The Tcpdump Group git mirrors - tcpdump/blob - print-gre.c

   1 /*
   2  * Copyright (c) 1996
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms are permitted
   6  * provided that the above copyright notice and this paragraph are
   7  * duplicated in all such forms and that any documentation,
   8  * advertising materials, and other materials related to such
   9  * distribution and use acknowledge that the software was developed
  10  * by the University of California, Lawrence Berkeley Laboratory,
  11  * Berkeley, CA.  The name of the University may not be used to
  12  * endorse or promote products derived from this software without
  13  * specific prior written permission.
  14  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
  15  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  16  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  17  *
  18  * Initial contribution from John Hawkinson <jhawk@bbnplanet.com>
  19  *
  20  * This module implements support for decoding GRE (Generic Routing
  21  * Encapsulation) tunnels; they're documented in RFC1701 and RFC1702.
  22  * This code only supports the IP encapsulation thereof.
  23  */
  24
  25 #ifndef lint
  26 static const char rcsid[] =
  27     "@(#) $Header: /tcpdump/master/tcpdump/print-gre.c,v 1.12 2001-03-13 01:03:17 fenner Exp $";
  28 #endif
  29
  30 #ifdef HAVE_CONFIG_H
  31 #include "config.h"
  32 #endif
  33
  34 #include <sys/param.h>
  35 #include <sys/time.h>
  36 #include <sys/uio.h>
  37 #include <sys/socket.h>
  38
  39 #include <netinet/in.h>
  40
  41 #include <netdb.h>
  42 #include <stdio.h>
  43
  44 #include "interface.h"
  45 #include "addrtoname.h"
  46 #include "extract.h"            /* must come after interface.h */
  47
  48 struct gre {
  49         u_int16_t flags;
  50         u_int16_t proto;
  51 };
  52
  53 /* RFC 2784 - GRE */
  54 #define GRE_CP          0x8000  /* Checksum Present */
  55 #define GRE_VER_MASK    0x0007  /* Version */
  56
  57 /* RFC 2890 - Key and Sequence extensions to GRE */
  58 #define GRE_KP          0x2000  /* Key Present */
  59 #define GRE_SP          0x1000  /* Sequence Present */
  60
  61 /* Legacy from RFC 1700 */
  62 #define GRE_RP          0x4000  /* Routing Present */
  63 #define GRE_sP          0x0800  /* strict source route present */
  64 #define GRE_RECUR_MASK  0x0700  /* Recursion Control */
  65 #define GRE_RECUR_SHIFT 8
  66
  67 #define GRE_COP         (GRE_RP|GRE_CP) /* Checksum & Offset Present */
  68
  69 /* "Enhanced GRE" from RFC2637 - PPTP */
  70 #define GRE_AP          0x0080  /* Ack present */
  71
  72 #define GRE_MBZ_MASK    0x0078  /* not defined */
  73
  74 /*
  75  * Deencapsulate and print a GRE-tunneled IP datagram
  76  */
  77 void
  78 gre_print(const u_char *bp, u_int length)
  79 {
  80         const u_char *cp = bp + 4;
  81         const struct gre *gre;
  82         u_int16_t flags, proto;
  83         u_short ver=0;
  84         u_short extracted_ethertype;
  85
  86         gre = (const struct gre *)bp;
  87
  88         TCHECK(gre->proto);
  89         flags = EXTRACT_16BITS(&gre->flags);
  90         proto = EXTRACT_16BITS(&gre->proto);
  91
  92         if (flags) {
  93                 /* Decode the flags */
  94                 putchar('[');
  95                 if (flags & GRE_CP)
  96                         putchar('C');
  97                 if (flags & GRE_RP)
  98                         putchar('R');
  99                 if (flags & GRE_KP)
 100                         putchar('K');
 101                 if (flags & GRE_SP)
 102                         putchar('S');
 103                 if (flags & GRE_sP)
 104                         putchar('s');
 105                 if (flags & GRE_AP)
 106                         putchar('A');
 107                 if (flags & GRE_RECUR_MASK)
 108                         printf("R%x", (flags & GRE_RECUR_MASK) >> GRE_RECUR_SHIFT);
 109                 ver = flags & GRE_VER_MASK;
 110                 printf("v%u", ver);
 111
 112                 if (flags & GRE_MBZ_MASK)
 113                         printf("!%x", flags & GRE_MBZ_MASK);
 114                 fputs("] ", stdout);
 115         }
 116
 117         if (flags & GRE_COP) {
 118                 int checksum, offset;
 119
 120                 TCHECK2(*cp, 4);
 121                 checksum = EXTRACT_16BITS(cp);
 122                 offset = EXTRACT_16BITS(cp + 2);
 123
 124                 if (flags & GRE_CP) {
 125                         /* Checksum present */
 126
 127                         /* todo: check checksum */
 128                         if (vflag > 1)
 129                                 printf("C:%04x ", checksum);
 130                 }
 131                 if (flags & GRE_RP) {
 132                         /* Offset present */
 133
 134                         if (vflag > 1)
 135                                 printf("O:%04x ", offset);
 136                 }
 137                 cp += 4;        /* skip checksum and offset */
 138         }
 139         if (flags & GRE_KP) {
 140                 TCHECK2(*cp, 4);
 141                 if (ver == 1) {         /* PPTP */
 142                         if (vflag > 1)
 143                                 printf("PL:%u ", EXTRACT_16BITS(cp));
 144                         printf("ID:%04x ", EXTRACT_16BITS(cp+2));
 145                 }
 146                 else
 147                         printf("K:%08x ", EXTRACT_32BITS(cp));
 148                 cp += 4;        /* skip key */
 149         }
 150         if (flags & GRE_SP) {
 151                 TCHECK2(*cp, 4);
 152                 printf("S:%u ", EXTRACT_32BITS(cp));
 153                 cp += 4;        /* skip seq */
 154         }
 155         if (flags & GRE_AP && ver >= 1) {
 156                 TCHECK2(*cp, 4);
 157                 printf("A:%u ", EXTRACT_32BITS(cp));
 158                 cp += 4;        /* skip ack */
 159         }
 160         /* We don't support routing fields (variable length) now. Punt. */
 161         if (flags & GRE_RP)
 162                 return;
 163
 164         TCHECK(cp[0]);
 165
 166         length -= cp - bp;
 167         if (ether_encap_print(proto, cp, length, length,
 168             &extracted_ethertype) == 0)
 169                 printf("gre-proto-0x%04X", proto);
 170         return;
 171
 172 trunc:
 173         fputs("[|gre]", stdout);
 174
 175 }