| /* |
| * NET Generic infrastructure for Network protocols. |
| * |
| * Authors: Arnaldo Carvalho de Melo <acme@conectiva.com.br> |
| * |
| * From code originally in include/net/tcp.h |
| * |
| * This program is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU General Public License |
| * as published by the Free Software Foundation; either version |
| * 2 of the License, or (at your option) any later version. |
| */ |
| |
| #include <linux/module.h> |
| #include <linux/random.h> |
| #include <linux/slab.h> |
| #include <linux/string.h> |
| #include <linux/tcp.h> |
| #include <linux/vmalloc.h> |
| |
| #include <net/request_sock.h> |
| |
| /* |
| * Maximum number of SYN_RECV sockets in queue per LISTEN socket. |
| * One SYN_RECV socket costs about 80bytes on a 32bit machine. |
| * It would be better to replace it with a global counter for all sockets |
| * but then some measure against one socket starving all other sockets |
| * would be needed. |
| * |
| * The minimum value of it is 128. Experiments with real servers show that |
| * it is absolutely not enough even at 100conn/sec. 256 cures most |
| * of problems. |
| * This value is adjusted to 128 for low memory machines, |
| * and it will increase in proportion to the memory of machine. |
| * Note : Dont forget somaxconn that may limit backlog too. |
| */ |
| int sysctl_max_syn_backlog = 256; |
| EXPORT_SYMBOL(sysctl_max_syn_backlog); |
| |
| int reqsk_queue_alloc(struct request_sock_queue *queue, |
| unsigned int nr_table_entries) |
| { |
| size_t lopt_size = sizeof(struct listen_sock); |
| struct listen_sock *lopt = NULL; |
| |
| nr_table_entries = min_t(u32, nr_table_entries, sysctl_max_syn_backlog); |
| nr_table_entries = max_t(u32, nr_table_entries, 8); |
| nr_table_entries = roundup_pow_of_two(nr_table_entries + 1); |
| |
| lopt = kzalloc(lopt_size, GFP_KERNEL); |
| if (!lopt) |
| return -ENOMEM; |
| |
| spin_lock_init(&queue->rskq_lock); |
| spin_lock_init(&queue->syn_wait_lock); |
| |
| spin_lock_init(&queue->fastopenq.lock); |
| queue->fastopenq.rskq_rst_head = NULL; |
| queue->fastopenq.rskq_rst_tail = NULL; |
| queue->fastopenq.qlen = 0; |
| queue->fastopenq.max_qlen = 0; |
| |
| queue->rskq_accept_head = NULL; |
| lopt->max_qlen_log = ilog2(nr_table_entries); |
| |
| spin_lock_bh(&queue->syn_wait_lock); |
| queue->listen_opt = lopt; |
| spin_unlock_bh(&queue->syn_wait_lock); |
| |
| return 0; |
| } |
| |
| void __reqsk_queue_destroy(struct request_sock_queue *queue) |
| { |
| /* This is an error recovery path only, no locking needed */ |
| kfree(queue->listen_opt); |
| } |
| |
| static inline struct listen_sock *reqsk_queue_yank_listen_sk( |
| struct request_sock_queue *queue) |
| { |
| struct listen_sock *lopt; |
| |
| spin_lock_bh(&queue->syn_wait_lock); |
| lopt = queue->listen_opt; |
| queue->listen_opt = NULL; |
| spin_unlock_bh(&queue->syn_wait_lock); |
| |
| return lopt; |
| } |
| |
| void reqsk_queue_destroy(struct request_sock_queue *queue) |
| { |
| struct listen_sock *lopt = reqsk_queue_yank_listen_sk(queue); |
| |
| /* cleaning is done by req timers */ |
| kfree(lopt); |
| } |
| |
| /* |
| * This function is called to set a Fast Open socket's "fastopen_rsk" field |
| * to NULL when a TFO socket no longer needs to access the request_sock. |
| * This happens only after 3WHS has been either completed or aborted (e.g., |
| * RST is received). |
| * |
| * Before TFO, a child socket is created only after 3WHS is completed, |
| * hence it never needs to access the request_sock. things get a lot more |
| * complex with TFO. A child socket, accepted or not, has to access its |
| * request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts, |
| * until 3WHS is either completed or aborted. Afterwards the req will stay |
| * until either the child socket is accepted, or in the rare case when the |
| * listener is closed before the child is accepted. |
| * |
| * In short, a request socket is only freed after BOTH 3WHS has completed |
| * (or aborted) and the child socket has been accepted (or listener closed). |
| * When a child socket is accepted, its corresponding req->sk is set to |
| * NULL since it's no longer needed. More importantly, "req->sk == NULL" |
| * will be used by the code below to determine if a child socket has been |
| * accepted or not, and the check is protected by the fastopenq->lock |
| * described below. |
| * |
| * Note that fastopen_rsk is only accessed from the child socket's context |
| * with its socket lock held. But a request_sock (req) can be accessed by |
| * both its child socket through fastopen_rsk, and a listener socket through |
| * icsk_accept_queue.rskq_accept_head. To protect the access a simple spin |
| * lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created. |
| * only in the rare case when both the listener and the child locks are held, |
| * e.g., in inet_csk_listen_stop() do we not need to acquire the lock. |
| * The lock also protects other fields such as fastopenq->qlen, which is |
| * decremented by this function when fastopen_rsk is no longer needed. |
| * |
| * Note that another solution was to simply use the existing socket lock |
| * from the listener. But first socket lock is difficult to use. It is not |
| * a simple spin lock - one must consider sock_owned_by_user() and arrange |
| * to use sk_add_backlog() stuff. But what really makes it infeasible is the |
| * locking hierarchy violation. E.g., inet_csk_listen_stop() may try to |
| * acquire a child's lock while holding listener's socket lock. A corner |
| * case might also exist in tcp_v4_hnd_req() that will trigger this locking |
| * order. |
| * |
| * This function also sets "treq->tfo_listener" to false. |
| * treq->tfo_listener is used by the listener so it is protected by the |
| * fastopenq->lock in this function. |
| */ |
| void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req, |
| bool reset) |
| { |
| struct sock *lsk = req->rsk_listener; |
| struct fastopen_queue *fastopenq; |
| |
| fastopenq = &inet_csk(lsk)->icsk_accept_queue.fastopenq; |
| |
| tcp_sk(sk)->fastopen_rsk = NULL; |
| spin_lock_bh(&fastopenq->lock); |
| fastopenq->qlen--; |
| tcp_rsk(req)->tfo_listener = false; |
| if (req->sk) /* the child socket hasn't been accepted yet */ |
| goto out; |
| |
| if (!reset || lsk->sk_state != TCP_LISTEN) { |
| /* If the listener has been closed don't bother with the |
| * special RST handling below. |
| */ |
| spin_unlock_bh(&fastopenq->lock); |
| reqsk_put(req); |
| return; |
| } |
| /* Wait for 60secs before removing a req that has triggered RST. |
| * This is a simple defense against TFO spoofing attack - by |
| * counting the req against fastopen.max_qlen, and disabling |
| * TFO when the qlen exceeds max_qlen. |
| * |
| * For more details see CoNext'11 "TCP Fast Open" paper. |
| */ |
| req->rsk_timer.expires = jiffies + 60*HZ; |
| if (fastopenq->rskq_rst_head == NULL) |
| fastopenq->rskq_rst_head = req; |
| else |
| fastopenq->rskq_rst_tail->dl_next = req; |
| |
| req->dl_next = NULL; |
| fastopenq->rskq_rst_tail = req; |
| fastopenq->qlen++; |
| out: |
| spin_unlock_bh(&fastopenq->lock); |
| } |