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

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Date:   Mon, 18 Jan 2021 11:43:50 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>, od@...c.me,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>
Subject: Re: [PATCH 1/3] drm: bridge/panel: Cleanup connector on bridge detach

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@...r.kernel.org> # 4.12+
> Cc: Andrzej Hajda <a.hajda@...sung.com>
> Cc: Neil Armstrong <narmstrong@...libre.com>
> Cc: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
> Cc: Jonas Karlman <jonas@...boo.se>
> Cc: Jernej Skrabec <jernej.skrabec@...l.net>
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  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