linux-kernel - Re: [PATCH 2/3] drm/ingenic: Register devm action to cleanup encoders

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Date:   Mon, 18 Jan 2021 11:37:49 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org, od@...c.me,
        dri-devel@...ts.freedesktop.org, Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH 2/3] drm/ingenic: Register devm action to cleanup encoders

Hi Laurent,

Le lun. 18 janv. 2021 à 11:43, Laurent Pinchart 
<laurent.pinchart@...asonboard.com> a écrit :
> 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 :(

-Paul

>>  Fixes: c369cb27c267 ("drm/ingenic: Support multiple panels/bridges")
>>  Cc: <stable@...r.kernel.org> # 5.8+
>>  Signed-off-by: Paul Cercueil <paul@...pouillou.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