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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 | void reqsk_queue_alloc(struct request_sock_queue *queue) | |
41 | { | |
42 | spin_lock_init(&queue->rskq_lock); | |
43 | ||
44 | spin_lock_init(&queue->fastopenq.lock); | |
45 | queue->fastopenq.rskq_rst_head = NULL; | |
46 | queue->fastopenq.rskq_rst_tail = NULL; | |
47 | queue->fastopenq.qlen = 0; | |
48 | ||
49 | queue->rskq_accept_head = NULL; | |
50 | } | |
51 | ||
52 | /* | |
53 | * This function is called to set a Fast Open socket's "fastopen_rsk" field | |
54 | * to NULL when a TFO socket no longer needs to access the request_sock. | |
55 | * This happens only after 3WHS has been either completed or aborted (e.g., | |
56 | * RST is received). | |
57 | * | |
58 | * Before TFO, a child socket is created only after 3WHS is completed, | |
59 | * hence it never needs to access the request_sock. things get a lot more | |
60 | * complex with TFO. A child socket, accepted or not, has to access its | |
61 | * request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts, | |
62 | * until 3WHS is either completed or aborted. Afterwards the req will stay | |
63 | * until either the child socket is accepted, or in the rare case when the | |
64 | * listener is closed before the child is accepted. | |
65 | * | |
66 | * In short, a request socket is only freed after BOTH 3WHS has completed | |
67 | * (or aborted) and the child socket has been accepted (or listener closed). | |
68 | * When a child socket is accepted, its corresponding req->sk is set to | |
69 | * NULL since it's no longer needed. More importantly, "req->sk == NULL" | |
70 | * will be used by the code below to determine if a child socket has been | |
71 | * accepted or not, and the check is protected by the fastopenq->lock | |
72 | * described below. | |
73 | * | |
74 | * Note that fastopen_rsk is only accessed from the child socket's context | |
75 | * with its socket lock held. But a request_sock (req) can be accessed by | |
76 | * both its child socket through fastopen_rsk, and a listener socket through | |
77 | * icsk_accept_queue.rskq_accept_head. To protect the access a simple spin | |
78 | * lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created. | |
79 | * only in the rare case when both the listener and the child locks are held, | |
80 | * e.g., in inet_csk_listen_stop() do we not need to acquire the lock. | |
81 | * The lock also protects other fields such as fastopenq->qlen, which is | |
82 | * decremented by this function when fastopen_rsk is no longer needed. | |
83 | * | |
84 | * Note that another solution was to simply use the existing socket lock | |
85 | * from the listener. But first socket lock is difficult to use. It is not | |
86 | * a simple spin lock - one must consider sock_owned_by_user() and arrange | |
87 | * to use sk_add_backlog() stuff. But what really makes it infeasible is the | |
88 | * locking hierarchy violation. E.g., inet_csk_listen_stop() may try to | |
89 | * acquire a child's lock while holding listener's socket lock. A corner | |
90 | * case might also exist in tcp_v4_hnd_req() that will trigger this locking | |
91 | * order. | |
92 | * | |
93 | * This function also sets "treq->tfo_listener" to false. | |
94 | * treq->tfo_listener is used by the listener so it is protected by the | |
95 | * fastopenq->lock in this function. | |
96 | */ | |
97 | void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req, | |
98 | bool reset) | |
99 | { | |
100 | struct sock *lsk = req->rsk_listener; | |
101 | struct fastopen_queue *fastopenq; | |
102 | ||
103 | fastopenq = &inet_csk(lsk)->icsk_accept_queue.fastopenq; | |
104 | ||
105 | tcp_sk(sk)->fastopen_rsk = NULL; | |
106 | spin_lock_bh(&fastopenq->lock); | |
107 | fastopenq->qlen--; | |
108 | tcp_rsk(req)->tfo_listener = false; | |
109 | if (req->sk) /* the child socket hasn't been accepted yet */ | |
110 | goto out; | |
111 | ||
112 | if (!reset || lsk->sk_state != TCP_LISTEN) { | |
113 | /* If the listener has been closed don't bother with the | |
114 | * special RST handling below. | |
115 | */ | |
116 | spin_unlock_bh(&fastopenq->lock); | |
117 | reqsk_put(req); | |
118 | return; | |
119 | } | |
120 | /* Wait for 60secs before removing a req that has triggered RST. | |
121 | * This is a simple defense against TFO spoofing attack - by | |
122 | * counting the req against fastopen.max_qlen, and disabling | |
123 | * TFO when the qlen exceeds max_qlen. | |
124 | * | |
125 | * For more details see CoNext'11 "TCP Fast Open" paper. | |
126 | */ | |
127 | req->rsk_timer.expires = jiffies + 60*HZ; | |
128 | if (fastopenq->rskq_rst_head == NULL) | |
129 | fastopenq->rskq_rst_head = req; | |
130 | else | |
131 | fastopenq->rskq_rst_tail->dl_next = req; | |
132 | ||
133 | req->dl_next = NULL; | |
134 | fastopenq->rskq_rst_tail = req; | |
135 | fastopenq->qlen++; | |
136 | out: | |
137 | spin_unlock_bh(&fastopenq->lock); | |
138 | } |