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Linux/net/ipv4/inet_timewait_sock.c

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  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);
306 

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