/*-
 * 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.
 */

/*
 * 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 "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 inline int  tcp_ecn_get_ace(uint16_t);
static inline void tcp_ecn_set_ace(uint16_t *, uint32_t);

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)
{
        switch (V_tcp_do_ecn) {
        case 0:
                return;
        case 1:
                /* FALLTHROUGH */
        case 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);
                }
                break;
        case 3:
                /* FALLTHROUGH */
        case 4:
                /*
                 * Decoding Accurate ECN according to
                 * table in section 3.1.1
                 *
                 * 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;
                }
                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;
        switch (V_tcp_do_ecn) {
        case 0:
                return;
        case 1:
                /* FALLTHROUGH */
        case 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);
                }
                break;
        case 3:
                /* FALLTHROUGH */
        case 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;
                }
                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;
                                if ((tp->t_state == TCPS_ESTABLISHED) ||
                                    (tp->t_state == TCPS_FIN_WAIT_1) ||
                                    (tp->t_state == TCPS_FIN_WAIT_2))
                                        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) {
                tcp_ecn_set_ace(thflags, tp->t_rcep);
                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;
                }
        }
}

/*
 * 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;
                }
        }
        return thflags;
}

static inline int
tcp_ecn_get_ace(uint16_t thflags)
{
        return ((thflags & (TH_AE|TH_CWR|TH_ECE)) >> TH_ACE_SHIFT);
}

static inline void
tcp_ecn_set_ace(uint16_t *thflags, uint32_t t_rcep)
{
        *thflags &= ~(TH_AE|TH_CWR|TH_ECE);
        *thflags |= ((t_rcep << TH_ACE_SHIFT) & (TH_AE|TH_CWR|TH_ECE));
}