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

[Andrzej Hajda <andrzej.hajda@xxxxxxxxx>]

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 <lkp@xxxxxxxxx>
> Reported-by: Dan Carpenter <error27@xxxxxxxxx>
> Signed-off-by: Maxime Ripard <maxime@xxxxxxxxxx>
Reviewed-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>

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);