linux-kernel - Re: drivers/gpu/drm/radeon/r600_blit.c: fix possible NULL pointer derefernce

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Date:	Wed, 21 Jul 2010 10:30:43 +1000
From:	Dave Airlie <airlied@...hat.com>
To:	"Alexander Y. Fomichev" <git.user@...il.com>
Cc:	Alex Deucher <alexdeucher@...il.com>,
	Robert Noland <rnoland@...p.net>,
	Matt Turner <mattst88@...il.com>,
	Jerome Glisse <jglisse@...hat.com>, akpm@...ux-foundation.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: drivers/gpu/drm/radeon/r600_blit.c: fix possible NULL pointer 
 derefernce

On Wed, 2010-07-21 at 01:07 +0400, Alexander Y. Fomichev wrote:
> On Wed, Jul 21, 2010 at 1:00 AM, Alex Deucher <alexdeucher@...il.com> wrote:
> > On Tue, Jul 20, 2010 at 4:13 PM, Alexander Y. Fomichev
> > <git.user@...il.com> wrote:
> >> On Tue, Jul 20, 2010 at 9:37 PM, Alex Deucher <alexdeucher@...il.com> wrote:
> >>> On Mon, Jul 19, 2010 at 5:42 PM, Alexander Y. Fomichev
> >>> <git.user@...il.com> wrote:
> >>>> This patch fix possible NULL pointer dereference when
> >>>> r600_prepare_blit_copy tries to fill dev_priv->blit_vb->file_priv
> >>>> without check of dev_priv->blit_vb. dev_priv->blit_vb should be
> >>>> filled by r600_nomm_get_vb but latest can fail with EAGAIN.
> >>>> Addresses: https://bugzilla.kernel.org/show_bug.cgi?id=16375
> >>>>
> >>>> ---
> >>>>  drivers/gpu/drm/radeon/r600_blit.c |    2 ++
> >>>>  1 files changed, 2 insertions(+), 0 deletions(-)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/radeon/r600_blit.c b/drivers/gpu/drm/radeon/r600_blit.c
> >>>> index f4fb88e..0df4a2b 100644
> >>>> --- a/drivers/gpu/drm/radeon/r600_blit.c
> >>>> +++ b/drivers/gpu/drm/radeon/r600_blit.c
> >>>> @@ -541,6 +541,8 @@ r600_prepare_blit_copy(struct drm_device *dev, struct drm_file *file_priv)
> >>>>        DRM_DEBUG("\n");
> >>>>
> >>>>        r600_nomm_get_vb(dev);
> >>>> +       if (!dev_priv->blit_vb)
> >>>> +               return;
> >>>
> >>> r600_prepare_blit_copy returns an int so something like this would be better:
> >>> --- a/drivers/gpu/drm/radeon/r600_blit.c
> >>> +++ b/drivers/gpu/drm/radeon/r600_blit.c
> >>> @@ -539,8 +539,10 @@ r600_prepare_blit_copy(struct drm_device *dev,
> >>> struct drm_file *file_priv)
> >>>  {
> >>>        drm_radeon_private_t *dev_priv = dev->dev_private;
> >>>        DRM_DEBUG("\n");
> >>> +       int ret = r600_nomm_get_vb(dev);
> >>>
> >>> -       r600_nomm_get_vb(dev);
> >>> +       if (ret)
> >>> +               return ret;
> >>>
> >>>        dev_priv->blit_vb->file_priv = file_priv;
> >>>
> >>>
> >>> Alex
> >>>
> >>>>
> >>>>        dev_priv->blit_vb->file_priv = file_priv;
> >>>>
> >>>> --
> >>>> 1.7.1.1
> >>>>
> >>>
> >>
> >> i haven't any preferneces, the only thing is - it would be logical
> >> to have every check in common style, so other cases
> >> (r600_blit_copy, r600_blit_swap) should be fixed, nop?
> >
> > Those are void functions so there's nothing to return.
> 
> i mean both of them call r600_nomm_get_vb and both of them
> check if (!dev_priv->blit_vb), not return  value.I mean would be
> logical to check it the same way everytime r600_nomm_get_vb
> gets called.

I'm going to go with Alex's patch, as none of the other callsites return
an error, and your patch doesn't return value from a function which has
a int return type, causing a warning.

Dave.



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