drm: crtc: integer overflow in drm_property_create_blob()

commit 9ac0934b upstream.

The size here comes from the user via the ioctl, it is a number between
1-u32max so the addition here could overflow on 32 bit systems.

Fixes: f453ba04 ('DRM: add mode setting support')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Dave Airlie <airlied@gmail.com>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@huawei.com>

drivers/gpu/drm/drm_crtc.c

@@ -2945,7 +2945,7 @@ static struct drm_property_blob *drm_property_create_blob(struct drm_device *dev
 	struct drm_property_blob *blob;
 	int ret;
 
-	if (!length || !data)
+	if (!length || length > ULONG_MAX - sizeof(struct drm_property_blob) || !data)
 		return NULL;
 
 	blob = kzalloc(sizeof(struct drm_property_blob)+length, GFP_KERNEL);