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

   1 /*
   2  * Copyright (c) 2014 The TCPDUMP project
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  15  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  16  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  17  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  18  * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  20  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  21  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  22  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  24  * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  25  * POSSIBILITY OF SUCH DAMAGE.
  26  */
  27
  28 /* \summary: Loopback Protocol printer */
  29
  30 /*
  31  * originally defined as the Ethernet Configuration Testing Protocol.
  32  * specification: https://www.mit.edu/people/jhawk/ctp.pdf
  33  */
  34
  35 #ifdef HAVE_CONFIG_H
  36 #include <config.h>
  37 #endif
  38
  39 #include "netdissect-stdinc.h"
  40
  41 #include "netdissect.h"
  42 #include "extract.h"
  43 #include "addrtoname.h"
  44
  45
  46 #define LOOPBACK_REPLY   1
  47 #define LOOPBACK_FWDDATA 2
  48
  49 static const struct tok fcode_str[] = {
  50         { LOOPBACK_REPLY,   "Reply"        },
  51         { LOOPBACK_FWDDATA, "Forward Data" },
  52         { 0, NULL }
  53 };
  54
  55 static void
  56 loopback_message_print(netdissect_options *ndo,
  57                        const u_char *cp, u_int len)
  58 {
  59         uint16_t function;
  60
  61         if (len < 2)
  62                 goto invalid;
  63         /* function */
  64         function = GET_LE_U_2(cp);
  65         cp += 2;
  66         len -= 2;
  67         ND_PRINT(", %s", tok2str(fcode_str, " invalid (%u)", function));
  68
  69         switch (function) {
  70                 case LOOPBACK_REPLY:
  71                         if (len < 2)
  72                                 goto invalid;
  73                         /* receipt number */
  74                         ND_PRINT(", receipt number %u", GET_LE_U_2(cp));
  75                         cp += 2;
  76                         len -= 2;
  77                         /* data */
  78                         ND_PRINT(", data (%u octets)", len);
  79                         ND_TCHECK_LEN(cp, len);
  80                         break;
  81                 case LOOPBACK_FWDDATA:
  82                         if (len < MAC_ADDR_LEN)
  83                                 goto invalid;
  84                         /* forwarding address */
  85                         ND_PRINT(", forwarding address %s", GET_ETHERADDR_STRING(cp));
  86                         cp += MAC_ADDR_LEN;
  87                         len -= MAC_ADDR_LEN;
  88                         /* data */
  89                         ND_PRINT(", data (%u octets)", len);
  90                         ND_TCHECK_LEN(cp, len);
  91                         break;
  92                 default:
  93                         ND_TCHECK_LEN(cp, len);
  94                         break;
  95         }
  96         return;
  97
  98 invalid:
  99         nd_print_invalid(ndo);
 100         ND_TCHECK_LEN(cp, len);
 101         return;
 102 trunc:
 103         nd_trunc(ndo);
 104 }
 105
 106 void
 107 loopback_print(netdissect_options *ndo,
 108                const u_char *cp, u_int len)
 109 {
 110         uint16_t skipCount;
 111
 112         ndo->ndo_protocol = "loopback";
 113         ND_PRINT("Loopback");
 114         if (len < 2)
 115                 goto invalid;
 116         /* skipCount */
 117         skipCount = GET_LE_U_2(cp);
 118         cp += 2;
 119         len -= 2;
 120         ND_PRINT(", skipCount %u", skipCount);
 121         if (skipCount % 8)
 122                 ND_PRINT(" (bogus)");
 123         if (skipCount > len)
 124                 goto invalid;
 125         /* the octets to skip */
 126         ND_TCHECK_LEN(cp, skipCount);
 127         cp += skipCount;
 128         len -= skipCount;
 129         /* the first message to decode */
 130         loopback_message_print(ndo, cp, len);
 131         return;
 132
 133 invalid:
 134         nd_print_invalid(ndo);
 135         ND_TCHECK_LEN(cp, len);
 136         return;
 137 trunc:
 138         nd_trunc(ndo);
 139 }
 140