drm/simple_kms_helper: Fix NULL pointer dereference with no active CRTC

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

1 files changed, 3 insertions, 7 deletions

diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c
index 6c327fdbaaee..2d324a5515f9 100644
--- 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_check(struct drm_plane *plane,
         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_check(struct drm_plane *plane,
                 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;