drm: Check property/enum name length

Reject requests to add properties/enums with an overly long name.
Previously we would have just silently truncated the string and exposed
it userspace.

v2: drm_property_create() returns a pointer
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180302140300.31110-1-ville.syrjala@linux.intel.comReviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_property.c

@@ -78,6 +78,9 @@ struct drm_property *drm_property_create(struct drm_device *dev, int flags,
 	struct drm_property *property = NULL;
 	int ret;
 
+	if (WARN_ON(strlen(name) >= DRM_PROP_NAME_LEN))
+		return NULL;
+
 	property = kzalloc(sizeof(struct drm_property), GFP_KERNEL);
 	if (!property)
 		return NULL;
@@ -372,6 +375,9 @@ int drm_property_add_enum(struct drm_property *property, int index,
 {
 	struct drm_property_enum *prop_enum;
 
+	if (WARN_ON(strlen(name) >= DRM_PROP_NAME_LEN))
+		return -EINVAL;
+
 	if (!(drm_property_type_is(property, DRM_MODE_PROP_ENUM) ||
 			drm_property_type_is(property, DRM_MODE_PROP_BITMASK)))
 		return -EINVAL;