// 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>
#include <net/tcp.h>
#include <net/psp.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_bind2_bucket *tb2 = tw->tw_tb2;
        struct inet_bind_bucket *tb = tw->tw_tb;

        if (!tb)
                return;

        __sk_del_bind_node((struct sock *)tw);
        tw->tw_tb = NULL;
        tw->tw_tb2 = NULL;
        inet_bind2_bucket_destroy(hashinfo->bind2_bucket_cachep, tb2);
        inet_bind_bucket_destroy(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, *bhead2;

        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)];
        bhead2 = inet_bhashfn_portaddr(hashinfo, (struct sock *)tw,
                                       twsk_net(tw), tw->tw_num);

        spin_lock(&bhead->lock);
        spin_lock(&bhead2->lock);
        inet_twsk_bind_unhash(tw, hashinfo);
        spin_unlock(&bhead2->lock);
        spin_unlock(&bhead->lock);

        refcount_dec(&tw->tw_dr->tw_refcount);
        inet_twsk_put(tw);
}

void inet_twsk_free(struct inet_timewait_sock *tw)
{
        struct module *owner = tw->tw_prot->owner;

        tcp_twsk_destructor((struct sock *)tw);
        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_schedule(struct inet_timewait_sock *tw, int timeo)
{
        __inet_twsk_schedule(tw, timeo, false);
}

/*
 * Enter the time wait state.
 * Essentially we whip up a timewait bucket, copy the relevant info into it
 * from the SK, and mess with hash chains and list linkage.
 *
 * The caller must not access @tw anymore after this function returns.
 */
void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw,
                                  struct sock *sk,
                                  struct inet_hashinfo *hashinfo,
                                  int timeo)
{
        const struct inet_sock *inet = inet_sk(sk);
        const struct inet_connection_sock *icsk = inet_csk(sk);
        spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
        struct inet_bind_hashbucket *bhead, *bhead2;

        /* 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)];
        bhead2 = inet_bhashfn_portaddr(hashinfo, sk, twsk_net(tw), inet->inet_num);

        local_bh_disable();
        spin_lock(&bhead->lock);
        spin_lock(&bhead2->lock);

        tw->tw_tb = icsk->icsk_bind_hash;
        WARN_ON(!icsk->icsk_bind_hash);

        tw->tw_tb2 = icsk->icsk_bind2_hash;
        WARN_ON(!icsk->icsk_bind2_hash);
        sk_add_bind_node((struct sock *)tw, &tw->tw_tb2->owners);

        spin_unlock(&bhead2->lock);
        spin_unlock(&bhead->lock);

        spin_lock(lock);

        /* tw_refcnt is set to 3 because we have :
         * - one reference for bhash chain.
         * - one reference for ehash chain.
         * - one reference for timer.
         * 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);

        /* Ensure tw_refcnt has been set before tw is published.
         * smp_wmb() provides the necessary memory barrier to enforce this
         * ordering.
         */
        smp_wmb();

        hlist_nulls_replace_init_rcu(&sk->sk_nulls_node, &tw->tw_node);
        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);

        inet_twsk_schedule(tw, timeo);

        spin_unlock(lock);
        local_bh_enable();
}

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

        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 (refcount_read(&dr->tw_refcount) - 1 >=
            READ_ONCE(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_test_bit(TRANSPARENT, sk);
                tw->tw_connect_bind = !!(sk->sk_userlocks & SOCK_CONNECT_BIND);
                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, 0);
#ifdef CONFIG_SOCK_VALIDATE_XMIT
                tw->tw_validate_xmit_skb = NULL;
#endif
                /*
                 * 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);
                psp_twsk_init(tw, sk);
        }

        return tw;
}

/* 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)
{
        struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
        spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);

        /* inet_twsk_purge() walks over all sockets, including tw ones,
         * and removes them via inet_twsk_deschedule_put() after a
         * refcount_inc_not_zero().
         *
         * inet_twsk_hashdance_schedule() must (re)init the refcount before
         * arming the timer, i.e. inet_twsk_purge can obtain a reference to
         * a twsk that did not yet schedule the timer.
         *
         * The ehash lock synchronizes these two:
         * After acquiring the lock, the timer is always scheduled (else
         * timer_shutdown returns false), because hashdance_schedule releases
         * the ehash lock only after completing the timer initialization.
         *
         * Without grabbing the ehash lock, we get:
         * 1) cpu x sets twsk refcount to 3
         * 2) cpu y bumps refcount to 4
         * 3) cpu y calls inet_twsk_deschedule_put() and shuts timer down
         * 4) cpu x tries to start timer, but mod_timer is a noop post-shutdown
         * -> timer refcount is never decremented.
         */
        spin_lock(lock);
        /*  Makes sure hashdance_schedule() has completed */
        spin_unlock(lock);

        if (timer_shutdown_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.
         */

        if (!rearm) {
                bool kill = timeo <= 4*HZ;

                __NET_INC_STATS(twsk_net(tw), kill ? LINUX_MIB_TIMEWAITKILLED :
                                                     LINUX_MIB_TIMEWAITED);
                BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
                refcount_inc(&tw->tw_dr->tw_refcount);
        } else {
                mod_timer_pending(&tw->tw_timer, jiffies + timeo);
        }
}

/* Remove all non full sockets (TIME_WAIT and NEW_SYN_RECV) for dead netns */
void inet_twsk_purge(struct inet_hashinfo *hashinfo)
{
        struct inet_ehash_bucket *head = &hashinfo->ehash[0];
        unsigned int ehash_mask = hashinfo->ehash_mask;
        struct hlist_nulls_node *node;
        unsigned int slot;
        struct sock *sk;

        for (slot = 0; slot <= ehash_mask; slot++, head++) {
                if (hlist_nulls_empty(&head->chain))
                        continue;

restart_rcu:
                cond_resched();
                rcu_read_lock();
restart:
                sk_nulls_for_each_rcu(sk, node, &head->chain) {
                        int state = inet_sk_state_load(sk);

                        if ((1 << state) & ~(TCPF_TIME_WAIT |
                                             TCPF_NEW_SYN_RECV))
                                continue;

                        if (check_net(sock_net(sk)))
                                continue;

                        if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
                                continue;

                        if (check_net(sock_net(sk))) {
                                sock_gen_put(sk);
                                goto restart;
                        }

                        rcu_read_unlock();
                        local_bh_disable();
                        if (state == TCP_TIME_WAIT) {
                                inet_twsk_deschedule_put(inet_twsk(sk));
                        } else {
                                struct request_sock *req = inet_reqsk(sk);

                                inet_csk_reqsk_queue_drop_and_put(req->rsk_listener,
                                                                  req);
                        }
                        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();
        }
}