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/* Masquerade.  Simple mapping which alters range to a local IP address
   (depending on route). */
#include <linux/config.h>
#include <linux/types.h>
#include <linux/ip.h>
#include <linux/timer.h>
#include <linux/module.h>
#include <linux/netfilter.h>
#include <net/protocol.h>
#include <net/checksum.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_ipv4/ip_nat_rule.h>
#include <linux/netfilter_ipv4/ip_tables.h>
 
#if 0
#define DEBUGP printk
#else
#define DEBUGP(format, args...)
#endif
 
/* Lock protects masq region inside conntrack */
static DECLARE_RWLOCK(masq_lock);
 
/* FIXME: Multiple targets. --RR */
static int
masquerade_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("masquerade_check: bad table `%s'.\n", tablename);
		return 0;
	}
	if (targinfosize != IPT_ALIGN(sizeof(*mr))) {
		DEBUGP("masquerade_check: size %u != %u.\n",
		       targinfosize, sizeof(*mr));
		return 0;
	}
	if (hook_mask & ~(1 << NF_IP_POST_ROUTING)) {
		DEBUGP("masquerade_check: bad hooks %x.\n", hook_mask);
		return 0;
	}
	if (mr->range[0].flags & IP_NAT_RANGE_MAP_IPS) {
		DEBUGP("masquerade_check: bad MAP_IPS.\n");
		return 0;
	}
	if (mr->rangesize != 1) {
		DEBUGP("masquerade_check: bad rangesize %u.\n", mr->rangesize);
		return 0;
	}
	return 1;
}
 
static unsigned int
masquerade_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;
	const struct ip_nat_multi_range *mr;
	struct ip_nat_multi_range newrange;
	u_int32_t newsrc;
	struct rtable *rt;
	struct rt_key key;
 
	IP_NF_ASSERT(hooknum == NF_IP_POST_ROUTING);
 
	/* FIXME: For the moment, don't do local packets, breaks
	   testsuite for 2.3.49 --RR */
	if ((*pskb)->sk)
		return NF_ACCEPT;
 
	ct = ip_conntrack_get(*pskb, &ctinfo);
	IP_NF_ASSERT(ct && (ctinfo == IP_CT_NEW
				  || ctinfo == IP_CT_RELATED));
 
	mr = targinfo;
 
	key.dst = (*pskb)->nh.iph->daddr;
	key.src = 0; /* Unknown: that's what we're trying to establish */
	key.tos = RT_TOS((*pskb)->nh.iph->tos)|RTO_CONN;
	key.oif = 0;
#ifdef CONFIG_IP_ROUTE_FWMARK
	key.fwmark = (*pskb)->nfmark;
#endif
	if (ip_route_output_key(&rt, &key) != 0) {
                /* Funky routing can do this. */
                if (net_ratelimit())
                        printk("MASQUERADE:"
                               " No route: Rusty's brain broke!\n");
                return NF_DROP;
        }
        if (rt->u.dst.dev != out) {
                if (net_ratelimit())
                        printk("MASQUERADE:"
                               " Route sent us somewhere else.\n");
		return NF_DROP;
	}
 
	newsrc = rt->rt_src;
	DEBUGP("newsrc = %u.%u.%u.%u\n", NIPQUAD(newsrc));
	ip_rt_put(rt);
 
	WRITE_LOCK(&masq_lock);
	ct->nat.masq_index = out->ifindex;
	WRITE_UNLOCK(&masq_lock);
 
	/* Transfer from original range. */
	newrange = ((struct ip_nat_multi_range)
		{ 1, { { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
			 newsrc, newsrc,
			 mr->range[0].min, mr->range[0].max } } });
 
	/* Hand modified range to generic setup. */
	return ip_nat_setup_info(ct, &newrange, hooknum);
}
 
static inline int
device_cmp(const struct ip_conntrack *i, void *_ina)
{
	int ret = 0;
	struct in_ifaddr *ina = _ina;
 
	READ_LOCK(&masq_lock);
	/* If it's masquerading out this interface with a different address,
	 * or we don't know the new address of this interface. */
	if (i->nat.masq_index == ina->ifa_dev->dev->ifindex
	    && i->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip != ina->ifa_address)
		ret = 1;
	READ_UNLOCK(&masq_lock);
 
	return ret;
}
 
static int masq_inet_event(struct notifier_block *this,
			   unsigned long event,
			   void *ptr)
{
	/* For some configurations, interfaces often come back with
	 * the same address.  If not, clean up old conntrack
	 * entries. */
	if (event == NETDEV_UP)
		ip_ct_selective_cleanup(device_cmp, ptr);
 
	return NOTIFY_DONE;
}
 
static struct notifier_block masq_inet_notifier = {
	.notifier_call = masq_inet_event
};
 
static struct ipt_target masquerade
= { { NULL, NULL }, "MASQUERADE", masquerade_target, masquerade_check, NULL,
    THIS_MODULE };
 
static int __init init(void)
{
	int ret;
 
	ret = ipt_register_target(&masquerade);
 
	if (ret == 0)
		/* Register IP address change reports */
		register_inetaddr_notifier(&masq_inet_notifier);
 
	return ret;
}
 
static void __exit fini(void)
{
	ipt_unregister_target(&masquerade);
	unregister_inetaddr_notifier(&masq_inet_notifier);	
}
 
module_init(init);
module_exit(fini);
MODULE_LICENSE("GPL");