2 * NET Generic infrastructure for Network protocols.
4 * Authors: Arnaldo Carvalho de Melo <acme@conectiva.com.br>
6 * From code originally in include/net/tcp.h
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.
14 #include <linux/module.h>
15 #include <linux/random.h>
16 #include <linux/slab.h>
17 #include <linux/string.h>
18 #include <linux/tcp.h>
19 #include <linux/vmalloc.h>
21 #include <net/request_sock.h>
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
30 * The minimum value of it is 128. Experiments with real servers show that
31 * it is absolutely not enough even at 100conn/sec. 256 cures most
33 * This value is adjusted to 128 for low memory machines,
34 * and it will increase in proportion to the memory of machine.
35 * Note : Dont forget somaxconn that may limit backlog too.
37 int sysctl_max_syn_backlog = 256;
38 EXPORT_SYMBOL(sysctl_max_syn_backlog);
40 int reqsk_queue_alloc(struct request_sock_queue *queue,
41 unsigned int nr_table_entries)
43 size_t lopt_size = sizeof(struct listen_sock);
44 struct listen_sock *lopt = NULL;
46 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 *);
51 if (lopt_size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
52 lopt = kzalloc(lopt_size, GFP_KERNEL |
56 lopt = vzalloc(lopt_size);
60 get_random_bytes(&lopt->hash_rnd, sizeof(lopt->hash_rnd));
61 spin_lock_init(&queue->syn_wait_lock);
63 spin_lock_init(&queue->fastopenq.lock);
64 queue->fastopenq.rskq_rst_head = NULL;
65 queue->fastopenq.rskq_rst_tail = NULL;
66 queue->fastopenq.qlen = 0;
67 queue->fastopenq.max_qlen = 0;
69 queue->rskq_accept_head = NULL;
70 lopt->nr_table_entries = nr_table_entries;
71 lopt->max_qlen_log = ilog2(nr_table_entries);
73 spin_lock_bh(&queue->syn_wait_lock);
74 queue->listen_opt = lopt;
75 spin_unlock_bh(&queue->syn_wait_lock);
80 void __reqsk_queue_destroy(struct request_sock_queue *queue)
82 /* This is an error recovery path only, no locking needed */
83 kvfree(queue->listen_opt);
86 static inline struct listen_sock *reqsk_queue_yank_listen_sk(
87 struct request_sock_queue *queue)
89 struct listen_sock *lopt;
91 spin_lock_bh(&queue->syn_wait_lock);
92 lopt = queue->listen_opt;
93 queue->listen_opt = NULL;
94 spin_unlock_bh(&queue->syn_wait_lock);
99 void reqsk_queue_destroy(struct request_sock_queue *queue)
101 /* make all the listen_opt local to us */
102 struct listen_sock *lopt = reqsk_queue_yank_listen_sk(queue);
104 if (listen_sock_qlen(lopt) != 0) {
107 for (i = 0; i < lopt->nr_table_entries; i++) {
108 struct request_sock *req;
110 spin_lock_bh(&queue->syn_wait_lock);
111 while ((req = lopt->syn_table[i]) != NULL) {
112 lopt->syn_table[i] = req->dl_next;
113 /* Because of following del_timer_sync(),
114 * we must release the spinlock here
115 * or risk a dead lock.
117 spin_unlock_bh(&queue->syn_wait_lock);
118 atomic_inc(&lopt->qlen_dec);
119 if (del_timer_sync(&req->rsk_timer))
122 spin_lock_bh(&queue->syn_wait_lock);
124 spin_unlock_bh(&queue->syn_wait_lock);
128 if (WARN_ON(listen_sock_qlen(lopt) != 0))
129 pr_err("qlen %u\n", listen_sock_qlen(lopt));
134 * This function is called to set a Fast Open socket's "fastopen_rsk" field
135 * to NULL when a TFO socket no longer needs to access the request_sock.
136 * This happens only after 3WHS has been either completed or aborted (e.g.,
139 * Before TFO, a child socket is created only after 3WHS is completed,
140 * hence it never needs to access the request_sock. things get a lot more
141 * complex with TFO. A child socket, accepted or not, has to access its
142 * request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts,
143 * until 3WHS is either completed or aborted. Afterwards the req will stay
144 * until either the child socket is accepted, or in the rare case when the
145 * listener is closed before the child is accepted.
147 * In short, a request socket is only freed after BOTH 3WHS has completed
148 * (or aborted) and the child socket has been accepted (or listener closed).
149 * When a child socket is accepted, its corresponding req->sk is set to
150 * NULL since it's no longer needed. More importantly, "req->sk == NULL"
151 * will be used by the code below to determine if a child socket has been
152 * accepted or not, and the check is protected by the fastopenq->lock
155 * Note that fastopen_rsk is only accessed from the child socket's context
156 * with its socket lock held. But a request_sock (req) can be accessed by
157 * both its child socket through fastopen_rsk, and a listener socket through
158 * icsk_accept_queue.rskq_accept_head. To protect the access a simple spin
159 * lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created.
160 * only in the rare case when both the listener and the child locks are held,
161 * e.g., in inet_csk_listen_stop() do we not need to acquire the lock.
162 * The lock also protects other fields such as fastopenq->qlen, which is
163 * decremented by this function when fastopen_rsk is no longer needed.
165 * Note that another solution was to simply use the existing socket lock
166 * from the listener. But first socket lock is difficult to use. It is not
167 * a simple spin lock - one must consider sock_owned_by_user() and arrange
168 * to use sk_add_backlog() stuff. But what really makes it infeasible is the
169 * locking hierarchy violation. E.g., inet_csk_listen_stop() may try to
170 * acquire a child's lock while holding listener's socket lock. A corner
171 * case might also exist in tcp_v4_hnd_req() that will trigger this locking
174 * This function also sets "treq->tfo_listener" to false.
175 * treq->tfo_listener is used by the listener so it is protected by the
176 * fastopenq->lock in this function.
178 void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
181 struct sock *lsk = req->rsk_listener;
182 struct fastopen_queue *fastopenq;
184 fastopenq = &inet_csk(lsk)->icsk_accept_queue.fastopenq;
186 tcp_sk(sk)->fastopen_rsk = NULL;
187 spin_lock_bh(&fastopenq->lock);
189 tcp_rsk(req)->tfo_listener = false;
190 if (req->sk) /* the child socket hasn't been accepted yet */
193 if (!reset || lsk->sk_state != TCP_LISTEN) {
194 /* If the listener has been closed don't bother with the
195 * special RST handling below.
197 spin_unlock_bh(&fastopenq->lock);
201 /* Wait for 60secs before removing a req that has triggered RST.
202 * This is a simple defense against TFO spoofing attack - by
203 * counting the req against fastopen.max_qlen, and disabling
204 * TFO when the qlen exceeds max_qlen.
206 * For more details see CoNext'11 "TCP Fast Open" paper.
208 req->rsk_timer.expires = jiffies + 60*HZ;
209 if (fastopenq->rskq_rst_head == NULL)
210 fastopenq->rskq_rst_head = req;
212 fastopenq->rskq_rst_tail->dl_next = req;
215 fastopenq->rskq_rst_tail = req;
218 spin_unlock_bh(&fastopenq->lock);