Wireshark-bugs: [Wireshark-bugs] [Bug 6098] New: Wrong decoding of RLC/MAC EGPRS Packet Downlink

Date: Wed, 6 Jul 2011 04:24:55 -0700 (PDT)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=6098

           Summary: Wrong decoding of RLC/MAC EGPRS Packet Downlink
                    Ack/Nack (3GGP TS 44.060)
           Product: Wireshark
           Version: 1.7.x (Experimental)
          Platform: x86
        OS/Version: Windows XP
            Status: NEW
          Severity: Major
          Priority: Low
         Component: Wireshark
        AssignedTo: bugzilla-admin@xxxxxxxxxxxxx
        ReportedBy: lhaessler@xxxxxxxxxxxxxxxxxx


Build Information:
Version 1.7.0-TEST_BUILD_LHA-01 (SVN Rev Unknown from unknown)

Copyright 1998-2011 Gerald Combs <gerald@xxxxxxxxxxxxx> and contributors.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled (32-bit) with GTK+ 2.22.1, with GLib 2.26.1, with WinPcap (version
unknown), with libz 1.2.5, without POSIX capabilities, without libpcre, with
SMI
0.4.8, with c-ares 1.7.1, with Lua 5.1, without Python, with GnuTLS 2.10.3,
with
Gcrypt 1.4.6, with MIT Kerberos, with GeoIP, with PortAudio V19-devel (built
Jul
 6 2011), with AirPcap.

Running on Windows XP Service Pack 3, build 2600, with WinPcap version 4.1.2
(packet.dll version 4.1.0.2001), based on libpcap version 1.0 branch 1_0_rel0b
(20091008), GnuTLS 2.10.3, Gcrypt 1.4.6, without AirPcap.

Built using Microsoft Visual C++ 9.0 build 21022

--
An issue has been observed in gsm_rlcmac_uplink dissector for EGPRS Packet
Downlink Ack/Nack (RLC/MAC control block) decoding.

The content of EGPRS Packet Downlink Ack/Nack is decoded as a Packet Downlink
Ack/Nack due a wrong setting in csnStreamDissector.



When loading the attached capture file (Wireshark_uplink_gprs_log.pcap) with
wireshark 1.6.0, the following error is observed when trying to decode the
uplink RLC/MAC control block = 40 22 eb fe f8 21 ec 01 0b 2b 2b 2b 2b 2b 2b 2b
2b 2b 2b 2b 2b 2b 2b 2b:
[Dissector bug, protocol GSM RLC MAC: tvbuff.c:1739: failed assertion
"DISSECTOR_ASSERT_NOT_REACHED"]

I've also attached the patch that fixes the issue, see file
Egprs_Packet_Downlink_AckNack.patch.

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