tcp: Fix a connect() race with timewait sockets

[deliverable/linux.git] / net / ipv4 / inet_timewait_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.
 *
 *              Generic TIME_WAIT sockets functions
 *
 *              From code orinally in TCP
 */

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


/*
 * unhash a timewait socket from established hash
 * lock must be hold by caller
 */
int inet_twsk_unhash(struct inet_timewait_sock *tw)
{
        if (hlist_nulls_unhashed(&tw->tw_node))
                return 0;

        hlist_nulls_del_rcu(&tw->tw_node);
        sk_nulls_node_init(&tw->tw_node);
        return 1;
}

/*
 * unhash a timewait socket from bind hash
 * lock must be hold by caller
 */
int inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
                          struct inet_hashinfo *hashinfo)
{
        struct inet_bind_bucket *tb = tw->tw_tb;

        if (!tb)
                return 0;

        __hlist_del(&tw->tw_bind_node);
        tw->tw_tb = NULL;
        inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
        return 1;
}

/* Must be called with locally disabled BHs. */
static void __inet_twsk_kill(struct inet_timewait_sock *tw,
                             struct inet_hashinfo *hashinfo)
{
        struct inet_bind_hashbucket *bhead;
        int refcnt;
        /* Unlink from established hashes. */
        spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);

        spin_lock(lock);
        refcnt = inet_twsk_unhash(tw);
        spin_unlock(lock);

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

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

#ifdef SOCK_REFCNT_DEBUG
        if (atomic_read(&tw->tw_refcnt) != 1) {
                printk(KERN_DEBUG "%s timewait_sock %p refcnt=%d\n",
                       tw->tw_prot->name, tw, atomic_read(&tw->tw_refcnt));
        }
#endif
        while (refcnt) {
                inet_twsk_put(tw);
                refcnt--;
        }
}

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

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

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

        spin_lock(lock);

        /*
         * Step 2: Hash TW into TIMEWAIT chain.
         * Should be done before removing sk from established chain
         * because readers are lockless and search established first.
         */
        inet_twsk_add_node_rcu(tw, &ehead->twchain);

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

        /*
         * Notes :
         * - We initially set tw_refcnt to 0 in inet_twsk_alloc()
         * - We add one reference for the bhash link
         * - We add one reference for the ehash link
         * - We want this refcnt update done before allowing other
         *   threads to find this tw in ehash chain.
         */
        atomic_add(1 + 1 + 1, &tw->tw_refcnt);

        spin_unlock(lock);
}

EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);

struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk, const int state)
{
        struct inet_timewait_sock *tw =
                kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
                                 GFP_ATOMIC);
        if (tw != NULL) {
                const struct inet_sock *inet = inet_sk(sk);

                kmemcheck_annotate_bitfield(tw, flags);

                /* Give us an identity. */
                tw->tw_daddr        = inet->inet_daddr;
                tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
                tw->tw_bound_dev_if = sk->sk_bound_dev_if;
                tw->tw_num          = inet->inet_num;
                tw->tw_state        = TCP_TIME_WAIT;
                tw->tw_substate     = state;
                tw->tw_sport        = inet->inet_sport;
                tw->tw_dport        = inet->inet_dport;
                tw->tw_family       = sk->sk_family;
                tw->tw_reuse        = sk->sk_reuse;
                tw->tw_hash         = sk->sk_hash;
                tw->tw_ipv6only     = 0;
                tw->tw_transparent  = inet->transparent;
                tw->tw_prot         = sk->sk_prot_creator;
                twsk_net_set(tw, hold_net(sock_net(sk)));
                /*
                 * Because we use RCU lookups, we should not set tw_refcnt
                 * to a non null value before everything is setup for this
                 * timewait socket.
                 */
                atomic_set(&tw->tw_refcnt, 0);
                inet_twsk_dead_node_init(tw);
                __module_get(tw->tw_prot->owner);
        }

        return tw;
}

EXPORT_SYMBOL_GPL(inet_twsk_alloc);

/* Returns non-zero if quota exceeded.  */
static int inet_twdr_do_twkill_work(struct inet_timewait_death_row *twdr,
                                    const int slot)
{
        struct inet_timewait_sock *tw;
        struct hlist_node *node;
        unsigned int killed;
        int ret;

        /* NOTE: compare this to previous version where lock
         * was released after detaching chain. It was racy,
         * because tw buckets are scheduled in not serialized context
         * in 2.3 (with netfilter), and with softnet it is common, because
         * soft irqs are not sequenced.
         */
        killed = 0;
        ret = 0;
rescan:
        inet_twsk_for_each_inmate(tw, node, &twdr->cells[slot]) {
                __inet_twsk_del_dead_node(tw);
                spin_unlock(&twdr->death_lock);
                __inet_twsk_kill(tw, twdr->hashinfo);
#ifdef CONFIG_NET_NS
                NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_TIMEWAITED);
#endif
                inet_twsk_put(tw);
                killed++;
                spin_lock(&twdr->death_lock);
                if (killed > INET_TWDR_TWKILL_QUOTA) {
                        ret = 1;
                        break;
                }

                /* While we dropped twdr->death_lock, another cpu may have
                 * killed off the next TW bucket in the list, therefore
                 * do a fresh re-read of the hlist head node with the
                 * lock reacquired.  We still use the hlist traversal
                 * macro in order to get the prefetches.
                 */
                goto rescan;
        }

        twdr->tw_count -= killed;
#ifndef CONFIG_NET_NS
        NET_ADD_STATS_BH(&init_net, LINUX_MIB_TIMEWAITED, killed);
#endif
        return ret;
}

void inet_twdr_hangman(unsigned long data)
{
        struct inet_timewait_death_row *twdr;
        int unsigned need_timer;

        twdr = (struct inet_timewait_death_row *)data;
        spin_lock(&twdr->death_lock);

        if (twdr->tw_count == 0)
                goto out;

        need_timer = 0;
        if (inet_twdr_do_twkill_work(twdr, twdr->slot)) {
                twdr->thread_slots |= (1 << twdr->slot);
                schedule_work(&twdr->twkill_work);
                need_timer = 1;
        } else {
                /* We purged the entire slot, anything left?  */
                if (twdr->tw_count)
                        need_timer = 1;
                twdr->slot = ((twdr->slot + 1) & (INET_TWDR_TWKILL_SLOTS - 1));
        }
        if (need_timer)
                mod_timer(&twdr->tw_timer, jiffies + twdr->period);
out:
        spin_unlock(&twdr->death_lock);
}

EXPORT_SYMBOL_GPL(inet_twdr_hangman);

void inet_twdr_twkill_work(struct work_struct *work)
{
        struct inet_timewait_death_row *twdr =
                container_of(work, struct inet_timewait_death_row, twkill_work);
        int i;

        BUILD_BUG_ON((INET_TWDR_TWKILL_SLOTS - 1) >
                        (sizeof(twdr->thread_slots) * 8));

        while (twdr->thread_slots) {
                spin_lock_bh(&twdr->death_lock);
                for (i = 0; i < INET_TWDR_TWKILL_SLOTS; i++) {
                        if (!(twdr->thread_slots & (1 << i)))
                                continue;

                        while (inet_twdr_do_twkill_work(twdr, i) != 0) {
                                if (need_resched()) {
                                        spin_unlock_bh(&twdr->death_lock);
                                        schedule();
                                        spin_lock_bh(&twdr->death_lock);
                                }
                        }

                        twdr->thread_slots &= ~(1 << i);
                }
                spin_unlock_bh(&twdr->death_lock);
        }
}

EXPORT_SYMBOL_GPL(inet_twdr_twkill_work);

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

/* This is for handling early-kills of TIME_WAIT sockets. */
void inet_twsk_deschedule(struct inet_timewait_sock *tw,
                          struct inet_timewait_death_row *twdr)
{
        spin_lock(&twdr->death_lock);
        if (inet_twsk_del_dead_node(tw)) {
                inet_twsk_put(tw);
                if (--twdr->tw_count == 0)
                        del_timer(&twdr->tw_timer);
        }
        spin_unlock(&twdr->death_lock);
        __inet_twsk_kill(tw, twdr->hashinfo);
}

EXPORT_SYMBOL(inet_twsk_deschedule);

void inet_twsk_schedule(struct inet_timewait_sock *tw,
                       struct inet_timewait_death_row *twdr,
                       const int timeo, const int timewait_len)
{
        struct hlist_head *list;
        int slot;

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

        spin_lock(&twdr->death_lock);

        /* Unlink it, if it was scheduled */
        if (inet_twsk_del_dead_node(tw))
                twdr->tw_count--;
        else
                atomic_inc(&tw->tw_refcnt);

        if (slot >= INET_TWDR_RECYCLE_SLOTS) {
                /* Schedule to slow timer */
                if (timeo >= timewait_len) {
                        slot = INET_TWDR_TWKILL_SLOTS - 1;
                } else {
                        slot = DIV_ROUND_UP(timeo, twdr->period);
                        if (slot >= INET_TWDR_TWKILL_SLOTS)
                                slot = INET_TWDR_TWKILL_SLOTS - 1;
                }
                tw->tw_ttd = jiffies + timeo;
                slot = (twdr->slot + slot) & (INET_TWDR_TWKILL_SLOTS - 1);
                list = &twdr->cells[slot];
        } else {
                tw->tw_ttd = jiffies + (slot << INET_TWDR_RECYCLE_TICK);

                if (twdr->twcal_hand < 0) {
                        twdr->twcal_hand = 0;
                        twdr->twcal_jiffie = jiffies;
                        twdr->twcal_timer.expires = twdr->twcal_jiffie +
                                              (slot << INET_TWDR_RECYCLE_TICK);
                        add_timer(&twdr->twcal_timer);
                } else {
                        if (time_after(twdr->twcal_timer.expires,
                                       jiffies + (slot << INET_TWDR_RECYCLE_TICK)))
                                mod_timer(&twdr->twcal_timer,
                                          jiffies + (slot << INET_TWDR_RECYCLE_TICK));
                        slot = (twdr->twcal_hand + slot) & (INET_TWDR_RECYCLE_SLOTS - 1);
                }
                list = &twdr->twcal_row[slot];
        }

        hlist_add_head(&tw->tw_death_node, list);

        if (twdr->tw_count++ == 0)
                mod_timer(&twdr->tw_timer, jiffies + twdr->period);
        spin_unlock(&twdr->death_lock);
}

EXPORT_SYMBOL_GPL(inet_twsk_schedule);

void inet_twdr_twcal_tick(unsigned long data)
{
        struct inet_timewait_death_row *twdr;
        int n, slot;
        unsigned long j;
        unsigned long now = jiffies;
        int killed = 0;
        int adv = 0;

        twdr = (struct inet_timewait_death_row *)data;

        spin_lock(&twdr->death_lock);
        if (twdr->twcal_hand < 0)
                goto out;

        slot = twdr->twcal_hand;
        j = twdr->twcal_jiffie;

        for (n = 0; n < INET_TWDR_RECYCLE_SLOTS; n++) {
                if (time_before_eq(j, now)) {
                        struct hlist_node *node, *safe;
                        struct inet_timewait_sock *tw;

                        inet_twsk_for_each_inmate_safe(tw, node, safe,
                                                       &twdr->twcal_row[slot]) {
                                __inet_twsk_del_dead_node(tw);
                                __inet_twsk_kill(tw, twdr->hashinfo);
#ifdef CONFIG_NET_NS
                                NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_TIMEWAITKILLED);
#endif
                                inet_twsk_put(tw);
                                killed++;
                        }
                } else {
                        if (!adv) {
                                adv = 1;
                                twdr->twcal_jiffie = j;
                                twdr->twcal_hand = slot;
                        }

                        if (!hlist_empty(&twdr->twcal_row[slot])) {
                                mod_timer(&twdr->twcal_timer, j);
                                goto out;
                        }
                }
                j += 1 << INET_TWDR_RECYCLE_TICK;
                slot = (slot + 1) & (INET_TWDR_RECYCLE_SLOTS - 1);
        }
        twdr->twcal_hand = -1;

out:
        if ((twdr->tw_count -= killed) == 0)
                del_timer(&twdr->tw_timer);
#ifndef CONFIG_NET_NS
        NET_ADD_STATS_BH(&init_net, LINUX_MIB_TIMEWAITKILLED, killed);
#endif
        spin_unlock(&twdr->death_lock);
}

EXPORT_SYMBOL_GPL(inet_twdr_twcal_tick);

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

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

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

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

                        rcu_read_unlock();
                        inet_twsk_deschedule(tw, twdr);
                        inet_twsk_put(tw);
                        goto restart_rcu;
                }
                /* If the nulls value we got at the end of this lookup is
                 * not the expected one, we must restart lookup.
                 * We probably met an item that was moved to another chain.
                 */
                if (get_nulls_value(node) != slot)
                        goto restart;
                rcu_read_unlock();
        }
}
EXPORT_SYMBOL_GPL(inet_twsk_purge);