packet-tpkt.c

   1 /* packet-tpkt.c
   2  *
   3  * Routine to check for RFC 1006 TPKT header and to dissect TPKT header
   4  * Copyright 2000, Philips Electronics N.V.
   5  * Andreas Sikkema <andreas.sikkema@philips.com>
   6  *
   7  * Routine to dissect RFC 1006 TPKT packet containing OSI TP PDU
   8  * Copyright 2001, Martin Thomas <Martin_A_Thomas@yahoo.com>
   9  *
  10  * $Id: packet-tpkt.c,v 1.22 2002/08/28 21:00:36 jmayer Exp $
  11  *
  12  * Ethereal - Network traffic analyzer
  13  * By Gerald Combs <gerald@ethereal.com>
  14  * Copyright 1998 Gerald Combs
  15  *
  16  * This program is free software; you can redistribute it and/or
  17  * modify it under the terms of the GNU General Public License
  18  * as published by the Free Software Foundation; either version 2
  19  * of the License, or (at your option) any later version.
  20  *
  21  * This program is distributed in the hope that it will be useful,
  22  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  23  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  24  * GNU General Public License for more details.
  25  *
  26  * You should have received a copy of the GNU General Public License
  27  * along with this program; if not, write to the Free Software
  28  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  29  */
  30
  31 #ifdef HAVE_CONFIG_H
  32 # include "config.h"
  33 #endif
  34
  35 #include <glib.h>
  36 #include <epan/packet.h>
  37
  38 #include <stdio.h>
  39 #include <string.h>
  40
  41 #include "packet-tpkt.h"
  42 #include "packet-frame.h"
  43 #include "prefs.h"
  44
  45 /* TPKT header fields             */
  46 static int proto_tpkt          = -1;
  47 static int hf_tpkt_version     = -1;
  48 static int hf_tpkt_reserved    = -1;
  49 static int hf_tpkt_length      = -1;
  50
  51 /* TPKT fields defining a sub tree */
  52 static gint ett_tpkt           = -1;
  53
  54 /* desegmentation of OSI over TPKT over TCP */
  55 static gboolean tpkt_desegment = TRUE;
  56
  57 #define TCP_PORT_TPKT   102
  58
  59 /* find the dissector for OSI TP (aka COTP) */
  60 static dissector_handle_t osi_tp_handle;
  61
  62 /*
  63  * Check whether this could be a TPKT-encapsulated PDU.
  64  * Returns -1 if it's not, and the PDU length from the TPKT header
  65  * if it is.
  66  *
  67  * "min_len" is the minimum length of the PDU; the length field in the
  68  * TPKT header must be at least "4+min_len" in order for this to be a
  69  * valid TPKT PDU for the protocol in question.
  70  */
  71 int
  72 is_tpkt(tvbuff_t *tvb, int min_len)
  73 {
  74         guint16 pkt_len;
  75
  76         /*
  77          * If TPKT is disabled, don't dissect it, just return -1, meaning
  78          * "this isn't TPKT".
  79          */
  80         if (!proto_is_protocol_enabled(proto_tpkt))
  81                 return -1;
  82
  83         /* There should at least be 4 bytes left in the frame */
  84         if (!tvb_bytes_exist(tvb, 0, 4))
  85                 return -1;      /* there aren't */
  86
  87         /*
  88          * The first octet should be 3 and the second one should be 0
  89          * The H.323 implementers guide suggests that this might not
  90          * always be the case....
  91          */
  92         if (!(tvb_get_guint8(tvb, 0) == 3 && tvb_get_guint8(tvb, 1) == 0))
  93                 return -1;      /* they're not */
  94
  95         /*
  96          * Get the length from the TPKT header.  Make sure it's large
  97          * enough.
  98          */
  99         pkt_len = tvb_get_ntohs(tvb, 2);
 100         if (pkt_len < 4 + min_len)
 101                 return -1;      /* it's not */
 102
 103         /*
 104          * Return the length from the header.
 105          */
 106         return pkt_len;
 107 }
 108
 109 /*
 110  * Dissect TPKT-encapsulated data in a TCP stream.
 111  */
 112 void
 113 dissect_tpkt_encap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
 114     gboolean desegment, dissector_handle_t subdissector_handle)
 115 {
 116         proto_item *ti = NULL;
 117         proto_tree *tpkt_tree = NULL;
 118         volatile int offset = 0;
 119         int length_remaining;
 120         int data_len;
 121         volatile int length;
 122         tvbuff_t *next_tvb;
 123         const char *saved_proto;
 124
 125         /*
 126          * If we're reassembling segmented TPKT PDUs, empty the COL_INFO
 127          * column, so subdissectors can append information
 128          * without having to worry about emptying the column.
 129          *
 130          * We use "col_add_str()" because the subdissector
 131          * might be appending information to the column, in
 132          * which case we'd have to zero the buffer out explicitly
 133          * anyway.
 134          */
 135         if (tpkt_desegment && check_col(pinfo->cinfo, COL_INFO))
 136                 col_add_str(pinfo->cinfo, COL_INFO, "");
 137
 138         while (tvb_reported_length_remaining(tvb, offset) != 0) {
 139                 /*
 140                  * Is the first byte of this putative TPKT header
 141                  * a valid TPKT version number, i.e. 3?
 142                  */
 143                 if (tvb_get_guint8(tvb, offset) != 3) {
 144                         /*
 145                          * No, so don't assume this is a TPKT header;
 146                          * we might be in the middle of TPKT data,
 147                          * so don't get the length and don't try to
 148                          * do reassembly.
 149                          */
 150                         if (check_col(pinfo->cinfo, COL_PROTOCOL))
 151                                 col_set_str(pinfo->cinfo, COL_PROTOCOL, "TPKT");
 152                         if (check_col(pinfo->cinfo, COL_INFO))
 153                                 col_set_str(pinfo->cinfo, COL_INFO, "Continuation");
 154                         if (tree) {
 155                                 ti = proto_tree_add_item(tree, proto_tpkt, tvb,
 156                                     offset, -1, FALSE);
 157                                 tpkt_tree = proto_item_add_subtree(ti, ett_tpkt);
 158
 159                                 proto_tree_add_text(tpkt_tree, tvb, offset, -1,
 160                                     "Continuation data");
 161                         }
 162                         return;
 163                 }
 164
 165                 length_remaining = tvb_length_remaining(tvb, offset);
 166
 167                 /*
 168                  * Can we do reassembly?
 169                  */
 170                 if (desegment && pinfo->can_desegment) {
 171                         /*
 172                          * Yes - is the TPKT header split across segment
 173                          * boundaries?
 174                          */
 175                         if (length_remaining < 4) {
 176                                 /*
 177                                  * Yes.  Tell the TCP dissector where
 178                                  * the data for this message starts in
 179                                  * the data it handed us, and how many
 180                                  * more bytes we need, and return.
 181                                  */
 182                                 pinfo->desegment_offset = offset;
 183                                 pinfo->desegment_len = 4 - length_remaining;
 184                                 return;
 185                         }
 186                 }
 187
 188                 /*
 189                  * Get the length from the TPKT header.
 190                  */
 191                 data_len = tvb_get_ntohs(tvb, offset + 2);
 192
 193                 /*
 194                  * Can we do reassembly?
 195                  */
 196                 if (desegment && pinfo->can_desegment) {
 197                         /*
 198                          * Yes - is the payload split across segment
 199                          * boundaries?
 200                          */
 201                         if (length_remaining < data_len) {
 202                                 /*
 203                                  * Yes.  Tell the TCP dissector where
 204                                  * the data for this message starts in
 205                                  * the data it handed us, and how many
 206                                  * more bytes we need, and return.
 207                                  */
 208                                 pinfo->desegment_offset = offset;
 209                                 pinfo->desegment_len =
 210                                     data_len - length_remaining;
 211                                 return;
 212                         }
 213                 }
 214
 215                 /*
 216                  * Dissect the TPKT header.
 217                  * Save and restore "pinfo->current_proto".
 218                  */
 219                 saved_proto = pinfo->current_proto;
 220                 pinfo->current_proto = "TPKT";
 221
 222                 if (check_col(pinfo->cinfo, COL_PROTOCOL))
 223                         col_set_str(pinfo->cinfo, COL_PROTOCOL, "TPKT");
 224                 /*
 225                  * Don't add the TPKT header information if we're
 226                  * reassembling segmented TPKT PDUs or if this
 227                  * PDU isn't reassembled.
 228                  *
 229                  * XXX - the first is so that subdissectors can append
 230                  * information without getting TPKT stuff in the middle;
 231                  * why the second?
 232                  */
 233                 if (!tpkt_desegment && !pinfo->fragmented
 234                     && check_col(pinfo->cinfo, COL_INFO)) {
 235                         col_add_fstr(pinfo->cinfo, COL_INFO,
 236                             "TPKT Data length = %u", data_len);
 237                 }
 238
 239                 if (tree) {
 240                         ti = proto_tree_add_item(tree, proto_tpkt, tvb,
 241                             offset, 4, FALSE);
 242                         tpkt_tree = proto_item_add_subtree(ti, ett_tpkt);
 243
 244                         /* Version */
 245                         proto_tree_add_item(tpkt_tree, hf_tpkt_version, tvb,
 246                             offset, 1, FALSE);
 247
 248                         /* Reserved octet*/
 249                         proto_tree_add_item(tpkt_tree, hf_tpkt_reserved, tvb,
 250                             offset + 1, 1, FALSE);
 251
 252                         /* Length */
 253                         proto_tree_add_uint(tpkt_tree, hf_tpkt_length, tvb,
 254                             offset + 2, 2, data_len);
 255                 }
 256                 pinfo->current_proto = saved_proto;
 257
 258                 /* Skip the TPKT header. */
 259                 offset += 4;
 260                 data_len -= 4;
 261
 262                 /*
 263                  * Construct a tvbuff containing the amount of the payload
 264                  * we have available.  Make its reported length the
 265                  * amount of data in this TPKT packet.
 266                  *
 267                  * XXX - if reassembly isn't enabled. the subdissector
 268                  * will throw a BoundsError exception, rather than a
 269                  * ReportedBoundsError exception.  We really want
 270                  * a tvbuff where the length is "length", the reported
 271                  * length is "plen + 2", and the "if the snapshot length
 272                  * were infinite" length were the minimum of the
 273                  * reported length of the tvbuff handed to us and "plen+2",
 274                  * with a new type of exception thrown if the offset is
 275                  * within the reported length but beyond that third length,
 276                  * with that exception getting the "Unreassembled Packet"
 277                  * error.
 278                  */
 279                 length = length_remaining - 4;
 280                 if (length > data_len)
 281                         length = data_len;
 282                 next_tvb = tvb_new_subset(tvb, offset, length, data_len);
 283
 284                 /*
 285                  * Call the subdissector.
 286                  *
 287                  * Catch the ReportedBoundsError exception; if this
 288                  * particular message happens to get a ReportedBoundsError
 289                  * exception, that doesn't mean that we should stop
 290                  * dissecting TPKT messages within this frame or chunk
 291                  * of reassembled data.
 292                  *
 293                  * If it gets a BoundsError, we can stop, as there's nothing
 294                  * more to see, so we just re-throw it.
 295                  */
 296                 TRY {
 297                         call_dissector(subdissector_handle, next_tvb, pinfo,
 298                             tree);
 299                 }
 300                 CATCH(BoundsError) {
 301                         RETHROW;
 302                 }
 303                 CATCH(ReportedBoundsError) {
 304                         show_reported_bounds_error(tvb, pinfo, tree);
 305                 }
 306                 ENDTRY;
 307
 308                 /*
 309                  * Skip the payload.
 310                  */
 311                 offset += length;
 312         }
 313 }
 314
 315 /*
 316  * Dissect RFC 1006 TPKT, which wraps a TPKT header around an OSI TP
 317  * PDU.
 318  */
 319 static void
 320 dissect_tpkt(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 321 {
 322         dissect_tpkt_encap(tvb, pinfo, tree, tpkt_desegment, osi_tp_handle);
 323 }
 324
 325 void
 326 proto_register_tpkt(void)
 327 {
 328         static hf_register_info hf[] =
 329         {
 330                 {
 331                         &hf_tpkt_version,
 332                         {
 333                                 "Version",
 334                                 "tpkt.version",
 335                                 FT_UINT8,
 336                                 BASE_DEC,
 337                                 NULL,
 338                                 0x0,
 339                                 "", HFILL
 340                         }
 341                 },
 342                 {
 343                         &hf_tpkt_reserved,
 344                         {
 345                                 "Reserved",
 346                                 "tpkt.reserved",
 347                                 FT_UINT8,
 348                                 BASE_DEC,
 349                                 NULL,
 350                                 0x0,
 351                                 "", HFILL
 352                         }
 353                 },
 354                 {
 355                         &hf_tpkt_length,
 356                         {
 357                                 "Length",
 358                                 "tpkt.length",
 359                                 FT_UINT16,
 360                                 BASE_DEC,
 361                                 NULL,
 362                                 0x0,
 363                                 "", HFILL
 364                         }
 365                 },
 366         };
 367
 368         static gint *ett[] =
 369         {
 370                 &ett_tpkt,
 371         };
 372         module_t *tpkt_module;
 373
 374         proto_tpkt = proto_register_protocol("TPKT", "TPKT", "tpkt");
 375         proto_register_field_array(proto_tpkt, hf, array_length(hf));
 376         proto_register_subtree_array(ett, array_length(ett));
 377
 378         tpkt_module = prefs_register_protocol(proto_tpkt, NULL);
 379         prefs_register_bool_preference(tpkt_module, "desegment",
 380             "Desegment all TPKT messages spanning multiple TCP segments",
 381             "Whether the TPKT dissector should desegment all messages spanning multiple TCP segments",
 382             &tpkt_desegment);
 383 }
 384
 385 void
 386 proto_reg_handoff_tpkt(void)
 387 {
 388         dissector_handle_t tpkt_handle;
 389
 390         osi_tp_handle = find_dissector("ositp");
 391         tpkt_handle = create_dissector_handle(dissect_tpkt, proto_tpkt);
 392         dissector_add("tcp.port", TCP_PORT_TPKT, tpkt_handle);
 393 }