From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Date: Thu, 22 Feb 2018 08:09:19 +0200
Subject: drm/simple_kms_helper: Fix NULL pointer dereference with no active
 CRTC
Git-commit: 4751cf733a1170876dd5ac46f225f5a25f59a67f
Patch-mainline: v4.17-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

It is possible that drm_simple_kms_plane_atomic_check called
with no CRTC set, e.g. when user-space application sets CRTC_ID/FB_ID
to 0 before doing any actual drawing. This leads to NULL pointer
dereference because in this case new CRTC state is NULL and must be
checked before accessing.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1519279759-7803-1-git-send-email-andr2000@gmail.com

Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/drm_simple_kms_helper.c |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

--- a/drivers/gpu/drm/drm_simple_kms_helper.c
+++ b/drivers/gpu/drm/drm_simple_kms_helper.c
@@ -112,12 +112,6 @@ static int drm_simple_kms_plane_atomic_c
 	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
 	crtc_state = drm_atomic_get_new_crtc_state(plane_state->state,
 						   &pipe->crtc);
-	if (!crtc_state->enable)
-		return 0; /* nothing to check when disabling or disabled */
-
-	if (crtc_state->enable)
-		drm_mode_get_hv_timing(&crtc_state->mode,
-				       &clip.x2, &clip.y2);
 
 	ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
 						  &clip,
@@ -128,7 +122,9 @@ static int drm_simple_kms_plane_atomic_c
 		return ret;
 
 	if (!plane_state->visible)
-		return -EINVAL;
+		return 0;
+
+	drm_mode_get_hv_timing(&crtc_state->mode, &clip.x2, &clip.y2);
 
 	if (!pipe->funcs || !pipe->funcs->check)
 		return 0;