[PATCH] drm/kmb: fix dereference before NULL check in kmb_plane_atomic_update()

[Zeng Jingxiang]

From: Zeng Jingxiang <linuszeng at tencent.com>

The "plane" pointer was access before checking if it was NULL.

The drm_atomic_get_old_plane_state() function will dereference
the pointer "plane".
345	struct drm_plane_state *old_plane_state =
		drm_atomic_get_old_plane_state(state, plane);
346	struct drm_plane_state *new_plane_state =
		drm_atomic_get_new_plane_state(state, plane);

A NULL check for "plane" indicates that it may be NULL
363	if (!plane || !new_plane_state || !old_plane_state)

Fixes: 977697e20b3d ("drm/atomic: Pass the full state to planes atomic disable and update")
Fixes: 37418bf14c13 ("drm: Use state helper instead of the plane state pointer")
Signed-off-by: Zeng Jingxiang <linuszeng at tencent.com>
---
 drivers/gpu/drm/kmb/kmb_plane.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/kmb/kmb_plane.c b/drivers/gpu/drm/kmb/kmb_plane.c
index 2735b8eb3537..d2bc998b65ce 100644
--- a/drivers/gpu/drm/kmb/kmb_plane.c
+++ b/drivers/gpu/drm/kmb/kmb_plane.c
@@ -342,10 +342,7 @@ static void kmb_plane_set_alpha(struct kmb_drm_private *kmb,
 static void kmb_plane_atomic_update(struct drm_plane *plane,
 				    struct drm_atomic_state *state)
 {
-	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state,
-										 plane);
-	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(state,
-										 plane);
+	struct drm_plane_state *old_plane_state, *new_plane_state;
 	struct drm_framebuffer *fb;
 	struct kmb_drm_private *kmb;
 	unsigned int width;
@@ -360,7 +357,13 @@ static void kmb_plane_atomic_update(struct drm_plane *plane,
 	static dma_addr_t addr[MAX_SUB_PLANES];
 	struct disp_cfg *init_disp_cfg;
 
-	if (!plane || !new_plane_state || !old_plane_state)
+	if (!plane)
+		return;
+
+	old_plane_state = drm_atomic_get_old_plane_state(state, plane);
+	new_plane_state = drm_atomic_get_new_plane_state(state, plane);
+
+	if (!new_plane_state || !old_plane_state)
 		return;
 
 	fb = new_plane_state->fb;
-- 
2.27.0