Re: [RFC 04/44] drm/i915: Fix null pointer dereference in error capture

Daniel Vetter
2014-07-07T18:49:36Z

On Tue, Jul 01, 2014 at 08:12:11AM +0100, Chris Wilson wrote:
> On Mon, Jun 30, 2014 at 02:40:05PM -0700, Jesse Barnes wrote:
> > On Thu, 26 Jun 2014 18:23:55 +0100
> > John.C.Harrison@Intel.com wrote:
> >
> > > From: John Harrison <John.C.Harrison@Intel.com>
> > >
> > > The i915_gem_record_rings() code was unconditionally querying and saving state
> > > for the batch_obj of a request structure. This is not necessarily set. Thus a
> > > null pointer dereference can occur.
> > > ---
> > > drivers/gpu/drm/i915/i915_gpu_error.c | 13 +++++++------
> > > 1 file changed, 7 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> > > index 87ec60e..0738f21 100644
> > > --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> > > +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> > > @@ -902,12 +902,13 @@ static void i915_gem_record_rings(struct drm_device *dev,
> > > * as the simplest method to avoid being overwritten
> > > * by userspace.
> > > */
> > > - error->ring[i].batchbuffer =
> > > - i915_error_object_create(dev_priv,
> > > - request->batch_obj,
> > > - request->ctx ?
> > > - request->ctx->vm :
> > > - &dev_priv->gtt.base);
> > > + if(request->batch_obj)
> > > + error->ring[i].batchbuffer =
> > > + i915_error_object_create(dev_priv,
> > > + request->batch_obj,
> > > + request->ctx ?
> > > + request->ctx->vm :
> > > + &dev_priv->gtt.base);
> > >
> > > if (HAS_BROKEN_CS_TLB(dev_priv->dev) &&
> > > ring->scratch.obj)
> >
> > Reviewed-by: Jesse Barnes <jbarnes@virtuosugeek.org>
>
> Nah, put the NULL check into the macro. i915_error_object_create() was
> originally written as a no-op on NULL pointers for cleanliness, we may
> as well do the check centrally and remove the extras we have grown.

Also the usual broken record from your maintainer: How does this blow up
and can we please have a testcase for it? Oscar provided a basic error
state check test, so the infrastructure for a new subtest is now there. I
hope ;-)
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch