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 | |
34 | void reqsk_queue_alloc(struct request_sock_queue *queue) |
35 | { |
36 | spin_lock_init(&queue->rskq_lock); |
37 | |
38 | spin_lock_init(&queue->fastopenq.lock); |
39 | queue->fastopenq.rskq_rst_head = NULL; |
40 | queue->fastopenq.rskq_rst_tail = NULL; |
41 | queue->fastopenq.qlen = 0; |
42 | |
43 | queue->rskq_accept_head = NULL; |
44 | } |
45 | |
46 | /* |
47 | * This function is called to set a Fast Open socket's "fastopen_rsk" field |
48 | * to NULL when a TFO socket no longer needs to access the request_sock. |
49 | * This happens only after 3WHS has been either completed or aborted (e.g., |
50 | * RST is received). |
51 | * |
52 | * Before TFO, a child socket is created only after 3WHS is completed, |
53 | * hence it never needs to access the request_sock. things get a lot more |
54 | * complex with TFO. A child socket, accepted or not, has to access its |
55 | * request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts, |
56 | * until 3WHS is either completed or aborted. Afterwards the req will stay |
57 | * until either the child socket is accepted, or in the rare case when the |
58 | * listener is closed before the child is accepted. |
59 | * |
60 | * In short, a request socket is only freed after BOTH 3WHS has completed |
61 | * (or aborted) and the child socket has been accepted (or listener closed). |
62 | * When a child socket is accepted, its corresponding req->sk is set to |
63 | * NULL since it's no longer needed. More importantly, "req->sk == NULL" |
64 | * will be used by the code below to determine if a child socket has been |
65 | * accepted or not, and the check is protected by the fastopenq->lock |
66 | * described below. |
67 | * |
68 | * Note that fastopen_rsk is only accessed from the child socket's context |
69 | * with its socket lock held. But a request_sock (req) can be accessed by |
70 | * both its child socket through fastopen_rsk, and a listener socket through |
71 | * icsk_accept_queue.rskq_accept_head. To protect the access a simple spin |
72 | * lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created. |
73 | * only in the rare case when both the listener and the child locks are held, |
74 | * e.g., in inet_csk_listen_stop() do we not need to acquire the lock. |
75 | * The lock also protects other fields such as fastopenq->qlen, which is |
76 | * decremented by this function when fastopen_rsk is no longer needed. |
77 | * |
78 | * Note that another solution was to simply use the existing socket lock |
79 | * from the listener. But first socket lock is difficult to use. It is not |
80 | * a simple spin lock - one must consider sock_owned_by_user() and arrange |
81 | * to use sk_add_backlog() stuff. But what really makes it infeasible is the |
82 | * locking hierarchy violation. E.g., inet_csk_listen_stop() may try to |
83 | * acquire a child's lock while holding listener's socket lock. A corner |
84 | * case might also exist in tcp_v4_hnd_req() that will trigger this locking |
85 | * order. |
86 | * |
87 | * This function also sets "treq->tfo_listener" to false. |
88 | * treq->tfo_listener is used by the listener so it is protected by the |
89 | * fastopenq->lock in this function. |
90 | */ |
91 | void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req, |
92 | bool reset) |
93 | { |
94 | struct sock *lsk = req->rsk_listener; |
95 | struct fastopen_queue *fastopenq; |
96 | |
97 | fastopenq = &inet_csk(sk: lsk)->icsk_accept_queue.fastopenq; |
98 | |
99 | RCU_INIT_POINTER(tcp_sk(sk)->fastopen_rsk, NULL); |
100 | spin_lock_bh(lock: &fastopenq->lock); |
101 | fastopenq->qlen--; |
102 | tcp_rsk(req)->tfo_listener = false; |
103 | if (req->sk) /* the child socket hasn't been accepted yet */ |
104 | goto out; |
105 | |
106 | if (!reset || lsk->sk_state != TCP_LISTEN) { |
107 | /* If the listener has been closed don't bother with the |
108 | * special RST handling below. |
109 | */ |
110 | spin_unlock_bh(lock: &fastopenq->lock); |
111 | reqsk_put(req); |
112 | return; |
113 | } |
114 | /* Wait for 60secs before removing a req that has triggered RST. |
115 | * This is a simple defense against TFO spoofing attack - by |
116 | * counting the req against fastopen.max_qlen, and disabling |
117 | * TFO when the qlen exceeds max_qlen. |
118 | * |
119 | * For more details see CoNext'11 "TCP Fast Open" paper. |
120 | */ |
121 | req->rsk_timer.expires = jiffies + 60*HZ; |
122 | if (fastopenq->rskq_rst_head == NULL) |
123 | fastopenq->rskq_rst_head = req; |
124 | else |
125 | fastopenq->rskq_rst_tail->dl_next = req; |
126 | |
127 | req->dl_next = NULL; |
128 | fastopenq->rskq_rst_tail = req; |
129 | fastopenq->qlen++; |
130 | out: |
131 | spin_unlock_bh(lock: &fastopenq->lock); |
132 | } |
133 | |