linux-kernel - Re: [PATCH v2] [next] drm/radeon: Replace one-element array with flexible-array member

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Date:   Tue, 1 Nov 2022 15:41:54 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Alex Deucher <alexdeucher@...il.com>
Cc:     Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] [next] drm/radeon: Replace one-element array with
 flexible-array member

On Tue, Nov 01, 2022 at 06:09:16PM -0400, Alex Deucher wrote:
> On Tue, Nov 1, 2022 at 5:54 PM Kees Cook <keescook@...omium.org> wrote:
> > Does the ROM always only have a single byte there? This seems unlikely
> > given the member "ucFakeEDIDLength" (and the code below).
> 
> I'm not sure.  I'm mostly concerned about this:
>
>             record += fake_edid_record->ucFakeEDIDLength ?
>                       fake_edid_record->ucFakeEDIDLength + 2 :
>                       sizeof(ATOM_FAKE_EDID_PATCH_RECORD);

But this is exactly what the code currently does, as noted in the commit
log: "It's worth mentioning that doing a build before/after this patch
results in no binary output differences.

> Presumably the record should only exist if ucFakeEDIDLength is non 0,
> but I don't know if there are some OEMs out there that just included
> an empty record for some reason.  Maybe the code is wrong today and
> there are some OEMs that include it and the array is already size 0.
> In that case, Paulo's original patches are probably more correct.

Right, but if true, that seems to be a distinctly separate bug fix?

-- 
Kees Cook