Re: [PATCH v3 8/9] drm/rockchip: gem: Don't alloc/free gem buf when dev_private is invalid

[jeffy]

Hi Daniel,

On 04/06/2017 04:26 PM, Daniel Vetter wrote:
> On Wed, Apr 05, 2017 at 12:28:40PM -0400, Sean Paul wrote:
> > On Wed, Apr 05, 2017 at 04:29:26PM +0800, Jeffy Chen wrote:
> > > After unbinding drm, the userspace may still has a chance to access
> > > gem buf.
> > >
> > > Add a sanity check for a NULL dev_private to prevent that from
> > > happening.
> >
> > I still don't understand how this is happening. You're saying that these hooks
> > can be called after rockchip_drm_unbind() has finished?
>
> Yeah this is supposed to be impossible. If it isn't, we need to debug and
> fix this properly. This smells like pretty bad duct-tape ...

it looks like after unbind, the user space may still own drm dev fd, and 
could be able to call ioctl:
lrwx------. 1 chronos chronos 64 Mar 15 12:53 28 -> /dev/dri/card1 (deleted)

and the drm_unplug_dev may help it, maybe we should call it in unbind? 
or just break drm_ioctl when drm_dev not registered?

> -Daniel
>
> > Sean
> >
> > > Signed-off-by: Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx>
> > > ---
> > >
> > > Changes in v3:
> > > Address Daniel Vetter <daniel@xxxxxxxx>'s comments.
> > > Update commit message.
> > >
> > > Changes in v2: None
> > >
> > >   drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 8 ++++++++
> > >   1 file changed, 8 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > > index df9e570..205a3dc 100644
> > > --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > > @@ -184,6 +184,9 @@ static int rockchip_gem_alloc_buf(struct rockchip_gem_object *rk_obj,
> > >   	struct drm_device *drm = obj->dev;
> > >   	struct rockchip_drm_private *private = drm->dev_private;
> > >
> > > +	if (!private)
> > > +		return -ENODEV;
> > > +
> > >   	if (private->domain)
> > >   		return rockchip_gem_alloc_iommu(rk_obj, alloc_kmap);
> > >   	else
> > > @@ -208,6 +211,11 @@ static void rockchip_gem_free_dma(struct rockchip_gem_object *rk_obj)
> > >
> > >   static void rockchip_gem_free_buf(struct rockchip_gem_object *rk_obj)
> > >   {
> > > +	struct drm_device *drm = rk_obj->base.dev;
> > > +
> > > +	if (!drm->dev_private)
> > > +		return;
> > > +
> > >   	if (rk_obj->pages)
> > >   		rockchip_gem_free_iommu(rk_obj);
> > >   	else
> > > --
> > > 2.1.4
> >
> > --
> > Sean Paul, Software Engineer, Google / Chromium OS
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