Re: [PATCH v3] media: v4l2-core: fix a use-after-free bug of sd->devnode

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On 11/20/19 1:22 PM, Dafna Hirschfeld wrote:
> sd->devnode is released after calling
> v4l2_subdev_release. Therefore it should be set
> to NULL so that the subdev won't hold a pointer
> to a released object. This fixes a reference
> after free bug in function
> v4l2_device_unregister_subdev
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 0e43734d4c46e ("media: v4l2-subdev: add release() internal op")
> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@xxxxxxxxxxxxx>
> Reviewed-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
> ---
> changes since v2:
> - since this is a regresion fix, I added Fixes and Cc to stable tags,
> - change the commit title and log to be more clear.
> 
>  drivers/media/v4l2-core/v4l2-device.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-device.c b/drivers/media/v4l2-core/v4l2-device.c
> index 63d6b147b21e..2b3595671d62 100644
> --- a/drivers/media/v4l2-core/v4l2-device.c
> +++ b/drivers/media/v4l2-core/v4l2-device.c
> @@ -177,6 +177,7 @@ static void v4l2_subdev_release(struct v4l2_subdev *sd)
>  {
>  	struct module *owner = !sd->owner_v4l2_dev ? sd->owner : NULL;
>  
> +	sd->devnode = NULL;
>  	if (sd->internal_ops && sd->internal_ops->release)
>  		sd->internal_ops->release(sd);

I'd move the sd->devnode = NULL; line here. That way the
sd->internal_ops->release(sd) callback can still use it.

Unless I am missing something?

>  	module_put(owner);
> 

Regards,

	Hans



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