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

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Message-ID: <3862c1d1-dd78-0b80-74c4-5f32a821fbef@roeck-us.net>
Date:   Tue, 11 May 2021 06:36:54 -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: Fix possible use-after-free in
 wdt_startup()

On 5/11/21 12:01 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/sbc60xxwdt.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/sbc60xxwdt.c b/drivers/watchdog/sbc60xxwdt.c
> index a947a63..7b97480 100644
> --- 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");
>   }
>