diff options
Diffstat (limited to 'kernel/net/core/request_sock.c')
-rw-r--r-- | kernel/net/core/request_sock.c | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/kernel/net/core/request_sock.c b/kernel/net/core/request_sock.c new file mode 100644 index 000000000..87b22c0bc --- /dev/null +++ b/kernel/net/core/request_sock.c @@ -0,0 +1,206 @@ +/* + * 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_size += nr_table_entries * sizeof(struct request_sock *); + + if (lopt_size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) + lopt = kzalloc(lopt_size, GFP_KERNEL | + __GFP_NOWARN | + __GFP_NORETRY); + if (!lopt) + lopt = vzalloc(lopt_size); + if (!lopt) + return -ENOMEM; + + get_random_bytes(&lopt->hash_rnd, sizeof(lopt->hash_rnd)); + spin_lock_init(&queue->syn_wait_lock); + queue->rskq_accept_head = NULL; + lopt->nr_table_entries = nr_table_entries; + 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 */ + kvfree(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) +{ + /* make all the listen_opt local to us */ + struct listen_sock *lopt = reqsk_queue_yank_listen_sk(queue); + + if (listen_sock_qlen(lopt) != 0) { + unsigned int i; + + for (i = 0; i < lopt->nr_table_entries; i++) { + struct request_sock *req; + + spin_lock_bh(&queue->syn_wait_lock); + while ((req = lopt->syn_table[i]) != NULL) { + lopt->syn_table[i] = req->dl_next; + atomic_inc(&lopt->qlen_dec); + if (del_timer(&req->rsk_timer)) + reqsk_put(req); + reqsk_put(req); + } + spin_unlock_bh(&queue->syn_wait_lock); + } + } + + if (WARN_ON(listen_sock_qlen(lopt) != 0)) + pr_err("qlen %u\n", listen_sock_qlen(lopt)); + kvfree(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); +} |