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         __hlist_del(&tw->tw_bind_node);
  39         tw->tw_tb = NULL;
  40         inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
  41
  42         __hlist_del(&tw->tw_bind2_node);
  43         tw->tw_tb2 = NULL;
  44         inet_bind2_bucket_destroy(hashinfo->bind2_bucket_cachep, tb2);
  45
  46         __sock_put((struct sock *)tw);
  47 }
  48
  49 /* Must be called with locally disabled BHs. */
  50 static void inet_twsk_kill(struct inet_timewait_sock *tw)
  51 {
  52         struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
  53         spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
  54         struct inet_bind_hashbucket *bhead, *bhead2;
  55
  56         spin_lock(lock);
  57         sk_nulls_del_node_init_rcu((struct sock *)tw);
  58         spin_unlock(lock);
  59
  60         /* Disassociate with bind bucket. */
  61         bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
  62                         hashinfo->bhash_size)];
  63         bhead2 = inet_bhashfn_portaddr(hashinfo, (struct sock *)tw,
  64                                        twsk_net(tw), tw->tw_num);
  65
  66         spin_lock(&bhead->lock);
  67         spin_lock(&bhead2->lock);
  68         inet_twsk_bind_unhash(tw, hashinfo);
  69         spin_unlock(&bhead2->lock);
  70         spin_unlock(&bhead->lock);
  71
  72         refcount_dec(&tw->tw_dr->tw_refcount);
  73         inet_twsk_put(tw);
  74 }
  75
  76 void inet_twsk_free(struct inet_timewait_sock *tw)
  77 {
  78         struct module *owner = tw->tw_prot->owner;
  79         twsk_destructor((struct sock *)tw);
  80         kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
  81         module_put(owner);
  82 }
  83
  84 void inet_twsk_put(struct inet_timewait_sock *tw)
  85 {
  86         if (refcount_dec_and_test(&tw->tw_refcnt))
  87                 inet_twsk_free(tw);
  88 }
  89 EXPORT_SYMBOL_GPL(inet_twsk_put);
  90
  91 static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
  92                                    struct hlist_nulls_head *list)
  93 {
  94         hlist_nulls_add_head_rcu(&tw->tw_node, list);
  95 }
  96
  97 static void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
  98                                     struct hlist_head *list)
  99 {
 100         hlist_add_head(&tw->tw_bind_node, list);
 101 }
 102
 103 static void inet_twsk_add_bind2_node(struct inet_timewait_sock *tw,
 104                                      struct hlist_head *list)
 105 {
 106         hlist_add_head(&tw->tw_bind2_node, list);
 107 }
 108
 109 /*
 110  * Enter the time wait state. This is called with locally disabled BH.
 111  * Essentially we whip up a timewait bucket, copy the relevant info into it
 112  * from the SK, and mess with hash chains and list linkage.
 113  */
 114 void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
 115                            struct inet_hashinfo *hashinfo)
 116 {
 117         const struct inet_sock *inet = inet_sk(sk);
 118         const struct inet_connection_sock *icsk = inet_csk(sk);
 119         struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
 120         spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 121         struct inet_bind_hashbucket *bhead, *bhead2;
 122
 123         /* Step 1: Put TW into bind hash. Original socket stays there too.
 124            Note, that any socket with inet->num != 0 MUST be bound in
 125            binding cache, even if it is closed.
 126          */
 127         bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
 128                         hashinfo->bhash_size)];
 129         bhead2 = inet_bhashfn_portaddr(hashinfo, sk, twsk_net(tw), inet->inet_num);
 130
 131         spin_lock(&bhead->lock);
 132         spin_lock(&bhead2->lock);
 133
 134         tw->tw_tb = icsk->icsk_bind_hash;
 135         WARN_ON(!icsk->icsk_bind_hash);
 136         inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
 137
 138         tw->tw_tb2 = icsk->icsk_bind2_hash;
 139         WARN_ON(!icsk->icsk_bind2_hash);
 140         inet_twsk_add_bind2_node(tw, &tw->tw_tb2->deathrow);
 141
 142         spin_unlock(&bhead2->lock);
 143         spin_unlock(&bhead->lock);
 144
 145         spin_lock(lock);
 146
 147         inet_twsk_add_node_rcu(tw, &ehead->chain);
 148
 149         /* Step 3: Remove SK from hash chain */
 150         if (__sk_nulls_del_node_init_rcu(sk))
 151                 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 152
 153         spin_unlock(lock);
 154
 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          * We can use atomic_set() because prior spin_lock()/spin_unlock()
 160          * committed into memory all tw fields.
 161          * Also note that after this point, we lost our implicit reference
 162          * so we are not allowed to use tw anymore.
 163          */
 164         refcount_set(&tw->tw_refcnt, 3);
 165 }
 166 EXPORT_SYMBOL_GPL(inet_twsk_hashdance);
 167
 168 static void tw_timer_handler(struct timer_list *t)
 169 {
 170         struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);
 171
 172         inet_twsk_kill(tw);
 173 }
 174
 175 struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
 176                                            struct inet_timewait_death_row *dr,
 177                                            const int state)
 178 {
 179         struct inet_timewait_sock *tw;
 180
 181         if (refcount_read(&dr->tw_refcount) - 1 >=
 182             READ_ONCE(dr->sysctl_max_tw_buckets))
 183                 return NULL;
 184
 185         tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
 186                               GFP_ATOMIC);
 187         if (tw) {
 188                 const struct inet_sock *inet = inet_sk(sk);
 189
 190                 tw->tw_dr           = dr;
 191                 /* Give us an identity. */
 192                 tw->tw_daddr        = inet->inet_daddr;
 193                 tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
 194                 tw->tw_bound_dev_if = sk->sk_bound_dev_if;
 195                 tw->tw_tos          = inet->tos;
 196                 tw->tw_num          = inet->inet_num;
 197                 tw->tw_state        = TCP_TIME_WAIT;
 198                 tw->tw_substate     = state;
 199                 tw->tw_sport        = inet->inet_sport;
 200                 tw->tw_dport        = inet->inet_dport;
 201                 tw->tw_family       = sk->sk_family;
 202                 tw->tw_reuse        = sk->sk_reuse;
 203                 tw->tw_reuseport    = sk->sk_reuseport;
 204                 tw->tw_hash         = sk->sk_hash;
 205                 tw->tw_ipv6only     = 0;
 206                 tw->tw_transparent  = inet_test_bit(TRANSPARENT, sk);
 207                 tw->tw_prot         = sk->sk_prot_creator;
 208                 atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
 209                 twsk_net_set(tw, sock_net(sk));
 210                 timer_setup(&tw->tw_timer, tw_timer_handler, TIMER_PINNED);
 211                 /*
 212                  * Because we use RCU lookups, we should not set tw_refcnt
 213                  * to a non null value before everything is setup for this
 214                  * timewait socket.
 215                  */
 216                 refcount_set(&tw->tw_refcnt, 0);
 217
 218                 __module_get(tw->tw_prot->owner);
 219         }
 220
 221         return tw;
 222 }
 223 EXPORT_SYMBOL_GPL(inet_twsk_alloc);
 224
 225 /* These are always called from BH context.  See callers in
 226  * tcp_input.c to verify this.
 227  */
 228
 229 /* This is for handling early-kills of TIME_WAIT sockets.
 230  * Warning : consume reference.
 231  * Caller should not access tw anymore.
 232  */
 233 void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
 234 {
 235         if (del_timer_sync(&tw->tw_timer))
 236                 inet_twsk_kill(tw);
 237         inet_twsk_put(tw);
 238 }
 239 EXPORT_SYMBOL(inet_twsk_deschedule_put);
 240
 241 void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
 242 {
 243         /* timeout := RTO * 3.5
 244          *
 245          * 3.5 = 1+2+0.5 to wait for two retransmits.
 246          *
 247          * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
 248          * our ACK acking that FIN can be lost. If N subsequent retransmitted
 249          * FINs (or previous seqments) are lost (probability of such event
 250          * is p^(N+1), where p is probability to lose single packet and
 251          * time to detect the loss is about RTO*(2^N - 1) with exponential
 252          * backoff). Normal timewait length is calculated so, that we
 253          * waited at least for one retransmitted FIN (maximal RTO is 120sec).
 254          * [ BTW Linux. following BSD, violates this requirement waiting
 255          *   only for 60sec, we should wait at least for 240 secs.
 256          *   Well, 240 consumes too much of resources 8)
 257          * ]
 258          * This interval is not reduced to catch old duplicate and
 259          * responces to our wandering segments living for two MSLs.
 260          * However, if we use PAWS to detect
 261          * old duplicates, we can reduce the interval to bounds required
 262          * by RTO, rather than MSL. So, if peer understands PAWS, we
 263          * kill tw bucket after 3.5*RTO (it is important that this number
 264          * is greater than TS tick!) and detect old duplicates with help
 265          * of PAWS.
 266          */
 267
 268         if (!rearm) {
 269                 bool kill = timeo <= 4*HZ;
 270
 271                 __NET_INC_STATS(twsk_net(tw), kill ? LINUX_MIB_TIMEWAITKILLED :
 272                                                      LINUX_MIB_TIMEWAITED);
 273                 BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
 274                 refcount_inc(&tw->tw_dr->tw_refcount);
 275         } else {
 276                 mod_timer_pending(&tw->tw_timer, jiffies + timeo);
 277         }
 278 }
 279 EXPORT_SYMBOL_GPL(__inet_twsk_schedule);
 280
 281 void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family)
 282 {
 283         struct inet_timewait_sock *tw;
 284         struct sock *sk;
 285         struct hlist_nulls_node *node;
 286         unsigned int slot;
 287
 288         for (slot = 0; slot <= hashinfo->ehash_mask; slot++) {
 289                 struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
 290 restart_rcu:
 291                 cond_resched();
 292                 rcu_read_lock();
 293 restart:
 294                 sk_nulls_for_each_rcu(sk, node, &head->chain) {
 295                         if (sk->sk_state != TCP_TIME_WAIT) {
 296                                 /* A kernel listener socket might not hold refcnt for net,
 297                                  * so reqsk_timer_handler() could be fired after net is
 298                                  * freed.  Userspace listener and reqsk never exist here.
 299                                  */
 300                                 if (unlikely(sk->sk_state == TCP_NEW_SYN_RECV &&
 301                                              hashinfo->pernet)) {
 302                                         struct request_sock *req = inet_reqsk(sk);
 303
 304                                         inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req);
 305                                 }
 306
 307                                 continue;
 308                         }
 309
 310                         tw = inet_twsk(sk);
 311                         if ((tw->tw_family != family) ||
 312                                 refcount_read(&twsk_net(tw)->ns.count))
 313                                 continue;
 314
 315                         if (unlikely(!refcount_inc_not_zero(&tw->tw_refcnt)))
 316                                 continue;
 317
 318                         if (unlikely((tw->tw_family != family) ||
 319                                      refcount_read(&twsk_net(tw)->ns.count))) {
 320                                 inet_twsk_put(tw);
 321                                 goto restart;
 322                         }
 323
 324                         rcu_read_unlock();
 325                         local_bh_disable();
 326                         inet_twsk_deschedule_put(tw);
 327                         local_bh_enable();
 328                         goto restart_rcu;
 329                 }
 330                 /* If the nulls value we got at the end of this lookup is
 331                  * not the expected one, we must restart lookup.
 332                  * We probably met an item that was moved to another chain.
 333                  */
 334                 if (get_nulls_value(node) != slot)
 335                         goto restart;
 336                 rcu_read_unlock();
 337         }
 338 }
 339 EXPORT_SYMBOL_GPL(inet_twsk_purge);