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_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 (refcount_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         inet_twsk_add_node_rcu(tw, &ehead->chain);
 124
 125         /* Step 3: Remove SK from hash chain */
 126         if (__sk_nulls_del_node_init_rcu(sk))
 127                 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 128
 129         spin_unlock(lock);
 130
 131         /* tw_refcnt is set to 3 because we have :
 132          * - one reference for bhash chain.
 133          * - one reference for ehash chain.
 134          * - one reference for timer.
 135          * We can use atomic_set() because prior spin_lock()/spin_unlock()
 136          * committed into memory all tw fields.
 137          * Also note that after this point, we lost our implicit reference
 138          * so we are not allowed to use tw anymore.
 139          */
 140         refcount_set(&tw->tw_refcnt, 3);
 141 }
 142 EXPORT_SYMBOL_GPL(inet_twsk_hashdance);
 143
 144 static void tw_timer_handler(struct timer_list *t)
 145 {
 146         struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);
 147
 148         if (tw->tw_kill)
 149                 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITKILLED);
 150         else
 151                 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITED);
 152         inet_twsk_kill(tw);
 153 }
 154
 155 struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
 156                                            struct inet_timewait_death_row *dr,
 157                                            const int state)
 158 {
 159         struct inet_timewait_sock *tw;
 160
 161         if (atomic_read(&dr->tw_count) >= dr->sysctl_max_tw_buckets)
 162                 return NULL;
 163
 164         tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
 165                               GFP_ATOMIC);
 166         if (tw) {
 167                 const struct inet_sock *inet = inet_sk(sk);
 168
 169                 tw->tw_dr           = dr;
 170                 /* Give us an identity. */
 171                 tw->tw_daddr        = inet->inet_daddr;
 172                 tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
 173                 tw->tw_bound_dev_if = sk->sk_bound_dev_if;
 174                 tw->tw_tos          = inet->tos;
 175                 tw->tw_num          = inet->inet_num;
 176                 tw->tw_state        = TCP_TIME_WAIT;
 177                 tw->tw_substate     = state;
 178                 tw->tw_sport        = inet->inet_sport;
 179                 tw->tw_dport        = inet->inet_dport;
 180                 tw->tw_family       = sk->sk_family;
 181                 tw->tw_reuse        = sk->sk_reuse;
 182                 tw->tw_reuseport    = sk->sk_reuseport;
 183                 tw->tw_hash         = sk->sk_hash;
 184                 tw->tw_ipv6only     = 0;
 185                 tw->tw_transparent  = inet->transparent;
 186                 tw->tw_prot         = sk->sk_prot_creator;
 187                 atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
 188                 twsk_net_set(tw, sock_net(sk));
 189                 timer_setup(&tw->tw_timer, tw_timer_handler, TIMER_PINNED);
 190                 /*
 191                  * Because we use RCU lookups, we should not set tw_refcnt
 192                  * to a non null value before everything is setup for this
 193                  * timewait socket.
 194                  */
 195                 refcount_set(&tw->tw_refcnt, 0);
 196
 197                 __module_get(tw->tw_prot->owner);
 198         }
 199
 200         return tw;
 201 }
 202 EXPORT_SYMBOL_GPL(inet_twsk_alloc);
 203
 204 /* These are always called from BH context.  See callers in
 205  * tcp_input.c to verify this.
 206  */
 207
 208 /* This is for handling early-kills of TIME_WAIT sockets.
 209  * Warning : consume reference.
 210  * Caller should not access tw anymore.
 211  */
 212 void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
 213 {
 214         if (del_timer_sync(&tw->tw_timer))
 215                 inet_twsk_kill(tw);
 216         inet_twsk_put(tw);
 217 }
 218 EXPORT_SYMBOL(inet_twsk_deschedule_put);
 219
 220 void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
 221 {
 222         /* timeout := RTO * 3.5
 223          *
 224          * 3.5 = 1+2+0.5 to wait for two retransmits.
 225          *
 226          * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
 227          * our ACK acking that FIN can be lost. If N subsequent retransmitted
 228          * FINs (or previous seqments) are lost (probability of such event
 229          * is p^(N+1), where p is probability to lose single packet and
 230          * time to detect the loss is about RTO*(2^N - 1) with exponential
 231          * backoff). Normal timewait length is calculated so, that we
 232          * waited at least for one retransmitted FIN (maximal RTO is 120sec).
 233          * [ BTW Linux. following BSD, violates this requirement waiting
 234          *   only for 60sec, we should wait at least for 240 secs.
 235          *   Well, 240 consumes too much of resources 8)
 236          * ]
 237          * This interval is not reduced to catch old duplicate and
 238          * responces to our wandering segments living for two MSLs.
 239          * However, if we use PAWS to detect
 240          * old duplicates, we can reduce the interval to bounds required
 241          * by RTO, rather than MSL. So, if peer understands PAWS, we
 242          * kill tw bucket after 3.5*RTO (it is important that this number
 243          * is greater than TS tick!) and detect old duplicates with help
 244          * of PAWS.
 245          */
 246
 247         tw->tw_kill = timeo <= 4*HZ;
 248         if (!rearm) {
 249                 BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
 250                 atomic_inc(&tw->tw_dr->tw_count);
 251         } else {
 252                 mod_timer_pending(&tw->tw_timer, jiffies + timeo);
 253         }
 254 }
 255 EXPORT_SYMBOL_GPL(__inet_twsk_schedule);
 256
 257 void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family)
 258 {
 259         struct inet_timewait_sock *tw;
 260         struct sock *sk;
 261         struct hlist_nulls_node *node;
 262         unsigned int slot;
 263
 264         for (slot = 0; slot <= hashinfo->ehash_mask; slot++) {
 265                 struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
 266 restart_rcu:
 267                 cond_resched();
 268                 rcu_read_lock();
 269 restart:
 270                 sk_nulls_for_each_rcu(sk, node, &head->chain) {
 271                         if (sk->sk_state != TCP_TIME_WAIT)
 272                                 continue;
 273                         tw = inet_twsk(sk);
 274                         if ((tw->tw_family != family) ||
 275                                 refcount_read(&twsk_net(tw)->ns.count))
 276                                 continue;
 277
 278                         if (unlikely(!refcount_inc_not_zero(&tw->tw_refcnt)))
 279                                 continue;
 280
 281                         if (unlikely((tw->tw_family != family) ||
 282                                      refcount_read(&twsk_net(tw)->ns.count))) {
 283                                 inet_twsk_put(tw);
 284                                 goto restart;
 285                         }
 286
 287                         rcu_read_unlock();
 288                         local_bh_disable();
 289                         inet_twsk_deschedule_put(tw);
 290                         local_bh_enable();
 291                         goto restart_rcu;
 292                 }
 293                 /* If the nulls value we got at the end of this lookup is
 294                  * not the expected one, we must restart lookup.
 295                  * We probably met an item that was moved to another chain.
 296                  */
 297                 if (get_nulls_value(node) != slot)
 298                         goto restart;
 299                 rcu_read_unlock();
 300         }
 301 }
 302 EXPORT_SYMBOL_GPL(inet_twsk_purge);