Wireshark-bugs: [Wireshark-bugs] [Bug 11286] New: Parse CFM Type Test signal (TST) without CRC
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From: bugzilla-daemon@xxxxxxxxxxxxx
Date: Thu, 18 Jun 2015 08:46:37 +0000
Bug ID 11286
Summary Parse CFM Type Test signal (TST) without CRC
Product Wireshark
Version 1.12.5
Hardware x86
OS Windows XP
Status UNCONFIRMED
Severity Minor
Priority Low
Component Dissection engine (libwireshark)
Assignee bugzilla-admin@wireshark.org
Reporter jiunrong@gmail.com 

Created attachment 13674 [details]
4 kind of cfm TST packet from test device

Build Information:
Paste the COMPLETE build information from "Help->About Wireshark", "wireshark
-v", or "tshark -v".
--
Hi advancer:

I found [Malformed Packet: CFM] when I receive CFM Type Test signal (TST)
without CRC32, but it is ok with CRC32.


I try to find what happen, so I download the source code.
I am new guide in wireshark, if I make mistake, please don’t laugh me.

in file: epan/dissectors/packet-cfm.c
Due to 

                tlv_data_offset += (cfm_tlv_length-5);

I assumption next line maybe need -1

                tlv_data_offset += cfm_tlv_length;  //maybe it need -1


if (cfm_tlv_length > 0) {

        switch (tlv_tst_test_pattern_type) {

        case 0:

        case 2:

                proto_tree_add_item(cfm_tlv_tree, hf_tlv_tst_test_pattern,

                                tvb, tlv_data_offset, cfm_tlv_length-1,
ENC_NA);

                tlv_data_offset += cfm_tlv_length;  //maybe it need -1

                break;

        case 1:

        case 3:

                proto_tree_add_item(cfm_tlv_tree, hf_tlv_tst_test_pattern,

                        tvb, tlv_data_offset, cfm_tlv_length-5, ENC_NA);

                tlv_data_offset += (cfm_tlv_length-5);

                proto_tree_add_item(cfm_tlv_tree, hf_tlv_tst_CRC32,

                                tvb, tlv_data_offset, 4, ENC_NA);

                tlv_data_offset += 4;

                break;

        }

}       

>From JustinKu

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