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      1 /* Shared library add-on to iptables to add static NAT support.
      2    Author: Svenning Soerensen <svenning (at) post5.tele.dk>
      3 */
      4 #include <stdio.h>
      5 #include <netdb.h>
      6 #include <string.h>
      7 #include <stdlib.h>
      8 #include <getopt.h>
      9 #include <xtables.h>
     10 #include <linux/netfilter/nf_nat.h>
     11 
     12 #define MODULENAME "NETMAP"
     13 
     14 enum {
     15 	O_TO = 0,
     16 };
     17 
     18 static const struct xt_option_entry NETMAP_opts[] = {
     19 	{.name = "to", .id = O_TO, .type = XTTYPE_HOSTMASK,
     20 	 .flags = XTOPT_MAND},
     21 	XTOPT_TABLEEND,
     22 };
     23 
     24 static void NETMAP_help(void)
     25 {
     26 	printf(MODULENAME" target options:\n"
     27 	       "  --%s address[/mask]\n"
     28 	       "				Network address to map to.\n\n",
     29 	       NETMAP_opts[0].name);
     30 }
     31 
     32 static int
     33 netmask2bits(uint32_t netmask)
     34 {
     35 	uint32_t bm;
     36 	int bits;
     37 
     38 	netmask = ntohl(netmask);
     39 	for (bits = 0, bm = 0x80000000; netmask & bm; netmask <<= 1)
     40 		bits++;
     41 	if (netmask)
     42 		return -1; /* holes in netmask */
     43 	return bits;
     44 }
     45 
     46 static void NETMAP_init(struct xt_entry_target *t)
     47 {
     48 	struct nf_nat_ipv4_multi_range_compat *mr = (struct nf_nat_ipv4_multi_range_compat *)t->data;
     49 
     50 	/* Actually, it's 0, but it's ignored at the moment. */
     51 	mr->rangesize = 1;
     52 }
     53 
     54 static void NETMAP_parse(struct xt_option_call *cb)
     55 {
     56 	struct nf_nat_ipv4_multi_range_compat *mr = cb->data;
     57 	struct nf_nat_ipv4_range *range = &mr->range[0];
     58 
     59 	xtables_option_parse(cb);
     60 	range->flags |= NF_NAT_RANGE_MAP_IPS;
     61 	range->min_ip = cb->val.haddr.ip & cb->val.hmask.ip;
     62 	range->max_ip = range->min_ip | ~cb->val.hmask.ip;
     63 }
     64 
     65 static void __NETMAP_print(const void *ip, const struct xt_entry_target *target,
     66 			   int numeric)
     67 {
     68 	const struct nf_nat_ipv4_multi_range_compat *mr = (const void *)target->data;
     69 	const struct nf_nat_ipv4_range *r = &mr->range[0];
     70 	struct in_addr a;
     71 	int bits;
     72 
     73 	a.s_addr = r->min_ip;
     74 	printf("%s", xtables_ipaddr_to_numeric(&a));
     75 	a.s_addr = ~(r->min_ip ^ r->max_ip);
     76 	bits = netmask2bits(a.s_addr);
     77 	if (bits < 0)
     78 		printf("/%s", xtables_ipaddr_to_numeric(&a));
     79 	else
     80 		printf("/%d", bits);
     81 }
     82 
     83 static void NETMAP_print(const void *ip, const struct xt_entry_target *target,
     84 			 int numeric)
     85 {
     86 	printf(" to:");
     87 	__NETMAP_print(ip, target, numeric);
     88 }
     89 
     90 static void NETMAP_save(const void *ip, const struct xt_entry_target *target)
     91 {
     92 	printf(" --%s ", NETMAP_opts[0].name);
     93 	__NETMAP_print(ip, target, 0);
     94 }
     95 
     96 static struct xtables_target netmap_tg_reg = {
     97 	.name		= MODULENAME,
     98 	.version	= XTABLES_VERSION,
     99 	.family		= NFPROTO_IPV4,
    100 	.size		= XT_ALIGN(sizeof(struct nf_nat_ipv4_multi_range_compat)),
    101 	.userspacesize	= XT_ALIGN(sizeof(struct nf_nat_ipv4_multi_range_compat)),
    102 	.help		= NETMAP_help,
    103 	.init		= NETMAP_init,
    104 	.x6_parse	= NETMAP_parse,
    105 	.print		= NETMAP_print,
    106 	.save		= NETMAP_save,
    107 	.x6_options	= NETMAP_opts,
    108 };
    109 
    110 void _init(void)
    111 {
    112 	xtables_register_target(&netmap_tg_reg);
    113 }
    114