/*

 * INET		An implementation of the TCP/IP protocol suite for the LINUX

 *		operating system.  INET is implemented using the  BSD Socket

 *		interface as the means of communication with the user level.

 *

 *		Implementation of the Transmission Control Protocol(TCP).

 *

 * Authors:	Ross Biro

 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>

 *		Mark Evans, <evansmp@uhura.aston.ac.uk>

 *		Corey Minyard <wf-rch!minyard@relay.EU.net>

 *		Florian La Roche, <flla@stud.uni-sb.de>

 *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>

 *		Linus Torvalds, <torvalds@cs.helsinki.fi>

 *		Alan Cox, <gw4pts@gw4pts.ampr.org>

 *		Matthew Dillon, <dillon@apollo.west.oic.com>

 *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>

 *		Jorge Cwik, <jorge@laser.satlink.net>

 */

#include <linux/module.h>

#include <net/tcp.h>

int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;

int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;

int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;

int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;

int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;

int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;

int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;

int sysctl_tcp_orphan_retries __read_mostly;

static void tcp_write_timer(unsigned long);

static void tcp_delack_timer(unsigned long);

static void tcp_keepalive_timer (unsigned long data);

void tcp_init_xmit_timers(struct sock *sk)

{

	inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,

				  &tcp_keepalive_timer);

}

EXPORT_SYMBOL(tcp_init_xmit_timers);

static void tcp_write_err(struct sock *sk)

{

	sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;

	sk->sk_error_report(sk);

	tcp_done(sk);

	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);

}

/* Do not allow orphaned sockets to eat all our resources.

 * This is direct violation of TCP specs, but it is required

 * to prevent DoS attacks. It is called when a retransmission timeout

 * or zero probe timeout occurs on orphaned socket.

 *

 * Criteria is still not confirmed experimentally and may change.

 * We kill the socket, if:

 * 1. If number of orphaned sockets exceeds an administratively configured

 *    limit.

 * 2. If we have strong memory pressure.

 */

static int tcp_out_of_resources(struct sock *sk, int do_reset)

{

	struct tcp_sock *tp = tcp_sk(sk);

	/* If peer does not open window for long time, or did not transmit

	 * anything for long time, penalize it. */

	if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)

		orphans <<= 1;

	/* If some dubious ICMP arrived, penalize even more. */

	if (sk->sk_err_soft)

		orphans <<= 1;

	if (tcp_too_many_orphans(sk, orphans)) {

		if (net_ratelimit())

			printk(KERN_INFO "Out of socket memory\n");

		/* Catch exceptional cases, when connection requires reset.

		 *      1. Last segment was sent recently. */

		if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||

		    /*  2. Window is closed. */

		    (!tp->snd_wnd && !tp->packets_out))

			do_reset = 1;

		if (do_reset)

			tcp_send_active_reset(sk, GFP_ATOMIC);

		tcp_done(sk);

		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);

		return 1;

	}

	return 0;

}

/* Calculate maximal number or retries on an orphaned socket. */

static int tcp_orphan_retries(struct sock *sk, int alive)

{

	int retries = sysctl_tcp_orphan_retries; /* May be zero. */

	/* We know from an ICMP that something is wrong. */

	if (sk->sk_err_soft && !alive)

		retries = 0;

	/* However, if socket sent something recently, select some safe

	 * number of retries. 8 corresponds to >100 seconds with minimal

	 * RTO of 200msec. */

	if (retries == 0 && alive)

		retries = 8;

	return retries;

}

static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)

{

	/* Black hole detection */

	if (sysctl_tcp_mtu_probing) {

		if (!icsk->icsk_mtup.enabled) {

			icsk->icsk_mtup.enabled = 1;

			tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);

		} else {

			struct tcp_sock *tp = tcp_sk(sk);

			int mss;

			mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;

			mss = min(sysctl_tcp_base_mss, mss);

			mss = max(mss, 68 - tp->tcp_header_len);

			icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);

			tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);

		}

	}

}

/* A write timeout has occurred. Process the after effects. */

static int tcp_write_timeout(struct sock *sk)

{

	struct inet_connection_sock *icsk = inet_csk(sk);

	int retry_until;

	if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {

		if (icsk->icsk_retransmits)

			dst_negative_advice(&sk->sk_dst_cache);

		retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;

	} else {

		if (icsk->icsk_retransmits >= sysctl_tcp_retries1) {

			/* Black hole detection */

			tcp_mtu_probing(icsk, sk);

			dst_negative_advice(&sk->sk_dst_cache);

		}

		retry_until = sysctl_tcp_retries2;

		if (sock_flag(sk, SOCK_DEAD)) {

			const int alive = (icsk->icsk_rto < TCP_RTO_MAX);

			retry_until = tcp_orphan_retries(sk, alive);

			if (tcp_out_of_resources(sk, alive || icsk->icsk_retransmits < retry_until))

				return 1;

		}

	}

	if (icsk->icsk_retransmits >= retry_until) {

		/* Has it gone just too far? */

		tcp_write_err(sk);

		return 1;

	}

	return 0;

}

static void tcp_delack_timer(unsigned long data)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct inet_connection_sock *icsk = inet_csk(sk);

	bh_lock_sock(sk);

	if (sock_owned_by_user(sk)) {

		/* Try again later. */

		icsk->icsk_ack.blocked = 1;

		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);

		sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);

		goto out_unlock;

	}

	sk_mem_reclaim_partial(sk);

	if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))

		goto out;

	if (time_after(icsk->icsk_ack.timeout, jiffies)) {

		sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);

		goto out;

	}

	icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;

	if (!skb_queue_empty(&tp->ucopy.prequeue)) {

		struct sk_buff *skb;

		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);

		while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)

			sk_backlog_rcv(sk, skb);

		tp->ucopy.memory = 0;

	}

	if (inet_csk_ack_scheduled(sk)) {

		if (!icsk->icsk_ack.pingpong) {

			/* Delayed ACK missed: inflate ATO. */

			icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);

		} else {

			/* Delayed ACK missed: leave pingpong mode and

			 * deflate ATO.

			 */

			icsk->icsk_ack.pingpong = 0;

			icsk->icsk_ack.ato      = TCP_ATO_MIN;

		}

		tcp_send_ack(sk);

		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);

	}

	TCP_CHECK_TIMER(sk);

out:

	if (tcp_memory_pressure)

		sk_mem_reclaim(sk);

out_unlock:

	bh_unlock_sock(sk);

	sock_put(sk);

}

static void tcp_probe_timer(struct sock *sk)

{

	struct inet_connection_sock *icsk = inet_csk(sk);

	struct tcp_sock *tp = tcp_sk(sk);

	int max_probes;

	if (tp->packets_out || !tcp_send_head(sk)) {

		icsk->icsk_probes_out = 0;

		return;

	}

	/* *WARNING* RFC 1122 forbids this

	 *

	 * It doesn't AFAIK, because we kill the retransmit timer -AK

	 *

	 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing

	 * this behaviour in Solaris down as a bug fix. [AC]

	 *

	 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs

	 * even if they advertise zero window. Hence, connection is killed only

	 * if we received no ACKs for normal connection timeout. It is not killed

	 * only because window stays zero for some time, window may be zero

	 * until armageddon and even later. We are in full accordance

	 * with RFCs, only probe timer combines both retransmission timeout

	 * and probe timeout in one bottle.				--ANK

	 */

	max_probes = sysctl_tcp_retries2;

	if (sock_flag(sk, SOCK_DEAD)) {

		const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);

		max_probes = tcp_orphan_retries(sk, alive);

		if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))

			return;

	}

	if (icsk->icsk_probes_out > max_probes) {

		tcp_write_err(sk);

	} else {

		/* Only send another probe if we didn't close things up. */

		tcp_send_probe0(sk);

	}

}

/*

 *	The TCP retransmit timer.

 */

static void tcp_retransmit_timer(struct sock *sk)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct inet_connection_sock *icsk = inet_csk(sk);

	if (!tp->packets_out)

		goto out;

	WARN_ON(tcp_write_queue_empty(sk));

	if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&

	    !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {

		/* Receiver dastardly shrinks window. Our retransmits

		 * become zero probes, but we should not timeout this

		 * connection. If the socket is an orphan, time it out,

		 * we cannot allow such beasts to hang infinitely.

		 */

#ifdef TCP_DEBUG

		struct inet_sock *inet = inet_sk(sk);

		if (sk->sk_family == AF_INET) {

			       inet->num, tp->snd_una, tp->snd_nxt);

		}

#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)

		else if (sk->sk_family == AF_INET6) {

			struct ipv6_pinfo *np = inet6_sk(sk);

			       inet->num, tp->snd_una, tp->snd_nxt);

		}

#endif

#endif

		if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {

			tcp_write_err(sk);

			goto out;

		}

		tcp_enter_loss(sk, 0);

		tcp_retransmit_skb(sk, tcp_write_queue_head(sk));

		__sk_dst_reset(sk);

		goto out_reset_timer;

	}

	if (tcp_write_timeout(sk))

		goto out;

	if (icsk->icsk_retransmits == 0) {

		int mib_idx;

		if (icsk->icsk_ca_state == TCP_CA_Disorder ||

		    icsk->icsk_ca_state == TCP_CA_Recovery) {

			if (tcp_is_sack(tp)) {

				if (icsk->icsk_ca_state == TCP_CA_Recovery)

					mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;

				else

					mib_idx = LINUX_MIB_TCPSACKFAILURES;

			} else {

				if (icsk->icsk_ca_state == TCP_CA_Recovery)

					mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;

				else

					mib_idx = LINUX_MIB_TCPRENOFAILURES;

			}

		} else if (icsk->icsk_ca_state == TCP_CA_Loss) {

			mib_idx = LINUX_MIB_TCPLOSSFAILURES;

		} else {

			mib_idx = LINUX_MIB_TCPTIMEOUTS;

		}

		NET_INC_STATS_BH(sock_net(sk), mib_idx);

	}

	if (tcp_use_frto(sk)) {

		tcp_enter_frto(sk);

	} else {

		tcp_enter_loss(sk, 0);

	}

	if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {

		/* Retransmission failed because of local congestion,

		 * do not backoff.

		 */

		if (!icsk->icsk_retransmits)

			icsk->icsk_retransmits = 1;

		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,

					  min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),

					  TCP_RTO_MAX);

		goto out;

	}

	/* Increase the timeout each time we retransmit.  Note that

	 * we do not increase the rtt estimate.  rto is initialized

	 * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests

	 * that doubling rto each time is the least we can get away with.

	 * In KA9Q, Karn uses this for the first few times, and then

	 * goes to quadratic.  netBSD doubles, but only goes up to *64,

	 * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is

	 * defined in the protocol as the maximum possible RTT.  I guess

	 * we'll have to use something other than TCP to talk to the

	 * University of Mars.

	 *

	 * PAWS allows us longer timeouts and large windows, so once

	 * implemented ftp to mars will work nicely. We will have to fix

	 * the 120 second clamps though!

	 */

	icsk->icsk_backoff++;

	icsk->icsk_retransmits++;

out_reset_timer:

	icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);

	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);

	if (icsk->icsk_retransmits > sysctl_tcp_retries1)

		__sk_dst_reset(sk);

out:;

}

static void tcp_write_timer(unsigned long data)

{

	struct inet_connection_sock *icsk = inet_csk(sk);

	int event;

	bh_lock_sock(sk);

	if (sock_owned_by_user(sk)) {

		/* Try again later */

		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));

		goto out_unlock;

	}

	if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)

		goto out;

	if (time_after(icsk->icsk_timeout, jiffies)) {

		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);

		goto out;

	}

	event = icsk->icsk_pending;

	icsk->icsk_pending = 0;

	switch (event) {

	case ICSK_TIME_RETRANS:

		tcp_retransmit_timer(sk);

		break;

	case ICSK_TIME_PROBE0:

		tcp_probe_timer(sk);

		break;

	}

	TCP_CHECK_TIMER(sk);

out:

	sk_mem_reclaim(sk);

out_unlock:

	bh_unlock_sock(sk);

	sock_put(sk);

}

/*

 *	Timer for listening sockets

 */

static void tcp_synack_timer(struct sock *sk)

{

	inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,

				   TCP_TIMEOUT_INIT, TCP_RTO_MAX);

}

void tcp_set_keepalive(struct sock *sk, int val)

{

	if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))

		return;

	if (val && !sock_flag(sk, SOCK_KEEPOPEN))

		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));

	else if (!val)

		inet_csk_delete_keepalive_timer(sk);

}

static void tcp_keepalive_timer (unsigned long data)

{

	struct sock *sk = (struct sock *) data;

	struct inet_connection_sock *icsk = inet_csk(sk);

	struct tcp_sock *tp = tcp_sk(sk);

	__u32 elapsed;

	/* Only process if socket is not in use. */

	bh_lock_sock(sk);

	if (sock_owned_by_user(sk)) {

		/* Try again later. */

		inet_csk_reset_keepalive_timer (sk, HZ/20);

		goto out;

	}

	if (sk->sk_state == TCP_LISTEN) {

		tcp_synack_timer(sk);

		goto out;

	}

	if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {

		if (tp->linger2 >= 0) {

			const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;

			if (tmo > 0) {

				tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);

				goto out;

			}

		}

		tcp_send_active_reset(sk, GFP_ATOMIC);

		goto death;

	}

	if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)

		goto out;

	elapsed = keepalive_time_when(tp);

	/* It is alive without keepalive 8) */

	if (tp->packets_out || tcp_send_head(sk))

		goto resched;

	elapsed = tcp_time_stamp - tp->rcv_tstamp;

	if (elapsed >= keepalive_time_when(tp)) {

		if ((!tp->keepalive_probes && icsk->icsk_probes_out >= sysctl_tcp_keepalive_probes) ||

		     (tp->keepalive_probes && icsk->icsk_probes_out >= tp->keepalive_probes)) {

			tcp_send_active_reset(sk, GFP_ATOMIC);

			tcp_write_err(sk);

			goto out;

		}

		if (tcp_write_wakeup(sk) <= 0) {

			icsk->icsk_probes_out++;

			elapsed = keepalive_intvl_when(tp);

		} else {

			/* If keepalive was lost due to local congestion,

			 * try harder.

			 */

			elapsed = TCP_RESOURCE_PROBE_INTERVAL;

		}

	} else {

		/* It is tp->rcv_tstamp + keepalive_time_when(tp) */

		elapsed = keepalive_time_when(tp) - elapsed;

	}

	TCP_CHECK_TIMER(sk);

	sk_mem_reclaim(sk);

resched: