net/ipv4/inet_timewait_sock.c

   1 /*
   2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3  *              operating system.  INET is implemented using the  BSD Socket
   4  *              interface as the means of communication with the user level.
   5  *
   6  *              Generic TIME_WAIT sockets functions
   7  *
   8  *              From code orinally in TCP
   9  */
  10
  11 #include <linux/kernel.h>
  12 #include <linux/slab.h>
  13 #include <linux/module.h>
  14 #include <net/inet_hashtables.h>
  15 #include <net/inet_timewait_sock.h>
  16 #include <net/ip.h>
  17
  18
  19 /**
  20  *      inet_twsk_bind_unhash - unhash a timewait socket from bind hash
  21  *      @tw: timewait socket
  22  *      @hashinfo: hashinfo pointer
  23  *
  24  *      unhash a timewait socket from bind hash, if hashed.
  25  *      bind hash lock must be held by caller.
  26  *      Returns 1 if caller should call inet_twsk_put() after lock release.
  27  */
  28 void inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
  29                           struct inet_hashinfo *hashinfo)
  30 {
  31         struct inet_bind_bucket *tb = tw->tw_tb;
  32
  33         if (!tb)
  34                 return;
  35
  36         __hlist_del(&tw->tw_bind_node);
  37         tw->tw_tb = NULL;
  38         inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
  39         __sock_put((struct sock *)tw);
  40 }
  41
  42 /* Must be called with locally disabled BHs. */
  43 static void inet_twsk_kill(struct inet_timewait_sock *tw)
  44 {
  45         struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
  46         spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
  47         struct inet_bind_hashbucket *bhead;
  48
  49         spin_lock(lock);
  50         sk_nulls_del_node_init_rcu((struct sock *)tw);
  51         spin_unlock(lock);
  52
  53         /* Disassociate with bind bucket. */
  54         bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
  55                         hashinfo->bhash_size)];
  56
  57         spin_lock(&bhead->lock);
  58         inet_twsk_bind_unhash(tw, hashinfo);
  59         spin_unlock(&bhead->lock);
  60
  61         atomic_dec(&tw->tw_dr->tw_count);
  62         inet_twsk_put(tw);
  63 }
  64
  65 void inet_twsk_free(struct inet_timewait_sock *tw)
  66 {
  67         struct module *owner = tw->tw_prot->owner;
  68         twsk_destructor((struct sock *)tw);
  69 #ifdef SOCK_REFCNT_DEBUG
  70         pr_debug("%s timewait_sock %p released\n", tw->tw_prot->name, tw);
  71 #endif
  72         kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
  73         module_put(owner);
  74 }
  75
  76 void inet_twsk_put(struct inet_timewait_sock *tw)
  77 {
  78         if (refcount_dec_and_test(&tw->tw_refcnt))
  79                 inet_twsk_free(tw);
  80 }
  81 EXPORT_SYMBOL_GPL(inet_twsk_put);
  82
  83 static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
  84                                    struct hlist_nulls_head *list)
  85 {
  86         hlist_nulls_add_head_rcu(&tw->tw_node, list);
  87 }
  88
  89 static void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
  90                                     struct hlist_head *list)
  91 {
  92         hlist_add_head(&tw->tw_bind_node, list);
  93 }
  94
  95 /*
  96  * Enter the time wait state. This is called with locally disabled BH.
  97  * Essentially we whip up a timewait bucket, copy the relevant info into it
  98  * from the SK, and mess with hash chains and list linkage.
  99  */
 100 void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
 101                            struct inet_hashinfo *hashinfo)
 102 {
 103         const struct inet_sock *inet = inet_sk(sk);
 104         const struct inet_connection_sock *icsk = inet_csk(sk);
 105         struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
 106         spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 107         struct inet_bind_hashbucket *bhead;
 108         /* Step 1: Put TW into bind hash. Original socket stays there too.
 109            Note, that any socket with inet->num != 0 MUST be bound in
 110            binding cache, even if it is closed.
 111          */
 112         bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
 113                         hashinfo->bhash_size)];
 114         spin_lock(&bhead->lock);
 115         tw->tw_tb = icsk->icsk_bind_hash;
 116         WARN_ON(!icsk->icsk_bind_hash);
 117         inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
 118         spin_unlock(&bhead->lock);
 119
 120         spin_lock(lock);
 121
 122         inet_twsk_add_node_rcu(tw, &ehead->chain);
 123
 124         /* Step 3: Remove SK from hash chain */
 125         if (__sk_nulls_del_node_init_rcu(sk))
 126                 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 127
 128         spin_unlock(lock);
 129
 130         /* tw_refcnt is set to 3 because we have :
 131          * - one reference for bhash chain.
 132          * - one reference for ehash chain.
 133          * - one reference for timer.
 134          * We can use atomic_set() because prior spin_lock()/spin_unlock()
 135          * committed into memory all tw fields.
 136          * Also note that after this point, we lost our implicit reference
 137          * so we are not allowed to use tw anymore.
 138          */
 139         refcount_set(&tw->tw_refcnt, 3);
 140 }
 141 EXPORT_SYMBOL_GPL(inet_twsk_hashdance);
 142
 143 static void tw_timer_handler(struct timer_list *t)
 144 {
 145         struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);
 146
 147         if (tw->tw_kill)
 148                 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITKILLED);
 149         else
 150                 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITED);
 151         inet_twsk_kill(tw);
 152 }
 153
 154 struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
 155                                            struct inet_timewait_death_row *dr,
 156                                            const int state)
 157 {
 158         struct inet_timewait_sock *tw;
 159
 160         if (atomic_read(&dr->tw_count) >= dr->sysctl_max_tw_buckets)
 161                 return NULL;
 162
 163         tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
 164                               GFP_ATOMIC);
 165         if (tw) {
 166                 const struct inet_sock *inet = inet_sk(sk);
 167
 168                 tw->tw_dr           = dr;
 169                 /* Give us an identity. */
 170                 tw->tw_daddr        = inet->inet_daddr;
 171                 tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
 172                 tw->tw_bound_dev_if = sk->sk_bound_dev_if;
 173                 tw->tw_tos          = inet->tos;
 174                 tw->tw_num          = inet->inet_num;
 175                 tw->tw_state        = TCP_TIME_WAIT;
 176                 tw->tw_substate     = state;
 177                 tw->tw_sport        = inet->inet_sport;
 178                 tw->tw_dport        = inet->inet_dport;
 179                 tw->tw_family       = sk->sk_family;
 180                 tw->tw_reuse        = sk->sk_reuse;
 181                 tw->tw_hash         = sk->sk_hash;
 182                 tw->tw_ipv6only     = 0;
 183                 tw->tw_transparent  = inet->transparent;
 184                 tw->tw_prot         = sk->sk_prot_creator;
 185                 atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
 186                 twsk_net_set(tw, sock_net(sk));
 187                 timer_setup(&tw->tw_timer, tw_timer_handler, TIMER_PINNED);
 188                 /*
 189                  * Because we use RCU lookups, we should not set tw_refcnt
 190                  * to a non null value before everything is setup for this
 191                  * timewait socket.
 192                  */
 193                 refcount_set(&tw->tw_refcnt, 0);
 194
 195                 __module_get(tw->tw_prot->owner);
 196         }
 197
 198         return tw;
 199 }
 200 EXPORT_SYMBOL_GPL(inet_twsk_alloc);
 201
 202 /* These are always called from BH context.  See callers in
 203  * tcp_input.c to verify this.
 204  */
 205
 206 /* This is for handling early-kills of TIME_WAIT sockets.
 207  * Warning : consume reference.
 208  * Caller should not access tw anymore.
 209  */
 210 void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
 211 {
 212         if (del_timer_sync(&tw->tw_timer))
 213                 inet_twsk_kill(tw);
 214         inet_twsk_put(tw);
 215 }
 216 EXPORT_SYMBOL(inet_twsk_deschedule_put);
 217
 218 void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
 219 {
 220         /* timeout := RTO * 3.5
 221          *
 222          * 3.5 = 1+2+0.5 to wait for two retransmits.
 223          *
 224          * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
 225          * our ACK acking that FIN can be lost. If N subsequent retransmitted
 226          * FINs (or previous seqments) are lost (probability of such event
 227          * is p^(N+1), where p is probability to lose single packet and
 228          * time to detect the loss is about RTO*(2^N - 1) with exponential
 229          * backoff). Normal timewait length is calculated so, that we
 230          * waited at least for one retransmitted FIN (maximal RTO is 120sec).
 231          * [ BTW Linux. following BSD, violates this requirement waiting
 232          *   only for 60sec, we should wait at least for 240 secs.
 233          *   Well, 240 consumes too much of resources 8)
 234          * ]
 235          * This interval is not reduced to catch old duplicate and
 236          * responces to our wandering segments living for two MSLs.
 237          * However, if we use PAWS to detect
 238          * old duplicates, we can reduce the interval to bounds required
 239          * by RTO, rather than MSL. So, if peer understands PAWS, we
 240          * kill tw bucket after 3.5*RTO (it is important that this number
 241          * is greater than TS tick!) and detect old duplicates with help
 242          * of PAWS.
 243          */
 244
 245         tw->tw_kill = timeo <= 4*HZ;
 246         if (!rearm) {
 247                 BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
 248                 atomic_inc(&tw->tw_dr->tw_count);
 249         } else {
 250                 mod_timer_pending(&tw->tw_timer, jiffies + timeo);
 251         }
 252 }
 253 EXPORT_SYMBOL_GPL(__inet_twsk_schedule);
 254
 255 void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family)
 256 {
 257         struct inet_timewait_sock *tw;
 258         struct sock *sk;
 259         struct hlist_nulls_node *node;
 260         unsigned int slot;
 261
 262         for (slot = 0; slot <= hashinfo->ehash_mask; slot++) {
 263                 struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
 264 restart_rcu:
 265                 cond_resched();
 266                 rcu_read_lock();
 267 restart:
 268                 sk_nulls_for_each_rcu(sk, node, &head->chain) {
 269                         if (sk->sk_state != TCP_TIME_WAIT)
 270                                 continue;
 271                         tw = inet_twsk(sk);
 272                         if ((tw->tw_family != family) ||
 273                                 refcount_read(&twsk_net(tw)->count))
 274                                 continue;
 275
 276                         if (unlikely(!refcount_inc_not_zero(&tw->tw_refcnt)))
 277                                 continue;
 278
 279                         if (unlikely((tw->tw_family != family) ||
 280                                      refcount_read(&twsk_net(tw)->count))) {
 281                                 inet_twsk_put(tw);
 282                                 goto restart;
 283                         }
 284
 285                         rcu_read_unlock();
 286                         local_bh_disable();
 287                         inet_twsk_deschedule_put(tw);
 288                         local_bh_enable();
 289                         goto restart_rcu;
 290                 }
 291                 /* If the nulls value we got at the end of this lookup is
 292                  * not the expected one, we must restart lookup.
 293                  * We probably met an item that was moved to another chain.
 294                  */
 295                 if (get_nulls_value(node) != slot)
 296                         goto restart;
 297                 rcu_read_unlock();
 298         }
 299 }
 300 EXPORT_SYMBOL_GPL(inet_twsk_purge);