// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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 TIME_WAIT sockets functions
 *
 *              From code orinally in TCP
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <net/inet_hashtables.h>
#include <net/inet_timewait_sock.h>
#include <net/ip.h>


/**
 *      inet_twsk_bind_unhash - unhash a timewait socket from bind hash
 *      @tw: timewait socket
 *      @hashinfo: hashinfo pointer
 *
 *      unhash a timewait socket from bind hash, if hashed.
 *      bind hash lock must be held by caller.
 *      Returns 1 if caller should call inet_twsk_put() after lock release.
 */
void inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
                          struct inet_hashinfo *hashinfo)
{
        struct inet_bind_bucket *tb = tw->tw_tb;

        if (!tb)
                return;

        __hlist_del(&tw->tw_bind_node);
        tw->tw_tb = NULL;
        inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
        __sock_put((struct sock *)tw);
}

/* Must be called with locally disabled BHs. */
static void inet_twsk_kill(struct inet_timewait_sock *tw)
{
        struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
        spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
        struct inet_bind_hashbucket *bhead;

        spin_lock(lock);
        sk_nulls_del_node_init_rcu((struct sock *)tw);
        spin_unlock(lock);

        /* Disassociate with bind bucket. */
        bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
                        hashinfo->bhash_size)];

        spin_lock(&bhead->lock);
        inet_twsk_bind_unhash(tw, hashinfo);
        spin_unlock(&bhead->lock);

        atomic_dec(&tw->tw_dr->tw_count);
        inet_twsk_put(tw);
}

void inet_twsk_free(struct inet_timewait_sock *tw)
{
        struct module *owner = tw->tw_prot->owner;
        twsk_destructor((struct sock *)tw);
#ifdef SOCK_REFCNT_DEBUG
        pr_debug("%s timewait_sock %p released\n", tw->tw_prot->name, tw);
#endif
        kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
        module_put(owner);
}

void inet_twsk_put(struct inet_timewait_sock *tw)
{
        if (refcount_dec_and_test(&tw->tw_refcnt))
                inet_twsk_free(tw);
}
EXPORT_SYMBOL_GPL(inet_twsk_put);

static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
                                   struct hlist_nulls_head *list)
{
        hlist_nulls_add_head_rcu(&tw->tw_node, list);
}

static void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
                                    struct hlist_head *list)
{
        hlist_add_head(&tw->tw_bind_node, list);
}

/*
 * Enter the time wait state. This is called with locally disabled BH.
 * Essentially we whip up a timewait bucket, copy the relevant info into it
 * from the SK, and mess with hash chains and list linkage.
 */
void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
                           struct inet_hashinfo *hashinfo)
{
        const struct inet_sock *inet = inet_sk(sk);
        const struct inet_connection_sock *icsk = inet_csk(sk);
        struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
        spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
        struct inet_bind_hashbucket *bhead;
        /* Step 1: Put TW into bind hash. Original socket stays there too.
           Note, that any socket with inet->num != 0 MUST be bound in
           binding cache, even if it is closed.
         */
        bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
                        hashinfo->bhash_size)];
        spin_lock(&bhead->lock);
        tw->tw_tb = icsk->icsk_bind_hash;
        WARN_ON(!icsk->icsk_bind_hash);
        inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
        spin_unlock(&bhead->lock);

        spin_lock(lock);

        inet_twsk_add_node_rcu(tw, &ehead->chain);

        /* Step 3: Remove SK from hash chain */
        if (__sk_nulls_del_node_init_rcu(sk))
                sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);

        spin_unlock(lock);

        /* tw_refcnt is set to 3 because we have :
         * - one reference for bhash chain.
         * - one reference for ehash chain.
         * - one reference for timer.
         * We can use atomic_set() because prior spin_lock()/spin_unlock()
         * committed into memory all tw fields.
         * Also note that after this point, we lost our implicit reference
         * so we are not allowed to use tw anymore.
         */
        refcount_set(&tw->tw_refcnt, 3);
}
EXPORT_SYMBOL_GPL(inet_twsk_hashdance);

static void tw_timer_handler(struct timer_list *t)
{
        struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);

        if (tw->tw_kill)
                __NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITKILLED);
        else
                __NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITED);
        inet_twsk_kill(tw);
}

struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
                                           struct inet_timewait_death_row *dr,
                                           const int state)
{
        struct inet_timewait_sock *tw;

        if (atomic_read(&dr->tw_count) >= dr->sysctl_max_tw_buckets)
                return NULL;

        tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
                              GFP_ATOMIC);
        if (tw) {
                const struct inet_sock *inet = inet_sk(sk);

                tw->tw_dr           = dr;
                /* Give us an identity. */
                tw->tw_daddr        = inet->inet_daddr;
                tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
                tw->tw_bound_dev_if = sk->sk_bound_dev_if;
                tw->tw_tos          = inet->tos;
                tw->tw_num          = inet->inet_num;
                tw->tw_state        = TCP_TIME_WAIT;
                tw->tw_substate     = state;
                tw->tw_sport        = inet->inet_sport;
                tw->tw_dport        = inet->inet_dport;
                tw->tw_family       = sk->sk_family;
                tw->tw_reuse        = sk->sk_reuse;
                tw->tw_reuseport    = sk->sk_reuseport;
                tw->tw_hash         = sk->sk_hash;
                tw->tw_ipv6only     = 0;
                tw->tw_transparent  = inet->transparent;
                tw->tw_prot         = sk->sk_prot_creator;
                atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
                twsk_net_set(tw, sock_net(sk));
                timer_setup(&tw->tw_timer, tw_timer_handler, TIMER_PINNED);
                /*
                 * Because we use RCU lookups, we should not set tw_refcnt
                 * to a non null value before everything is setup for this
                 * timewait socket.
                 */
                refcount_set(&tw->tw_refcnt, 0);

                __module_get(tw->tw_prot->owner);
        }

        return tw;
}
EXPORT_SYMBOL_GPL(inet_twsk_alloc);

/* These are always called from BH context.  See callers in
 * tcp_input.c to verify this.
 */

/* This is for handling early-kills of TIME_WAIT sockets.
 * Warning : consume reference.
 * Caller should not access tw anymore.
 */
void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
{
        if (del_timer_sync(&tw->tw_timer))
                inet_twsk_kill(tw);
        inet_twsk_put(tw);
}
EXPORT_SYMBOL(inet_twsk_deschedule_put);

void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
{
        /* timeout := RTO * 3.5
         *
         * 3.5 = 1+2+0.5 to wait for two retransmits.
         *
         * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
         * our ACK acking that FIN can be lost. If N subsequent retransmitted
         * FINs (or previous seqments) are lost (probability of such event
         * is p^(N+1), where p is probability to lose single packet and
         * time to detect the loss is about RTO*(2^N - 1) with exponential
         * backoff). Normal timewait length is calculated so, that we
         * waited at least for one retransmitted FIN (maximal RTO is 120sec).
         * [ BTW Linux. following BSD, violates this requirement waiting
         *   only for 60sec, we should wait at least for 240 secs.
         *   Well, 240 consumes too much of resources 8)
         * ]
         * This interval is not reduced to catch old duplicate and
         * responces to our wandering segments living for two MSLs.
         * However, if we use PAWS to detect
         * old duplicates, we can reduce the interval to bounds required
         * by RTO, rather than MSL. So, if peer understands PAWS, we
         * kill tw bucket after 3.5*RTO (it is important that this number
         * is greater than TS tick!) and detect old duplicates with help
         * of PAWS.
         */

        tw->tw_kill = timeo <= 4*HZ;
        if (!rearm) {
                BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
                atomic_inc(&tw->tw_dr->tw_count);
        } else {
                mod_timer_pending(&tw->tw_timer, jiffies + timeo);
        }
}
EXPORT_SYMBOL_GPL(__inet_twsk_schedule);

void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family)
{
        struct inet_timewait_sock *tw;
        struct sock *sk;
        struct hlist_nulls_node *node;
        unsigned int slot;

        for (slot = 0; slot <= hashinfo->ehash_mask; slot++) {
                struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
restart_rcu:
                cond_resched();
                rcu_read_lock();
restart:
                sk_nulls_for_each_rcu(sk, node, &head->chain) {
                        if (sk->sk_state != TCP_TIME_WAIT)
                                continue;
                        tw = inet_twsk(sk);
                        if ((tw->tw_family != family) ||
                                refcount_read(&twsk_net(tw)->ns.count))
                                continue;

                        if (unlikely(!refcount_inc_not_zero(&tw->tw_refcnt)))
                                continue;

                        if (unlikely((tw->tw_family != family) ||
                                     refcount_read(&twsk_net(tw)->ns.count))) {
                                inet_twsk_put(tw);
                                goto restart;
                        }

                        rcu_read_unlock();
                        local_bh_disable();
                        inet_twsk_deschedule_put(tw);
                        local_bh_enable();
                        goto restart_rcu;
                }
                /* 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 restart;
                rcu_read_unlock();
        }
}
EXPORT_SYMBOL_GPL(inet_twsk_purge);