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

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Date: Sun, 24 Mar 2024 10:25:47 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Duoming Zhou <duoming@....edu.cn>, linux-watchdog@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, wim@...ux-watchdog.org
Subject: Re: [PATCH] watchdog: cpu5wdt.c: Fix use-after-free bug caused by
 cpu5wdt_trigger

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@....edu.cn>

Reviewed-by: Guenter Roeck <linux@...ck-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);