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

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Message-ID: <CADnq5_PxjyL9kqdge-SOMkjLk176sPbSxM9Ng+N8f_-zj9NMqw@mail.gmail.com>
Date:   Wed, 2 Nov 2022 12:11:09 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Kees Cook <keescook@...omium.org>
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 1, 2022 at 6:41 PM Kees Cook <keescook@...omium.org> wrote:
>
> 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?

You've convinced me.  Applied.

Thanks,

Alex

>
> --
> Kees Cook