]

On 5/11/21 12:04 AM, Zou Wei wrote:
> 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>

> ---
>   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 e66e6b9..ca65468 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 */
>   	wdt_config(0);
>