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Arnaldo Carvalho de Melo0e875062005-06-18 22:47:59 -07001/*
2 * NET Generic infrastructure for Network protocols.
3 *
4 * Authors: Arnaldo Carvalho de Melo <acme@conectiva.com.br>
5 *
6 * From code originally in include/net/tcp.h
7 *
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License
10 * as published by the Free Software Foundation; either version
11 * 2 of the License, or (at your option) any later version.
12 */
13
14#include <linux/module.h>
15#include <linux/random.h>
16#include <linux/slab.h>
17#include <linux/string.h>
Jerry Chu83368862012-08-31 12:29:12 +000018#include <linux/tcp.h>
Eric Dumazet72a3eff2006-11-16 02:30:37 -080019#include <linux/vmalloc.h>
Arnaldo Carvalho de Melo0e875062005-06-18 22:47:59 -070020
21#include <net/request_sock.h>
22
David S. Millere52c1f12005-06-18 22:49:40 -070023/*
24 * Maximum number of SYN_RECV sockets in queue per LISTEN socket.
25 * One SYN_RECV socket costs about 80bytes on a 32bit machine.
26 * It would be better to replace it with a global counter for all sockets
27 * but then some measure against one socket starving all other sockets
28 * would be needed.
29 *
Peter Pan(潘卫平)99b53bd2011-12-05 21:39:41 +000030 * The minimum value of it is 128. Experiments with real servers show that
David S. Millere52c1f12005-06-18 22:49:40 -070031 * it is absolutely not enough even at 100conn/sec. 256 cures most
Peter Pan(潘卫平)99b53bd2011-12-05 21:39:41 +000032 * of problems.
33 * This value is adjusted to 128 for low memory machines,
34 * and it will increase in proportion to the memory of machine.
Eric Dumazet72a3eff2006-11-16 02:30:37 -080035 * Note : Dont forget somaxconn that may limit backlog too.
David S. Millere52c1f12005-06-18 22:49:40 -070036 */
37int sysctl_max_syn_backlog = 256;
David S. Miller493f3772010-12-02 12:14:29 -080038EXPORT_SYMBOL(sysctl_max_syn_backlog);
David S. Millere52c1f12005-06-18 22:49:40 -070039
Arnaldo Carvalho de Melo0e875062005-06-18 22:47:59 -070040int reqsk_queue_alloc(struct request_sock_queue *queue,
Eric Dumazet72a3eff2006-11-16 02:30:37 -080041 unsigned int nr_table_entries)
Arnaldo Carvalho de Melo0e875062005-06-18 22:47:59 -070042{
Eric Dumazet72a3eff2006-11-16 02:30:37 -080043 size_t lopt_size = sizeof(struct listen_sock);
44 struct listen_sock *lopt;
Arnaldo Carvalho de Melo0e875062005-06-18 22:47:59 -070045
Eric Dumazet72a3eff2006-11-16 02:30:37 -080046 nr_table_entries = min_t(u32, nr_table_entries, sysctl_max_syn_backlog);
47 nr_table_entries = max_t(u32, nr_table_entries, 8);
48 nr_table_entries = roundup_pow_of_two(nr_table_entries + 1);
49 lopt_size += nr_table_entries * sizeof(struct request_sock *);
50 if (lopt_size > PAGE_SIZE)
Eric Dumazet7a1c8e52010-11-20 07:46:35 +000051 lopt = vzalloc(lopt_size);
Eric Dumazet72a3eff2006-11-16 02:30:37 -080052 else
53 lopt = kzalloc(lopt_size, GFP_KERNEL);
Arnaldo Carvalho de Melo0e875062005-06-18 22:47:59 -070054 if (lopt == NULL)
55 return -ENOMEM;
56
Eric Dumazet72a3eff2006-11-16 02:30:37 -080057 for (lopt->max_qlen_log = 3;
58 (1 << lopt->max_qlen_log) < nr_table_entries;
Arnaldo Carvalho de Melo0e875062005-06-18 22:47:59 -070059 lopt->max_qlen_log++);
60
61 get_random_bytes(&lopt->hash_rnd, sizeof(lopt->hash_rnd));
62 rwlock_init(&queue->syn_wait_lock);
Norbert Kiesel3eb48012006-03-26 17:39:55 -080063 queue->rskq_accept_head = NULL;
Arnaldo Carvalho de Melo83e36092005-08-09 19:33:31 -070064 lopt->nr_table_entries = nr_table_entries;
Arnaldo Carvalho de Melo0e875062005-06-18 22:47:59 -070065
66 write_lock_bh(&queue->syn_wait_lock);
67 queue->listen_opt = lopt;
68 write_unlock_bh(&queue->syn_wait_lock);
69
70 return 0;
71}
72
Pavel Emelyanovdab6ba32007-11-15 02:57:06 -080073void __reqsk_queue_destroy(struct request_sock_queue *queue)
74{
75 struct listen_sock *lopt;
76 size_t lopt_size;
77
78 /*
79 * this is an error recovery path only
80 * no locking needed and the lopt is not NULL
81 */
82
83 lopt = queue->listen_opt;
84 lopt_size = sizeof(struct listen_sock) +
85 lopt->nr_table_entries * sizeof(struct request_sock *);
86
87 if (lopt_size > PAGE_SIZE)
88 vfree(lopt);
89 else
90 kfree(lopt);
91}
92
Pavel Emelyanovdab6ba32007-11-15 02:57:06 -080093static inline struct listen_sock *reqsk_queue_yank_listen_sk(
94 struct request_sock_queue *queue)
95{
96 struct listen_sock *lopt;
97
98 write_lock_bh(&queue->syn_wait_lock);
99 lopt = queue->listen_opt;
100 queue->listen_opt = NULL;
101 write_unlock_bh(&queue->syn_wait_lock);
102
103 return lopt;
104}
105
Arnaldo Carvalho de Melo83e36092005-08-09 19:33:31 -0700106void reqsk_queue_destroy(struct request_sock_queue *queue)
107{
108 /* make all the listen_opt local to us */
109 struct listen_sock *lopt = reqsk_queue_yank_listen_sk(queue);
Eric Dumazet72a3eff2006-11-16 02:30:37 -0800110 size_t lopt_size = sizeof(struct listen_sock) +
111 lopt->nr_table_entries * sizeof(struct request_sock *);
Arnaldo Carvalho de Melo83e36092005-08-09 19:33:31 -0700112
113 if (lopt->qlen != 0) {
Eric Dumazet72a3eff2006-11-16 02:30:37 -0800114 unsigned int i;
Arnaldo Carvalho de Melo83e36092005-08-09 19:33:31 -0700115
116 for (i = 0; i < lopt->nr_table_entries; i++) {
117 struct request_sock *req;
118
119 while ((req = lopt->syn_table[i]) != NULL) {
120 lopt->syn_table[i] = req->dl_next;
121 lopt->qlen--;
122 reqsk_free(req);
123 }
124 }
125 }
126
Ilpo Järvinen547b7922008-07-25 21:43:18 -0700127 WARN_ON(lopt->qlen != 0);
Eric Dumazet72a3eff2006-11-16 02:30:37 -0800128 if (lopt_size > PAGE_SIZE)
129 vfree(lopt);
130 else
131 kfree(lopt);
Arnaldo Carvalho de Melo83e36092005-08-09 19:33:31 -0700132}
133
Jerry Chu83368862012-08-31 12:29:12 +0000134/*
135 * This function is called to set a Fast Open socket's "fastopen_rsk" field
136 * to NULL when a TFO socket no longer needs to access the request_sock.
137 * This happens only after 3WHS has been either completed or aborted (e.g.,
138 * RST is received).
139 *
140 * Before TFO, a child socket is created only after 3WHS is completed,
141 * hence it never needs to access the request_sock. things get a lot more
142 * complex with TFO. A child socket, accepted or not, has to access its
143 * request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts,
144 * until 3WHS is either completed or aborted. Afterwards the req will stay
145 * until either the child socket is accepted, or in the rare case when the
146 * listener is closed before the child is accepted.
147 *
148 * In short, a request socket is only freed after BOTH 3WHS has completed
149 * (or aborted) and the child socket has been accepted (or listener closed).
150 * When a child socket is accepted, its corresponding req->sk is set to
151 * NULL since it's no longer needed. More importantly, "req->sk == NULL"
152 * will be used by the code below to determine if a child socket has been
153 * accepted or not, and the check is protected by the fastopenq->lock
154 * described below.
155 *
156 * Note that fastopen_rsk is only accessed from the child socket's context
157 * with its socket lock held. But a request_sock (req) can be accessed by
158 * both its child socket through fastopen_rsk, and a listener socket through
159 * icsk_accept_queue.rskq_accept_head. To protect the access a simple spin
160 * lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created.
161 * only in the rare case when both the listener and the child locks are held,
162 * e.g., in inet_csk_listen_stop() do we not need to acquire the lock.
163 * The lock also protects other fields such as fastopenq->qlen, which is
164 * decremented by this function when fastopen_rsk is no longer needed.
165 *
166 * Note that another solution was to simply use the existing socket lock
167 * from the listener. But first socket lock is difficult to use. It is not
168 * a simple spin lock - one must consider sock_owned_by_user() and arrange
169 * to use sk_add_backlog() stuff. But what really makes it infeasible is the
170 * locking hierarchy violation. E.g., inet_csk_listen_stop() may try to
171 * acquire a child's lock while holding listener's socket lock. A corner
172 * case might also exist in tcp_v4_hnd_req() that will trigger this locking
173 * order.
174 *
175 * When a TFO req is created, it needs to sock_hold its listener to prevent
176 * the latter data structure from going away.
177 *
178 * This function also sets "treq->listener" to NULL and unreference listener
179 * socket. treq->listener is used by the listener so it is protected by the
180 * fastopenq->lock in this function.
181 */
182void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
183 bool reset)
184{
185 struct sock *lsk = tcp_rsk(req)->listener;
186 struct fastopen_queue *fastopenq =
187 inet_csk(lsk)->icsk_accept_queue.fastopenq;
188
Jerry Chu83368862012-08-31 12:29:12 +0000189 tcp_sk(sk)->fastopen_rsk = NULL;
190 spin_lock_bh(&fastopenq->lock);
191 fastopenq->qlen--;
192 tcp_rsk(req)->listener = NULL;
193 if (req->sk) /* the child socket hasn't been accepted yet */
194 goto out;
195
196 if (!reset || lsk->sk_state != TCP_LISTEN) {
197 /* If the listener has been closed don't bother with the
198 * special RST handling below.
199 */
200 spin_unlock_bh(&fastopenq->lock);
201 sock_put(lsk);
202 reqsk_free(req);
203 return;
204 }
205 /* Wait for 60secs before removing a req that has triggered RST.
206 * This is a simple defense against TFO spoofing attack - by
207 * counting the req against fastopen.max_qlen, and disabling
208 * TFO when the qlen exceeds max_qlen.
209 *
210 * For more details see CoNext'11 "TCP Fast Open" paper.
211 */
212 req->expires = jiffies + 60*HZ;
213 if (fastopenq->rskq_rst_head == NULL)
214 fastopenq->rskq_rst_head = req;
215 else
216 fastopenq->rskq_rst_tail->dl_next = req;
217
218 req->dl_next = NULL;
219 fastopenq->rskq_rst_tail = req;
220 fastopenq->qlen++;
221out:
222 spin_unlock_bh(&fastopenq->lock);
223 sock_put(lsk);
Jerry Chu83368862012-08-31 12:29:12 +0000224}