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

[Ezequiel Garcia <ezequiel@collabora.com>]

On Thu, 2020-01-16 at 12:57 +0100, Hans Verkuil wrote:
> 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@vger.kernel.org
> > Fixes: 0e43734d4c46e ("media: v4l2-subdev: add release() internal op")
> > Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
> > Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>
> > ---
> > 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.
> 

Hi everyone,

Please note this fix is useful to fix a kernel oops
when rkisp1 driver is removed.

Can we get a v4 addressing Hans' feedback?

Thanks,
Ezequiel

> Unless I am missing something?
> 
> >  	module_put(owner);
> > 
> 
> Regards,
> 
> 	Hans