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 1.16 2002-08-01 08:53:08 risso Exp $";
  28 #endif
  29
  30 #ifdef HAVE_CONFIG_H
  31 #include "config.h"
  32 #endif
  33
  34 #include <tcpdump-stdinc.h>
  35
  36 #include <stdio.h>
  37
  38 #include "interface.h"
  39 #include "addrtoname.h"
  40 #include "extract.h"            /* must come after interface.h */
  41
  42 struct gre {
  43         u_int16_t flags;
  44         u_int16_t proto;
  45 };
  46
  47 /* RFC 2784 - GRE */
  48 #define GRE_CP          0x8000  /* Checksum Present */
  49 #define GRE_VER_MASK    0x0007  /* Version */
  50
  51 /* RFC 2890 - Key and Sequence extensions to GRE */
  52 #define GRE_KP          0x2000  /* Key Present */
  53 #define GRE_SP          0x1000  /* Sequence Present */
  54
  55 /* Legacy from RFC 1700 */
  56 #define GRE_RP          0x4000  /* Routing Present */
  57 #define GRE_sP          0x0800  /* strict source route present */
  58 #define GRE_RECUR_MASK  0x0700  /* Recursion Control */
  59 #define GRE_RECUR_SHIFT 8
  60
  61 #define GRE_COP         (GRE_RP|GRE_CP) /* Checksum & Offset Present */
  62
  63 /* "Enhanced GRE" from RFC2637 - PPTP */
  64 #define GRE_AP          0x0080  /* Ack present */
  65
  66 #define GRE_MBZ_MASK    0x0078  /* not defined */
  67
  68 /*
  69  * Deencapsulate and print a GRE-tunneled IP datagram
  70  */
  71 void
  72 gre_print(const u_char *bp, u_int length)
  73 {
  74         const u_char *cp = bp + 4;
  75         const struct gre *gre;
  76         u_int16_t flags, proto;
  77         u_short ver=0;
  78         u_short extracted_ethertype;
  79
  80         gre = (const struct gre *)bp;
  81
  82         TCHECK(gre->proto);
  83         flags = EXTRACT_16BITS(&gre->flags);
  84         proto = EXTRACT_16BITS(&gre->proto);
  85         (void)printf("gre ");
  86
  87         if (flags) {
  88                 /* Decode the flags */
  89                 putchar('[');
  90                 if (flags & GRE_CP)
  91                         putchar('C');
  92                 if (flags & GRE_RP)
  93                         putchar('R');
  94                 if (flags & GRE_KP)
  95                         putchar('K');
  96                 if (flags & GRE_SP)
  97                         putchar('S');
  98                 if (flags & GRE_sP)
  99                         putchar('s');
 100                 if (flags & GRE_AP)
 101                         putchar('A');
 102                 if (flags & GRE_RECUR_MASK)
 103                         printf("R%x", (flags & GRE_RECUR_MASK) >> GRE_RECUR_SHIFT);
 104                 ver = flags & GRE_VER_MASK;
 105                 printf("v%u", ver);
 106
 107                 if (flags & GRE_MBZ_MASK)
 108                         printf("!%x", flags & GRE_MBZ_MASK);
 109                 fputs("] ", stdout);
 110         }
 111
 112         if (flags & GRE_COP) {
 113                 int checksum, offset;
 114
 115                 TCHECK2(*cp, 4);
 116                 checksum = EXTRACT_16BITS(cp);
 117                 offset = EXTRACT_16BITS(cp + 2);
 118
 119                 if (flags & GRE_CP) {
 120                         /* Checksum present */
 121
 122                         /* todo: check checksum */
 123                         if (vflag > 1)
 124                                 printf("C:%04x ", checksum);
 125                 }
 126                 if (flags & GRE_RP) {
 127                         /* Offset present */
 128
 129                         if (vflag > 1)
 130                                 printf("O:%04x ", offset);
 131                 }
 132                 cp += 4;        /* skip checksum and offset */
 133         }
 134         if (flags & GRE_KP) {
 135                 TCHECK2(*cp, 4);
 136                 if (ver == 1) {         /* PPTP */
 137                         if (vflag > 1)
 138                                 printf("PL:%u ", EXTRACT_16BITS(cp));
 139                         printf("ID:%04x ", EXTRACT_16BITS(cp+2));
 140                 }
 141                 else
 142                         printf("K:%08x ", EXTRACT_32BITS(cp));
 143                 cp += 4;        /* skip key */
 144         }
 145         if (flags & GRE_SP) {
 146                 TCHECK2(*cp, 4);
 147                 printf("S:%u ", EXTRACT_32BITS(cp));
 148                 cp += 4;        /* skip seq */
 149         }
 150         if (flags & GRE_AP && ver >= 1) {
 151                 TCHECK2(*cp, 4);
 152                 printf("A:%u ", EXTRACT_32BITS(cp));
 153                 cp += 4;        /* skip ack */
 154         }
 155         /* We don't support routing fields (variable length) now. Punt. */
 156         if (flags & GRE_RP)
 157                 return;
 158
 159         TCHECK(cp[0]);
 160
 161         length -= cp - bp;
 162         if (ether_encap_print(proto, cp, length, length,
 163             &extracted_ethertype) == 0)
 164                 printf("gre-proto-0x%04X", proto);
 165         return;
 166
 167 trunc:
 168         fputs("[|gre]", stdout);
 169
 170 }