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/* Shared library add-on to iptables to add source-NAT support. */
#include <stdio.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <getopt.h>
#include <iptables.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv4/ip_nat_rule.h>
/* Source NAT data consists of a multi-range, indicating where to map
to. */
struct ipt_natinfo
{
struct ipt_entry_target t;
struct ip_nat_multi_range mr;
};
/* Function which prints out usage message. */
static void
help(void)
{
printf(
"SNAT v%s options:\n"
" --to-source <ipaddr>[-<ipaddr>][:port-port]\n"
" Address to map source to.\n"
" (You can use this more than once)\n\n",
NETFILTER_VERSION);
}
static struct option opts[] = {
{ "to-source", 1, 0, '1' },
{ 0 }
};
/* Initialize the target. */
static void
init(struct ipt_entry_target *t, unsigned int *nfcache)
{
/* Can't cache this */
*nfcache |= NFC_UNKNOWN;
}
static struct ipt_natinfo *
append_range(struct ipt_natinfo *info, const struct ip_nat_range *range)
{
unsigned int size;
/* One rangesize already in struct ipt_natinfo */
size = IPT_ALIGN(sizeof(*info) + info->mr.rangesize * sizeof(*range));
info = realloc(info, size);
if (!info)
exit_error(OTHER_PROBLEM, "Out of memory\n");
info->t.u.target_size = size;
info->mr.range[info->mr.rangesize] = *range;
info->mr.rangesize++;
return info;
}
/* Ranges expected in network order. */
static struct ipt_entry_target *
parse_to(char *arg, int portok, struct ipt_natinfo *info)
{
struct ip_nat_range range;
char *colon, *dash;
struct in_addr *ip;
memset(&range, 0, sizeof(range));
colon = strchr(arg, ':');
if (colon) {
int port;
if (!portok)
exit_error(PARAMETER_PROBLEM,
"Need TCP or UDP with port specification");
range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
port = atoi(colon+1);
if (port == 0 || port > 65535)
exit_error(PARAMETER_PROBLEM,
"Port `%s' not valid\n", colon+1);
dash = strchr(colon, '-');
if (!dash) {
range.min.tcp.port
= range.max.tcp.port
= htons(port);
} else {
int maxport;
maxport = atoi(dash + 1);
if (maxport == 0 || maxport > 65535)
exit_error(PARAMETER_PROBLEM,
"Port `%s' not valid\n", dash+1);
if (maxport < port)
/* People are stupid. */
exit_error(PARAMETER_PROBLEM,
"Port range `%s' funky\n", colon+1);
range.min.tcp.port = htons(port);
range.max.tcp.port = htons(maxport);
}
/* Starts with a colon? No IP info...*/
if (colon == arg)
return &(append_range(info, &range)->t);
*colon = '\0';
}
range.flags |= IP_NAT_RANGE_MAP_IPS;
dash = strchr(arg, '-');
if (colon && dash && dash > colon)
dash = NULL;
if (dash)
*dash = '\0';
ip = dotted_to_addr(arg);
if (!ip)
exit_error(PARAMETER_PROBLEM, "Bad IP address `%s'\n",
arg);
range.min_ip = ip->s_addr;
if (dash) {
ip = dotted_to_addr(dash+1);
if (!ip)
exit_error(PARAMETER_PROBLEM, "Bad IP address `%s'\n",
dash+1);
range.max_ip = ip->s_addr;
} else
range.max_ip = range.min_ip;
return &(append_range(info, &range)->t);
}
/* Function which parses command options; returns true if it
ate an option */
static int
parse(int c, char **argv, int invert, unsigned int *flags,
const struct ipt_entry *entry,
struct ipt_entry_target **target)
{
struct ipt_natinfo *info = (void *)*target;
int portok;
if (entry->ip.proto == IPPROTO_TCP
|| entry->ip.proto == IPPROTO_UDP)
portok = 1;
else
portok = 0;
switch (c) {
case '1':
if (check_inverse(optarg, &invert))
exit_error(PARAMETER_PROBLEM,
"Unexpected `!' after --to-source");
*target = parse_to(optarg, portok, info);
*flags = 1;
return 1;
default:
return 0;
}
}
/* Final check; must have specfied --to-source. */
static void final_check(unsigned int flags)
{
if (!flags)
exit_error(PARAMETER_PROBLEM,
"You must specify --to-source");
}
static void print_range(const struct ip_nat_range *r)
{
if (r->flags & IP_NAT_RANGE_MAP_IPS) {
struct in_addr a;
a.s_addr = r->min_ip;
printf("%s", addr_to_dotted(&a));
if (r->max_ip != r->min_ip) {
a.s_addr = r->max_ip;
printf("-%s", addr_to_dotted(&a));
}
}
if (r->flags & IP_NAT_RANGE_PROTO_SPECIFIED) {
printf(":");
printf("%hu", ntohs(r->min.tcp.port));
if (r->max.tcp.port != r->min.tcp.port)
printf("-%hu", ntohs(r->max.tcp.port));
}
}
/* Prints out the targinfo. */
static void
print(const struct ipt_ip *ip,
const struct ipt_entry_target *target,
int numeric)
{
struct ipt_natinfo *info = (void *)target;
unsigned int i = 0;
printf("to:");
for (i = 0; i < info->mr.rangesize; i++) {
print_range(&info->mr.range[i]);
printf(" ");
}
}
/* Saves the union ipt_targinfo in parsable form to stdout. */
static void
save(const struct ipt_ip *ip, const struct ipt_entry_target *target)
{
struct ipt_natinfo *info = (void *)target;
unsigned int i = 0;
for (i = 0; i < info->mr.rangesize; i++) {
printf("--to-source ");
print_range(&info->mr.range[i]);
printf(" ");
}
}
struct iptables_target snat
= { NULL,
"SNAT",
NETFILTER_VERSION,
IPT_ALIGN(sizeof(struct ip_nat_multi_range)),
IPT_ALIGN(sizeof(struct ip_nat_multi_range)),
&help,
&init,
&parse,
&final_check,
&print,
&save,
opts
};
void _init(void)
{
register_target(&snat);
}
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