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

[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@zju.edu.cn>
---
 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

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

[Guenter Roeck]

On 3/24/24 07:04, Duoming Zhou wrote:
> 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@zju.edu.cn>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
>   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);