New dissector for GSM L2RCOP (3GPP TS 27.002)
This is a dissector for the GSM "Layer 2 Relay Character Oriented Protocol" as used in non-transparent CSD (Circuit Switched Data) calls in GSM and UMTS cellular networks.
This commit is contained in:
Alexis La Goutte
parent
f64e8f0796
commit
ae38e9b092
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@ -1191,6 +1191,7 @@ set(DISSECTOR_SRC
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${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_cbsp.c
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${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_gsup.c
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${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_ipa.c
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${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_l2rcop.c
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${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_osmux.c
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${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_r_uus1.c
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${CMAKE_CURRENT_SOURCE_DIR}/packet-gsm_rlcmac.c
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@ -0,0 +1,167 @@
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/* packet-gsm_l2rcop.c
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* Routines for GSM L2RCOP (3GPP TS 27.002) dissection
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* (C) 2023 Harald Welte <laforge@osmocom.org>
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*
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* Wireshark - Network traffic analyzer
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* By Gerald Combs <gerald@wireshark.org>
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* Copyright 1998
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*
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* SPDX-License-Identifier: GPL-2.0-or-later
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*/
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#include "config.h"
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#include <epan/packet.h>
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#include <epan/prefs.h>
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#include <epan/xdlc.h>
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#include <epan/reassemble.h>
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#include <epan/conversation.h>
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void proto_register_gsm_l2rcop(void);
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static int proto_l2rcop = -1;
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static int hf_l2rcop_sa = -1;
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static int hf_l2rcop_sb = -1;
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static int hf_l2rcop_x = -1;
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static int hf_l2rcop_addr = -1;
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static int hf_l2rcop_break = -1;
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static int hf_l2rcop_break_ack = -1;
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static int ett_l2rcop = -1;
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static const value_string addr_vals[] = {
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{ 31, "last status change, remainder empty" },
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{ 30, "last status change, remainder full of characters" },
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{ 29, "destructive break signal, remainder empty" },
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{ 28, "destructive break acknowledge, remainder empty" },
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{ 27, "extended address in ext octet" },
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{ 0, NULL }
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};
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static void
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add_characters(proto_tree *tree, packet_info *pinfo, tvbuff_t *tvb, guint offset, guint len)
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{
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tvbuff_t *next_tvb = tvb_new_subset_length(tvb, offset, len);
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call_data_dissector(next_tvb, pinfo, tree);
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}
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/* Dissect a L2RCOP message as described in 3GPP TS 27.002 */
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static int
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dissect_l2rcop(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
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{
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int reported_len = tvb_reported_length(tvb);
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guint cur;
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/* we currently support RLP v0 + v1 (first octet is always status octet) */
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for (cur = 0; cur < (guint)reported_len; ) {
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guint8 oct = tvb_get_guint8(tvb, cur);
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guint8 addr = oct & 0x1f;
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proto_tree *l2rcop_tree;
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proto_item *ti;
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const gchar *addr_str = val_to_str(addr, addr_vals, "%u characters");
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ti = proto_tree_add_protocol_format(tree, proto_l2rcop, tvb, 0, reported_len,
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"GSM L2RCOP Chunk Status=0x%02x (Addr: %s)", oct, addr_str);
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l2rcop_tree = proto_item_add_subtree(ti, ett_l2rcop);
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proto_tree_add_item(l2rcop_tree, hf_l2rcop_sa, tvb, cur, 1, ENC_BIG_ENDIAN);
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proto_tree_add_item(l2rcop_tree, hf_l2rcop_sb, tvb, cur, 1, ENC_BIG_ENDIAN);
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proto_tree_add_item(l2rcop_tree, hf_l2rcop_x, tvb, cur, 1, ENC_BIG_ENDIAN);
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proto_tree_add_item(l2rcop_tree, hf_l2rcop_addr, tvb, cur, 1, ENC_BIG_ENDIAN);
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switch (addr) {
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case 31: /* last status change, remainder empty */
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return reported_len;
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case 30: /* last status change, remainder full of characters */
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add_characters(l2rcop_tree, pinfo, tvb, cur+1, reported_len-cur-1);
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return reported_len;
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case 29: /* destructive break signal, remainder empty */
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proto_tree_add_item(l2rcop_tree, hf_l2rcop_break, tvb, cur, 1, ENC_BIG_ENDIAN);
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return reported_len;
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case 28: /* destructive break acknowledge, remainder empty */
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proto_tree_add_item(l2rcop_tree, hf_l2rcop_break_ack, tvb, cur, 1, ENC_BIG_ENDIAN);
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return reported_len;
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case 27: /* extended address in ext octet */
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cur++;
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addr = tvb_get_guint8(tvb, cur) & 0x3f;
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/* This "cannot happen"; let's abort processing right now. */
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if (addr == 0)
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return reported_len;
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proto_tree_add_uint(l2rcop_tree, hf_l2rcop_addr, tvb, cur, 1, addr);
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add_characters(l2rcop_tree, pinfo, tvb, cur+1, addr);
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cur += 1 + addr;
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break;
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case 0:
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/* This "cannot happen"; let's abort processing right now. */
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return reported_len;
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default:
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/* This "cannot happen"; let's abort processing right now. */
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if (addr == 0)
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return reported_len;
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add_characters(l2rcop_tree, pinfo, tvb, cur+1, addr);
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cur += 1 + addr;
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break;
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}
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}
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return reported_len;
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}
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static const true_false_string x_vals = {
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"flow control ACTIVE", "flow control inactive"
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};
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static const true_false_string sab_vals = {
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"OFF", "ON"
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};
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void
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proto_register_gsm_l2rcop(void)
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{
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static hf_register_info hf[] = {
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{ &hf_l2rcop_sa,
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{ "SA", "gsm_l2rcop.sa", FT_BOOLEAN, 8, TFS(&sab_vals), 0x80,
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NULL, HFILL }},
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{ &hf_l2rcop_sb,
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{ "SB", "gsm_l2rcop.sb", FT_BOOLEAN, 8, TFS(&sab_vals), 0x40,
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NULL, HFILL }},
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{ &hf_l2rcop_x,
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{ "X", "gsm_l2rcop.x", FT_BOOLEAN, 8, TFS(&x_vals), 0x20,
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NULL, HFILL }},
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{ &hf_l2rcop_addr,
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{ "Address", "gsm_l2rcop.addr", FT_UINT8, BASE_DEC|BASE_SPECIAL_VALS, VALS(addr_vals), 0x1f,
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NULL, HFILL }},
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{ &hf_l2rcop_break,
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{ "Break", "gsm_l2rcop.break", FT_UINT8, BASE_DEC, NULL, 0x00,
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NULL, HFILL }},
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{ &hf_l2rcop_break_ack,
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{ "Break Ack", "gsm_l2rcop.break_ack", FT_UINT8, BASE_DEC, NULL, 0x00,
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NULL, HFILL }},
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};
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static gint *ett[] = {
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&ett_l2rcop,
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};
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proto_l2rcop = proto_register_protocol("GSM L2R Character Oriented Protocol (L2RCOP)", "GSM-L2RCOP",
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"gsm_l2rcop");
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proto_register_field_array(proto_l2rcop, hf, array_length(hf));
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proto_register_subtree_array(ett, array_length(ett));
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register_dissector("gsm_l2rcop", dissect_l2rcop, proto_l2rcop);
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}
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/*
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* Editor modelines - https://www.wireshark.org/tools/modelines.html
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*
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* Local variables:
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* c-basic-offset: 4
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* tab-width: 8
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* indent-tabs-mode: nil
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* End:
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*
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* vi: set shiftwidth=4 tabstop=8 expandtab:
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* :indentSize=4:tabSize=8:noTabs=true:
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*/
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@ -40,6 +40,9 @@ static int ett_gsmrlp_xid = -1;
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static expert_field ei_gsmrlp_fcs_bad = EI_INIT;
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static dissector_handle_t l2rcop_handle;
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static gboolean decode_as_l2rcop = true;
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/* 3GPP TS 24.002 Section 5.2.1 */
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enum rlp_ftype {
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RLP_FT_U,
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@ -247,7 +250,10 @@ dissect_gsmrlp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _
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/* dispatch user data */
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data_len = reported_len - 2 /* header */ - 3 /* FCS */;
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next_tvb = tvb_new_subset_length(tvb, 2, data_len);
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call_data_dissector(next_tvb, pinfo, rlp_tree);
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if (decode_as_l2rcop && l2rcop_handle)
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call_dissector(l2rcop_handle, next_tvb, pinfo, rlp_tree);
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else
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call_data_dissector(next_tvb, pinfo, rlp_tree);
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}
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/* FCS is always the last 3 bytes of the message */
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@ -317,6 +323,15 @@ proto_register_gsmrlp(void)
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expert_register_field_array(expert_gsmrlp, ei, array_length(ei));
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register_dissector("gsm_rlp", dissect_gsmrlp, proto_gsmrlp);
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rlp_module = prefs_register_protocol(proto_gsmrlp, NULL);
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prefs_register_bool_preference(rlp_module, "decode_as_l2rcop", "Decode payload as L2RCOP",
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NULL, &decode_as_l2rcop);
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}
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void
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proto_reg_handoff_gsmrlp(void)
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{
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l2rcop_handle = find_dissector_add_dependency("gsm_l2rcop", proto_gsmrlp);
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}
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/*
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