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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 | */ |
37 | int sysctl_max_syn_backlog = 256; |
38 | EXPORT_SYMBOL(sysctl_max_syn_backlog); |
39 | |
40 | 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 | 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 | |
73 | 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 | 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 | |
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 | 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 | |
106 | 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 | 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 | */ |
182 | void 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++; |
221 | out: |
222 | spin_unlock_bh(&fastopenq->lock); |
223 | sock_put(lsk); |
224 | } |
225 |
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