tcp: ensure prior synack rtx behavior with small backlogs

[mirror_ubuntu-bionic-kernel.git] / net / ipv4 / inet_connection_sock.c

/*
 * 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>
#include <net/tcp.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

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);

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

        /*
         * 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 &&
                    !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) &&
                            (!reuseport || !sk2->sk_reuseport ||
                            (sk2->sk_state != TCP_TIME_WAIT &&
                             !uid_eq(uid, sock_i_uid(sk2))))) {

                                if (!sk2->sk_rcv_saddr || !sk->sk_rcv_saddr ||
                                    sk2->sk_rcv_saddr == sk->sk_rcv_saddr)
                                        break;
                        }
                        if (!relax && reuse && sk2->sk_reuse &&
                            sk2->sk_state != TCP_LISTEN) {

                                if (!sk2->sk_rcv_saddr || !sk->sk_rcv_saddr ||
                                    sk2->sk_rcv_saddr == sk->sk_rcv_saddr)
                                        break;
                        }
                }
        }
        return sk2 != 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 inet_bind_bucket *tb;
        int ret, attempts = 5;
        struct net *net = sock_net(sk);
        int smallest_size = -1, smallest_rover;
        kuid_t uid = sock_i_uid(sk);
        int attempt_half = (sk->sk_reuse == SK_CAN_REUSE) ? 1 : 0;

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

again:
                inet_get_local_port_range(net, &low, &high);
                if (attempt_half) {
                        int half = low + ((high - low) >> 1);

                        if (attempt_half == 1)
                                high = half;
                        else
                                low = half;
                }
                remaining = (high - low) + 1;
                smallest_rover = rover = prandom_u32() % remaining + low;

                smallest_size = -1;
                do {
                        if (inet_is_local_reserved_port(net, rover))
                                goto next_nolock;
                        head = &hashinfo->bhash[inet_bhashfn(net, rover,
                                        hashinfo->bhash_size)];
                        spin_lock(&head->lock);
                        inet_bind_bucket_for_each(tb, &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->fastreuseport > 0 &&
                                              sk->sk_reuseport &&
                                              uid_eq(tb->fastuid, uid))) &&
                                            (tb->num_owners < smallest_size || smallest_size == -1)) {
                                                smallest_size = tb->num_owners;
                                                smallest_rover = rover;
                                        }
                                        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;
                        }
                        if (attempt_half == 1) {
                                /* OK we now try the upper half of the range */
                                attempt_half = 2;
                                goto again;
                        }
                        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, &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) ||
                     (tb->fastreuseport > 0 &&
                      sk->sk_reuseport && uid_eq(tb->fastuid, uid))) &&
                    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) ||
                                     (tb->fastreuseport > 0 &&
                                      sk->sk_reuseport && uid_eq(tb->fastuid, uid))) &&
                                    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;
                if (sk->sk_reuseport) {
                        tb->fastreuseport = 1;
                        tb->fastuid = uid;
                } else
                        tb->fastreuseport = 0;
        } else {
                if (tb->fastreuse &&
                    (!sk->sk_reuse || sk->sk_state == TCP_LISTEN))
                        tb->fastreuse = 0;
                if (tb->fastreuseport &&
                    (!sk->sk_reuseport || !uid_eq(tb->fastuid, uid)))
                        tb->fastreuseport = 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);
                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)
{
        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 (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)(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(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 = ireq->opt;
        struct rtable *rt;

        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));
        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(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;

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

        rcu_read_lock();
        opt = rcu_dereference(newinet->inet_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));
        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);

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

/* 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->num_timeout >= thresh;
                *resend = 1;
                return;
        }
        *expire = req->num_timeout >= thresh &&
                  (!inet_rsk(req)->acked || req->num_timeout >= 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->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);

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

        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;
}

void inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req)
{
        if (reqsk_queue_unlink(&inet_csk(sk)->icsk_accept_queue, req)) {
                reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
                reqsk_put(req);
        }
}
EXPORT_SYMBOL(inet_csk_reqsk_queue_drop);

static void reqsk_timer_handler(unsigned long data)
{
        struct request_sock *req = (struct request_sock *)data;
        struct sock *sk_listener = req->rsk_listener;
        struct inet_connection_sock *icsk = inet_csk(sk_listener);
        struct request_sock_queue *queue = &icsk->icsk_accept_queue;
        int qlen, expire = 0, resend = 0;
        int max_retries, thresh;
        u8 defer_accept;

        if (sk_listener->sk_state != TCP_LISTEN)
                goto drop;

        max_retries = icsk->icsk_syn_retries ? : sysctl_tcp_synack_retries;
        thresh = max_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.
         */
        qlen = reqsk_queue_len(queue);
        if ((qlen << 1) > max(8U, sk_listener->sk_max_ack_backlog)) {
                int young = reqsk_queue_len_young(queue) << 1;

                while (thresh > 2) {
                        if (qlen < young)
                                break;
                        thresh--;
                        young <<= 1;
                }
        }
        defer_accept = READ_ONCE(queue->rskq_defer_accept);
        if (defer_accept)
                max_retries = defer_accept;
        syn_ack_recalc(req, thresh, max_retries, 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_pinned(&req->rsk_timer, jiffies + timeo);
                return;
        }
drop:
        inet_csk_reqsk_queue_drop(sk_listener, req);
        reqsk_put(req);
}

static void reqsk_queue_hash_req(struct request_sock *req,
                                 unsigned long timeout)
{
        req->num_retrans = 0;
        req->num_timeout = 0;
        req->sk = NULL;

        setup_timer(&req->rsk_timer, reqsk_timer_handler, (unsigned long)req);
        mod_timer_pinned(&req->rsk_timer, jiffies + timeout);

        inet_ehash_insert(req_to_sk(req), NULL);
        /* before letting lookups find us, make sure all req fields
         * are committed to memory and refcnt initialized.
         */
        smp_wmb();
        atomic_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);

/**
 *      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);

                newsk->sk_state = 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);
                newsk->sk_write_space = sk_stream_write_space;

                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;

                /* 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);

/* 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);

        /* The below has to be done to allow calling inet_csk_destroy_sock */
        sock_set_flag(sk, SOCK_DEAD);
        percpu_counter_inc(sk->sk_prot->orphan_count);
        inet_sk(sk)->inet_num = 0;
}
EXPORT_SYMBOL(inet_csk_prepare_forced_close);

int inet_csk_listen_start(struct sock *sk, const int nr_table_entries)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        struct inet_sock *inet = inet_sk(sk);

        reqsk_queue_alloc(&icsk->icsk_accept_queue);

        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;
        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 *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;

                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)->tfo_listener) {
                        BUG_ON(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().
                         */
                        tcp_sk(child)->fastopen_rsk = NULL;
                }
                inet_csk_destroy_sock(child);

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

                reqsk_put(req);
                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(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)
                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)
                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);