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

[Andrzej Hajda]

On 02.01.2023 13:01, Maxime Ripard wrote:

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 <l...@intel.com>
Reported-by: Dan Carpenter <erro...@gmail.com>
Signed-off-by: Maxime Ripard <max...@cerno.tech>

Reviewed-by: Andrzej Hajda <andrzej.ha...@intel.com>

Regards
Andrzej

---
  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);