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freebsd-dev/sys/netinet/tcp_ecn.c
Gleb Smirnoff eaabc93764 tcp: retire TCPDEBUG 
This subsystem is superseded by modern debugging facilities,
e.g. DTrace probes and TCP black box logging.

We intentionally leave SO_DEBUG in place, as many utilities may
set it on a socket.  Also the tcp::debug DTrace probes look at
this flag on a socket.

Reviewed by:		gnn, tuexen
Discussed with:		rscheff, rrs, jtl
Differential revision:	https://reviews.freebsd.org/D37694
2022-12-14 09:54:06 -08:00

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/*-
* 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 <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;
switch (iptos & IPTOS_ECN_MASK) {
case IPTOS_ECN_CE:
TCPSTAT_INC(tcps_ecn_rcvce);
break;
case IPTOS_ECN_ECT0:
TCPSTAT_INC(tcps_ecn_rcvect0);
break;
case IPTOS_ECN_ECT1:
TCPSTAT_INC(tcps_ecn_rcvect1);
break;
}
if (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) {
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) {
if (tp->t_flags2 & TF2_ECN_USE_ECT1) {
ipecn = IPTOS_ECN_ECT1;
TCPSTAT_INC(tcps_ecn_sndect1);
} else {
ipecn = IPTOS_ECN_ECT0;
TCPSTAT_INC(tcps_ecn_sndect0);
}
}
/*
* 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 (iptos & IPTOS_ECN_MASK) {
case IPTOS_ECN_CE:
TCPSTAT_INC(tcps_ecn_rcvce);
break;
case IPTOS_ECN_ECT0:
TCPSTAT_INC(tcps_ecn_rcvect0);
break;
case IPTOS_ECN_ECT1:
TCPSTAT_INC(tcps_ecn_rcvect1);
break;
}
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;
}
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