// 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.
 *
 *              Support for INET connection oriented protocols.
 *
 * Authors:     See the TCP sources
 */

#include <linux/module.h>
#include <linux/jhash.h>

#include <net/inet_connection_sock.h>
#include <net/inet_hashtables.h>
#include <net/inet_timewait_sock.h>
#include <net/ip.h>
#include <net/route.h>
#include <net/tcp_states.h>
#include <net/xfrm.h>
#include <net/tcp.h>
#include <net/sock_reuseport.h>
#include <net/addrconf.h>

#if IS_ENABLED(CONFIG_IPV6)
/* match_sk*_wildcard == true:  IPV6_ADDR_ANY equals to any IPv6 addresses
 *                              if IPv6 only, and any IPv4 addresses
 *                              if not IPv6 only
 * match_sk*_wildcard == false: addresses must be exactly the same, i.e.
 *                              IPV6_ADDR_ANY only equals to IPV6_ADDR_ANY,
 *                              and 0.0.0.0 equals to 0.0.0.0 only
 */
static bool ipv6_rcv_saddr_equal(const struct in6_addr *sk1_rcv_saddr6,
                                 const struct in6_addr *sk2_rcv_saddr6,
                                 __be32 sk1_rcv_saddr, __be32 sk2_rcv_saddr,
                                 bool sk1_ipv6only, bool sk2_ipv6only,
                                 bool match_sk1_wildcard,
                                 bool match_sk2_wildcard)
{
        int addr_type = ipv6_addr_type(sk1_rcv_saddr6);
        int addr_type2 = sk2_rcv_saddr6 ? ipv6_addr_type(sk2_rcv_saddr6) : IPV6_ADDR_MAPPED;

        /* if both are mapped, treat as IPv4 */
        if (addr_type == IPV6_ADDR_MAPPED && addr_type2 == IPV6_ADDR_MAPPED) {
                if (!sk2_ipv6only) {
                        if (sk1_rcv_saddr == sk2_rcv_saddr)
                                return true;
                        return (match_sk1_wildcard && !sk1_rcv_saddr) ||
                                (match_sk2_wildcard && !sk2_rcv_saddr);
                }
                return false;
        }

        if (addr_type == IPV6_ADDR_ANY && addr_type2 == IPV6_ADDR_ANY)
                return true;

        if (addr_type2 == IPV6_ADDR_ANY && match_sk2_wildcard &&
            !(sk2_ipv6only && addr_type == IPV6_ADDR_MAPPED))
                return true;

        if (addr_type == IPV6_ADDR_ANY && match_sk1_wildcard &&
            !(sk1_ipv6only && addr_type2 == IPV6_ADDR_MAPPED))
                return true;

        if (sk2_rcv_saddr6 &&
            ipv6_addr_equal(sk1_rcv_saddr6, sk2_rcv_saddr6))
                return true;

        return false;
}
#endif

/* match_sk*_wildcard == true:  0.0.0.0 equals to any IPv4 addresses
 * match_sk*_wildcard == false: addresses must be exactly the same, i.e.
 *                              0.0.0.0 only equals to 0.0.0.0
 */
static bool ipv4_rcv_saddr_equal(__be32 sk1_rcv_saddr, __be32 sk2_rcv_saddr,
                                 bool sk2_ipv6only, bool match_sk1_wildcard,
                                 bool match_sk2_wildcard)
{
        if (!sk2_ipv6only) {
                if (sk1_rcv_saddr == sk2_rcv_saddr)
                        return true;
                return (match_sk1_wildcard && !sk1_rcv_saddr) ||
                        (match_sk2_wildcard && !sk2_rcv_saddr);
        }
        return false;
}

bool inet_rcv_saddr_equal(const struct sock *sk, const struct sock *sk2,
                          bool match_wildcard)
{
#if IS_ENABLED(CONFIG_IPV6)
        if (sk->sk_family == AF_INET6)
                return ipv6_rcv_saddr_equal(&sk->sk_v6_rcv_saddr,
                                            inet6_rcv_saddr(sk2),
                                            sk->sk_rcv_saddr,
                                            sk2->sk_rcv_saddr,
                                            ipv6_only_sock(sk),
                                            ipv6_only_sock(sk2),
                                            match_wildcard,
                                            match_wildcard);
#endif
        return ipv4_rcv_saddr_equal(sk->sk_rcv_saddr, sk2->sk_rcv_saddr,
                                    ipv6_only_sock(sk2), match_wildcard,
                                    match_wildcard);
}
EXPORT_SYMBOL(inet_rcv_saddr_equal);

bool inet_rcv_saddr_any(const struct sock *sk)
{
#if IS_ENABLED(CONFIG_IPV6)
        if (sk->sk_family == AF_INET6)
                return ipv6_addr_any(&sk->sk_v6_rcv_saddr);
#endif
        return !sk->sk_rcv_saddr;
}

void inet_get_local_port_range(struct net *net, int *low, int *high)
{
        unsigned int seq;

        do {
                seq = read_seqbegin(&net->ipv4.ip_local_ports.lock);

                *low = net->ipv4.ip_local_ports.range[0];
                *high = net->ipv4.ip_local_ports.range[1];
        } while (read_seqretry(&net->ipv4.ip_local_ports.lock, seq));
}
EXPORT_SYMBOL(inet_get_local_port_range);

static int inet_csk_bind_conflict(const struct sock *sk,
                                  const struct inet_bind_bucket *tb,
                                  bool relax, bool reuseport_ok)
{
        struct sock *sk2;
        bool reuseport_cb_ok;
        bool reuse = sk->sk_reuse;
        bool reuseport = !!sk->sk_reuseport;
        struct sock_reuseport *reuseport_cb;
        kuid_t uid = sock_i_uid((struct sock *)sk);

        rcu_read_lock();
        reuseport_cb = rcu_dereference(sk->sk_reuseport_cb);
        /* paired with WRITE_ONCE() in __reuseport_(add|detach)_closed_sock */
        reuseport_cb_ok = !reuseport_cb || READ_ONCE(reuseport_cb->num_closed_socks);
        rcu_read_unlock();

        /*
         * Unlike other sk lookup places we do not check
         * for sk_net here, since _all_ the socks listed
         * in tb->owners list belong to the same net - the
         * one this bucket belongs to.
         */

        sk_for_each_bound(sk2, &tb->owners) {
                if (sk != sk2 &&
                    (!sk->sk_bound_dev_if ||
                     !sk2->sk_bound_dev_if ||
                     sk->sk_bound_dev_if == sk2->sk_bound_dev_if)) {
                        if (reuse && sk2->sk_reuse &&
                            sk2->sk_state != TCP_LISTEN) {
                                if ((!relax ||
                                     (!reuseport_ok &&
                                      reuseport && sk2->sk_reuseport &&
                                      reuseport_cb_ok &&
                                      (sk2->sk_state == TCP_TIME_WAIT ||
                                       uid_eq(uid, sock_i_uid(sk2))))) &&
                                    inet_rcv_saddr_equal(sk, sk2, true))
                                        break;
                        } else if (!reuseport_ok ||
                                   !reuseport || !sk2->sk_reuseport ||
                                   !reuseport_cb_ok ||
                                   (sk2->sk_state != TCP_TIME_WAIT &&
                                    !uid_eq(uid, sock_i_uid(sk2)))) {
                                if (inet_rcv_saddr_equal(sk, sk2, true))
                                        break;
                        }
                }
        }
        return sk2 != NULL;
}

/*
 * Find an open port number for the socket.  Returns with the
 * inet_bind_hashbucket lock held.
 */
static struct inet_bind_hashbucket *
inet_csk_find_open_port(struct sock *sk, struct inet_bind_bucket **tb_ret, int *port_ret)
{
        struct inet_hashinfo *hinfo = sk->sk_prot->h.hashinfo;
        int port = 0;
        struct inet_bind_hashbucket *head;
        struct net *net = sock_net(sk);
        bool relax = false;
        int i, low, high, attempt_half;
        struct inet_bind_bucket *tb;
        u32 remaining, offset;
        int l3mdev;

        l3mdev = inet_sk_bound_l3mdev(sk);
ports_exhausted:
        attempt_half = (sk->sk_reuse == SK_CAN_REUSE) ? 1 : 0;
other_half_scan:
        inet_get_local_port_range(net, &low, &high);
        high++; /* [32768, 60999] -> [32768, 61000[ */
        if (high - low < 4)
                attempt_half = 0;
        if (attempt_half) {
                int half = low + (((high - low) >> 2) << 1);

                if (attempt_half == 1)
                        high = half;
                else
                        low = half;
        }
        remaining = high - low;
        if (likely(remaining > 1))
                remaining &= ~1U;

        offset = prandom_u32() % remaining;
        /* __inet_hash_connect() favors ports having @low parity
         * We do the opposite to not pollute connect() users.
         */
        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);
                inet_bind_bucket_for_each(tb, &head->chain)
                        if (net_eq(ib_net(tb), net) && tb->l3mdev == l3mdev &&
                            tb->port == port) {
                                if (!inet_csk_bind_conflict(sk, tb, relax, false))
                                        goto success;
                                goto next_port;
                        }
                tb = NULL;
                goto success;
next_port:
                spin_unlock_bh(&head->lock);
                cond_resched();
        }

        offset--;
        if (!(offset & 1))
                goto other_parity_scan;

        if (attempt_half == 1) {
                /* OK we now try the upper half of the range */
                attempt_half = 2;
                goto other_half_scan;
        }

        if (net->ipv4.sysctl_ip_autobind_reuse && !relax) {
                /* We still have a chance to connect to different destinations */
                relax = true;
                goto ports_exhausted;
        }
        return NULL;
success:
        *port_ret = port;
        *tb_ret = tb;
        return head;
}

static inline int sk_reuseport_match(struct inet_bind_bucket *tb,
                                     struct sock *sk)
{
        kuid_t uid = sock_i_uid(sk);

        if (tb->fastreuseport <= 0)
                return 0;
        if (!sk->sk_reuseport)
                return 0;
        if (rcu_access_pointer(sk->sk_reuseport_cb))
                return 0;
        if (!uid_eq(tb->fastuid, uid))
                return 0;
        /* We only need to check the rcv_saddr if this tb was once marked
         * without fastreuseport and then was reset, as we can only know that
         * the fast_*rcv_saddr doesn't have any conflicts with the socks on the
         * owners list.
         */
        if (tb->fastreuseport == FASTREUSEPORT_ANY)
                return 1;
#if IS_ENABLED(CONFIG_IPV6)
        if (tb->fast_sk_family == AF_INET6)
                return ipv6_rcv_saddr_equal(&tb->fast_v6_rcv_saddr,
                                            inet6_rcv_saddr(sk),
                                            tb->fast_rcv_saddr,
                                            sk->sk_rcv_saddr,
                                            tb->fast_ipv6_only,
                                            ipv6_only_sock(sk), true, false);
#endif
        return ipv4_rcv_saddr_equal(tb->fast_rcv_saddr, sk->sk_rcv_saddr,
                                    ipv6_only_sock(sk), true, false);
}

void inet_csk_update_fastreuse(struct inet_bind_bucket *tb,
                               struct sock *sk)
{
        kuid_t uid = sock_i_uid(sk);
        bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;

        if (hlist_empty(&tb->owners)) {
                tb->fastreuse = reuse;
                if (sk->sk_reuseport) {
                        tb->fastreuseport = FASTREUSEPORT_ANY;
                        tb->fastuid = uid;
                        tb->fast_rcv_saddr = sk->sk_rcv_saddr;
                        tb->fast_ipv6_only = ipv6_only_sock(sk);
                        tb->fast_sk_family = sk->sk_family;
#if IS_ENABLED(CONFIG_IPV6)
                        tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
#endif
                } else {
                        tb->fastreuseport = 0;
                }
        } else {
                if (!reuse)
                        tb->fastreuse = 0;
                if (sk->sk_reuseport) {
                        /* We didn't match or we don't have fastreuseport set on
                         * the tb, but we have sk_reuseport set on this socket
                         * and we know that there are no bind conflicts with
                         * this socket in this tb, so reset our tb's reuseport
                         * settings so that any subsequent sockets that match
                         * our current socket will be put on the fast path.
                         *
                         * If we reset we need to set FASTREUSEPORT_STRICT so we
                         * do extra checking for all subsequent sk_reuseport
                         * socks.
                         */
                        if (!sk_reuseport_match(tb, sk)) {
                                tb->fastreuseport = FASTREUSEPORT_STRICT;
                                tb->fastuid = uid;
                                tb->fast_rcv_saddr = sk->sk_rcv_saddr;
                                tb->fast_ipv6_only = ipv6_only_sock(sk);
                                tb->fast_sk_family = sk->sk_family;
#if IS_ENABLED(CONFIG_IPV6)
                                tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
#endif
                        }
                } else {
                        tb->fastreuseport = 0;
                }
        }
}

/* Obtain a reference to a local port for the given sock,
 * if snum is zero it means select any available local port.
 * We try to allocate an odd port (and leave even ports for connect())
 */
int inet_csk_get_port(struct sock *sk, unsigned short snum)
{
        bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;
        struct inet_hashinfo *hinfo = sk->sk_prot->h.hashinfo;
        int ret = 1, port = snum;
        struct inet_bind_hashbucket *head;
        struct net *net = sock_net(sk);
        struct inet_bind_bucket *tb = NULL;
        int l3mdev;

        l3mdev = inet_sk_bound_l3mdev(sk);

        if (!port) {
                head = inet_csk_find_open_port(sk, &tb, &port);
                if (!head)
                        return ret;
                if (!tb)
                        goto tb_not_found;
                goto success;
        }
        head = &hinfo->bhash[inet_bhashfn(net, port,
                                          hinfo->bhash_size)];
        spin_lock_bh(&head->lock);
        inet_bind_bucket_for_each(tb, &head->chain)
                if (net_eq(ib_net(tb), net) && tb->l3mdev == l3mdev &&
                    tb->port == port)
                        goto tb_found;
tb_not_found:
        tb = inet_bind_bucket_create(hinfo->bind_bucket_cachep,
                                     net, head, port, l3mdev);
        if (!tb)
                goto fail_unlock;
tb_found:
        if (!hlist_empty(&tb->owners)) {
                if (sk->sk_reuse == SK_FORCE_REUSE)
                        goto success;

                if ((tb->fastreuse > 0 && reuse) ||
                    sk_reuseport_match(tb, sk))
                        goto success;
                if (inet_csk_bind_conflict(sk, tb, true, true))
                        goto fail_unlock;
        }
success:
        inet_csk_update_fastreuse(tb, sk);

        if (!inet_csk(sk)->icsk_bind_hash)
                inet_bind_hash(sk, tb, port);
        WARN_ON(inet_csk(sk)->icsk_bind_hash != tb);
        ret = 0;

fail_unlock:
        spin_unlock_bh(&head->lock);
        return ret;
}
EXPORT_SYMBOL_GPL(inet_csk_get_port);

/*
 * Wait for an incoming connection, avoid race conditions. This must be called
 * with the socket locked.
 */
static int inet_csk_wait_for_connect(struct sock *sk, long timeo)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        DEFINE_WAIT(wait);
        int err;

        /*
         * True wake-one mechanism for incoming connections: only
         * one process gets woken up, not the 'whole herd'.
         * Since we do not 'race & poll' for established sockets
         * anymore, the common case will execute the loop only once.
         *
         * Subtle issue: "add_wait_queue_exclusive()" will be added
         * after any current non-exclusive waiters, and we know that
         * it will always _stay_ after any new non-exclusive waiters
         * because all non-exclusive waiters are added at the
         * beginning of the wait-queue. As such, it's ok to "drop"
         * our exclusiveness temporarily when we get woken up without
         * having to remove and re-insert us on the wait queue.
         */
        for (;;) {
                prepare_to_wait_exclusive(sk_sleep(sk), &wait,
                                          TASK_INTERRUPTIBLE);
                release_sock(sk);
                if (reqsk_queue_empty(&icsk->icsk_accept_queue))
                        timeo = schedule_timeout(timeo);
                sched_annotate_sleep();
                lock_sock(sk);
                err = 0;
                if (!reqsk_queue_empty(&icsk->icsk_accept_queue))
                        break;
                err = -EINVAL;
                if (sk->sk_state != TCP_LISTEN)
                        break;
                err = sock_intr_errno(timeo);
                if (signal_pending(current))
                        break;
                err = -EAGAIN;
                if (!timeo)
                        break;
        }
        finish_wait(sk_sleep(sk), &wait);
        return err;
}

/*
 * This will accept the next outstanding connection.
 */
struct sock *inet_csk_accept(struct sock *sk, int flags, int *err, bool kern)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        struct request_sock_queue *queue = &icsk->icsk_accept_queue;
        struct request_sock *req;
        struct sock *newsk;
        int error;

        lock_sock(sk);

        /* We need to make sure that this socket is listening,
         * and that it has something pending.
         */
        error = -EINVAL;
        if (sk->sk_state != TCP_LISTEN)
                goto out_err;

        /* Find already established connection */
        if (reqsk_queue_empty(queue)) {
                long timeo = sock_rcvtimeo(sk, flags & O_NONBLOCK);

                /* If this is a non blocking socket don't sleep */
                error = -EAGAIN;
                if (!timeo)
                        goto out_err;

                error = inet_csk_wait_for_connect(sk, timeo);
                if (error)
                        goto out_err;
        }
        req = reqsk_queue_remove(queue, sk);
        newsk = req->sk;

        if (sk->sk_protocol == IPPROTO_TCP &&
            tcp_rsk(req)->tfo_listener) {
                spin_lock_bh(&queue->fastopenq.lock);
                if (tcp_rsk(req)->tfo_listener) {
                        /* We are still waiting for the final ACK from 3WHS
                         * so can't free req now. Instead, we set req->sk to
                         * NULL to signify that the child socket is taken
                         * so reqsk_fastopen_remove() will free the req
                         * when 3WHS finishes (or is aborted).
                         */
                        req->sk = NULL;
                        req = NULL;
                }
                spin_unlock_bh(&queue->fastopenq.lock);
        }

out:
        release_sock(sk);
        if (newsk && mem_cgroup_sockets_enabled) {
                int amt;

                /* atomically get the memory usage, set and charge the
                 * newsk->sk_memcg.
                 */
                lock_sock(newsk);

                /* The socket has not been accepted yet, no need to look at
                 * newsk->sk_wmem_queued.
                 */
                amt = sk_mem_pages(newsk->sk_forward_alloc +
                                   atomic_read(&newsk->sk_rmem_alloc));
                mem_cgroup_sk_alloc(newsk);
                if (newsk->sk_memcg && amt)
                        mem_cgroup_charge_skmem(newsk->sk_memcg, amt,
                                                GFP_KERNEL | __GFP_NOFAIL);

                release_sock(newsk);
        }
        if (req)
                reqsk_put(req);
        return newsk;
out_err:
        newsk = NULL;
        req = NULL;
        *err = error;
        goto out;
}
EXPORT_SYMBOL(inet_csk_accept);

/*
 * Using different timers for retransmit, delayed acks and probes
 * We may wish use just one timer maintaining a list of expire jiffies
 * to optimize.
 */
void inet_csk_init_xmit_timers(struct sock *sk,
                               void (*retransmit_handler)(struct timer_list *t),
                               void (*delack_handler)(struct timer_list *t),
                               void (*keepalive_handler)(struct timer_list *t))
{
        struct inet_connection_sock *icsk = inet_csk(sk);

        timer_setup(&icsk->icsk_retransmit_timer, retransmit_handler, 0);
        timer_setup(&icsk->icsk_delack_timer, delack_handler, 0);
        timer_setup(&sk->sk_timer, keepalive_handler, 0);
        icsk->icsk_pending = icsk->icsk_ack.pending = 0;
}
EXPORT_SYMBOL(inet_csk_init_xmit_timers);

void inet_csk_clear_xmit_timers(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);

        icsk->icsk_pending = icsk->icsk_ack.pending = 0;

        sk_stop_timer(sk, &icsk->icsk_retransmit_timer);
        sk_stop_timer(sk, &icsk->icsk_delack_timer);
        sk_stop_timer(sk, &sk->sk_timer);
}
EXPORT_SYMBOL(inet_csk_clear_xmit_timers);

void inet_csk_delete_keepalive_timer(struct sock *sk)
{
        sk_stop_timer(sk, &sk->sk_timer);
}
EXPORT_SYMBOL(inet_csk_delete_keepalive_timer);

void inet_csk_reset_keepalive_timer(struct sock *sk, unsigned long len)
{
        sk_reset_timer(sk, &sk->sk_timer, jiffies + len);
}
EXPORT_SYMBOL(inet_csk_reset_keepalive_timer);

struct dst_entry *inet_csk_route_req(const struct sock *sk,
                                     struct flowi4 *fl4,
                                     const struct request_sock *req)
{
        const struct inet_request_sock *ireq = inet_rsk(req);
        struct net *net = read_pnet(&ireq->ireq_net);
        struct ip_options_rcu *opt;
        struct rtable *rt;

        rcu_read_lock();
        opt = rcu_dereference(ireq->ireq_opt);

        flowi4_init_output(fl4, ireq->ir_iif, ireq->ir_mark,
                           RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
                           sk->sk_protocol, inet_sk_flowi_flags(sk),
                           (opt && opt->opt.srr) ? opt->opt.faddr : ireq->ir_rmt_addr,
                           ireq->ir_loc_addr, ireq->ir_rmt_port,
                           htons(ireq->ir_num), sk->sk_uid);
        security_req_classify_flow(req, flowi4_to_flowi_common(fl4));
        rt = ip_route_output_flow(net, fl4, sk);
        if (IS_ERR(rt))
                goto no_route;
        if (opt && opt->opt.is_strictroute && rt->rt_uses_gateway)
                goto route_err;
        rcu_read_unlock();
        return &rt->dst;

route_err:
        ip_rt_put(rt);
no_route:
        rcu_read_unlock();
        __IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
        return NULL;
}
EXPORT_SYMBOL_GPL(inet_csk_route_req);

struct dst_entry *inet_csk_route_child_sock(const struct sock *sk,
                                            struct sock *newsk,
                                            const struct request_sock *req)
{
        const struct inet_request_sock *ireq = inet_rsk(req);
        struct net *net = read_pnet(&ireq->ireq_net);
        struct inet_sock *newinet = inet_sk(newsk);
        struct ip_options_rcu *opt;
        struct flowi4 *fl4;
        struct rtable *rt;

        opt = rcu_dereference(ireq->ireq_opt);
        fl4 = &newinet->cork.fl.u.ip4;

        flowi4_init_output(fl4, ireq->ir_iif, ireq->ir_mark,
                           RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
                           sk->sk_protocol, inet_sk_flowi_flags(sk),
                           (opt && opt->opt.srr) ? opt->opt.faddr : ireq->ir_rmt_addr,
                           ireq->ir_loc_addr, ireq->ir_rmt_port,
                           htons(ireq->ir_num), sk->sk_uid);
        security_req_classify_flow(req, flowi4_to_flowi_common(fl4));
        rt = ip_route_output_flow(net, fl4, sk);
        if (IS_ERR(rt))
                goto no_route;
        if (opt && opt->opt.is_strictroute && rt->rt_uses_gateway)
                goto route_err;
        return &rt->dst;

route_err:
        ip_rt_put(rt);
no_route:
        __IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
        return NULL;
}
EXPORT_SYMBOL_GPL(inet_csk_route_child_sock);

/* Decide when to expire the request and when to resend SYN-ACK */
static void syn_ack_recalc(struct request_sock *req,
                           const int max_syn_ack_retries,
                           const u8 rskq_defer_accept,
                           int *expire, int *resend)
{
        if (!rskq_defer_accept) {
                *expire = req->num_timeout >= max_syn_ack_retries;
                *resend = 1;
                return;
        }
        *expire = req->num_timeout >= max_syn_ack_retries &&
                  (!inet_rsk(req)->acked || req->num_timeout >= rskq_defer_accept);
        /* Do not resend while waiting for data after ACK,
         * start to resend on end of deferring period to give
         * last chance for data or ACK to create established socket.
         */
        *resend = !inet_rsk(req)->acked ||
                  req->num_timeout >= rskq_defer_accept - 1;
}

int inet_rtx_syn_ack(const struct sock *parent, struct request_sock *req)
{
        int err = req->rsk_ops->rtx_syn_ack(parent, req);

        if (!err)
                req->num_retrans++;
        return err;
}
EXPORT_SYMBOL(inet_rtx_syn_ack);

static struct request_sock *inet_reqsk_clone(struct request_sock *req,
                                             struct sock *sk)
{
        struct sock *req_sk, *nreq_sk;
        struct request_sock *nreq;

        nreq = kmem_cache_alloc(req->rsk_ops->slab, GFP_ATOMIC | __GFP_NOWARN);
        if (!nreq) {
                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);

                /* paired with refcount_inc_not_zero() in reuseport_migrate_sock() */
                sock_put(sk);
                return NULL;
        }

        req_sk = req_to_sk(req);
        nreq_sk = req_to_sk(nreq);

        memcpy(nreq_sk, req_sk,
               offsetof(struct sock, sk_dontcopy_begin));
        memcpy(&nreq_sk->sk_dontcopy_end, &req_sk->sk_dontcopy_end,
               req->rsk_ops->obj_size - offsetof(struct sock, sk_dontcopy_end));

        sk_node_init(&nreq_sk->sk_node);
        nreq_sk->sk_tx_queue_mapping = req_sk->sk_tx_queue_mapping;
#ifdef CONFIG_XPS
        nreq_sk->sk_rx_queue_mapping = req_sk->sk_rx_queue_mapping;
#endif
        nreq_sk->sk_incoming_cpu = req_sk->sk_incoming_cpu;

        nreq->rsk_listener = sk;

        /* We need not acquire fastopenq->lock
         * because the child socket is locked in inet_csk_listen_stop().
         */
        if (sk->sk_protocol == IPPROTO_TCP && tcp_rsk(nreq)->tfo_listener)
                rcu_assign_pointer(tcp_sk(nreq->sk)->fastopen_rsk, nreq);

        return nreq;
}

static void reqsk_queue_migrated(struct request_sock_queue *queue,
                                 const struct request_sock *req)
{
        if (req->num_timeout == 0)
                atomic_inc(&queue->young);
        atomic_inc(&queue->qlen);
}

static void reqsk_migrate_reset(struct request_sock *req)
{
        req->saved_syn = NULL;
#if IS_ENABLED(CONFIG_IPV6)
        inet_rsk(req)->ipv6_opt = NULL;
        inet_rsk(req)->pktopts = NULL;
#else
        inet_rsk(req)->ireq_opt = NULL;
#endif
}

/* return true if req was found in the ehash table */
static bool reqsk_queue_unlink(struct request_sock *req)
{
        struct inet_hashinfo *hashinfo = req_to_sk(req)->sk_prot->h.hashinfo;
        bool found = false;

        if (sk_hashed(req_to_sk(req))) {
                spinlock_t *lock = inet_ehash_lockp(hashinfo, req->rsk_hash);

                spin_lock(lock);
                found = __sk_nulls_del_node_init_rcu(req_to_sk(req));
                spin_unlock(lock);
        }
        if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer))
                reqsk_put(req);
        return found;
}

bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req)
{
        bool unlinked = reqsk_queue_unlink(req);

        if (unlinked) {
                reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
                reqsk_put(req);
        }
        return unlinked;
}
EXPORT_SYMBOL(inet_csk_reqsk_queue_drop);

void inet_csk_reqsk_queue_drop_and_put(struct sock *sk, struct request_sock *req)
{
        inet_csk_reqsk_queue_drop(sk, req);
        reqsk_put(req);
}
EXPORT_SYMBOL(inet_csk_reqsk_queue_drop_and_put);

static void reqsk_timer_handler(struct timer_list *t)
{
        struct request_sock *req = from_timer(req, t, rsk_timer);
        struct request_sock *nreq = NULL, *oreq = req;
        struct sock *sk_listener = req->rsk_listener;
        struct inet_connection_sock *icsk;
        struct request_sock_queue *queue;
        struct net *net;
        int max_syn_ack_retries, qlen, expire = 0, resend = 0;

        if (inet_sk_state_load(sk_listener) != TCP_LISTEN) {
                struct sock *nsk;

                nsk = reuseport_migrate_sock(sk_listener, req_to_sk(req), NULL);
                if (!nsk)
                        goto drop;

                nreq = inet_reqsk_clone(req, nsk);
                if (!nreq)
                        goto drop;

                /* The new timer for the cloned req can decrease the 2
                 * by calling inet_csk_reqsk_queue_drop_and_put(), so
                 * hold another count to prevent use-after-free and
                 * call reqsk_put() just before return.
                 */
                refcount_set(&nreq->rsk_refcnt, 2 + 1);
                timer_setup(&nreq->rsk_timer, reqsk_timer_handler, TIMER_PINNED);
                reqsk_queue_migrated(&inet_csk(nsk)->icsk_accept_queue, req);

                req = nreq;
                sk_listener = nsk;
        }

        icsk = inet_csk(sk_listener);
        net = sock_net(sk_listener);
        max_syn_ack_retries = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_synack_retries;
        /* Normally all the openreqs are young and become mature
         * (i.e. converted to established socket) for first timeout.
         * If synack was not acknowledged for 1 second, it means
         * one of the following things: synack was lost, ack was lost,
         * rtt is high or nobody planned to ack (i.e. synflood).
         * When server is a bit loaded, queue is populated with old
         * open requests, reducing effective size of queue.
         * When server is well loaded, queue size reduces to zero
         * after several minutes of work. It is not synflood,
         * it is normal operation. The solution is pruning
         * too old entries overriding normal timeout, when
         * situation becomes dangerous.
         *
         * Essentially, we reserve half of room for young
         * embrions; and abort old ones without pity, if old
         * ones are about to clog our table.
         */
        queue = &icsk->icsk_accept_queue;
        qlen = reqsk_queue_len(queue);
        if ((qlen << 1) > max(8U, READ_ONCE(sk_listener->sk_max_ack_backlog))) {
                int young = reqsk_queue_len_young(queue) << 1;

                while (max_syn_ack_retries > 2) {
                        if (qlen < young)
                                break;
                        max_syn_ack_retries--;
                        young <<= 1;
                }
        }
        syn_ack_recalc(req, max_syn_ack_retries, READ_ONCE(queue->rskq_defer_accept),
                       &expire, &resend);
        req->rsk_ops->syn_ack_timeout(req);
        if (!expire &&
            (!resend ||
             !inet_rtx_syn_ack(sk_listener, req) ||
             inet_rsk(req)->acked)) {
                unsigned long timeo;

                if (req->num_timeout++ == 0)
                        atomic_dec(&queue->young);
                timeo = min(TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
                mod_timer(&req->rsk_timer, jiffies + timeo);

                if (!nreq)
                        return;

                if (!inet_ehash_insert(req_to_sk(nreq), req_to_sk(oreq), NULL)) {
                        /* delete timer */
                        inet_csk_reqsk_queue_drop(sk_listener, nreq);
                        goto no_ownership;
                }

                __NET_INC_STATS(net, LINUX_MIB_TCPMIGRATEREQSUCCESS);
                reqsk_migrate_reset(oreq);
                reqsk_queue_removed(&inet_csk(oreq->rsk_listener)->icsk_accept_queue, oreq);
                reqsk_put(oreq);

                reqsk_put(nreq);
                return;
        }

        /* Even if we can clone the req, we may need not retransmit any more
         * SYN+ACKs (nreq->num_timeout > max_syn_ack_retries, etc), or another
         * CPU may win the "own_req" race so that inet_ehash_insert() fails.
         */
        if (nreq) {
                __NET_INC_STATS(net, LINUX_MIB_TCPMIGRATEREQFAILURE);
no_ownership:
                reqsk_migrate_reset(nreq);
                reqsk_queue_removed(queue, nreq);
                __reqsk_free(nreq);
        }

drop:
        inet_csk_reqsk_queue_drop_and_put(oreq->rsk_listener, oreq);
}

static void reqsk_queue_hash_req(struct request_sock *req,
                                 unsigned long timeout)
{
        timer_setup(&req->rsk_timer, reqsk_timer_handler, TIMER_PINNED);
        mod_timer(&req->rsk_timer, jiffies + timeout);

        inet_ehash_insert(req_to_sk(req), NULL, NULL);
        /* before letting lookups find us, make sure all req fields
         * are committed to memory and refcnt initialized.
         */
        smp_wmb();
        refcount_set(&req->rsk_refcnt, 2 + 1);
}

void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
                                   unsigned long timeout)
{
        reqsk_queue_hash_req(req, timeout);
        inet_csk_reqsk_queue_added(sk);
}
EXPORT_SYMBOL_GPL(inet_csk_reqsk_queue_hash_add);

static void inet_clone_ulp(const struct request_sock *req, struct sock *newsk,
                           const gfp_t priority)
{
        struct inet_connection_sock *icsk = inet_csk(newsk);

        if (!icsk->icsk_ulp_ops)
                return;

        if (icsk->icsk_ulp_ops->clone)
                icsk->icsk_ulp_ops->clone(req, newsk, priority);
}

/**
 *      inet_csk_clone_lock - clone an inet socket, and lock its clone
 *      @sk: the socket to clone
 *      @req: request_sock
 *      @priority: for allocation (%GFP_KERNEL, %GFP_ATOMIC, etc)
 *
 *      Caller must unlock socket even in error path (bh_unlock_sock(newsk))
 */
struct sock *inet_csk_clone_lock(const struct sock *sk,
                                 const struct request_sock *req,
                                 const gfp_t priority)
{
        struct sock *newsk = sk_clone_lock(sk, priority);

        if (newsk) {
                struct inet_connection_sock *newicsk = inet_csk(newsk);

                inet_sk_set_state(newsk, TCP_SYN_RECV);
                newicsk->icsk_bind_hash = NULL;

                inet_sk(newsk)->inet_dport = inet_rsk(req)->ir_rmt_port;
                inet_sk(newsk)->inet_num = inet_rsk(req)->ir_num;
                inet_sk(newsk)->inet_sport = htons(inet_rsk(req)->ir_num);

                /* listeners have SOCK_RCU_FREE, not the children */
                sock_reset_flag(newsk, SOCK_RCU_FREE);

                inet_sk(newsk)->mc_list = NULL;

                newsk->sk_mark = inet_rsk(req)->ir_mark;
                atomic64_set(&newsk->sk_cookie,
                             atomic64_read(&inet_rsk(req)->ir_cookie));

                newicsk->icsk_retransmits = 0;
                newicsk->icsk_backoff     = 0;
                newicsk->icsk_probes_out  = 0;
                newicsk->icsk_probes_tstamp = 0;

                /* Deinitialize accept_queue to trap illegal accesses. */
                memset(&newicsk->icsk_accept_queue, 0, sizeof(newicsk->icsk_accept_queue));

                inet_clone_ulp(req, newsk, priority);

                security_inet_csk_clone(newsk, req);
        }
        return newsk;
}
EXPORT_SYMBOL_GPL(inet_csk_clone_lock);

/*
 * At this point, there should be no process reference to this
 * socket, and thus no user references at all.  Therefore we
 * can assume the socket waitqueue is inactive and nobody will
 * try to jump onto it.
 */
void inet_csk_destroy_sock(struct sock *sk)
{

        WARN_ON(sk->sk_state != TCP_CLOSE);
        WARN_ON(!sock_flag(sk, SOCK_DEAD));

        /* It cannot be in hash table! */
        WARN_ON(!sk_unhashed(sk));

        /* If it has not 0 inet_sk(sk)->inet_num, it must be bound */
        WARN_ON(inet_sk(sk)->inet_num && !inet_csk(sk)->icsk_bind_hash);

        sk->sk_prot->destroy(sk);

        sk_stream_kill_queues(sk);

        xfrm_sk_free_policy(sk);

        sk_refcnt_debug_release(sk);

        percpu_counter_dec(sk->sk_prot->orphan_count);

        sock_put(sk);
}
EXPORT_SYMBOL(inet_csk_destroy_sock);

/* This function allows to force a closure of a socket after the call to
 * tcp/dccp_create_openreq_child().
 */
void inet_csk_prepare_forced_close(struct sock *sk)
        __releases(&sk->sk_lock.slock)
{
        /* sk_clone_lock locked the socket and set refcnt to 2 */
        bh_unlock_sock(sk);
        sock_put(sk);
        inet_csk_prepare_for_destroy_sock(sk);
        inet_sk(sk)->inet_num = 0;
}
EXPORT_SYMBOL(inet_csk_prepare_forced_close);

int inet_csk_listen_start(struct sock *sk, int backlog)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        struct inet_sock *inet = inet_sk(sk);
        int err = -EADDRINUSE;

        reqsk_queue_alloc(&icsk->icsk_accept_queue);

        sk->sk_ack_backlog = 0;
        inet_csk_delack_init(sk);

        /* There is race window here: we announce ourselves listening,
         * but this transition is still not validated by get_port().
         * It is OK, because this socket enters to hash table only
         * after validation is complete.
         */
        inet_sk_state_store(sk, TCP_LISTEN);
        if (!sk->sk_prot->get_port(sk, inet->inet_num)) {
                inet->inet_sport = htons(inet->inet_num);

                sk_dst_reset(sk);
                err = sk->sk_prot->hash(sk);

                if (likely(!err))
                        return 0;
        }

        inet_sk_set_state(sk, TCP_CLOSE);
        return err;
}
EXPORT_SYMBOL_GPL(inet_csk_listen_start);

static void inet_child_forget(struct sock *sk, struct request_sock *req,
                              struct sock *child)
{
        sk->sk_prot->disconnect(child, O_NONBLOCK);

        sock_orphan(child);

        percpu_counter_inc(sk->sk_prot->orphan_count);

        if (sk->sk_protocol == IPPROTO_TCP && tcp_rsk(req)->tfo_listener) {
                BUG_ON(rcu_access_pointer(tcp_sk(child)->fastopen_rsk) != req);
                BUG_ON(sk != req->rsk_listener);

                /* Paranoid, to prevent race condition if
                 * an inbound pkt destined for child is
                 * blocked by sock lock in tcp_v4_rcv().
                 * Also to satisfy an assertion in
                 * tcp_v4_destroy_sock().
                 */
                RCU_INIT_POINTER(tcp_sk(child)->fastopen_rsk, NULL);
        }
        inet_csk_destroy_sock(child);
}

struct sock *inet_csk_reqsk_queue_add(struct sock *sk,
                                      struct request_sock *req,
                                      struct sock *child)
{
        struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;

        spin_lock(&queue->rskq_lock);
        if (unlikely(sk->sk_state != TCP_LISTEN)) {
                inet_child_forget(sk, req, child);
                child = NULL;
        } else {
                req->sk = child;
                req->dl_next = NULL;
                if (queue->rskq_accept_head == NULL)
                        WRITE_ONCE(queue->rskq_accept_head, req);
                else
                        queue->rskq_accept_tail->dl_next = req;
                queue->rskq_accept_tail = req;
                sk_acceptq_added(sk);
        }
        spin_unlock(&queue->rskq_lock);
        return child;
}
EXPORT_SYMBOL(inet_csk_reqsk_queue_add);

struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child,
                                         struct request_sock *req, bool own_req)
{
        if (own_req) {
                inet_csk_reqsk_queue_drop(req->rsk_listener, req);
                reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req);

                if (sk != req->rsk_listener) {
                        /* another listening sk has been selected,
                         * migrate the req to it.
                         */
                        struct request_sock *nreq;

                        /* hold a refcnt for the nreq->rsk_listener
                         * which is assigned in inet_reqsk_clone()
                         */
                        sock_hold(sk);
                        nreq = inet_reqsk_clone(req, sk);
                        if (!nreq) {
                                inet_child_forget(sk, req, child);
                                goto child_put;
                        }

                        refcount_set(&nreq->rsk_refcnt, 1);
                        if (inet_csk_reqsk_queue_add(sk, nreq, child)) {
                                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQSUCCESS);
                                reqsk_migrate_reset(req);
                                reqsk_put(req);
                                return child;
                        }

                        __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
                        reqsk_migrate_reset(nreq);
                        __reqsk_free(nreq);
                } else if (inet_csk_reqsk_queue_add(sk, req, child)) {
                        return child;
                }
        }
        /* Too bad, another child took ownership of the request, undo. */
child_put:
        bh_unlock_sock(child);
        sock_put(child);
        return NULL;
}
EXPORT_SYMBOL(inet_csk_complete_hashdance);

/*
 *      This routine closes sockets which have been at least partially
 *      opened, but not yet accepted.
 */
void inet_csk_listen_stop(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        struct request_sock_queue *queue = &icsk->icsk_accept_queue;
        struct request_sock *next, *req;

        /* Following specs, it would be better either to send FIN
         * (and enter FIN-WAIT-1, it is normal close)
         * or to send active reset (abort).
         * Certainly, it is pretty dangerous while synflood, but it is
         * bad justification for our negligence 8)
         * To be honest, we are not able to make either
         * of the variants now.                 --ANK
         */
        while ((req = reqsk_queue_remove(queue, sk)) != NULL) {
                struct sock *child = req->sk, *nsk;
                struct request_sock *nreq;

                local_bh_disable();
                bh_lock_sock(child);
                WARN_ON(sock_owned_by_user(child));
                sock_hold(child);

                nsk = reuseport_migrate_sock(sk, child, NULL);
                if (nsk) {
                        nreq = inet_reqsk_clone(req, nsk);
                        if (nreq) {
                                refcount_set(&nreq->rsk_refcnt, 1);

                                if (inet_csk_reqsk_queue_add(nsk, nreq, child)) {
                                        __NET_INC_STATS(sock_net(nsk),
                                                        LINUX_MIB_TCPMIGRATEREQSUCCESS);
                                        reqsk_migrate_reset(req);
                                } else {
                                        __NET_INC_STATS(sock_net(nsk),
                                                        LINUX_MIB_TCPMIGRATEREQFAILURE);
                                        reqsk_migrate_reset(nreq);
                                        __reqsk_free(nreq);
                                }

                                /* inet_csk_reqsk_queue_add() has already
                                 * called inet_child_forget() on failure case.
                                 */
                                goto skip_child_forget;
                        }
                }

                inet_child_forget(sk, req, child);
skip_child_forget:
                reqsk_put(req);
                bh_unlock_sock(child);
                local_bh_enable();
                sock_put(child);

                cond_resched();
        }
        if (queue->fastopenq.rskq_rst_head) {
                /* Free all the reqs queued in rskq_rst_head. */
                spin_lock_bh(&queue->fastopenq.lock);
                req = queue->fastopenq.rskq_rst_head;
                queue->fastopenq.rskq_rst_head = NULL;
                spin_unlock_bh(&queue->fastopenq.lock);
                while (req != NULL) {
                        next = req->dl_next;
                        reqsk_put(req);
                        req = next;
                }
        }
        WARN_ON_ONCE(sk->sk_ack_backlog);
}
EXPORT_SYMBOL_GPL(inet_csk_listen_stop);

void inet_csk_addr2sockaddr(struct sock *sk, struct sockaddr *uaddr)
{
        struct sockaddr_in *sin = (struct sockaddr_in *)uaddr;
        const struct inet_sock *inet = inet_sk(sk);

        sin->sin_family         = AF_INET;
        sin->sin_addr.s_addr    = inet->inet_daddr;
        sin->sin_port           = inet->inet_dport;
}
EXPORT_SYMBOL_GPL(inet_csk_addr2sockaddr);

static struct dst_entry *inet_csk_rebuild_route(struct sock *sk, struct flowi *fl)
{
        const struct inet_sock *inet = inet_sk(sk);
        const struct ip_options_rcu *inet_opt;
        __be32 daddr = inet->inet_daddr;
        struct flowi4 *fl4;
        struct rtable *rt;

        rcu_read_lock();
        inet_opt = rcu_dereference(inet->inet_opt);
        if (inet_opt && inet_opt->opt.srr)
                daddr = inet_opt->opt.faddr;
        fl4 = &fl->u.ip4;
        rt = ip_route_output_ports(sock_net(sk), fl4, sk, daddr,
                                   inet->inet_saddr, inet->inet_dport,
                                   inet->inet_sport, sk->sk_protocol,
                                   RT_CONN_FLAGS(sk), sk->sk_bound_dev_if);
        if (IS_ERR(rt))
                rt = NULL;
        if (rt)
                sk_setup_caps(sk, &rt->dst);
        rcu_read_unlock();

        return &rt->dst;
}

struct dst_entry *inet_csk_update_pmtu(struct sock *sk, u32 mtu)
{
        struct dst_entry *dst = __sk_dst_check(sk, 0);
        struct inet_sock *inet = inet_sk(sk);

        if (!dst) {
                dst = inet_csk_rebuild_route(sk, &inet->cork.fl);
                if (!dst)
                        goto out;
        }
        dst->ops->update_pmtu(dst, sk, NULL, mtu, true);

        dst = __sk_dst_check(sk, 0);
        if (!dst)
                dst = inet_csk_rebuild_route(sk, &inet->cork.fl);
out:
        return dst;
}
EXPORT_SYMBOL_GPL(inet_csk_update_pmtu);