extensions/libipt_TTL.c

   1 /* Shared library add-on to iptables for the TTL target
   2  * (C) 2000 by Harald Welte <laforge@gnumonks.org>
   3  *
   4  * $Id$
   5  *
   6  * This program is distributed under the terms of GNU GPL
   7  */
   8 #include <stdio.h>
   9 #include <string.h>
  10 #include <stdlib.h>
  11 #include <getopt.h>
  12 #include <iptables.h>
  13
  14 #include <linux/netfilter_ipv4/ip_tables.h>
  15 #include <linux/netfilter_ipv4/ipt_TTL.h>
  16
  17 #define IPT_TTL_USED    1
  18
  19 static void TTL_help(void)
  20 {
  21         printf(
  22 "TTL target options\n"
  23 "  --ttl-set value              Set TTL to <value 0-255>\n"
  24 "  --ttl-dec value              Decrement TTL by <value 1-255>\n"
  25 "  --ttl-inc value              Increment TTL by <value 1-255>\n");
  26 }
  27
  28 static int TTL_parse(int c, char **argv, int invert, unsigned int *flags,
  29                      const void *entry, struct xt_entry_target **target)
  30 {
  31         struct ipt_TTL_info *info = (struct ipt_TTL_info *) (*target)->data;
  32         unsigned int value;
  33
  34         if (*flags & IPT_TTL_USED) {
  35                 exit_error(PARAMETER_PROBLEM,
  36                                 "Can't specify TTL option twice");
  37         }
  38
  39         if (!optarg)
  40                 exit_error(PARAMETER_PROBLEM,
  41                                 "TTL: You must specify a value");
  42
  43         if (check_inverse(optarg, &invert, NULL, 0))
  44                 exit_error(PARAMETER_PROBLEM,
  45                                 "TTL: unexpected `!'");
  46
  47         if (string_to_number(optarg, 0, 255, &value) == -1)
  48                 exit_error(PARAMETER_PROBLEM,
  49                            "TTL: Expected value between 0 and 255");
  50
  51         switch (c) {
  52
  53                 case '1':
  54                         info->mode = IPT_TTL_SET;
  55                         break;
  56
  57                 case '2':
  58                         if (value == 0) {
  59                                 exit_error(PARAMETER_PROBLEM,
  60                                         "TTL: decreasing by 0?");
  61                         }
  62
  63                         info->mode = IPT_TTL_DEC;
  64                         break;
  65
  66                 case '3':
  67                         if (value == 0) {
  68                                 exit_error(PARAMETER_PROBLEM,
  69                                         "TTL: increasing by 0?");
  70                         }
  71
  72                         info->mode = IPT_TTL_INC;
  73                         break;
  74
  75                 default:
  76                         return 0;
  77
  78         }
  79
  80         info->ttl = value;
  81         *flags |= IPT_TTL_USED;
  82
  83         return 1;
  84 }
  85
  86 static void TTL_check(unsigned int flags)
  87 {
  88         if (!(flags & IPT_TTL_USED))
  89                 exit_error(PARAMETER_PROBLEM,
  90                                 "TTL: You must specify an action");
  91 }
  92
  93 static void TTL_save(const void *ip, const struct xt_entry_target *target)
  94 {
  95         const struct ipt_TTL_info *info =
  96                 (struct ipt_TTL_info *) target->data;
  97
  98         switch (info->mode) {
  99                 case IPT_TTL_SET:
 100                         printf("--ttl-set ");
 101                         break;
 102                 case IPT_TTL_DEC:
 103                         printf("--ttl-dec ");
 104                         break;
 105
 106                 case IPT_TTL_INC:
 107                         printf("--ttl-inc ");
 108                         break;
 109         }
 110         printf("%u ", info->ttl);
 111 }
 112
 113 static void TTL_print(const void *ip, const struct xt_entry_target *target,
 114                       int numeric)
 115 {
 116         const struct ipt_TTL_info *info =
 117                 (struct ipt_TTL_info *) target->data;
 118
 119         printf("TTL ");
 120         switch (info->mode) {
 121                 case IPT_TTL_SET:
 122                         printf("set to ");
 123                         break;
 124                 case IPT_TTL_DEC:
 125                         printf("decrement by ");
 126                         break;
 127                 case IPT_TTL_INC:
 128                         printf("increment by ");
 129                         break;
 130         }
 131         printf("%u ", info->ttl);
 132 }
 133
 134 static const struct option TTL_opts[] = {
 135         { "ttl-set", 1, NULL, '1' },
 136         { "ttl-dec", 1, NULL, '2' },
 137         { "ttl-inc", 1, NULL, '3' },
 138         { .name = NULL }
 139 };
 140
 141 static struct xtables_target ttl_tg_reg = {
 142         .name           = "TTL",
 143         .version        = XTABLES_VERSION,
 144         .family         = PF_INET,
 145         .size           = XT_ALIGN(sizeof(struct ipt_TTL_info)),
 146         .userspacesize  = XT_ALIGN(sizeof(struct ipt_TTL_info)),
 147         .help           = TTL_help,
 148         .parse          = TTL_parse,
 149         .final_check    = TTL_check,
 150         .print          = TTL_print,
 151         .save           = TTL_save,
 152         .extra_opts     = TTL_opts,
 153 };
 154
 155 void _init(void)
 156 {
 157         xtables_register_target(&ttl_tg_reg);
 158 }