/* * 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 <linux/gfp.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;int sysctl_tcp_thin_linear_timeouts __read_mostly; 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);	int shift = 0; 	/* 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)		shift++; 	/* If some dubious ICMP arrived, penalize even more. */	if (sk->sk_err_soft)		shift++; 	if (tcp_check_oom(sk, shift)) {		/* 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);		}	}} /* This function calculates a "timeout" which is equivalent to the timeout of a * TCP connection after "boundary" unsuccessful, exponentially backed-off * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if * syn_set flag is set. */static bool retransmits_timed_out(struct sock *sk,				  unsigned int boundary,				  unsigned int timeout,				  bool syn_set){	unsigned int linear_backoff_thresh, start_ts;	unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN; 	if (!inet_csk(sk)->icsk_retransmits)		return false; 	if (unlikely(!tcp_sk(sk)->retrans_stamp))		start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;	else		start_ts = tcp_sk(sk)->retrans_stamp; 	if (likely(timeout == 0)) {		linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base); 		if (boundary <= linear_backoff_thresh)			timeout = ((2 << boundary) - 1) * rto_base;		else			timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +				(boundary - linear_backoff_thresh) * TCP_RTO_MAX;	}	return (tcp_time_stamp - start_ts) >= timeout;} /* 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);	struct tcp_sock *tp = tcp_sk(sk);	int retry_until;	bool do_reset, syn_set = false; 	if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {		if (icsk->icsk_retransmits) {			dst_negative_advice(sk);			if (tp->syn_fastopen || tp->syn_data)				tcp_fastopen_cache_set(sk, 0, NULL, true);		}		retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;		syn_set = true;	} else {		if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {			/* Black hole detection */			tcp_mtu_probing(icsk, sk); 			dst_negative_advice(sk);		} 		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);			do_reset = alive ||				!retransmits_timed_out(sk, retry_until, 0, 0); 			if (tcp_out_of_resources(sk, do_reset))				return 1;		}	} 	if (retransmits_timed_out(sk, retry_until,				  syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {		/* Has it gone just too far? */		tcp_write_err(sk);		return 1;	}	return 0;} void tcp_delack_timer_handler(struct sock *sk){	struct tcp_sock *tp = tcp_sk(sk);	struct inet_connection_sock *icsk = inet_csk(sk); 	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);	} out:	if (sk_under_memory_pressure(sk))		sk_mem_reclaim(sk);} static void tcp_delack_timer(unsigned long data){	struct sock *sk = (struct sock *)data; 	bh_lock_sock(sk);	if (!sock_owned_by_user(sk)) {		tcp_delack_timer_handler(sk);	} else {		inet_csk(sk)->icsk_ack.blocked = 1;		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);		/* deleguate our work to tcp_release_cb() */		if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))			sock_hold(sk);	}	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);	}} /* *	Timer for Fast Open socket to retransmit SYNACK. Note that the *	sk here is the child socket, not the parent (listener) socket. */static void tcp_fastopen_synack_timer(struct sock *sk){	struct inet_connection_sock *icsk = inet_csk(sk);	int max_retries = icsk->icsk_syn_retries ? :	    sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */	struct request_sock *req; 	req = tcp_sk(sk)->fastopen_rsk;	req->rsk_ops->syn_ack_timeout(sk, req); 	if (req->num_timeout >= max_retries) {		tcp_write_err(sk);		return;	}	/* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error	 * returned from rtx_syn_ack() to make it more persistent like	 * regular retransmit because if the child socket has been accepted	 * it's not good to give up too easily.	 */	inet_rtx_syn_ack(sk, req);	req->num_timeout++;	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,			  TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);} /* *	The TCP retransmit timer. */ void tcp_retransmit_timer(struct sock *sk){	struct tcp_sock *tp = tcp_sk(sk);	struct inet_connection_sock *icsk = inet_csk(sk); 	if (tp->fastopen_rsk) {		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&			     sk->sk_state != TCP_FIN_WAIT1);		tcp_fastopen_synack_timer(sk);		/* Before we receive ACK to our SYN-ACK don't retransmit		 * anything else (e.g., data or FIN segments).		 */		return;	}	if (!tp->packets_out)		goto out; 	WARN_ON(tcp_write_queue_empty(sk)); 	tp->tlp_high_seq = 0; 	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.		 */		struct inet_sock *inet = inet_sk(sk);		if (sk->sk_family == AF_INET) {			LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),				       &inet->inet_daddr,				       ntohs(inet->inet_dport), inet->inet_num,				       tp->snd_una, tp->snd_nxt);		}#if IS_ENABLED(CONFIG_IPV6)		else if (sk->sk_family == AF_INET6) {			LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),				       &sk->sk_v6_daddr,				       ntohs(inet->inet_dport), inet->inet_num,				       tp->snd_una, tp->snd_nxt);		}#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_Recovery) {			if (tcp_is_sack(tp))				mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;			else				mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;		} else if (icsk->icsk_ca_state == TCP_CA_Loss) {			mib_idx = LINUX_MIB_TCPLOSSFAILURES;		} else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||			   tp->sacked_out) {			if (tcp_is_sack(tp))				mib_idx = LINUX_MIB_TCPSACKFAILURES;			else				mib_idx = LINUX_MIB_TCPRENOFAILURES;		} else {			mib_idx = LINUX_MIB_TCPTIMEOUTS;		}		NET_INC_STATS_BH(sock_net(sk), mib_idx);	} 	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:	/* If stream is thin, use linear timeouts. Since 'icsk_backoff' is	 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this	 * might be increased if the stream oscillates between thin and thick,	 * thus the old value might already be too high compared to the value	 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without	 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating	 * exponential backoff behaviour to avoid continue hammering	 * linear-timeout retransmissions into a black hole	 */	if (sk->sk_state == TCP_ESTABLISHED &&	    (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&	    tcp_stream_is_thin(tp) &&	    icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {		icsk->icsk_backoff = 0;		icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);	} else {		/* Use normal (exponential) backoff */		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 (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))		__sk_dst_reset(sk); out:;} void tcp_write_timer_handler(struct sock *sk){	struct inet_connection_sock *icsk = inet_csk(sk);	int event; 	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; 	switch (event) {	case ICSK_TIME_EARLY_RETRANS:		tcp_resume_early_retransmit(sk);		break;	case ICSK_TIME_LOSS_PROBE:

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