xref: /freebsd/sys/netinet/tcp_ecn.c (revision 004bb636ca65f3239da284c20abb7f9d1d953dee)

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
 *      The Regents of the University of California.  All rights reserved.
 * Copyright (c) 2007-2008,2010
 *      Swinburne University of Technology, Melbourne, Australia.
 * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
 * Copyright (c) 2010 The FreeBSD Foundation
 * Copyright (c) 2010-2011 Juniper Networks, Inc.
 * Copyright (c) 2019 Richard Scheffenegger <srichard@netapp.com>
 * All rights reserved.
 *
 * Portions of this software were developed at the Centre for Advanced Internet
 * Architectures, Swinburne University of Technology, by Lawrence Stewart,
 * James Healy and David Hayes, made possible in part by a grant from the Cisco
 * University Research Program Fund at Community Foundation Silicon Valley.
 *
 * Portions of this software were developed at the Centre for Advanced
 * Internet Architectures, Swinburne University of Technology, Melbourne,
 * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
 *
 * Portions of this software were developed by Robert N. M. Watson under
 * contract to Juniper Networks, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)tcp_ecn.c 8.12 (Berkeley) 5/24/95
 */

/*
 * Utility functions to deal with Explicit Congestion Notification in TCP
 * implementing the essential parts of the Accurate ECN extension
 * https://tools.ietf.org/html/draft-ietf-tcpm-accurate-ecn-09
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_tcpdebug.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>

#include <machine/cpu.h>

#include <vm/uma.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/route.h>
#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_var.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_pcb.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_syncache.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcpip.h>
#include <netinet/tcp_ecn.h>

static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "TCP ECN");

VNET_DEFINE(int, tcp_do_ecn) = 2;
SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable,
    CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_do_ecn), 0,
    "TCP ECN support");

VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries,
    CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_ecn_maxretries), 0,
    "Max retries before giving up on ECN");

/*
 * Process incoming SYN,ACK packet
 */
void
tcp_ecn_input_syn_sent(struct tcpcb *tp, uint16_t thflags, int iptos)
{

	if (V_tcp_do_ecn == 0)
		return;
	if ((V_tcp_do_ecn == 1) ||
	    (V_tcp_do_ecn == 2)) {
		/* RFC3168 ECN handling */
		if ((thflags & (TH_CWR | TH_ECE)) == (0 | TH_ECE)) {
			tp->t_flags2 |= TF2_ECN_PERMIT;
			tp->t_flags2 &= ~TF2_ACE_PERMIT;
			TCPSTAT_INC(tcps_ecn_shs);
		}
	} else
	/* decoding Accurate ECN according to table in section 3.1.1 */
	if ((V_tcp_do_ecn == 3) ||
	    (V_tcp_do_ecn == 4)) {
		/*
		 * on the SYN,ACK, process the AccECN
		 * flags indicating the state the SYN
		 * was delivered.
		 * Reactions to Path ECN mangling can
		 * come here.
		 */
		switch (thflags & (TH_AE | TH_CWR | TH_ECE)) {
		/* RFC3168 SYN */
		case (0|0|TH_ECE):
			tp->t_flags2 |= TF2_ECN_PERMIT;
			tp->t_flags2 &= ~TF2_ACE_PERMIT;
			TCPSTAT_INC(tcps_ecn_shs);
			break;
		/* non-ECT SYN */
		case (0|TH_CWR|0):
			tp->t_flags2 |= TF2_ACE_PERMIT;
			tp->t_flags2 &= ~TF2_ECN_PERMIT;
			tp->t_scep = 5;
			TCPSTAT_INC(tcps_ecn_shs);
			TCPSTAT_INC(tcps_ace_nect);
			break;
		/* ECT0 SYN */
		case (TH_AE|0|0):
			tp->t_flags2 |= TF2_ACE_PERMIT;
			tp->t_flags2 &= ~TF2_ECN_PERMIT;
			tp->t_scep = 5;
			TCPSTAT_INC(tcps_ecn_shs);
			TCPSTAT_INC(tcps_ace_ect0);
			break;
		/* ECT1 SYN */
		case (0|TH_CWR|TH_ECE):
			tp->t_flags2 |= TF2_ACE_PERMIT;
			tp->t_flags2 &= ~TF2_ECN_PERMIT;
			tp->t_scep = 5;
			TCPSTAT_INC(tcps_ecn_shs);
			TCPSTAT_INC(tcps_ace_ect1);
			break;
		/* CE SYN */
		case (TH_AE|TH_CWR|0):
			tp->t_flags2 |= TF2_ACE_PERMIT;
			tp->t_flags2 &= ~TF2_ECN_PERMIT;
			tp->t_scep = 6;
			/*
			 * reduce the IW to 2 MSS (to
			 * account for delayed acks) if
			 * the SYN,ACK was CE marked
			 */
			tp->snd_cwnd = 2 * tcp_maxseg(tp);
			TCPSTAT_INC(tcps_ecn_shs);
			TCPSTAT_INC(tcps_ace_nect);
			break;
		default:
			tp->t_flags2 &= ~(TF2_ECN_PERMIT | TF2_ACE_PERMIT);
			break;
		}
		/*
		 * Set the AccECN Codepoints on
		 * the outgoing <ACK> to the ECN
		 * state of the <SYN,ACK>
		 * according to table 3 in the
		 * AccECN draft
		 */
		switch (iptos & IPTOS_ECN_MASK) {
		case (IPTOS_ECN_NOTECT):
			tp->t_rcep = 0b010;
			break;
		case (IPTOS_ECN_ECT0):
			tp->t_rcep = 0b100;
			break;
		case (IPTOS_ECN_ECT1):
			tp->t_rcep = 0b011;
			break;
		case (IPTOS_ECN_CE):
			tp->t_rcep = 0b110;
			break;
		}
	}
}

/*
 * Handle parallel SYN for ECN
 */
void
tcp_ecn_input_parallel_syn(struct tcpcb *tp, uint16_t thflags, int iptos)
{
	if (thflags & TH_ACK)
		return;
	if (V_tcp_do_ecn == 0)
		return;
	if ((V_tcp_do_ecn == 1) ||
	    (V_tcp_do_ecn == 2)) {
		/* RFC3168 ECN handling */
		if ((thflags & (TH_CWR | TH_ECE)) == (TH_CWR | TH_ECE)) {
			tp->t_flags2 |= TF2_ECN_PERMIT;
			tp->t_flags2 &= ~TF2_ACE_PERMIT;
			tp->t_flags2 |= TF2_ECN_SND_ECE;
			TCPSTAT_INC(tcps_ecn_shs);
		}
	} else
	if ((V_tcp_do_ecn == 3) ||
	    (V_tcp_do_ecn == 4)) {
		/* AccECN handling */
		switch (thflags & (TH_AE | TH_CWR | TH_ECE)) {
		default:
		case (0|0|0):
			tp->t_flags2 &= ~(TF2_ECN_PERMIT | TF2_ACE_PERMIT);
			break;
		case (0|TH_CWR|TH_ECE):
			tp->t_flags2 |= TF2_ECN_PERMIT;
			tp->t_flags2 &= ~TF2_ACE_PERMIT;
			tp->t_flags2 |= TF2_ECN_SND_ECE;
			TCPSTAT_INC(tcps_ecn_shs);
			break;
		case (TH_AE|TH_CWR|TH_ECE):
			tp->t_flags2 |= TF2_ACE_PERMIT;
			tp->t_flags2 &= ~TF2_ECN_PERMIT;
			TCPSTAT_INC(tcps_ecn_shs);
			/*
			 * Set the AccECN Codepoints on
			 * the outgoing <ACK> to the ECN
			 * state of the <SYN,ACK>
			 * according to table 3 in the
			 * AccECN draft
			 */
			switch (iptos & IPTOS_ECN_MASK) {
			case (IPTOS_ECN_NOTECT):
				tp->t_rcep = 0b010;
				break;
			case (IPTOS_ECN_ECT0):
				tp->t_rcep = 0b100;
				break;
			case (IPTOS_ECN_ECT1):
				tp->t_rcep = 0b011;
				break;
			case (IPTOS_ECN_CE):
				tp->t_rcep = 0b110;
				break;
			}
			break;
		}
	}
}

/*
 * TCP ECN processing.
 */
int
tcp_ecn_input_segment(struct tcpcb *tp, uint16_t thflags, int tlen, int pkts, int iptos)
{
	int delta_cep = 0;

	if (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) {
		switch (iptos & IPTOS_ECN_MASK) {
		case IPTOS_ECN_CE:
			TCPSTAT_INC(tcps_ecn_ce);
			break;
		case IPTOS_ECN_ECT0:
			TCPSTAT_INC(tcps_ecn_ect0);
			break;
		case IPTOS_ECN_ECT1:
			TCPSTAT_INC(tcps_ecn_ect1);
			break;
		}

		if (tp->t_flags2 & TF2_ACE_PERMIT) {
			if ((iptos & IPTOS_ECN_MASK) == IPTOS_ECN_CE)
				tp->t_rcep += 1;
			if (tp->t_flags2 & TF2_ECN_PERMIT) {
				delta_cep = (tcp_ecn_get_ace(thflags) + 8 -
					    (tp->t_scep & 7)) & 7;
				if (delta_cep < pkts)
					delta_cep = pkts -
					    ((pkts - delta_cep) & 7);
				tp->t_scep += delta_cep;
			} else {
				/*
				 * process the final ACK of the 3WHS
				 * see table 3 in draft-ietf-tcpm-accurate-ecn
				 */
				switch (tcp_ecn_get_ace(thflags)) {
				case 0b010:
					/* nonECT SYN or SYN,ACK */
					/* Fallthrough */
				case 0b011:
					/* ECT1 SYN or SYN,ACK */
					/* Fallthrough */
				case 0b100:
					/* ECT0 SYN or SYN,ACK */
					tp->t_scep = 5;
					break;
				case 0b110:
					/* CE SYN or SYN,ACK */
					tp->t_scep = 6;
					tp->snd_cwnd = 2 * tcp_maxseg(tp);
					break;
				default:
					/* mangled AccECN handshake */
					tp->t_scep = 5;
					break;
				}
				tp->t_flags2 |= TF2_ECN_PERMIT;
			}
		} else {
			/* RFC3168 ECN handling */
			if ((thflags & (TH_SYN | TH_ECE)) == TH_ECE) {
				delta_cep = 1;
				tp->t_scep++;
			}
			if (thflags & TH_CWR) {
				tp->t_flags2 &= ~TF2_ECN_SND_ECE;
				tp->t_flags |= TF_ACKNOW;
			}
			if ((iptos & IPTOS_ECN_MASK) == IPTOS_ECN_CE)
				tp->t_flags2 |= TF2_ECN_SND_ECE;
		}

		/* Process a packet differently from RFC3168. */
		cc_ecnpkt_handler_flags(tp, thflags, iptos);
	}

	return delta_cep;
}

/*
 * Send ECN setup <SYN> packet header flags
 */
uint16_t
tcp_ecn_output_syn_sent(struct tcpcb *tp)
{
	uint16_t thflags = 0;

	if (V_tcp_do_ecn == 0)
		return thflags;
	if (V_tcp_do_ecn == 1) {
		/* Send a RFC3168 ECN setup <SYN> packet */
		if (tp->t_rxtshift >= 1) {
			if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
				thflags = TH_ECE|TH_CWR;
		} else
			thflags = TH_ECE|TH_CWR;
	} else
	if (V_tcp_do_ecn == 3) {
		/* Send an Accurate ECN setup <SYN> packet */
		if (tp->t_rxtshift >= 1) {
			if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
				thflags = TH_ECE|TH_CWR|TH_AE;
		} else
			thflags = TH_ECE|TH_CWR|TH_AE;
	}

	return thflags;
}

/*
 * output processing of ECN feature
 * returning IP ECN header codepoint
 */
int
tcp_ecn_output_established(struct tcpcb *tp, uint16_t *thflags, int len, bool rxmit)
{
	int ipecn = IPTOS_ECN_NOTECT;
	bool newdata;

	/*
	 * If the peer has ECN, mark data packets with
	 * ECN capable transmission (ECT).
	 * Ignore pure control packets, retransmissions
	 * and window probes.
	 */
	newdata = (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
		    !rxmit &&
		    !((tp->t_flags & TF_FORCEDATA) && len == 1));
	/* RFC3168 ECN marking, only new data segments */
	if (newdata) {
		ipecn = IPTOS_ECN_ECT0;
		TCPSTAT_INC(tcps_ecn_ect0);
	}
	/*
	 * Reply with proper ECN notifications.
	 */
	if (tp->t_flags2 & TF2_ACE_PERMIT) {
		*thflags &= ~(TH_AE|TH_CWR|TH_ECE);
		if (tp->t_rcep & 0x01)
			*thflags |= TH_ECE;
		if (tp->t_rcep & 0x02)
			*thflags |= TH_CWR;
		if (tp->t_rcep & 0x04)
			*thflags |= TH_AE;
		if (!(tp->t_flags2 & TF2_ECN_PERMIT)) {
			/*
			 * here we process the final
			 * ACK of the 3WHS
			 */
			if (tp->t_rcep == 0b110) {
				tp->t_rcep = 6;
			} else {
				tp->t_rcep = 5;
			}
			tp->t_flags2 |= TF2_ECN_PERMIT;
		}
	} else {
		if (newdata &&
		    (tp->t_flags2 & TF2_ECN_SND_CWR)) {
			*thflags |= TH_CWR;
			tp->t_flags2 &= ~TF2_ECN_SND_CWR;
		}
		if (tp->t_flags2 & TF2_ECN_SND_ECE)
			*thflags |= TH_ECE;
	}

	return ipecn;
}

/*
 * Set up the ECN related tcpcb fields from
 * a syncache entry
 */
void
tcp_ecn_syncache_socket(struct tcpcb *tp, struct syncache *sc)
{
	if (sc->sc_flags & SCF_ECN_MASK) {
		switch (sc->sc_flags & SCF_ECN_MASK) {
		case SCF_ECN:
			tp->t_flags2 |= TF2_ECN_PERMIT;
			break;
		case SCF_ACE_N:
			/* Fallthrough */
		case SCF_ACE_0:
			/* Fallthrough */
		case SCF_ACE_1:
			tp->t_flags2 |= TF2_ACE_PERMIT;
			tp->t_scep = 5;
			tp->t_rcep = 5;
			break;
		case SCF_ACE_CE:
			tp->t_flags2 |= TF2_ACE_PERMIT;
			tp->t_scep = 6;
			tp->t_rcep = 6;
			break;
		/* undefined SCF codepoint */
		default:
			break;
		}
	}
}

/*
 * Process a <SYN> packets ECN information, and provide the
 * syncache with the relevant information.
 */
int
tcp_ecn_syncache_add(uint16_t thflags, int iptos)
{
	int scflags = 0;

	switch (thflags & (TH_AE|TH_CWR|TH_ECE)) {
	/* no ECN */
	case (0|0|0):
		break;
	/* legacy ECN */
	case (0|TH_CWR|TH_ECE):
		scflags = SCF_ECN;
		break;
	/* Accurate ECN */
	case (TH_AE|TH_CWR|TH_ECE):
		if ((V_tcp_do_ecn == 3) ||
		    (V_tcp_do_ecn == 4)) {
			switch (iptos & IPTOS_ECN_MASK) {
			case IPTOS_ECN_CE:
				scflags = SCF_ACE_CE;
				break;
			case IPTOS_ECN_ECT0:
				scflags = SCF_ACE_0;
				break;
			case IPTOS_ECN_ECT1:
				scflags = SCF_ACE_1;
				break;
			case IPTOS_ECN_NOTECT:
				scflags = SCF_ACE_N;
				break;
			}
		} else
			scflags = SCF_ECN;
		break;
	/* Default Case (section 3.1.2) */
	default:
		if ((V_tcp_do_ecn == 3) ||
		    (V_tcp_do_ecn == 4)) {
			switch (iptos & IPTOS_ECN_MASK) {
			case IPTOS_ECN_CE:
				scflags = SCF_ACE_CE;
				break;
			case IPTOS_ECN_ECT0:
				scflags = SCF_ACE_0;
				break;
			case IPTOS_ECN_ECT1:
				scflags = SCF_ACE_1;
				break;
			case IPTOS_ECN_NOTECT:
				scflags = SCF_ACE_N;
				break;
			}
		}
		break;
	}
	return scflags;
}

/*
 * Set up the ECN information for the <SYN,ACK> from
 * syncache information.
 */
uint16_t
tcp_ecn_syncache_respond(uint16_t thflags, struct syncache *sc)
{
	if ((thflags & TH_SYN) &&
	    (sc->sc_flags & SCF_ECN_MASK)) {
		switch (sc->sc_flags & SCF_ECN_MASK) {
		case SCF_ECN:
			thflags |= (0 | 0 | TH_ECE);
			TCPSTAT_INC(tcps_ecn_shs);
			break;
		case SCF_ACE_N:
			thflags |= (0 | TH_CWR | 0);
			TCPSTAT_INC(tcps_ecn_shs);
			TCPSTAT_INC(tcps_ace_nect);
			break;
		case SCF_ACE_0:
			thflags |= (TH_AE | 0 | 0);
			TCPSTAT_INC(tcps_ecn_shs);
			TCPSTAT_INC(tcps_ace_ect0);
			break;
		case SCF_ACE_1:
			thflags |= (0 | TH_ECE | TH_CWR);
			TCPSTAT_INC(tcps_ecn_shs);
			TCPSTAT_INC(tcps_ace_ect1);
			break;
		case SCF_ACE_CE:
			thflags |= (TH_AE | TH_CWR | 0);
			TCPSTAT_INC(tcps_ecn_shs);
			TCPSTAT_INC(tcps_ace_ce);
			break;
		/* undefined SCF codepoint */
		default:
			break;
		}
	}
	return thflags;
}

int
tcp_ecn_get_ace(uint16_t thflags)
{
	int ace = 0;

	if (thflags & TH_ECE)
		ace += 1;
	if (thflags & TH_CWR)
		ace += 2;
	if (thflags & TH_AE)
		ace += 4;
	return ace;
}