/* packet-tpkt.c * * Routine to check for RFC 1006 TPKT header and to dissect TPKT header * Copyright 2000, Philips Electronics N.V. * Andreas Sikkema * * Routine to dissect RFC 1006 TPKT packet containing OSI TP PDU * Copyright 2001, Martin Thomas * * $Id: packet-tpkt.c,v 1.22 2002/08/28 21:00:36 jmayer Exp $ * * Ethereal - Network traffic analyzer * By Gerald Combs * Copyright 1998 Gerald Combs * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #ifdef HAVE_CONFIG_H # include "config.h" #endif #include #include #include #include #include "packet-tpkt.h" #include "packet-frame.h" #include "prefs.h" /* TPKT header fields */ static int proto_tpkt = -1; static int hf_tpkt_version = -1; static int hf_tpkt_reserved = -1; static int hf_tpkt_length = -1; /* TPKT fields defining a sub tree */ static gint ett_tpkt = -1; /* desegmentation of OSI over TPKT over TCP */ static gboolean tpkt_desegment = TRUE; #define TCP_PORT_TPKT 102 /* find the dissector for OSI TP (aka COTP) */ static dissector_handle_t osi_tp_handle; /* * Check whether this could be a TPKT-encapsulated PDU. * Returns -1 if it's not, and the PDU length from the TPKT header * if it is. * * "min_len" is the minimum length of the PDU; the length field in the * TPKT header must be at least "4+min_len" in order for this to be a * valid TPKT PDU for the protocol in question. */ int is_tpkt(tvbuff_t *tvb, int min_len) { guint16 pkt_len; /* * If TPKT is disabled, don't dissect it, just return -1, meaning * "this isn't TPKT". */ if (!proto_is_protocol_enabled(proto_tpkt)) return -1; /* There should at least be 4 bytes left in the frame */ if (!tvb_bytes_exist(tvb, 0, 4)) return -1; /* there aren't */ /* * The first octet should be 3 and the second one should be 0 * The H.323 implementers guide suggests that this might not * always be the case.... */ if (!(tvb_get_guint8(tvb, 0) == 3 && tvb_get_guint8(tvb, 1) == 0)) return -1; /* they're not */ /* * Get the length from the TPKT header. Make sure it's large * enough. */ pkt_len = tvb_get_ntohs(tvb, 2); if (pkt_len < 4 + min_len) return -1; /* it's not */ /* * Return the length from the header. */ return pkt_len; } /* * Dissect TPKT-encapsulated data in a TCP stream. */ void dissect_tpkt_encap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, gboolean desegment, dissector_handle_t subdissector_handle) { proto_item *ti = NULL; proto_tree *tpkt_tree = NULL; volatile int offset = 0; int length_remaining; int data_len; volatile int length; tvbuff_t *next_tvb; const char *saved_proto; /* * If we're reassembling segmented TPKT PDUs, empty the COL_INFO * column, so subdissectors can append information * without having to worry about emptying the column. * * We use "col_add_str()" because the subdissector * might be appending information to the column, in * which case we'd have to zero the buffer out explicitly * anyway. */ if (tpkt_desegment && check_col(pinfo->cinfo, COL_INFO)) col_add_str(pinfo->cinfo, COL_INFO, ""); while (tvb_reported_length_remaining(tvb, offset) != 0) { /* * Is the first byte of this putative TPKT header * a valid TPKT version number, i.e. 3? */ if (tvb_get_guint8(tvb, offset) != 3) { /* * No, so don't assume this is a TPKT header; * we might be in the middle of TPKT data, * so don't get the length and don't try to * do reassembly. */ if (check_col(pinfo->cinfo, COL_PROTOCOL)) col_set_str(pinfo->cinfo, COL_PROTOCOL, "TPKT"); if (check_col(pinfo->cinfo, COL_INFO)) col_set_str(pinfo->cinfo, COL_INFO, "Continuation"); if (tree) { ti = proto_tree_add_item(tree, proto_tpkt, tvb, offset, -1, FALSE); tpkt_tree = proto_item_add_subtree(ti, ett_tpkt); proto_tree_add_text(tpkt_tree, tvb, offset, -1, "Continuation data"); } return; } length_remaining = tvb_length_remaining(tvb, offset); /* * Can we do reassembly? */ if (desegment && pinfo->can_desegment) { /* * Yes - is the TPKT header split across segment * boundaries? */ if (length_remaining < 4) { /* * Yes. Tell the TCP dissector where * the data for this message starts in * the data it handed us, and how many * more bytes we need, and return. */ pinfo->desegment_offset = offset; pinfo->desegment_len = 4 - length_remaining; return; } } /* * Get the length from the TPKT header. */ data_len = tvb_get_ntohs(tvb, offset + 2); /* * Can we do reassembly? */ if (desegment && pinfo->can_desegment) { /* * Yes - is the payload split across segment * boundaries? */ if (length_remaining < data_len) { /* * Yes. Tell the TCP dissector where * the data for this message starts in * the data it handed us, and how many * more bytes we need, and return. */ pinfo->desegment_offset = offset; pinfo->desegment_len = data_len - length_remaining; return; } } /* * Dissect the TPKT header. * Save and restore "pinfo->current_proto". */ saved_proto = pinfo->current_proto; pinfo->current_proto = "TPKT"; if (check_col(pinfo->cinfo, COL_PROTOCOL)) col_set_str(pinfo->cinfo, COL_PROTOCOL, "TPKT"); /* * Don't add the TPKT header information if we're * reassembling segmented TPKT PDUs or if this * PDU isn't reassembled. * * XXX - the first is so that subdissectors can append * information without getting TPKT stuff in the middle; * why the second? */ if (!tpkt_desegment && !pinfo->fragmented && check_col(pinfo->cinfo, COL_INFO)) { col_add_fstr(pinfo->cinfo, COL_INFO, "TPKT Data length = %u", data_len); } if (tree) { ti = proto_tree_add_item(tree, proto_tpkt, tvb, offset, 4, FALSE); tpkt_tree = proto_item_add_subtree(ti, ett_tpkt); /* Version */ proto_tree_add_item(tpkt_tree, hf_tpkt_version, tvb, offset, 1, FALSE); /* Reserved octet*/ proto_tree_add_item(tpkt_tree, hf_tpkt_reserved, tvb, offset + 1, 1, FALSE); /* Length */ proto_tree_add_uint(tpkt_tree, hf_tpkt_length, tvb, offset + 2, 2, data_len); } pinfo->current_proto = saved_proto; /* Skip the TPKT header. */ offset += 4; data_len -= 4; /* * Construct a tvbuff containing the amount of the payload * we have available. Make its reported length the * amount of data in this TPKT packet. * * XXX - if reassembly isn't enabled. the subdissector * will throw a BoundsError exception, rather than a * ReportedBoundsError exception. We really want * a tvbuff where the length is "length", the reported * length is "plen + 2", and the "if the snapshot length * were infinite" length were the minimum of the * reported length of the tvbuff handed to us and "plen+2", * with a new type of exception thrown if the offset is * within the reported length but beyond that third length, * with that exception getting the "Unreassembled Packet" * error. */ length = length_remaining - 4; if (length > data_len) length = data_len; next_tvb = tvb_new_subset(tvb, offset, length, data_len); /* * Call the subdissector. * * Catch the ReportedBoundsError exception; if this * particular message happens to get a ReportedBoundsError * exception, that doesn't mean that we should stop * dissecting TPKT messages within this frame or chunk * of reassembled data. * * If it gets a BoundsError, we can stop, as there's nothing * more to see, so we just re-throw it. */ TRY { call_dissector(subdissector_handle, next_tvb, pinfo, tree); } CATCH(BoundsError) { RETHROW; } CATCH(ReportedBoundsError) { show_reported_bounds_error(tvb, pinfo, tree); } ENDTRY; /* * Skip the payload. */ offset += length; } } /* * Dissect RFC 1006 TPKT, which wraps a TPKT header around an OSI TP * PDU. */ static void dissect_tpkt(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree) { dissect_tpkt_encap(tvb, pinfo, tree, tpkt_desegment, osi_tp_handle); } void proto_register_tpkt(void) { static hf_register_info hf[] = { { &hf_tpkt_version, { "Version", "tpkt.version", FT_UINT8, BASE_DEC, NULL, 0x0, "", HFILL } }, { &hf_tpkt_reserved, { "Reserved", "tpkt.reserved", FT_UINT8, BASE_DEC, NULL, 0x0, "", HFILL } }, { &hf_tpkt_length, { "Length", "tpkt.length", FT_UINT16, BASE_DEC, NULL, 0x0, "", HFILL } }, }; static gint *ett[] = { &ett_tpkt, }; module_t *tpkt_module; proto_tpkt = proto_register_protocol("TPKT", "TPKT", "tpkt"); proto_register_field_array(proto_tpkt, hf, array_length(hf)); proto_register_subtree_array(ett, array_length(ett)); tpkt_module = prefs_register_protocol(proto_tpkt, NULL); prefs_register_bool_preference(tpkt_module, "desegment", "Desegment all TPKT messages spanning multiple TCP segments", "Whether the TPKT dissector should desegment all messages spanning multiple TCP segments", &tpkt_desegment); } void proto_reg_handoff_tpkt(void) { dissector_handle_t tpkt_handle; osi_tp_handle = find_dissector("ositp"); tpkt_handle = create_dissector_handle(dissect_tpkt, proto_tpkt); dissector_add("tcp.port", TCP_PORT_TPKT, tpkt_handle); }