/*-
 * Copyright (c) 2016-2020 Netflix, 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.
 *
 * 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.
 *
 */
/*
 * Author: Randall Stewart <rrs@netflix.com>
 * This work is based on the ACM Queue paper
 * BBR - Congestion Based Congestion Control
 * and also numerous discussions with Neal, Yuchung and Van.
 */

#include <sys/cdefs.h>
#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_ratelimit.h"
#include <sys/param.h>
#include <sys/arb.h>
#include <sys/module.h>
#include <sys/kernel.h>
#ifdef TCP_HHOOK
#include <sys/hhook.h>
#endif
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/proc.h>
#include <sys/qmath.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/tree.h>
#ifdef NETFLIX_STATS
#include <sys/stats.h> /* Must come after qmath.h and tree.h */
#endif
#include <sys/refcount.h>
#include <sys/queue.h>
#include <sys/smp.h>
#include <sys/kthread.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/tim_filter.h>
#include <sys/time.h>
#include <vm/uma.h>
#include <sys/kern_prefetch.h>

#include <net/route.h>
#include <net/vnet.h>
#include <net/ethernet.h>
#include <net/bpf.h>

#define TCPSTATES               /* for logging */

#include <netinet/in.h>
#include <netinet/in_kdtrace.h>
#include <netinet/in_pcb.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/ip6.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcpip.h>
#include <netinet/tcp_ecn.h>
#include <netinet/tcp_hpts.h>
#include <netinet/tcp_lro.h>
#include <netinet/cc/cc.h>
#include <netinet/tcp_log_buf.h>
#ifdef TCP_OFFLOAD
#include <netinet/tcp_offload.h>
#endif
#ifdef INET6
#include <netinet6/tcp6_var.h>
#endif
#include <netinet/tcp_fastopen.h>

#include <netipsec/ipsec_support.h>
#include <net/if.h>
#include <net/if_var.h>
#include <net/if_private.h>

#if defined(IPSEC) || defined(IPSEC_SUPPORT)
#include <netipsec/ipsec.h>
#include <netipsec/ipsec6.h>
#endif                          /* IPSEC */

#include <netinet/udp.h>
#include <netinet/udp_var.h>
#include <machine/in_cksum.h>

#ifdef MAC
#include <security/mac/mac_framework.h>
#endif
#include "rack_bbr_common.h"

/*
 * Common TCP Functions - These are shared by borth
 * rack and BBR.
 */
static int
ctf_get_enet_type(struct ifnet *ifp, struct mbuf *m)
{
        struct ether_header *eh;
#ifdef INET6
        struct ip6_hdr *ip6 = NULL;     /* Keep compiler happy. */
#endif
#ifdef INET
        struct ip *ip = NULL;           /* Keep compiler happy. */
#endif
#if defined(INET) || defined(INET6)
        struct tcphdr *th;
        int32_t tlen;
        uint16_t drop_hdrlen;
#endif
        uint16_t etype;
#ifdef INET
        uint8_t iptos;
#endif

        /* Is it the easy way? */
        if (m->m_flags & M_LRO_EHDRSTRP)
                return (m->m_pkthdr.lro_etype);
        /*
         * Ok this is the old style call, the ethernet header is here.
         * This also means no checksum or BPF were done. This
         * can happen if the race to setup the inp fails and
         * LRO sees no INP at packet input, but by the time
         * we queue the packets an INP gets there. Its rare
         * but it can occur so we will handle it. Note that
         * this means duplicated work but with the rarity of it
         * its not worth worrying about.
         */
        /* Let the BPF see the packet */
        if (bpf_peers_present(ifp->if_bpf))
                ETHER_BPF_MTAP(ifp, m);
        /* Now the csum */
        eh = mtod(m, struct ether_header *);
        etype = ntohs(eh->ether_type);
        m_adj(m,  sizeof(*eh));
        switch (etype) {
#ifdef INET6
                case ETHERTYPE_IPV6:
                {
                        if (m->m_len < (sizeof(*ip6) + sizeof(*th))) {
                                m = m_pullup(m, sizeof(*ip6) + sizeof(*th));
                                if (m == NULL) {
                                        KMOD_TCPSTAT_INC(tcps_rcvshort);
                                        return (-1);
                                }
                        }
                        ip6 = (struct ip6_hdr *)(eh + 1);
                        th = (struct tcphdr *)(ip6 + 1);
                        drop_hdrlen = sizeof(*ip6);
                        tlen = ntohs(ip6->ip6_plen);
                        if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
                                if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
                                        th->th_sum = m->m_pkthdr.csum_data;
                                else
                                        th->th_sum = in6_cksum_pseudo(ip6, tlen,
                                                                      IPPROTO_TCP,
                                                                      m->m_pkthdr.csum_data);
                                th->th_sum ^= 0xffff;
                        } else
                                th->th_sum = in6_cksum(m, IPPROTO_TCP, drop_hdrlen, tlen);
                        if (th->th_sum) {
                                KMOD_TCPSTAT_INC(tcps_rcvbadsum);
                                m_freem(m);
                                return (-1);
                        }
                        return (etype);
                }
#endif
#ifdef INET
                case ETHERTYPE_IP:
                {
                        if (m->m_len < sizeof (struct tcpiphdr)) {
                                m = m_pullup(m, sizeof (struct tcpiphdr));
                                if (m == NULL) {
                                        KMOD_TCPSTAT_INC(tcps_rcvshort);
                                        return (-1);
                                }
                        }
                        ip = (struct ip *)(eh + 1);
                        th = (struct tcphdr *)(ip + 1);
                        drop_hdrlen = sizeof(*ip);
                        iptos = ip->ip_tos;
                        tlen = ntohs(ip->ip_len) - sizeof(struct ip);
                        if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
                                if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
                                        th->th_sum = m->m_pkthdr.csum_data;
                                else
                                        th->th_sum = in_pseudo(ip->ip_src.s_addr,
                                                               ip->ip_dst.s_addr,
                                                               htonl(m->m_pkthdr.csum_data + tlen + IPPROTO_TCP));
                                th->th_sum ^= 0xffff;
                        } else {
                                int len;
                                struct ipovly *ipov = (struct ipovly *)ip;
                                /*
                                 * Checksum extended TCP header and data.
                                 */
                                len = drop_hdrlen + tlen;
                                bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
                                ipov->ih_len = htons(tlen);
                                th->th_sum = in_cksum(m, len);
                                /* Reset length for SDT probes. */
                                ip->ip_len = htons(len);
                                /* Reset TOS bits */
                                ip->ip_tos = iptos;
                                /* Re-initialization for later version check */
                                ip->ip_v = IPVERSION;
                                ip->ip_hl = sizeof(*ip) >> 2;
                        }
                        if (th->th_sum) {
                                KMOD_TCPSTAT_INC(tcps_rcvbadsum);
                                m_freem(m);
                                return (-1);
                        }
                        break;
                }
#endif
        };
        return (etype);
}

/*
 * The function ctf_process_inbound_raw() is used by
 * transport developers to do the steps needed to
 * support MBUF Queuing i.e. the flags in
 * inp->inp_flags2:
 *
 * - INP_SUPPORTS_MBUFQ
 * - INP_MBUF_QUEUE_READY
 * - INP_DONT_SACK_QUEUE
 * - INP_MBUF_ACKCMP
 *
 * These flags help control how LRO will deliver
 * packets to the transport. You first set in inp_flags2
 * the INP_SUPPORTS_MBUFQ to tell the LRO code that you
 * will gladly take a queue of packets instead of a compressed
 * single packet. You also set in your t_fb pointer the
 * tfb_do_queued_segments to point to ctf_process_inbound_raw.
 *
 * This then gets you lists of inbound ACK's/Data instead
 * of a condensed compressed ACK/DATA packet. Why would you
 * want that? This will get you access to all the arrival
 * times of at least LRO and possibly at the Hardware (if
 * the interface card supports that) of the actual ACK/DATA.
 * In some transport designs this is important since knowing
 * the actual time we got the packet is useful information.
 *
 * A new special type of mbuf may also be supported by the transport
 * if it has set the INP_MBUF_ACKCMP flag. If its set, LRO will
 * possibly create a M_ACKCMP type mbuf. This is a mbuf with
 * an array of "acks". One thing also to note is that when this
 * occurs a subsequent LRO may find at the back of the untouched
 * mbuf queue chain a M_ACKCMP and append on to it. This means
 * that until the transport pulls in the mbuf chain queued
 * for it more ack's may get on the mbufs that were already
 * delivered. There currently is a limit of 6 acks condensed
 * into 1 mbuf which means often when this is occuring, we
 * don't get that effect but it does happen.
 *
 * Now there are some interesting Caveats that the transport
 * designer needs to take into account when using this feature.
 *
 * 1) It is used with HPTS and pacing, when the pacing timer
 *    for output calls it will first call the input.
 * 2) When you set INP_MBUF_QUEUE_READY this tells LRO
 *    queue normal packets, I am busy pacing out data and
 *    will process the queued packets before my tfb_tcp_output
 *    call from pacing. If a non-normal packet arrives, (e.g. sack)
 *    you will be awoken immediately.
 * 3) Finally you can add the INP_DONT_SACK_QUEUE to not even
 *    be awoken if a SACK has arrived. You would do this when
 *    you were not only running a pacing for output timer
 *    but a Rack timer as well i.e. you know you are in recovery
 *    and are in the process (via the timers) of dealing with
 *    the loss.
 *
 * Now a critical thing you must be aware of here is that the
 * use of the flags has a far greater scope then just your
 * typical LRO. Why? Well thats because in the normal compressed
 * LRO case at the end of a driver interupt all packets are going
 * to get presented to the transport no matter if there is one
 * or 100. With the MBUF_QUEUE model, this is not true. You will
 * only be awoken to process the queue of packets when:
 *     a) The flags discussed above allow it.
 *          <or>
 *     b) You exceed a ack or data limit (by default the
 *        ack limit is infinity (64k acks) and the data
 *        limit is 64k of new TCP data)
 *         <or>
 *     c) The push bit has been set by the peer
 */

static int
ctf_process_inbound_raw(struct tcpcb *tp, struct mbuf *m, int has_pkt)
{
        /*
         * We are passed a raw change of mbuf packets
         * that arrived in LRO. They are linked via
         * the m_nextpkt link in the pkt-headers.
         *
         * We process each one by:
         * a) saving off the next
         * b) stripping off the ether-header
         * c) formulating the arguments for tfb_do_segment_nounlock()
         * d) calling each mbuf to tfb_do_segment_nounlock()
         *    after adjusting the time to match the arrival time.
         * Note that the LRO code assures no IP options are present.
         *
         * The symantics for calling tfb_do_segment_nounlock() are the
         * following:
         * 1) It returns 0 if all went well and you (the caller) need
         *    to release the lock.
         * 2) If nxt_pkt is set, then the function will surpress calls
         *    to tcp_output() since you are promising to call again
         *    with another packet.
         * 3) If it returns 1, then you must free all the packets being
         *    shipped in, the tcb has been destroyed (or about to be destroyed).
         */
        struct mbuf *m_save;
        struct tcphdr *th;
#ifdef INET6
        struct ip6_hdr *ip6 = NULL;     /* Keep compiler happy. */
#endif
#ifdef INET
        struct ip *ip = NULL;           /* Keep compiler happy. */
#endif
        struct ifnet *ifp;
        struct timeval tv;
        struct inpcb *inp __diagused;
        int32_t retval, nxt_pkt, tlen, off;
        int etype = 0;
        uint16_t drop_hdrlen;
        uint8_t iptos;

        inp = tptoinpcb(tp);
        INP_WLOCK_ASSERT(inp);
        NET_EPOCH_ASSERT();
        KASSERT(m != NULL, ("ctf_process_inbound_raw: m == NULL"));
        ifp = m_rcvif(m);
        KASSERT(ifp != NULL, ("ctf_process_inbound_raw: ifp == NULL"));
        CURVNET_SET(ifp->if_vnet);
        tcp_get_usecs(&tv);
        while (m) {
                m_save = m->m_nextpkt;
                m->m_nextpkt = NULL;
                if ((m->m_flags & M_ACKCMP) == 0) {
                        /* Now lets get the ether header */
                        etype = ctf_get_enet_type(ifp, m);
                        if (etype == -1) {
                                /* Skip this packet it was freed by checksum */
                                goto skipped_pkt;
                        }
                        KASSERT(((etype == ETHERTYPE_IPV6) || (etype == ETHERTYPE_IP)),
                                ("tp:%p m:%p etype:0x%x -- not IP or IPv6", tp, m, etype));
                        /* Trim off the ethernet header */
                        switch (etype) {
#ifdef INET6
                        case ETHERTYPE_IPV6:
                                ip6 = mtod(m, struct ip6_hdr *);
                                th = (struct tcphdr *)(ip6 + 1);
                                tlen = ntohs(ip6->ip6_plen);
                                drop_hdrlen = sizeof(*ip6);
                                iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
                                break;
#endif
#ifdef INET
                        case ETHERTYPE_IP:
                                ip = mtod(m, struct ip *);
                                th = (struct tcphdr *)(ip + 1);
                                drop_hdrlen = sizeof(*ip);
                                iptos = ip->ip_tos;
                                tlen = ntohs(ip->ip_len) - sizeof(struct ip);
                                break;
#endif
                        } /* end switch */
                        off = th->th_off << 2;
                        if (off < sizeof (struct tcphdr) || off > tlen) {
                                printf("off:%d < hdrlen:%zu || > tlen:%u -- dump\n",
                                       off,
                                       sizeof(struct tcphdr),
                                       tlen);
                                KMOD_TCPSTAT_INC(tcps_rcvbadoff);
                                m_freem(m);
                                goto skipped_pkt;
                        }
                        tlen -= off;
                        drop_hdrlen += off;
                        /*
                         * Now lets setup the timeval to be when we should
                         * have been called (if we can).
                         */
                        m->m_pkthdr.lro_nsegs = 1;
                        /* Now what about next packet? */
                } else {
                        /*
                         * This mbuf is an array of acks that have
                         * been compressed. We assert the inp has
                         * the flag set to enable this!
                         */
                        KASSERT((tp->t_flags2 & TF2_MBUF_ACKCMP),
                            ("tp:%p no TF2_MBUF_ACKCMP flags?", tp));
                        tlen = 0;
                        drop_hdrlen = 0;
                        th = NULL;
                        iptos = 0;
                }
                tcp_get_usecs(&tv);
                if (m_save || has_pkt)
                        nxt_pkt = 1;
                else
                        nxt_pkt = 0;
                if ((m->m_flags & M_ACKCMP) == 0)
                        KMOD_TCPSTAT_INC(tcps_rcvtotal);
                else
                        KMOD_TCPSTAT_ADD(tcps_rcvtotal, (m->m_len / sizeof(struct tcp_ackent)));
                retval = (*tp->t_fb->tfb_do_segment_nounlock)(tp, m, th,
                    drop_hdrlen, tlen, iptos, nxt_pkt, &tv);
                if (retval) {
                        /* We lost the lock and tcb probably */
                        m = m_save;
                        while(m) {
                                m_save = m->m_nextpkt;
                                m->m_nextpkt = NULL;
                                m_freem(m);
                                m = m_save;
                        }
                        CURVNET_RESTORE();
                        INP_UNLOCK_ASSERT(inp);
                        return (retval);
                }
skipped_pkt:
                m = m_save;
        }
        CURVNET_RESTORE();
        return (0);
}

int
ctf_do_queued_segments(struct tcpcb *tp, int have_pkt)
{
        struct mbuf *m;

        /* First lets see if we have old packets */
        if ((m = STAILQ_FIRST(&tp->t_inqueue)) != NULL) {
                STAILQ_INIT(&tp->t_inqueue);
                if (ctf_process_inbound_raw(tp, m, have_pkt)) {
                        /* We lost the tcpcb (maybe a RST came in)? */
                        return(1);
                }
        }
        return (0);
}

uint32_t
ctf_outstanding(struct tcpcb *tp)
{
        uint32_t bytes_out;

        bytes_out = tp->snd_max - tp->snd_una;
        if (tp->t_state < TCPS_ESTABLISHED)
                bytes_out++;
        if (tp->t_flags & TF_SENTFIN)
                bytes_out++;
        return (bytes_out);
}

uint32_t
ctf_flight_size(struct tcpcb *tp, uint32_t rc_sacked)
{
        if (rc_sacked <= ctf_outstanding(tp))
                return(ctf_outstanding(tp) - rc_sacked);
        else {
                return (0);
        }
}

void
ctf_do_dropwithreset(struct mbuf *m, struct tcpcb *tp, struct tcphdr *th,
    int32_t tlen)
{
        tcp_dropwithreset(m, th, tp, tlen);
        if (tp != NULL)
                INP_WUNLOCK(tptoinpcb(tp));
}

void
ctf_ack_war_checks(struct tcpcb *tp)
{
        sbintime_t now;

        if ((V_tcp_ack_war_time_window > 0) && (V_tcp_ack_war_cnt > 0)) {
                now = getsbinuptime();
                if (tp->t_challenge_ack_end < now) {
                        tp->t_challenge_ack_cnt = 0;
                        tp->t_challenge_ack_end = now +
                            V_tcp_ack_war_time_window * SBT_1MS;
                }
                if (tp->t_challenge_ack_cnt < V_tcp_ack_war_cnt) {
                        tp->t_challenge_ack_cnt++;
                        tp->t_flags |= TF_ACKNOW;
                } else
                        tp->t_flags &= ~TF_ACKNOW;
        } else
                tp->t_flags |= TF_ACKNOW;
}

/*
 * ctf_drop_checks returns 1 for you should not proceed. It places
 * in ret_val what should be returned 1/0 by the caller. The 1 indicates
 * that the TCB is unlocked and probably dropped. The 0 indicates the
 * TCB is still valid and locked.
 */
int
ctf_drop_checks(struct tcpopt *to, struct mbuf *m, struct tcphdr *th,
                struct tcpcb *tp, int32_t *tlenp,
                int32_t *thf, int32_t *drop_hdrlen, int32_t *ret_val)
{
        int32_t todrop;
        int32_t thflags;
        int32_t tlen;

        thflags = *thf;
        tlen = *tlenp;
        todrop = tp->rcv_nxt - th->th_seq;
        if (todrop > 0) {
                if (thflags & TH_SYN) {
                        thflags &= ~TH_SYN;
                        th->th_seq++;
                        if (th->th_urp > 1)
                                th->th_urp--;
                        else
                                thflags &= ~TH_URG;
                        todrop--;
                }
                /*
                 * Following if statement from Stevens, vol. 2, p. 960.
                 */
                if (todrop > tlen
                    || (todrop == tlen && (thflags & TH_FIN) == 0)) {
                        /*
                         * Any valid FIN must be to the left of the window.
                         * At this point the FIN must be a duplicate or out
                         * of sequence; drop it.
                         */
                        thflags &= ~TH_FIN;
                        /*
                         * Send an ACK to resynchronize and drop any data.
                         * But keep on processing for RST or ACK.
                         */
                        ctf_ack_war_checks(tp);
                        todrop = tlen;
                        KMOD_TCPSTAT_INC(tcps_rcvduppack);
                        KMOD_TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
                } else {
                        KMOD_TCPSTAT_INC(tcps_rcvpartduppack);
                        KMOD_TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
                }
                /*
                 * DSACK - add SACK block for dropped range
                 */
                if ((todrop > 0) && (tp->t_flags & TF_SACK_PERMIT)) {
                        /*
                         * ACK now, as the next in-sequence segment
                         * will clear the DSACK block again
                         */
                        ctf_ack_war_checks(tp);
                        if (tp->t_flags & TF_ACKNOW)
                                tcp_update_sack_list(tp, th->th_seq,
                                                     th->th_seq + todrop);
                }
                *drop_hdrlen += todrop; /* drop from the top afterwards */
                th->th_seq += todrop;
                tlen -= todrop;
                if (th->th_urp > todrop)
                        th->th_urp -= todrop;
                else {
                        thflags &= ~TH_URG;
                        th->th_urp = 0;
                }
        }
        /*
         * If segment ends after window, drop trailing data (and PUSH and
         * FIN); if nothing left, just ACK.
         */
        todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
        if (todrop > 0) {
                KMOD_TCPSTAT_INC(tcps_rcvpackafterwin);
                if (todrop >= tlen) {
                        KMOD_TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
                        /*
                         * If window is closed can only take segments at
                         * window edge, and have to drop data and PUSH from
                         * incoming segments.  Continue processing, but
                         * remember to ack.  Otherwise, drop segment and
                         * ack.
                         */
                        if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
                                ctf_ack_war_checks(tp);
                                KMOD_TCPSTAT_INC(tcps_rcvwinprobe);
                        } else {
                                ctf_do_dropafterack(m, tp, th, thflags, tlen, ret_val);
                                return (1);
                        }
                } else
                        KMOD_TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
                m_adj(m, -todrop);
                tlen -= todrop;
                thflags &= ~(TH_PUSH | TH_FIN);
        }
        *thf = thflags;
        *tlenp = tlen;
        return (0);
}

/*
 * The value in ret_val informs the caller
 * if we dropped the tcb (and lock) or not.
 * 1 = we dropped it, 0 = the TCB is still locked
 * and valid.
 */
void
ctf_do_dropafterack(struct mbuf *m, struct tcpcb *tp, struct tcphdr *th, int32_t thflags, int32_t tlen, int32_t *ret_val)
{
        /*
         * Generate an ACK dropping incoming segment if it occupies sequence
         * space, where the ACK reflects our state.
         *
         * We can now skip the test for the RST flag since all paths to this
         * code happen after packets containing RST have been dropped.
         *
         * In the SYN-RECEIVED state, don't send an ACK unless the segment
         * we received passes the SYN-RECEIVED ACK test. If it fails send a
         * RST.  This breaks the loop in the "LAND" DoS attack, and also
         * prevents an ACK storm between two listening ports that have been
         * sent forged SYN segments, each with the source address of the
         * other.
         */
        if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
            (SEQ_GT(tp->snd_una, th->th_ack) ||
            SEQ_GT(th->th_ack, tp->snd_max))) {
                *ret_val = 1;
                ctf_do_dropwithreset(m, tp, th, tlen);
                return;
        } else
                *ret_val = 0;
        ctf_ack_war_checks(tp);
        if (m)
                m_freem(m);
}

void
ctf_do_drop(struct mbuf *m, struct tcpcb *tp)
{

        /*
         * Drop space held by incoming segment and return.
         */
        if (tp != NULL)
                INP_WUNLOCK(tptoinpcb(tp));
        if (m)
                m_freem(m);
}

int
ctf_process_rst(struct mbuf *m, struct tcphdr *th, struct socket *so,
                struct tcpcb *tp)
{
        /*
         * RFC5961 Section 3.2
         *
         * - RST drops connection only if SEG.SEQ == RCV.NXT. - If RST is in
         * window, we send challenge ACK.
         *
         * Note: to take into account delayed ACKs, we should test against
         * last_ack_sent instead of rcv_nxt. Note 2: we handle special case
         * of closed window, not covered by the RFC.
         */
        int dropped = 0;

        if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
            SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) ||
            (tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
                KASSERT(tp->t_state != TCPS_SYN_SENT,
                    ("%s: TH_RST for TCPS_SYN_SENT th %p tp %p",
                    __func__, th, tp));

                if (V_tcp_insecure_rst ||
                    (tp->last_ack_sent == th->th_seq) ||
                    (tp->rcv_nxt == th->th_seq)) {
                        KMOD_TCPSTAT_INC(tcps_drops);
                        /* Drop the connection. */
                        switch (tp->t_state) {
                        case TCPS_SYN_RECEIVED:
                                so->so_error = ECONNREFUSED;
                                goto close;
                        case TCPS_ESTABLISHED:
                        case TCPS_FIN_WAIT_1:
                        case TCPS_FIN_WAIT_2:
                        case TCPS_CLOSE_WAIT:
                        case TCPS_CLOSING:
                        case TCPS_LAST_ACK:
                                so->so_error = ECONNRESET;
                close:
                                /* FALLTHROUGH */
                        default:
                                tcp_log_end_status(tp, TCP_EI_STATUS_CLIENT_RST);
                                tp = tcp_close(tp);
                        }
                        dropped = 1;
                        ctf_do_drop(m, tp);
                } else {
                        KMOD_TCPSTAT_INC(tcps_badrst);
                        tcp_send_challenge_ack(tp, th, m);
                }
        } else {
                m_freem(m);
        }
        return (dropped);
}

/*
 * The value in ret_val informs the caller
 * if we dropped the tcb (and lock) or not.
 * 1 = we dropped it, 0 = the TCB is still locked
 * and valid.
 */
void
ctf_challenge_ack(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp, uint8_t iptos, int32_t * ret_val)
{

        NET_EPOCH_ASSERT();

        KMOD_TCPSTAT_INC(tcps_badsyn);
        if (V_tcp_insecure_syn &&
            SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
            SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
                tp = tcp_drop(tp, ECONNRESET);
                *ret_val = 1;
                ctf_do_drop(m, tp);
        } else {
                tcp_ecn_input_syn_sent(tp, tcp_get_flags(th), iptos);
                /* Send challenge ACK. */
                tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
                    tp->snd_nxt, TH_ACK);
                tp->last_ack_sent = tp->rcv_nxt;
                m = NULL;
                *ret_val = 0;
                ctf_do_drop(m, NULL);
        }
}

/*
 * ctf_ts_check returns 1 for you should not proceed, the state
 * machine should return. It places in ret_val what should
 * be returned 1/0 by the caller (hpts_do_segment). The 1 indicates
 * that the TCB is unlocked and probably dropped. The 0 indicates the
 * TCB is still valid and locked.
 */
int
ctf_ts_check(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
    int32_t tlen, int32_t thflags, int32_t * ret_val)
{

        if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
                /*
                 * Invalidate ts_recent.  If this segment updates ts_recent,
                 * the age will be reset later and ts_recent will get a
                 * valid value.  If it does not, setting ts_recent to zero
                 * will at least satisfy the requirement that zero be placed
                 * in the timestamp echo reply when ts_recent isn't valid.
                 * The age isn't reset until we get a valid ts_recent
                 * because we don't want out-of-order segments to be dropped
                 * when ts_recent is old.
                 */
                tp->ts_recent = 0;
        } else {
                KMOD_TCPSTAT_INC(tcps_rcvduppack);
                KMOD_TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
                KMOD_TCPSTAT_INC(tcps_pawsdrop);
                *ret_val = 0;
                if (tlen) {
                        ctf_do_dropafterack(m, tp, th, thflags, tlen, ret_val);
                } else {
                        ctf_do_drop(m, NULL);
                }
                return (1);
        }
        return (0);
}

int
ctf_ts_check_ac(struct tcpcb *tp, int32_t thflags)
{

        if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
                /*
                 * Invalidate ts_recent.  If this segment updates ts_recent,
                 * the age will be reset later and ts_recent will get a
                 * valid value.  If it does not, setting ts_recent to zero
                 * will at least satisfy the requirement that zero be placed
                 * in the timestamp echo reply when ts_recent isn't valid.
                 * The age isn't reset until we get a valid ts_recent
                 * because we don't want out-of-order segments to be dropped
                 * when ts_recent is old.
                 */
                tp->ts_recent = 0;
        } else {
                KMOD_TCPSTAT_INC(tcps_rcvduppack);
                KMOD_TCPSTAT_INC(tcps_pawsdrop);
                return (1);
        }
        return (0);
}



void
ctf_calc_rwin(struct socket *so, struct tcpcb *tp)
{
        int32_t win;

        /*
         * Calculate amount of space in receive window, and then do TCP
         * input processing. Receive window is amount of space in rcv queue,
         * but not less than advertised window.
         */
        win = sbspace(&so->so_rcv);
        if (win < 0)
                win = 0;
        tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
}

void
ctf_do_dropwithreset_conn(struct mbuf *m, struct tcpcb *tp, struct tcphdr *th,
    int32_t tlen)
{

        tcp_dropwithreset(m, th, tp, tlen);
        tp = tcp_drop(tp, ETIMEDOUT);
        if (tp)
                INP_WUNLOCK(tptoinpcb(tp));
}

uint32_t
ctf_fixed_maxseg(struct tcpcb *tp)
{
        return (tcp_fixed_maxseg(tp));
}

void
ctf_log_sack_filter(struct tcpcb *tp, int num_sack_blks, struct sackblk *sack_blocks)
{
        if (tcp_bblogging_on(tp)) {
                union tcp_log_stackspecific log;
                struct timeval tv;

                memset(&log, 0, sizeof(log));
                log.u_bbr.timeStamp = tcp_get_usecs(&tv);
                log.u_bbr.flex8 = num_sack_blks;
                if (num_sack_blks > 0) {
                        log.u_bbr.flex1 = sack_blocks[0].start;
                        log.u_bbr.flex2 = sack_blocks[0].end;
                }
                if (num_sack_blks > 1) {
                        log.u_bbr.flex3 = sack_blocks[1].start;
                        log.u_bbr.flex4 = sack_blocks[1].end;
                }
                if (num_sack_blks > 2) {
                        log.u_bbr.flex5 = sack_blocks[2].start;
                        log.u_bbr.flex6 = sack_blocks[2].end;
                }
                if (num_sack_blks > 3) {
                        log.u_bbr.applimited = sack_blocks[3].start;
                        log.u_bbr.pkts_out = sack_blocks[3].end;
                }
                TCP_LOG_EVENTP(tp, NULL,
                    &tptosocket(tp)->so_rcv,
                    &tptosocket(tp)->so_snd,
                    TCP_SACK_FILTER_RES, 0,
                    0, &log, false, &tv);
        }
}

uint32_t
ctf_decay_count(uint32_t count, uint32_t decay)
{
        /*
         * Given a count, decay it by a set percentage. The
         * percentage is in thousands i.e. 100% = 1000,
         * 19.3% = 193.
         */
        uint64_t perc_count, decay_per;
        uint32_t decayed_count;
        if (decay > 1000) {
                /* We don't raise it */
                return (count);
        }
        perc_count = count;
        decay_per = decay;
        perc_count *= decay_per;
        perc_count /= 1000;
        /*
         * So now perc_count holds the
         * count decay value.
         */
        decayed_count = count - (uint32_t)perc_count;
        return(decayed_count);
}

int32_t
ctf_progress_timeout_check(struct tcpcb *tp, bool log)
{
        if (tp->t_maxunacktime && tp->t_acktime && TSTMP_GT(ticks, tp->t_acktime)) {
                if ((ticks - tp->t_acktime) >= tp->t_maxunacktime) {
                        /*
                         * There is an assumption that the caller
                         * will drop the connection so we will
                         * increment the counters here.
                         */
                        if (log)
                                tcp_log_end_status(tp, TCP_EI_STATUS_PROGRESS);
#ifdef NETFLIX_STATS
                        KMOD_TCPSTAT_INC(tcps_progdrops);
#endif
                        return (1);
                }
        }
        return (0);
}