inet_connection_sock.c

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/*
 * 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
 *
 *      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/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>

#ifdef INET_CSK_DEBUG
const char inet_csk_timer_bug_msg[] = "inet_csk BUG: unknown timer value\n";
EXPORT_SYMBOL(inet_csk_timer_bug_msg);
#endif

/*
 * This struct holds the first and last local port number.
 */
struct local_ports sysctl_local_ports __read_mostly = {
    .lock = __SEQLOCK_UNLOCKED(sysctl_local_ports.lock),
    .range = { 32768, 61000 },
};

unsigned long *sysctl_local_reserved_ports;
EXPORT_SYMBOL(sysctl_local_reserved_ports);

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

    do {
        seq = read_seqbegin(&sysctl_local_ports.lock);

        *low = sysctl_local_ports.range[0];
        *high = sysctl_local_ports.range[1];
    } while (read_seqretry(&sysctl_local_ports.lock, seq));
}
EXPORT_SYMBOL(inet_get_local_port_range);

int inet_csk_bind_conflict(const struct sock *sk,
               const struct inet_bind_bucket *tb, bool relax)
{
    struct sock *sk2;
    struct hlist_node *node;
    int reuse = sk->sk_reuse;

    /*
     * 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, node, &tb->owners) {
        if (sk != sk2 &&
            !inet_v6_ipv6only(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) {
                const __be32 sk2_rcv_saddr = sk_rcv_saddr(sk2);
                if (!sk2_rcv_saddr || !sk_rcv_saddr(sk) ||
                    sk2_rcv_saddr == sk_rcv_saddr(sk))
                    break;
            }
            if (!relax && reuse && sk2->sk_reuse &&
                sk2->sk_state != TCP_LISTEN) {
                const __be32 sk2_rcv_saddr = sk_rcv_saddr(sk2);

                if (!sk2_rcv_saddr || !sk_rcv_saddr(sk) ||
                    sk2_rcv_saddr == sk_rcv_saddr(sk))
                    break;
            }
        }
    }
    return node != NULL;
}
EXPORT_SYMBOL_GPL(inet_csk_bind_conflict);

/* Obtain a reference to a local port for the given sock,
 * if snum is zero it means select any available local port.
 */
int inet_csk_get_port(struct sock *sk, unsigned short snum)
{
    struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
    struct inet_bind_hashbucket *head;
    struct hlist_node *node;
    struct inet_bind_bucket *tb;
    int ret, attempts = 5;
    struct net *net = sock_net(sk);
    int smallest_size = -1, smallest_rover;

    local_bh_disable();
    if (!snum) {
        int remaining, rover, low, high;

again:
        inet_get_local_port_range(&low, &high);
        remaining = (high - low) + 1;
        smallest_rover = rover = net_random() % remaining + low;

        smallest_size = -1;
        do {
            if (inet_is_reserved_local_port(rover))
                goto next_nolock;
            head = &hashinfo->bhash[inet_bhashfn(net, rover,
                    hashinfo->bhash_size)];
            spin_lock(&head->lock);
            inet_bind_bucket_for_each(tb, node, &head->chain)
                if (net_eq(ib_net(tb), net) && tb->port == rover) {
                    if (tb->fastreuse > 0 &&
                        sk->sk_reuse &&
                        sk->sk_state != TCP_LISTEN &&
                        (tb->num_owners < smallest_size || smallest_size == -1)) {
                        smallest_size = tb->num_owners;
                        smallest_rover = rover;
                        if (atomic_read(&hashinfo->bsockets) > (high - low) + 1 &&
                            !inet_csk(sk)->icsk_af_ops->bind_conflict(sk, tb, false)) {
                            snum = smallest_rover;
                            goto tb_found;
                        }
                    }
                    if (!inet_csk(sk)->icsk_af_ops->bind_conflict(sk, tb, false)) {
                        snum = rover;
                        goto tb_found;
                    }
                    goto next;
                }
            break;
        next:
            spin_unlock(&head->lock);
        next_nolock:
            if (++rover > high)
                rover = low;
        } while (--remaining > 0);

        /* Exhausted local port range during search?  It is not
         * possible for us to be holding one of the bind hash
         * locks if this test triggers, because if 'remaining'
         * drops to zero, we broke out of the do/while loop at
         * the top level, not from the 'break;' statement.
         */
        ret = 1;
        if (remaining <= 0) {
            if (smallest_size != -1) {
                snum = smallest_rover;
                goto have_snum;
            }
            goto fail;
        }
        /* OK, here is the one we will use.  HEAD is
         * non-NULL and we hold it's mutex.
         */
        snum = rover;
    } else {
have_snum:
        head = &hashinfo->bhash[inet_bhashfn(net, snum,
                hashinfo->bhash_size)];
        spin_lock(&head->lock);
        inet_bind_bucket_for_each(tb, node, &head->chain)
            if (net_eq(ib_net(tb), net) && tb->port == snum)
                goto tb_found;
    }
    tb = NULL;
    goto tb_not_found;
tb_found:
    if (!hlist_empty(&tb->owners)) {
        if (sk->sk_reuse == SK_FORCE_REUSE)
            goto success;

        if (tb->fastreuse > 0 &&
            sk->sk_reuse && sk->sk_state != TCP_LISTEN &&
            smallest_size == -1) {
            goto success;
        } else {
            ret = 1;
            if (inet_csk(sk)->icsk_af_ops->bind_conflict(sk, tb, true)) {
                if (sk->sk_reuse && sk->sk_state != TCP_LISTEN &&
                    smallest_size != -1 && --attempts >= 0) {
                    spin_unlock(&head->lock);
                    goto again;
                }

                goto fail_unlock;
            }
        }
    }
tb_not_found:
    ret = 1;
    if (!tb && (tb = inet_bind_bucket_create(hashinfo->bind_bucket_cachep,
                    net, head, snum)) == NULL)
        goto fail_unlock;
    if (hlist_empty(&tb->owners)) {
        if (sk->sk_reuse && sk->sk_state != TCP_LISTEN)
            tb->fastreuse = 1;
        else
            tb->fastreuse = 0;
    } else if (tb->fastreuse &&
           (!sk->sk_reuse || sk->sk_state == TCP_LISTEN))
        tb->fastreuse = 0;
success:
    if (!inet_csk(sk)->icsk_bind_hash)
        inet_bind_hash(sk, tb, snum);
    WARN_ON(inet_csk(sk)->icsk_bind_hash != tb);
    ret = 0;

fail_unlock:
    spin_unlock(&head->lock);
fail:
    local_bh_enable();
    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);
        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)
{
    struct inet_connection_sock *icsk = inet_csk(sk);
    struct request_sock_queue *queue = &icsk->icsk_accept_queue;
    struct sock *newsk;
    struct request_sock *req;
    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);
    newsk = req->sk;

    sk_acceptq_removed(sk);
    if (sk->sk_protocol == IPPROTO_TCP && queue->fastopenq != NULL) {
        spin_lock_bh(&queue->fastopenq->lock);
        if (tcp_rsk(req)->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 (req)
        __reqsk_free(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)(unsigned long),
                   void (*delack_handler)(unsigned long),
                   void (*keepalive_handler)(unsigned long))
{
    struct inet_connection_sock *icsk = inet_csk(sk);

    setup_timer(&icsk->icsk_retransmit_timer, retransmit_handler,
            (unsigned long)sk);
    setup_timer(&icsk->icsk_delack_timer, delack_handler,
            (unsigned long)sk);
    setup_timer(&sk->sk_timer, keepalive_handler, (unsigned long)sk);
    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 = icsk->icsk_ack.blocked = 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(struct sock *sk,
                     struct flowi4 *fl4,
                     const struct request_sock *req)
{
    struct rtable *rt;
    const struct inet_request_sock *ireq = inet_rsk(req);
    struct ip_options_rcu *opt = inet_rsk(req)->opt;
    struct net *net = sock_net(sk);
    int flags = inet_sk_flowi_flags(sk);

    flowi4_init_output(fl4, sk->sk_bound_dev_if, sk->sk_mark,
               RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
               sk->sk_protocol,
               flags,
               (opt && opt->opt.srr) ? opt->opt.faddr : ireq->rmt_addr,
               ireq->loc_addr, ireq->rmt_port, inet_sk(sk)->inet_sport);
    security_req_classify_flow(req, flowi4_to_flowi(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_BH(net, IPSTATS_MIB_OUTNOROUTES);
    return NULL;
}
EXPORT_SYMBOL_GPL(inet_csk_route_req);

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

    fl4 = &newinet->cork.fl.u.ip4;

    rcu_read_lock();
    opt = rcu_dereference(newinet->inet_opt);
    flowi4_init_output(fl4, sk->sk_bound_dev_if, sk->sk_mark,
               RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
               sk->sk_protocol, inet_sk_flowi_flags(sk),
               (opt && opt->opt.srr) ? opt->opt.faddr : ireq->rmt_addr,
               ireq->loc_addr, ireq->rmt_port, inet_sk(sk)->inet_sport);
    security_req_classify_flow(req, flowi4_to_flowi(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_BH(net, IPSTATS_MIB_OUTNOROUTES);
    return NULL;
}
EXPORT_SYMBOL_GPL(inet_csk_route_child_sock);

static inline u32 inet_synq_hash(const __be32 raddr, const __be16 rport,
                 const u32 rnd, const u32 synq_hsize)
{
    return jhash_2words((__force u32)raddr, (__force u32)rport, rnd) & (synq_hsize - 1);
}

#if IS_ENABLED(CONFIG_IPV6)
#define AF_INET_FAMILY(fam) ((fam) == AF_INET)
#else
#define AF_INET_FAMILY(fam) 1
#endif

struct request_sock *inet_csk_search_req(const struct sock *sk,
                     struct request_sock ***prevp,
                     const __be16 rport, const __be32 raddr,
                     const __be32 laddr)
{
    const struct inet_connection_sock *icsk = inet_csk(sk);
    struct listen_sock *lopt = icsk->icsk_accept_queue.listen_opt;
    struct request_sock *req, **prev;

    for (prev = &lopt->syn_table[inet_synq_hash(raddr, rport, lopt->hash_rnd,
                            lopt->nr_table_entries)];
         (req = *prev) != NULL;
         prev = &req->dl_next) {
        const struct inet_request_sock *ireq = inet_rsk(req);

        if (ireq->rmt_port == rport &&
            ireq->rmt_addr == raddr &&
            ireq->loc_addr == laddr &&
            AF_INET_FAMILY(req->rsk_ops->family)) {
            WARN_ON(req->sk);
            *prevp = prev;
            break;
        }
    }

    return req;
}
EXPORT_SYMBOL_GPL(inet_csk_search_req);

void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
                   unsigned long timeout)
{
    struct inet_connection_sock *icsk = inet_csk(sk);
    struct listen_sock *lopt = icsk->icsk_accept_queue.listen_opt;
    const u32 h = inet_synq_hash(inet_rsk(req)->rmt_addr, inet_rsk(req)->rmt_port,
                     lopt->hash_rnd, lopt->nr_table_entries);

    reqsk_queue_hash_req(&icsk->icsk_accept_queue, h, req, timeout);
    inet_csk_reqsk_queue_added(sk, timeout);
}
EXPORT_SYMBOL_GPL(inet_csk_reqsk_queue_hash_add);

/* Only thing we need from tcp.h */
extern int sysctl_tcp_synack_retries;


/* Decide when to expire the request and when to resend SYN-ACK */
static inline void syn_ack_recalc(struct request_sock *req, const int thresh,
                  const int max_retries,
                  const u8 rskq_defer_accept,
                  int *expire, int *resend)
{
    if (!rskq_defer_accept) {
        *expire = req->retrans >= thresh;
        *resend = 1;
        return;
    }
    *expire = req->retrans >= thresh &&
          (!inet_rsk(req)->acked || req->retrans >= max_retries);
    /*
     * 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->retrans >= rskq_defer_accept - 1;
}

void inet_csk_reqsk_queue_prune(struct sock *parent,
                const unsigned long interval,
                const unsigned long timeout,
                const unsigned long max_rto)
{
    struct inet_connection_sock *icsk = inet_csk(parent);
    struct request_sock_queue *queue = &icsk->icsk_accept_queue;
    struct listen_sock *lopt = queue->listen_opt;
    int max_retries = icsk->icsk_syn_retries ? : sysctl_tcp_synack_retries;
    int thresh = max_retries;
    unsigned long now = jiffies;
    struct request_sock **reqp, *req;
    int i, budget;

    if (lopt == NULL || lopt->qlen == 0)
        return;

    /* 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.
     */
    if (lopt->qlen>>(lopt->max_qlen_log-1)) {
        int young = (lopt->qlen_young<<1);

        while (thresh > 2) {
            if (lopt->qlen < young)
                break;
            thresh--;
            young <<= 1;
        }
    }

    if (queue->rskq_defer_accept)
        max_retries = queue->rskq_defer_accept;

    budget = 2 * (lopt->nr_table_entries / (timeout / interval));
    i = lopt->clock_hand;

    do {
        reqp=&lopt->syn_table[i];
        while ((req = *reqp) != NULL) {
            if (time_after_eq(now, req->expires)) {
                int expire = 0, resend = 0;

                syn_ack_recalc(req, thresh, max_retries,
                           queue->rskq_defer_accept,
                           &expire, &resend);
                req->rsk_ops->syn_ack_timeout(parent, req);
                if (!expire &&
                    (!resend ||
                     !req->rsk_ops->rtx_syn_ack(parent, req, NULL) ||
                     inet_rsk(req)->acked)) {
                    unsigned long timeo;

                    if (req->retrans++ == 0)
                        lopt->qlen_young--;
                    timeo = min((timeout << req->retrans), max_rto);
                    req->expires = now + timeo;
                    reqp = &req->dl_next;
                    continue;
                }

                /* Drop this request */
                inet_csk_reqsk_queue_unlink(parent, req, reqp);
                reqsk_queue_removed(queue, req);
                reqsk_free(req);
                continue;
            }
            reqp = &req->dl_next;
        }

        i = (i + 1) & (lopt->nr_table_entries - 1);

    } while (--budget > 0);

    lopt->clock_hand = i;

    if (lopt->qlen)
        inet_csk_reset_keepalive_timer(parent, interval);
}
EXPORT_SYMBOL_GPL(inet_csk_reqsk_queue_prune);

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 != NULL) {
        struct inet_connection_sock *newicsk = inet_csk(newsk);

        newsk->sk_state = TCP_SYN_RECV;
        newicsk->icsk_bind_hash = NULL;

        inet_sk(newsk)->inet_dport = inet_rsk(req)->rmt_port;
        inet_sk(newsk)->inet_num = ntohs(inet_rsk(req)->loc_port);
        inet_sk(newsk)->inet_sport = inet_rsk(req)->loc_port;
        newsk->sk_write_space = sk_stream_write_space;

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

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

        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);

int inet_csk_listen_start(struct sock *sk, const int nr_table_entries)
{
    struct inet_sock *inet = inet_sk(sk);
    struct inet_connection_sock *icsk = inet_csk(sk);
    int rc = reqsk_queue_alloc(&icsk->icsk_accept_queue, nr_table_entries);

    if (rc != 0)
        return rc;

    sk->sk_max_ack_backlog = 0;
    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.
     */
    sk->sk_state = TCP_LISTEN;
    if (!sk->sk_prot->get_port(sk, inet->inet_num)) {
        inet->inet_sport = htons(inet->inet_num);

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

        return 0;
    }

    sk->sk_state = TCP_CLOSE;
    __reqsk_queue_destroy(&icsk->icsk_accept_queue);
    return -EADDRINUSE;
}
EXPORT_SYMBOL_GPL(inet_csk_listen_start);

/*
 *  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 *acc_req;
    struct request_sock *req;

    inet_csk_delete_keepalive_timer(sk);

    /* make all the listen_opt local to us */
    acc_req = reqsk_queue_yank_acceptq(queue);

    /* 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
     */
    reqsk_queue_destroy(queue);

    while ((req = acc_req) != NULL) {
        struct sock *child = req->sk;

        acc_req = req->dl_next;

        local_bh_disable();
        bh_lock_sock(child);
        WARN_ON(sock_owned_by_user(child));
        sock_hold(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)->listener) {
            BUG_ON(tcp_sk(child)->fastopen_rsk != req);
            BUG_ON(sk != tcp_rsk(req)->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().
             */
            tcp_sk(child)->fastopen_rsk = NULL;
            sock_put(sk);
        }
        inet_csk_destroy_sock(child);

        bh_unlock_sock(child);
        local_bh_enable();
        sock_put(child);

        sk_acceptq_removed(sk);
        __reqsk_free(req);
    }
    if (queue->fastopenq != NULL) {
        /* Free all the reqs queued in rskq_rst_head. */
        spin_lock_bh(&queue->fastopenq->lock);
        acc_req = queue->fastopenq->rskq_rst_head;
        queue->fastopenq->rskq_rst_head = NULL;
        spin_unlock_bh(&queue->fastopenq->lock);
        while ((req = acc_req) != NULL) {
            acc_req = req->dl_next;
            __reqsk_free(req);
        }
    }
    WARN_ON(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);

#ifdef CONFIG_COMPAT
int inet_csk_compat_getsockopt(struct sock *sk, int level, int optname,
                   char __user *optval, int __user *optlen)
{
    const struct inet_connection_sock *icsk = inet_csk(sk);

    if (icsk->icsk_af_ops->compat_getsockopt != NULL)
        return icsk->icsk_af_ops->compat_getsockopt(sk, level, optname,
                                optval, optlen);
    return icsk->icsk_af_ops->getsockopt(sk, level, optname,
                         optval, optlen);
}
EXPORT_SYMBOL_GPL(inet_csk_compat_getsockopt);

int inet_csk_compat_setsockopt(struct sock *sk, int level, int optname,
                   char __user *optval, unsigned int optlen)
{
    const struct inet_connection_sock *icsk = inet_csk(sk);

    if (icsk->icsk_af_ops->compat_setsockopt != NULL)
        return icsk->icsk_af_ops->compat_setsockopt(sk, level, optname,
                                optval, optlen);
    return icsk->icsk_af_ops->setsockopt(sk, level, optname,
                         optval, optlen);
}
EXPORT_SYMBOL_GPL(inet_csk_compat_setsockopt);
#endif

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);

    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);