Wireshark · Wireshark-users: [Wireshark-users] Parse CFM Type Test signal (TST) without CRC

["Jiunrong" <jiunrong@xxxxxxxxx>]

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 think 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