Re: [PATCH v2 1/2] HID: wacom: Fix Use-After-Free in wacom_intuos_pad

[Markus Elfring]

…
> +++ b/drivers/hid/wacom_sys.c
> @@ -877,10 +877,16 @@ static void wacom_remove_shared_data(void *res)
>  		data = container_of(wacom_wac->shared, struct wacom_hdev_data,
>  				    shared);
>  
> -		if (wacom_wac->shared->touch == wacom->hdev)
> +		mutex_lock(&wacom_udev_list_lock);
> +		if (wacom_wac->shared->touch == wacom->hdev) {
>  			wacom_wac->shared->touch = NULL;
…
> +		}
> +		mutex_unlock(&wacom_udev_list_lock);
> +
> +		synchronize_rcu();
>  
>  		kref_put(&data->kref, wacom_release_shared_data);
…

Under which circumstances would you dare to apply another lock guard?
https://elixir.bootlin.com/linux/v7.1-rc5/source/include/linux/mutex.h#L253

Regards,
Markus