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 */
29void 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. */
44static 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
66void 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
77void inet_twsk_put(struct inet_timewait_sock *tw)
78{
79	if (atomic_dec_and_test(&tw->tw_refcnt))
80		inet_twsk_free(tw);
81}
82EXPORT_SYMBOL_GPL(inet_twsk_put);
83
84static 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
90static 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 */
101void __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}
143EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);
144
145static 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
156struct 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}
204EXPORT_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 */
214void 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}
220EXPORT_SYMBOL(inet_twsk_deschedule_put);
221
222void __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}
257EXPORT_SYMBOL_GPL(__inet_twsk_schedule);
258
259void 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];
269restart_rcu:
270		cond_resched();
271		rcu_read_lock();
272restart:
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}
305EXPORT_SYMBOL_GPL(inet_twsk_purge);
306