Re: GTP sequence number equal to zero problem

["POZUELO Gloria (BCS/PSD)" <gloria.pozuelo () bics com>]

Hello again,

I’ve received an email in which I’m notified that there’s a buildbot failure on Ubuntu regarding to this fix. Do I have 
to do something else concerning to this fix or do you take over this problem? I’m developing for Windows platform, so I 
don’t have the needed platform to debug that compilation error.

Regards.

From: wireshark-dev-bounces () wireshark org [mailto:wireshark-dev-bounces () wireshark org] On Behalf Of POZUELO 
Gloria (BCS/PSD)
Sent: Tuesday 3 November 2015 16:33
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] GTP sequence number equal to zero problem

Thank you Pascal. I’ll fix the bug then ☺

Regards.

From: wireshark-dev-bounces () wireshark org<mailto:wireshark-dev-bounces () wireshark org> 
[mailto:wireshark-dev-bounces () wireshark org] On Behalf Of Pascal Quantin
Sent: Tuesday 3 November 2015 16:27
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] GTP sequence number equal to zero problem



2015-11-03 16:13 GMT+01:00 POZUELO Gloria (BCS/PSD) <gloria.pozuelo () bics com<mailto:gloria.pozuelo () bics com>>:
Hi all,

I’m developing an extension for the GTPv1 dissector and while I was debugging I’ve encountered something that it seems 
to me a bit confusing. In the dissect_gtp_common function from the packet-gtp.c source, there is a section that makes 
the matching between requests and responses. The thing is that I have a pcap in which I have a create PDP context 
request with sequence number equal to 0, then when in the code asks if the message has sequence number, it never enters 
in that part because, I guess, that 0 is equal than NULL.

If (seq_no) {
                /* matching is done */
}

I don’t know If this is a little bug or maybe the sequence number can’t be equal to 0. Can someone help me?

Thanks!

Regards.


Hi Gloria,
at first glance this seems to be a bug. Per 3GPP 29.060 chapter 9.3.1.1<http://9.3.1.1>:
9.3.1.1 Usage of Sequence Number
The sending GGSN and SRNC shall use 0 for the value of the Sequence Number of the first G-PDU in a tunnel, only during 
the PDP context activation, and shall increment the Sequence Number for each following G-PDU. The value shall wrap to 
zero after 65535.
The receiving GGSN and SRNC shall set the content of a counter to zero, only during the PDP context activation. When 
the receiving GGSN and SRNC receives a valid G-PDU, it shall increment this counter by one. This counter shall wrap to 
zero after 65535. It defines the "Expected Sequence Number".

Could you please fill a bug on https://bugs.wireshark.org and even better, upload a fix on Gerrit (see 
https://www.wireshark.org/docs/wsdg_html_chunked/ChSrcContribute.html for details) ? Presumably we should have a 
booleab telling whether a sequence number was retrieved or not and test it (instead of seq_no being different from 0).
Regards,
Pascal.

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