/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

/* Everything about the rules for NAT. */
#include <linux/types.h>
#include <linux/ip.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/module.h>
#include <linux/kmod.h>
#include <linux/skbuff.h>
#include <linux/proc_fs.h>
#include <net/checksum.h>
#include <net/route.h>
#include <linux/bitops.h>

#include <linux/netfilter_ipv4/ip_tables.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_core.h>
#include <net/netfilter/nf_nat_rule.h>

#define NAT_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
                         (1 << NF_INET_POST_ROUTING) | \
                         (1 << NF_INET_LOCAL_OUT))

static const struct
{
        struct ipt_replace repl;
        struct ipt_standard entries[3];
        struct ipt_error term;
} nat_initial_table __net_initdata = {
        .repl = {
                .name = "nat",
                .valid_hooks = NAT_VALID_HOOKS,
                .num_entries = 4,
                .size = sizeof(struct ipt_standard) * 3 + sizeof(struct ipt_error),
                .hook_entry = {
                        [NF_INET_PRE_ROUTING] = 0,
                        [NF_INET_POST_ROUTING] = sizeof(struct ipt_standard),
                        [NF_INET_LOCAL_OUT] = sizeof(struct ipt_standard) * 2
                },
                .underflow = {
                        [NF_INET_PRE_ROUTING] = 0,
                        [NF_INET_POST_ROUTING] = sizeof(struct ipt_standard),
                        [NF_INET_LOCAL_OUT] = sizeof(struct ipt_standard) * 2
                },
        },
        .entries = {
                IPT_STANDARD_INIT(NF_ACCEPT),   /* PRE_ROUTING */
                IPT_STANDARD_INIT(NF_ACCEPT),   /* POST_ROUTING */
                IPT_STANDARD_INIT(NF_ACCEPT),   /* LOCAL_OUT */
        },
        .term = IPT_ERROR_INIT,                 /* ERROR */
};

static const struct xt_table nat_table = {
        .name           = "nat",
        .valid_hooks    = NAT_VALID_HOOKS,
        .me             = THIS_MODULE,
        .af             = NFPROTO_IPV4,
};

/* Source NAT */
static unsigned int
ipt_snat_target(struct sk_buff *skb, const struct xt_target_param *par)
{
        struct nf_conn *ct;
        enum ip_conntrack_info ctinfo;
        const struct nf_nat_multi_range_compat *mr = par->targinfo;

        NF_CT_ASSERT(par->hooknum == NF_INET_POST_ROUTING);

        ct = nf_ct_get(skb, &ctinfo);

        /* Connection must be valid and new. */
        NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
                            ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));
        NF_CT_ASSERT(par->out != NULL);

        return nf_nat_setup_info(ct, &mr->range[0], IP_NAT_MANIP_SRC);
}

static unsigned int
ipt_dnat_target(struct sk_buff *skb, const struct xt_target_param *par)
{
        struct nf_conn *ct;
        enum ip_conntrack_info ctinfo;
        const struct nf_nat_multi_range_compat *mr = par->targinfo;

        NF_CT_ASSERT(par->hooknum == NF_INET_PRE_ROUTING ||
                     par->hooknum == NF_INET_LOCAL_OUT);

        ct = nf_ct_get(skb, &ctinfo);

        /* Connection must be valid and new. */
        NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED));

        return nf_nat_setup_info(ct, &mr->range[0], IP_NAT_MANIP_DST);
}

static bool ipt_snat_checkentry(const struct xt_tgchk_param *par)
{
        const struct nf_nat_multi_range_compat *mr = par->targinfo;

        /* Must be a valid range */
        if (mr->rangesize != 1) {
                printk("SNAT: multiple ranges no longer supported\n");
                return false;
        }
        return true;
}

static bool ipt_dnat_checkentry(const struct xt_tgchk_param *par)
{
        const struct nf_nat_multi_range_compat *mr = par->targinfo;

        /* Must be a valid range */
        if (mr->rangesize != 1) {
                printk("DNAT: multiple ranges no longer supported\n");
                return false;
        }
        return true;
}

unsigned int
alloc_null_binding(struct nf_conn *ct, unsigned int hooknum)
{
        /* Force range to this IP; let proto decide mapping for
           per-proto parts (hence not IP_NAT_RANGE_PROTO_SPECIFIED).
           Use reply in case it's already been mangled (eg local packet).
        */
        __be32 ip
                = (HOOK2MANIP(hooknum) == IP_NAT_MANIP_SRC
                   ? ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip
                   : ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3.ip);
        struct nf_nat_range range
                = { IP_NAT_RANGE_MAP_IPS, ip, ip, { 0 }, { 0 } };

        pr_debug("Allocating NULL binding for %p (%pI4)\n", ct, &ip);
        return nf_nat_setup_info(ct, &range, HOOK2MANIP(hooknum));
}

int nf_nat_rule_find(struct sk_buff *skb,
                     unsigned int hooknum,
                     const struct net_device *in,
                     const struct net_device *out,
                     struct nf_conn *ct)
{
        struct net *net = nf_ct_net(ct);
        int ret;

        ret = ipt_do_table(skb, hooknum, in, out, net->ipv4.nat_table);

        if (ret == NF_ACCEPT) {
                if (!nf_nat_initialized(ct, HOOK2MANIP(hooknum)))
                        /* NUL mapping */
                        ret = alloc_null_binding(ct, hooknum);
        }
        return ret;
}

static struct xt_target ipt_snat_reg __read_mostly = {
        .name           = "SNAT",
        .target         = ipt_snat_target,
        .targetsize     = sizeof(struct nf_nat_multi_range_compat),
        .table          = "nat",
        .hooks          = 1 << NF_INET_POST_ROUTING,
        .checkentry     = ipt_snat_checkentry,
        .family         = AF_INET,
};

static struct xt_target ipt_dnat_reg __read_mostly = {
        .name           = "DNAT",
        .target         = ipt_dnat_target,
        .targetsize     = sizeof(struct nf_nat_multi_range_compat),
        .table          = "nat",
        .hooks          = (1 << NF_INET_PRE_ROUTING) | (1 << NF_INET_LOCAL_OUT),
        .checkentry     = ipt_dnat_checkentry,
        .family         = AF_INET,
};

static int __net_init nf_nat_rule_net_init(struct net *net)
{
        net->ipv4.nat_table = ipt_register_table(net, &nat_table,
                                                 &nat_initial_table.repl);
        if (IS_ERR(net->ipv4.nat_table))
                return PTR_ERR(net->ipv4.nat_table);
        return 0;
}

static void __net_exit nf_nat_rule_net_exit(struct net *net)
{
        ipt_unregister_table(net->ipv4.nat_table);
}

static struct pernet_operations nf_nat_rule_net_ops = {
        .init = nf_nat_rule_net_init,
        .exit = nf_nat_rule_net_exit,
};

int __init nf_nat_rule_init(void)
{
        int ret;

        ret = register_pernet_subsys(&nf_nat_rule_net_ops);
        if (ret != 0)
                goto out;
        ret = xt_register_target(&ipt_snat_reg);
        if (ret != 0)
                goto unregister_table;

        ret = xt_register_target(&ipt_dnat_reg);
        if (ret != 0)
                goto unregister_snat;

        return ret;

 unregister_snat:
        xt_unregister_target(&ipt_snat_reg);
 unregister_table:
        unregister_pernet_subsys(&nf_nat_rule_net_ops);
 out:
        return ret;
}

void nf_nat_rule_cleanup(void)
{
        xt_unregister_target(&ipt_dnat_reg);
        xt_unregister_target(&ipt_snat_reg);
        unregister_pernet_subsys(&nf_nat_rule_net_ops);
}