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Date:   Mon, 18 Jan 2021 13:52:54 +0100
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Paul Cercueil <paul@crapouillou.net>
Cc:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org, od@zcrc.me,
        dri-devel@lists.freedesktop.org, Sam Ravnborg <sam@ravnborg.org>
Subject: Re: [PATCH 2/3] drm/ingenic: Register devm action to cleanup encoders
Message-ID: <YAWEpjU6BmeK8deo@phenom.ffwll.local>
Mail-Followup-To: Paul Cercueil <paul@crapouillou.net>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        David Airlie <airlied@linux.ie>, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org, od@zcrc.me, dri-devel@lists.freedesktop.org,
        Sam Ravnborg <sam@ravnborg.org>
References: <20210117112646.98353-1-paul@crapouillou.net>
 <20210117112646.98353-3-paul@crapouillou.net>
 <YAVYUzR9+ic5lEjE@pendragon.ideasonboard.com>
 <1BO4NQ.1RZAXLMVC01T@crapouillou.net>
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On Mon, Jan 18, 2021 at 11:37:49AM +0000, Paul Cercueil wrote:
> Hi Laurent,
> 
> Le lun. 18 janv. 2021 ? 11:43, Laurent Pinchart
> <laurent.pinchart@ideasonboard.com> a ?crit :
> > Hi Paul,
> > 
> > Thank you for the patch.
> > 
> > On Sun, Jan 17, 2021 at 11:26:45AM +0000, Paul Cercueil wrote:
> > >  Since the encoders have been devm-allocated, they will be freed way
> > >  before drm_mode_config_cleanup() is called. To avoid use-after-free
> > >  conditions, we then must ensure that drm_encoder_cleanup() is called
> > >  before the encoders are freed.
> > 
> > How about allocating the encoder with drmm_encoder_alloc() instead ?
> 
> That would work, but it is not yet in drm-misc-fixes :(

Well I think then we should only fix this in drm-misc-next. Adding more
broken usage of devm_ isn't really a good idea.

If you want this in -fixes, then I think hand-roll it. But devm_ for drm
objects really is the wrong fix.
-Daniel

> 
> -Paul
> 
> > >  Fixes: c369cb27c267 ("drm/ingenic: Support multiple panels/bridges")
> > >  Cc: <stable@vger.kernel.org> # 5.8+
> > >  Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > >  ---
> > >   drivers/gpu/drm/ingenic/ingenic-drm-drv.c | 10 ++++++++++
> > >   1 file changed, 10 insertions(+)
> > > 
> > >  diff --git a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> > > b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> > >  index 368bfef8b340..d23a3292a0e0 100644
> > >  --- a/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> > >  +++ b/drivers/gpu/drm/ingenic/ingenic-drm-drv.c
> > >  @@ -803,6 +803,11 @@ static void __maybe_unused
> > > ingenic_drm_release_rmem(void *d)
> > >   	of_reserved_mem_device_release(d);
> > >   }
> > > 
> > >  +static void ingenic_drm_encoder_cleanup(void *encoder)
> > >  +{
> > >  +	drm_encoder_cleanup(encoder);
> > >  +}
> > >  +
> > >   static int ingenic_drm_bind(struct device *dev, bool
> > > has_components)
> > >   {
> > >   	struct platform_device *pdev = to_platform_device(dev);
> > >  @@ -1011,6 +1016,11 @@ static int ingenic_drm_bind(struct device
> > > *dev, bool has_components)
> > >   			return ret;
> > >   		}
> > > 
> > >  +		ret = devm_add_action_or_reset(dev, ingenic_drm_encoder_cleanup,
> > >  +					       encoder);
> > >  +		if (ret)
> > >  +			return ret;
> > >  +
> > >   		ret = drm_bridge_attach(encoder, bridge, NULL, 0);
> > >   		if (ret) {
> > >   			dev_err(dev, "Unable to attach bridge\n");
> > 
> > --
> > Regards,
> > 
> > Laurent Pinchart
> 
> 

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