[PATCH] drm/qxl: Add check for drm_cvt_mode

[Chen Ni]

Add check for the return value of drm_cvt_mode() and return the error if
it fails in order to avoid NULL pointer dereference.

Fixes: 1b043677d4be ("drm/qxl: add qxl_add_mode helper function")
Signed-off-by: Chen Ni <nic...@iscas.ac.cn>
---
 drivers/gpu/drm/qxl/qxl_display.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/qxl/qxl_display.c 
b/drivers/gpu/drm/qxl/qxl_display.c
index c6d35c33d5d6..86a5dea710c0 100644
--- a/drivers/gpu/drm/qxl/qxl_display.c
+++ b/drivers/gpu/drm/qxl/qxl_display.c
@@ -236,6 +236,9 @@ static int qxl_add_mode(struct drm_connector *connector,
                return 0;
 
        mode = drm_cvt_mode(dev, width, height, 60, false, false, false);
+       if (!mode)
+               return 0;
+
        if (preferred)
                mode->type |= DRM_MODE_TYPE_PREFERRED;
        mode->hdisplay = width;
-- 
2.25.1