[FFmpeg-devel] [PATCH 2/3] avformat: reject FFmpeg-style merged side data in raw packets
Michael Niedermayer
michael at niedermayer.cc
Thu Mar 9 13:42:11 EET 2017
On Thu, Mar 09, 2017 at 12:16:09PM +0100, Nicolas George wrote:
> Le nonidi 19 ventôse, an CCXXV, Michael Niedermayer a écrit :
> > This is very basic really but lets elaborate
> > for each side data type T
> > possiblity A
> > nothing uses side data type T
> >
> > possiblity B
> > something uses side data type T
> >
> > Its the same with a codec, either a codec is used in some case or
> > its used in no case.
> >
> > If something is used in no case then it has been eliminated as you
> > describe.
> > If somehing is still used in a case it has not been eliminated
> >
> > If as you describe side data has been eliminated then you could
> > remove side data as a whole from the source code.
> >
> > If you cannot remove side data or a specific side data type from
> > the source code then it has not been eliminated
> >
> > your change removes one way for an attacker to set side data but
> > by the fact that you dont remove any of the side data types its
> > clear you are aware of that every is still in use in some code path.
> >
> > a attacker may need to use a specific container format to set a
> > specific side data type or may depend on a specific demuxer lib or
> > application that allows him to set a side data type.
> >
> > now if you remove every way to set side data for an attacker then
> > you can remove that side data type as a whole from the code.
> > Of course that removes whatever the side data is for.
> >
> > Let me provide a specific example
> > If a container suports changing extradata mid stream it will either
> > be support or not.
> > if any demuxer supports it then you have not eliminated the possiblity
> > for an attacker
> >
> > I hope writing a elaborate reply will not lead to this discussion
> > to shift onto some unrelated detail
>
> You are rehashing a lot of obvious facts, but you do not address the
> important questions.
yes, i was trying to clarify a reply that was apparently unclear and
not understood.
its like
statement -> point out disagreement -> do not understand -> clarify
and
clarify -> "You are rehashing a lot of obvious facts"
Sorry if that felt off topic, it probably was
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Does the universe only have a finite lifespan? No, its going to go on
forever, its just that you wont like living in it. -- Hiranya Peiri
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