/* * 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; 	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)		lopt = vzalloc(lopt_size);	else		lopt = kzalloc(lopt_size, GFP_KERNEL);	if (lopt == NULL)		return -ENOMEM; 	for (lopt->max_qlen_log = 3;	     (1 << lopt->max_qlen_log) < nr_table_entries;	     lopt->max_qlen_log++); 	get_random_bytes(&lopt->hash_rnd, sizeof(lopt->hash_rnd));	rwlock_init(&queue->syn_wait_lock);	queue->rskq_accept_head = NULL;	lopt->nr_table_entries = nr_table_entries; 	write_lock_bh(&queue->syn_wait_lock);	queue->listen_opt = lopt;	write_unlock_bh(&queue->syn_wait_lock); 	return 0;} void __reqsk_queue_destroy(struct request_sock_queue *queue){	struct listen_sock *lopt;	size_t lopt_size; 	/*	 * this is an error recovery path only	 * no locking needed and the lopt is not NULL	 */ 	lopt = queue->listen_opt;	lopt_size = sizeof(struct listen_sock) +		lopt->nr_table_entries * sizeof(struct request_sock *); 	if (lopt_size > PAGE_SIZE)		vfree(lopt);	else		kfree(lopt);} static inline struct listen_sock *reqsk_queue_yank_listen_sk(		struct request_sock_queue *queue){	struct listen_sock *lopt; 	write_lock_bh(&queue->syn_wait_lock);	lopt = queue->listen_opt;	queue->listen_opt = NULL;	write_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);	size_t lopt_size = sizeof(struct listen_sock) +		lopt->nr_table_entries * sizeof(struct request_sock *); 	if (lopt->qlen != 0) {		unsigned int i; 		for (i = 0; i < lopt->nr_table_entries; i++) {			struct request_sock *req; 			while ((req = lopt->syn_table[i]) != NULL) {				lopt->syn_table[i] = req->dl_next;				lopt->qlen--;				reqsk_free(req);			}		}	} 	WARN_ON(lopt->qlen != 0);	if (lopt_size > PAGE_SIZE)		vfree(lopt);	else		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. * * When a TFO req is created, it needs to sock_hold its listener to prevent * the latter data structure from going away. * * This function also sets "treq->listener" to NULL and unreference listener * socket. treq->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 = tcp_rsk(req)->listener;	struct fastopen_queue *fastopenq =	    inet_csk(lsk)->icsk_accept_queue.fastopenq; 	tcp_sk(sk)->fastopen_rsk = NULL;	spin_lock_bh(&fastopenq->lock);	fastopenq->qlen--;	tcp_rsk(req)->listener = NULL;	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);		sock_put(lsk);		reqsk_free(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->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);	sock_put(lsk);	return;}