netfilter: nf_conntrack: add direction support for zones

[deliverable/linux.git] / net / netfilter / nf_nat_core.c

/*
 * (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
 * (C) 2011 Patrick McHardy <kaber@trash.net>
 *
 * 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 <linux/gfp.h>
#include <net/xfrm.h>
#include <linux/jhash.h>
#include <linux/rtnetlink.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_l3proto.h>
#include <net/netfilter/nf_nat_l4proto.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_seqadj.h>
#include <net/netfilter/nf_conntrack_l3proto.h>
#include <net/netfilter/nf_conntrack_zones.h>
#include <linux/netfilter/nf_nat.h>

static DEFINE_SPINLOCK(nf_nat_lock);

static DEFINE_MUTEX(nf_nat_proto_mutex);
static const struct nf_nat_l3proto __rcu *nf_nat_l3protos[NFPROTO_NUMPROTO]
                                                __read_mostly;
static const struct nf_nat_l4proto __rcu **nf_nat_l4protos[NFPROTO_NUMPROTO]
                                                __read_mostly;


inline const struct nf_nat_l3proto *
__nf_nat_l3proto_find(u8 family)
{
        return rcu_dereference(nf_nat_l3protos[family]);
}

inline const struct nf_nat_l4proto *
__nf_nat_l4proto_find(u8 family, u8 protonum)
{
        return rcu_dereference(nf_nat_l4protos[family][protonum]);
}
EXPORT_SYMBOL_GPL(__nf_nat_l4proto_find);

#ifdef CONFIG_XFRM
static void __nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl)
{
        const struct nf_nat_l3proto *l3proto;
        const struct nf_conn *ct;
        enum ip_conntrack_info ctinfo;
        enum ip_conntrack_dir dir;
        unsigned  long statusbit;
        u8 family;

        ct = nf_ct_get(skb, &ctinfo);
        if (ct == NULL)
                return;

        family = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.l3num;
        rcu_read_lock();
        l3proto = __nf_nat_l3proto_find(family);
        if (l3proto == NULL)
                goto out;

        dir = CTINFO2DIR(ctinfo);
        if (dir == IP_CT_DIR_ORIGINAL)
                statusbit = IPS_DST_NAT;
        else
                statusbit = IPS_SRC_NAT;

        l3proto->decode_session(skb, ct, dir, statusbit, fl);
out:
        rcu_read_unlock();
}

int nf_xfrm_me_harder(struct sk_buff *skb, unsigned int family)
{
        struct flowi fl;
        unsigned int hh_len;
        struct dst_entry *dst;
        int err;

        err = xfrm_decode_session(skb, &fl, family);
        if (err < 0)
                return err;

        dst = skb_dst(skb);
        if (dst->xfrm)
                dst = ((struct xfrm_dst *)dst)->route;
        dst_hold(dst);

        dst = xfrm_lookup(dev_net(dst->dev), dst, &fl, skb->sk, 0);
        if (IS_ERR(dst))
                return PTR_ERR(dst);

        skb_dst_drop(skb);
        skb_dst_set(skb, dst);

        /* Change in oif may mean change in hh_len. */
        hh_len = skb_dst(skb)->dev->hard_header_len;
        if (skb_headroom(skb) < hh_len &&
            pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
                return -ENOMEM;
        return 0;
}
EXPORT_SYMBOL(nf_xfrm_me_harder);
#endif /* CONFIG_XFRM */

/* 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 = jhash2((u32 *)&tuple->src, sizeof(tuple->src) / sizeof(u32),
                      tuple->dst.protonum ^ nf_conntrack_hash_rnd);

        return reciprocal_scale(hash, net->ct.nat_htable_size);
}

/* 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_nat_l3proto *l3proto,
                    const struct nf_nat_l4proto *l4proto,
                    const struct nf_conntrack_tuple *tuple,
                    const struct nf_nat_range *range)
{
        /* 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 & NF_NAT_RANGE_MAP_IPS &&
            !l3proto->in_range(tuple, range))
                return 0;

        if (!(range->flags & NF_NAT_RANGE_PROTO_SPECIFIED) ||
            l4proto->in_range(tuple, NF_NAT_MANIP_SRC,
                              &range->min_proto, &range->max_proto))
                return 1;

        return 0;
}

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 &&
                nf_inet_addr_cmp(&t->src.u3, &tuple->src.u3) &&
                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_zone *zone,
                     const struct nf_nat_l3proto *l3proto,
                     const struct nf_nat_l4proto *l4proto,
                     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;

        hlist_for_each_entry_rcu(nat, &net->ct.nat_bysource[h], bysource) {
                ct = nat->ct;
                if (same_src(ct, tuple) &&
                    nf_ct_zone_equal(ct, zone, IP_CT_DIR_ORIGINAL)) {
                        /* 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(l3proto, l4proto, result, range))
                                return 1;
                }
        }
        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(const struct nf_conntrack_zone *zone,
                    struct nf_conntrack_tuple *tuple,
                    const struct nf_nat_range *range,
                    const struct nf_conn *ct,
                    enum nf_nat_manip_type maniptype)
{
        union nf_inet_addr *var_ipp;
        unsigned int i, max;
        /* Host order */
        u32 minip, maxip, j, dist;
        bool full_range;

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

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

        /* Fast path: only one choice. */
        if (nf_inet_addr_cmp(&range->min_addr, &range->max_addr)) {
                *var_ipp = range->min_addr;
                return;
        }

        if (nf_ct_l3num(ct) == NFPROTO_IPV4)
                max = sizeof(var_ipp->ip) / sizeof(u32) - 1;
        else
                max = sizeof(var_ipp->ip6) / sizeof(u32) - 1;

        /* 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.
         */
        j = jhash2((u32 *)&tuple->src.u3, sizeof(tuple->src.u3) / sizeof(u32),
                   range->flags & NF_NAT_RANGE_PERSISTENT ?
                        0 : (__force u32)tuple->dst.u3.all[max] ^ zone->id);

        full_range = false;
        for (i = 0; i <= max; i++) {
                /* If first bytes of the address are at the maximum, use the
                 * distance. Otherwise use the full range.
                 */
                if (!full_range) {
                        minip = ntohl((__force __be32)range->min_addr.all[i]);
                        maxip = ntohl((__force __be32)range->max_addr.all[i]);
                        dist  = maxip - minip + 1;
                } else {
                        minip = 0;
                        dist  = ~0;
                }

                var_ipp->all[i] = (__force __u32)
                        htonl(minip + reciprocal_scale(j, dist));
                if (var_ipp->all[i] != range->max_addr.all[i])
                        full_range = true;

                if (!(range->flags & NF_NAT_RANGE_PERSISTENT))
                        j ^= (__force u32)tuple->dst.u3.all[i];
        }
}

/* 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)
{
        const struct nf_conntrack_zone *zone;
        const struct nf_nat_l3proto *l3proto;
        const struct nf_nat_l4proto *l4proto;
        struct net *net = nf_ct_net(ct);

        zone = nf_ct_zone(ct);

        rcu_read_lock();
        l3proto = __nf_nat_l3proto_find(orig_tuple->src.l3num);
        l4proto = __nf_nat_l4proto_find(orig_tuple->src.l3num,
                                        orig_tuple->dst.protonum);

        /* 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 == NF_NAT_MANIP_SRC &&
            !(range->flags & NF_NAT_RANGE_PROTO_RANDOM_ALL)) {
                /* try the original tuple first */
                if (in_range(l3proto, l4proto, orig_tuple, range)) {
                        if (!nf_nat_used_tuple(orig_tuple, ct)) {
                                *tuple = *orig_tuple;
                                goto out;
                        }
                } else if (find_appropriate_src(net, zone, l3proto, l4proto,
                                                orig_tuple, tuple, range)) {
                        pr_debug("get_unique_tuple: Found current src map\n");
                        if (!nf_nat_used_tuple(tuple, ct))
                                goto out;
                }
        }

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

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

        /* Only bother mapping if it's not already in range and unique */
        if (!(range->flags & NF_NAT_RANGE_PROTO_RANDOM_ALL)) {
                if (range->flags & NF_NAT_RANGE_PROTO_SPECIFIED) {
                        if (l4proto->in_range(tuple, maniptype,
                                              &range->min_proto,
                                              &range->max_proto) &&
                            (range->min_proto.all == range->max_proto.all ||
                             !nf_nat_used_tuple(tuple, ct)))
                                goto out;
                } else if (!nf_nat_used_tuple(tuple, ct)) {
                        goto out;
                }
        }

        /* Last change: get protocol to try to obtain unique tuple. */
        l4proto->unique_tuple(l3proto, tuple, range, maniptype, ct);
out:
        rcu_read_unlock();
}

struct nf_conn_nat *nf_ct_nat_ext_add(struct nf_conn *ct)
{
        struct nf_conn_nat *nat = nfct_nat(ct);
        if (nat)
                return nat;

        if (!nf_ct_is_confirmed(ct))
                nat = nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC);

        return nat;
}
EXPORT_SYMBOL_GPL(nf_ct_nat_ext_add);

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;

        /* nat helper or nfctnetlink also setup binding */
        nat = nf_ct_nat_ext_add(ct);
        if (nat == NULL)
                return NF_ACCEPT;

        NF_CT_ASSERT(maniptype == NF_NAT_MANIP_SRC ||
                     maniptype == NF_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 = ct->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 == NF_NAT_MANIP_SRC)
                        ct->status |= IPS_SRC_NAT;
                else
                        ct->status |= IPS_DST_NAT;

                if (nfct_help(ct))
                        nfct_seqadj_ext_add(ct);
        }

        if (maniptype == NF_NAT_MANIP_SRC) {
                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 extension aera */
                nat = nfct_nat(ct);
                nat->ct = ct;
                hlist_add_head_rcu(&nat->bysource,
                                   &net->ct.nat_bysource[srchash]);
                spin_unlock_bh(&nf_nat_lock);
        }

        /* It's done. */
        if (maniptype == NF_NAT_MANIP_DST)
                ct->status |= IPS_DST_NAT_DONE;
        else
                ct->status |= IPS_SRC_NAT_DONE;

        return NF_ACCEPT;
}
EXPORT_SYMBOL(nf_nat_setup_info);

static unsigned int
__nf_nat_alloc_null_binding(struct nf_conn *ct, enum nf_nat_manip_type manip)
{
        /* 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).
         */
        union nf_inet_addr ip =
                (manip == NF_NAT_MANIP_SRC ?
                ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3 :
                ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3);
        struct nf_nat_range range = {
                .flags          = NF_NAT_RANGE_MAP_IPS,
                .min_addr       = ip,
                .max_addr       = ip,
        };
        return nf_nat_setup_info(ct, &range, manip);
}

unsigned int
nf_nat_alloc_null_binding(struct nf_conn *ct, unsigned int hooknum)
{
        return __nf_nat_alloc_null_binding(ct, HOOK2MANIP(hooknum));
}
EXPORT_SYMBOL_GPL(nf_nat_alloc_null_binding);

/* 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)
{
        const struct nf_nat_l3proto *l3proto;
        const struct nf_nat_l4proto *l4proto;
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
        unsigned long statusbit;
        enum nf_nat_manip_type mtype = HOOK2MANIP(hooknum);

        if (mtype == NF_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);

                l3proto = __nf_nat_l3proto_find(target.src.l3num);
                l4proto = __nf_nat_l4proto_find(target.src.l3num,
                                                target.dst.protonum);
                if (!l3proto->manip_pkt(skb, 0, l4proto, &target, mtype))
                        return NF_DROP;
        }
        return NF_ACCEPT;
}
EXPORT_SYMBOL_GPL(nf_nat_packet);

struct nf_nat_proto_clean {
        u8      l3proto;
        u8      l4proto;
};

/* kill conntracks with affected NAT section */
static int nf_nat_proto_remove(struct nf_conn *i, void *data)
{
        const struct nf_nat_proto_clean *clean = data;
        struct nf_conn_nat *nat = nfct_nat(i);

        if (!nat)
                return 0;

        if ((clean->l3proto && nf_ct_l3num(i) != clean->l3proto) ||
            (clean->l4proto && nf_ct_protonum(i) != clean->l4proto))
                return 0;

        return i->status & IPS_NAT_MASK ? 1 : 0;
}

static int nf_nat_proto_clean(struct nf_conn *ct, void *data)
{
        struct nf_conn_nat *nat = nfct_nat(ct);

        if (nf_nat_proto_remove(ct, data))
                return 1;

        if (!nat || !nat->ct)
                return 0;

        /* This netns is being destroyed, and conntrack has nat null binding.
         * Remove it from bysource hash, as the table will be freed soon.
         *
         * Else, when the conntrack is destoyed, nf_nat_cleanup_conntrack()
         * will delete entry from already-freed table.
         */
        if (!del_timer(&ct->timeout))
                return 1;

        spin_lock_bh(&nf_nat_lock);
        hlist_del_rcu(&nat->bysource);
        ct->status &= ~IPS_NAT_DONE_MASK;
        nat->ct = NULL;
        spin_unlock_bh(&nf_nat_lock);

        add_timer(&ct->timeout);

        /* don't delete conntrack.  Although that would make things a lot
         * simpler, we'd end up flushing all conntracks on nat rmmod.
         */
        return 0;
}

static void nf_nat_l4proto_clean(u8 l3proto, u8 l4proto)
{
        struct nf_nat_proto_clean clean = {
                .l3proto = l3proto,
                .l4proto = l4proto,
        };
        struct net *net;

        rtnl_lock();
        for_each_net(net)
                nf_ct_iterate_cleanup(net, nf_nat_proto_remove, &clean, 0, 0);
        rtnl_unlock();
}

static void nf_nat_l3proto_clean(u8 l3proto)
{
        struct nf_nat_proto_clean clean = {
                .l3proto = l3proto,
        };
        struct net *net;

        rtnl_lock();

        for_each_net(net)
                nf_ct_iterate_cleanup(net, nf_nat_proto_remove, &clean, 0, 0);
        rtnl_unlock();
}

/* Protocol registration. */
int nf_nat_l4proto_register(u8 l3proto, const struct nf_nat_l4proto *l4proto)
{
        const struct nf_nat_l4proto **l4protos;
        unsigned int i;
        int ret = 0;

        mutex_lock(&nf_nat_proto_mutex);
        if (nf_nat_l4protos[l3proto] == NULL) {
                l4protos = kmalloc(IPPROTO_MAX * sizeof(struct nf_nat_l4proto *),
                                   GFP_KERNEL);
                if (l4protos == NULL) {
                        ret = -ENOMEM;
                        goto out;
                }

                for (i = 0; i < IPPROTO_MAX; i++)
                        RCU_INIT_POINTER(l4protos[i], &nf_nat_l4proto_unknown);

                /* Before making proto_array visible to lockless readers,
                 * we must make sure its content is committed to memory.
                 */
                smp_wmb();

                nf_nat_l4protos[l3proto] = l4protos;
        }

        if (rcu_dereference_protected(
                        nf_nat_l4protos[l3proto][l4proto->l4proto],
                        lockdep_is_held(&nf_nat_proto_mutex)
                        ) != &nf_nat_l4proto_unknown) {
                ret = -EBUSY;
                goto out;
        }
        RCU_INIT_POINTER(nf_nat_l4protos[l3proto][l4proto->l4proto], l4proto);
 out:
        mutex_unlock(&nf_nat_proto_mutex);
        return ret;
}
EXPORT_SYMBOL_GPL(nf_nat_l4proto_register);

/* No one stores the protocol anywhere; simply delete it. */
void nf_nat_l4proto_unregister(u8 l3proto, const struct nf_nat_l4proto *l4proto)
{
        mutex_lock(&nf_nat_proto_mutex);
        RCU_INIT_POINTER(nf_nat_l4protos[l3proto][l4proto->l4proto],
                         &nf_nat_l4proto_unknown);
        mutex_unlock(&nf_nat_proto_mutex);
        synchronize_rcu();

        nf_nat_l4proto_clean(l3proto, l4proto->l4proto);
}
EXPORT_SYMBOL_GPL(nf_nat_l4proto_unregister);

int nf_nat_l3proto_register(const struct nf_nat_l3proto *l3proto)
{
        int err;

        err = nf_ct_l3proto_try_module_get(l3proto->l3proto);
        if (err < 0)
                return err;

        mutex_lock(&nf_nat_proto_mutex);
        RCU_INIT_POINTER(nf_nat_l4protos[l3proto->l3proto][IPPROTO_TCP],
                         &nf_nat_l4proto_tcp);
        RCU_INIT_POINTER(nf_nat_l4protos[l3proto->l3proto][IPPROTO_UDP],
                         &nf_nat_l4proto_udp);
        mutex_unlock(&nf_nat_proto_mutex);

        RCU_INIT_POINTER(nf_nat_l3protos[l3proto->l3proto], l3proto);
        return 0;
}
EXPORT_SYMBOL_GPL(nf_nat_l3proto_register);

void nf_nat_l3proto_unregister(const struct nf_nat_l3proto *l3proto)
{
        mutex_lock(&nf_nat_proto_mutex);
        RCU_INIT_POINTER(nf_nat_l3protos[l3proto->l3proto], NULL);
        mutex_unlock(&nf_nat_proto_mutex);
        synchronize_rcu();

        nf_nat_l3proto_clean(l3proto->l3proto);
        nf_ct_l3proto_module_put(l3proto->l3proto);
}
EXPORT_SYMBOL_GPL(nf_nat_l3proto_unregister);

/* No one 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_SRC_NAT_DONE);

        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_SRC_NAT_DONE))
                return;

        spin_lock_bh(&nf_nat_lock);
        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 IS_ENABLED(CONFIG_NF_CT_NETLINK)

#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_l4proto *l4proto;
        int err;

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

        l4proto = __nf_nat_l4proto_find(nf_ct_l3num(ct), nf_ct_protonum(ct));
        if (l4proto->nlattr_to_range)
                err = l4proto->nlattr_to_range(tb, range);

        return err;
}

static const struct nla_policy nat_nla_policy[CTA_NAT_MAX+1] = {
        [CTA_NAT_V4_MINIP]      = { .type = NLA_U32 },
        [CTA_NAT_V4_MAXIP]      = { .type = NLA_U32 },
        [CTA_NAT_V6_MINIP]      = { .len = sizeof(struct in6_addr) },
        [CTA_NAT_V6_MAXIP]      = { .len = sizeof(struct in6_addr) },
        [CTA_NAT_PROTO]         = { .type = NLA_NESTED },
};

static int
nfnetlink_parse_nat(const struct nlattr *nat,
                    const struct nf_conn *ct, struct nf_nat_range *range,
                    const struct nf_nat_l3proto *l3proto)
{
        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;

        err = l3proto->nlattr_to_range(tb, range);
        if (err < 0)
                return err;

        if (!tb[CTA_NAT_PROTO])
                return 0;

        return nfnetlink_parse_nat_proto(tb[CTA_NAT_PROTO], ct, range);
}

/* This function is called under rcu_read_lock() */
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;
        const struct nf_nat_l3proto *l3proto;
        int err;

        /* Should not happen, restricted to creating new conntracks
         * via ctnetlink.
         */
        if (WARN_ON_ONCE(nf_nat_initialized(ct, manip)))
                return -EEXIST;

        /* Make sure that L3 NAT is there by when we call nf_nat_setup_info to
         * attach the null binding, otherwise this may oops.
         */
        l3proto = __nf_nat_l3proto_find(nf_ct_l3num(ct));
        if (l3proto == NULL)
                return -EAGAIN;

        /* No NAT information has been passed, allocate the null-binding */
        if (attr == NULL)
                return __nf_nat_alloc_null_binding(ct, manip);

        err = nfnetlink_parse_nat(attr, ct, &range, l3proto);
        if (err < 0)
                return err;

        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->ct.nat_htable_size = net->ct.htable_size;
        net->ct.nat_bysource = nf_ct_alloc_hashtable(&net->ct.nat_htable_size, 0);
        if (!net->ct.nat_bysource)
                return -ENOMEM;
        return 0;
}

static void __net_exit nf_nat_net_exit(struct net *net)
{
        struct nf_nat_proto_clean clean = {};

        nf_ct_iterate_cleanup(net, nf_nat_proto_clean, &clean, 0, 0);
        synchronize_rcu();
        nf_ct_free_hashtable(net->ct.nat_bysource, net->ct.nat_htable_size);
}

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

static struct nf_ct_helper_expectfn follow_master_nat = {
        .name           = "nat-follow-master",
        .expectfn       = nf_nat_follow_master,
};

static int __init nf_nat_init(void)
{
        int ret;

        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;

        nf_ct_helper_expectfn_register(&follow_master_nat);

        /* Initialize fake conntrack so that NAT will skip it */
        nf_ct_untracked_status_or(IPS_NAT_DONE_MASK);

        BUG_ON(nfnetlink_parse_nat_setup_hook != NULL);
        RCU_INIT_POINTER(nfnetlink_parse_nat_setup_hook,
                           nfnetlink_parse_nat_setup);
#ifdef CONFIG_XFRM
        BUG_ON(nf_nat_decode_session_hook != NULL);
        RCU_INIT_POINTER(nf_nat_decode_session_hook, __nf_nat_decode_session);
#endif
        return 0;

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

static void __exit nf_nat_cleanup(void)
{
        unsigned int i;

        unregister_pernet_subsys(&nf_nat_net_ops);
        nf_ct_extend_unregister(&nat_extend);
        nf_ct_helper_expectfn_unregister(&follow_master_nat);
        RCU_INIT_POINTER(nfnetlink_parse_nat_setup_hook, NULL);
#ifdef CONFIG_XFRM
        RCU_INIT_POINTER(nf_nat_decode_session_hook, NULL);
#endif
        for (i = 0; i < NFPROTO_NUMPROTO; i++)
                kfree(nf_nat_l4protos[i]);
        synchronize_net();
}

MODULE_LICENSE("GPL");

module_init(nf_nat_init);
module_exit(nf_nat_cleanup);