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

From: Daniel Vetter <daniel@ffwll.ch>
To: Paul Cercueil <paul@crapouillou.net>
Cc: David Airlie <airlied@linux.ie>, Sam Ravnborg <sam@ravnborg.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	od@zcrc.me, dri-devel <dri-devel@lists.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	stable <stable@vger.kernel.org>,
	Andrzej Hajda <a.hajda@samsung.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	Jernej Skrabec <jernej.skrabec@siol.net>
Subject: Re: [PATCH v2 1/3] drm: bridge/panel: Cleanup connector on bridge detach
Date: Wed, 20 Jan 2021 18:38:03 +0100	[thread overview]
Message-ID: <CAKMK7uFHYPvJm46f-LXBO=nERGBBO3i_=YXZyAUi0ZXJFLmXVw@mail.gmail.com> (raw)
In-Reply-To: <4YQ8NQ.HNQ7IMBKVEBV2@crapouillou.net>

On Wed, Jan 20, 2021 at 6:12 PM Paul Cercueil <paul@crapouillou.net> wrote:
>
>
>
> Le mer. 20 janv. 2021 à 17:03, Daniel Vetter <daniel@ffwll.ch> a
> écrit :
> > On Wed, Jan 20, 2021 at 1:35 PM Paul Cercueil <paul@crapouillou.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.

Hm right pure drmm_ doesn't work for panel or bridge since it's
usually a separate driver. But devm_ also doesn't work. I think what
we need here is two-stage: first kmalloc the panel (or bridge, it's
really the same) in the panel/bridge driver load. Then when we bind it
to the drm_device we can tie it into the managed resources with
drmm_add_action_or_reset. Passing the drm_device to the point where we
allocate the panel/bridge doesn't work for these.

I think minimally we need a FIXME here and ack from Laurent on how
this should be solved at least, since panel bridge is used rather
widely.
-Daniel

>
> 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@vger.kernel.org> # 4.12+
> >>  Cc: Andrzej Hajda <a.hajda@samsung.com>
> >>  Cc: Neil Armstrong <narmstrong@baylibre.com>
> >>  Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
> >>  Cc: Jonas Karlman <jonas@kwiboo.se>
> >>  Cc: Jernej Skrabec <jernej.skrabec@siol.net>
> >>  Signed-off-by: Paul Cercueil <paul@crapouillou.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
>
>

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch