[PATCH] drm/qxl: fix null pointer dereference in qxl_add_mode

[PATCH] drm/qxl: fix null pointer dereference in qxl_add_mode

[Ma Ke]

In qxl_add_mode(), the return value of drm_cvt_mode() is assigned to mode,
which will lead to a possible NULL pointer dereference on failure of
drm_cvt_mode(). Add a check to avoid npd.

Signed-off-by: Ma Ke <make24@iscas.ac.cn>
---
 drivers/gpu/drm/qxl/qxl_display.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
index c6d35c33d5d6..7c11383cd3c4 100644
--- a/drivers/gpu/drm/qxl/qxl_display.c
+++ b/drivers/gpu/drm/qxl/qxl_display.c
@@ -236,6 +236,8 @@ 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 -ENOMEM;
 	if (preferred)
 		mode->type |= DRM_MODE_TYPE_PREFERRED;
 	mode->hdisplay = width;
-- 
2.25.1

Re: [PATCH] drm/qxl: fix null pointer dereference in qxl_add_mode

[Markus Elfring]

> In qxl_add_mode(), the return value of drm_cvt_mode() is assigned to mode,
> which will lead to a possible NULL pointer dereference on failure of
> drm_cvt_mode(). Add a check to avoid npd.

1. Can a wording approach (like the following) be a better change description?

   A null pointer is stored in the local variable “mode” after a call
   of the function “drm_cvt_mode” failed. This pointer was used
   in subsequent statements where an undesirable dereference
   will be performed then.
   Thus add a corresponding return value check.


2. Would you like to add any tags (like “Fixes” and “Cc”) accordingly?


3. How do you think about to append parentheses to the function name
   in the summary phrase?


Regards,
Markus