drm/msm/sde: Fix NULL pointer dereferencing

Plane count maybe passed to sort function as argument without
being checked against NULL value in crtc atomic check and blend
setup mixer. Add check to use plane count as argument only
when it has a valid value.

Change-Id: Ibddd9a630fd5afe55c861975d5fce6985daf1401
Signed-off-by: Shubhashree Dhar <[email protected]>

Author: Shubhashree Dhar

drivers/gpu/drm/msm/sde/sde_crtc.c

@@ -2016,7 +2016,8 @@ static void _sde_crtc_blend_setup_mixer(struct drm_crtc *crtc,
 		cnt++;
 	}
 
-	sort(pstates, cnt, sizeof(pstates[0]), pstate_cmp, NULL);
+	if (cnt)
+		sort(pstates, cnt, sizeof(pstates[0]), pstate_cmp, NULL);
 	_sde_crtc_set_src_split_order(crtc, pstates, cnt);
 
 	if (lm && lm->ops.setup_dim_layer) {
@@ -5278,7 +5279,8 @@ static int sde_crtc_atomic_check(struct drm_crtc *crtc,
 	}
 
 	/* assign mixer stages based on sorted zpos property */
-	sort(pstates, cnt, sizeof(pstates[0]), pstate_cmp, NULL);
+	if (cnt)
+		sort(pstates, cnt, sizeof(pstates[0]), pstate_cmp, NULL);
 
 	rc = _sde_crtc_excl_dim_layer_check(state, pstates, cnt);
 	if (rc)