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      1 /* Shared library add-on to iptables to add TTL matching support
      2  * (C) 2000 by Harald Welte <laforge (at) gnumonks.org>
      3  *
      4  * This program is released under the terms of GNU GPL */
      5 #include <stdio.h>
      6 #include <xtables.h>
      7 #include <linux/netfilter_ipv4/ipt_ttl.h>
      8 
      9 enum {
     10 	O_TTL_EQ = 0,
     11 	O_TTL_LT,
     12 	O_TTL_GT,
     13 	F_TTL_EQ = 1 << O_TTL_EQ,
     14 	F_TTL_LT = 1 << O_TTL_LT,
     15 	F_TTL_GT = 1 << O_TTL_GT,
     16 	F_ANY    = F_TTL_EQ | F_TTL_LT | F_TTL_GT,
     17 };
     18 
     19 static void ttl_help(void)
     20 {
     21 	printf(
     22 "ttl match options:\n"
     23 "[!] --ttl-eq value	Match time to live value\n"
     24 "  --ttl-lt value	Match TTL < value\n"
     25 "  --ttl-gt value	Match TTL > value\n");
     26 }
     27 
     28 static void ttl_parse(struct xt_option_call *cb)
     29 {
     30 	struct ipt_ttl_info *info = cb->data;
     31 
     32 	xtables_option_parse(cb);
     33 	switch (cb->entry->id) {
     34 	case O_TTL_EQ:
     35 		info->mode = cb->invert ? IPT_TTL_NE : IPT_TTL_EQ;
     36 		break;
     37 	case O_TTL_LT:
     38 		info->mode = IPT_TTL_LT;
     39 		break;
     40 	case O_TTL_GT:
     41 		info->mode = IPT_TTL_GT;
     42 		break;
     43 	}
     44 }
     45 
     46 static void ttl_check(struct xt_fcheck_call *cb)
     47 {
     48 	if (!(cb->xflags & F_ANY))
     49 		xtables_error(PARAMETER_PROBLEM,
     50 			"TTL match: You must specify one of "
     51 			"`--ttl-eq', `--ttl-lt', `--ttl-gt");
     52 }
     53 
     54 static void ttl_print(const void *ip, const struct xt_entry_match *match,
     55                       int numeric)
     56 {
     57 	const struct ipt_ttl_info *info =
     58 		(struct ipt_ttl_info *) match->data;
     59 
     60 	printf(" TTL match ");
     61 	switch (info->mode) {
     62 		case IPT_TTL_EQ:
     63 			printf("TTL ==");
     64 			break;
     65 		case IPT_TTL_NE:
     66 			printf("TTL !=");
     67 			break;
     68 		case IPT_TTL_LT:
     69 			printf("TTL <");
     70 			break;
     71 		case IPT_TTL_GT:
     72 			printf("TTL >");
     73 			break;
     74 	}
     75 	printf(" %u", info->ttl);
     76 }
     77 
     78 static void ttl_save(const void *ip, const struct xt_entry_match *match)
     79 {
     80 	const struct ipt_ttl_info *info =
     81 		(struct ipt_ttl_info *) match->data;
     82 
     83 	switch (info->mode) {
     84 		case IPT_TTL_EQ:
     85 			printf(" --ttl-eq");
     86 			break;
     87 		case IPT_TTL_NE:
     88 			printf(" ! --ttl-eq");
     89 			break;
     90 		case IPT_TTL_LT:
     91 			printf(" --ttl-lt");
     92 			break;
     93 		case IPT_TTL_GT:
     94 			printf(" --ttl-gt");
     95 			break;
     96 		default:
     97 			/* error */
     98 			break;
     99 	}
    100 	printf(" %u", info->ttl);
    101 }
    102 
    103 static int ttl_xlate(struct xt_xlate *xl,
    104 		     const struct xt_xlate_mt_params *params)
    105 {
    106 	const struct ipt_ttl_info *info =
    107 		(struct ipt_ttl_info *) params->match->data;
    108 
    109 		switch (info->mode) {
    110 		case IPT_TTL_EQ:
    111 			xt_xlate_add(xl, "ip ttl");
    112 			break;
    113 		case IPT_TTL_NE:
    114 			xt_xlate_add(xl, "ip ttl !=");
    115 			break;
    116 		case IPT_TTL_LT:
    117 			xt_xlate_add(xl, "ip ttl lt");
    118 			break;
    119 		case IPT_TTL_GT:
    120 			xt_xlate_add(xl, "ip ttl gt");
    121 			break;
    122 		default:
    123 			/* Should not happen. */
    124 			break;
    125 	}
    126 
    127 	xt_xlate_add(xl, " %u", info->ttl);
    128 
    129 	return 1;
    130 }
    131 
    132 #define s struct ipt_ttl_info
    133 static const struct xt_option_entry ttl_opts[] = {
    134 	{.name = "ttl-lt", .id = O_TTL_LT, .excl = F_ANY, .type = XTTYPE_UINT8,
    135 	 .flags = XTOPT_PUT, XTOPT_POINTER(s, ttl)},
    136 	{.name = "ttl-gt", .id = O_TTL_GT, .excl = F_ANY, .type = XTTYPE_UINT8,
    137 	 .flags = XTOPT_PUT, XTOPT_POINTER(s, ttl)},
    138 	{.name = "ttl-eq", .id = O_TTL_EQ, .excl = F_ANY, .type = XTTYPE_UINT8,
    139 	 .flags = XTOPT_INVERT | XTOPT_PUT, XTOPT_POINTER(s, ttl)},
    140 	{.name = "ttl", .id = O_TTL_EQ, .excl = F_ANY, .type = XTTYPE_UINT8,
    141 	 .flags = XTOPT_PUT, XTOPT_POINTER(s, ttl)},
    142 	XTOPT_TABLEEND,
    143 };
    144 #undef s
    145 
    146 static struct xtables_match ttl_mt_reg = {
    147 	.name		= "ttl",
    148 	.version	= XTABLES_VERSION,
    149 	.family		= NFPROTO_IPV4,
    150 	.size		= XT_ALIGN(sizeof(struct ipt_ttl_info)),
    151 	.userspacesize	= XT_ALIGN(sizeof(struct ipt_ttl_info)),
    152 	.help		= ttl_help,
    153 	.print		= ttl_print,
    154 	.save		= ttl_save,
    155 	.x6_parse	= ttl_parse,
    156 	.x6_fcheck	= ttl_check,
    157 	.x6_options	= ttl_opts,
    158 	.xlate		= ttl_xlate,
    159 };
    160 
    161 
    162 void _init(void)
    163 {
    164 	xtables_register_match(&ttl_mt_reg);
    165 }
    166