aboutsummaryrefslogtreecommitdiffstats
path: root/packet-gre.c
blob: 1b15b48a38de3e9529c39f0e504ad7217cfa078b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
/* packet-gre.c
 * Routines for the Generic Routing Encapsulation (GRE) protocol
 * Brad Robel-Forrest <brad.robel-forrest@watchguard.com>
 *
 * $Id: packet-gre.c,v 1.54 2003/06/10 05:38:52 guy Exp $
 *
 * Ethereal - Network traffic analyzer
 * By Gerald Combs <gerald@ethereal.com>
 * 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 <glib.h>
#include <epan/packet.h>
#include "packet-wccp.h"
#include "in_cksum.h"
#include "etypes.h"
#include "greproto.h"
#include "ipproto.h"
#include "llcsaps.h"

/*
 * See RFC 1701 "Generic Routing Encapsulation (GRE)", RFC 1702
 * "Generic Routing Encapsulation over IPv4 networks", RFC 2637
 * "Point-to-Point Tunneling Protocol (PPTP)", RFC 2784 "Generic
 * Routing Encapsulation (GRE)", and RFC 2890 "Key and Sequence
 * Number Extensions to GRE".
 */

static int proto_gre = -1;
static int hf_gre_proto = -1;

static gint ett_gre = -1;
static gint ett_gre_flags = -1;
static gint ett_gre_wccp2_redirect_header = -1;

static dissector_table_t gre_dissector_table;
static dissector_handle_t data_handle;

/* bit positions for flags in header */
#define GH_B_C		0x8000
#define GH_B_R		0x4000
#define GH_B_K		0x2000
#define GH_B_S		0x1000
#define GH_B_s		0x0800
#define GH_B_RECUR	0x0700
#define GH_P_A		0x0080	/* only in special PPTPized GRE header */
#define GH_P_FLAGS	0x0078	/* only in special PPTPized GRE header */
#define GH_R_FLAGS	0x00F8
#define GH_B_VER	0x0007

static void add_flags_and_ver(proto_tree *, guint16, tvbuff_t *, int, int);
static void dissect_gre_wccp2_redirect_header(tvbuff_t *, int, proto_tree *);

static const value_string typevals[] = {
	{ ETHERTYPE_PPP,       "PPP" },
	{ ETHERTYPE_IP,        "IP" },
	{ SAP_OSINL5,          "OSI"},
	{ GRE_WCCP,            "WCCP"},
	{ ETHERTYPE_IPX,       "IPX"},
	{ ETHERTYPE_ETHBRIDGE, "Transparent Ethernet bridging" },
	{ GRE_FR,              "Frame Relay"},
	{ 0,                   NULL }
};

static void
dissect_gre(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
  int		offset = 0;
  guint16	flags_and_ver;
  guint16	type;
  gboolean	is_ppp = FALSE;
  gboolean	is_wccp2 = FALSE;
  guint 	len = 4;
  proto_item 	*ti;
  proto_tree 	*gre_tree = NULL;
  guint16	sre_af;
  guint8	sre_length;
  tvbuff_t	*next_tvb;

  flags_and_ver = tvb_get_ntohs(tvb, offset);
  type = tvb_get_ntohs(tvb, offset + sizeof(flags_and_ver));

  if (check_col(pinfo->cinfo, COL_PROTOCOL))
    col_set_str(pinfo->cinfo, COL_PROTOCOL, "GRE");

  if (check_col(pinfo->cinfo, COL_INFO)) {
    col_add_fstr(pinfo->cinfo, COL_INFO, "Encapsulated %s",
		 val_to_str(type, typevals, "0x%04X (unknown)"));
  }

  if (flags_and_ver & GH_B_C || flags_and_ver & GH_B_R)
    len += 4;
  if (flags_and_ver & GH_B_K)
    len += 4;
  if (flags_and_ver & GH_B_S)
    len += 4;
  switch (type) {

  case ETHERTYPE_PPP:
    if (flags_and_ver & GH_P_A)
      len += 4;
    is_ppp = TRUE;
    break;

  case GRE_WCCP:
    /* WCCP2 puts an extra 4 octets into the header, but uses the same
       encapsulation type; if it looks as if the first octet of the packet
       isn't the beginning of an IPv4 header, assume it's WCCP2. */
    if ((tvb_get_guint8(tvb, offset + sizeof(flags_and_ver) + sizeof(type)) & 0xF0) != 0x40) {
      len += 4;
      is_wccp2 = TRUE;
    }
    break;
  }

  if (tree) {
    ti = proto_tree_add_protocol_format(tree, proto_gre, tvb, offset, len,
      "Generic Routing Encapsulation (%s)",
      val_to_str(type, typevals, "0x%04X - unknown"));
    gre_tree = proto_item_add_subtree(ti, ett_gre);
    add_flags_and_ver(gre_tree, flags_and_ver, tvb, offset, is_ppp);
  }
  offset += sizeof(flags_and_ver);

  if (tree) {
    proto_tree_add_uint(gre_tree, hf_gre_proto, tvb, offset, sizeof(type), type);
  }
  offset += sizeof(type);

  if (flags_and_ver & GH_B_C || flags_and_ver & GH_B_R) {
    if (tree) {
      guint length, reported_length;
      vec_t cksum_vec[1];
      guint16 cksum, computed_cksum;

      cksum = tvb_get_ntohs(tvb, offset);
      length = tvb_length(tvb);
      reported_length = tvb_reported_length(tvb);
      if ((flags_and_ver & GH_B_C) && !pinfo->fragmented
		&& length >= reported_length) {
	/* The Checksum Present bit is set, and the packet isn't part of a
	   fragmented datagram and isn't truncated, so we can checksum it. */

	cksum_vec[0].ptr = tvb_get_ptr(tvb, 0, reported_length);
	cksum_vec[0].len = reported_length;
	computed_cksum = in_cksum(cksum_vec, 1);
	if (computed_cksum == 0) {
	  proto_tree_add_text(gre_tree, tvb, offset, 2,
			"Checksum: 0x%04x (correct)", cksum);
	} else {
	  proto_tree_add_text(gre_tree, tvb, offset, 2,
			"Checksum: 0x%04x (incorrect, should be 0x%04x)",
			cksum, in_cksum_shouldbe(cksum, computed_cksum));
	}
      } else {
	proto_tree_add_text(gre_tree, tvb, offset, 2,
			  "Checksum: 0x%04x", cksum);
      }
    }
    offset += 2;
  }

  if (flags_and_ver & GH_B_C || flags_and_ver & GH_B_R) {
    if (tree) {
      proto_tree_add_text(gre_tree, tvb, offset, 2,
			  "Offset: %u", tvb_get_ntohs(tvb, offset));
    }
    offset += 2;
  }

  if (flags_and_ver & GH_B_K) {
    if (is_ppp) {
      if (tree) {
	proto_tree_add_text(gre_tree, tvb, offset, 2,
			    "Payload length: %u", tvb_get_ntohs(tvb, offset));
      }
      offset += 2;
      if (tree) {
	proto_tree_add_text(gre_tree, tvb, offset, 2,
			    "Call ID: %u", tvb_get_ntohs(tvb, offset));
      }
      offset += 2;
    }
    else {
      if (tree) {
	proto_tree_add_text(gre_tree, tvb, offset, 4,
			    "Key: %u", tvb_get_ntohl(tvb, offset));
      }
      offset += 4;
    }
  }

  if (flags_and_ver & GH_B_S) {
    if (tree) {
      proto_tree_add_text(gre_tree, tvb, offset, 4,
			  "Sequence number: %u", tvb_get_ntohl(tvb, offset));
    }
    offset += 4;
  }

  if (is_ppp && flags_and_ver & GH_P_A) {
    if (tree) {
      proto_tree_add_text(gre_tree, tvb, offset, 4,
			  "Acknowledgement number: %u", tvb_get_ntohl(tvb, offset));
    }
    offset += 4;
  }

  if (flags_and_ver & GH_B_R) {
    for (;;) {
      sre_af = tvb_get_ntohs(tvb, offset);
      if (tree) {
        proto_tree_add_text(gre_tree, tvb, offset, sizeof(guint16),
  			  "Address family: %u", sre_af);
      }
      offset += sizeof(guint16);
      if (tree) {
        proto_tree_add_text(gre_tree, tvb, offset, 1,
			  "SRE offset: %u", tvb_get_guint8(tvb, offset));
      }
      offset += sizeof(guint8);
      sre_length = tvb_get_guint8(tvb, offset);
      if (tree) {
        proto_tree_add_text(gre_tree, tvb, offset, sizeof(guint8),
			  "SRE length: %u", sre_length);
      }
      offset += sizeof(guint8);
      if (sre_af == 0 && sre_length == 0)
	break;
      offset += sre_length;
    }
  }

  if (type == GRE_WCCP) {
    if (is_wccp2) {
      if (tree)
        dissect_gre_wccp2_redirect_header(tvb, offset, gre_tree);
      offset += 4;
    }
  }

  /* If the S bit is not set, this packet might not have a payload, so
     check whether there's any data left, first.

     XXX - the S bit isn't in RFC 2784, which deprecates that bit
     and some other bits in RFC 1701 and says that they should be
     zero for RFC 2784-compliant GRE; as such, the absence of the
     S bit doesn't necessarily mean there's no payload.  */
  if (!(flags_and_ver & GH_B_S)) {
    if (tvb_reported_length_remaining(tvb, offset) <= 0)
      return;	/* no payload */
  }
  next_tvb = tvb_new_subset(tvb, offset, -1, -1);
  if (!dissector_try_port(gre_dissector_table, type, next_tvb, pinfo, tree))
    call_dissector(data_handle,next_tvb, pinfo, gre_tree);
}

static void
add_flags_and_ver(proto_tree *tree, guint16 flags_and_ver, tvbuff_t *tvb,
    int offset, int is_ppp)
{
  proto_item *	ti;
  proto_tree *	fv_tree;
  int		nbits = sizeof(flags_and_ver) * 8;

  ti = proto_tree_add_text(tree, tvb, offset, 2,
			   "Flags and version: %#04x", flags_and_ver);
  fv_tree = proto_item_add_subtree(ti, ett_gre_flags);

  proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
		      decode_boolean_bitfield(flags_and_ver, GH_B_C, nbits,
					      "Checksum", "No checksum"));
  proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
		      decode_boolean_bitfield(flags_and_ver, GH_B_R, nbits,
					      "Routing", "No routing"));
  proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
		      decode_boolean_bitfield(flags_and_ver, GH_B_K, nbits,
					      "Key", "No key"));
  proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
		      decode_boolean_bitfield(flags_and_ver, GH_B_S, nbits,
					      "Sequence number", "No sequence number"));
  proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
		      decode_boolean_bitfield(flags_and_ver, GH_B_s, nbits,
					      "Strict source route", "No strict source route"));
  proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
		      decode_numeric_bitfield(flags_and_ver, GH_B_RECUR, nbits,
					      "Recursion control: %u"));
  if (is_ppp) {
    proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
			decode_boolean_bitfield(flags_and_ver, GH_P_A, nbits,
						"Acknowledgment number", "No acknowledgment number"));
    proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
			decode_numeric_bitfield(flags_and_ver, GH_P_FLAGS, nbits,
						"Flags: %u"));
  }
  else {
    proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
			decode_numeric_bitfield(flags_and_ver, GH_R_FLAGS, nbits,
						"Flags: %u"));
  }

  proto_tree_add_text(fv_tree, tvb, offset, sizeof(flags_and_ver), "%s",
		      decode_numeric_bitfield(flags_and_ver, GH_B_VER, nbits,
					      "Version: %u"));
 }

static void
dissect_gre_wccp2_redirect_header(tvbuff_t *tvb, int offset, proto_tree *tree)
{
  proto_item *	ti;
  proto_tree *	rh_tree;
  guint8	rh_flags;

  ti = proto_tree_add_text(tree, tvb, offset, 4, "Redirect header");
  rh_tree = proto_item_add_subtree(ti, ett_gre_wccp2_redirect_header);

  rh_flags = tvb_get_guint8(tvb, offset);
  proto_tree_add_text(rh_tree, tvb, offset, 1, "%s",
		      decode_boolean_bitfield(rh_flags, 0x80, 8,
				      "Dynamic service", "Well-known service"));
  proto_tree_add_text(rh_tree, tvb, offset, 1, "%s",
		      decode_boolean_bitfield(rh_flags, 0x40, 8,
			      "Alternative bucket used", "Alternative bucket not used"));

  proto_tree_add_text(rh_tree, tvb, offset + 1, 1, "Service ID: %s",
      val_to_str(tvb_get_guint8(tvb, offset + 1), service_id_vals, "Unknown (0x%02X)"));
  if (rh_flags & 0x40)
    proto_tree_add_text(rh_tree, tvb, offset + 2, 1, "Alternative bucket index: %u",
			tvb_get_guint8(tvb, offset + 2));
  proto_tree_add_text(rh_tree, tvb, offset + 3, 1, "Primary bucket index: %u",
			tvb_get_guint8(tvb, offset + 3));
}

void
proto_register_gre(void)
{
	static hf_register_info hf[] = {
		{ &hf_gre_proto,
			{ "Protocol Type", "gre.proto", FT_UINT16, BASE_HEX, VALS(typevals), 0x0,
				"The protocol that is GRE encapsulated", HFILL }
		},
	};
	static gint *ett[] = {
		&ett_gre,
		&ett_gre_flags,
		&ett_gre_wccp2_redirect_header,
	};

        proto_gre = proto_register_protocol("Generic Routing Encapsulation",
	    "GRE", "gre");
        proto_register_field_array(proto_gre, hf, array_length(hf));
	proto_register_subtree_array(ett, array_length(ett));

	/* subdissector code */
	gre_dissector_table = register_dissector_table("gre.proto",
	    "GRE protocol type", FT_UINT16, BASE_HEX);
}

void
proto_reg_handoff_gre(void)
{
	dissector_handle_t gre_handle;

	gre_handle = create_dissector_handle(dissect_gre, proto_gre);
	dissector_add("ip.proto", IP_PROTO_GRE, gre_handle);
	data_handle = find_dissector("data");
}