[PATCH v2] drm/qxl: fix NULL dereference in qxl_add_mode

[Aleksandr Burakov <a.burakov@xxxxxxxxxxxx>]

Return value of a function 'drm_cvt_mode' is dereferenced without
checking for NULL but drm_mode_create() in drm_cvt_mode() may
return NULL value in case of memory allocation error.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 1b043677d4be ("drm/qxl: add qxl_add_mode helper function")
Signed-off-by: Aleksandr Burakov <a.burakov@xxxxxxxxxxxx>
---
v2: case with false value of 'preferred' is now taken into account
 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 a152a7c6db21..d6dece7a0ed2 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