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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 */
37int sysctl_max_syn_backlog = 256;
38EXPORT_SYMBOL(sysctl_max_syn_backlog);
39
40int 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 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)
51 lopt = vzalloc(lopt_size);
52 else
53 lopt = kzalloc(lopt_size, GFP_KERNEL);
54 if (lopt == NULL)
55 return -ENOMEM;
56
57 for (lopt->max_qlen_log = 3;
58 (1 << lopt->max_qlen_log) < nr_table_entries;
59 lopt->max_qlen_log++);
60
61 get_random_bytes(&lopt->hash_rnd, sizeof(lopt->hash_rnd));
62 rwlock_init(&queue->syn_wait_lock);
63 queue->rskq_accept_head = NULL;
64 lopt->nr_table_entries = nr_table_entries;
65
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
73void __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
93static 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
106void 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 size_t lopt_size = sizeof(struct listen_sock) +
111 lopt->nr_table_entries * sizeof(struct request_sock *);
112
113 if (lopt->qlen != 0) {
114 unsigned int i;
115
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
127 WARN_ON(lopt->qlen != 0);
128 if (lopt_size > PAGE_SIZE)
129 vfree(lopt);
130 else
131 kfree(lopt);
132}
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 */
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
189 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);
224}
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * NET Generic infrastructure for Network protocols.
4 *
5 * Authors: Arnaldo Carvalho de Melo <acme@conectiva.com.br>
6 *
7 * From code originally in include/net/tcp.h
8 */
9
10#include <linux/module.h>
11#include <linux/random.h>
12#include <linux/slab.h>
13#include <linux/string.h>
14#include <linux/tcp.h>
15#include <linux/vmalloc.h>
16
17#include <net/request_sock.h>
18
19/*
20 * Maximum number of SYN_RECV sockets in queue per LISTEN socket.
21 * One SYN_RECV socket costs about 80bytes on a 32bit machine.
22 * It would be better to replace it with a global counter for all sockets
23 * but then some measure against one socket starving all other sockets
24 * would be needed.
25 *
26 * The minimum value of it is 128. Experiments with real servers show that
27 * it is absolutely not enough even at 100conn/sec. 256 cures most
28 * of problems.
29 * This value is adjusted to 128 for low memory machines,
30 * and it will increase in proportion to the memory of machine.
31 * Note : Dont forget somaxconn that may limit backlog too.
32 */
33
34void reqsk_queue_alloc(struct request_sock_queue *queue)
35{
36 queue->fastopenq.rskq_rst_head = NULL;
37 queue->fastopenq.rskq_rst_tail = NULL;
38 queue->fastopenq.qlen = 0;
39
40 queue->rskq_accept_head = NULL;
41}
42
43/*
44 * This function is called to set a Fast Open socket's "fastopen_rsk" field
45 * to NULL when a TFO socket no longer needs to access the request_sock.
46 * This happens only after 3WHS has been either completed or aborted (e.g.,
47 * RST is received).
48 *
49 * Before TFO, a child socket is created only after 3WHS is completed,
50 * hence it never needs to access the request_sock. things get a lot more
51 * complex with TFO. A child socket, accepted or not, has to access its
52 * request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts,
53 * until 3WHS is either completed or aborted. Afterwards the req will stay
54 * until either the child socket is accepted, or in the rare case when the
55 * listener is closed before the child is accepted.
56 *
57 * In short, a request socket is only freed after BOTH 3WHS has completed
58 * (or aborted) and the child socket has been accepted (or listener closed).
59 * When a child socket is accepted, its corresponding req->sk is set to
60 * NULL since it's no longer needed. More importantly, "req->sk == NULL"
61 * will be used by the code below to determine if a child socket has been
62 * accepted or not, and the check is protected by the fastopenq->lock
63 * described below.
64 *
65 * Note that fastopen_rsk is only accessed from the child socket's context
66 * with its socket lock held. But a request_sock (req) can be accessed by
67 * both its child socket through fastopen_rsk, and a listener socket through
68 * icsk_accept_queue.rskq_accept_head. To protect the access a simple spin
69 * lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created.
70 * only in the rare case when both the listener and the child locks are held,
71 * e.g., in inet_csk_listen_stop() do we not need to acquire the lock.
72 * The lock also protects other fields such as fastopenq->qlen, which is
73 * decremented by this function when fastopen_rsk is no longer needed.
74 *
75 * Note that another solution was to simply use the existing socket lock
76 * from the listener. But first socket lock is difficult to use. It is not
77 * a simple spin lock - one must consider sock_owned_by_user() and arrange
78 * to use sk_add_backlog() stuff. But what really makes it infeasible is the
79 * locking hierarchy violation. E.g., inet_csk_listen_stop() may try to
80 * acquire a child's lock while holding listener's socket lock. A corner
81 * case might also exist in tcp_v4_hnd_req() that will trigger this locking
82 * order.
83 *
84 * This function also sets "treq->tfo_listener" to false.
85 * treq->tfo_listener is used by the listener so it is protected by the
86 * fastopenq->lock in this function.
87 */
88void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
89 bool reset)
90{
91 struct sock *lsk = req->rsk_listener;
92 struct fastopen_queue *fastopenq;
93
94 fastopenq = &inet_csk(lsk)->icsk_accept_queue.fastopenq;
95
96 RCU_INIT_POINTER(tcp_sk(sk)->fastopen_rsk, NULL);
97 spin_lock_bh(&fastopenq->lock);
98 fastopenq->qlen--;
99 tcp_rsk(req)->tfo_listener = false;
100 if (req->sk) /* the child socket hasn't been accepted yet */
101 goto out;
102
103 if (!reset || lsk->sk_state != TCP_LISTEN) {
104 /* If the listener has been closed don't bother with the
105 * special RST handling below.
106 */
107 spin_unlock_bh(&fastopenq->lock);
108 reqsk_put(req);
109 return;
110 }
111 /* Wait for 60secs before removing a req that has triggered RST.
112 * This is a simple defense against TFO spoofing attack - by
113 * counting the req against fastopen.max_qlen, and disabling
114 * TFO when the qlen exceeds max_qlen.
115 *
116 * For more details see CoNext'11 "TCP Fast Open" paper.
117 */
118 req->rsk_timer.expires = jiffies + 60*HZ;
119 if (fastopenq->rskq_rst_head == NULL)
120 fastopenq->rskq_rst_head = req;
121 else
122 fastopenq->rskq_rst_tail->dl_next = req;
123
124 req->dl_next = NULL;
125 fastopenq->rskq_rst_tail = req;
126 fastopenq->qlen++;
127out:
128 spin_unlock_bh(&fastopenq->lock);
129}