net/ipv4/inet_timewait_sock.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   4  *              operating system.  INET is implemented using the  BSD Socket
   5  *              interface as the means of communication with the user level.
   6  *
   7  *              Generic TIME_WAIT sockets functions
   8  *
   9  *              From code orinally in TCP
  10  */
  11
  12 #include <linux/kernel.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_bind2_bucket *tb2 = tw->tw_tb2;
  33         struct inet_bind_bucket *tb = tw->tw_tb;
  34
  35         if (!tb)
  36                 return;
  37
  38         __sk_del_bind_node((struct sock *)tw);
  39         tw->tw_tb = NULL;
  40         tw->tw_tb2 = NULL;
  41         inet_bind2_bucket_destroy(hashinfo->bind2_bucket_cachep, tb2);
  42         inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
  43
  44         __sock_put((struct sock *)tw);
  45 }
  46
  47 /* Must be called with locally disabled BHs. */
  48 static void inet_twsk_kill(struct inet_timewait_sock *tw)
  49 {
  50         struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
  51         spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
  52         struct inet_bind_hashbucket *bhead, *bhead2;
  53
  54         spin_lock(lock);
  55         sk_nulls_del_node_init_rcu((struct sock *)tw);
  56         spin_unlock(lock);
  57
  58         /* Disassociate with bind bucket. */
  59         bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
  60                         hashinfo->bhash_size)];
  61         bhead2 = inet_bhashfn_portaddr(hashinfo, (struct sock *)tw,
  62                                        twsk_net(tw), tw->tw_num);
  63
  64         spin_lock(&bhead->lock);
  65         spin_lock(&bhead2->lock);
  66         inet_twsk_bind_unhash(tw, hashinfo);
  67         spin_unlock(&bhead2->lock);
  68         spin_unlock(&bhead->lock);
  69
  70         refcount_dec(&tw->tw_dr->tw_refcount);
  71         inet_twsk_put(tw);
  72 }
  73
  74 void inet_twsk_free(struct inet_timewait_sock *tw)
  75 {
  76         struct module *owner = tw->tw_prot->owner;
  77         twsk_destructor((struct sock *)tw);
  78         kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
  79         module_put(owner);
  80 }
  81
  82 void inet_twsk_put(struct inet_timewait_sock *tw)
  83 {
  84         if (refcount_dec_and_test(&tw->tw_refcnt))
  85                 inet_twsk_free(tw);
  86 }
  87 EXPORT_SYMBOL_GPL(inet_twsk_put);
  88
  89 static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
  90                                    struct hlist_nulls_head *list)
  91 {
  92         hlist_nulls_add_head_rcu(&tw->tw_node, list);
  93 }
  94
  95 static void inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo)
  96 {
  97         __inet_twsk_schedule(tw, timeo, false);
  98 }
  99
 100 /*
 101  * Enter the time wait state.
 102  * Essentially we whip up a timewait bucket, copy the relevant info into it
 103  * from the SK, and mess with hash chains and list linkage.
 104  *
 105  * The caller must not access @tw anymore after this function returns.
 106  */
 107 void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw,
 108                                   struct sock *sk,
 109                                   struct inet_hashinfo *hashinfo,
 110                                   int timeo)
 111 {
 112         const struct inet_sock *inet = inet_sk(sk);
 113         const struct inet_connection_sock *icsk = inet_csk(sk);
 114         struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
 115         spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 116         struct inet_bind_hashbucket *bhead, *bhead2;
 117
 118         /* Step 1: Put TW into bind hash. Original socket stays there too.
 119            Note, that any socket with inet->num != 0 MUST be bound in
 120            binding cache, even if it is closed.
 121          */
 122         bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
 123                         hashinfo->bhash_size)];
 124         bhead2 = inet_bhashfn_portaddr(hashinfo, sk, twsk_net(tw), inet->inet_num);
 125
 126         local_bh_disable();
 127         spin_lock(&bhead->lock);
 128         spin_lock(&bhead2->lock);
 129
 130         tw->tw_tb = icsk->icsk_bind_hash;
 131         WARN_ON(!icsk->icsk_bind_hash);
 132
 133         tw->tw_tb2 = icsk->icsk_bind2_hash;
 134         WARN_ON(!icsk->icsk_bind2_hash);
 135         sk_add_bind_node((struct sock *)tw, &tw->tw_tb2->owners);
 136
 137         spin_unlock(&bhead2->lock);
 138         spin_unlock(&bhead->lock);
 139
 140         spin_lock(lock);
 141
 142         /* Step 2: Hash TW into tcp ehash chain */
 143         inet_twsk_add_node_rcu(tw, &ehead->chain);
 144
 145         /* Step 3: Remove SK from hash chain */
 146         if (__sk_nulls_del_node_init_rcu(sk))
 147                 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 148
 149
 150         /* Ensure above writes are committed into memory before updating the
 151          * refcount.
 152          * Provides ordering vs later refcount_inc().
 153          */
 154         smp_wmb();
 155         /* tw_refcnt is set to 3 because we have :
 156          * - one reference for bhash chain.
 157          * - one reference for ehash chain.
 158          * - one reference for timer.
 159          * Also note that after this point, we lost our implicit reference
 160          * so we are not allowed to use tw anymore.
 161          */
 162         refcount_set(&tw->tw_refcnt, 3);
 163
 164         inet_twsk_schedule(tw, timeo);
 165
 166         spin_unlock(lock);
 167         local_bh_enable();
 168 }
 169 EXPORT_SYMBOL_GPL(inet_twsk_hashdance_schedule);
 170
 171 static void tw_timer_handler(struct timer_list *t)
 172 {
 173         struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);
 174
 175         inet_twsk_kill(tw);
 176 }
 177
 178 struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
 179                                            struct inet_timewait_death_row *dr,
 180                                            const int state)
 181 {
 182         struct inet_timewait_sock *tw;
 183
 184         if (refcount_read(&dr->tw_refcount) - 1 >=
 185             READ_ONCE(dr->sysctl_max_tw_buckets))
 186                 return NULL;
 187
 188         tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
 189                               GFP_ATOMIC);
 190         if (tw) {
 191                 const struct inet_sock *inet = inet_sk(sk);
 192
 193                 tw->tw_dr           = dr;
 194                 /* Give us an identity. */
 195                 tw->tw_daddr        = inet->inet_daddr;
 196                 tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
 197                 tw->tw_bound_dev_if = sk->sk_bound_dev_if;
 198                 tw->tw_tos          = inet->tos;
 199                 tw->tw_num          = inet->inet_num;
 200                 tw->tw_state        = TCP_TIME_WAIT;
 201                 tw->tw_substate     = state;
 202                 tw->tw_sport        = inet->inet_sport;
 203                 tw->tw_dport        = inet->inet_dport;
 204                 tw->tw_family       = sk->sk_family;
 205                 tw->tw_reuse        = sk->sk_reuse;
 206                 tw->tw_reuseport    = sk->sk_reuseport;
 207                 tw->tw_hash         = sk->sk_hash;
 208                 tw->tw_ipv6only     = 0;
 209                 tw->tw_transparent  = inet_test_bit(TRANSPARENT, sk);
 210                 tw->tw_prot         = sk->sk_prot_creator;
 211                 atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
 212                 twsk_net_set(tw, sock_net(sk));
 213                 timer_setup(&tw->tw_timer, tw_timer_handler, 0);
 214                 /*
 215                  * Because we use RCU lookups, we should not set tw_refcnt
 216                  * to a non null value before everything is setup for this
 217                  * timewait socket.
 218                  */
 219                 refcount_set(&tw->tw_refcnt, 0);
 220
 221                 __module_get(tw->tw_prot->owner);
 222         }
 223
 224         return tw;
 225 }
 226 EXPORT_SYMBOL_GPL(inet_twsk_alloc);
 227
 228 /* These are always called from BH context.  See callers in
 229  * tcp_input.c to verify this.
 230  */
 231
 232 /* This is for handling early-kills of TIME_WAIT sockets.
 233  * Warning : consume reference.
 234  * Caller should not access tw anymore.
 235  */
 236 void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
 237 {
 238         struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
 239         spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
 240
 241         /* inet_twsk_purge() walks over all sockets, including tw ones,
 242          * and removes them via inet_twsk_deschedule_put() after a
 243          * refcount_inc_not_zero().
 244          *
 245          * inet_twsk_hashdance_schedule() must (re)init the refcount before
 246          * arming the timer, i.e. inet_twsk_purge can obtain a reference to
 247          * a twsk that did not yet schedule the timer.
 248          *
 249          * The ehash lock synchronizes these two:
 250          * After acquiring the lock, the timer is always scheduled (else
 251          * timer_shutdown returns false), because hashdance_schedule releases
 252          * the ehash lock only after completing the timer initialization.
 253          *
 254          * Without grabbing the ehash lock, we get:
 255          * 1) cpu x sets twsk refcount to 3
 256          * 2) cpu y bumps refcount to 4
 257          * 3) cpu y calls inet_twsk_deschedule_put() and shuts timer down
 258          * 4) cpu x tries to start timer, but mod_timer is a noop post-shutdown
 259          * -> timer refcount is never decremented.
 260          */
 261         spin_lock(lock);
 262         /*  Makes sure hashdance_schedule() has completed */
 263         spin_unlock(lock);
 264
 265         if (timer_shutdown_sync(&tw->tw_timer))
 266                 inet_twsk_kill(tw);
 267         inet_twsk_put(tw);
 268 }
 269 EXPORT_SYMBOL(inet_twsk_deschedule_put);
 270
 271 void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
 272 {
 273         /* timeout := RTO * 3.5
 274          *
 275          * 3.5 = 1+2+0.5 to wait for two retransmits.
 276          *
 277          * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
 278          * our ACK acking that FIN can be lost. If N subsequent retransmitted
 279          * FINs (or previous seqments) are lost (probability of such event
 280          * is p^(N+1), where p is probability to lose single packet and
 281          * time to detect the loss is about RTO*(2^N - 1) with exponential
 282          * backoff). Normal timewait length is calculated so, that we
 283          * waited at least for one retransmitted FIN (maximal RTO is 120sec).
 284          * [ BTW Linux. following BSD, violates this requirement waiting
 285          *   only for 60sec, we should wait at least for 240 secs.
 286          *   Well, 240 consumes too much of resources 8)
 287          * ]
 288          * This interval is not reduced to catch old duplicate and
 289          * responces to our wandering segments living for two MSLs.
 290          * However, if we use PAWS to detect
 291          * old duplicates, we can reduce the interval to bounds required
 292          * by RTO, rather than MSL. So, if peer understands PAWS, we
 293          * kill tw bucket after 3.5*RTO (it is important that this number
 294          * is greater than TS tick!) and detect old duplicates with help
 295          * of PAWS.
 296          */
 297
 298         if (!rearm) {
 299                 bool kill = timeo <= 4*HZ;
 300
 301                 __NET_INC_STATS(twsk_net(tw), kill ? LINUX_MIB_TIMEWAITKILLED :
 302                                                      LINUX_MIB_TIMEWAITED);
 303                 BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
 304                 refcount_inc(&tw->tw_dr->tw_refcount);
 305         } else {
 306                 mod_timer_pending(&tw->tw_timer, jiffies + timeo);
 307         }
 308 }
 309 EXPORT_SYMBOL_GPL(__inet_twsk_schedule);
 310
 311 /* Remove all non full sockets (TIME_WAIT and NEW_SYN_RECV) for dead netns */
 312 void inet_twsk_purge(struct inet_hashinfo *hashinfo)
 313 {
 314         struct inet_ehash_bucket *head = &hashinfo->ehash[0];
 315         unsigned int ehash_mask = hashinfo->ehash_mask;
 316         struct hlist_nulls_node *node;
 317         unsigned int slot;
 318         struct sock *sk;
 319
 320         for (slot = 0; slot <= ehash_mask; slot++, head++) {
 321                 if (hlist_nulls_empty(&head->chain))
 322                         continue;
 323
 324 restart_rcu:
 325                 cond_resched();
 326                 rcu_read_lock();
 327 restart:
 328                 sk_nulls_for_each_rcu(sk, node, &head->chain) {
 329                         int state = inet_sk_state_load(sk);
 330
 331                         if ((1 << state) & ~(TCPF_TIME_WAIT |
 332                                              TCPF_NEW_SYN_RECV))
 333                                 continue;
 334
 335                         if (refcount_read(&sock_net(sk)->ns.count))
 336                                 continue;
 337
 338                         if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
 339                                 continue;
 340
 341                         if (refcount_read(&sock_net(sk)->ns.count)) {
 342                                 sock_gen_put(sk);
 343                                 goto restart;
 344                         }
 345
 346                         rcu_read_unlock();
 347                         local_bh_disable();
 348                         if (state == TCP_TIME_WAIT) {
 349                                 inet_twsk_deschedule_put(inet_twsk(sk));
 350                         } else {
 351                                 struct request_sock *req = inet_reqsk(sk);
 352
 353                                 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener,
 354                                                                   req);
 355                         }
 356                         local_bh_enable();
 357                         goto restart_rcu;
 358                 }
 359                 /* If the nulls value we got at the end of this lookup is
 360                  * not the expected one, we must restart lookup.
 361                  * We probably met an item that was moved to another chain.
 362                  */
 363                 if (get_nulls_value(node) != slot)
 364                         goto restart;
 365                 rcu_read_unlock();
 366         }
 367 }
 368 EXPORT_SYMBOL_GPL(inet_twsk_purge);