f4f3208a00
handed looks as if it contains only a TPKT header (4 bytes long, and those 4 bytes look like a TPKT header according to "is_tpkt()"), call the "dissect TPKT over a TCP stream" routine. If we're doing reassembly, that routine will force a reassembly because the TPKT payload isn't in that segment, and the various heuristic XXX-over-TPKT dissectors will be called again, this time with enough data for them to say whether the TPKT payload is for them or not; if we're not doing reassembly, we'll dissect the TPKT header and then call the "dissect a Q.931 PDU" routine, which will throw an exception because there isn't any payload from which to fetch data (and that's what we want to happen). In the "dissect TPKT over a TCP stream" routine, if reassembly is enabled, do the check to see if we need to do reassembly to get the payload before dissecting the TPKT header, so that we don't dissect the TPKT header and then decide "oops, we need some more data to get the TPKT payload". svn path=/trunk/; revision=4792
338 lines
8.3 KiB
C
338 lines
8.3 KiB
C
/* packet-tpkt.c
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*
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* Routine to check for RFC 1006 TPKT header and to dissect TPKT header
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* Copyright 2000, Philips Electronics N.V.
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* Andreas Sikkema <andreas.sikkema@philips.com>
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*
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* Routine to dissect RFC 1006 TPKT packet containing OSI TP PDU
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* Copyright 2001, Martin Thomas <Martin_A_Thomas@yahoo.com>
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*
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* $Id: packet-tpkt.c,v 1.16 2002/02/23 21:07:48 guy Exp $
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*
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* Ethereal - Network traffic analyzer
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* By Gerald Combs <gerald@ethereal.com>
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* Copyright 1998 Gerald Combs
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*/
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#ifdef HAVE_CONFIG_H
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# include "config.h"
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#endif
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#include <glib.h>
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#include <epan/packet.h>
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#ifdef HAVE_SYS_TYPES_H
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# include <sys/types.h>
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#endif
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#ifdef HAVE_NETINET_IN_H
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# include <netinet/in.h>
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#endif
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#include <stdio.h>
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#include <string.h>
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#include "packet-tpkt.h"
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#include "packet-frame.h"
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#include "prefs.h"
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/* TPKT header fields */
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static int proto_tpkt = -1;
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static int hf_tpkt_version = -1;
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static int hf_tpkt_reserved = -1;
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static int hf_tpkt_length = -1;
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/* TPKT fields defining a sub tree */
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static gint ett_tpkt = -1;
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/* desegmentation of OSI over TPKT over TCP */
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static gboolean tpkt_desegment = TRUE;
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#define TCP_PORT_TPKT 102
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/* find the dissector for OSI TP (aka COTP) */
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static dissector_handle_t osi_tp_handle;
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/*
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* Check whether this could be a TPKT-encapsulated PDU.
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* Returns -1 if it's not, and the PDU length from the TPKT header
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* if it is.
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*/
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int
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is_tpkt(tvbuff_t *tvb)
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{
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/*
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* If TPKT is disabled, don't dissect it, just return -1, meaning
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* "this isn't TPKT".
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*/
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if (!proto_is_protocol_enabled(proto_tpkt))
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return -1;
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/* There should at least be 4 bytes left in the frame */
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if (!tvb_bytes_exist(tvb, 0, 4))
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return -1; /* there aren't */
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/*
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* The first octet should be 3 and the second one should be 0
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* The H.323 implementers guide suggests that this might not
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* always be the case....
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*/
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if (!(tvb_get_guint8(tvb, 0) == 3 && tvb_get_guint8(tvb, 1) == 0))
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return -1; /* They're not */
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/*
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* Return the length from the TPKT header.
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*/
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return tvb_get_ntohs(tvb, 2);
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}
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/*
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* Dissect TPKT-encapsulated data in a TCP stream.
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*/
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void
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dissect_tpkt_encap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
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gboolean desegment, dissector_handle_t subdissector_handle)
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{
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proto_item *ti = NULL;
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proto_tree *tpkt_tree = NULL;
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volatile int offset = 0;
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int length_remaining;
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int data_len;
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volatile int length;
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tvbuff_t *next_tvb;
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const char *saved_proto;
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while (tvb_reported_length_remaining(tvb, offset) != 0) {
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length_remaining = tvb_length_remaining(tvb, offset);
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/*
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* Can we do reassembly?
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*/
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if (desegment && pinfo->can_desegment) {
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/*
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* Yes - is the TPKT header split across segment
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* boundaries?
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*/
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if (length_remaining < 4) {
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/*
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* Yes. Tell the TCP dissector where
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* the data for this message starts in
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* the data it handed us, and how many
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* more bytes we need, and return.
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*/
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pinfo->desegment_offset = offset;
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pinfo->desegment_len = 4 - length_remaining;
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return;
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}
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}
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/*
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* Get the length from the TPKT header.
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*/
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data_len = tvb_get_ntohs(tvb, offset + 2);
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/*
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* Can we do reassembly?
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*/
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if (desegment && pinfo->can_desegment) {
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/*
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* Yes - is the payload split across segment
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* boundaries?
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*/
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if (length_remaining < data_len + 4) {
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/*
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* Yes. Tell the TCP dissector where
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* the data for this message starts in
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* the data it handed us, and how many
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* more bytes we need, and return.
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*/
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pinfo->desegment_offset = offset;
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pinfo->desegment_len =
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(data_len + 4) - length_remaining;
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return;
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}
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}
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/*
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* Dissect the TPKT header.
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* Save and restore "pinfo->current_proto".
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*/
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saved_proto = pinfo->current_proto;
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pinfo->current_proto = "TPKT";
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if (check_col(pinfo->cinfo, COL_PROTOCOL))
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col_set_str(pinfo->cinfo, COL_PROTOCOL, "TPKT");
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if (check_col(pinfo->cinfo, COL_INFO)) {
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col_add_fstr(pinfo->cinfo, COL_INFO,
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"TPKT Data length = %u", data_len);
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}
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if (tree) {
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ti = proto_tree_add_item(tree, proto_tpkt, tvb,
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offset, 4, FALSE);
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tpkt_tree = proto_item_add_subtree(ti, ett_tpkt);
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/* Version */
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proto_tree_add_item(tpkt_tree, hf_tpkt_version, tvb,
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offset, 1, FALSE);
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/* Reserved octet*/
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proto_tree_add_item(tpkt_tree, hf_tpkt_reserved, tvb,
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offset + 1, 1, FALSE);
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/* Length */
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proto_tree_add_uint(tpkt_tree, hf_tpkt_length, tvb,
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offset + 2, 2, data_len);
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}
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pinfo->current_proto = saved_proto;
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/* Skip the TPKT header. */
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offset += 4;
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/*
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* Construct a tvbuff containing the amount of the payload
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* we have available. Make its reported length the
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* amount of data in this TPKT packet.
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*
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* XXX - if reassembly isn't enabled. the subdissector
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* will throw a BoundsError exception, rather than a
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* ReportedBoundsError exception. We really want
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* a tvbuff where the length is "length", the reported
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* length is "plen + 2", and the "if the snapshot length
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* were infinite" length were the minimum of the
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* reported length of the tvbuff handed to us and "plen+2",
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* with a new type of exception thrown if the offset is
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* within the reported length but beyond that third length,
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* with that exception getting the "Unreassembled Packet"
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* error.
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*/
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length = length_remaining - 4;
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if (length > data_len)
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length = data_len;
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next_tvb = tvb_new_subset(tvb, offset, length, data_len);
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/*
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* Call the subdissector.
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*
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* Catch the ReportedBoundsError exception; if this
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* particular message happens to get a ReportedBoundsError
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* exception, that doesn't mean that we should stop
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* dissecting TPKT messages within this frame or chunk
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* of reassembled data.
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*
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* If it gets a BoundsError, we can stop, as there's nothing
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* more to see, so we just re-throw it.
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*/
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TRY {
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call_dissector(subdissector_handle, next_tvb, pinfo,
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tree);
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}
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CATCH(BoundsError) {
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RETHROW;
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}
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CATCH(ReportedBoundsError) {
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show_reported_bounds_error(tvb, pinfo, tree);
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}
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ENDTRY;
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/*
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* Skip the payload.
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*/
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offset += length;
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}
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}
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/*
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* Dissect RFC 1006 TPKT, which wraps a TPKT header around an OSI TP
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* PDU.
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*/
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static void
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dissect_tpkt(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
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{
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dissect_tpkt_encap(tvb, pinfo, tree, tpkt_desegment, osi_tp_handle);
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}
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void
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proto_register_tpkt(void)
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{
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static hf_register_info hf[] =
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{
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{
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&hf_tpkt_version,
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{
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"Version",
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"tpkt.version",
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FT_UINT8,
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BASE_DEC,
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NULL,
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0x0,
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"", HFILL
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}
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},
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{
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&hf_tpkt_reserved,
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{
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"Reserved",
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"tpkt.reserved",
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FT_UINT8,
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BASE_DEC,
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NULL,
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0x0,
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"", HFILL
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}
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},
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{
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&hf_tpkt_length,
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{
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"Length",
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"tpkt.length",
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FT_UINT16,
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BASE_DEC,
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NULL,
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0x0,
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"", HFILL
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}
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},
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};
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static gint *ett[] =
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{
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&ett_tpkt,
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};
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module_t *tpkt_module;
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proto_tpkt = proto_register_protocol("TPKT", "TPKT", "tpkt");
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proto_register_field_array(proto_tpkt, hf, array_length(hf));
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proto_register_subtree_array(ett, array_length(ett));
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tpkt_module = prefs_register_protocol(proto_tpkt, NULL);
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prefs_register_bool_preference(tpkt_module, "desegment",
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"Desegment all TPKT messages spanning multiple TCP segments",
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"Whether the TPKT dissector should desegment all messages spanning multiple TCP segments",
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&tpkt_desegment);
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}
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void
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proto_reg_handoff_tpkt(void)
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{
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dissector_handle_t tpkt_handle;
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osi_tp_handle = find_dissector("ositp");
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tpkt_handle = create_dissector_handle(dissect_tpkt, proto_tpkt);
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dissector_add("tcp.port", TCP_PORT_TPKT, tpkt_handle);
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}
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