linux-kernel - Re: [PATCH][next] drm/kmb: fix array out-of-bounds writes to kmb->plane

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Message-ID: <20201113145557.GB3647624@ravnborg.org>
Date:   Fri, 13 Nov 2020 15:55:57 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Colin King <colin.king@...onical.com>
Cc:     Anitha Chrisanthus <anitha.chrisanthus@...el.com>,
        Edmund Dea <edmund.j.dea@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] drm/kmb: fix array out-of-bounds writes to
 kmb->plane_status[]

Hi Colin.

On Fri, Nov 13, 2020 at 12:01:21PM +0000, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Writes to elements in the kmb->plane_status array in function
> kmb_plane_atomic_disable are overrunning the array when plane_id is
> more than 1 because currently the array is KMB_MAX_PLANES elements
> in size and this is currently #defined as 1.  Fix this by defining
> KMB_MAX_PLANES to 4.

I fail to follow you here.
In kmb_plane_init() only one plane is allocated - with id set to 0.
So for now only one plane is allocated thus kmb_plane_atomic_disable()
is only called for this plane.

With your change we will start allocating four planes, something that is
not tested.

Do I miss something?

	Sam