2 * NET Generic infrastructure for Network protocols.
4 * Authors: Arnaldo Carvalho de Melo <acme@conectiva.com.br>
6 * From code originally in include/net/tcp.h
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.
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>
21 #include <net/request_sock.h>
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
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
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.
37 int sysctl_max_syn_backlog
= 256;
38 EXPORT_SYMBOL(sysctl_max_syn_backlog
);
40 int reqsk_queue_alloc(struct request_sock_queue
*queue
,
41 unsigned int nr_table_entries
)
43 size_t lopt_size
= sizeof(struct listen_sock
);
44 struct listen_sock
*lopt
= NULL
;
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
*);
51 if (lopt_size
<= (PAGE_SIZE
<< PAGE_ALLOC_COSTLY_ORDER
))
52 lopt
= kzalloc(lopt_size
, GFP_KERNEL
|
56 lopt
= vzalloc(lopt_size
);
60 get_random_bytes(&lopt
->hash_rnd
, sizeof(lopt
->hash_rnd
));
61 rwlock_init(&queue
->syn_wait_lock
);
62 queue
->rskq_accept_head
= NULL
;
63 lopt
->nr_table_entries
= nr_table_entries
;
64 lopt
->max_qlen_log
= ilog2(nr_table_entries
);
66 write_lock_bh(&queue
->syn_wait_lock
);
67 queue
->listen_opt
= lopt
;
68 write_unlock_bh(&queue
->syn_wait_lock
);
73 void __reqsk_queue_destroy(struct request_sock_queue
*queue
)
75 /* This is an error recovery path only, no locking needed */
76 kvfree(queue
->listen_opt
);
79 static inline struct listen_sock
*reqsk_queue_yank_listen_sk(
80 struct request_sock_queue
*queue
)
82 struct listen_sock
*lopt
;
84 write_lock_bh(&queue
->syn_wait_lock
);
85 lopt
= queue
->listen_opt
;
86 queue
->listen_opt
= NULL
;
87 write_unlock_bh(&queue
->syn_wait_lock
);
92 void reqsk_queue_destroy(struct request_sock_queue
*queue
)
94 /* make all the listen_opt local to us */
95 struct listen_sock
*lopt
= reqsk_queue_yank_listen_sk(queue
);
97 if (lopt
->qlen
!= 0) {
100 for (i
= 0; i
< lopt
->nr_table_entries
; i
++) {
101 struct request_sock
*req
;
103 while ((req
= lopt
->syn_table
[i
]) != NULL
) {
104 lopt
->syn_table
[i
] = req
->dl_next
;
111 WARN_ON(lopt
->qlen
!= 0);
116 * This function is called to set a Fast Open socket's "fastopen_rsk" field
117 * to NULL when a TFO socket no longer needs to access the request_sock.
118 * This happens only after 3WHS has been either completed or aborted (e.g.,
121 * Before TFO, a child socket is created only after 3WHS is completed,
122 * hence it never needs to access the request_sock. things get a lot more
123 * complex with TFO. A child socket, accepted or not, has to access its
124 * request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts,
125 * until 3WHS is either completed or aborted. Afterwards the req will stay
126 * until either the child socket is accepted, or in the rare case when the
127 * listener is closed before the child is accepted.
129 * In short, a request socket is only freed after BOTH 3WHS has completed
130 * (or aborted) and the child socket has been accepted (or listener closed).
131 * When a child socket is accepted, its corresponding req->sk is set to
132 * NULL since it's no longer needed. More importantly, "req->sk == NULL"
133 * will be used by the code below to determine if a child socket has been
134 * accepted or not, and the check is protected by the fastopenq->lock
137 * Note that fastopen_rsk is only accessed from the child socket's context
138 * with its socket lock held. But a request_sock (req) can be accessed by
139 * both its child socket through fastopen_rsk, and a listener socket through
140 * icsk_accept_queue.rskq_accept_head. To protect the access a simple spin
141 * lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created.
142 * only in the rare case when both the listener and the child locks are held,
143 * e.g., in inet_csk_listen_stop() do we not need to acquire the lock.
144 * The lock also protects other fields such as fastopenq->qlen, which is
145 * decremented by this function when fastopen_rsk is no longer needed.
147 * Note that another solution was to simply use the existing socket lock
148 * from the listener. But first socket lock is difficult to use. It is not
149 * a simple spin lock - one must consider sock_owned_by_user() and arrange
150 * to use sk_add_backlog() stuff. But what really makes it infeasible is the
151 * locking hierarchy violation. E.g., inet_csk_listen_stop() may try to
152 * acquire a child's lock while holding listener's socket lock. A corner
153 * case might also exist in tcp_v4_hnd_req() that will trigger this locking
156 * When a TFO req is created, it needs to sock_hold its listener to prevent
157 * the latter data structure from going away.
159 * This function also sets "treq->listener" to NULL and unreference listener
160 * socket. treq->listener is used by the listener so it is protected by the
161 * fastopenq->lock in this function.
163 void reqsk_fastopen_remove(struct sock
*sk
, struct request_sock
*req
,
166 struct sock
*lsk
= tcp_rsk(req
)->listener
;
167 struct fastopen_queue
*fastopenq
=
168 inet_csk(lsk
)->icsk_accept_queue
.fastopenq
;
170 tcp_sk(sk
)->fastopen_rsk
= NULL
;
171 spin_lock_bh(&fastopenq
->lock
);
173 tcp_rsk(req
)->listener
= NULL
;
174 if (req
->sk
) /* the child socket hasn't been accepted yet */
177 if (!reset
|| lsk
->sk_state
!= TCP_LISTEN
) {
178 /* If the listener has been closed don't bother with the
179 * special RST handling below.
181 spin_unlock_bh(&fastopenq
->lock
);
186 /* Wait for 60secs before removing a req that has triggered RST.
187 * This is a simple defense against TFO spoofing attack - by
188 * counting the req against fastopen.max_qlen, and disabling
189 * TFO when the qlen exceeds max_qlen.
191 * For more details see CoNext'11 "TCP Fast Open" paper.
193 req
->expires
= jiffies
+ 60*HZ
;
194 if (fastopenq
->rskq_rst_head
== NULL
)
195 fastopenq
->rskq_rst_head
= req
;
197 fastopenq
->rskq_rst_tail
->dl_next
= req
;
200 fastopenq
->rskq_rst_tail
= req
;
203 spin_unlock_bh(&fastopenq
->lock
);
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