linux-kernel - Re: [PATCH -next] watchdog: sc520_wdt: Fix possible use-after-free in wdt

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Message-ID: <78638328-536d-edf6-f913-38f6d3acb1d3@roeck-us.net>
Date:   Tue, 11 May 2021 06:37:09 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Zou Wei <zou_wei@...wei.com>, wim@...ux-watchdog.org
Cc:     linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] watchdog: sc520_wdt: Fix possible use-after-free in
 wdt_turnoff()

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@...wei.com>
> Signed-off-by: Zou Wei <zou_wei@...wei.com>

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