/* * 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_thin_linear_timeouts __read_mostly; /** *  tcp_write_err() - close socket and save error info *  @sk:  The socket the error has appeared on. * *  Returns: Nothing (void) */ 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(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);} /** *  tcp_out_of_resources() - Close socket if out of resources *  @sk:        pointer to current socket *  @do_reset:  send a last packet with reset flag * *  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, bool 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_jiffies32 - 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_jiffies32 - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||		    /*  2. Window is closed. */		    (!tp->snd_wnd && !tp->packets_out))			do_reset = true;		if (do_reset)			tcp_send_active_reset(sk, GFP_ATOMIC);		tcp_done(sk);		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);		return 1;	}	return 0;} /** *  tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket *  @sk:    Pointer to the current socket. *  @alive: bool, socket alive state */static int tcp_orphan_retries(struct sock *sk, bool alive){	int retries = sock_net(sk)->ipv4.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){	struct net *net = sock_net(sk); 	/* Black hole detection */	if (net->ipv4.sysctl_tcp_mtu_probing) {		if (!icsk->icsk_mtup.enabled) {			icsk->icsk_mtup.enabled = 1;			icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;			tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);		} else {			struct net *net = sock_net(sk);			struct tcp_sock *tp = tcp_sk(sk);			int mss; 			mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;			mss = min(net->ipv4.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);		}	}}  /** *  retransmits_timed_out() - returns true if this connection has timed out *  @sk:       The current socket *  @boundary: max number of retransmissions *  @timeout:  A custom timeout value. *             If set to 0 the default timeout is calculated and used. *             Using TCP_RTO_MIN and the number of unsuccessful retransmits. * * The default "timeout" value this function can calculate and use * is equivalent to the timeout of a TCP Connection * after "boundary" unsuccessful, exponentially backed-off * retransmissions with an initial RTO of TCP_RTO_MIN. */static bool retransmits_timed_out(struct sock *sk,				  unsigned int boundary,				  unsigned int timeout){	const unsigned int rto_base = TCP_RTO_MIN;	unsigned int linear_backoff_thresh, start_ts; 	if (!inet_csk(sk)->icsk_retransmits)		return false; 	start_ts = tcp_sk(sk)->retrans_stamp;	if (unlikely(!start_ts))		start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk)); 	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(tcp_sk(sk)) - start_ts) >= jiffies_to_msecs(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);	struct net *net = sock_net(sk);	bool expired, do_reset;	int retry_until; 	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, 0);			if (tp->syn_data && icsk->icsk_retransmits == 1)				NET_INC_STATS(sock_net(sk),					      LINUX_MIB_TCPFASTOPENACTIVEFAIL);		} else if (!tp->syn_data && !tp->syn_fastopen) {			sk_rethink_txhash(sk);		}		retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;		expired = icsk->icsk_retransmits >= retry_until;	} else {		if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0)) {			/* Some middle-boxes may black-hole Fast Open _after_			 * the handshake. Therefore we conservatively disable			 * Fast Open on this path on recurring timeouts after			 * successful Fast Open.			 */			if (tp->syn_data_acked) {				tcp_fastopen_cache_set(sk, 0, NULL, true, 0);				if (icsk->icsk_retransmits == net->ipv4.sysctl_tcp_retries1)					NET_INC_STATS(sock_net(sk),						      LINUX_MIB_TCPFASTOPENACTIVEFAIL);			}			/* Black hole detection */			tcp_mtu_probing(icsk, sk); 			dst_negative_advice(sk);		} else {			sk_rethink_txhash(sk);		} 		retry_until = net->ipv4.sysctl_tcp_retries2;		if (sock_flag(sk, SOCK_DEAD)) {			const bool alive = icsk->icsk_rto < TCP_RTO_MAX; 			retry_until = tcp_orphan_retries(sk, alive);			do_reset = alive ||				!retransmits_timed_out(sk, retry_until, 0); 			if (tcp_out_of_resources(sk, do_reset))				return 1;		}		expired = retransmits_timed_out(sk, retry_until,						icsk->icsk_user_timeout);	}	if (expired) {		/* Has it gone just too far? */		tcp_write_err(sk);		return 1;	}	return 0;} /* Called with BH disabled */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 (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||	    !(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(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(sock_net(sk), LINUX_MIB_DELAYEDACKS);	} out:	if (tcp_under_memory_pressure(sk))		sk_mem_reclaim(sk);}  /** *  tcp_delack_timer() - The TCP delayed ACK timeout handler *  @data:  Pointer to the current socket. (gets casted to struct sock *) * *  This function gets (indirectly) called when the kernel timer for a TCP packet *  of this socket expires. Calls tcp_delack_timer_handler() to do the actual work. * *  Returns: Nothing (void) */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(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);		/* deleguate our work to tcp_release_cb() */		if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &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;	u32 start_ts; 	if (tp->packets_out || !tcp_send_head(sk)) {		icsk->icsk_probes_out = 0;		return;	} 	/* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as	 * long as the receiver continues to respond probes. We support this by	 * default and reset icsk_probes_out with incoming ACKs. But if the	 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we	 * kill the socket when the retry count and the time exceeds the	 * corresponding system limit. We also implement similar policy when	 * we use RTO to probe window in tcp_retransmit_timer().	 */	start_ts = tcp_skb_timestamp(tcp_send_head(sk));	if (!start_ts)		tcp_send_head(sk)->skb_mstamp = tp->tcp_mstamp;	else if (icsk->icsk_user_timeout &&		 (s32)(tcp_time_stamp(tp) - start_ts) >		 jiffies_to_msecs(icsk->icsk_user_timeout))		goto abort; 	max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2;	if (sock_flag(sk, SOCK_DEAD)) {		const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX; 		max_probes = tcp_orphan_retries(sk, alive);		if (!alive && icsk->icsk_backoff >= max_probes)			goto abort;		if (tcp_out_of_resources(sk, true))			return;	} 	if (icsk->icsk_probes_out > max_probes) {abort:		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 ? :	    sock_net(sk)->ipv4.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(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++;	icsk->icsk_retransmits++;	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,			  TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);}  /** *  tcp_retransmit_timer() - The TCP retransmit timeout handler *  @sk:  Pointer to the current socket. * *  This function gets called when the kernel timer for a TCP packet *  of this socket expires. * *  It handles retransmission, timer adjustment and other necesarry measures. * *  Returns: Nothing (void) */void tcp_retransmit_timer(struct sock *sk){	struct tcp_sock *tp = tcp_sk(sk);	struct net *net = sock_net(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) {			net_dbg_ratelimited("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) {			net_dbg_ratelimited("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_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX) {			tcp_write_err(sk);			goto out;		}		tcp_enter_loss(sk);		tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1);		__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(sock_net(sk), mib_idx);	} 	tcp_enter_loss(sk); 	if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1) > 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

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