linux-kernel - Re: [PATCH v5 02/15] drm/edid: Break out reading block 0 of the EDID

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Message-ID: <CAD=FV=W07iZigvNaxv1WodhQZVm8hD-1NxTuBuapJYifi6ROng@mail.gmail.com>
Date:   Mon, 4 Oct 2021 09:26:06 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Steev Klimaszewski <steev@...i.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Linus W <linus.walleij@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Maxime Ripard <mripard@...nel.org>,
        Jani Nikula <jani.nikula@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v5 02/15] drm/edid: Break out reading block 0 of the EDID

Hi,

On Mon, Oct 4, 2021 at 8:42 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> > -       if ((edid = kmalloc(EDID_LENGTH, GFP_KERNEL)) == NULL)
> > +       edid = (u8 *)drm_do_get_edid_base_block(get_edid_block, data,
> > +                                               &connector->edid_corrupt,
> > +                                               &connector->null_edid_counter);
> > +       if (IS_ERR_OR_NULL(edid)) {
> > +               if (IS_ERR(edid))
>
> So edid is an error code, not a valid pointer...
>
> > +                       connector_bad_edid(connector, edid, 1);
>
> ... while connector_bad_edid() expects edid to be a valid pointer,
> causing a crash:
>
> Unable to handle kernel NULL pointer dereference at virtual address

Sigh. Thanks for the report and analysis. I guess I don't have any
displays reporting invalid EDIDs to test with. Hopefully this will
help:

https://lore.kernel.org/r/20211004092100.1.Ic90a5ebd44c75db963112be167a03cc96f9fb249@changeid/

-Doug