// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * INET         An implementation of the TCP/IP protocol suite for the LINUX
 *              operating system.  INET is implemented using the BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              Generic INET transport hashtables
 *
 * Authors:     Lotsa people, from code originally in tcp
 */

#include <linux/module.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/wait.h>
#include <linux/vmalloc.h>
#include <linux/memblock.h>

#include <net/addrconf.h>
#include <net/inet_connection_sock.h>
#include <net/inet_hashtables.h>
#include <net/secure_seq.h>
#include <net/ip.h>
#include <net/tcp.h>
#include <net/sock_reuseport.h>

static u32 inet_ehashfn(const struct net *net, const __be32 laddr,
                        const __u16 lport, const __be32 faddr,
                        const __be16 fport)
{
        static u32 inet_ehash_secret __read_mostly;

        net_get_random_once(&inet_ehash_secret, sizeof(inet_ehash_secret));

        return __inet_ehashfn(laddr, lport, faddr, fport,
                              inet_ehash_secret + net_hash_mix(net));
}

/* This function handles inet_sock, but also timewait and request sockets
 * for IPv4/IPv6.
 */
static u32 sk_ehashfn(const struct sock *sk)
{
#if IS_ENABLED(CONFIG_IPV6)
        if (sk->sk_family == AF_INET6 &&
            !ipv6_addr_v4mapped(&sk->sk_v6_daddr))
                return inet6_ehashfn(sock_net(sk),
                                     &sk->sk_v6_rcv_saddr, sk->sk_num,
                                     &sk->sk_v6_daddr, sk->sk_dport);
#endif
        return inet_ehashfn(sock_net(sk),
                            sk->sk_rcv_saddr, sk->sk_num,
                            sk->sk_daddr, sk->sk_dport);
}

/*
 * Allocate and initialize a new local port bind bucket.
 * The bindhash mutex for snum's hash chain must be held here.
 */
struct inet_bind_bucket *inet_bind_bucket_create(struct kmem_cache *cachep,
                                                 struct net *net,
                                                 struct inet_bind_hashbucket *head,
                                                 const unsigned short snum,
                                                 int l3mdev)
{
        struct inet_bind_bucket *tb = kmem_cache_alloc(cachep, GFP_ATOMIC);

        if (tb) {
                write_pnet(&tb->ib_net, net);
                tb->l3mdev    = l3mdev;
                tb->port      = snum;
                tb->fastreuse = 0;
                tb->fastreuseport = 0;
                INIT_HLIST_HEAD(&tb->owners);
                hlist_add_head(&tb->node, &head->chain);
        }
        return tb;
}

/*
 * Caller must hold hashbucket lock for this tb with local BH disabled
 */
void inet_bind_bucket_destroy(struct kmem_cache *cachep, struct inet_bind_bucket *tb)
{
        if (hlist_empty(&tb->owners)) {
                __hlist_del(&tb->node);
                kmem_cache_free(cachep, tb);
        }
}

void inet_bind_hash(struct sock *sk, struct inet_bind_bucket *tb,
                    const unsigned short snum)
{
        inet_sk(sk)->inet_num = snum;
        sk_add_bind_node(sk, &tb->owners);
        inet_csk(sk)->icsk_bind_hash = tb;
}

/*
 * Get rid of any references to a local port held by the given sock.
 */
static void __inet_put_port(struct sock *sk)
{
        struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
        const int bhash = inet_bhashfn(sock_net(sk), inet_sk(sk)->inet_num,
                        hashinfo->bhash_size);
        struct inet_bind_hashbucket *head = &hashinfo->bhash[bhash];
        struct inet_bind_bucket *tb;

        spin_lock(&head->lock);
        tb = inet_csk(sk)->icsk_bind_hash;
        __sk_del_bind_node(sk);
        inet_csk(sk)->icsk_bind_hash = NULL;
        inet_sk(sk)->inet_num = 0;
        inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
        spin_unlock(&head->lock);
}

void inet_put_port(struct sock *sk)
{
        local_bh_disable();
        __inet_put_port(sk);
        local_bh_enable();
}
EXPORT_SYMBOL(inet_put_port);

int __inet_inherit_port(const struct sock *sk, struct sock *child)
{
        struct inet_hashinfo *table = sk->sk_prot->h.hashinfo;
        unsigned short port = inet_sk(child)->inet_num;
        const int bhash = inet_bhashfn(sock_net(sk), port,
                        table->bhash_size);
        struct inet_bind_hashbucket *head = &table->bhash[bhash];
        struct inet_bind_bucket *tb;
        int l3mdev;

        spin_lock(&head->lock);
        tb = inet_csk(sk)->icsk_bind_hash;
        if (unlikely(!tb)) {
                spin_unlock(&head->lock);
                return -ENOENT;
        }
        if (tb->port != port) {
                l3mdev = inet_sk_bound_l3mdev(sk);

                /* NOTE: using tproxy and redirecting skbs to a proxy
                 * on a different listener port breaks the assumption
                 * that the listener socket's icsk_bind_hash is the same
                 * as that of the child socket. We have to look up or
                 * create a new bind bucket for the child here. */
                inet_bind_bucket_for_each(tb, &head->chain) {
                        if (net_eq(ib_net(tb), sock_net(sk)) &&
                            tb->l3mdev == l3mdev && tb->port == port)
                                break;
                }
                if (!tb) {
                        tb = inet_bind_bucket_create(table->bind_bucket_cachep,
                                                     sock_net(sk), head, port,
                                                     l3mdev);
                        if (!tb) {
                                spin_unlock(&head->lock);
                                return -ENOMEM;
                        }
                }
                inet_csk_update_fastreuse(tb, child);
        }
        inet_bind_hash(child, tb, port);
        spin_unlock(&head->lock);

        return 0;
}
EXPORT_SYMBOL_GPL(__inet_inherit_port);

static struct inet_listen_hashbucket *
inet_lhash2_bucket_sk(struct inet_hashinfo *h, struct sock *sk)
{
        u32 hash;

#if IS_ENABLED(CONFIG_IPV6)
        if (sk->sk_family == AF_INET6)
                hash = ipv6_portaddr_hash(sock_net(sk),
                                          &sk->sk_v6_rcv_saddr,
                                          inet_sk(sk)->inet_num);
        else
#endif
                hash = ipv4_portaddr_hash(sock_net(sk),
                                          inet_sk(sk)->inet_rcv_saddr,
                                          inet_sk(sk)->inet_num);
        return inet_lhash2_bucket(h, hash);
}

static void inet_hash2(struct inet_hashinfo *h, struct sock *sk)
{
        struct inet_listen_hashbucket *ilb2;

        if (!h->lhash2)
                return;

        ilb2 = inet_lhash2_bucket_sk(h, sk);

        spin_lock(&ilb2->lock);
        if (sk->sk_reuseport && sk->sk_family == AF_INET6)
                hlist_add_tail_rcu(&inet_csk(sk)->icsk_listen_portaddr_node,
                                   &ilb2->head);
        else
                hlist_add_head_rcu(&inet_csk(sk)->icsk_listen_portaddr_node,
                                   &ilb2->head);
        ilb2->count++;
        spin_unlock(&ilb2->lock);
}

static void inet_unhash2(struct inet_hashinfo *h, struct sock *sk)
{
        struct inet_listen_hashbucket *ilb2;

        if (!h->lhash2 ||
            WARN_ON_ONCE(hlist_unhashed(&inet_csk(sk)->icsk_listen_portaddr_node)))
                return;

        ilb2 = inet_lhash2_bucket_sk(h, sk);

        spin_lock(&ilb2->lock);
        hlist_del_init_rcu(&inet_csk(sk)->icsk_listen_portaddr_node);
        ilb2->count--;
        spin_unlock(&ilb2->lock);
}

static inline int compute_score(struct sock *sk, struct net *net,
                                const unsigned short hnum, const __be32 daddr,
                                const int dif, const int sdif, bool exact_dif)
{
        int score = -1;

        if (net_eq(sock_net(sk), net) && sk->sk_num == hnum &&
                        !ipv6_only_sock(sk)) {
                if (sk->sk_rcv_saddr != daddr)
                        return -1;

                if (!inet_sk_bound_dev_eq(net, sk->sk_bound_dev_if, dif, sdif))
                        return -1;

                score = sk->sk_family == PF_INET ? 2 : 1;
                if (READ_ONCE(sk->sk_incoming_cpu) == raw_smp_processor_id())
                        score++;
        }
        return score;
}

static inline struct sock *lookup_reuseport(struct net *net, struct sock *sk,
                                            struct sk_buff *skb, int doff,
                                            __be32 saddr, __be16 sport,
                                            __be32 daddr, unsigned short hnum)
{
        struct sock *reuse_sk = NULL;
        u32 phash;

        if (sk->sk_reuseport) {
                phash = inet_ehashfn(net, daddr, hnum, saddr, sport);
                reuse_sk = reuseport_select_sock(sk, phash, skb, doff);
        }
        return reuse_sk;
}

/*
 * Here are some nice properties to exploit here. The BSD API
 * does not allow a listening sock to specify the remote port nor the
 * remote address for the connection. So always assume those are both
 * wildcarded during the search since they can never be otherwise.
 */

/* called with rcu_read_lock() : No refcount taken on the socket */
static struct sock *inet_lhash2_lookup(struct net *net,
                                struct inet_listen_hashbucket *ilb2,
                                struct sk_buff *skb, int doff,
                                const __be32 saddr, __be16 sport,
                                const __be32 daddr, const unsigned short hnum,
                                const int dif, const int sdif)
{
        bool exact_dif = inet_exact_dif_match(net, skb);
        struct inet_connection_sock *icsk;
        struct sock *sk, *result = NULL;
        int score, hiscore = 0;

        inet_lhash2_for_each_icsk_rcu(icsk, &ilb2->head) {
                sk = (struct sock *)icsk;
                score = compute_score(sk, net, hnum, daddr,
                                      dif, sdif, exact_dif);
                if (score > hiscore) {
                        result = lookup_reuseport(net, sk, skb, doff,
                                                  saddr, sport, daddr, hnum);
                        if (result)
                                return result;

                        result = sk;
                        hiscore = score;
                }
        }

        return result;
}

static inline struct sock *inet_lookup_run_bpf(struct net *net,
                                               struct inet_hashinfo *hashinfo,
                                               struct sk_buff *skb, int doff,
                                               __be32 saddr, __be16 sport,
                                               __be32 daddr, u16 hnum)
{
        struct sock *sk, *reuse_sk;
        bool no_reuseport;

        if (hashinfo != &tcp_hashinfo)
                return NULL; /* only TCP is supported */

        no_reuseport = bpf_sk_lookup_run_v4(net, IPPROTO_TCP,
                                            saddr, sport, daddr, hnum, &sk);
        if (no_reuseport || IS_ERR_OR_NULL(sk))
                return sk;

        reuse_sk = lookup_reuseport(net, sk, skb, doff, saddr, sport, daddr, hnum);
        if (reuse_sk)
                sk = reuse_sk;
        return sk;
}

struct sock *__inet_lookup_listener(struct net *net,
                                    struct inet_hashinfo *hashinfo,
                                    struct sk_buff *skb, int doff,
                                    const __be32 saddr, __be16 sport,
                                    const __be32 daddr, const unsigned short hnum,
                                    const int dif, const int sdif)
{
        struct inet_listen_hashbucket *ilb2;
        struct sock *result = NULL;
        unsigned int hash2;

        /* Lookup redirect from BPF */
        if (static_branch_unlikely(&bpf_sk_lookup_enabled)) {
                result = inet_lookup_run_bpf(net, hashinfo, skb, doff,
                                             saddr, sport, daddr, hnum);
                if (result)
                        goto done;
        }

        hash2 = ipv4_portaddr_hash(net, daddr, hnum);
        ilb2 = inet_lhash2_bucket(hashinfo, hash2);

        result = inet_lhash2_lookup(net, ilb2, skb, doff,
                                    saddr, sport, daddr, hnum,
                                    dif, sdif);
        if (result)
                goto done;

        /* Lookup lhash2 with INADDR_ANY */
        hash2 = ipv4_portaddr_hash(net, htonl(INADDR_ANY), hnum);
        ilb2 = inet_lhash2_bucket(hashinfo, hash2);

        result = inet_lhash2_lookup(net, ilb2, skb, doff,
                                    saddr, sport, htonl(INADDR_ANY), hnum,
                                    dif, sdif);
done:
        if (IS_ERR(result))
                return NULL;
        return result;
}
EXPORT_SYMBOL_GPL(__inet_lookup_listener);

/* All sockets share common refcount, but have different destructors */
void sock_gen_put(struct sock *sk)
{
        if (!refcount_dec_and_test(&sk->sk_refcnt))
                return;

        if (sk->sk_state == TCP_TIME_WAIT)
                inet_twsk_free(inet_twsk(sk));
        else if (sk->sk_state == TCP_NEW_SYN_RECV)
                reqsk_free(inet_reqsk(sk));
        else
                sk_free(sk);
}
EXPORT_SYMBOL_GPL(sock_gen_put);

void sock_edemux(struct sk_buff *skb)
{
        sock_gen_put(skb->sk);
}
EXPORT_SYMBOL(sock_edemux);

struct sock *__inet_lookup_established(struct net *net,
                                  struct inet_hashinfo *hashinfo,
                                  const __be32 saddr, const __be16 sport,
                                  const __be32 daddr, const u16 hnum,
                                  const int dif, const int sdif)
{
        INET_ADDR_COOKIE(acookie, saddr, daddr);
        const __portpair ports = INET_COMBINED_PORTS(sport, hnum);
        struct sock *sk;
        const struct hlist_nulls_node *node;
        /* Optimize here for direct hit, only listening connections can
         * have wildcards anyways.
         */
        unsigned int hash = inet_ehashfn(net, daddr, hnum, saddr, sport);
        unsigned int slot = hash & hashinfo->ehash_mask;
        struct inet_ehash_bucket *head = &hashinfo->ehash[slot];

begin:
        sk_nulls_for_each_rcu(sk, node, &head->chain) {
                if (sk->sk_hash != hash)
                        continue;
                if (likely(INET_MATCH(sk, net, acookie,
                                      saddr, daddr, ports, dif, sdif))) {
                        if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
                                goto out;
                        if (unlikely(!INET_MATCH(sk, net, acookie,
                                                 saddr, daddr, ports,
                                                 dif, sdif))) {
                                sock_gen_put(sk);
                                goto begin;
                        }
                        goto found;
                }
        }
        /*
         * if the nulls value we got at the end of this lookup is
         * not the expected one, we must restart lookup.
         * We probably met an item that was moved to another chain.
         */
        if (get_nulls_value(node) != slot)
                goto begin;
out:
        sk = NULL;
found:
        return sk;
}
EXPORT_SYMBOL_GPL(__inet_lookup_established);

/* called with local bh disabled */
static int __inet_check_established(struct inet_timewait_death_row *death_row,
                                    struct sock *sk, __u16 lport,
                                    struct inet_timewait_sock **twp)
{
        struct inet_hashinfo *hinfo = death_row->hashinfo;
        struct inet_sock *inet = inet_sk(sk);
        __be32 daddr = inet->inet_rcv_saddr;
        __be32 saddr = inet->inet_daddr;
        int dif = sk->sk_bound_dev_if;
        struct net *net = sock_net(sk);
        int sdif = l3mdev_master_ifindex_by_index(net, dif);
        INET_ADDR_COOKIE(acookie, saddr, daddr);
        const __portpair ports = INET_COMBINED_PORTS(inet->inet_dport, lport);
        unsigned int hash = inet_ehashfn(net, daddr, lport,
                                         saddr, inet->inet_dport);
        struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
        spinlock_t *lock = inet_ehash_lockp(hinfo, hash);
        struct sock *sk2;
        const struct hlist_nulls_node *node;
        struct inet_timewait_sock *tw = NULL;

        spin_lock(lock);

        sk_nulls_for_each(sk2, node, &head->chain) {
                if (sk2->sk_hash != hash)
                        continue;

                if (likely(INET_MATCH(sk2, net, acookie,
                                         saddr, daddr, ports, dif, sdif))) {
                        if (sk2->sk_state == TCP_TIME_WAIT) {
                                tw = inet_twsk(sk2);
                                if (twsk_unique(sk, sk2, twp))
                                        break;
                        }
                        goto not_unique;
                }
        }

        /* Must record num and sport now. Otherwise we will see
         * in hash table socket with a funny identity.
         */
        inet->inet_num = lport;
        inet->inet_sport = htons(lport);
        sk->sk_hash = hash;
        WARN_ON(!sk_unhashed(sk));
        __sk_nulls_add_node_rcu(sk, &head->chain);
        if (tw) {
                sk_nulls_del_node_init_rcu((struct sock *)tw);
                __NET_INC_STATS(net, LINUX_MIB_TIMEWAITRECYCLED);
        }
        spin_unlock(lock);
        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);

        if (twp) {
                *twp = tw;
        } else if (tw) {
                /* Silly. Should hash-dance instead... */
                inet_twsk_deschedule_put(tw);
        }
        return 0;

not_unique:
        spin_unlock(lock);
        return -EADDRNOTAVAIL;
}

static u32 inet_sk_port_offset(const struct sock *sk)
{
        const struct inet_sock *inet = inet_sk(sk);

        return secure_ipv4_port_ephemeral(inet->inet_rcv_saddr,
                                          inet->inet_daddr,
                                          inet->inet_dport);
}

/* insert a socket into ehash, and eventually remove another one
 * (The another one can be a SYN_RECV or TIMEWAIT
 */
bool inet_ehash_insert(struct sock *sk, struct sock *osk)
{
        struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
        struct hlist_nulls_head *list;
        struct inet_ehash_bucket *head;
        spinlock_t *lock;
        bool ret = true;

        WARN_ON_ONCE(!sk_unhashed(sk));

        sk->sk_hash = sk_ehashfn(sk);
        head = inet_ehash_bucket(hashinfo, sk->sk_hash);
        list = &head->chain;
        lock = inet_ehash_lockp(hashinfo, sk->sk_hash);

        spin_lock(lock);
        if (osk) {
                WARN_ON_ONCE(sk->sk_hash != osk->sk_hash);
                ret = sk_nulls_del_node_init_rcu(osk);
        }
        if (ret)
                __sk_nulls_add_node_rcu(sk, list);
        spin_unlock(lock);
        return ret;
}

bool inet_ehash_nolisten(struct sock *sk, struct sock *osk)
{
        bool ok = inet_ehash_insert(sk, osk);

        if (ok) {
                sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
        } else {
                percpu_counter_inc(sk->sk_prot->orphan_count);
                inet_sk_set_state(sk, TCP_CLOSE);
                sock_set_flag(sk, SOCK_DEAD);
                inet_csk_destroy_sock(sk);
        }
        return ok;
}
EXPORT_SYMBOL_GPL(inet_ehash_nolisten);

static int inet_reuseport_add_sock(struct sock *sk,
                                   struct inet_listen_hashbucket *ilb)
{
        struct inet_bind_bucket *tb = inet_csk(sk)->icsk_bind_hash;
        const struct hlist_nulls_node *node;
        struct sock *sk2;
        kuid_t uid = sock_i_uid(sk);

        sk_nulls_for_each_rcu(sk2, node, &ilb->nulls_head) {
                if (sk2 != sk &&
                    sk2->sk_family == sk->sk_family &&
                    ipv6_only_sock(sk2) == ipv6_only_sock(sk) &&
                    sk2->sk_bound_dev_if == sk->sk_bound_dev_if &&
                    inet_csk(sk2)->icsk_bind_hash == tb &&
                    sk2->sk_reuseport && uid_eq(uid, sock_i_uid(sk2)) &&
                    inet_rcv_saddr_equal(sk, sk2, false))
                        return reuseport_add_sock(sk, sk2,
                                                  inet_rcv_saddr_any(sk));
        }

        return reuseport_alloc(sk, inet_rcv_saddr_any(sk));
}

int __inet_hash(struct sock *sk, struct sock *osk)
{
        struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
        struct inet_listen_hashbucket *ilb;
        int err = 0;

        if (sk->sk_state != TCP_LISTEN) {
                inet_ehash_nolisten(sk, osk);
                return 0;
        }
        WARN_ON(!sk_unhashed(sk));
        ilb = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];

        spin_lock(&ilb->lock);
        if (sk->sk_reuseport) {
                err = inet_reuseport_add_sock(sk, ilb);
                if (err)
                        goto unlock;
        }
        if (IS_ENABLED(CONFIG_IPV6) && sk->sk_reuseport &&
                sk->sk_family == AF_INET6)
                __sk_nulls_add_node_tail_rcu(sk, &ilb->nulls_head);
        else
                __sk_nulls_add_node_rcu(sk, &ilb->nulls_head);
        inet_hash2(hashinfo, sk);
        ilb->count++;
        sock_set_flag(sk, SOCK_RCU_FREE);
        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
unlock:
        spin_unlock(&ilb->lock);

        return err;
}
EXPORT_SYMBOL(__inet_hash);

int inet_hash(struct sock *sk)
{
        int err = 0;

        if (sk->sk_state != TCP_CLOSE) {
                local_bh_disable();
                err = __inet_hash(sk, NULL);
                local_bh_enable();
        }

        return err;
}
EXPORT_SYMBOL_GPL(inet_hash);

void inet_unhash(struct sock *sk)
{
        struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
        struct inet_listen_hashbucket *ilb = NULL;
        spinlock_t *lock;

        if (sk_unhashed(sk))
                return;

        if (sk->sk_state == TCP_LISTEN) {
                ilb = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
                lock = &ilb->lock;
        } else {
                lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
        }
        spin_lock_bh(lock);
        if (sk_unhashed(sk))
                goto unlock;

        if (rcu_access_pointer(sk->sk_reuseport_cb))
                reuseport_detach_sock(sk);
        if (ilb) {
                inet_unhash2(hashinfo, sk);
                ilb->count--;
        }
        __sk_nulls_del_node_init_rcu(sk);
        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
unlock:
        spin_unlock_bh(lock);
}
EXPORT_SYMBOL_GPL(inet_unhash);

int __inet_hash_connect(struct inet_timewait_death_row *death_row,
                struct sock *sk, u32 port_offset,
                int (*check_established)(struct inet_timewait_death_row *,
                        struct sock *, __u16, struct inet_timewait_sock **))
{
        struct inet_hashinfo *hinfo = death_row->hashinfo;
        struct inet_timewait_sock *tw = NULL;
        struct inet_bind_hashbucket *head;
        int port = inet_sk(sk)->inet_num;
        struct net *net = sock_net(sk);
        struct inet_bind_bucket *tb;
        u32 remaining, offset;
        int ret, i, low, high;
        static u32 hint;
        int l3mdev;

        if (port) {
                head = &hinfo->bhash[inet_bhashfn(net, port,
                                                  hinfo->bhash_size)];
                tb = inet_csk(sk)->icsk_bind_hash;
                spin_lock_bh(&head->lock);
                if (sk_head(&tb->owners) == sk && !sk->sk_bind_node.next) {
                        inet_ehash_nolisten(sk, NULL);
                        spin_unlock_bh(&head->lock);
                        return 0;
                }
                spin_unlock(&head->lock);
                /* No definite answer... Walk to established hash table */
                ret = check_established(death_row, sk, port, NULL);
                local_bh_enable();
                return ret;
        }

        l3mdev = inet_sk_bound_l3mdev(sk);

        inet_get_local_port_range(net, &low, &high);
        high++; /* [32768, 60999] -> [32768, 61000[ */
        remaining = high - low;
        if (likely(remaining > 1))
                remaining &= ~1U;

        offset = (hint + port_offset) % remaining;
        /* In first pass we try ports of @low parity.
         * inet_csk_get_port() does the opposite choice.
         */
        offset &= ~1U;
other_parity_scan:
        port = low + offset;
        for (i = 0; i < remaining; i += 2, port += 2) {
                if (unlikely(port >= high))
                        port -= remaining;
                if (inet_is_local_reserved_port(net, port))
                        continue;
                head = &hinfo->bhash[inet_bhashfn(net, port,
                                                  hinfo->bhash_size)];
                spin_lock_bh(&head->lock);

                /* Does not bother with rcv_saddr checks, because
                 * the established check is already unique enough.
                 */
                inet_bind_bucket_for_each(tb, &head->chain) {
                        if (net_eq(ib_net(tb), net) && tb->l3mdev == l3mdev &&
                            tb->port == port) {
                                if (tb->fastreuse >= 0 ||
                                    tb->fastreuseport >= 0)
                                        goto next_port;
                                WARN_ON(hlist_empty(&tb->owners));
                                if (!check_established(death_row, sk,
                                                       port, &tw))
                                        goto ok;
                                goto next_port;
                        }
                }

                tb = inet_bind_bucket_create(hinfo->bind_bucket_cachep,
                                             net, head, port, l3mdev);
                if (!tb) {
                        spin_unlock_bh(&head->lock);
                        return -ENOMEM;
                }
                tb->fastreuse = -1;
                tb->fastreuseport = -1;
                goto ok;
next_port:
                spin_unlock_bh(&head->lock);
                cond_resched();
        }

        offset++;
        if ((offset & 1) && remaining > 1)
                goto other_parity_scan;

        return -EADDRNOTAVAIL;

ok:
        hint += i + 2;

        /* Head lock still held and bh's disabled */
        inet_bind_hash(sk, tb, port);
        if (sk_unhashed(sk)) {
                inet_sk(sk)->inet_sport = htons(port);
                inet_ehash_nolisten(sk, (struct sock *)tw);
        }
        if (tw)
                inet_twsk_bind_unhash(tw, hinfo);
        spin_unlock(&head->lock);
        if (tw)
                inet_twsk_deschedule_put(tw);
        local_bh_enable();
        return 0;
}

/*
 * Bind a port for a connect operation and hash it.
 */
int inet_hash_connect(struct inet_timewait_death_row *death_row,
                      struct sock *sk)
{
        u32 port_offset = 0;

        if (!inet_sk(sk)->inet_num)
                port_offset = inet_sk_port_offset(sk);
        return __inet_hash_connect(death_row, sk, port_offset,
                                   __inet_check_established);
}
EXPORT_SYMBOL_GPL(inet_hash_connect);

void inet_hashinfo_init(struct inet_hashinfo *h)
{
        int i;

        for (i = 0; i < INET_LHTABLE_SIZE; i++) {
                spin_lock_init(&h->listening_hash[i].lock);
                INIT_HLIST_NULLS_HEAD(&h->listening_hash[i].nulls_head,
                                      i + LISTENING_NULLS_BASE);
                h->listening_hash[i].count = 0;
        }

        h->lhash2 = NULL;
}
EXPORT_SYMBOL_GPL(inet_hashinfo_init);

static void init_hashinfo_lhash2(struct inet_hashinfo *h)
{
        int i;

        for (i = 0; i <= h->lhash2_mask; i++) {
                spin_lock_init(&h->lhash2[i].lock);
                INIT_HLIST_HEAD(&h->lhash2[i].head);
                h->lhash2[i].count = 0;
        }
}

void __init inet_hashinfo2_init(struct inet_hashinfo *h, const char *name,
                                unsigned long numentries, int scale,
                                unsigned long low_limit,
                                unsigned long high_limit)
{
        h->lhash2 = alloc_large_system_hash(name,
                                            sizeof(*h->lhash2),
                                            numentries,
                                            scale,
                                            0,
                                            NULL,
                                            &h->lhash2_mask,
                                            low_limit,
                                            high_limit);
        init_hashinfo_lhash2(h);
}

int inet_hashinfo2_init_mod(struct inet_hashinfo *h)
{
        h->lhash2 = kmalloc_array(INET_LHTABLE_SIZE, sizeof(*h->lhash2), GFP_KERNEL);
        if (!h->lhash2)
                return -ENOMEM;

        h->lhash2_mask = INET_LHTABLE_SIZE - 1;
        /* INET_LHTABLE_SIZE must be a power of 2 */
        BUG_ON(INET_LHTABLE_SIZE & h->lhash2_mask);

        init_hashinfo_lhash2(h);
        return 0;
}
EXPORT_SYMBOL_GPL(inet_hashinfo2_init_mod);

int inet_ehash_locks_alloc(struct inet_hashinfo *hashinfo)
{
        unsigned int locksz = sizeof(spinlock_t);
        unsigned int i, nblocks = 1;

        if (locksz != 0) {
                /* allocate 2 cache lines or at least one spinlock per cpu */
                nblocks = max(2U * L1_CACHE_BYTES / locksz, 1U);
                nblocks = roundup_pow_of_two(nblocks * num_possible_cpus());

                /* no more locks than number of hash buckets */
                nblocks = min(nblocks, hashinfo->ehash_mask + 1);

                hashinfo->ehash_locks = kvmalloc_array(nblocks, locksz, GFP_KERNEL);
                if (!hashinfo->ehash_locks)
                        return -ENOMEM;

                for (i = 0; i < nblocks; i++)
                        spin_lock_init(&hashinfo->ehash_locks[i]);
        }
        hashinfo->ehash_locks_mask = nblocks - 1;
        return 0;
}
EXPORT_SYMBOL_GPL(inet_ehash_locks_alloc);