iptable_nat.c

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/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <[email protected]>
 * (C) 2011 Patrick McHardy <[email protected]>
 *
 * 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.
 */

#include <linux/module.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/ip.h>
#include <net/ip.h>

#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_core.h>
#include <net/netfilter/nf_nat_l3proto.h>

static const struct xt_table nf_nat_ipv4_table = {
    .name       = "nat",
    .valid_hooks    = (1 << NF_INET_PRE_ROUTING) |
              (1 << NF_INET_POST_ROUTING) |
              (1 << NF_INET_LOCAL_OUT) |
              (1 << NF_INET_LOCAL_IN),
    .me     = THIS_MODULE,
    .af     = NFPROTO_IPV4,
};

static 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).
     */
    struct nf_nat_range range;

    range.flags = 0;
    pr_debug("Allocating NULL binding for %p (%pI4)\n", ct,
         HOOK2MANIP(hooknum) == NF_NAT_MANIP_SRC ?
         &ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip :
         &ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3.ip);

    return nf_nat_setup_info(ct, &range, HOOK2MANIP(hooknum));
}

static unsigned 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);
    unsigned 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)))
            ret = alloc_null_binding(ct, hooknum);
    }
    return ret;
}

static unsigned int
nf_nat_ipv4_fn(unsigned int hooknum,
           struct sk_buff *skb,
           const struct net_device *in,
           const struct net_device *out,
           int (*okfn)(struct sk_buff *))
{
    struct nf_conn *ct;
    enum ip_conntrack_info ctinfo;
    struct nf_conn_nat *nat;
    /* maniptype == SRC for postrouting. */
    enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);

    /* We never see fragments: conntrack defrags on pre-routing
     * and local-out, and nf_nat_out protects post-routing.
     */
    NF_CT_ASSERT(!ip_is_fragment(ip_hdr(skb)));

    ct = nf_ct_get(skb, &ctinfo);
    /* Can't track?  It's not due to stress, or conntrack would
     * have dropped it.  Hence it's the user's responsibilty to
     * packet filter it out, or implement conntrack/NAT for that
     * protocol. 8) --RR
     */
    if (!ct)
        return NF_ACCEPT;

    /* Don't try to NAT if this packet is not conntracked */
    if (nf_ct_is_untracked(ct))
        return NF_ACCEPT;

    nat = nfct_nat(ct);
    if (!nat) {
        /* NAT module was loaded late. */
        if (nf_ct_is_confirmed(ct))
            return NF_ACCEPT;
        nat = nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC);
        if (nat == NULL) {
            pr_debug("failed to add NAT extension\n");
            return NF_ACCEPT;
        }
    }

    switch (ctinfo) {
    case IP_CT_RELATED:
    case IP_CT_RELATED_REPLY:
        if (ip_hdr(skb)->protocol == IPPROTO_ICMP) {
            if (!nf_nat_icmp_reply_translation(skb, ct, ctinfo,
                               hooknum))
                return NF_DROP;
            else
                return NF_ACCEPT;
        }
        /* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
    case IP_CT_NEW:
        /* Seen it before?  This can happen for loopback, retrans,
         * or local packets.
         */
        if (!nf_nat_initialized(ct, maniptype)) {
            unsigned int ret;

            ret = nf_nat_rule_find(skb, hooknum, in, out, ct);
            if (ret != NF_ACCEPT)
                return ret;
        } else
            pr_debug("Already setup manip %s for ct %p\n",
                 maniptype == NF_NAT_MANIP_SRC ? "SRC" : "DST",
                 ct);
        break;

    default:
        /* ESTABLISHED */
        NF_CT_ASSERT(ctinfo == IP_CT_ESTABLISHED ||
                 ctinfo == IP_CT_ESTABLISHED_REPLY);
    }

    return nf_nat_packet(ct, ctinfo, hooknum, skb);
}

static unsigned int
nf_nat_ipv4_in(unsigned int hooknum,
           struct sk_buff *skb,
           const struct net_device *in,
           const struct net_device *out,
           int (*okfn)(struct sk_buff *))
{
    unsigned int ret;
    __be32 daddr = ip_hdr(skb)->daddr;

    ret = nf_nat_ipv4_fn(hooknum, skb, in, out, okfn);
    if (ret != NF_DROP && ret != NF_STOLEN &&
        daddr != ip_hdr(skb)->daddr)
        skb_dst_drop(skb);

    return ret;
}

static unsigned int
nf_nat_ipv4_out(unsigned int hooknum,
        struct sk_buff *skb,
        const struct net_device *in,
        const struct net_device *out,
        int (*okfn)(struct sk_buff *))
{
#ifdef CONFIG_XFRM
    const struct nf_conn *ct;
    enum ip_conntrack_info ctinfo;
#endif
    unsigned int ret;

    /* root is playing with raw sockets. */
    if (skb->len < sizeof(struct iphdr) ||
        ip_hdrlen(skb) < sizeof(struct iphdr))
        return NF_ACCEPT;

    ret = nf_nat_ipv4_fn(hooknum, skb, in, out, okfn);
#ifdef CONFIG_XFRM
    if (ret != NF_DROP && ret != NF_STOLEN &&
        !(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
        (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);

        if ((ct->tuplehash[dir].tuple.src.u3.ip !=
             ct->tuplehash[!dir].tuple.dst.u3.ip) ||
            (ct->tuplehash[dir].tuple.dst.protonum != IPPROTO_ICMP &&
             ct->tuplehash[dir].tuple.src.u.all !=
             ct->tuplehash[!dir].tuple.dst.u.all))
            if (nf_xfrm_me_harder(skb, AF_INET) < 0)
                ret = NF_DROP;
    }
#endif
    return ret;
}

static unsigned int
nf_nat_ipv4_local_fn(unsigned int hooknum,
             struct sk_buff *skb,
             const struct net_device *in,
             const struct net_device *out,
             int (*okfn)(struct sk_buff *))
{
    const struct nf_conn *ct;
    enum ip_conntrack_info ctinfo;
    unsigned int ret;

    /* root is playing with raw sockets. */
    if (skb->len < sizeof(struct iphdr) ||
        ip_hdrlen(skb) < sizeof(struct iphdr))
        return NF_ACCEPT;

    ret = nf_nat_ipv4_fn(hooknum, skb, in, out, okfn);
    if (ret != NF_DROP && ret != NF_STOLEN &&
        (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);

        if (ct->tuplehash[dir].tuple.dst.u3.ip !=
            ct->tuplehash[!dir].tuple.src.u3.ip) {
            if (ip_route_me_harder(skb, RTN_UNSPEC))
                ret = NF_DROP;
        }
#ifdef CONFIG_XFRM
        else if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
             ct->tuplehash[dir].tuple.dst.protonum != IPPROTO_ICMP &&
             ct->tuplehash[dir].tuple.dst.u.all !=
             ct->tuplehash[!dir].tuple.src.u.all)
            if (nf_xfrm_me_harder(skb, AF_INET) < 0)
                ret = NF_DROP;
#endif
    }
    return ret;
}

static struct nf_hook_ops nf_nat_ipv4_ops[] __read_mostly = {
    /* Before packet filtering, change destination */
    {
        .hook       = nf_nat_ipv4_in,
        .owner      = THIS_MODULE,
        .pf     = NFPROTO_IPV4,
        .hooknum    = NF_INET_PRE_ROUTING,
        .priority   = NF_IP_PRI_NAT_DST,
    },
    /* After packet filtering, change source */
    {
        .hook       = nf_nat_ipv4_out,
        .owner      = THIS_MODULE,
        .pf     = NFPROTO_IPV4,
        .hooknum    = NF_INET_POST_ROUTING,
        .priority   = NF_IP_PRI_NAT_SRC,
    },
    /* Before packet filtering, change destination */
    {
        .hook       = nf_nat_ipv4_local_fn,
        .owner      = THIS_MODULE,
        .pf     = NFPROTO_IPV4,
        .hooknum    = NF_INET_LOCAL_OUT,
        .priority   = NF_IP_PRI_NAT_DST,
    },
    /* After packet filtering, change source */
    {
        .hook       = nf_nat_ipv4_fn,
        .owner      = THIS_MODULE,
        .pf     = NFPROTO_IPV4,
        .hooknum    = NF_INET_LOCAL_IN,
        .priority   = NF_IP_PRI_NAT_SRC,
    },
};

static int __net_init iptable_nat_net_init(struct net *net)
{
    struct ipt_replace *repl;

    repl = ipt_alloc_initial_table(&nf_nat_ipv4_table);
    if (repl == NULL)
        return -ENOMEM;
    net->ipv4.nat_table = ipt_register_table(net, &nf_nat_ipv4_table, repl);
    kfree(repl);
    if (IS_ERR(net->ipv4.nat_table))
        return PTR_ERR(net->ipv4.nat_table);
    return 0;
}

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

static struct pernet_operations iptable_nat_net_ops = {
    .init   = iptable_nat_net_init,
    .exit   = iptable_nat_net_exit,
};

static int __init iptable_nat_init(void)
{
    int err;

    err = register_pernet_subsys(&iptable_nat_net_ops);
    if (err < 0)
        goto err1;

    err = nf_register_hooks(nf_nat_ipv4_ops, ARRAY_SIZE(nf_nat_ipv4_ops));
    if (err < 0)
        goto err2;
    return 0;

err2:
    unregister_pernet_subsys(&iptable_nat_net_ops);
err1:
    return err;
}

static void __exit iptable_nat_exit(void)
{
    nf_unregister_hooks(nf_nat_ipv4_ops, ARRAY_SIZE(nf_nat_ipv4_ops));
    unregister_pernet_subsys(&iptable_nat_net_ops);
}

module_init(iptable_nat_init);
module_exit(iptable_nat_exit);

MODULE_LICENSE("GPL");