linux-kernel - Re: [PATCH v1 RFC] video/hdmi: Fix HDMI_VENDOR_INFOFRAME

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Message-ID: <Y+oa6O6+s5UXvOP6@intel.com>
Date:   Mon, 13 Feb 2023 13:11:36 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     dri-devel@...ts.freedesktop.org, Helge Deller <deller@....de>,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hans Verkuil <hans.verkuil@...co.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Bernard Zhao <bernard@...o.com>
Subject: Re: [PATCH v1 RFC] video/hdmi: Fix HDMI_VENDOR_INFOFRAME_SIZE

On Sat, Feb 11, 2023 at 09:43:50PM +0100, Martin Blumenstingl wrote:
> Hello Ville.
> 
> On Mon, Feb 6, 2023 at 10:58 AM Ville Syrjälä
> <ville.syrjala@...ux.intel.com> wrote:
> [...]
> > > Change HDMI_VENDOR_INFOFRAME_SIZE to 6 bytes so
> > > hdmi_vendor_infoframe_pack_only() can properly check the passed buffer
> > > size and avoid an out of bounds write to ptr[8] or ptr[9].
> >
> > The function should return -ENOSPC if the caller didn't
> > provide a big enough buffer.
> Indeed, I'm not sure why I didn't notice when I sent the patch.
> 
> > Are you saying there are drivers that are passing a bogus size here?
> Thankfully not - at least when I checked the last time drivers passed
> a 10 byte - or bigger - buffer.
> My main concern is the HDMI_INFOFRAME_SIZE macro. It's used in various
> drivers like this:
>   u8 buffer[HDMI_INFOFRAME_SIZE(AVI)];
> 
> One could use HDMI_VENDOR_INFOFRAME_SIZE with this as well:
>   u8 buffer[HDMI_INFOFRAME_SIZE(VENDOR)];
> But it would only result in an 8 byte wide buffer.
> Nobody uses it like this yet.

Not sure that would make any sense since a vendor
specific infoframe has no defined size until you
figure out which vendor defined it (via the OUI).

I suppose the current value of 4 is also a bit nonsense
as well then, becasue that is a legal value for the
HDMI 1.4 vendor specific infoframe, but might not be
valid for any other infoframe.

We should perhaps just get rid of HDMI_VENDOR_INFOFRAME_SIZE
entirely.

> 
> Do you see any reason why my patch could cause problems?
> If not then I want to re-send it with an updated description.
> 
> 
> Best regards,
> Martin

-- 
Ville Syrjälä
Intel