linux-kernel - RE: [PATCH] drm/of: free the iterator object on failure

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Date:   Mon, 12 Jul 2021 16:03:55 +0000
From:   Biju Das <biju.das.jz@...renesas.com>
To:     Steven Price <steven.price@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Pavel Machek <pavel@...x.de>
Subject: RE: [PATCH] drm/of: free the iterator object on failure

+ Pavel

> -----Original Message-----
> From: Steven Price <steven.price@....com>
> Sent: 12 July 2021 16:58
> To: Daniel Vetter <daniel@...ll.ch>; David Airlie <airlied@...ux.ie>;
> Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>; Maxime Ripard
> <mripard@...nel.org>; Thomas Zimmermann <tzimmermann@...e.de>
> Cc: Steven Price <steven.price@....com>; dri-devel@...ts.freedesktop.org;
> linux-kernel@...r.kernel.org; Biju Das <biju.das.jz@...renesas.com>;
> Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Subject: [PATCH] drm/of: free the iterator object on failure
> 
> When bailing out due to the sanity check the iterator value needs to be
> freed because the early return prevents for_each_child_of_node() from
> doing the dereference itself.
> 
> Fixes: 4ee48cc5586b ("drm: of: Fix double-free bug")
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  drivers/gpu/drm/drm_of.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> Daniel's email[1] made me take a look at this function and it appears that
> for_each_child_of_node()'s interface had caused a bad bug fix due to the
> hidden reference counting in the iterator.
> 
> [1]
> https://jpn01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ker
> nel.org%2Fr%2FYOxQ5TbkNrqCGBDJ%2540phenom.ffwll.local&amp;data=04%7C01%7Cb
> iju.das.jz%40bp.renesas.com%7Cb0570b66e03a43fb8fa008d9454dddaa%7C53d82571d
> a1947e49cb4625a166a4a2a%7C0%7C0%7C637617023006562683%7CUnknown%7CTWFpbGZsb
> 3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C10
> 00&amp;sdata=cQICPYJzmgNkFsNw1wMH9Or73rohnCCGH1DrUg3hvhw%3D&amp;reserved=0
> 
> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c index
> 197c57477344..997b8827fed2 100644
> --- a/drivers/gpu/drm/drm_of.c
> +++ b/drivers/gpu/drm/drm_of.c
> @@ -331,8 +331,10 @@ static int drm_of_lvds_get_remote_pixels_type(
>  		 * configurations by passing the endpoints explicitly to
>  		 * drm_of_lvds_get_dual_link_pixel_order().
>  		 */
> -		if (!current_pt || pixels_type != current_pt)
> +		if (!current_pt || pixels_type != current_pt) {
> +			of_node_put(endpoint);
>  			return -EINVAL;
> +		}
>  	}
> 
>  	return pixels_type;
> --
> 2.20.1