[PATCH] New static NAT target
Svenning Soerensen
svenning@post5.tele.dk
Fri, 20 Apr 2001 00:53:39 +0200
Hello there.
I've hacked up a new target which provides static 1:1 NAT mapping.
This is similar to the Fast NAT option, except that Netfilter's
connection tracking doesn't coexist happily with Fast NAT.
It can be applied to PREROUTING and/or POSTROUTING.
I've given it the name `STATIC', but I'm not sure if another name
would have been better (Actually, I was tempted to call it simply
`NAT', because it actually performs *Network Address* Translation,
but... :-)).
Of course, if you accept the patch, you're welcome to rename it to
anything you like.
Svenning
diff -urN iptables-1.2.1a/extensions/.STATIC-test iptables.static/extensions/.STATIC-test
--- iptables-1.2.1a/extensions/.STATIC-test Thu Jan 1 01:00:00 1970
+++ iptables.static/extensions/.STATIC-test Thu Apr 19 23:15:25 2001
@@ -0,0 +1,2 @@
+#! /bin/sh
+[ -f $KERNEL_DIR/net/ipv4/netfilter/ipt_STATIC.c ] && echo STATIC
diff -urN iptables-1.2.1a/extensions/libipt_STATIC.c iptables.static/extensions/libipt_STATIC.c
--- iptables-1.2.1a/extensions/libipt_STATIC.c Thu Jan 1 01:00:00 1970
+++ iptables.static/extensions/libipt_STATIC.c Thu Apr 19 23:15:11 2001
@@ -0,0 +1,201 @@
+/* Shared library add-on to iptables to add static NAT support.
+ Author: Svenning Soerensen <svenning@post5.tele.dk>
+*/
+
+#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>
+
+#define MODULENAME "STATIC"
+
+static struct option opts[] = {
+ { "to", 1, 0, '1' },
+ { 0 }
+};
+
+/* Function which prints out usage message. */
+static void
+help(void)
+{
+ printf(MODULENAME" v%s options:\n"
+ " --%s address[/mask]\n"
+ " Network address to map to.\n\n",
+ NETFILTER_VERSION, opts[0].name);
+}
+
+static u_int32_t
+bits2netmask(int bits)
+{
+ u_int32_t netmask, bm;
+
+ if (bits >= 32 || bits < 0)
+ return(~0);
+ for (netmask = 0, bm = 0x80000000; bits; bits--, bm >>= 1)
+ netmask |= bm;
+ return htonl(netmask);
+}
+
+static int
+netmask2bits(u_int32_t netmask)
+{
+ u_int32_t bm;
+ int bits;
+
+ netmask = ntohl(netmask);
+ for (bits = 0, bm = 0x80000000; netmask & bm; netmask <<= 1)
+ bits++;
+ if (netmask)
+ return -1; /* holes in netmask */
+ return bits;
+}
+
+/* Initialize the target. */
+static void
+init(struct ipt_entry_target *t, unsigned int *nfcache)
+{
+ struct ip_nat_multi_range *mr = (struct ip_nat_multi_range *)t->data;
+
+ /* Actually, it's 0, but it's ignored at the moment. */
+ mr->rangesize = 1;
+
+ /* Can't cache this */
+ *nfcache |= NFC_UNKNOWN;
+}
+
+/* Parses network address */
+static void
+parse_to(char *arg, struct ip_nat_range *range)
+{
+ char *slash;
+ struct in_addr *ip;
+ u_int32_t netmask;
+ int bits;
+
+ range->flags |= IP_NAT_RANGE_MAP_IPS;
+ slash = strchr(arg, '/');
+ if (slash)
+ *slash = '\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 (slash) {
+ if (strchr(slash+1, '.')) {
+ ip = dotted_to_addr(slash+1);
+ if (!ip)
+ exit_error(PARAMETER_PROBLEM, "Bad netmask `%s'\n",
+ slash+1);
+ netmask = ip->s_addr;
+ }
+ else {
+ if ((bits = string_to_number(slash+1, 0, 32)) == -1)
+ exit_error(PARAMETER_PROBLEM, "Bad netmask `%s'\n",
+ slash+1);
+ netmask = bits2netmask(bits);
+ }
+ /* Don't allow /0 (/1 is probably insane, too) */
+ if (netmask == 0)
+ exit_error(PARAMETER_PROBLEM, "Netmask needed\n");
+ }
+ else
+ netmask = ~0;
+
+ if (range->min_ip & ~netmask) {
+ if (slash)
+ *slash = '/';
+ exit_error(PARAMETER_PROBLEM, "Bad network address `%s'\n",
+ arg);
+ }
+ range->max_ip = range->min_ip | ~netmask;
+}
+
+/* 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 ip_nat_multi_range *mr
+ = (struct ip_nat_multi_range *)(*target)->data;
+
+ switch (c) {
+ case '1':
+ if (check_inverse(optarg, &invert))
+ exit_error(PARAMETER_PROBLEM,
+ "Unexpected `!' after --%s", opts[0].name);
+
+ parse_to(optarg, &mr->range[0]);
+ *flags = 1;
+ return 1;
+
+ default:
+ return 0;
+ }
+}
+
+/* Final check; need --to */
+static void final_check(unsigned int flags)
+{
+ if (!flags)
+ exit_error(PARAMETER_PROBLEM,
+ MODULENAME" needs --%s", opts[0].name);
+}
+
+/* Prints out the targinfo. */
+static void
+print(const struct ipt_ip *ip,
+ const struct ipt_entry_target *target,
+ int numeric)
+{
+ struct ip_nat_multi_range *mr
+ = (struct ip_nat_multi_range *)target->data;
+ struct ip_nat_range *r = &mr->range[0];
+ struct in_addr a;
+ int bits;
+
+ a.s_addr = r->min_ip;
+ printf("%s", addr_to_dotted(&a));
+ a.s_addr = ~(r->min_ip ^ r->max_ip);
+ bits = netmask2bits(a.s_addr);
+ if (bits < 0)
+ printf("/%s", addr_to_dotted(&a));
+ else
+ printf("/%d", bits);
+}
+
+/* Saves the targinfo in parsable form to stdout. */
+static void
+save(const struct ipt_ip *ip, const struct ipt_entry_target *target)
+{
+ printf("--%s ", opts[0].name);
+ print(ip, target, 0);
+}
+
+struct iptables_target target_module
+= { NULL,
+ MODULENAME,
+ 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(&target_module);
+}
+
diff -urN iptables-1.2.1a/patch-o-matic/STATIC.patch iptables.static/patch-o-matic/STATIC.patch
--- iptables-1.2.1a/patch-o-matic/STATIC.patch Thu Jan 1 01:00:00 1970
+++ iptables.static/patch-o-matic/STATIC.patch Thu Apr 19 23:02:32 2001
@@ -0,0 +1,110 @@
+diff -uN linux.orig/net/ipv4/netfilter/ipt_STATIC.c linux/net/ipv4/netfilter/ipt_STATIC.c
+--- linux.orig/net/ipv4/netfilter/ipt_STATIC.c Thu Jan 1 01:00:00 1970
++++ linux/net/ipv4/netfilter/ipt_STATIC.c Thu Apr 19 17:30:18 2001
+@@ -0,0 +1,106 @@
++/* STATIC - static NAT mapping of IP network addresses (1:1).
++ The mapping can be applied to source (POSTROUTING),
++ destination (PREROUTING), or both (with separate rules).
++
++ Author: Svenning Soerensen <svenning@post5.tele.dk>
++*/
++
++#include <linux/config.h>
++#include <linux/ip.h>
++#include <linux/module.h>
++#include <linux/netdevice.h>
++#include <linux/netfilter.h>
++#include <linux/netfilter_ipv4.h>
++#include <linux/netfilter_ipv4/ip_nat_rule.h>
++
++#define MODULENAME "STATIC"
++
++#if 0
++#define DEBUGP printk
++#else
++#define DEBUGP(format, args...)
++#endif
++
++static int
++check(const char *tablename,
++ const struct ipt_entry *e,
++ void *targinfo,
++ unsigned int targinfosize,
++ unsigned int hook_mask)
++{
++ const struct ip_nat_multi_range *mr = targinfo;
++
++ if (strcmp(tablename, "nat") != 0) {
++ DEBUGP(MODULENAME":check: bad table `%s'.\n", tablename);
++ return 0;
++ }
++ if (targinfosize != IPT_ALIGN(sizeof(*mr))) {
++ DEBUGP(MODULENAME":check: size %u.\n", targinfosize);
++ return 0;
++ }
++ if (hook_mask & ~((1 << NF_IP_PRE_ROUTING) | (1 << NF_IP_POST_ROUTING))) {
++ DEBUGP(MODULENAME":check: bad hooks %x.\n", hook_mask);
++ return 0;
++ }
++ if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
++ DEBUGP(MODULENAME":check: bad MAP_IPS.\n");
++ return 0;
++ }
++ if (mr->rangesize != 1) {
++ DEBUGP(MODULENAME":check: bad rangesize %u.\n", mr->rangesize);
++ return 0;
++ }
++ return 1;
++}
++
++static unsigned int
++target(struct sk_buff **pskb,
++ unsigned int hooknum,
++ const struct net_device *in,
++ const struct net_device *out,
++ const void *targinfo,
++ void *userinfo)
++{
++ struct ip_conntrack *ct;
++ enum ip_conntrack_info ctinfo;
++ u_int32_t new_ip, netmask;
++ const struct ip_nat_multi_range *mr = targinfo;
++ struct ip_nat_multi_range newrange;
++
++ IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
++ || hooknum == NF_IP_POST_ROUTING);
++ ct = ip_conntrack_get(*pskb, &ctinfo);
++
++ netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
++
++ if (hooknum == NF_IP_PRE_ROUTING)
++ new_ip = (*pskb)->nh.iph->daddr & ~netmask;
++ else
++ new_ip = (*pskb)->nh.iph->saddr & ~netmask;
++ new_ip |= mr->range[0].min_ip & netmask;
++
++ newrange = ((struct ip_nat_multi_range)
++ { 1, { { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
++ new_ip, new_ip,
++ mr->range[0].min, mr->range[0].max } } });
++
++ /* Hand modified range to generic setup. */
++ return ip_nat_setup_info(ct, &newrange, hooknum);
++}
++
++static struct ipt_target target_module
++= { { NULL, NULL }, MODULENAME, target, check, NULL,
++ THIS_MODULE };
++
++static int __init init(void)
++{
++ return ipt_register_target(&target_module);
++}
++
++static void __exit fini(void)
++{
++ ipt_unregister_target(&target_module);
++}
++
++module_init(init);
++module_exit(fini);
diff -urN iptables-1.2.1a/patch-o-matic/STATIC.patch.configure.help iptables.static/patch-o-matic/STATIC.patch.configure.help
--- iptables-1.2.1a/patch-o-matic/STATIC.patch.configure.help Thu Jan 1 01:00:00 1970
+++ iptables.static/patch-o-matic/STATIC.patch.configure.help Thu Apr 19 23:41:20 2001
@@ -0,0 +1,11 @@
+CONFIG_IP_NF_TARGET_REDIRECT
+STATIC target support
+CONFIG_IP_NF_TARGET_STATIC
+ STATIC is an implementation of static 1:1 NAT mapping of network
+ addresses. It maps the network address part, while keeping the
+ host address part intact. It is similar to Fast NAT, except that
+ Netfilter's connection tracking doesn't work well with Fast NAT.
+
+ If you want to compile it as a module, say M here and read
+ Documentation/modules.txt. The module will be called
+ ipt_STATIC.o. If unsure, say `N'.
diff -urN iptables-1.2.1a/patch-o-matic/STATIC.patch.config.in iptables.static/patch-o-matic/STATIC.patch.config.in
--- iptables-1.2.1a/patch-o-matic/STATIC.patch.config.in Thu Jan 1 01:00:00 1970
+++ iptables.static/patch-o-matic/STATIC.patch.config.in Thu Apr 19 23:43:22 2001
@@ -0,0 +1,2 @@
+ dep_tristate ' REDIRECT target support' CONFIG_IP_NF_TARGET_REDIRECT $CONFIG_IP_NF_NAT
+ dep_tristate ' STATIC target support' CONFIG_IP_NF_TARGET_STATIC $CONFIG_IP_NF_NAT
diff -urN iptables-1.2.1a/patch-o-matic/STATIC.patch.help iptables.static/patch-o-matic/STATIC.patch.help
--- iptables-1.2.1a/patch-o-matic/STATIC.patch.help Thu Jan 1 01:00:00 1970
+++ iptables.static/patch-o-matic/STATIC.patch.help Thu Apr 19 23:36:04 2001
@@ -0,0 +1,16 @@
+Author: Svenning Soerensen <svenning@post5.tele.dk>
+Status: Experimental
+
+This adds CONFIG_IP_NF_TARGET_STATIC option, which provides a target for
+the nat table. It creates a static 1:1 mapping of the network address,
+while keeping host addresses intact. It can be applied to the
+PREROUTING chain to alter the destination of incoming connections,
+to the POSTROUTING chain to alter the source of outgoing connections,
+or both (with separate rules).
+
+Examples:
+
+iptables -t nat -A PREROUTING -d 1.2.3.0/24 -j STATIC --to 5.6.7.0/24
+
+iptables -t nat -A POSTROUTING -s 5.6.7.0/24 -j STATIC --to 1.2.3.0/24
+
diff -urN iptables-1.2.1a/patch-o-matic/STATIC.patch.makefile iptables.static/patch-o-matic/STATIC.patch.makefile
--- iptables-1.2.1a/patch-o-matic/STATIC.patch.makefile Thu Jan 1 01:00:00 1970
+++ iptables.static/patch-o-matic/STATIC.patch.makefile Thu Apr 19 23:45:14 2001
@@ -0,0 +1,2 @@
+obj-$(CONFIG_IP_NF_TARGET_REDIRECT) += ipt_REDIRECT.o
+obj-$(CONFIG_IP_NF_TARGET_STATIC) += ipt_STATIC.o