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

[Andrzej Hajda <andrzej.hajda@intel.com>]

On 05.05.2023 10:22, 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>

I wonder if it wouldn't be safer to move the check to 
intel_crtc_needs_modeset, up to you.

Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>

Regards
Andrzej

> ---
>   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)) {
>   			ret = i915_sw_fence_await_reservation(&state->commit_ready,
>   							      old_obj->base.resv,
>   							      false, 0,