Branch data Line data Source code
1 : : /*
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>
18 : : #include <linux/tcp.h>
19 : : #include <linux/vmalloc.h>
20 : :
21 : : #include <net/request_sock.h>
22 : :
23 : : /*
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 : : *
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
32 : : * 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.
35 : : * Note : Dont forget somaxconn that may limit backlog too.
36 : : */
37 : : int sysctl_max_syn_backlog = 256;
38 : : EXPORT_SYMBOL(sysctl_max_syn_backlog);
39 : :
40 : 0 : int reqsk_queue_alloc(struct request_sock_queue *queue,
41 : : unsigned int nr_table_entries)
42 : : {
43 : : size_t lopt_size = sizeof(struct listen_sock);
44 : : struct listen_sock *lopt;
45 : :
46 : 9 : nr_table_entries = min_t(u32, nr_table_entries, sysctl_max_syn_backlog);
47 : 9 : nr_table_entries = max_t(u32, nr_table_entries, 8);
48 [ - + ][ # # ]: 9 : nr_table_entries = roundup_pow_of_two(nr_table_entries + 1);
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49 : 9 : lopt_size += nr_table_entries * sizeof(struct request_sock *);
50 [ - + ]: 9 : if (lopt_size > PAGE_SIZE)
51 : 0 : lopt = vzalloc(lopt_size);
52 : : else
53 : : lopt = kzalloc(lopt_size, GFP_KERNEL);
54 [ + - ]: 9 : if (lopt == NULL)
55 : : return -ENOMEM;
56 : :
57 [ + + ]: 18 : for (lopt->max_qlen_log = 3;
58 : 18 : (1 << lopt->max_qlen_log) < nr_table_entries;
59 : 9 : lopt->max_qlen_log++);
60 : :
61 : 9 : get_random_bytes(&lopt->hash_rnd, sizeof(lopt->hash_rnd));
62 : 9 : rwlock_init(&queue->syn_wait_lock);
63 : 9 : queue->rskq_accept_head = NULL;
64 : 9 : lopt->nr_table_entries = nr_table_entries;
65 : :
66 : 9 : write_lock_bh(&queue->syn_wait_lock);
67 : 9 : queue->listen_opt = lopt;
68 : 9 : write_unlock_bh(&queue->syn_wait_lock);
69 : :
70 : 9 : return 0;
71 : : }
72 : :
73 : 0 : void __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 : 0 : lopt = queue->listen_opt;
84 : 0 : lopt_size = sizeof(struct listen_sock) +
85 : 0 : lopt->nr_table_entries * sizeof(struct request_sock *);
86 : :
87 [ # # ]: 0 : if (lopt_size > PAGE_SIZE)
88 : 0 : vfree(lopt);
89 : : else
90 : 0 : kfree(lopt);
91 : 0 : }
92 : :
93 : : static inline struct listen_sock *reqsk_queue_yank_listen_sk(
94 : : struct request_sock_queue *queue)
95 : : {
96 : : struct listen_sock *lopt;
97 : :
98 : 9 : write_lock_bh(&queue->syn_wait_lock);
99 : 9 : lopt = queue->listen_opt;
100 : 9 : queue->listen_opt = NULL;
101 : 9 : write_unlock_bh(&queue->syn_wait_lock);
102 : :
103 : : return lopt;
104 : : }
105 : :
106 : 0 : void 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);
110 : 9 : size_t lopt_size = sizeof(struct listen_sock) +
111 : 9 : lopt->nr_table_entries * sizeof(struct request_sock *);
112 : :
113 [ - + ]: 9 : if (lopt->qlen != 0) {
114 : : unsigned int i;
115 : :
116 [ # # ]: 0 : for (i = 0; i < lopt->nr_table_entries; i++) {
117 : : struct request_sock *req;
118 : :
119 [ # # ]: 0 : while ((req = lopt->syn_table[i]) != NULL) {
120 : 0 : lopt->syn_table[i] = req->dl_next;
121 : 0 : lopt->qlen--;
122 : : reqsk_free(req);
123 : : }
124 : : }
125 : : }
126 : :
127 [ - - ]: 9 : WARN_ON(lopt->qlen != 0);
128 [ - + ]: 9 : if (lopt_size > PAGE_SIZE)
129 : 0 : vfree(lopt);
130 : : else
131 : 9 : kfree(lopt);
132 : 9 : }
133 : :
134 : : /*
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 : : */
182 : 0 : void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
183 : : bool reset)
184 : : {
185 : 0 : struct sock *lsk = tcp_rsk(req)->listener;
186 : 0 : struct fastopen_queue *fastopenq =
187 : : inet_csk(lsk)->icsk_accept_queue.fastopenq;
188 : :
189 : 0 : tcp_sk(sk)->fastopen_rsk = NULL;
190 : : spin_lock_bh(&fastopenq->lock);
191 : 0 : fastopenq->qlen--;
192 : 0 : tcp_rsk(req)->listener = NULL;
193 [ # # ]: 0 : if (req->sk) /* the child socket hasn't been accepted yet */
194 : : goto out;
195 : :
196 [ # # ][ # # ]: 0 : 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 : 0 : req->expires = jiffies + 60*HZ;
213 [ # # ]: 0 : if (fastopenq->rskq_rst_head == NULL)
214 : 0 : fastopenq->rskq_rst_head = req;
215 : : else
216 : 0 : fastopenq->rskq_rst_tail->dl_next = req;
217 : :
218 : 0 : req->dl_next = NULL;
219 : 0 : fastopenq->rskq_rst_tail = req;
220 : 0 : fastopenq->qlen++;
221 : : out:
222 : : spin_unlock_bh(&fastopenq->lock);
223 : : sock_put(lsk);
224 : : return;
225 : : }
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