Re: Handling TCP packets reordering

[Jeff Morriss <jeff.morriss.ws () gmail com>]

Max Dmitrichenko wrote:
> Hi!
>
> I'm continue to write dissector for an encrypted protocol. Everything
> works fine until I receive an out-of-order TCP segment, i.e. previous
> was lost.
> Since I'm trying to decrypt it, I fail with it and break the whole
> decryption context. Is there any way to:
> 1) Detect that this packet is out of order in given conversation?
> 2) Ask the TCP dissector to feed this packet later again when all
> previous segments will be retransmitted?

I would think desegment_tcp() should be able to handle this by not 
calling your dissector for an out-of-order segment: it should be able to 
only call your dissector once it has a completely reassembled 
(desegmented) PDU.  Looking through the code, it's not immediately 
obvious to me what the problem is.

A bug report with a sample capture (with your dissector, I guess) would 
be helpful.  Hmm, I guess I might be able to build such a capture file 
from an existing one (if I find the time).

Or to start if you can find what line number the TCP dissector is on 
when you get the out-of-order packet, that might shed some light on it.

> And as far as I understand, there can be a situation when packet is
> duplicated. This should be handled too. How?

That should, too, already be handled.  (Only recently did it start 
working when the first segment of a PDU was retransmitted.)
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