netfilter: nf_conntrack: fix hash resizing with namespaces

[linux-2.6/libata-dev.git] / net / ipv4 / netfilter / nf_nat_core.c

/* NAT for netfilter; shared with compatibility layer. */

/* (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.
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/timer.h>
#include <linux/skbuff.h>
#include <net/checksum.h>
#include <net/icmp.h>
#include <net/ip.h>
#include <net/tcp.h>  /* For tcp_prot in getorigdst */
#include <linux/icmp.h>
#include <linux/udp.h>
#include <linux/jhash.h>

#include <linux/netfilter_ipv4.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_protocol.h>
#include <net/netfilter/nf_nat_core.h>
#include <net/netfilter/nf_nat_helper.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_l3proto.h>
#include <net/netfilter/nf_conntrack_l4proto.h>

static DEFINE_SPINLOCK(nf_nat_lock);

static struct nf_conntrack_l3proto *l3proto __read_mostly;

#define MAX_IP_NAT_PROTO 256
static const struct nf_nat_protocol *nf_nat_protos[MAX_IP_NAT_PROTO]
                                                __read_mostly;

static inline const struct nf_nat_protocol *
__nf_nat_proto_find(u_int8_t protonum)
{
        return rcu_dereference(nf_nat_protos[protonum]);
}

const struct nf_nat_protocol *
nf_nat_proto_find_get(u_int8_t protonum)
{
        const struct nf_nat_protocol *p;

        rcu_read_lock();
        p = __nf_nat_proto_find(protonum);
        if (!try_module_get(p->me))
                p = &nf_nat_unknown_protocol;
        rcu_read_unlock();

        return p;
}
EXPORT_SYMBOL_GPL(nf_nat_proto_find_get);

void
nf_nat_proto_put(const struct nf_nat_protocol *p)
{
        module_put(p->me);
}
EXPORT_SYMBOL_GPL(nf_nat_proto_put);

/* We keep an extra hash for each conntrack, for fast searching. */
static inline unsigned int
hash_by_src(const struct net *net, const struct nf_conntrack_tuple *tuple)
{
        unsigned int hash;

        /* Original src, to ensure we map it consistently if poss. */
        hash = jhash_3words((__force u32)tuple->src.u3.ip,
                            (__force u32)tuple->src.u.all,
                            tuple->dst.protonum, 0);
        return ((u64)hash * net->ipv4.nat_htable_size) >> 32;
}

/* Is this tuple already taken? (not by us) */
int
nf_nat_used_tuple(const struct nf_conntrack_tuple *tuple,
                  const struct nf_conn *ignored_conntrack)
{
        /* Conntrack tracking doesn't keep track of outgoing tuples; only
           incoming ones.  NAT means they don't have a fixed mapping,
           so we invert the tuple and look for the incoming reply.

           We could keep a separate hash if this proves too slow. */
        struct nf_conntrack_tuple reply;

        nf_ct_invert_tuplepr(&reply, tuple);
        return nf_conntrack_tuple_taken(&reply, ignored_conntrack);
}
EXPORT_SYMBOL(nf_nat_used_tuple);

/* If we source map this tuple so reply looks like reply_tuple, will
 * that meet the constraints of range. */
static int
in_range(const struct nf_conntrack_tuple *tuple,
         const struct nf_nat_range *range)
{
        const struct nf_nat_protocol *proto;
        int ret = 0;

        /* If we are supposed to map IPs, then we must be in the
           range specified, otherwise let this drag us onto a new src IP. */
        if (range->flags & IP_NAT_RANGE_MAP_IPS) {
                if (ntohl(tuple->src.u3.ip) < ntohl(range->min_ip) ||
                    ntohl(tuple->src.u3.ip) > ntohl(range->max_ip))
                        return 0;
        }

        rcu_read_lock();
        proto = __nf_nat_proto_find(tuple->dst.protonum);
        if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED) ||
            proto->in_range(tuple, IP_NAT_MANIP_SRC,
                            &range->min, &range->max))
                ret = 1;
        rcu_read_unlock();

        return ret;
}

static inline int
same_src(const struct nf_conn *ct,
         const struct nf_conntrack_tuple *tuple)
{
        const struct nf_conntrack_tuple *t;

        t = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
        return (t->dst.protonum == tuple->dst.protonum &&
                t->src.u3.ip == tuple->src.u3.ip &&
                t->src.u.all == tuple->src.u.all);
}

/* Only called for SRC manip */
static int
find_appropriate_src(struct net *net,
                     const struct nf_conntrack_tuple *tuple,
                     struct nf_conntrack_tuple *result,
                     const struct nf_nat_range *range)
{
        unsigned int h = hash_by_src(net, tuple);
        const struct nf_conn_nat *nat;
        const struct nf_conn *ct;
        const struct hlist_node *n;

        rcu_read_lock();
        hlist_for_each_entry_rcu(nat, n, &net->ipv4.nat_bysource[h], bysource) {
                ct = nat->ct;
                if (same_src(ct, tuple)) {
                        /* Copy source part from reply tuple. */
                        nf_ct_invert_tuplepr(result,
                                       &ct->tuplehash[IP_CT_DIR_REPLY].tuple);
                        result->dst = tuple->dst;

                        if (in_range(result, range)) {
                                rcu_read_unlock();
                                return 1;
                        }
                }
        }
        rcu_read_unlock();
        return 0;
}

/* For [FUTURE] fragmentation handling, we want the least-used
   src-ip/dst-ip/proto triple.  Fairness doesn't come into it.  Thus
   if the range specifies 1.2.3.4 ports 10000-10005 and 1.2.3.5 ports
   1-65535, we don't do pro-rata allocation based on ports; we choose
   the ip with the lowest src-ip/dst-ip/proto usage.
*/
static void
find_best_ips_proto(struct nf_conntrack_tuple *tuple,
                    const struct nf_nat_range *range,
                    const struct nf_conn *ct,
                    enum nf_nat_manip_type maniptype)
{
        __be32 *var_ipp;
        /* Host order */
        u_int32_t minip, maxip, j;

        /* No IP mapping?  Do nothing. */
        if (!(range->flags & IP_NAT_RANGE_MAP_IPS))
                return;

        if (maniptype == IP_NAT_MANIP_SRC)
                var_ipp = &tuple->src.u3.ip;
        else
                var_ipp = &tuple->dst.u3.ip;

        /* Fast path: only one choice. */
        if (range->min_ip == range->max_ip) {
                *var_ipp = range->min_ip;
                return;
        }

        /* Hashing source and destination IPs gives a fairly even
         * spread in practice (if there are a small number of IPs
         * involved, there usually aren't that many connections
         * anyway).  The consistency means that servers see the same
         * client coming from the same IP (some Internet Banking sites
         * like this), even across reboots. */
        minip = ntohl(range->min_ip);
        maxip = ntohl(range->max_ip);
        j = jhash_2words((__force u32)tuple->src.u3.ip,
                         range->flags & IP_NAT_RANGE_PERSISTENT ?
                                0 : (__force u32)tuple->dst.u3.ip, 0);
        j = ((u64)j * (maxip - minip + 1)) >> 32;
        *var_ipp = htonl(minip + j);
}

/* Manipulate the tuple into the range given.  For NF_INET_POST_ROUTING,
 * we change the source to map into the range.  For NF_INET_PRE_ROUTING
 * and NF_INET_LOCAL_OUT, we change the destination to map into the
 * range.  It might not be possible to get a unique tuple, but we try.
 * At worst (or if we race), we will end up with a final duplicate in
 * __ip_conntrack_confirm and drop the packet. */
static void
get_unique_tuple(struct nf_conntrack_tuple *tuple,
                 const struct nf_conntrack_tuple *orig_tuple,
                 const struct nf_nat_range *range,
                 struct nf_conn *ct,
                 enum nf_nat_manip_type maniptype)
{
        struct net *net = nf_ct_net(ct);
        const struct nf_nat_protocol *proto;

        /* 1) If this srcip/proto/src-proto-part is currently mapped,
           and that same mapping gives a unique tuple within the given
           range, use that.

           This is only required for source (ie. NAT/masq) mappings.
           So far, we don't do local source mappings, so multiple
           manips not an issue.  */
        if (maniptype == IP_NAT_MANIP_SRC &&
            !(range->flags & IP_NAT_RANGE_PROTO_RANDOM)) {
                if (find_appropriate_src(net, orig_tuple, tuple, range)) {
                        pr_debug("get_unique_tuple: Found current src map\n");
                        if (!nf_nat_used_tuple(tuple, ct))
                                return;
                }
        }

        /* 2) Select the least-used IP/proto combination in the given
           range. */
        *tuple = *orig_tuple;
        find_best_ips_proto(tuple, range, ct, maniptype);

        /* 3) The per-protocol part of the manip is made to map into
           the range to make a unique tuple. */

        rcu_read_lock();
        proto = __nf_nat_proto_find(orig_tuple->dst.protonum);

        /* Change protocol info to have some randomization */
        if (range->flags & IP_NAT_RANGE_PROTO_RANDOM) {
                proto->unique_tuple(tuple, range, maniptype, ct);
                goto out;
        }

        /* Only bother mapping if it's not already in range and unique */
        if ((!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED) ||
             proto->in_range(tuple, maniptype, &range->min, &range->max)) &&
            !nf_nat_used_tuple(tuple, ct))
                goto out;

        /* Last change: get protocol to try to obtain unique tuple. */
        proto->unique_tuple(tuple, range, maniptype, ct);
out:
        rcu_read_unlock();
}

unsigned int
nf_nat_setup_info(struct nf_conn *ct,
                  const struct nf_nat_range *range,
                  enum nf_nat_manip_type maniptype)
{
        struct net *net = nf_ct_net(ct);
        struct nf_conntrack_tuple curr_tuple, new_tuple;
        struct nf_conn_nat *nat;
        int have_to_hash = !(ct->status & IPS_NAT_DONE_MASK);

        /* nat helper or nfctnetlink also setup binding */
        nat = nfct_nat(ct);
        if (!nat) {
                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;
                }
        }

        NF_CT_ASSERT(maniptype == IP_NAT_MANIP_SRC ||
                     maniptype == IP_NAT_MANIP_DST);
        BUG_ON(nf_nat_initialized(ct, maniptype));

        /* What we've got will look like inverse of reply. Normally
           this is what is in the conntrack, except for prior
           manipulations (future optimization: if num_manips == 0,
           orig_tp =
           conntrack->tuplehash[IP_CT_DIR_ORIGINAL].tuple) */
        nf_ct_invert_tuplepr(&curr_tuple,
                             &ct->tuplehash[IP_CT_DIR_REPLY].tuple);

        get_unique_tuple(&new_tuple, &curr_tuple, range, ct, maniptype);

        if (!nf_ct_tuple_equal(&new_tuple, &curr_tuple)) {
                struct nf_conntrack_tuple reply;

                /* Alter conntrack table so will recognize replies. */
                nf_ct_invert_tuplepr(&reply, &new_tuple);
                nf_conntrack_alter_reply(ct, &reply);

                /* Non-atomic: we own this at the moment. */
                if (maniptype == IP_NAT_MANIP_SRC)
                        ct->status |= IPS_SRC_NAT;
                else
                        ct->status |= IPS_DST_NAT;
        }

        /* Place in source hash if this is the first time. */
        if (have_to_hash) {
                unsigned int srchash;

                srchash = hash_by_src(net, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
                spin_lock_bh(&nf_nat_lock);
                /* nf_conntrack_alter_reply might re-allocate exntension aera */
                nat = nfct_nat(ct);
                nat->ct = ct;
                hlist_add_head_rcu(&nat->bysource,
                                   &net->ipv4.nat_bysource[srchash]);
                spin_unlock_bh(&nf_nat_lock);
        }

        /* It's done. */
        if (maniptype == IP_NAT_MANIP_DST)
                set_bit(IPS_DST_NAT_DONE_BIT, &ct->status);
        else
                set_bit(IPS_SRC_NAT_DONE_BIT, &ct->status);

        return NF_ACCEPT;
}
EXPORT_SYMBOL(nf_nat_setup_info);

/* Returns true if succeeded. */
static bool
manip_pkt(u_int16_t proto,
          struct sk_buff *skb,
          unsigned int iphdroff,
          const struct nf_conntrack_tuple *target,
          enum nf_nat_manip_type maniptype)
{
        struct iphdr *iph;
        const struct nf_nat_protocol *p;

        if (!skb_make_writable(skb, iphdroff + sizeof(*iph)))
                return false;

        iph = (void *)skb->data + iphdroff;

        /* Manipulate protcol part. */

        /* rcu_read_lock()ed by nf_hook_slow */
        p = __nf_nat_proto_find(proto);
        if (!p->manip_pkt(skb, iphdroff, target, maniptype))
                return false;

        iph = (void *)skb->data + iphdroff;

        if (maniptype == IP_NAT_MANIP_SRC) {
                csum_replace4(&iph->check, iph->saddr, target->src.u3.ip);
                iph->saddr = target->src.u3.ip;
        } else {
                csum_replace4(&iph->check, iph->daddr, target->dst.u3.ip);
                iph->daddr = target->dst.u3.ip;
        }
        return true;
}

/* Do packet manipulations according to nf_nat_setup_info. */
unsigned int nf_nat_packet(struct nf_conn *ct,
                           enum ip_conntrack_info ctinfo,
                           unsigned int hooknum,
                           struct sk_buff *skb)
{
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
        unsigned long statusbit;
        enum nf_nat_manip_type mtype = HOOK2MANIP(hooknum);

        if (mtype == IP_NAT_MANIP_SRC)
                statusbit = IPS_SRC_NAT;
        else
                statusbit = IPS_DST_NAT;

        /* Invert if this is reply dir. */
        if (dir == IP_CT_DIR_REPLY)
                statusbit ^= IPS_NAT_MASK;

        /* Non-atomic: these bits don't change. */
        if (ct->status & statusbit) {
                struct nf_conntrack_tuple target;

                /* We are aiming to look like inverse of other direction. */
                nf_ct_invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);

                if (!manip_pkt(target.dst.protonum, skb, 0, &target, mtype))
                        return NF_DROP;
        }
        return NF_ACCEPT;
}
EXPORT_SYMBOL_GPL(nf_nat_packet);

/* Dir is direction ICMP is coming from (opposite to packet it contains) */
int nf_nat_icmp_reply_translation(struct nf_conn *ct,
                                  enum ip_conntrack_info ctinfo,
                                  unsigned int hooknum,
                                  struct sk_buff *skb)
{
        struct {
                struct icmphdr icmp;
                struct iphdr ip;
        } *inside;
        const struct nf_conntrack_l4proto *l4proto;
        struct nf_conntrack_tuple inner, target;
        int hdrlen = ip_hdrlen(skb);
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
        unsigned long statusbit;
        enum nf_nat_manip_type manip = HOOK2MANIP(hooknum);

        if (!skb_make_writable(skb, hdrlen + sizeof(*inside)))
                return 0;

        inside = (void *)skb->data + ip_hdrlen(skb);

        /* We're actually going to mangle it beyond trivial checksum
           adjustment, so make sure the current checksum is correct. */
        if (nf_ip_checksum(skb, hooknum, hdrlen, 0))
                return 0;

        /* Must be RELATED */
        NF_CT_ASSERT(skb->nfctinfo == IP_CT_RELATED ||
                     skb->nfctinfo == IP_CT_RELATED+IP_CT_IS_REPLY);

        /* Redirects on non-null nats must be dropped, else they'll
           start talking to each other without our translation, and be
           confused... --RR */
        if (inside->icmp.type == ICMP_REDIRECT) {
                /* If NAT isn't finished, assume it and drop. */
                if ((ct->status & IPS_NAT_DONE_MASK) != IPS_NAT_DONE_MASK)
                        return 0;

                if (ct->status & IPS_NAT_MASK)
                        return 0;
        }

        pr_debug("icmp_reply_translation: translating error %p manip %u "
                 "dir %s\n", skb, manip,
                 dir == IP_CT_DIR_ORIGINAL ? "ORIG" : "REPLY");

        /* rcu_read_lock()ed by nf_hook_slow */
        l4proto = __nf_ct_l4proto_find(PF_INET, inside->ip.protocol);

        if (!nf_ct_get_tuple(skb,
                             ip_hdrlen(skb) + sizeof(struct icmphdr),
                             (ip_hdrlen(skb) +
                              sizeof(struct icmphdr) + inside->ip.ihl * 4),
                             (u_int16_t)AF_INET,
                             inside->ip.protocol,
                             &inner, l3proto, l4proto))
                return 0;

        /* Change inner back to look like incoming packet.  We do the
           opposite manip on this hook to normal, because it might not
           pass all hooks (locally-generated ICMP).  Consider incoming
           packet: PREROUTING (DST manip), routing produces ICMP, goes
           through POSTROUTING (which must correct the DST manip). */
        if (!manip_pkt(inside->ip.protocol, skb,
                       ip_hdrlen(skb) + sizeof(inside->icmp),
                       &ct->tuplehash[!dir].tuple,
                       !manip))
                return 0;

        if (skb->ip_summed != CHECKSUM_PARTIAL) {
                /* Reloading "inside" here since manip_pkt inner. */
                inside = (void *)skb->data + ip_hdrlen(skb);
                inside->icmp.checksum = 0;
                inside->icmp.checksum =
                        csum_fold(skb_checksum(skb, hdrlen,
                                               skb->len - hdrlen, 0));
        }

        /* Change outer to look the reply to an incoming packet
         * (proto 0 means don't invert per-proto part). */
        if (manip == IP_NAT_MANIP_SRC)
                statusbit = IPS_SRC_NAT;
        else
                statusbit = IPS_DST_NAT;

        /* Invert if this is reply dir. */
        if (dir == IP_CT_DIR_REPLY)
                statusbit ^= IPS_NAT_MASK;

        if (ct->status & statusbit) {
                nf_ct_invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);
                if (!manip_pkt(0, skb, 0, &target, manip))
                        return 0;
        }

        return 1;
}
EXPORT_SYMBOL_GPL(nf_nat_icmp_reply_translation);

/* Protocol registration. */
int nf_nat_protocol_register(const struct nf_nat_protocol *proto)
{
        int ret = 0;

        spin_lock_bh(&nf_nat_lock);
        if (nf_nat_protos[proto->protonum] != &nf_nat_unknown_protocol) {
                ret = -EBUSY;
                goto out;
        }
        rcu_assign_pointer(nf_nat_protos[proto->protonum], proto);
 out:
        spin_unlock_bh(&nf_nat_lock);
        return ret;
}
EXPORT_SYMBOL(nf_nat_protocol_register);

/* Noone stores the protocol anywhere; simply delete it. */
void nf_nat_protocol_unregister(const struct nf_nat_protocol *proto)
{
        spin_lock_bh(&nf_nat_lock);
        rcu_assign_pointer(nf_nat_protos[proto->protonum],
                           &nf_nat_unknown_protocol);
        spin_unlock_bh(&nf_nat_lock);
        synchronize_rcu();
}
EXPORT_SYMBOL(nf_nat_protocol_unregister);

/* Noone using conntrack by the time this called. */
static void nf_nat_cleanup_conntrack(struct nf_conn *ct)
{
        struct nf_conn_nat *nat = nf_ct_ext_find(ct, NF_CT_EXT_NAT);

        if (nat == NULL || nat->ct == NULL)
                return;

        NF_CT_ASSERT(nat->ct->status & IPS_NAT_DONE_MASK);

        spin_lock_bh(&nf_nat_lock);
        hlist_del_rcu(&nat->bysource);
        spin_unlock_bh(&nf_nat_lock);
}

static void nf_nat_move_storage(void *new, void *old)
{
        struct nf_conn_nat *new_nat = new;
        struct nf_conn_nat *old_nat = old;
        struct nf_conn *ct = old_nat->ct;

        if (!ct || !(ct->status & IPS_NAT_DONE_MASK))
                return;

        spin_lock_bh(&nf_nat_lock);
        new_nat->ct = ct;
        hlist_replace_rcu(&old_nat->bysource, &new_nat->bysource);
        spin_unlock_bh(&nf_nat_lock);
}

static struct nf_ct_ext_type nat_extend __read_mostly = {
        .len            = sizeof(struct nf_conn_nat),
        .align          = __alignof__(struct nf_conn_nat),
        .destroy        = nf_nat_cleanup_conntrack,
        .move           = nf_nat_move_storage,
        .id             = NF_CT_EXT_NAT,
        .flags          = NF_CT_EXT_F_PREALLOC,
};

#if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)

#include <linux/netfilter/nfnetlink.h>
#include <linux/netfilter/nfnetlink_conntrack.h>

static const struct nla_policy protonat_nla_policy[CTA_PROTONAT_MAX+1] = {
        [CTA_PROTONAT_PORT_MIN] = { .type = NLA_U16 },
        [CTA_PROTONAT_PORT_MAX] = { .type = NLA_U16 },
};

static int nfnetlink_parse_nat_proto(struct nlattr *attr,
                                     const struct nf_conn *ct,
                                     struct nf_nat_range *range)
{
        struct nlattr *tb[CTA_PROTONAT_MAX+1];
        const struct nf_nat_protocol *npt;
        int err;

        err = nla_parse_nested(tb, CTA_PROTONAT_MAX, attr, protonat_nla_policy);
        if (err < 0)
                return err;

        npt = nf_nat_proto_find_get(nf_ct_protonum(ct));
        if (npt->nlattr_to_range)
                err = npt->nlattr_to_range(tb, range);
        nf_nat_proto_put(npt);
        return err;
}

static const struct nla_policy nat_nla_policy[CTA_NAT_MAX+1] = {
        [CTA_NAT_MINIP]         = { .type = NLA_U32 },
        [CTA_NAT_MAXIP]         = { .type = NLA_U32 },
};

static int
nfnetlink_parse_nat(const struct nlattr *nat,
                    const struct nf_conn *ct, struct nf_nat_range *range)
{
        struct nlattr *tb[CTA_NAT_MAX+1];
        int err;

        memset(range, 0, sizeof(*range));

        err = nla_parse_nested(tb, CTA_NAT_MAX, nat, nat_nla_policy);
        if (err < 0)
                return err;

        if (tb[CTA_NAT_MINIP])
                range->min_ip = nla_get_be32(tb[CTA_NAT_MINIP]);

        if (!tb[CTA_NAT_MAXIP])
                range->max_ip = range->min_ip;
        else
                range->max_ip = nla_get_be32(tb[CTA_NAT_MAXIP]);

        if (range->min_ip)
                range->flags |= IP_NAT_RANGE_MAP_IPS;

        if (!tb[CTA_NAT_PROTO])
                return 0;

        err = nfnetlink_parse_nat_proto(tb[CTA_NAT_PROTO], ct, range);
        if (err < 0)
                return err;

        return 0;
}

static int
nfnetlink_parse_nat_setup(struct nf_conn *ct,
                          enum nf_nat_manip_type manip,
                          const struct nlattr *attr)
{
        struct nf_nat_range range;

        if (nfnetlink_parse_nat(attr, ct, &range) < 0)
                return -EINVAL;
        if (nf_nat_initialized(ct, manip))
                return -EEXIST;

        return nf_nat_setup_info(ct, &range, manip);
}
#else
static int
nfnetlink_parse_nat_setup(struct nf_conn *ct,
                          enum nf_nat_manip_type manip,
                          const struct nlattr *attr)
{
        return -EOPNOTSUPP;
}
#endif

static int __net_init nf_nat_net_init(struct net *net)
{
        /* Leave them the same for the moment. */
        net->ipv4.nat_htable_size = net->ct.htable_size;
        net->ipv4.nat_bysource = nf_ct_alloc_hashtable(&net->ipv4.nat_htable_size,
                                                       &net->ipv4.nat_vmalloced, 0);
        if (!net->ipv4.nat_bysource)
                return -ENOMEM;
        return 0;
}

/* Clear NAT section of all conntracks, in case we're loaded again. */
static int clean_nat(struct nf_conn *i, void *data)
{
        struct nf_conn_nat *nat = nfct_nat(i);

        if (!nat)
                return 0;
        memset(nat, 0, sizeof(*nat));
        i->status &= ~(IPS_NAT_MASK | IPS_NAT_DONE_MASK | IPS_SEQ_ADJUST);
        return 0;
}

static void __net_exit nf_nat_net_exit(struct net *net)
{
        nf_ct_iterate_cleanup(net, &clean_nat, NULL);
        synchronize_rcu();
        nf_ct_free_hashtable(net->ipv4.nat_bysource, net->ipv4.nat_vmalloced,
                             net->ipv4.nat_htable_size);
}

static struct pernet_operations nf_nat_net_ops = {
        .init = nf_nat_net_init,
        .exit = nf_nat_net_exit,
};

static int __init nf_nat_init(void)
{
        size_t i;
        int ret;

        need_ipv4_conntrack();

        ret = nf_ct_extend_register(&nat_extend);
        if (ret < 0) {
                printk(KERN_ERR "nf_nat_core: Unable to register extension\n");
                return ret;
        }

        ret = register_pernet_subsys(&nf_nat_net_ops);
        if (ret < 0)
                goto cleanup_extend;

        /* Sew in builtin protocols. */
        spin_lock_bh(&nf_nat_lock);
        for (i = 0; i < MAX_IP_NAT_PROTO; i++)
                rcu_assign_pointer(nf_nat_protos[i], &nf_nat_unknown_protocol);
        rcu_assign_pointer(nf_nat_protos[IPPROTO_TCP], &nf_nat_protocol_tcp);
        rcu_assign_pointer(nf_nat_protos[IPPROTO_UDP], &nf_nat_protocol_udp);
        rcu_assign_pointer(nf_nat_protos[IPPROTO_ICMP], &nf_nat_protocol_icmp);
        spin_unlock_bh(&nf_nat_lock);

        /* Initialize fake conntrack so that NAT will skip it */
        nf_conntrack_untracked.status |= IPS_NAT_DONE_MASK;

        l3proto = nf_ct_l3proto_find_get((u_int16_t)AF_INET);

        BUG_ON(nf_nat_seq_adjust_hook != NULL);
        rcu_assign_pointer(nf_nat_seq_adjust_hook, nf_nat_seq_adjust);
        BUG_ON(nfnetlink_parse_nat_setup_hook != NULL);
        rcu_assign_pointer(nfnetlink_parse_nat_setup_hook,
                           nfnetlink_parse_nat_setup);
        BUG_ON(nf_ct_nat_offset != NULL);
        rcu_assign_pointer(nf_ct_nat_offset, nf_nat_get_offset);
        return 0;

 cleanup_extend:
        nf_ct_extend_unregister(&nat_extend);
        return ret;
}

static void __exit nf_nat_cleanup(void)
{
        unregister_pernet_subsys(&nf_nat_net_ops);
        nf_ct_l3proto_put(l3proto);
        nf_ct_extend_unregister(&nat_extend);
        rcu_assign_pointer(nf_nat_seq_adjust_hook, NULL);
        rcu_assign_pointer(nfnetlink_parse_nat_setup_hook, NULL);
        rcu_assign_pointer(nf_ct_nat_offset, NULL);
        synchronize_net();
}

MODULE_LICENSE("GPL");
MODULE_ALIAS("nf-nat-ipv4");

module_init(nf_nat_init);
module_exit(nf_nat_cleanup);