Re: [PATCH 1/3] drm: bridge/panel: Cleanup connector on bridge detach

[Laurent Pinchart]

Hi Paul,

Thank you for the patch.

On Sun, Jan 17, 2021 at 11:26:44AM +0000, Paul Cercueil wrote:
> If we don't call drm_connector_cleanup() manually in
> panel_bridge_detach(), the connector will be cleaned up with the other
> DRM objects in the call to drm_mode_config_cleanup(). However, since our
> drm_connector is devm-allocated, by the time drm_mode_config_cleanup()
> will be called, our connector will be long gone. Therefore, the
> connector must be cleaned up when the bridge is detached to avoid
> use-after-free conditions.
> 
> Fixes: 13dfc0540a57 ("drm/bridge: Refactor out the panel wrapper from the lvds-encoder bridge.")
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.12+
> Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> Cc: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
> Cc: Laurent Pinchart <Laurent.pinchart@xxxxxxxxxxxxxxxx>
> Cc: Jonas Karlman <jonas@xxxxxxxxx>
> Cc: Jernej Skrabec <jernej.skrabec@xxxxxxxx>
> Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/bridge/panel.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
> index 0ddc37551194..975d65c14c9c 100644
> --- a/drivers/gpu/drm/bridge/panel.c
> +++ b/drivers/gpu/drm/bridge/panel.c
> @@ -87,6 +87,10 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
>  
>  static void panel_bridge_detach(struct drm_bridge *bridge)
>  {
> +	struct panel_bridge *panel_bridge = drm_bridge_to_panel_bridge(bridge);
> +	struct drm_connector *connector = &panel_bridge->connector;
> +
> +	drm_connector_cleanup(connector);

The panel bridge driver only creates the connector if the
DRM_BRIDGE_ATTACH_NO_CONNECTOR flag wasn't set in panel_bridge_attach().
We shouldn't clean up the connector unconditionally.

A better fix would be to stop using the devm_* API, but that's more
complicated.

>  }
>  
>  static void panel_bridge_pre_enable(struct drm_bridge *bridge)

-- 
Regards,

Laurent Pinchart