/*
 * 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
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */

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

#include <net/inet_connection_sock.h>
#include <net/inet_hashtables.h>
#include <net/ip.h>

/*
 * 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 inet_bind_hashbucket *head,
                                                 const unsigned short snum)
{
        struct inet_bind_bucket *tb = kmem_cache_alloc(cachep, GFP_ATOMIC);

        if (tb != NULL) {
                tb->port      = snum;
                tb->fastreuse = 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)->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 inet_hashinfo *hashinfo, struct sock *sk)
{
        const int bhash = inet_bhashfn(inet_sk(sk)->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)->num = 0;
        inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
        spin_unlock(&head->lock);
}

void inet_put_port(struct inet_hashinfo *hashinfo, struct sock *sk)
{
        local_bh_disable();
        __inet_put_port(hashinfo, sk);
        local_bh_enable();
}

EXPORT_SYMBOL(inet_put_port);

/*
 * This lock without WQ_FLAG_EXCLUSIVE is good on UP and it can be very bad on SMP.
 * Look, when several writers sleep and reader wakes them up, all but one
 * immediately hit write lock and grab all the cpus. Exclusive sleep solves
 * this, _but_ remember, it adds useless work on UP machines (wake up each
 * exclusive lock release). It should be ifdefed really.
 */
void inet_listen_wlock(struct inet_hashinfo *hashinfo)
{
        write_lock(&hashinfo->lhash_lock);

        if (atomic_read(&hashinfo->lhash_users)) {
                DEFINE_WAIT(wait);

                for (;;) {
                        prepare_to_wait_exclusive(&hashinfo->lhash_wait,
                                                  &wait, TASK_UNINTERRUPTIBLE);
                        if (!atomic_read(&hashinfo->lhash_users))
                                break;
                        write_unlock_bh(&hashinfo->lhash_lock);
                        schedule();
                        write_lock_bh(&hashinfo->lhash_lock);
                }

                finish_wait(&hashinfo->lhash_wait, &wait);
        }
}

EXPORT_SYMBOL(inet_listen_wlock);

/*
 * Don't inline this cruft. 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.
 */
static struct sock *inet_lookup_listener_slow(const struct hlist_head *head,
                                              const __be32 daddr,
                                              const unsigned short hnum,
                                              const int dif)
{
        struct sock *result = NULL, *sk;
        const struct hlist_node *node;
        int hiscore = -1;

        sk_for_each(sk, node, head) {
                const struct inet_sock *inet = inet_sk(sk);

                if (inet->num == hnum && !ipv6_only_sock(sk)) {
                        const __be32 rcv_saddr = inet->rcv_saddr;
                        int score = sk->sk_family == PF_INET ? 1 : 0;

                        if (rcv_saddr) {
                                if (rcv_saddr != daddr)
                                        continue;
                                score += 2;
                        }
                        if (sk->sk_bound_dev_if) {
                                if (sk->sk_bound_dev_if != dif)
                                        continue;
                                score += 2;
                        }
                        if (score == 5)
                                return sk;
                        if (score > hiscore) {
                                hiscore = score;
                                result  = sk;
                        }
                }
        }
        return result;
}

/* Optimize the common listener case. */
struct sock *__inet_lookup_listener(struct inet_hashinfo *hashinfo,
                                    const __be32 daddr, const unsigned short hnum,
                                    const int dif)
{
        struct sock *sk = NULL;
        const struct hlist_head *head;

        read_lock(&hashinfo->lhash_lock);
        head = &hashinfo->listening_hash[inet_lhashfn(hnum)];
        if (!hlist_empty(head)) {
                const struct inet_sock *inet = inet_sk((sk = __sk_head(head)));

                if (inet->num == hnum && !sk->sk_node.next &&
                    (!inet->rcv_saddr || inet->rcv_saddr == daddr) &&
                    (sk->sk_family == PF_INET || !ipv6_only_sock(sk)) &&
                    !sk->sk_bound_dev_if)
                        goto sherry_cache;
                sk = inet_lookup_listener_slow(head, daddr, hnum, dif);
        }
        if (sk) {
sherry_cache:
                sock_hold(sk);
        }
        read_unlock(&hashinfo->lhash_lock);
        return sk;
}
EXPORT_SYMBOL_GPL(__inet_lookup_listener);

/* 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->rcv_saddr;
        __be32 saddr = inet->daddr;
        int dif = sk->sk_bound_dev_if;
        INET_ADDR_COOKIE(acookie, saddr, daddr)
        const __portpair ports = INET_COMBINED_PORTS(inet->dport, lport);
        unsigned int hash = inet_ehashfn(daddr, lport, saddr, inet->dport);
        struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
        rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
        struct sock *sk2;
        const struct hlist_node *node;
        struct inet_timewait_sock *tw;

        prefetch(head->chain.first);
        write_lock(lock);

        /* Check TIME-WAIT sockets first. */
        sk_for_each(sk2, node, &head->twchain) {
                tw = inet_twsk(sk2);

                if (INET_TW_MATCH(sk2, hash, acookie, saddr, daddr, ports, dif)) {
                        if (twsk_unique(sk, sk2, twp))
                                goto unique;
                        else
                                goto not_unique;
                }
        }
        tw = NULL;

        /* And established part... */
        sk_for_each(sk2, node, &head->chain) {
                if (INET_MATCH(sk2, hash, acookie, saddr, daddr, ports, dif))
                        goto not_unique;
        }

unique:
        /* Must record num and sport now. Otherwise we will see
         * in hash table socket with a funny identity. */
        inet->num = lport;
        inet->sport = htons(lport);
        sk->sk_hash = hash;
        BUG_TRAP(sk_unhashed(sk));
        __sk_add_node(sk, &head->chain);
        sock_prot_inc_use(sk->sk_prot);
        write_unlock(lock);

        if (twp) {
                *twp = tw;
                NET_INC_STATS_BH(LINUX_MIB_TIMEWAITRECYCLED);
        } else if (tw) {
                /* Silly. Should hash-dance instead... */
                inet_twsk_deschedule(tw, death_row);
                NET_INC_STATS_BH(LINUX_MIB_TIMEWAITRECYCLED);

                inet_twsk_put(tw);
        }

        return 0;

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

static inline u32 inet_sk_port_offset(const struct sock *sk)
{
        const struct inet_sock *inet = inet_sk(sk);
        return secure_ipv4_port_ephemeral(inet->rcv_saddr, inet->daddr,
                                          inet->dport);
}

/*
 * Bind a port for a connect operation and hash it.
 */
int inet_hash_connect(struct inet_timewait_death_row *death_row,
                      struct sock *sk)
{
        struct inet_hashinfo *hinfo = death_row->hashinfo;
        const unsigned short snum = inet_sk(sk)->num;
        struct inet_bind_hashbucket *head;
        struct inet_bind_bucket *tb;
        int ret;

        if (!snum) {
                int i, remaining, low, high, port;
                static u32 hint;
                u32 offset = hint + inet_sk_port_offset(sk);
                struct hlist_node *node;
                struct inet_timewait_sock *tw = NULL;

                inet_get_local_port_range(&low, &high);
                remaining = (high - low) + 1;

                local_bh_disable();
                for (i = 1; i <= remaining; i++) {
                        port = low + (i + offset) % remaining;
                        head = &hinfo->bhash[inet_bhashfn(port, hinfo->bhash_size)];
                        spin_lock(&head->lock);

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

                        tb = inet_bind_bucket_create(hinfo->bind_bucket_cachep, head, port);
                        if (!tb) {
                                spin_unlock(&head->lock);
                                break;
                        }
                        tb->fastreuse = -1;
                        goto ok;

                next_port:
                        spin_unlock(&head->lock);
                }
                local_bh_enable();

                return -EADDRNOTAVAIL;

ok:
                hint += i;

                /* Head lock still held and bh's disabled */
                inet_bind_hash(sk, tb, port);
                if (sk_unhashed(sk)) {
                        inet_sk(sk)->sport = htons(port);
                        __inet_hash(hinfo, sk, 0);
                }
                spin_unlock(&head->lock);

                if (tw) {
                        inet_twsk_deschedule(tw, death_row);
                        inet_twsk_put(tw);
                }

                ret = 0;
                goto out;
        }

        head = &hinfo->bhash[inet_bhashfn(snum, 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_hash(hinfo, sk, 0);
                spin_unlock_bh(&head->lock);
                return 0;
        } else {
                spin_unlock(&head->lock);
                /* No definite answer... Walk to established hash table */
                ret = __inet_check_established(death_row, sk, snum, NULL);
out:
                local_bh_enable();
                return ret;
        }
}

EXPORT_SYMBOL_GPL(inet_hash_connect);