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 return; 225 } 226