/* Netfilter messages via netlink socket. Allows for user space
 * protocol helpers and general trouble making from userspace.
 *
 * (C) 2001 by Jay Schulist <jschlst@samba.org>,
 * (C) 2002-2005 by Harald Welte <laforge@gnumonks.org>
 * (C) 2005-2017 by Pablo Neira Ayuso <pablo@netfilter.org>
 *
 * Initial netfilter messages via netlink development funded and
 * generally made possible by Network Robots, Inc. (www.networkrobots.com)
 *
 * Further development of this code funded by Astaro AG (http://www.astaro.com)
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/socket.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/sockios.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <linux/uaccess.h>
#include <net/sock.h>
#include <linux/init.h>
#include <linux/sched/signal.h>

#include <net/netlink.h>
#include <net/netns/generic.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nfnetlink.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER);
MODULE_DESCRIPTION("Netfilter messages via netlink socket");

#define nfnl_dereference_protected(id) \
        rcu_dereference_protected(table[(id)].subsys, \
                                  lockdep_nfnl_is_held((id)))

#define NFNL_MAX_ATTR_COUNT     32

static unsigned int nfnetlink_pernet_id __read_mostly;

#ifdef CONFIG_NF_CONNTRACK_EVENTS
static DEFINE_SPINLOCK(nfnl_grp_active_lock);
#endif

struct nfnl_net {
        struct sock *nfnl;
};

static struct {
        struct mutex                            mutex;
        const struct nfnetlink_subsystem __rcu  *subsys;
} table[NFNL_SUBSYS_COUNT];

static struct lock_class_key nfnl_lockdep_keys[NFNL_SUBSYS_COUNT];

static const char *const nfnl_lockdep_names[NFNL_SUBSYS_COUNT] = {
        [NFNL_SUBSYS_NONE] = "nfnl_subsys_none",
        [NFNL_SUBSYS_CTNETLINK] = "nfnl_subsys_ctnetlink",
        [NFNL_SUBSYS_CTNETLINK_EXP] = "nfnl_subsys_ctnetlink_exp",
        [NFNL_SUBSYS_QUEUE] = "nfnl_subsys_queue",
        [NFNL_SUBSYS_ULOG] = "nfnl_subsys_ulog",
        [NFNL_SUBSYS_OSF] = "nfnl_subsys_osf",
        [NFNL_SUBSYS_IPSET] = "nfnl_subsys_ipset",
        [NFNL_SUBSYS_ACCT] = "nfnl_subsys_acct",
        [NFNL_SUBSYS_CTNETLINK_TIMEOUT] = "nfnl_subsys_cttimeout",
        [NFNL_SUBSYS_CTHELPER] = "nfnl_subsys_cthelper",
        [NFNL_SUBSYS_NFTABLES] = "nfnl_subsys_nftables",
        [NFNL_SUBSYS_NFT_COMPAT] = "nfnl_subsys_nftcompat",
        [NFNL_SUBSYS_HOOK] = "nfnl_subsys_hook",
};

static const int nfnl_group2type[NFNLGRP_MAX+1] = {
        [NFNLGRP_CONNTRACK_NEW]         = NFNL_SUBSYS_CTNETLINK,
        [NFNLGRP_CONNTRACK_UPDATE]      = NFNL_SUBSYS_CTNETLINK,
        [NFNLGRP_CONNTRACK_DESTROY]     = NFNL_SUBSYS_CTNETLINK,
        [NFNLGRP_CONNTRACK_EXP_NEW]     = NFNL_SUBSYS_CTNETLINK_EXP,
        [NFNLGRP_CONNTRACK_EXP_UPDATE]  = NFNL_SUBSYS_CTNETLINK_EXP,
        [NFNLGRP_CONNTRACK_EXP_DESTROY] = NFNL_SUBSYS_CTNETLINK_EXP,
        [NFNLGRP_NFTABLES]              = NFNL_SUBSYS_NFTABLES,
        [NFNLGRP_ACCT_QUOTA]            = NFNL_SUBSYS_ACCT,
        [NFNLGRP_NFTRACE]               = NFNL_SUBSYS_NFTABLES,
};

static struct nfnl_net *nfnl_pernet(struct net *net)
{
        return net_generic(net, nfnetlink_pernet_id);
}

void nfnl_lock(__u8 subsys_id)
{
        mutex_lock(&table[subsys_id].mutex);
}
EXPORT_SYMBOL_GPL(nfnl_lock);

void nfnl_unlock(__u8 subsys_id)
{
        mutex_unlock(&table[subsys_id].mutex);
}
EXPORT_SYMBOL_GPL(nfnl_unlock);

#ifdef CONFIG_PROVE_LOCKING
bool lockdep_nfnl_is_held(u8 subsys_id)
{
        return lockdep_is_held(&table[subsys_id].mutex);
}
EXPORT_SYMBOL_GPL(lockdep_nfnl_is_held);
#endif

int nfnetlink_subsys_register(const struct nfnetlink_subsystem *n)
{
        u8 cb_id;

        /* Sanity-check attr_count size to avoid stack buffer overflow. */
        for (cb_id = 0; cb_id < n->cb_count; cb_id++)
                if (WARN_ON(n->cb[cb_id].attr_count > NFNL_MAX_ATTR_COUNT))
                        return -EINVAL;

        nfnl_lock(n->subsys_id);
        if (table[n->subsys_id].subsys) {
                nfnl_unlock(n->subsys_id);
                return -EBUSY;
        }
        rcu_assign_pointer(table[n->subsys_id].subsys, n);
        nfnl_unlock(n->subsys_id);

        return 0;
}
EXPORT_SYMBOL_GPL(nfnetlink_subsys_register);

int nfnetlink_subsys_unregister(const struct nfnetlink_subsystem *n)
{
        nfnl_lock(n->subsys_id);
        table[n->subsys_id].subsys = NULL;
        nfnl_unlock(n->subsys_id);
        synchronize_rcu();
        return 0;
}
EXPORT_SYMBOL_GPL(nfnetlink_subsys_unregister);

static inline const struct nfnetlink_subsystem *nfnetlink_get_subsys(u16 type)
{
        u8 subsys_id = NFNL_SUBSYS_ID(type);

        if (subsys_id >= NFNL_SUBSYS_COUNT)
                return NULL;

        return rcu_dereference(table[subsys_id].subsys);
}

static inline const struct nfnl_callback *
nfnetlink_find_client(u16 type, const struct nfnetlink_subsystem *ss)
{
        u8 cb_id = NFNL_MSG_TYPE(type);

        if (cb_id >= ss->cb_count)
                return NULL;

        return &ss->cb[cb_id];
}

int nfnetlink_has_listeners(struct net *net, unsigned int group)
{
        struct nfnl_net *nfnlnet = nfnl_pernet(net);

        return netlink_has_listeners(nfnlnet->nfnl, group);
}
EXPORT_SYMBOL_GPL(nfnetlink_has_listeners);

int nfnetlink_send(struct sk_buff *skb, struct net *net, u32 portid,
                   unsigned int group, int echo, gfp_t flags)
{
        struct nfnl_net *nfnlnet = nfnl_pernet(net);

        return nlmsg_notify(nfnlnet->nfnl, skb, portid, group, echo, flags);
}
EXPORT_SYMBOL_GPL(nfnetlink_send);

int nfnetlink_set_err(struct net *net, u32 portid, u32 group, int error)
{
        struct nfnl_net *nfnlnet = nfnl_pernet(net);

        return netlink_set_err(nfnlnet->nfnl, portid, group, error);
}
EXPORT_SYMBOL_GPL(nfnetlink_set_err);

int nfnetlink_unicast(struct sk_buff *skb, struct net *net, u32 portid)
{
        struct nfnl_net *nfnlnet = nfnl_pernet(net);
        int err;

        err = nlmsg_unicast(nfnlnet->nfnl, skb, portid);
        if (err == -EAGAIN)
                err = -ENOBUFS;

        return err;
}
EXPORT_SYMBOL_GPL(nfnetlink_unicast);

void nfnetlink_broadcast(struct net *net, struct sk_buff *skb, __u32 portid,
                         __u32 group, gfp_t allocation)
{
        struct nfnl_net *nfnlnet = nfnl_pernet(net);

        netlink_broadcast(nfnlnet->nfnl, skb, portid, group, allocation);
}
EXPORT_SYMBOL_GPL(nfnetlink_broadcast);

/* Process one complete nfnetlink message. */
static int nfnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
                             struct netlink_ext_ack *extack)
{
        struct net *net = sock_net(skb->sk);
        const struct nfnl_callback *nc;
        const struct nfnetlink_subsystem *ss;
        int type, err;

        /* All the messages must at least contain nfgenmsg */
        if (nlmsg_len(nlh) < sizeof(struct nfgenmsg))
                return 0;

        type = nlh->nlmsg_type;
replay:
        rcu_read_lock();

        ss = nfnetlink_get_subsys(type);
        if (!ss) {
#ifdef CONFIG_MODULES
                rcu_read_unlock();
                request_module("nfnetlink-subsys-%d", NFNL_SUBSYS_ID(type));
                rcu_read_lock();
                ss = nfnetlink_get_subsys(type);
                if (!ss)
#endif
                {
                        rcu_read_unlock();
                        return -EINVAL;
                }
        }

        nc = nfnetlink_find_client(type, ss);
        if (!nc) {
                rcu_read_unlock();
                return -EINVAL;
        }

        {
                int min_len = nlmsg_total_size(sizeof(struct nfgenmsg));
                struct nfnl_net *nfnlnet = nfnl_pernet(net);
                u8 cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type);
                struct nlattr *cda[NFNL_MAX_ATTR_COUNT + 1];
                struct nlattr *attr = (void *)nlh + min_len;
                int attrlen = nlh->nlmsg_len - min_len;
                __u8 subsys_id = NFNL_SUBSYS_ID(type);
                struct nfnl_info info = {
                        .net    = net,
                        .sk     = nfnlnet->nfnl,
                        .nlh    = nlh,
                        .nfmsg  = nlmsg_data(nlh),
                        .extack = extack,
                };

                /* Sanity-check NFNL_MAX_ATTR_COUNT */
                if (ss->cb[cb_id].attr_count > NFNL_MAX_ATTR_COUNT) {
                        rcu_read_unlock();
                        return -ENOMEM;
                }

                err = nla_parse_deprecated(cda, ss->cb[cb_id].attr_count,
                                           attr, attrlen,
                                           ss->cb[cb_id].policy, extack);
                if (err < 0) {
                        rcu_read_unlock();
                        return err;
                }

                if (!nc->call) {
                        rcu_read_unlock();
                        return -EINVAL;
                }

                switch (nc->type) {
                case NFNL_CB_RCU:
                        err = nc->call(skb, &info, (const struct nlattr **)cda);
                        rcu_read_unlock();
                        break;
                case NFNL_CB_MUTEX:
                        rcu_read_unlock();
                        nfnl_lock(subsys_id);
                        if (nfnl_dereference_protected(subsys_id) != ss ||
                            nfnetlink_find_client(type, ss) != nc) {
                                nfnl_unlock(subsys_id);
                                err = -EAGAIN;
                                break;
                        }
                        err = nc->call(skb, &info, (const struct nlattr **)cda);
                        nfnl_unlock(subsys_id);
                        break;
                default:
                        rcu_read_unlock();
                        err = -EINVAL;
                        break;
                }
                if (err == -EAGAIN)
                        goto replay;
                return err;
        }
}

struct nfnl_err {
        struct list_head        head;
        struct nlmsghdr         *nlh;
        int                     err;
        struct netlink_ext_ack  extack;
};

static int nfnl_err_add(struct list_head *list, struct nlmsghdr *nlh, int err,
                        const struct netlink_ext_ack *extack)
{
        struct nfnl_err *nfnl_err;

        nfnl_err = kmalloc_obj(struct nfnl_err);
        if (nfnl_err == NULL)
                return -ENOMEM;

        nfnl_err->nlh = nlh;
        nfnl_err->err = err;
        nfnl_err->extack = *extack;
        list_add_tail(&nfnl_err->head, list);

        return 0;
}

static void nfnl_err_del(struct nfnl_err *nfnl_err)
{
        list_del(&nfnl_err->head);
        kfree(nfnl_err);
}

static void nfnl_err_reset(struct list_head *err_list)
{
        struct nfnl_err *nfnl_err, *next;

        list_for_each_entry_safe(nfnl_err, next, err_list, head)
                nfnl_err_del(nfnl_err);
}

static void nfnl_err_deliver(struct list_head *err_list, struct sk_buff *skb)
{
        struct nfnl_err *nfnl_err, *next;

        list_for_each_entry_safe(nfnl_err, next, err_list, head) {
                netlink_ack(skb, nfnl_err->nlh, nfnl_err->err,
                            &nfnl_err->extack);
                nfnl_err_del(nfnl_err);
        }
}

enum {
        NFNL_BATCH_FAILURE      = (1 << 0),
        NFNL_BATCH_DONE         = (1 << 1),
        NFNL_BATCH_REPLAY       = (1 << 2),
};

static void nfnetlink_rcv_batch(struct sk_buff *skb, struct nlmsghdr *nlh,
                                u16 subsys_id, u32 genid)
{
        struct sk_buff *oskb = skb;
        struct net *net = sock_net(skb->sk);
        const struct nfnetlink_subsystem *ss;
        const struct nfnl_callback *nc;
        struct netlink_ext_ack extack;
        struct nlmsghdr *onlh = nlh;
        LIST_HEAD(err_list);
        u32 status;
        int err;

        if (subsys_id >= NFNL_SUBSYS_COUNT)
                return netlink_ack(skb, nlh, -EINVAL, NULL);
replay:
        status = 0;
replay_abort:
        skb = netlink_skb_clone(oskb, GFP_KERNEL);
        nlh = onlh;
        if (!skb)
                return netlink_ack(oskb, nlh, -ENOMEM, NULL);

        nfnl_lock(subsys_id);
        ss = nfnl_dereference_protected(subsys_id);
        if (!ss) {
#ifdef CONFIG_MODULES
                nfnl_unlock(subsys_id);
                request_module("nfnetlink-subsys-%d", subsys_id);
                nfnl_lock(subsys_id);
                ss = nfnl_dereference_protected(subsys_id);
                if (!ss)
#endif
                {
                        nfnl_unlock(subsys_id);
                        netlink_ack(oskb, nlh, -EOPNOTSUPP, NULL);
                        return consume_skb(skb);
                }
        }

        if (!ss->valid_genid || !ss->commit || !ss->abort) {
                nfnl_unlock(subsys_id);
                netlink_ack(oskb, nlh, -EOPNOTSUPP, NULL);
                return consume_skb(skb);
        }

        if (!try_module_get(ss->owner)) {
                nfnl_unlock(subsys_id);
                netlink_ack(oskb, nlh, -EOPNOTSUPP, NULL);
                return consume_skb(skb);
        }

        if (!ss->valid_genid(net, genid)) {
                module_put(ss->owner);
                nfnl_unlock(subsys_id);
                netlink_ack(oskb, nlh, -ERESTART, NULL);
                return consume_skb(skb);
        }

        nfnl_unlock(subsys_id);

        if (nlh->nlmsg_flags & NLM_F_ACK) {
                memset(&extack, 0, sizeof(extack));
                nfnl_err_add(&err_list, nlh, 0, &extack);
        }

        while (skb->len >= nlmsg_total_size(0)) {
                int msglen, type;

                if (fatal_signal_pending(current)) {
                        nfnl_err_reset(&err_list);
                        err = -EINTR;
                        status = NFNL_BATCH_FAILURE;
                        goto done;
                }

                memset(&extack, 0, sizeof(extack));
                nlh = nlmsg_hdr(skb);
                err = 0;

                if (nlh->nlmsg_len < NLMSG_HDRLEN ||
                    skb->len < nlh->nlmsg_len ||
                    nlmsg_len(nlh) < sizeof(struct nfgenmsg)) {
                        nfnl_err_reset(&err_list);
                        status |= NFNL_BATCH_FAILURE;
                        goto done;
                }

                /* Only requests are handled by the kernel */
                if (!(nlh->nlmsg_flags & NLM_F_REQUEST)) {
                        err = -EINVAL;
                        goto ack;
                }

                type = nlh->nlmsg_type;
                if (type == NFNL_MSG_BATCH_BEGIN) {
                        /* Malformed: Batch begin twice */
                        nfnl_err_reset(&err_list);
                        status |= NFNL_BATCH_FAILURE;
                        goto done;
                } else if (type == NFNL_MSG_BATCH_END) {
                        status |= NFNL_BATCH_DONE;
                        goto done;
                } else if (type < NLMSG_MIN_TYPE) {
                        err = -EINVAL;
                        goto ack;
                }

                /* We only accept a batch with messages for the same
                 * subsystem.
                 */
                if (NFNL_SUBSYS_ID(type) != subsys_id) {
                        err = -EINVAL;
                        goto ack;
                }

                nc = nfnetlink_find_client(type, ss);
                if (!nc) {
                        err = -EINVAL;
                        goto ack;
                }

                if (nc->type != NFNL_CB_BATCH) {
                        err = -EINVAL;
                        goto ack;
                }

                {
                        int min_len = nlmsg_total_size(sizeof(struct nfgenmsg));
                        struct nfnl_net *nfnlnet = nfnl_pernet(net);
                        struct nlattr *cda[NFNL_MAX_ATTR_COUNT + 1];
                        struct nlattr *attr = (void *)nlh + min_len;
                        u8 cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type);
                        int attrlen = nlh->nlmsg_len - min_len;
                        struct nfnl_info info = {
                                .net    = net,
                                .sk     = nfnlnet->nfnl,
                                .nlh    = nlh,
                                .nfmsg  = nlmsg_data(nlh),
                                .extack = &extack,
                        };

                        /* Sanity-check NFTA_MAX_ATTR */
                        if (ss->cb[cb_id].attr_count > NFNL_MAX_ATTR_COUNT) {
                                err = -ENOMEM;
                                goto ack;
                        }

                        err = nla_parse_deprecated(cda,
                                                   ss->cb[cb_id].attr_count,
                                                   attr, attrlen,
                                                   ss->cb[cb_id].policy, &extack);
                        if (err < 0)
                                goto ack;

                        err = nc->call(skb, &info, (const struct nlattr **)cda);

                        /* The lock was released to autoload some module, we
                         * have to abort and start from scratch using the
                         * original skb.
                         */
                        if (err == -EAGAIN) {
                                status |= NFNL_BATCH_REPLAY;
                                goto done;
                        }
                }
ack:
                if (nlh->nlmsg_flags & NLM_F_ACK || err) {
                        /* Errors are delivered once the full batch has been
                         * processed, this avoids that the same error is
                         * reported several times when replaying the batch.
                         */
                        if (err == -ENOMEM ||
                            nfnl_err_add(&err_list, nlh, err, &extack) < 0) {
                                /* We failed to enqueue an error, reset the
                                 * list of errors and send OOM to userspace
                                 * pointing to the batch header.
                                 */
                                nfnl_err_reset(&err_list);
                                netlink_ack(oskb, nlmsg_hdr(oskb), -ENOMEM,
                                            NULL);
                                status |= NFNL_BATCH_FAILURE;
                                goto done;
                        }
                        /* We don't stop processing the batch on errors, thus,
                         * userspace gets all the errors that the batch
                         * triggers.
                         */
                        if (err)
                                status |= NFNL_BATCH_FAILURE;
                }

                msglen = NLMSG_ALIGN(nlh->nlmsg_len);
                if (msglen > skb->len)
                        msglen = skb->len;
                skb_pull(skb, msglen);
        }
done:
        if (status & NFNL_BATCH_REPLAY) {
                ss->abort(net, oskb, NFNL_ABORT_AUTOLOAD);
                nfnl_err_reset(&err_list);
                consume_skb(skb);
                module_put(ss->owner);
                goto replay;
        } else if (status == NFNL_BATCH_DONE) {
                err = ss->commit(net, oskb);
                if (err == -EAGAIN) {
                        status |= NFNL_BATCH_REPLAY;
                        goto done;
                } else if (err) {
                        ss->abort(net, oskb, NFNL_ABORT_NONE);
                        netlink_ack(oskb, nlmsg_hdr(oskb), err, NULL);
                } else if (nlh->nlmsg_flags & NLM_F_ACK) {
                        memset(&extack, 0, sizeof(extack));
                        nfnl_err_add(&err_list, nlh, 0, &extack);
                }
        } else {
                enum nfnl_abort_action abort_action;

                if (status & NFNL_BATCH_FAILURE)
                        abort_action = NFNL_ABORT_NONE;
                else
                        abort_action = NFNL_ABORT_VALIDATE;

                err = ss->abort(net, oskb, abort_action);
                if (err == -EAGAIN) {
                        nfnl_err_reset(&err_list);
                        consume_skb(skb);
                        module_put(ss->owner);
                        status |= NFNL_BATCH_FAILURE;
                        goto replay_abort;
                }
        }

        nfnl_err_deliver(&err_list, oskb);
        consume_skb(skb);
        module_put(ss->owner);
}

static const struct nla_policy nfnl_batch_policy[NFNL_BATCH_MAX + 1] = {
        [NFNL_BATCH_GENID]      = { .type = NLA_U32 },
};

static void nfnetlink_rcv_skb_batch(struct sk_buff *skb, struct nlmsghdr *nlh)
{
        int min_len = nlmsg_total_size(sizeof(struct nfgenmsg));
        struct nlattr *attr = (void *)nlh + min_len;
        struct nlattr *cda[NFNL_BATCH_MAX + 1];
        int attrlen = nlh->nlmsg_len - min_len;
        struct nfgenmsg *nfgenmsg;
        int msglen, err;
        u32 gen_id = 0;
        u16 res_id;

        msglen = NLMSG_ALIGN(nlh->nlmsg_len);
        if (msglen > skb->len)
                msglen = skb->len;

        if (skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
                return;

        err = nla_parse_deprecated(cda, NFNL_BATCH_MAX, attr, attrlen,
                                   nfnl_batch_policy, NULL);
        if (err < 0) {
                netlink_ack(skb, nlh, err, NULL);
                return;
        }
        if (cda[NFNL_BATCH_GENID])
                gen_id = ntohl(nla_get_be32(cda[NFNL_BATCH_GENID]));

        nfgenmsg = nlmsg_data(nlh);
        skb_pull(skb, msglen);
        /* Work around old nft using host byte order */
        if (nfgenmsg->res_id == (__force __be16)NFNL_SUBSYS_NFTABLES)
                res_id = NFNL_SUBSYS_NFTABLES;
        else
                res_id = ntohs(nfgenmsg->res_id);

        nfnetlink_rcv_batch(skb, nlh, res_id, gen_id);
}

static void nfnetlink_rcv(struct sk_buff *skb)
{
        struct nlmsghdr *nlh = nlmsg_hdr(skb);

        if (skb->len < NLMSG_HDRLEN ||
            nlh->nlmsg_len < NLMSG_HDRLEN ||
            skb->len < nlh->nlmsg_len)
                return;

        if (!netlink_net_capable(skb, CAP_NET_ADMIN)) {
                netlink_ack(skb, nlh, -EPERM, NULL);
                return;
        }

        if (nlh->nlmsg_type == NFNL_MSG_BATCH_BEGIN)
                nfnetlink_rcv_skb_batch(skb, nlh);
        else
                netlink_rcv_skb(skb, nfnetlink_rcv_msg);
}

static void nfnetlink_bind_event(struct net *net, unsigned int group)
{
#ifdef CONFIG_NF_CONNTRACK_EVENTS
        int type, group_bit;
        u8 v;

        /* All NFNLGRP_CONNTRACK_* group bits fit into u8.
         * The other groups are not relevant and can be ignored.
         */
        if (group >= 8)
                return;

        type = nfnl_group2type[group];

        switch (type) {
        case NFNL_SUBSYS_CTNETLINK:
                break;
        case NFNL_SUBSYS_CTNETLINK_EXP:
                break;
        default:
                return;
        }

        group_bit = (1 << group);

        spin_lock(&nfnl_grp_active_lock);
        v = READ_ONCE(nf_ctnetlink_has_listener);
        if ((v & group_bit) == 0) {
                v |= group_bit;

                /* read concurrently without nfnl_grp_active_lock held. */
                WRITE_ONCE(nf_ctnetlink_has_listener, v);
        }

        spin_unlock(&nfnl_grp_active_lock);
#endif
}

static int nfnetlink_bind(struct net *net, int group)
{
        const struct nfnetlink_subsystem *ss;
        int type;

        if (group <= NFNLGRP_NONE || group > NFNLGRP_MAX)
                return 0;

        type = nfnl_group2type[group];

        rcu_read_lock();
        ss = nfnetlink_get_subsys(type << 8);
        rcu_read_unlock();
        if (!ss)
                request_module_nowait("nfnetlink-subsys-%d", type);

        nfnetlink_bind_event(net, group);
        return 0;
}

static void nfnetlink_unbind(struct net *net, int group)
{
#ifdef CONFIG_NF_CONNTRACK_EVENTS
        int type, group_bit;

        if (group <= NFNLGRP_NONE || group > NFNLGRP_MAX)
                return;

        type = nfnl_group2type[group];

        switch (type) {
        case NFNL_SUBSYS_CTNETLINK:
                break;
        case NFNL_SUBSYS_CTNETLINK_EXP:
                break;
        default:
                return;
        }

        /* ctnetlink_has_listener is u8 */
        if (group >= 8)
                return;

        group_bit = (1 << group);

        spin_lock(&nfnl_grp_active_lock);
        if (!nfnetlink_has_listeners(net, group)) {
                u8 v = READ_ONCE(nf_ctnetlink_has_listener);

                v &= ~group_bit;

                /* read concurrently without nfnl_grp_active_lock held. */
                WRITE_ONCE(nf_ctnetlink_has_listener, v);
        }
        spin_unlock(&nfnl_grp_active_lock);
#endif
}

static int __net_init nfnetlink_net_init(struct net *net)
{
        struct nfnl_net *nfnlnet = nfnl_pernet(net);
        struct netlink_kernel_cfg cfg = {
                .groups = NFNLGRP_MAX,
                .input  = nfnetlink_rcv,
                .bind   = nfnetlink_bind,
                .unbind = nfnetlink_unbind,
        };

        nfnlnet->nfnl = netlink_kernel_create(net, NETLINK_NETFILTER, &cfg);
        if (!nfnlnet->nfnl)
                return -ENOMEM;
        return 0;
}

static void __net_exit nfnetlink_net_exit_batch(struct list_head *net_exit_list)
{
        struct nfnl_net *nfnlnet;
        struct net *net;

        list_for_each_entry(net, net_exit_list, exit_list) {
                nfnlnet = nfnl_pernet(net);

                netlink_kernel_release(nfnlnet->nfnl);
        }
}

static struct pernet_operations nfnetlink_net_ops = {
        .init           = nfnetlink_net_init,
        .exit_batch     = nfnetlink_net_exit_batch,
        .id             = &nfnetlink_pernet_id,
        .size           = sizeof(struct nfnl_net),
};

static int __init nfnetlink_init(void)
{
        int i;

        for (i = NFNLGRP_NONE + 1; i <= NFNLGRP_MAX; i++)
                BUG_ON(nfnl_group2type[i] == NFNL_SUBSYS_NONE);

        for (i=0; i<NFNL_SUBSYS_COUNT; i++)
                __mutex_init(&table[i].mutex, nfnl_lockdep_names[i], &nfnl_lockdep_keys[i]);

        return register_pernet_subsys(&nfnetlink_net_ops);
}

static void __exit nfnetlink_exit(void)
{
        unregister_pernet_subsys(&nfnetlink_net_ops);
}
module_init(nfnetlink_init);
module_exit(nfnetlink_exit);