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 02:06:34PM +0300, Ville Syrjälä wrote:
> On Fri, May 05, 2023 at 02:05:27PM +0300, Lisovskiy, Stanislav wrote:
> > On Fri, May 05, 2023 at 02:02:43PM +0300, Ville Syrjälä wrote:
> > > On Fri, May 05, 2023 at 01:58:03PM +0300, Lisovskiy, Stanislav wrote:
> > > > 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.
> > > 
> > > It didn't even finish CI. Please revert.
> > 
> > Swati did run CI and verified that fix helps. I'm _not_ going to revert.
> 
> Fine. I'll do it.

Problem is that you don't even care to explain, why this fix is wrong, but simply
act in authoritarian way, instead of having constructive discussion.
I told that we had verified the fix and that we always do those checks in
many places anyway where we get new_crtc_state.
However there were no even reasons to reject mentioned here. 
I don't really think that bringing personality traits and authoritarian
discussion style is a professional behaviour.
Thanks for cooperation. 

> 
> > 
> > > 
> > > > 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
> > > 
> > > -- 
> > > Ville Syrjälä
> > > Intel
> 
> -- 
> Ville Syrjälä
> Intel