linux-kernel - Re: [PATCH v2 1/3] drm: bridge/panel: Cleanup connector on bridge detach

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Date:   Wed, 20 Jan 2021 16:25:16 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     David Airlie <airlied@...ux.ie>, Sam Ravnborg <sam@...nborg.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        od@...c.me, dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <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 v2 1/3] drm: bridge/panel: Cleanup connector on bridge
 detach



Le mer. 20 janv. 2021 à 17:03, Daniel Vetter <daniel@...ll.ch> a 
écrit :
> On Wed, Jan 20, 2021 at 1:35 PM Paul Cercueil <paul@...pouillou.net> 
> 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.
> 
> For -fixes this sounds ok, but for -next I think switching to drmm_
> would be much better.

The API would need to change to have access to the drm_device struct, 
though. That would be quite a big patch, there are a few dozens source 
files that use this API already.

Cheers,
-Paul

> 
>>  v2: Cleanup connector only if it was created
>> 
>>  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 | 6 ++++++
>>   1 file changed, 6 insertions(+)
>> 
>>  diff --git a/drivers/gpu/drm/bridge/panel.c 
>> b/drivers/gpu/drm/bridge/panel.c
>>  index 0ddc37551194..df86b0ee0549 100644
>>  --- a/drivers/gpu/drm/bridge/panel.c
>>  +++ b/drivers/gpu/drm/bridge/panel.c
>>  @@ -87,6 +87,12 @@ 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;
>>  +
>>  +       /* Cleanup the connector if we know it was initialized */
>>  +       if (!!panel_bridge->connector.dev)
>>  +               drm_connector_cleanup(connector);
>>   }
>> 
>>   static void panel_bridge_pre_enable(struct drm_bridge *bridge)
>>  --
>>  2.29.2
>> 
> 
> 
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch