[PATCH 1/1] drm/mediatek: Fix access violation in mtk_drm_crtc_dma_dev_get

[Stuart Lee <stuart.lee@mediatek.com>]

Add error handling to check NULL input in
mtk_drm_crtc_dma_dev_get function.

While display path is not configured correctly, none of crtc is
established. So the caller of mtk_drm_crtc_dma_dev_get may pass
input parameter *crtc as NULL, Which may cause coredump when
we try to get the container of NULL pointer.

Fixes: cb1d6bcca542 ("drm/mediatek: Add dma dev get function")
Signed-off-by: Stuart Lee <stuart.lee@mediatek.com>
Cc: stable@vger.kernel.org
---
 drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
index c277b9fae950..047c9a31d306 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
@@ -921,7 +921,14 @@ static int mtk_drm_crtc_init_comp_planes(struct drm_device *drm_dev,
 
 struct device *mtk_drm_crtc_dma_dev_get(struct drm_crtc *crtc)
 {
-	struct mtk_drm_crtc *mtk_crtc = to_mtk_crtc(crtc);
+	struct mtk_drm_crtc *mtk_crtc = NULL;
+
+	if (!crtc)
+		return NULL;
+
+	mtk_crtc = to_mtk_crtc(crtc);
+	if (!mtk_crtc)
+		return NULL;
 
 	return mtk_crtc->dma_dev;
 }
-- 
2.18.0