/* 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
                            || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));

        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");
                        ip_rt_put(rt);
                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(struct ip_conntrack *i, void *ifindex)
{
        int ret;

        READ_LOCK(&masq_lock);
        ret = (i->nat.masq_index == (int)(long)ifindex);
        READ_UNLOCK(&masq_lock);

        return ret;
}

static int masq_device_event(struct notifier_block *this,
                             unsigned long event,
                             void *ptr)
{
        struct net_device *dev = ptr;

        if (event == NETDEV_DOWN) {
                /* Device was downed.  Search entire table for
                   conntracks which were associated with that device,
                   and forget them. */
                IP_NF_ASSERT(dev->ifindex != 0);
 
                ip_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
        }

        return NOTIFY_DONE;
}


static int masq_inet_event(struct notifier_block *this,
                           unsigned long event,
                           void *ptr)
{
        struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;

        if (event == NETDEV_DOWN) {
                /* IP address was deleted.  Search entire table for
                   conntracks which were associated with that device,
                   and forget them. */
                IP_NF_ASSERT(dev->ifindex != 0);

                ip_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
        }

        return NOTIFY_DONE;
}

static struct notifier_block masq_dev_notifier = {
        .notifier_call  = masq_device_event,
};

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 for device down reports */
                register_netdevice_notifier(&masq_dev_notifier);
                /* Register IP address change reports */
                register_inetaddr_notifier(&masq_inet_notifier);
        }

        return ret;
}

static void __exit fini(void)
{
        ipt_unregister_target(&masquerade);
        unregister_netdevice_notifier(&masq_dev_notifier);
        unregister_inetaddr_notifier(&masq_inet_notifier);      
}

module_init(init);
module_exit(fini);
MODULE_LICENSE("GPL");