176 lines
4.3 KiB
C
176 lines
4.3 KiB
C
/*
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* Copyright (c) 1996
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms are permitted
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* provided that the above copyright notice and this paragraph are
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* duplicated in all such forms and that any documentation,
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* advertising materials, and other materials related to such
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* distribution and use acknowledge that the software was developed
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* by the University of California, Lawrence Berkeley Laboratory,
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* Berkeley, CA. The name of the University may not be used to
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* endorse or promote products derived from this software without
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* specific prior written permission.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
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* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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*
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* Initial contribution from John Hawkinson <jhawk@bbnplanet.com>
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*
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* This module implements support for decoding GRE (Generic Routing
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* Encapsulation) tunnels; they're documented in RFC1701 and RFC1702.
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* This code only supports the IP encapsulation thereof.
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*/
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#ifndef lint
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static const char rcsid[] =
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"@(#) $Header: /tcpdump/master/tcpdump/print-gre.c,v 1.13.4.1 2002/06/01 23:51:13 guy Exp $";
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#endif
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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 <sys/param.h>
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#include <sys/time.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <netdb.h>
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#include <stdio.h>
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#include "interface.h"
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#include "addrtoname.h"
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#include "extract.h" /* must come after interface.h */
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struct gre {
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u_int16_t flags;
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u_int16_t proto;
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};
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/* RFC 2784 - GRE */
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#define GRE_CP 0x8000 /* Checksum Present */
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#define GRE_VER_MASK 0x0007 /* Version */
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/* RFC 2890 - Key and Sequence extensions to GRE */
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#define GRE_KP 0x2000 /* Key Present */
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#define GRE_SP 0x1000 /* Sequence Present */
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/* Legacy from RFC 1700 */
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#define GRE_RP 0x4000 /* Routing Present */
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#define GRE_sP 0x0800 /* strict source route present */
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#define GRE_RECUR_MASK 0x0700 /* Recursion Control */
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#define GRE_RECUR_SHIFT 8
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#define GRE_COP (GRE_RP|GRE_CP) /* Checksum & Offset Present */
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/* "Enhanced GRE" from RFC2637 - PPTP */
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#define GRE_AP 0x0080 /* Ack present */
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#define GRE_MBZ_MASK 0x0078 /* not defined */
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/*
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* Deencapsulate and print a GRE-tunneled IP datagram
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*/
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void
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gre_print(const u_char *bp, u_int length)
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{
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const u_char *cp = bp + 4;
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const struct gre *gre;
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u_int16_t flags, proto;
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u_short ver=0;
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u_short extracted_ethertype;
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gre = (const struct gre *)bp;
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TCHECK(gre->proto);
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flags = EXTRACT_16BITS(&gre->flags);
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proto = EXTRACT_16BITS(&gre->proto);
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(void)printf("gre ");
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if (flags) {
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/* Decode the flags */
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putchar('[');
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if (flags & GRE_CP)
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putchar('C');
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if (flags & GRE_RP)
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putchar('R');
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if (flags & GRE_KP)
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putchar('K');
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if (flags & GRE_SP)
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putchar('S');
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if (flags & GRE_sP)
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putchar('s');
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if (flags & GRE_AP)
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putchar('A');
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if (flags & GRE_RECUR_MASK)
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printf("R%x", (flags & GRE_RECUR_MASK) >> GRE_RECUR_SHIFT);
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ver = flags & GRE_VER_MASK;
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printf("v%u", ver);
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if (flags & GRE_MBZ_MASK)
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printf("!%x", flags & GRE_MBZ_MASK);
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fputs("] ", stdout);
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}
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if (flags & GRE_COP) {
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int checksum, offset;
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TCHECK2(*cp, 4);
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checksum = EXTRACT_16BITS(cp);
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offset = EXTRACT_16BITS(cp + 2);
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if (flags & GRE_CP) {
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/* Checksum present */
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/* todo: check checksum */
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if (vflag > 1)
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printf("C:%04x ", checksum);
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}
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if (flags & GRE_RP) {
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/* Offset present */
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if (vflag > 1)
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printf("O:%04x ", offset);
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}
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cp += 4; /* skip checksum and offset */
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}
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if (flags & GRE_KP) {
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TCHECK2(*cp, 4);
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if (ver == 1) { /* PPTP */
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if (vflag > 1)
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printf("PL:%u ", EXTRACT_16BITS(cp));
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printf("ID:%04x ", EXTRACT_16BITS(cp+2));
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}
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else
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printf("K:%08x ", EXTRACT_32BITS(cp));
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cp += 4; /* skip key */
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}
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if (flags & GRE_SP) {
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TCHECK2(*cp, 4);
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printf("S:%u ", EXTRACT_32BITS(cp));
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cp += 4; /* skip seq */
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}
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if (flags & GRE_AP && ver >= 1) {
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TCHECK2(*cp, 4);
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printf("A:%u ", EXTRACT_32BITS(cp));
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cp += 4; /* skip ack */
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}
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/* We don't support routing fields (variable length) now. Punt. */
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if (flags & GRE_RP)
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return;
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TCHECK(cp[0]);
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length -= cp - bp;
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if (ether_encap_print(proto, cp, length, length,
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&extracted_ethertype) == 0)
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printf("gre-proto-0x%04X", proto);
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return;
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trunc:
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fputs("[|gre]", stdout);
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}
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