Re: [Intel-gfx] [PATCH] drm/i915: Fix NULL ptr deref by checking new_crtc_state

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Fri, May 05, 2023 at 01:54:14PM +0300, Ville Syrjälä wrote:
> On Fri, May 05, 2023 at 11:22:12AM +0300, Stanislav Lisovskiy wrote:
> > intel_atomic_get_new_crtc_state can return NULL, unless crtc state wasn't
> > obtained previously with intel_atomic_get_crtc_state, so we must check it
> > for NULLness here, just as in many other places, where we can't guarantee
> > that intel_atomic_get_crtc_state was called.
> > We are currently getting NULL ptr deref because of that, so this fix was
> > confirmed to help.
> > 
> > Fixes: 74a75dc90869 ("drm/i915/display: move plane prepare/cleanup to intel_atomic_plane.c")
> > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_atomic_plane.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> > index 9f670dcfe76e..4125ee07a271 100644
> > --- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> > +++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> > @@ -1029,7 +1029,7 @@ intel_prepare_plane_fb(struct drm_plane *_plane,
> >  	int ret;
> >  
> >  	if (old_obj) {
> > -		const struct intel_crtc_state *crtc_state =
> > +		const struct intel_crtc_state *new_crtc_state =
> >  			intel_atomic_get_new_crtc_state(state,
> >  							to_intel_crtc(old_plane_state->hw.crtc));
> >  
> > @@ -1044,7 +1044,7 @@ intel_prepare_plane_fb(struct drm_plane *_plane,
> >  		 * This should only fail upon a hung GPU, in which case we
> >  		 * can safely continue.
> >  		 */
> > -		if (intel_crtc_needs_modeset(crtc_state)) {
> > +		if (new_crtc_state && intel_crtc_needs_modeset(new_crtc_state)) {
> 
> NAK. We need to fix the bug instead of paparing over it.

I had pushed this already. Moreover as I understand we need to check that new_crtc_state
for being NULL anyway. We do check it for being NULL in other places.
But if you have another solution - go for it.

Stan


> 
> >  			ret = i915_sw_fence_await_reservation(&state->commit_ready,
> >  							      old_obj->base.resv,
> >  							      false, 0,
> > -- 
> > 2.37.3
> 
> -- 
> Ville Syrjälä
> Intel