[PATCH] drm/bridge: panel: Prevent ERR_PTR Dereference

[Maxime Ripard]

Commit 5ea6b1702781 ("drm/panel: Add prepare_prev_first flag to
drm_panel") introduced an access to the bridge pointer in the
devm_drm_panel_bridge_add_typed() function.

However, due to the unusual ERR_PTR check when getting that pointer, the
pointer access is done even though the pointer might be an error
pointer.

Rework the function for a more traditional design that will return
immediately if it gets an ERR_PTR so that we never access the pointer in
that case.

Fixes: 5ea6b1702781 ("drm/panel: Add prepare_prev_first flag to drm_panel")
Reported-by: kernel test robot <lkp at intel.com>
Reported-by: Dan Carpenter <error27 at gmail.com>
Signed-off-by: Maxime Ripard <maxime at cerno.tech>
---
 drivers/gpu/drm/bridge/panel.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
index 1708098fba6d..e8aae3cdc73d 100644
--- a/drivers/gpu/drm/bridge/panel.c
+++ b/drivers/gpu/drm/bridge/panel.c
@@ -357,15 +357,16 @@ struct drm_bridge *devm_drm_panel_bridge_add_typed(struct device *dev,
 		return ERR_PTR(-ENOMEM);
 
 	bridge = drm_panel_bridge_add_typed(panel, connector_type);
-	if (!IS_ERR(bridge)) {
-		*ptr = bridge;
-		devres_add(dev, ptr);
-	} else {
+	if (IS_ERR(bridge)) {
 		devres_free(ptr);
+		return bridge;
 	}
 
 	bridge->pre_enable_prev_first = panel->prepare_prev_first;
 
+	*ptr = bridge;
+	devres_add(dev, ptr);
+
 	return bridge;
 }
 EXPORT_SYMBOL(devm_drm_panel_bridge_add_typed);
-- 
2.38.1