Wireshark · Wireshark-dev: Re: [Wireshark-dev] Handling TCP packets reordering

[Jeff Morriss <jeff.morriss.ws@xxxxxxxxx>]

Sake Blok wrote:
> On 4 mei 2011, at 22:48, Jeff Morriss wrote:
> > Sake Blok wrote:
> > > On 4 mei 2011, at 22:11, Jeff Morriss wrote:
> > > > 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.
> > > One case that can cause a problem is when the first segment of a PDU is received out-of-order. Or did your recent work also handle this exception, Jeff?
> > Yep, that's the case rev 36304 fixed.
>
> Unfortunately not, I just constructed a file in which the first segment of the HTTP-response PDU comes after the second segment of that PDU. And dissection still fails as there is not yet a segment in tcpd->fwd->multisegment_pdus for that seq. 

Doh! You're right.  In fact what I fixed was when you actually *see* the 
first packet more than once.