linux-kernel - Re: [PATCH] watchdog: Fix NULL pointer dereference when releasing cdev

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Date:   Wed, 23 Jun 2021 04:31:46 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Curtis Klein <curtis.klein@....com>
Cc:     wim@...ux-watchdog.org, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: Fix NULL pointer dereference when releasing
 cdev

On Tue, Jun 22, 2021 at 11:26:23PM -0700, Curtis Klein wrote:
> watchdog_hrtimer_pretimeout_stop needs the watchdog device to have a
> valid pointer to the watchdog core data to stop the pretimeout hrtimer.
> Therefore it needs to be called before the pointers are cleared in
> watchdog_cdev_unregister.
> 
> Fixes: 7b7d2fdc8c3e ("watchdog: Add hrtimer-based pretimeout feature")
> Reported-by: Colin Ian King <colin.king@...onical.com>
> Signed-off-by: Curtis Klein <curtis.klein@....com>

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

> ---
>  drivers/watchdog/watchdog_dev.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 3bab324..ffd8f1a 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -1096,6 +1096,8 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
>  		watchdog_stop(wdd);
>  	}
>  
> +	watchdog_hrtimer_pretimeout_stop(wdd);
> +
>  	mutex_lock(&wd_data->lock);
>  	wd_data->wdd = NULL;
>  	wdd->wd_data = NULL;
> @@ -1103,7 +1105,6 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
>  
>  	hrtimer_cancel(&wd_data->timer);
>  	kthread_cancel_work_sync(&wd_data->work);
> -	watchdog_hrtimer_pretimeout_stop(wdd);
>  
>  	put_device(&wd_data->dev);
>  }
> -- 
> 2.7.4
>