[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: sta...@vger.kernel.org
Fixes: cf13909aee05 ("drm/fb-helper: Move out modeset config code")
Signed-off-by: Ma Ke <mak...@iscas.ac.cn>
---
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