[PATCH v4] drm/client: fix null pointer dereference in drm_client_modeset_probe

[Ma Ke]

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

Cc: stable@xxxxxxxxxxxxxxx
Fixes: cf13909aee05 ("drm/fb-helper: Move out modeset config code")
Signed-off-by: Ma Ke <make24@xxxxxxxxxxx>
---
Changes in v4:
- modified patch, set ret and break to handle error rightly.
Changes in v3:
- modified patch as suggestions, returned error directly when failing to 
get modeset->mode.
Changes in v2:
- added the recipient's email address, due to the prolonged absence of a 
response from the recipients.
- added Cc stable.
---
 drivers/gpu/drm/drm_client_modeset.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/drm_client_modeset.c b/drivers/gpu/drm/drm_client_modeset.c
index 31af5cf37a09..cee5eafbfb81 100644
--- a/drivers/gpu/drm/drm_client_modeset.c
+++ b/drivers/gpu/drm/drm_client_modeset.c
@@ -880,6 +880,11 @@ int drm_client_modeset_probe(struct drm_client_dev *client, unsigned int width,
 
 			kfree(modeset->mode);
 			modeset->mode = drm_mode_duplicate(dev, mode);
+			if (!modeset->mode) {
+				ret = -ENOMEM;
+				break;
+			}
+
 			drm_connector_get(connector);
 			modeset->connectors[modeset->num_connectors++] = connector;
 			modeset->x = offset->x;
-- 
2.25.1