[PATCH v2] drm/sti: avoid potential dereference of error pointers

[Ma Ke]

The return value of drm_atomic_get_crtc_state() needs to be
checked. To avoid use of error pointer 'crtc_state' in case
of the failure.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: dd86dc2f9ae1 ("drm/sti: implement atomic_check for the planes")
Signed-off-by: Ma Ke <make24@xxxxxxxxxxx>
---
Changes in v2:
- modified the Fixes tag according to suggestions;
- added necessary blank line.
---
 drivers/gpu/drm/sti/sti_cursor.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/sti/sti_cursor.c b/drivers/gpu/drm/sti/sti_cursor.c
index db0a1eb53532..c59fcb4dca32 100644
--- a/drivers/gpu/drm/sti/sti_cursor.c
+++ b/drivers/gpu/drm/sti/sti_cursor.c
@@ -200,6 +200,9 @@ static int sti_cursor_atomic_check(struct drm_plane *drm_plane,
 		return 0;
 
 	crtc_state = drm_atomic_get_crtc_state(state, crtc);
+	if (IS_ERR(crtc_state))
+		return PTR_ERR(crtc_state);
+
 	mode = &crtc_state->mode;
 	dst_x = new_plane_state->crtc_x;
 	dst_y = new_plane_state->crtc_y;
-- 
2.25.1