[FFmpeg-devel] [PATCH] oops I broke rdt.c

Michael Niedermayer michaelni
Wed Dec 17 18:51:06 CET 2008

On Wed, Dec 17, 2008 at 12:24:43PM -0500, Ronald S. Bultje wrote:
> Hi,
> On Wed, Dec 17, 2008 at 12:04 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > this sounds fragile.
> > st->id is 2 different things in one file (rmdec.c)
> No it isn't (?). In rdt.c, it's one, in rmdec.c, it's the other.
> I think you're confused because a subset of the code in rmdec.c can be
> called from within rdt.c.

change that subset and you have an exploitable bug

> However, that is not the code that uses
> st->id (just do a quick grep, you'll see that use of the value in
> st->id is restricted to sync(), that's also true for
> rm->current_stream (which can take the value of st->id). So, st->id in
> rmdec.c is only used within sync(), which is and will never be used
> for RTSP. sync() syncs on the RM packet header, which preceedes the RM
> packet data. In RDT, a RDT/RTSP packet header preceedes the RM packet
> data instead, there is no RM packet header.

> For RM streams, st->id is the RM packet header ID of each stream.

that part makes sense, the "id" is the id ...

> For RDT/RTSP streams, st->id is the index of the stream within the set
> of identical content streams.

that is a misuse of the variable IMHO

> The two are exclusive, they both precede RM packet data parsing, but
> for different kind of streams that both happen to encapsulate RM
> packet data.
> Again, I don't mind getting rid of st->id, but I want to make it clear
> that this part of the code is theoretically and practically not
> exploitable. If you want I can take the shared code out of rmdec.c
> into a new file so that a grep for st->id in that new file is
> negative, but that seems kind of overkill to me.

> (I guess I'll just remove use of st->id in rdt.c to make you happy. :-).)

yes, this in indeed will make me happy

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
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