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/kmemcheck.h>
  13 #include <linux/slab.h>
  14 #include <linux/module.h>
  15 #include <net/inet_hashtables.h>
  16 #include <net/inet_timewait_sock.h>
  17 #include <net/ip.h>
  18
  19
  20 /**
  21  *      inet_twsk_bind_unhash - unhash a timewait socket from bind hash
  22  *      @tw: timewait socket
  23  *      @hashinfo: hashinfo pointer
  24  *
  25  *      unhash a timewait socket from bind hash, if hashed.
  26  *      bind hash lock must be held by caller.
  27  *      Returns 1 if caller should call inet_twsk_put() after lock release.
  28  */
  29 void inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
  30                           struct inet_hashinfo *hashinfo)
  31 {
  32         struct inet_bind_bucket *tb = tw->tw_tb;
  33
  34         if (!tb)
  35                 return;
  36
  37         __hlist_del(&tw->tw_bind_node);
  38         tw->tw_tb = NULL;
  39         inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
  40         __sock_put((struct sock *)tw);
  41 }
  42
  43 /* Must be called with locally disabled BHs. */
  44 static void inet_twsk_kill(struct inet_timewait_sock *tw)
  45 {
  46         struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
  47         spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
  48         struct inet_bind_hashbucket *bhead;
  49
  50         spin_lock(lock);
  51         sk_nulls_del_node_init_rcu((struct sock *)tw);
  52         spin_unlock(lock);
  53
  54         /* Disassociate with bind bucket. */
  55         bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
  56                         hashinfo->bhash_size)];
  57
  58         spin_lock(&bhead->lock);
  59         inet_twsk_bind_unhash(tw, hashinfo);
  60         spin_unlock(&bhead->lock);
  61
  62         atomic_dec(&tw->tw_dr->tw_count);
  63         inet_twsk_put(tw);
  64 }
  65
  66 void inet_twsk_free(struct inet_timewait_sock *tw)
  67 {
  68         struct module *owner = tw->tw_prot->owner;
  69         twsk_destructor((struct sock *)tw);
  70 #ifdef SOCK_REFCNT_DEBUG
  71         pr_debug("%s timewait_sock %p released\n", tw->tw_prot->name, tw);
  72 #endif
  73         kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
  74         module_put(owner);
  75 }
  76
  77 void inet_twsk_put(struct inet_timewait_sock *tw)
  78 {
  79         if (atomic_dec_and_test(&tw->tw_refcnt))
  80                 inet_twsk_free(tw);
  81 }
  82 EXPORT_SYMBOL_GPL(inet_twsk_put);
  83
  84 static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
  85                                    struct hlist_nulls_head *list)
  86 {
  87         hlist_nulls_add_head_rcu(&tw->tw_node, list);
  88 }
  89
  90 static void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
  91                                     struct hlist_head *list)
  92 {
  93         hlist_add_head(&tw->tw_bind_node, list);
  94 }
  95
  96 /*
  97  * Enter the time wait state. This is called with locally disabled BH.
  98  * Essentially we whip up a timewait bucket, copy the relevant info into it
  99  * from the SK, and mess with hash chains and list linkage.
 100  */
 101 void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
 102                            struct inet_hashinfo *hashinfo)
 103 {
 104         const struct inet_sock *inet = inet_sk(sk);
 105         const struct inet_connection_sock *icsk = inet_csk(sk);
 106         struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
 107         spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 108         struct inet_bind_hashbucket *bhead;
 109         /* Step 1: Put TW into bind hash. Original socket stays there too.
 110            Note, that any socket with inet->num != 0 MUST be bound in
 111            binding cache, even if it is closed.
 112          */
 113         bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
 114                         hashinfo->bhash_size)];
 115         spin_lock(&bhead->lock);
 116         tw->tw_tb = icsk->icsk_bind_hash;
 117         WARN_ON(!icsk->icsk_bind_hash);
 118         inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
 119         spin_unlock(&bhead->lock);
 120
 121         spin_lock(lock);
 122
 123         /*
 124          * Step 2: Hash TW into tcp ehash chain.
 125          * Notes :
 126          * - tw_refcnt is set to 4 because :
 127          * - We have one reference from bhash chain.
 128          * - We have one reference from ehash chain.
 129          * - We have one reference from timer.
 130          * - One reference for ourself (our caller will release it).
 131          * We can use atomic_set() because prior spin_lock()/spin_unlock()
 132          * committed into memory all tw fields.
 133          */
 134         atomic_set(&tw->tw_refcnt, 4);
 135         inet_twsk_add_node_rcu(tw, &ehead->chain);
 136
 137         /* Step 3: Remove SK from hash chain */
 138         if (__sk_nulls_del_node_init_rcu(sk))
 139                 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 140
 141         spin_unlock(lock);
 142 }
 143 EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);
 144
 145 static void tw_timer_handler(unsigned long data)
 146 {
 147         struct inet_timewait_sock *tw = (struct inet_timewait_sock *)data;
 148
 149         if (tw->tw_kill)
 150                 NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_TIMEWAITKILLED);
 151         else
 152                 NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_TIMEWAITED);
 153         inet_twsk_kill(tw);
 154 }
 155
 156 struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
 157                                            struct inet_timewait_death_row *dr,
 158                                            const int state)
 159 {
 160         struct inet_timewait_sock *tw;
 161
 162         if (atomic_read(&dr->tw_count) >= dr->sysctl_max_tw_buckets)
 163                 return NULL;
 164
 165         tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
 166                               GFP_ATOMIC);
 167         if (tw) {
 168                 const struct inet_sock *inet = inet_sk(sk);
 169
 170                 kmemcheck_annotate_bitfield(tw, flags);
 171
 172                 tw->tw_dr           = dr;
 173                 /* Give us an identity. */
 174                 tw->tw_daddr        = inet->inet_daddr;
 175                 tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
 176                 tw->tw_bound_dev_if = sk->sk_bound_dev_if;
 177                 tw->tw_tos          = inet->tos;
 178                 tw->tw_num          = inet->inet_num;
 179                 tw->tw_state        = TCP_TIME_WAIT;
 180                 tw->tw_substate     = state;
 181                 tw->tw_sport        = inet->inet_sport;
 182                 tw->tw_dport        = inet->inet_dport;
 183                 tw->tw_family       = sk->sk_family;
 184                 tw->tw_reuse        = sk->sk_reuse;
 185                 tw->tw_hash         = sk->sk_hash;
 186                 tw->tw_ipv6only     = 0;
 187                 tw->tw_transparent  = inet->transparent;
 188                 tw->tw_prot         = sk->sk_prot_creator;
 189                 atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
 190                 twsk_net_set(tw, sock_net(sk));
 191                 setup_timer(&tw->tw_timer, tw_timer_handler, (unsigned long)tw);
 192                 /*
 193                  * Because we use RCU lookups, we should not set tw_refcnt
 194                  * to a non null value before everything is setup for this
 195                  * timewait socket.
 196                  */
 197                 atomic_set(&tw->tw_refcnt, 0);
 198
 199                 __module_get(tw->tw_prot->owner);
 200         }
 201
 202         return tw;
 203 }
 204 EXPORT_SYMBOL_GPL(inet_twsk_alloc);
 205
 206 /* These are always called from BH context.  See callers in
 207  * tcp_input.c to verify this.
 208  */
 209
 210 /* This is for handling early-kills of TIME_WAIT sockets.
 211  * Warning : consume reference.
 212  * Caller should not access tw anymore.
 213  */
 214 void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
 215 {
 216         if (del_timer_sync(&tw->tw_timer))
 217                 inet_twsk_kill(tw);
 218         inet_twsk_put(tw);
 219 }
 220 EXPORT_SYMBOL(inet_twsk_deschedule_put);
 221
 222 void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
 223 {
 224         /* timeout := RTO * 3.5
 225          *
 226          * 3.5 = 1+2+0.5 to wait for two retransmits.
 227          *
 228          * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
 229          * our ACK acking that FIN can be lost. If N subsequent retransmitted
 230          * FINs (or previous seqments) are lost (probability of such event
 231          * is p^(N+1), where p is probability to lose single packet and
 232          * time to detect the loss is about RTO*(2^N - 1) with exponential
 233          * backoff). Normal timewait length is calculated so, that we
 234          * waited at least for one retransmitted FIN (maximal RTO is 120sec).
 235          * [ BTW Linux. following BSD, violates this requirement waiting
 236          *   only for 60sec, we should wait at least for 240 secs.
 237          *   Well, 240 consumes too much of resources 8)
 238          * ]
 239          * This interval is not reduced to catch old duplicate and
 240          * responces to our wandering segments living for two MSLs.
 241          * However, if we use PAWS to detect
 242          * old duplicates, we can reduce the interval to bounds required
 243          * by RTO, rather than MSL. So, if peer understands PAWS, we
 244          * kill tw bucket after 3.5*RTO (it is important that this number
 245          * is greater than TS tick!) and detect old duplicates with help
 246          * of PAWS.
 247          */
 248
 249         tw->tw_kill = timeo <= 4*HZ;
 250         if (!rearm) {
 251                 BUG_ON(mod_timer_pinned(&tw->tw_timer, jiffies + timeo));
 252                 atomic_inc(&tw->tw_dr->tw_count);
 253         } else {
 254                 mod_timer_pending(&tw->tw_timer, jiffies + timeo);
 255         }
 256 }
 257 EXPORT_SYMBOL_GPL(__inet_twsk_schedule);
 258
 259 void inet_twsk_purge(struct inet_hashinfo *hashinfo,
 260                      struct inet_timewait_death_row *twdr, int family)
 261 {
 262         struct inet_timewait_sock *tw;
 263         struct sock *sk;
 264         struct hlist_nulls_node *node;
 265         unsigned int slot;
 266
 267         for (slot = 0; slot <= hashinfo->ehash_mask; slot++) {
 268                 struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
 269 restart_rcu:
 270                 cond_resched();
 271                 rcu_read_lock();
 272 restart:
 273                 sk_nulls_for_each_rcu(sk, node, &head->chain) {
 274                         if (sk->sk_state != TCP_TIME_WAIT)
 275                                 continue;
 276                         tw = inet_twsk(sk);
 277                         if ((tw->tw_family != family) ||
 278                                 atomic_read(&twsk_net(tw)->count))
 279                                 continue;
 280
 281                         if (unlikely(!atomic_inc_not_zero(&tw->tw_refcnt)))
 282                                 continue;
 283
 284                         if (unlikely((tw->tw_family != family) ||
 285                                      atomic_read(&twsk_net(tw)->count))) {
 286                                 inet_twsk_put(tw);
 287                                 goto restart;
 288                         }
 289
 290                         rcu_read_unlock();
 291                         local_bh_disable();
 292                         inet_twsk_deschedule_put(tw);
 293                         local_bh_enable();
 294                         goto restart_rcu;
 295                 }
 296                 /* If the nulls value we got at the end of this lookup is
 297                  * not the expected one, we must restart lookup.
 298                  * We probably met an item that was moved to another chain.
 299                  */
 300                 if (get_nulls_value(node) != slot)
 301                         goto restart;
 302                 rcu_read_unlock();
 303         }
 304 }
 305 EXPORT_SYMBOL_GPL(inet_twsk_purge);