xnu-792.21.3.tar.gz

[apple/xnu.git] / bsd / netinet / tcp_input.c

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
 *	The Regents of the University of California.  All rights reserved.
 *
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. 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_input.c	8.12 (Berkeley) 5/24/95
 * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.16 2001/08/22 00:59:12 silby Exp $
 */


#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/proc.h>		/* for proc0 declaration */
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/syslog.h>

#include <kern/cpu_number.h>	/* before tcp_seq.h, for tcp_random18() */

#include <net/if.h>
#include <net/if_types.h>
#include <net/route.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>    /* for ICMP_BANDLIM		*/   
#include <netinet/in_var.h>
#include <netinet/icmp_var.h>	/* for ICMP_BANDLIM	*/
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#if INET6
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_pcb.h>
#endif
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#if INET6
#include <netinet6/tcp6_var.h>
#endif
#include <netinet/tcpip.h>
#if TCPDEBUG
#include <netinet/tcp_debug.h>
u_char tcp_saveipgen[40]; /* the size must be of max ip header, now IPv6 */
struct tcphdr tcp_savetcp;
#endif /* TCPDEBUG */

#if IPSEC
#include <netinet6/ipsec.h>
#if INET6
#include <netinet6/ipsec6.h>
#endif
#include <netkey/key.h>
#endif /*IPSEC*/

#include <sys/kdebug.h>

#ifndef __APPLE__
MALLOC_DEFINE(M_TSEGQ, "tseg_qent", "TCP segment queue entry");
#endif

#define DBG_LAYER_BEG		NETDBG_CODE(DBG_NETTCP, 0)
#define DBG_LAYER_END		NETDBG_CODE(DBG_NETTCP, 2)
#define DBG_FNC_TCP_INPUT       NETDBG_CODE(DBG_NETTCP, (3 << 8))
#define DBG_FNC_TCP_NEWCONN     NETDBG_CODE(DBG_NETTCP, (7 << 8))

static int	tcprexmtthresh = 3;
tcp_cc	tcp_ccgen;
extern int apple_hwcksum_rx;

#if IPSEC
extern int ipsec_bypass;
extern lck_mtx_t *sadb_mutex;
#endif

struct	tcpstat tcpstat;

static int log_in_vain = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW, 
    &log_in_vain, 0, "Log all incoming TCP connections");

static int blackhole = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW,
	&blackhole, 0, "Do not send RST when dropping refused connections");

int tcp_delack_enabled = 3;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW, 
    &tcp_delack_enabled, 0, 
    "Delay ACK to try and piggyback it onto a data packet");

int tcp_lq_overflow = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_lq_overflow, CTLFLAG_RW,
    &tcp_lq_overflow, 0, 
    "Listen Queue Overflow");

#if TCP_DROP_SYNFIN
static int drop_synfin = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
    &drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
#endif

SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
    "TCP Segment Reassembly Queue");

__private_extern__ int tcp_reass_maxseg = 0;
SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RW,
    &tcp_reass_maxseg, 0,
    "Global maximum number of TCP Segments in Reassembly Queue");

__private_extern__ int tcp_reass_qsize = 0;
SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD,
    &tcp_reass_qsize, 0,
    "Global number of TCP Segments currently in Reassembly Queue");

static int tcp_reass_overflows = 0;
SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD,
    &tcp_reass_overflows, 0,
    "Global number of TCP Segment Reassembly Queue Overflows");


__private_extern__ int slowlink_wsize = 8192;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowlink_wsize, CTLFLAG_RW,
	&slowlink_wsize, 0, "Maximum advertised window size for slowlink");


u_long tcp_now;
struct inpcbhead tcb;
#define	tcb6	tcb  /* for KAME src sync over BSD*'s */
struct inpcbinfo tcbinfo;

static void	 tcp_dooptions(struct tcpcb *,
	    u_char *, int, struct tcphdr *, struct tcpopt *);
static void	 tcp_pulloutofband(struct socket *,
	    struct tcphdr *, struct mbuf *, int);
static int	 tcp_reass(struct tcpcb *, struct tcphdr *, int *,
				struct mbuf *);
static void	tcp_xmit_timer(struct tcpcb *, int);

/* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */
#if INET6
#define ND6_HINT(tp) \
do { \
	if ((tp) && (tp)->t_inpcb && \
	    ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0 && \
	    (tp)->t_inpcb->in6p_route.ro_rt) \
		nd6_nud_hint((tp)->t_inpcb->in6p_route.ro_rt, NULL, 0); \
} while (0)
#else
#define ND6_HINT(tp)
#endif

extern u_long	*delack_bitmask;

extern  void    ipfwsyslog( int level, char *format,...);
extern int ChkAddressOK( __uint32_t dstaddr, __uint32_t srcaddr );
extern int fw_verbose;

#define log_in_vain_log( a ) {            \
        if ( (log_in_vain == 3 ) && (fw_verbose == 2)) {        /* Apple logging, log to ipfw.log */ \
                ipfwsyslog a ;  \
        }                       \
        else log a ;            \
}

/*
 * Indicate whether this ack should be delayed.  
 * We can delay the ack if:
 *  - delayed acks are enabled (set to 1) and
 *      - our last ack wasn't a 0-sized window.  We never want to delay
 *	  the ack that opens up a 0-sized window.
 *  - delayed acks are enabled (set to 2, "more compatible") and
 *      - our last ack wasn't a 0-sized window.
 *      - if the peer hasn't sent us a TH_PUSH data packet (this solves 3649245)
 *      - the peer hasn't sent us a TH_PUSH data packet, if he did, take this as a clue that we
 *        need to ACK with no delay. This helps higher level protocols who won't send
 *        us more data even if the window is open because their last "segment" hasn't been ACKed
 *  - delayed acks are enabled (set to 3, "streaming detection") and
 *  	- if we receive more than 4 full packets per second on this socket, we're streaming acts as "1".
 *  	- if we don't meet that criteria, acts like "2". Allowing faster acking while browsing for example.
 *
 */
#define DELAY_ACK(tp) \
	(((tcp_delack_enabled == 1) && ((tp->t_flags & TF_RXWIN0SENT) == 0)) || \
	 (((tcp_delack_enabled == 2) && (tp->t_flags & TF_RXWIN0SENT) == 0) && \
	   ((thflags & TH_PUSH) == 0) && ((tp->t_flags & TF_DELACK) == 0)) || \
	 (((tcp_delack_enabled == 3) && (tp->t_flags & TF_RXWIN0SENT) == 0) && \
	   (((tp->t_rcvtime == 0) && (tp->rcv_byps > (4* tp->t_maxseg)))  || (((thflags & TH_PUSH) == 0) && ((tp->t_flags & TF_DELACK) == 0)))))


static int tcpdropdropablreq(struct socket *head);
static void tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th);


static int
tcp_reass(tp, th, tlenp, m)
	register struct tcpcb *tp;
	register struct tcphdr *th;
	int *tlenp;
	struct mbuf *m;
{
	struct tseg_qent *q;
	struct tseg_qent *p = NULL;
	struct tseg_qent *nq;
	struct tseg_qent *te = NULL;
	struct socket *so = tp->t_inpcb->inp_socket;
	int flags;
	int dowakeup = 0;

	/*
	 * Call with th==0 after become established to
	 * force pre-ESTABLISHED data up to user socket.
	 */
	if (th == NULL)
		goto present;

	/*
	 * Limit the number of segments in the reassembly queue to prevent
	 * holding on to too many segments (and thus running out of mbufs).
	 * Make sure to let the missing segment through which caused this
	 * queue.  Always keep one global queue entry spare to be able to
	 * process the missing segment.
	 */
	if (th->th_seq != tp->rcv_nxt &&
	    tcp_reass_qsize + 1 >= tcp_reass_maxseg) {
		tcp_reass_overflows++;
		tcpstat.tcps_rcvmemdrop++;
		m_freem(m);
		return (0);
	}

	/* Allocate a new queue entry. If we can't, just drop the pkt. XXX */
	MALLOC(te, struct tseg_qent *, sizeof (struct tseg_qent), M_TSEGQ,
	       M_NOWAIT);
	if (te == NULL) {
		tcpstat.tcps_rcvmemdrop++;
		m_freem(m);
		return (0);
	}
	tcp_reass_qsize++;

	/*
	 * Find a segment which begins after this one does.
	 */
	LIST_FOREACH(q, &tp->t_segq, tqe_q) {
		if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
			break;
		p = q;
	}

	/*
	 * If there is a preceding segment, it may provide some of
	 * our data already.  If so, drop the data from the incoming
	 * segment.  If it provides all of our data, drop us.
	 */
	if (p != NULL) {
		register int i;
		/* conversion to int (in i) handles seq wraparound */
		i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
		if (i > 0) {
			if (i >= *tlenp) {
				tcpstat.tcps_rcvduppack++;
				tcpstat.tcps_rcvdupbyte += *tlenp;
				m_freem(m);
				FREE(te, M_TSEGQ);
				tcp_reass_qsize--;
				/*
				 * Try to present any queued data
				 * at the left window edge to the user.
				 * This is needed after the 3-WHS
				 * completes.
				 */
				goto present;	/* ??? */
			}
			m_adj(m, i);
			*tlenp -= i;
			th->th_seq += i;
		}
	}
	tcpstat.tcps_rcvoopack++;
	tcpstat.tcps_rcvoobyte += *tlenp;

	/*
	 * While we overlap succeeding segments trim them or,
	 * if they are completely covered, dequeue them.
	 */
	while (q) {
		register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
		if (i <= 0)
			break;
		if (i < q->tqe_len) {
			q->tqe_th->th_seq += i;
			q->tqe_len -= i;
			m_adj(q->tqe_m, i);
			break;
		}

		nq = LIST_NEXT(q, tqe_q);
		LIST_REMOVE(q, tqe_q);
		m_freem(q->tqe_m);
		FREE(q, M_TSEGQ);
		tcp_reass_qsize--;
		q = nq;
	}

	/* Insert the new segment queue entry into place. */
	te->tqe_m = m;
	te->tqe_th = th;
	te->tqe_len = *tlenp;

	if (p == NULL) {
		LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
	} else {
		LIST_INSERT_AFTER(p, te, tqe_q);
	}

present:
	/*
	 * Present data to user, advancing rcv_nxt through
	 * completed sequence space.
	 */
	if (!TCPS_HAVEESTABLISHED(tp->t_state))
		return (0);
	q = LIST_FIRST(&tp->t_segq);
	if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
		return (0);
	do {
		tp->rcv_nxt += q->tqe_len;
		flags = q->tqe_th->th_flags & TH_FIN;
		nq = LIST_NEXT(q, tqe_q);
		LIST_REMOVE(q, tqe_q);
		if (so->so_state & SS_CANTRCVMORE)
			m_freem(q->tqe_m);
		else {
			if (sbappend(&so->so_rcv, q->tqe_m))
				dowakeup = 1;
		}
		FREE(q, M_TSEGQ);
		tcp_reass_qsize--;
		q = nq;
	} while (q && q->tqe_th->th_seq == tp->rcv_nxt);
	ND6_HINT(tp);

#if INET6
	if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) {
	
		KERNEL_DEBUG(DBG_LAYER_BEG,
		     ((tp->t_inpcb->inp_fport << 16) | tp->t_inpcb->inp_lport),
		     (((tp->t_inpcb->in6p_laddr.s6_addr16[0] & 0xffff) << 16) |
		      (tp->t_inpcb->in6p_faddr.s6_addr16[0] & 0xffff)),
		     0,0,0);
	}
	else
#endif
	{
		KERNEL_DEBUG(DBG_LAYER_BEG,
		     ((tp->t_inpcb->inp_fport << 16) | tp->t_inpcb->inp_lport),
		     (((tp->t_inpcb->inp_laddr.s_addr & 0xffff) << 16) |
		      (tp->t_inpcb->inp_faddr.s_addr & 0xffff)),
		     0,0,0);
	}
	if (dowakeup)
		sorwakeup(so); /* done with socket lock held */
	return (flags);

}


/*
 * TCP input routine, follows pages 65-76 of the
 * protocol specification dated September, 1981 very closely.
 */
#if INET6
int
tcp6_input(mp, offp)
	struct mbuf **mp;
	int *offp;
{
	register struct mbuf *m = *mp;
	struct in6_ifaddr *ia6;

	IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), return IPPROTO_DONE);

	/*
	 * draft-itojun-ipv6-tcp-to-anycast
	 * better place to put this in?
	 */
	ia6 = ip6_getdstifaddr(m);
	if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {		
		struct ip6_hdr *ip6;

		ip6 = mtod(m, struct ip6_hdr *);
		icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
			    (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
		return IPPROTO_DONE;
	}

	tcp_input(m, *offp);
	return IPPROTO_DONE;
}
#endif

void
tcp_input(m, off0)
	struct mbuf *m;
	int off0;
{
	register struct tcphdr *th;
	register struct ip *ip = NULL;
	register struct ipovly *ipov;
	register struct inpcb *inp;
	u_char *optp = NULL;
	int optlen = 0;
	int len, tlen, off;
	int drop_hdrlen;
	register struct tcpcb *tp = 0;
	register int thflags;
	struct socket *so = 0;
	int todrop, acked, ourfinisacked, needoutput = 0;
	struct in_addr laddr;
#if INET6
	struct in6_addr laddr6;
#endif
	int dropsocket = 0;
	int iss = 0;
	int nosock = 0;
	u_long tiwin;
	struct tcpopt to;		/* options in this segment */
	struct rmxp_tao *taop;		/* pointer to our TAO cache entry */
	struct rmxp_tao	tao_noncached;	/* in case there's no cached entry */
	struct sockaddr_in *next_hop = NULL;
#if TCPDEBUG
	short ostate = 0;
#endif
	struct m_tag *fwd_tag;

	/* Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain. */
	fwd_tag = m_tag_locate(m, KERNEL_MODULE_TAG_ID, KERNEL_TAG_TYPE_IPFORWARD, NULL);
	if (fwd_tag != NULL) {
		struct ip_fwd_tag *ipfwd_tag = (struct ip_fwd_tag *)(fwd_tag+1);
		
		next_hop = ipfwd_tag->next_hop;
		m_tag_delete(m, fwd_tag);
	}
	
#if INET6
	struct ip6_hdr *ip6 = NULL;
	int isipv6;
#endif /* INET6 */
	int rstreason; /* For badport_bandlim accounting purposes */
	struct proc *proc0=current_proc();
	
	KERNEL_DEBUG(DBG_FNC_TCP_INPUT | DBG_FUNC_START,0,0,0,0,0);

#if INET6
	isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
#endif
	bzero((char *)&to, sizeof(to));

	tcpstat.tcps_rcvtotal++;



#if INET6
	if (isipv6) {
		/* IP6_EXTHDR_CHECK() is already done at tcp6_input() */
		ip6 = mtod(m, struct ip6_hdr *);
		tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
		if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) {
			tcpstat.tcps_rcvbadsum++;
			goto dropnosock;
		}
		th = (struct tcphdr *)((caddr_t)ip6 + off0);

		KERNEL_DEBUG(DBG_LAYER_BEG, ((th->th_dport << 16) | th->th_sport),
		     (((ip6->ip6_src.s6_addr16[0]) << 16) | (ip6->ip6_dst.s6_addr16[0])),
		     th->th_seq, th->th_ack, th->th_win);
		/*
		 * Be proactive about unspecified IPv6 address in source.
		 * As we use all-zero to indicate unbounded/unconnected pcb,
		 * unspecified IPv6 address can be used to confuse us.
		 *
		 * Note that packets with unspecified IPv6 destination is
		 * already dropped in ip6_input.
		 */
		if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
			/* XXX stat */
			goto dropnosock;
		}
	} else
#endif /* INET6 */
	{
	/*
	 * Get IP and TCP header together in first mbuf.
	 * Note: IP leaves IP header in first mbuf.
	 */
	if (off0 > sizeof (struct ip)) {
		ip_stripoptions(m, (struct mbuf *)0);
		off0 = sizeof(struct ip);
		if (m->m_pkthdr.csum_flags & CSUM_TCP_SUM16)
			m->m_pkthdr.csum_flags = 0; /* invalidate hwcksuming */

	}
	if (m->m_len < sizeof (struct tcpiphdr)) {
		if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) {
			tcpstat.tcps_rcvshort++;
			return;
		}
	}
	ip = mtod(m, struct ip *);
	ipov = (struct ipovly *)ip;
	th = (struct tcphdr *)((caddr_t)ip + off0);
	tlen = ip->ip_len;

	KERNEL_DEBUG(DBG_LAYER_BEG, ((th->th_dport << 16) | th->th_sport),
		     (((ip->ip_src.s_addr & 0xffff) << 16) | (ip->ip_dst.s_addr & 0xffff)),
		     th->th_seq, th->th_ack, th->th_win);

	if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
		if (apple_hwcksum_rx && (m->m_pkthdr.csum_flags & CSUM_TCP_SUM16)) {
			u_short pseudo;
			char b[9];
			*(uint32_t*)&b[0] = *(uint32_t*)&ipov->ih_x1[0];
			*(uint32_t*)&b[4] = *(uint32_t*)&ipov->ih_x1[4];
			*(uint8_t*)&b[8] = *(uint8_t*)&ipov->ih_x1[8];
			
			bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
			ipov->ih_len = (u_short)tlen;
			HTONS(ipov->ih_len);
			pseudo = in_cksum(m, sizeof (struct ip));
			
			*(uint32_t*)&ipov->ih_x1[0] = *(uint32_t*)&b[0];
			*(uint32_t*)&ipov->ih_x1[4] = *(uint32_t*)&b[4];
			*(uint8_t*)&ipov->ih_x1[8] = *(uint8_t*)&b[8];
			
			th->th_sum = in_addword(pseudo, (m->m_pkthdr.csum_data & 0xFFFF));
		} else {
			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 +
					ip->ip_len + IPPROTO_TCP));
		}
		th->th_sum ^= 0xffff;
	} else {
		char b[9];
		/*
		 * Checksum extended TCP header and data.
		 */
		*(uint32_t*)&b[0] = *(uint32_t*)&ipov->ih_x1[0];
		*(uint32_t*)&b[4] = *(uint32_t*)&ipov->ih_x1[4];
		*(uint8_t*)&b[8] = *(uint8_t*)&ipov->ih_x1[8];
		
		len = sizeof (struct ip) + tlen;
		bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
		ipov->ih_len = (u_short)tlen;
		HTONS(ipov->ih_len);
		th->th_sum = in_cksum(m, len);
		
		*(uint32_t*)&ipov->ih_x1[0] = *(uint32_t*)&b[0];
		*(uint32_t*)&ipov->ih_x1[4] = *(uint32_t*)&b[4];
		*(uint8_t*)&ipov->ih_x1[8] = *(uint8_t*)&b[8];
	}
	if (th->th_sum) {
		tcpstat.tcps_rcvbadsum++;
		goto dropnosock;
	}
#if INET6
	/* Re-initialization for later version check */
	ip->ip_v = IPVERSION;
#endif
	}

	/*
	 * Check that TCP offset makes sense,
	 * pull out TCP options and adjust length.		XXX
	 */
	off = th->th_off << 2;
	if (off < sizeof (struct tcphdr) || off > tlen) {
		tcpstat.tcps_rcvbadoff++;
		goto dropnosock;
	}
	tlen -= off;	/* tlen is used instead of ti->ti_len */
	if (off > sizeof (struct tcphdr)) {
#if INET6
		if (isipv6) {
			IP6_EXTHDR_CHECK(m, off0, off, return);
			ip6 = mtod(m, struct ip6_hdr *);
			th = (struct tcphdr *)((caddr_t)ip6 + off0);
		} else
#endif /* INET6 */
	      {
		if (m->m_len < sizeof(struct ip) + off) {
			if ((m = m_pullup(m, sizeof (struct ip) + off)) == 0) {
				tcpstat.tcps_rcvshort++;
				return;
			}
			ip = mtod(m, struct ip *);
			ipov = (struct ipovly *)ip;
			th = (struct tcphdr *)((caddr_t)ip + off0);
		}
	      }
		optlen = off - sizeof (struct tcphdr);
		optp = (u_char *)(th + 1);
		/* 
		 * Do quick retrieval of timestamp options ("options
		 * prediction?").  If timestamp is the only option and it's
		 * formatted as recommended in RFC 1323 appendix A, we
		 * quickly get the values now and not bother calling
		 * tcp_dooptions(), etc.
		 */
		if ((optlen == TCPOLEN_TSTAMP_APPA ||
		     (optlen > TCPOLEN_TSTAMP_APPA &&
			optp[TCPOLEN_TSTAMP_APPA] == TCPOPT_EOL)) &&
		     *(u_int32_t *)optp == htonl(TCPOPT_TSTAMP_HDR) &&
		     (th->th_flags & TH_SYN) == 0) {
			to.to_flags |= TOF_TS;
			to.to_tsval = ntohl(*(u_int32_t *)(optp + 4));
			to.to_tsecr = ntohl(*(u_int32_t *)(optp + 8));
			optp = NULL;	/* we've parsed the options */
		}
	}
	thflags = th->th_flags;

#if TCP_DROP_SYNFIN
	/*
	 * If the drop_synfin option is enabled, drop all packets with
	 * both the SYN and FIN bits set. This prevents e.g. nmap from
	 * identifying the TCP/IP stack.
	 *
	 * This is a violation of the TCP specification.
	 */
	if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
		goto dropnosock;
#endif

	/*
	 * Convert TCP protocol specific fields to host format.
	 */
	NTOHL(th->th_seq);
	NTOHL(th->th_ack);
	NTOHS(th->th_win);
	NTOHS(th->th_urp);

	/*
	 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options,
	 * until after ip6_savecontrol() is called and before other functions
	 * which don't want those proto headers.
	 * Because ip6_savecontrol() is going to parse the mbuf to
	 * search for data to be passed up to user-land, it wants mbuf
	 * parameters to be unchanged.
	 */
	drop_hdrlen = off0 + off;

	/*
	 * Locate pcb for segment.
	 */
findpcb:
#if IPFIREWALL_FORWARD
	if (next_hop != NULL
#if INET6
	    && isipv6 == NULL /* IPv6 support is not yet */
#endif /* INET6 */
	    ) {
		/*
		 * Diverted. Pretend to be the destination.
		 * already got one like this? 
		 */
		inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
			ip->ip_dst, th->th_dport, 0, m->m_pkthdr.rcvif);
		if (!inp) {
			/* 
			 * No, then it's new. Try find the ambushing socket
			 */
			if (!next_hop->sin_port) {
				inp = in_pcblookup_hash(&tcbinfo, ip->ip_src,
				    th->th_sport, next_hop->sin_addr,
				    th->th_dport, 1, m->m_pkthdr.rcvif);
			} else {
				inp = in_pcblookup_hash(&tcbinfo,
				    ip->ip_src, th->th_sport,
	    			    next_hop->sin_addr,
				    ntohs(next_hop->sin_port), 1,
				    m->m_pkthdr.rcvif);
			}
		}
	} else
#endif	/* IPFIREWALL_FORWARD */
      {
#if INET6
	if (isipv6)
		inp = in6_pcblookup_hash(&tcbinfo, &ip6->ip6_src, th->th_sport,
					 &ip6->ip6_dst, th->th_dport, 1,
					 m->m_pkthdr.rcvif);
	else
#endif /* INET6 */
	inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport,
	    ip->ip_dst, th->th_dport, 1, m->m_pkthdr.rcvif);
      }

#if IPSEC
	if (ipsec_bypass == 0)  {
		lck_mtx_lock(sadb_mutex);
#if INET6
		if (isipv6) {
		       	if (inp != NULL && ipsec6_in_reject_so(m, inp->inp_socket)) {
				ipsec6stat.in_polvio++;
				lck_mtx_unlock(sadb_mutex);
				goto dropnosock;
			}
		} else
#endif /* INET6 */
			if (inp != NULL && ipsec4_in_reject_so(m, inp->inp_socket)) {
				ipsecstat.in_polvio++;
				lck_mtx_unlock(sadb_mutex);
				goto dropnosock;
			}
		lck_mtx_unlock(sadb_mutex);
	}
#endif /*IPSEC*/

	/*
	 * If the state is CLOSED (i.e., TCB does not exist) then
	 * all data in the incoming segment is discarded.
	 * If the TCB exists but is in CLOSED state, it is embryonic,
	 * but should either do a listen or a connect soon.
	 */
	if (inp == NULL) {
		if (log_in_vain) {
#if INET6
			char dbuf[MAX_IPv6_STR_LEN], sbuf[MAX_IPv6_STR_LEN];
#else /* INET6 */
			char dbuf[MAX_IPv4_STR_LEN], sbuf[MAX_IPv4_STR_LEN];
#endif /* INET6 */

#if INET6
			if (isipv6) {
				inet_ntop(AF_INET6, &ip6->ip6_dst, dbuf, sizeof(dbuf));
				inet_ntop(AF_INET6, &ip6->ip6_src, sbuf, sizeof(sbuf));
			} else
#endif
			{
				inet_ntop(AF_INET, &ip->ip_dst, dbuf, sizeof(dbuf));
				inet_ntop(AF_INET, &ip->ip_src, sbuf, sizeof(sbuf));
			}
			switch (log_in_vain) {
			case 1:
				if(thflags & TH_SYN)
					log(LOG_INFO,
						"Connection attempt to TCP %s:%d from %s:%d\n",
						dbuf, ntohs(th->th_dport),
						sbuf,
						ntohs(th->th_sport));
				break;
			case 2:
				log(LOG_INFO,
					"Connection attempt to TCP %s:%d from %s:%d flags:0x%x\n",
					dbuf, ntohs(th->th_dport), sbuf,
					ntohs(th->th_sport), thflags);
				break;
			case 3:
				if ((thflags & TH_SYN) &&
					!(m->m_flags & (M_BCAST | M_MCAST)) &&
#if INET6
					((isipv6 && !IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) ||
					 (!isipv6 && ip->ip_dst.s_addr != ip->ip_src.s_addr))
#else
					ip->ip_dst.s_addr != ip->ip_src.s_addr
#endif
					 )
					log_in_vain_log((LOG_INFO,
						"Stealth Mode connection attempt to TCP %s:%d from %s:%d\n",
						dbuf, ntohs(th->th_dport),
						sbuf,
						ntohs(th->th_sport)));
				break;
			default:
				break;
			}
		}
		if (blackhole) { 
			if (m->m_pkthdr.rcvif && m->m_pkthdr.rcvif->if_type != IFT_LOOP)
				switch (blackhole) {
				case 1:
					if (thflags & TH_SYN)
						goto dropnosock;
					break;
				case 2:
					goto dropnosock;
				default:
					goto dropnosock;
				}
		}
		rstreason = BANDLIM_RST_CLOSEDPORT;
		goto dropwithresetnosock;
	}
	so = inp->inp_socket;
	if (so == NULL) {
		if (in_pcb_checkstate(inp, WNT_RELEASE, 1) == WNT_STOPUSING) 
			inp = NULL;	// pretend we didn't find it 
#if TEMPDEBUG
		printf("tcp_input: no more socket for inp=%x\n", inp);
#endif
		goto dropnosock;
	}

#ifdef __APPLE__
        /* 
         * Bogus state when listening port owned by SharedIP with loopback as the 
         * only configured interface: BlueBox does not filters loopback
         */ 
	if (so == &tcbinfo.nat_dummy_socket)
		goto drop;

#endif
	tcp_lock(so, 1, 2);
	if (in_pcb_checkstate(inp, WNT_RELEASE, 1) == WNT_STOPUSING) {
		tcp_unlock(so, 1, 2);
		inp = NULL;	// pretend we didn't find it 
		goto dropnosock;
	}

	tp = intotcpcb(inp);
	if (tp == 0) {
		rstreason = BANDLIM_RST_CLOSEDPORT;
		goto dropwithreset;
	}
	if (tp->t_state == TCPS_CLOSED)
		goto drop;

	/* Unscale the window into a 32-bit value. */
	if ((thflags & TH_SYN) == 0)
		tiwin = th->th_win << tp->snd_scale;
	else
		tiwin = th->th_win;

	if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
#if TCPDEBUG
		if (so->so_options & SO_DEBUG) {
			ostate = tp->t_state;
#if INET6
			if (isipv6)
				bcopy((char *)ip6, (char *)tcp_saveipgen,
				      sizeof(*ip6));
			else
#endif /* INET6 */
			bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
			tcp_savetcp = *th;
		}
#endif
		if (so->so_options & SO_ACCEPTCONN) {
		    register struct tcpcb *tp0 = tp;
			struct socket *so2;
			struct socket *oso;
			struct sockaddr_storage from;
#if INET6
			struct inpcb *oinp = sotoinpcb(so);
#endif /* INET6 */
			int ogencnt = so->so_gencnt;

#if !IPSEC
			/*
			 * Current IPsec implementation makes incorrect IPsec
			 * cache if this check is done here.
			 * So delay this until duplicated socket is created.
			 */
			if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
				/*
				 * Note: dropwithreset makes sure we don't
				 * send a RST in response to a RST.
				 */
				if (thflags & TH_ACK) {
					tcpstat.tcps_badsyn++;
					rstreason = BANDLIM_RST_OPENPORT;
					goto dropwithreset;
				}
				goto drop;
			}
#endif
			KERNEL_DEBUG(DBG_FNC_TCP_NEWCONN | DBG_FUNC_START,0,0,0,0,0);

#if INET6
			/*
			 * If deprecated address is forbidden,
			 * we do not accept SYN to deprecated interface
			 * address to prevent any new inbound connection from
			 * getting established.
			 * When we do not accept SYN, we send a TCP RST,
			 * with deprecated source address (instead of dropping
			 * it).  We compromise it as it is much better for peer
			 * to send a RST, and RST will be the final packet
			 * for the exchange.
			 *
			 * If we do not forbid deprecated addresses, we accept
			 * the SYN packet.  RFC2462 does not suggest dropping
			 * SYN in this case.
			 * If we decipher RFC2462 5.5.4, it says like this:
			 * 1. use of deprecated addr with existing
			 *    communication is okay - "SHOULD continue to be
			 *    used"
			 * 2. use of it with new communication:
			 *   (2a) "SHOULD NOT be used if alternate address
			 *        with sufficient scope is available"
			 *   (2b) nothing mentioned otherwise.
			 * Here we fall into (2b) case as we have no choice in
			 * our source address selection - we must obey the peer.
			 *
			 * The wording in RFC2462 is confusing, and there are
			 * multiple description text for deprecated address
			 * handling - worse, they are not exactly the same.
			 * I believe 5.5.4 is the best one, so we follow 5.5.4.
			 */
			if (isipv6 && !ip6_use_deprecated) {
				struct in6_ifaddr *ia6;

				if ((ia6 = ip6_getdstifaddr(m)) &&
				    (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
					tp = NULL;
					rstreason = BANDLIM_RST_OPENPORT;
					goto dropwithreset;
				}
			}
#endif
			if (so->so_filt) {
				if (isipv6) {
					struct sockaddr_in6	*sin6 = (struct sockaddr_in6*)&from;
					
					sin6->sin6_len = sizeof(*sin6);
					sin6->sin6_family = AF_INET6;
					sin6->sin6_port = th->th_sport;
					sin6->sin6_flowinfo = 0;
					sin6->sin6_addr = ip6->ip6_src;
					sin6->sin6_scope_id = 0;
				} else {
					struct sockaddr_in *sin = (struct sockaddr_in*)&from;
					
					sin->sin_len = sizeof(*sin);
					sin->sin_family = AF_INET;
					sin->sin_port = th->th_sport;
					sin->sin_addr = ip->ip_src;
				}
				so2 = sonewconn(so, 0, (struct sockaddr*)&from);
			} else {
				so2 = sonewconn(so, 0, NULL);
			}
			if (so2 == 0) {
				tcpstat.tcps_listendrop++;
				if (tcpdropdropablreq(so)) {
					if (so->so_filt)
						so2 = sonewconn(so, 0, (struct sockaddr*)&from);
					else
						so2 = sonewconn(so, 0, NULL);
				}
				if (!so2) 
					goto drop;
			}
			/*
			 * Make sure listening socket did not get closed during socket allocation,
			 * not only this is incorrect but it is know to cause panic
			 */
			if (so->so_gencnt != ogencnt)
				goto drop;

			oso = so;
			tcp_unlock(so, 0, 0); /* Unlock but keep a reference on listener for now */

			so = so2;
			tcp_lock(so, 1, 0);
			/*
			 * This is ugly, but ....
			 *
			 * Mark socket as temporary until we're
			 * committed to keeping it.  The code at
			 * ``drop'' and ``dropwithreset'' check the
			 * flag dropsocket to see if the temporary
			 * socket created here should be discarded.
			 * We mark the socket as discardable until
			 * we're committed to it below in TCPS_LISTEN.
			 */
			dropsocket++;
			inp = (struct inpcb *)so->so_pcb;
#if INET6
			if (isipv6)
				inp->in6p_laddr = ip6->ip6_dst;
			else {
				inp->inp_vflag &= ~INP_IPV6;
				inp->inp_vflag |= INP_IPV4;
#endif /* INET6 */
			inp->inp_laddr = ip->ip_dst;
#if INET6
			}
#endif /* INET6 */
			inp->inp_lport = th->th_dport;
			if (in_pcbinshash(inp, 0) != 0) {
				/*
				 * Undo the assignments above if we failed to
				 * put the PCB on the hash lists.
				 */
#if INET6
				if (isipv6)
					inp->in6p_laddr = in6addr_any;
				else
#endif /* INET6 */
				inp->inp_laddr.s_addr = INADDR_ANY;
				inp->inp_lport = 0;
				tcp_lock(oso, 0, 0);	/* release ref on parent */
				tcp_unlock(oso, 1, 0);
				goto drop;
			}
#if IPSEC
			/*
			 * To avoid creating incorrectly cached IPsec
			 * association, this is need to be done here.
			 *
			 * Subject: (KAME-snap 748)
			 * From: Wayne Knowles <w.knowles@niwa.cri.nz>
			 * ftp://ftp.kame.net/pub/mail-list/snap-users/748
			 */
			if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
				/*
				 * Note: dropwithreset makes sure we don't
				 * send a RST in response to a RST.
				 */
				tcp_lock(oso, 0, 0);	/* release ref on parent */
				tcp_unlock(oso, 1, 0);
				if (thflags & TH_ACK) {
					tcpstat.tcps_badsyn++;
					rstreason = BANDLIM_RST_OPENPORT;
					goto dropwithreset;
				}
				goto drop;
			}
#endif
#if INET6
			if (isipv6) {
  				/*
 				 * Inherit socket options from the listening
  				 * socket.
 				 * Note that in6p_inputopts are not (even
 				 * should not be) copied, since it stores
				 * previously received options and is used to
 				 * detect if each new option is different than
 				 * the previous one and hence should be passed
 				 * to a user.
 				 * If we copied in6p_inputopts, a user would
 				 * not be able to receive options just after
 				 * calling the accept system call.
 				 */
				inp->inp_flags |=
					oinp->inp_flags & INP_CONTROLOPTS;
 				if (oinp->in6p_outputopts)
 					inp->in6p_outputopts =
 						ip6_copypktopts(oinp->in6p_outputopts,
 								M_NOWAIT);
			} else
#endif /* INET6 */
			inp->inp_options = ip_srcroute();
			tcp_lock(oso, 0, 0);
#if IPSEC
			/* copy old policy into new socket's */
			if (sotoinpcb(oso)->inp_sp)
			{
				int error = 0;
				lck_mtx_lock(sadb_mutex);
				/* Is it a security hole here to silently fail to copy the policy? */
				if (inp->inp_sp != NULL)
					error = ipsec_init_policy(so, &inp->inp_sp);
				if (error != 0 || ipsec_copy_policy(sotoinpcb(oso)->inp_sp, inp->inp_sp))
					printf("tcp_input: could not copy policy\n");
				lck_mtx_unlock(sadb_mutex);
			}
#endif
			tcp_unlock(oso, 1, 0);	/* now drop the reference on the listener */
			tp = intotcpcb(inp);
			tp->t_state = TCPS_LISTEN;
			tp->t_flags |= tp0->t_flags & (TF_NOPUSH|TF_NOOPT|TF_NODELAY);
			tp->t_inpcb->inp_ip_ttl = tp0->t_inpcb->inp_ip_ttl;
			/* Compute proper scaling value from buffer space */
			while (tp->request_r_scale < TCP_MAX_WINSHIFT &&
			   TCP_MAXWIN << tp->request_r_scale <
			   so->so_rcv.sb_hiwat)
				tp->request_r_scale++;

			KERNEL_DEBUG(DBG_FNC_TCP_NEWCONN | DBG_FUNC_END,0,0,0,0,0);
		}
	}

#if 1
	lck_mtx_assert(((struct inpcb *)so->so_pcb)->inpcb_mtx, LCK_MTX_ASSERT_OWNED);
#endif
 	/*
 	 * Radar 3529618
	 * This is the second part of the MSS DoS prevention code (after
	 * minmss on the sending side) and it deals with too many too small
	 * tcp packets in a too short timeframe (1 second).
	 *
	 * For every full second we count the number of received packets
	 * and bytes. If we get a lot of packets per second for this connection
	 * (tcp_minmssoverload) we take a closer look at it and compute the
	 * average packet size for the past second. If that is less than
	 * tcp_minmss we get too many packets with very small payload which
	 * is not good and burdens our system (and every packet generates
	 * a wakeup to the process connected to our socket). We can reasonable
	 * expect this to be small packet DoS attack to exhaust our CPU
	 * cycles.
	 *
	 * Care has to be taken for the minimum packet overload value. This
	 * value defines the minimum number of packets per second before we
	 * start to worry. This must not be too low to avoid killing for
	 * example interactive connections with many small packets like
	 * telnet or SSH.
	 *
	 *
	 * Account for packet if payload packet, skip over ACK, etc.
	 *
	 * The packet per second count is done all the time and is also used
	 * by "DELAY_ACK" to detect streaming situations.
	 *
	 */
	if (tp->t_state == TCPS_ESTABLISHED && tlen > 0) {
		if (tp->rcv_reset > tcp_now) {
			tp->rcv_pps++;
			tp->rcv_byps += tlen + off;
		/*
		 * Setting either tcp_minmssoverload or tcp_minmss to "0" disables
		 * the check. 
		 */
			if (tcp_minmss && tcp_minmssoverload && tp->rcv_pps > tcp_minmssoverload) {
				if ((tp->rcv_byps / tp->rcv_pps) < tcp_minmss) {
					char	ipstrbuf[MAX_IPv6_STR_LEN];
					printf("too many small tcp packets from "
					       "%s:%u, av. %lubyte/packet, "
					       "dropping connection\n",
#ifdef INET6
						isipv6 ?
						inet_ntop(AF_INET6, &inp->in6p_faddr, ipstrbuf,
								  sizeof(ipstrbuf)) :
#endif
						inet_ntop(AF_INET, &inp->inp_faddr, ipstrbuf,
								  sizeof(ipstrbuf)),
						inp->inp_fport,
						tp->rcv_byps / tp->rcv_pps);
					tp = tcp_drop(tp, ECONNRESET);
/*					tcpstat.tcps_minmssdrops++; */
					goto drop;
				}
			}
		} else {
			tp->rcv_reset = tcp_now + PR_SLOWHZ;
			tp->rcv_pps = 1;
			tp->rcv_byps = tlen + off;
		}
	}
	
	/*
	 * Segment received on connection.
	 * Reset idle time and keep-alive timer.
	 */
	tp->t_rcvtime = 0;
	if (TCPS_HAVEESTABLISHED(tp->t_state))
		tp->t_timer[TCPT_KEEP] = TCP_KEEPIDLE(tp);

	/*
	 * Process options if not in LISTEN state,
	 * else do it below (after getting remote address).
	 */
	if (tp->t_state != TCPS_LISTEN && optp)
		tcp_dooptions(tp, optp, optlen, th, &to);

	if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
		if (to.to_flags & TOF_SCALE) {
			tp->t_flags |= TF_RCVD_SCALE;
			tp->requested_s_scale = to.to_requested_s_scale;
		}
		if (to.to_flags & TOF_TS) {
			tp->t_flags |= TF_RCVD_TSTMP;
			tp->ts_recent = to.to_tsval;
			tp->ts_recent_age = tcp_now;
		}
		if (to.to_flags & TOF_MSS)
			tcp_mss(tp, to.to_mss);
		if (tp->sack_enable) {
			if (!(to.to_flags & TOF_SACK))
				tp->sack_enable = 0;
			else
				tp->t_flags |= TF_SACK_PERMIT;
		}
	}

	/*
	 * Header prediction: check for the two common cases
	 * of a uni-directional data xfer.  If the packet has
	 * no control flags, is in-sequence, the window didn't
	 * change and we're not retransmitting, it's a
	 * candidate.  If the length is zero and the ack moved
	 * forward, we're the sender side of the xfer.  Just
	 * free the data acked & wake any higher level process
	 * that was blocked waiting for space.  If the length
	 * is non-zero and the ack didn't move, we're the
	 * receiver side.  If we're getting packets in-order
	 * (the reassembly queue is empty), add the data to
	 * the socket buffer and note that we need a delayed ack.
	 * Make sure that the hidden state-flags are also off.
	 * Since we check for TCPS_ESTABLISHED above, it can only
	 * be TH_NEEDSYN.
	 */
	if (tp->t_state == TCPS_ESTABLISHED &&
	    (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
	    ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
	    ((to.to_flags & TOF_TS) == 0 ||
	     TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
	    th->th_seq == tp->rcv_nxt &&
	    tiwin && tiwin == tp->snd_wnd &&
	    tp->snd_nxt == tp->snd_max) {

		/*
		 * If last ACK falls within this segment's sequence numbers,
		 * record the timestamp.
		 * NOTE that the test is modified according to the latest
		 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
		 */
		if ((to.to_flags & TOF_TS) != 0 &&
		   SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
			tp->ts_recent_age = tcp_now;
			tp->ts_recent = to.to_tsval;
		}

		if (tlen == 0) {
			if (SEQ_GT(th->th_ack, tp->snd_una) &&
			    SEQ_LEQ(th->th_ack, tp->snd_max) &&
			    tp->snd_cwnd >= tp->snd_wnd &&
			    ((!tcp_do_newreno && !tp->sack_enable &&
			      tp->t_dupacks < tcprexmtthresh) ||
			     ((tcp_do_newreno || tp->sack_enable) &&
			      !IN_FASTRECOVERY(tp) && to.to_nsacks == 0 &&
			      TAILQ_EMPTY(&tp->snd_holes)))) {
				/*
				 * this is a pure ack for outstanding data.
				 */
				++tcpstat.tcps_predack;
				/*
				 * "bad retransmit" recovery
				 */
				if (tp->t_rxtshift == 1 &&
				    tcp_now < tp->t_badrxtwin) { 
					tp->snd_cwnd = tp->snd_cwnd_prev;
					tp->snd_ssthresh =
					    tp->snd_ssthresh_prev;
					tp->snd_recover = tp->snd_recover_prev;
					if (tp->t_flags & TF_WASFRECOVERY)
					    ENTER_FASTRECOVERY(tp);
					tp->snd_nxt = tp->snd_max;
					tp->t_badrxtwin = 0;
				}
				if (((to.to_flags & TOF_TS) != 0) && (to.to_tsecr != 0)) /* Makes sure we already have a TS */
					tcp_xmit_timer(tp,
					    tcp_now - to.to_tsecr + 1);
				else if (tp->t_rtttime &&
					    SEQ_GT(th->th_ack, tp->t_rtseq))
					tcp_xmit_timer(tp, tp->t_rtttime);
				acked = th->th_ack - tp->snd_una;
				tcpstat.tcps_rcvackpack++;
				tcpstat.tcps_rcvackbyte += acked;
				sbdrop(&so->so_snd, acked);
				if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
				    SEQ_LEQ(th->th_ack, tp->snd_recover))
					tp->snd_recover = th->th_ack - 1;
				tp->snd_una = th->th_ack;
				/*
				 * pull snd_wl2 up to prevent seq wrap relative
				 * to th_ack.
				 */
				tp->snd_wl2 = th->th_ack;
				tp->t_dupacks = 0;
				m_freem(m);
				ND6_HINT(tp); /* some progress has been done */

				/*
				 * If all outstanding data are acked, stop
				 * retransmit timer, otherwise restart timer
				 * using current (possibly backed-off) value.
				 * If process is waiting for space,
				 * wakeup/selwakeup/signal.  If data
				 * are ready to send, let tcp_output
				 * decide between more output or persist.
				 */
				if (tp->snd_una == tp->snd_max)
					tp->t_timer[TCPT_REXMT] = 0;
				else if (tp->t_timer[TCPT_PERSIST] == 0)
					tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;

				sowwakeup(so); /* has to be done with socket lock held */
				if ((so->so_snd.sb_cc) || (tp->t_flags & TF_ACKNOW))
					(void) tcp_output(tp);
				tcp_unlock(so, 1, 0);
				KERNEL_DEBUG(DBG_FNC_TCP_INPUT | DBG_FUNC_END,0,0,0,0,0);
				return;
			}
		} else if (th->th_ack == tp->snd_una &&
		    LIST_EMPTY(&tp->t_segq) &&
		    tlen <= sbspace(&so->so_rcv)) {
			/*
			 * this is a pure, in-sequence data packet
			 * with nothing on the reassembly queue and
			 * we have enough buffer space to take it.
			 */
			/* Clean receiver SACK report if present */
			if (tp->sack_enable && tp->rcv_numsacks)
				tcp_clean_sackreport(tp);
			++tcpstat.tcps_preddat;
			tp->rcv_nxt += tlen;
			/*
			 * Pull snd_wl1 up to prevent seq wrap relative to
			 * th_seq.
			 */
			tp->snd_wl1 = th->th_seq;
			/*
			 * Pull rcv_up up to prevent seq wrap relative to
			 * rcv_nxt.
			 */
			tp->rcv_up = tp->rcv_nxt;
			tcpstat.tcps_rcvpack++;
			tcpstat.tcps_rcvbyte += tlen;
			ND6_HINT(tp);	/* some progress has been done */
			/*
			 * Add data to socket buffer.
			 */
			m_adj(m, drop_hdrlen);	/* delayed header drop */
			if (sbappend(&so->so_rcv, m))
				sorwakeup(so);
#if INET6
			if (isipv6) {
				KERNEL_DEBUG(DBG_LAYER_END, ((th->th_dport << 16) | th->th_sport),
		     			(((ip6->ip6_src.s6_addr16[0]) << 16) | (ip6->ip6_dst.s6_addr16[0])),
			     		th->th_seq, th->th_ack, th->th_win); 
			}
			else
#endif 
			{
				KERNEL_DEBUG(DBG_LAYER_END, ((th->th_dport << 16) | th->th_sport),
		     			(((ip->ip_src.s_addr & 0xffff) << 16) | (ip->ip_dst.s_addr & 0xffff)),
			     		th->th_seq, th->th_ack, th->th_win); 
			}
			if (DELAY_ACK(tp))  {
			    tp->t_flags |= TF_DELACK;
			} else {
				tp->t_flags |= TF_ACKNOW;
				tcp_output(tp);
			}
			tcp_unlock(so, 1, 0);
			KERNEL_DEBUG(DBG_FNC_TCP_INPUT | DBG_FUNC_END,0,0,0,0,0);
			return;
		}
	}

	/*
	 * 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.
	 */
#if 1
	lck_mtx_assert(((struct inpcb *)so->so_pcb)->inpcb_mtx, LCK_MTX_ASSERT_OWNED);
#endif
	{ int win;

	win = sbspace(&so->so_rcv);
	if (win < 0)
		win = 0;
	else {	/* clip rcv window to 4K for modems */
		if (tp->t_flags & TF_SLOWLINK && slowlink_wsize > 0)
			win = min(win, slowlink_wsize);
	}
	tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
	}

	switch (tp->t_state) {

	/*
	 * If the state is LISTEN then ignore segment if it contains an RST.
	 * If the segment contains an ACK then it is bad and send a RST.
	 * If it does not contain a SYN then it is not interesting; drop it.
	 * If it is from this socket, drop it, it must be forged.
	 * Don't bother responding if the destination was a broadcast.
	 * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
	 * tp->iss, and send a segment:
	 *     <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
	 * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
	 * Fill in remote peer address fields if not previously specified.
	 * Enter SYN_RECEIVED state, and process any other fields of this
	 * segment in this state.
	 */
	case TCPS_LISTEN: {
		register struct sockaddr_in *sin;
#if INET6
		register struct sockaddr_in6 *sin6;
#endif

#if 1
		lck_mtx_assert(((struct inpcb *)so->so_pcb)->inpcb_mtx, LCK_MTX_ASSERT_OWNED);
#endif
		if (thflags & TH_RST) 
			goto drop;
		if (thflags & TH_ACK) {
			rstreason = BANDLIM_RST_OPENPORT;
			goto dropwithreset;
		}
		if ((thflags & TH_SYN) == 0)
			goto drop;
		if (th->th_dport == th->th_sport) {
#if INET6
			if (isipv6) {
				if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
						       &ip6->ip6_src))
					goto drop;
			} else
#endif /* INET6 */
			if (ip->ip_dst.s_addr == ip->ip_src.s_addr)
				goto drop;
		}
		/*
		 * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
		 * in_broadcast() should never return true on a received
		 * packet with M_BCAST not set.
 		 *
 		 * Packets with a multicast source address should also
 		 * be discarded.
		 */
		if (m->m_flags & (M_BCAST|M_MCAST))
			goto drop;
#if INET6
		if (isipv6) {
			if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
			    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
				goto drop;
		} else
#endif
		if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
		    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
		    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
		    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
			goto drop;
#if INET6
		if (isipv6) {
			MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6,
			       M_SONAME, M_NOWAIT);
			if (sin6 == NULL)
				goto drop;
			bzero(sin6, sizeof(*sin6));
			sin6->sin6_family = AF_INET6;
			sin6->sin6_len = sizeof(*sin6);
			sin6->sin6_addr = ip6->ip6_src;
			sin6->sin6_port = th->th_sport;
			laddr6 = inp->in6p_laddr;
			if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
				inp->in6p_laddr = ip6->ip6_dst;
			if (in6_pcbconnect(inp, (struct sockaddr *)sin6,
					   proc0)) {
				inp->in6p_laddr = laddr6;
				FREE(sin6, M_SONAME);
				goto drop;
			}
			FREE(sin6, M_SONAME);
		} else
#endif
	    {
#if 1
			lck_mtx_assert(((struct inpcb *)so->so_pcb)->inpcb_mtx, LCK_MTX_ASSERT_OWNED);
#endif
			MALLOC(sin, struct sockaddr_in *, sizeof *sin, M_SONAME,
		       M_NOWAIT);
			if (sin == NULL)
				goto drop;
			sin->sin_family = AF_INET;
			sin->sin_len = sizeof(*sin);
			sin->sin_addr = ip->ip_src;
			sin->sin_port = th->th_sport;
			bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero));
			laddr = inp->inp_laddr;
			if (inp->inp_laddr.s_addr == INADDR_ANY)
				inp->inp_laddr = ip->ip_dst;
			if (in_pcbconnect(inp, (struct sockaddr *)sin, proc0)) {
				inp->inp_laddr = laddr;
				FREE(sin, M_SONAME);
				goto drop;
			}
			FREE(sin, M_SONAME);
		}

		tcp_dooptions(tp, optp, optlen, th, &to);

		if (tp->sack_enable) {
			if (!(to.to_flags & TOF_SACK))
				tp->sack_enable = 0;
			else
				tp->t_flags |= TF_SACK_PERMIT;
		}
		
		if (iss)
			tp->iss = iss;
		else {
			tp->iss = tcp_new_isn(tp);
 		}
		tp->irs = th->th_seq;
		tcp_sendseqinit(tp);
		tcp_rcvseqinit(tp);
		tp->snd_recover = tp->snd_una;
		/*
		 * Initialization of the tcpcb for transaction;
		 *   set SND.WND = SEG.WND,
		 *   initialize CCsend and CCrecv.
		 */
		tp->snd_wnd = tiwin;	/* initial send-window */
		tp->t_flags |= TF_ACKNOW;
		tp->t_state = TCPS_SYN_RECEIVED;
		tp->t_timer[TCPT_KEEP] = tcp_keepinit;
		dropsocket = 0;		/* committed to socket */
		tcpstat.tcps_accepts++;
		goto trimthenstep6;
		}

	/*
	 * If the state is SYN_RECEIVED:
	 *	if seg contains an ACK, but not for our SYN/ACK, send a RST.
	 */
	case TCPS_SYN_RECEIVED:
		if ((thflags & TH_ACK) &&
		    (SEQ_LEQ(th->th_ack, tp->snd_una) ||
		     SEQ_GT(th->th_ack, tp->snd_max))) {
				rstreason = BANDLIM_RST_OPENPORT;
				goto dropwithreset;
		}
		break;

	/*
	 * If the state is SYN_SENT:
	 *	if seg contains an ACK, but not for our SYN, drop the input.
	 *	if seg contains a RST, then drop the connection.
	 *	if seg does not contain SYN, then drop it.
	 * Otherwise this is an acceptable SYN segment
	 *	initialize tp->rcv_nxt and tp->irs
	 *	if seg contains ack then advance tp->snd_una
	 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
	 *	arrange for segment to be acked (eventually)
	 *	continue processing rest of data/controls, beginning with URG
	 */
	case TCPS_SYN_SENT:
		if ((thflags & TH_ACK) &&
		    (SEQ_LEQ(th->th_ack, tp->iss) ||
		     SEQ_GT(th->th_ack, tp->snd_max))) {
			rstreason = BANDLIM_UNLIMITED;
			goto dropwithreset;
		}
		if (thflags & TH_RST) {
			if (thflags & TH_ACK) {
				tp = tcp_drop(tp, ECONNREFUSED);
				postevent(so, 0, EV_RESET);
		  }
			goto drop;
		}
		if ((thflags & TH_SYN) == 0)
			goto drop;
		tp->snd_wnd = th->th_win;	/* initial send window */

		tp->irs = th->th_seq;
		tcp_rcvseqinit(tp);
		if (thflags & TH_ACK) {
			tcpstat.tcps_connects++;
			soisconnected(so);
			/* Do window scaling on this connection? */
			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
				tp->snd_scale = tp->requested_s_scale;
				tp->rcv_scale = tp->request_r_scale;
			}
			tp->rcv_adv += tp->rcv_wnd;
			tp->snd_una++;		/* SYN is acked */
			/*
			 * If there's data, delay ACK; if there's also a FIN
			 * ACKNOW will be turned on later.
			 */
			if (DELAY_ACK(tp) && tlen != 0) {
				tp->t_flags |= TF_DELACK;
			}
			else {
				tp->t_flags |= TF_ACKNOW;
			}
			/*
			 * Received <SYN,ACK> in SYN_SENT[*] state.
			 * Transitions:
			 *	SYN_SENT  --> ESTABLISHED
			 *	SYN_SENT* --> FIN_WAIT_1
			 */
			tp->t_starttime = 0;
			if (tp->t_flags & TF_NEEDFIN) {
				tp->t_state = TCPS_FIN_WAIT_1;
				tp->t_flags &= ~TF_NEEDFIN;
				thflags &= ~TH_SYN;
			} else {
				tp->t_state = TCPS_ESTABLISHED;
				tp->t_timer[TCPT_KEEP] = TCP_KEEPIDLE(tp);
			}
		} else {
		/*
		 *  Received initial SYN in SYN-SENT[*] state => simul-
		 *  taneous open.  If segment contains CC option and there is
		 *  a cached CC, apply TAO test; if it succeeds, connection is
		 *  half-synchronized.  Otherwise, do 3-way handshake:
		 *        SYN-SENT -> SYN-RECEIVED
		 *        SYN-SENT* -> SYN-RECEIVED*
		 */
			tp->t_flags |= TF_ACKNOW;
			tp->t_timer[TCPT_REXMT] = 0;
			tp->t_state = TCPS_SYN_RECEIVED;

		}

trimthenstep6:
		/*
		 * Advance th->th_seq to correspond to first data byte.
		 * If data, trim to stay within window,
		 * dropping FIN if necessary.
		 */
		th->th_seq++;
		if (tlen > tp->rcv_wnd) {
			todrop = tlen - tp->rcv_wnd;
			m_adj(m, -todrop);
			tlen = tp->rcv_wnd;
			thflags &= ~TH_FIN;
			tcpstat.tcps_rcvpackafterwin++;
			tcpstat.tcps_rcvbyteafterwin += todrop;
		}
		tp->snd_wl1 = th->th_seq - 1;
		tp->rcv_up = th->th_seq;
		/*
		 *  Client side of transaction: already sent SYN and data.
		 *  If the remote host used T/TCP to validate the SYN,
		 *  our data will be ACK'd; if so, enter normal data segment
		 *  processing in the middle of step 5, ack processing.
		 *  Otherwise, goto step 6.
		 */
 		if (thflags & TH_ACK)
			goto process_ACK;
		goto step6;
	/*
	 * If the state is LAST_ACK or CLOSING or TIME_WAIT:
	 *      do normal processing.
	 *
	 * NB: Leftover from RFC1644 T/TCP.  Cases to be reused later.
	 */
	case TCPS_LAST_ACK:
	case TCPS_CLOSING:
	case TCPS_TIME_WAIT:
 		break;  /* continue normal processing */

	/* Received a SYN while connection is already established.
	 * This is a "half open connection and other anomalies" described
	 * in RFC793 page 34, send an ACK so the remote reset the connection
	 * or recovers by adjusting its sequence numberering 
	 */
	case TCPS_ESTABLISHED:
		if (thflags & TH_SYN)  
			goto dropafterack; 
		break;
	}

	/*
	 * States other than LISTEN or SYN_SENT.
	 * First check the RST flag and sequence number since reset segments
	 * are exempt from the timestamp and connection count tests.  This
	 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
	 * below which allowed reset segments in half the sequence space
	 * to fall though and be processed (which gives forged reset
	 * segments with a random sequence number a 50 percent chance of
	 * killing a connection).
	 * Then check timestamp, if present.
	 * Then check the connection count, if present.
	 * Then check that at least some bytes of segment are within
	 * receive window.  If segment begins before rcv_nxt,
	 * drop leading data (and SYN); if nothing left, just ack.
	 *
	 *
	 * If the RST bit is set, check the sequence number to see
	 * if this is a valid reset segment.
	 * RFC 793 page 37:
	 *   In all states except SYN-SENT, all reset (RST) segments
	 *   are validated by checking their SEQ-fields.  A reset is
	 *   valid if its sequence number is in the window.
	 * Note: this does not take into account delayed ACKs, so
	 *   we should test against last_ack_sent instead of rcv_nxt.
	 *   The sequence number in the reset segment is normally an
	 *   echo of our outgoing acknowlegement numbers, but some hosts
	 *   send a reset with the sequence number at the rightmost edge
	 *   of our receive window, and we have to handle this case.
	 * Note 2: Paul Watson's paper "Slipping in the Window" has shown
	 *   that brute force RST attacks are possible.  To combat this,
	 *   we use a much stricter check while in the ESTABLISHED state,
	 *   only accepting RSTs where the sequence number is equal to
	 *   last_ack_sent.  In all other states (the states in which a
	 *   RST is more likely), the more permissive check is used.
	 * If we have multiple segments in flight, the intial reset
	 * segment sequence numbers will be to the left of last_ack_sent,
	 * but they will eventually catch up.
	 * In any case, it never made sense to trim reset segments to
	 * fit the receive window since RFC 1122 says:
	 *   4.2.2.12  RST Segment: RFC-793 Section 3.4
	 *
	 *    A TCP SHOULD allow a received RST segment to include data.
	 *
	 *    DISCUSSION
	 *         It has been suggested that a RST segment could contain
	 *         ASCII text that encoded and explained the cause of the
	 *         RST.  No standard has yet been established for such
	 *         data.
	 *
	 * If the reset segment passes the sequence number test examine
	 * the state:
	 *    SYN_RECEIVED STATE:
	 *	If passive open, return to LISTEN state.
	 *	If active open, inform user that connection was refused.
	 *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES:
	 *	Inform user that connection was reset, and close tcb.
	 *    CLOSING, LAST_ACK STATES:
	 *	Close the tcb.
	 *    TIME_WAIT STATE:
	 *	Drop the segment - see Stevens, vol. 2, p. 964 and
	 *      RFC 1337.
	 */
	if (thflags & TH_RST) {
		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)) {
			switch (tp->t_state) {

			case TCPS_SYN_RECEIVED:
				so->so_error = ECONNREFUSED;
				goto close;

			case TCPS_ESTABLISHED:
				if (tp->last_ack_sent != th->th_seq) {
					goto drop;
				}
			case TCPS_FIN_WAIT_1:
			case TCPS_CLOSE_WAIT:
				/*
				  Drop through ...
				*/
			case TCPS_FIN_WAIT_2:
				so->so_error = ECONNRESET;
			close:
				postevent(so, 0, EV_RESET);
				tp->t_state = TCPS_CLOSED;
				tcpstat.tcps_drops++;
				tp = tcp_close(tp);
				break;

			case TCPS_CLOSING:
			case TCPS_LAST_ACK:
				tp = tcp_close(tp);
				break;

			case TCPS_TIME_WAIT:
				break;
			}
		}
		goto drop;
	}

#if 1
	lck_mtx_assert(((struct inpcb *)so->so_pcb)->inpcb_mtx, LCK_MTX_ASSERT_OWNED);
#endif
	/*
	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
	 * and it's less than ts_recent, drop it.
	 */
	if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
	    TSTMP_LT(to.to_tsval, tp->ts_recent)) {

		/* Check to see if ts_recent is over 24 days old.  */
		if ((int)(tcp_now - 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 {
			tcpstat.tcps_rcvduppack++;
			tcpstat.tcps_rcvdupbyte += tlen;
			tcpstat.tcps_pawsdrop++;
			if (tlen)
				goto dropafterack;
			goto drop;
		}
	}

	/*
	 * In the SYN-RECEIVED state, validate that the packet belongs to
	 * this connection before trimming the data to fit the receive
	 * window.  Check the sequence number versus IRS since we know
	 * the sequence numbers haven't wrapped.  This is a partial fix
	 * for the "LAND" DoS attack.
	 */
	if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
		rstreason = BANDLIM_RST_OPENPORT;
		goto dropwithreset;
	}

	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.
			 */
			tp->t_flags |= TF_ACKNOW;
			todrop = tlen;
			tcpstat.tcps_rcvduppack++;
			tcpstat.tcps_rcvdupbyte += todrop;
		} else {
			tcpstat.tcps_rcvpartduppack++;
			tcpstat.tcps_rcvpartdupbyte += 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 new data are received on a connection after the
	 * user processes are gone, then RST the other end.
	 */
	if ((so->so_state & SS_NOFDREF) &&
	    tp->t_state > TCPS_CLOSE_WAIT && tlen) {
		tp = tcp_close(tp);
		tcpstat.tcps_rcvafterclose++;
		rstreason = BANDLIM_UNLIMITED;
		goto dropwithreset;
	}

	/*
	 * 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) {
		tcpstat.tcps_rcvpackafterwin++;
		if (todrop >= tlen) {
			tcpstat.tcps_rcvbyteafterwin += tlen;
			/*
			 * If a new connection request is received
			 * while in TIME_WAIT, drop the old connection
			 * and start over if the sequence numbers
			 * are above the previous ones.
			 */
			if (thflags & TH_SYN &&
			    tp->t_state == TCPS_TIME_WAIT &&
			    SEQ_GT(th->th_seq, tp->rcv_nxt)) {
				iss = tcp_new_isn(tp);
				tp = tcp_close(tp);
				tcp_unlock(so, 1, 0);
				goto findpcb;
			}
			/*
			 * 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) {
				tp->t_flags |= TF_ACKNOW;
				tcpstat.tcps_rcvwinprobe++;
			} else
				goto dropafterack;
		} else
			tcpstat.tcps_rcvbyteafterwin += todrop;
		m_adj(m, -todrop);
		tlen -= todrop;
		thflags &= ~(TH_PUSH|TH_FIN);
	}

	/*
	 * If last ACK falls within this segment's sequence numbers,
	 * record its timestamp.
	 * NOTE: 
	 * 1) That the test incorporates suggestions from the latest
	 *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
	 * 2) That updating only on newer timestamps interferes with
	 *    our earlier PAWS tests, so this check should be solely
	 *    predicated on the sequence space of this segment.
	 * 3) That we modify the segment boundary check to be 
	 *        Last.ACK.Sent <= SEG.SEQ + SEG.Len  
	 *    instead of RFC1323's
	 *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
	 *    This modified check allows us to overcome RFC1323's
	 *    limitations as described in Stevens TCP/IP Illustrated
	 *    Vol. 2 p.869. In such cases, we can still calculate the
	 *    RTT correctly when RCV.NXT == Last.ACK.Sent.
	 */
	if ((to.to_flags & TOF_TS) != 0 &&
	    SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
	    SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
		((thflags & (TH_SYN|TH_FIN)) != 0))) {
		tp->ts_recent_age = tcp_now;
		tp->ts_recent = to.to_tsval;
	}

	/*
	 * If a SYN is in the window, then this is an
	 * error and we send an RST and drop the connection.
	 */
	if (thflags & TH_SYN) {
		tp = tcp_drop(tp, ECONNRESET);
		rstreason = BANDLIM_UNLIMITED;
		postevent(so, 0, EV_RESET);
		goto dropwithreset;
	}

	/*
	 * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
	 * flag is on (half-synchronized state), then queue data for
	 * later processing; else drop segment and return.
	 */
	if ((thflags & TH_ACK) == 0) {
		if (tp->t_state == TCPS_SYN_RECEIVED ||
		    (tp->t_flags & TF_NEEDSYN))
			goto step6;
		else
			goto drop;
	}

	/*
	 * Ack processing.
	 */
	switch (tp->t_state) {

	/*
	 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
	 * ESTABLISHED state and continue processing.
	 * The ACK was checked above.
	 */
	case TCPS_SYN_RECEIVED:

		tcpstat.tcps_connects++;
		soisconnected(so);

		/* Do window scaling? */
		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
			tp->snd_scale = tp->requested_s_scale;
			tp->rcv_scale = tp->request_r_scale;
		}
		/*
		 * Make transitions:
		 *      SYN-RECEIVED  -> ESTABLISHED
		 *      SYN-RECEIVED* -> FIN-WAIT-1
		 */
		tp->t_starttime = 0;
		if (tp->t_flags & TF_NEEDFIN) {
			tp->t_state = TCPS_FIN_WAIT_1;
			tp->t_flags &= ~TF_NEEDFIN;
		} else {
			tp->t_state = TCPS_ESTABLISHED;
			tp->t_timer[TCPT_KEEP] = TCP_KEEPIDLE(tp);
		}
		/*
		 * If segment contains data or ACK, will call tcp_reass()
		 * later; if not, do so now to pass queued data to user.
		 */
		if (tlen == 0 && (thflags & TH_FIN) == 0)
			(void) tcp_reass(tp, (struct tcphdr *)0, 0,
			    (struct mbuf *)0);
		tp->snd_wl1 = th->th_seq - 1;
		/* FALLTHROUGH */

	/*
	 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
	 * ACKs.  If the ack is in the range
	 *	tp->snd_una < th->th_ack <= tp->snd_max
	 * then advance tp->snd_una to th->th_ack and drop
	 * data from the retransmission queue.  If this ACK reflects
	 * more up to date window information we update our window information.
	 */
	case TCPS_ESTABLISHED:
	case TCPS_FIN_WAIT_1:
	case TCPS_FIN_WAIT_2:
	case TCPS_CLOSE_WAIT:
	case TCPS_CLOSING:
	case TCPS_LAST_ACK:
	case TCPS_TIME_WAIT:
		if (SEQ_GT(th->th_ack, tp->snd_max)) {
			tcpstat.tcps_rcvacktoomuch++;
			goto dropafterack;
		}
		if (tp->sack_enable &&
		    (to.to_nsacks > 0 || !TAILQ_EMPTY(&tp->snd_holes)))
			tcp_sack_doack(tp, &to, th->th_ack);
		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
			if (tlen == 0 && tiwin == tp->snd_wnd) {
				tcpstat.tcps_rcvdupack++;
				/*
				 * If we have outstanding data (other than
				 * a window probe), this is a completely
				 * duplicate ack (ie, window info didn't
				 * change), the ack is the biggest we've
				 * seen and we've seen exactly our rexmt
				 * threshhold of them, assume a packet
				 * has been dropped and retransmit it.
				 * Kludge snd_nxt & the congestion
				 * window so we send only this one
				 * packet.
				 *
				 * We know we're losing at the current
				 * window size so do congestion avoidance
				 * (set ssthresh to half the current window
				 * and pull our congestion window back to
				 * the new ssthresh).
				 *
				 * Dup acks mean that packets have left the
				 * network (they're now cached at the receiver)
				 * so bump cwnd by the amount in the receiver
				 * to keep a constant cwnd packets in the
				 * network.
				 */
				if (tp->t_timer[TCPT_REXMT] == 0 ||
				    th->th_ack != tp->snd_una)
					tp->t_dupacks = 0;
				else if (++tp->t_dupacks > tcprexmtthresh ||
					 ((tcp_do_newreno || tp->sack_enable) &&
					  IN_FASTRECOVERY(tp))) {
                                        if (tp->sack_enable && IN_FASTRECOVERY(tp)) {
						int awnd;
						
						/*
						 * Compute the amount of data in flight first.
						 * We can inject new data into the pipe iff 
						 * we have less than 1/2 the original window's 	
						 * worth of data in flight.
						 */
						awnd = (tp->snd_nxt - tp->snd_fack) +
							tp->sackhint.sack_bytes_rexmit;
						if (awnd < tp->snd_ssthresh) {
							tp->snd_cwnd += tp->t_maxseg;
							if (tp->snd_cwnd > tp->snd_ssthresh)
								tp->snd_cwnd = tp->snd_ssthresh;
						}
					} else
						tp->snd_cwnd += tp->t_maxseg;
					(void) tcp_output(tp);
					goto drop;
				} else if (tp->t_dupacks == tcprexmtthresh) {
					tcp_seq onxt = tp->snd_nxt;
					u_int win;

					/*
					 * If we're doing sack, check to
					 * see if we're already in sack
					 * recovery. If we're not doing sack,
					 * check to see if we're in newreno
					 * recovery.
					 */
					if (tp->sack_enable) {
						if (IN_FASTRECOVERY(tp)) {
							tp->t_dupacks = 0;
							break;
						}
					} else if (tcp_do_newreno) {
						if (SEQ_LEQ(th->th_ack,
						    tp->snd_recover)) {
							tp->t_dupacks = 0;
							break;
						}
					}
					win = min(tp->snd_wnd, tp->snd_cwnd) /
					    2 / tp->t_maxseg;
					if (win < 2)
						win = 2;
					tp->snd_ssthresh = win * tp->t_maxseg;
					ENTER_FASTRECOVERY(tp);
					tp->snd_recover = tp->snd_max;
					tp->t_timer[TCPT_REXMT] = 0;
					tp->t_rtttime = 0;
					if (tp->sack_enable) {
						tcpstat.tcps_sack_recovery_episode++;
						tp->sack_newdata = tp->snd_nxt;
						tp->snd_cwnd = tp->t_maxseg;
						(void) tcp_output(tp);
						goto drop;
					}
					tp->snd_nxt = th->th_ack;
					tp->snd_cwnd = tp->t_maxseg;
					(void) tcp_output(tp);
					tp->snd_cwnd = tp->snd_ssthresh +
					     tp->t_maxseg * tp->t_dupacks;
					if (SEQ_GT(onxt, tp->snd_nxt))
						tp->snd_nxt = onxt;
					goto drop;
				}
			} else
				tp->t_dupacks = 0;
			break;
		}
		/*
		 * If the congestion window was inflated to account
		 * for the other side's cached packets, retract it.
		 */
		if (tcp_do_newreno || tp->sack_enable) {
			if (IN_FASTRECOVERY(tp)) {
				if (SEQ_LT(th->th_ack, tp->snd_recover)) {
					if (tp->sack_enable)
						tcp_sack_partialack(tp, th);
					else
						tcp_newreno_partial_ack(tp, th);
				} else {
					/*
					 * Out of fast recovery.
					 * Window inflation should have left us
					 * with approximately snd_ssthresh
					 * outstanding data.
					 * But in case we would be inclined to
					 * send a burst, better to do it via
					 * the slow start mechanism.
					 */
					if (SEQ_GT(th->th_ack +
							tp->snd_ssthresh,
						   tp->snd_max))
						tp->snd_cwnd = tp->snd_max -
								th->th_ack +
								tp->t_maxseg;
					else
						tp->snd_cwnd = tp->snd_ssthresh;
				}
			}
		} else {
			if (tp->t_dupacks >= tcprexmtthresh &&
			    tp->snd_cwnd > tp->snd_ssthresh)
				tp->snd_cwnd = tp->snd_ssthresh;
		}
		tp->t_dupacks = 0;
		/*
		 * If we reach this point, ACK is not a duplicate,
		 *     i.e., it ACKs something we sent.
		 */
		if (tp->t_flags & TF_NEEDSYN) {
			/*
			 * T/TCP: Connection was half-synchronized, and our
			 * SYN has been ACK'd (so connection is now fully
			 * synchronized).  Go to non-starred state,
			 * increment snd_una for ACK of SYN, and check if
			 * we can do window scaling.
			 */
			tp->t_flags &= ~TF_NEEDSYN;
			tp->snd_una++;
			/* Do window scaling? */
			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
				tp->snd_scale = tp->requested_s_scale;
				tp->rcv_scale = tp->request_r_scale;
			}
		}

process_ACK:
		acked = th->th_ack - tp->snd_una;
		tcpstat.tcps_rcvackpack++;
		tcpstat.tcps_rcvackbyte += acked;

		/*
		 * If we just performed our first retransmit, and the ACK
		 * arrives within our recovery window, then it was a mistake
		 * to do the retransmit in the first place.  Recover our
		 * original cwnd and ssthresh, and proceed to transmit where
		 * we left off.
		 */
		if (tp->t_rxtshift == 1 && tcp_now < tp->t_badrxtwin) {
			tp->snd_cwnd = tp->snd_cwnd_prev;
			tp->snd_ssthresh = tp->snd_ssthresh_prev;
			tp->snd_recover = tp->snd_recover_prev;
			if (tp->t_flags & TF_WASFRECOVERY)
				ENTER_FASTRECOVERY(tp);
			tp->snd_nxt = tp->snd_max;
			tp->t_badrxtwin = 0;	/* XXX probably not required */ 
		}

		/*
		 * If we have a timestamp reply, update smoothed
		 * round trip time.  If no timestamp is present but
		 * transmit timer is running and timed sequence
		 * number was acked, update smoothed round trip time.
		 * Since we now have an rtt measurement, cancel the
		 * timer backoff (cf., Phil Karn's retransmit alg.).
		 * Recompute the initial retransmit timer.
		 * Also makes sure we have a valid time stamp in hand
		 */
		if (((to.to_flags & TOF_TS) != 0) && (to.to_tsecr != 0))
			tcp_xmit_timer(tp, tcp_now - to.to_tsecr + 1);
		else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq))
			tcp_xmit_timer(tp, tp->t_rtttime);

		/*
		 * If all outstanding data is acked, stop retransmit
		 * timer and remember to restart (more output or persist).
		 * If there is more data to be acked, restart retransmit
		 * timer, using current (possibly backed-off) value.
		 */
		if (th->th_ack == tp->snd_max) {
			tp->t_timer[TCPT_REXMT] = 0;
			needoutput = 1;
		} else if (tp->t_timer[TCPT_PERSIST] == 0)
			tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;

		/*
		 * If no data (only SYN) was ACK'd,
		 *    skip rest of ACK processing.
		 */
		if (acked == 0)
			goto step6;

		/*
		 * When new data is acked, open the congestion window.
		 * If the window gives us less than ssthresh packets
		 * in flight, open exponentially (maxseg per packet).
		 * Otherwise open linearly: maxseg per window
		 * (maxseg^2 / cwnd per packet).
		 */
		if ((!tcp_do_newreno && !tp->sack_enable) ||
		    !IN_FASTRECOVERY(tp)) {
			register u_int cw = tp->snd_cwnd;
			register u_int incr = tp->t_maxseg;
			if (cw > tp->snd_ssthresh)
				incr = incr * incr / cw;
			tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
		}
		if (acked > so->so_snd.sb_cc) {
			tp->snd_wnd -= so->so_snd.sb_cc;
			sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
			ourfinisacked = 1;
		} else {
			sbdrop(&so->so_snd, acked);
			tp->snd_wnd -= acked;
			ourfinisacked = 0;
		}
		sowwakeup(so);
		/* detect una wraparound */
		if ((tcp_do_newreno || tp->sack_enable) &&
		    !IN_FASTRECOVERY(tp) &&
		    SEQ_GT(tp->snd_una, tp->snd_recover) &&
		    SEQ_LEQ(th->th_ack, tp->snd_recover))
			tp->snd_recover = th->th_ack - 1;
		if ((tcp_do_newreno || tp->sack_enable) &&
		    IN_FASTRECOVERY(tp) &&
		    SEQ_GEQ(th->th_ack, tp->snd_recover))
			EXIT_FASTRECOVERY(tp);
		tp->snd_una = th->th_ack;
		if (tp->sack_enable) {
			if (SEQ_GT(tp->snd_una, tp->snd_recover))
				tp->snd_recover = tp->snd_una;
		}
		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
			tp->snd_nxt = tp->snd_una;

		switch (tp->t_state) {

		/*
		 * In FIN_WAIT_1 STATE in addition to the processing
		 * for the ESTABLISHED state if our FIN is now acknowledged
		 * then enter FIN_WAIT_2.
		 */
		case TCPS_FIN_WAIT_1:
			if (ourfinisacked) {
				/*
				 * If we can't receive any more
				 * data, then closing user can proceed.
				 * Starting the timer is contrary to the
				 * specification, but if we don't get a FIN
				 * we'll hang forever.
				 */
				if (so->so_state & SS_CANTRCVMORE) {
					soisdisconnected(so);
					tp->t_timer[TCPT_2MSL] = tcp_maxidle;
				}
				add_to_time_wait(tp);
				tp->t_state = TCPS_FIN_WAIT_2;
				goto drop;
			}
			break;

	 	/*
		 * In CLOSING STATE in addition to the processing for
		 * the ESTABLISHED state if the ACK acknowledges our FIN
		 * then enter the TIME-WAIT state, otherwise ignore
		 * the segment.
		 */
		case TCPS_CLOSING:
			if (ourfinisacked) {
				tp->t_state = TCPS_TIME_WAIT;
				tcp_canceltimers(tp);
				/* Shorten TIME_WAIT [RFC-1644, p.28] */
				if (tp->cc_recv != 0 &&
				    tp->t_starttime < tcp_msl)
					tp->t_timer[TCPT_2MSL] =
					    tp->t_rxtcur * TCPTV_TWTRUNC;
				else
					tp->t_timer[TCPT_2MSL] = 2 * tcp_msl;
				add_to_time_wait(tp);
				soisdisconnected(so);
			}
			break;

		/*
		 * In LAST_ACK, we may still be waiting for data to drain
		 * and/or to be acked, as well as for the ack of our FIN.
		 * If our FIN is now acknowledged, delete the TCB,
		 * enter the closed state and return.
		 */
		case TCPS_LAST_ACK:
			if (ourfinisacked) {
				tp = tcp_close(tp);
				goto drop;
			}
			break;

		/*
		 * In TIME_WAIT state the only thing that should arrive
		 * is a retransmission of the remote FIN.  Acknowledge
		 * it and restart the finack timer.
		 */
		case TCPS_TIME_WAIT:
			tp->t_timer[TCPT_2MSL] = 2 * tcp_msl;
			add_to_time_wait(tp);
			goto dropafterack;
		}
	}

step6:
	/*
	 * Update window information.
	 * Don't look at window if no ACK: TAC's send garbage on first SYN.
	 */
	if ((thflags & TH_ACK) &&
	    (SEQ_LT(tp->snd_wl1, th->th_seq) ||
	    (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
	     (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
		/* keep track of pure window updates */
		if (tlen == 0 &&
		    tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
			tcpstat.tcps_rcvwinupd++;
		tp->snd_wnd = tiwin;
		tp->snd_wl1 = th->th_seq;
		tp->snd_wl2 = th->th_ack;
		if (tp->snd_wnd > tp->max_sndwnd)
			tp->max_sndwnd = tp->snd_wnd;
		needoutput = 1;
	}

	/*
	 * Process segments with URG.
	 */
	if ((thflags & TH_URG) && th->th_urp &&
	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
		/*
		 * This is a kludge, but if we receive and accept
		 * random urgent pointers, we'll crash in
		 * soreceive.  It's hard to imagine someone
		 * actually wanting to send this much urgent data.
		 */
		if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
			th->th_urp = 0;			/* XXX */
			thflags &= ~TH_URG;		/* XXX */
			goto dodata;			/* XXX */
		}
		/*
		 * If this segment advances the known urgent pointer,
		 * then mark the data stream.  This should not happen
		 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
		 * a FIN has been received from the remote side.
		 * In these states we ignore the URG.
		 *
		 * According to RFC961 (Assigned Protocols),
		 * the urgent pointer points to the last octet
		 * of urgent data.  We continue, however,
		 * to consider it to indicate the first octet
		 * of data past the urgent section as the original
		 * spec states (in one of two places).
		 */
		if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
			tp->rcv_up = th->th_seq + th->th_urp;
			so->so_oobmark = so->so_rcv.sb_cc +
			    (tp->rcv_up - tp->rcv_nxt) - 1;
			if (so->so_oobmark == 0) {
				so->so_state |= SS_RCVATMARK;
				postevent(so, 0, EV_OOB);
			}
			sohasoutofband(so);
			tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
		}
		/*
		 * Remove out of band data so doesn't get presented to user.
		 * This can happen independent of advancing the URG pointer,
		 * but if two URG's are pending at once, some out-of-band
		 * data may creep in... ick.
		 */
		if (th->th_urp <= (u_long)tlen
#if SO_OOBINLINE
		     && (so->so_options & SO_OOBINLINE) == 0
#endif
		     )
			tcp_pulloutofband(so, th, m,
				drop_hdrlen);	/* hdr drop is delayed */
	} else
		/*
		 * If no out of band data is expected,
		 * pull receive urgent pointer along
		 * with the receive window.
		 */
		if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
			tp->rcv_up = tp->rcv_nxt;
dodata:							/* XXX */

	/*
	 * Process the segment text, merging it into the TCP sequencing queue,
	 * and arranging for acknowledgment of receipt if necessary.
	 * This process logically involves adjusting tp->rcv_wnd as data
	 * is presented to the user (this happens in tcp_usrreq.c,
	 * case PRU_RCVD).  If a FIN has already been received on this
	 * connection then we just ignore the text.
	 */
	if ((tlen || (thflags&TH_FIN)) &&
	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
		tcp_seq save_start = th->th_seq;
		tcp_seq save_end = th->th_seq + tlen;
		m_adj(m, drop_hdrlen);	/* delayed header drop */
		/*
		 * Insert segment which includes th into TCP reassembly queue
		 * with control block tp.  Set thflags to whether reassembly now
		 * includes a segment with FIN.  This handles the common case
		 * inline (segment is the next to be received on an established
		 * connection, and the queue is empty), avoiding linkage into
		 * and removal from the queue and repetition of various
		 * conversions.
		 * Set DELACK for segments received in order, but ack
		 * immediately when segments are out of order (so
		 * fast retransmit can work).
		 */
		if (th->th_seq == tp->rcv_nxt &&
		    LIST_EMPTY(&tp->t_segq) &&
		    TCPS_HAVEESTABLISHED(tp->t_state)) {
			if (DELAY_ACK(tp) && ((tp->t_flags & TF_ACKNOW) == 0)) {
				tp->t_flags |= TF_DELACK;
			}         
			else {
				tp->t_flags |= TF_ACKNOW;
			}
			tp->rcv_nxt += tlen;
			thflags = th->th_flags & TH_FIN;
			tcpstat.tcps_rcvpack++;
			tcpstat.tcps_rcvbyte += tlen;
			ND6_HINT(tp);
			if (sbappend(&so->so_rcv, m))
				sorwakeup(so);
		} else {
			thflags = tcp_reass(tp, th, &tlen, m);
			tp->t_flags |= TF_ACKNOW;
		}

		if (tlen > 0 && tp->sack_enable)
			tcp_update_sack_list(tp, save_start, save_end);

		if (tp->t_flags & TF_DELACK) 
		{
#if INET6
			if (isipv6) {
				KERNEL_DEBUG(DBG_LAYER_END, ((th->th_dport << 16) | th->th_sport),
		     			(((ip6->ip6_src.s6_addr16[0]) << 16) | (ip6->ip6_dst.s6_addr16[0])),
			     		th->th_seq, th->th_ack, th->th_win); 
			}
			else
#endif
			{
				KERNEL_DEBUG(DBG_LAYER_END, ((th->th_dport << 16) | th->th_sport),
		     			(((ip->ip_src.s_addr & 0xffff) << 16) | (ip->ip_dst.s_addr & 0xffff)),
			     		th->th_seq, th->th_ack, th->th_win); 
			}
				
		}
		/*
		 * Note the amount of data that peer has sent into
		 * our window, in order to estimate the sender's
		 * buffer size.
		 */
		len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
	} else {
		m_freem(m);
		thflags &= ~TH_FIN;
	}

	/*
	 * If FIN is received ACK the FIN and let the user know
	 * that the connection is closing.
	 */
	if (thflags & TH_FIN) {
		if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
			socantrcvmore(so);
			postevent(so, 0, EV_FIN);
			/*
			 *  If connection is half-synchronized
			 *  (ie NEEDSYN flag on) then delay ACK,
			 * If connection is half-synchronized
			 * (ie NEEDSYN flag on) then delay ACK,
			 * so it may be piggybacked when SYN is sent.
			 * Otherwise, since we received a FIN then no
			 * more input can be expected, send ACK now.
			 */
			if (DELAY_ACK(tp) && (tp->t_flags & TF_NEEDSYN)) {
				tp->t_flags |= TF_DELACK;
			}
			else {
				tp->t_flags |= TF_ACKNOW;
			}
			tp->rcv_nxt++;
		}
		switch (tp->t_state) {

	 	/*
		 * In SYN_RECEIVED and ESTABLISHED STATES
		 * enter the CLOSE_WAIT state.
		 */
		case TCPS_SYN_RECEIVED:
			tp->t_starttime = 0;
		case TCPS_ESTABLISHED:
			tp->t_state = TCPS_CLOSE_WAIT;
			break;

	 	/*
		 * If still in FIN_WAIT_1 STATE FIN has not been acked so
		 * enter the CLOSING state.
		 */
		case TCPS_FIN_WAIT_1:
			tp->t_state = TCPS_CLOSING;
			break;

	 	/*
		 * In FIN_WAIT_2 state enter the TIME_WAIT state,
		 * starting the time-wait timer, turning off the other
		 * standard timers.
		 */
		case TCPS_FIN_WAIT_2:
			tp->t_state = TCPS_TIME_WAIT;
			tcp_canceltimers(tp);
			/* Shorten TIME_WAIT [RFC-1644, p.28] */
			if (tp->cc_recv != 0 &&
			    tp->t_starttime < tcp_msl) {
				tp->t_timer[TCPT_2MSL] =
				    tp->t_rxtcur * TCPTV_TWTRUNC;
				/* For transaction client, force ACK now. */
				tp->t_flags |= TF_ACKNOW;
			}
			else
				tp->t_timer[TCPT_2MSL] = 2 * tcp_msl;

			add_to_time_wait(tp);
			soisdisconnected(so);
			break;

		/*
		 * In TIME_WAIT state restart the 2 MSL time_wait timer.
		 */
		case TCPS_TIME_WAIT:
			tp->t_timer[TCPT_2MSL] = 2 * tcp_msl;
			add_to_time_wait(tp);
			break;
		}
	}
#if TCPDEBUG
	if (so->so_options & SO_DEBUG)
		tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
			  &tcp_savetcp, 0);
#endif

	/*
	 * Return any desired output.
	 */
	if (needoutput || (tp->t_flags & TF_ACKNOW))
		(void) tcp_output(tp);
	tcp_unlock(so, 1, 0);
	KERNEL_DEBUG(DBG_FNC_TCP_INPUT | DBG_FUNC_END,0,0,0,0,0);
	return;

dropafterack:
	/*
	 * 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)) ) {
		rstreason = BANDLIM_RST_OPENPORT;
		goto dropwithreset;
	}
#if TCPDEBUG
	if (so->so_options & SO_DEBUG)
		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
			  &tcp_savetcp, 0);
#endif
	m_freem(m);
	tp->t_flags |= TF_ACKNOW;
	(void) tcp_output(tp);
	tcp_unlock(so, 1, 0);
	KERNEL_DEBUG(DBG_FNC_TCP_INPUT | DBG_FUNC_END,0,0,0,0,0);
	return;
dropwithresetnosock:
	nosock = 1;
dropwithreset:
	/*
	 * Generate a RST, dropping incoming segment.
	 * Make ACK acceptable to originator of segment.
	 * Don't bother to respond if destination was broadcast/multicast.
	 */
	if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
		goto drop;
#if INET6
	if (isipv6) {
		if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
		    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
			goto drop;
	} else
#endif /* INET6 */
	if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
	    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
	    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
	    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
		goto drop;
	/* IPv6 anycast check is done at tcp6_input() */

	/* 
	 * Perform bandwidth limiting.
	 */
#if ICMP_BANDLIM
	if (badport_bandlim(rstreason) < 0)
		goto drop;
#endif

#if TCPDEBUG
	if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
			  &tcp_savetcp, 0);
#endif
	if (thflags & TH_ACK)
		/* mtod() below is safe as long as hdr dropping is delayed */
		tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack,
			    TH_RST);
	else {
		if (thflags & TH_SYN)
			tlen++;
		/* mtod() below is safe as long as hdr dropping is delayed */
		tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
			    (tcp_seq)0, TH_RST|TH_ACK);
	}
	/* destroy temporarily created socket */
	if (dropsocket) {
		(void) soabort(so); 
		tcp_unlock(so, 1, 0);
	}
	else
		if ((inp != NULL) && (nosock == 0))
			tcp_unlock(so, 1, 0);
	KERNEL_DEBUG(DBG_FNC_TCP_INPUT | DBG_FUNC_END,0,0,0,0,0);
	return;
dropnosock:
	nosock = 1;
drop:
	/*
	 * Drop space held by incoming segment and return.
	 */
#if TCPDEBUG
	if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
		tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
			  &tcp_savetcp, 0);
#endif
	m_freem(m);
	/* destroy temporarily created socket */
	if (dropsocket) {
		(void) soabort(so); 
		tcp_unlock(so, 1, 0);
	}
	else
		if (nosock == 0)
			tcp_unlock(so, 1, 0);
	KERNEL_DEBUG(DBG_FNC_TCP_INPUT | DBG_FUNC_END,0,0,0,0,0);
	return;
}

static void
tcp_dooptions(tp, cp, cnt, th, to)
/*
 * Parse TCP options and place in tcpopt.
 */
	struct tcpcb *tp;
	u_char *cp;
	int cnt;
	struct tcphdr *th;
	struct tcpopt *to;
{
	u_short mss = 0;
	int opt, optlen;

	for (; cnt > 0; cnt -= optlen, cp += optlen) {
		opt = cp[0];
		if (opt == TCPOPT_EOL)
			break;
		if (opt == TCPOPT_NOP)
			optlen = 1;
		else {
			if (cnt < 2)
				break;
			optlen = cp[1];
			if (optlen < 2 || optlen > cnt)
				break;
		}
		switch (opt) {

		default:
			continue;

		case TCPOPT_MAXSEG:
			if (optlen != TCPOLEN_MAXSEG)
				continue;
			if (!(th->th_flags & TH_SYN))
				continue;
			bcopy((char *) cp + 2, (char *) &mss, sizeof(mss));
			NTOHS(mss);
			break;

		case TCPOPT_WINDOW:
			if (optlen != TCPOLEN_WINDOW)
				continue;
			if (!(th->th_flags & TH_SYN))
				continue;
			tp->t_flags |= TF_RCVD_SCALE;
			tp->requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
			break;

		case TCPOPT_TIMESTAMP:
			if (optlen != TCPOLEN_TIMESTAMP)
				continue;
			to->to_flags |= TOF_TS;
			bcopy((char *)cp + 2,
			    (char *)&to->to_tsval, sizeof(to->to_tsval));
			NTOHL(to->to_tsval);
			bcopy((char *)cp + 6,
			    (char *)&to->to_tsecr, sizeof(to->to_tsecr));
			NTOHL(to->to_tsecr);

			/*
			 * A timestamp received in a SYN makes
			 * it ok to send timestamp requests and replies.
			 */
			if (th->th_flags & TH_SYN) {
				tp->t_flags |= TF_RCVD_TSTMP;
				tp->ts_recent = to->to_tsval;
				tp->ts_recent_age = tcp_now;
			}
			break;
		case TCPOPT_SACK_PERMITTED:
			if (!tcp_do_sack ||
			    optlen != TCPOLEN_SACK_PERMITTED)
				continue;
			if (th->th_flags & TH_SYN)
				to->to_flags |= TOF_SACK;
			break;
		case TCPOPT_SACK:
			if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
				continue;
			to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
			to->to_sacks = cp + 2;
			tcpstat.tcps_sack_rcv_blocks++;

			break;
		}
	}
	if (th->th_flags & TH_SYN)
		tcp_mss(tp, mss);	/* sets t_maxseg */
}

/*
 * Pull out of band byte out of a segment so
 * it doesn't appear in the user's data queue.
 * It is still reflected in the segment length for
 * sequencing purposes.
 */
static void
tcp_pulloutofband(so, th, m, off)
	struct socket *so;
	struct tcphdr *th;
	register struct mbuf *m;
	int off;		/* delayed to be droped hdrlen */
{
	int cnt = off + th->th_urp - 1;

	while (cnt >= 0) {
		if (m->m_len > cnt) {
			char *cp = mtod(m, caddr_t) + cnt;
			struct tcpcb *tp = sototcpcb(so);

			tp->t_iobc = *cp;
			tp->t_oobflags |= TCPOOB_HAVEDATA;
			bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
			m->m_len--;
			if (m->m_flags & M_PKTHDR)
				m->m_pkthdr.len--;
			return;
		}
		cnt -= m->m_len;
		m = m->m_next;
		if (m == 0)
			break;
	}
	panic("tcp_pulloutofband");
}

/*
 * Collect new round-trip time estimate
 * and update averages and current timeout.
 */
static void
tcp_xmit_timer(tp, rtt)
	register struct tcpcb *tp;
	int rtt;
{
	register int delta;

	tcpstat.tcps_rttupdated++;
	tp->t_rttupdated++;
	if (tp->t_srtt != 0) {
		/*
		 * srtt is stored as fixed point with 5 bits after the
		 * binary point (i.e., scaled by 8).  The following magic
		 * is equivalent to the smoothing algorithm in rfc793 with
		 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
		 * point).  Adjust rtt to origin 0.
		 */
		delta = ((rtt - 1) << TCP_DELTA_SHIFT)
			- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));

		if ((tp->t_srtt += delta) <= 0)
			tp->t_srtt = 1;

		/*
		 * We accumulate a smoothed rtt variance (actually, a
		 * smoothed mean difference), then set the retransmit
		 * timer to smoothed rtt + 4 times the smoothed variance.
		 * rttvar is stored as fixed point with 4 bits after the
		 * binary point (scaled by 16).  The following is
		 * equivalent to rfc793 smoothing with an alpha of .75
		 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
		 * rfc793's wired-in beta.
		 */
		if (delta < 0)
			delta = -delta;
		delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
		if ((tp->t_rttvar += delta) <= 0)
			tp->t_rttvar = 1;
	} else {
		/*
		 * No rtt measurement yet - use the unsmoothed rtt.
		 * Set the variance to half the rtt (so our first
		 * retransmit happens at 3*rtt).
		 */
		tp->t_srtt = rtt << TCP_RTT_SHIFT;
		tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
	}
	tp->t_rtttime = 0;
	tp->t_rxtshift = 0;

	/*
	 * the retransmit should happen at rtt + 4 * rttvar.
	 * Because of the way we do the smoothing, srtt and rttvar
	 * will each average +1/2 tick of bias.  When we compute
	 * the retransmit timer, we want 1/2 tick of rounding and
	 * 1 extra tick because of +-1/2 tick uncertainty in the
	 * firing of the timer.  The bias will give us exactly the
	 * 1.5 tick we need.  But, because the bias is
	 * statistical, we have to test that we don't drop below
	 * the minimum feasible timer (which is 2 ticks).
	 */
	TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
		      max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);

	/*
	 * We received an ack for a packet that wasn't retransmitted;
	 * it is probably safe to discard any error indications we've
	 * received recently.  This isn't quite right, but close enough
	 * for now (a route might have failed after we sent a segment,
	 * and the return path might not be symmetrical).
	 */
	tp->t_softerror = 0;
}

/*
 * Determine a reasonable value for maxseg size.
 * If the route is known, check route for mtu.
 * If none, use an mss that can be handled on the outgoing
 * interface without forcing IP to fragment; if bigger than
 * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
 * to utilize large mbufs.  If no route is found, route has no mtu,
 * or the destination isn't local, use a default, hopefully conservative
 * size (usually 512 or the default IP max size, but no more than the mtu
 * of the interface), as we can't discover anything about intervening
 * gateways or networks.  We also initialize the congestion/slow start
 * window to be a single segment if the destination isn't local.
 * While looking at the routing entry, we also initialize other path-dependent
 * parameters from pre-set or cached values in the routing entry.
 *
 * Also take into account the space needed for options that we
 * send regularly.  Make maxseg shorter by that amount to assure
 * that we can send maxseg amount of data even when the options
 * are present.  Store the upper limit of the length of options plus
 * data in maxopd.
 *
 * NOTE that this routine is only called when we process an incoming
 * segment, for outgoing segments only tcp_mssopt is called.
 *
 * In case of T/TCP, we call this routine during implicit connection
 * setup as well (offer = -1), to initialize maxseg from the cached
 * MSS of our peer.
 */
void
tcp_mss(tp, offer)
	struct tcpcb *tp;
	int offer;
{
	register struct rtentry *rt;
	struct ifnet *ifp;
	register int rtt, mss;
	u_long bufsize;
	struct inpcb *inp;
	struct socket *so;
	struct rmxp_tao *taop;
	int origoffer = offer;
#if INET6
	int isipv6;
	int min_protoh;
#endif

	inp = tp->t_inpcb;
#if INET6
	isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
	min_protoh = isipv6 ? sizeof (struct ip6_hdr) + sizeof (struct tcphdr)
			    : sizeof (struct tcpiphdr);
#else
#define min_protoh  (sizeof (struct tcpiphdr))
#endif
#if INET6
	if (isipv6)
		rt = tcp_rtlookup6(inp);
	else
#endif /* INET6 */
	rt = tcp_rtlookup(inp);
	if (rt == NULL) {
		tp->t_maxopd = tp->t_maxseg =
#if INET6
		isipv6 ? tcp_v6mssdflt :
#endif /* INET6 */
		tcp_mssdflt;
		return;
	}
	ifp = rt->rt_ifp;
	/*
	 * Slower link window correction:
	 * If a value is specificied for slowlink_wsize use it for PPP links
	 * believed to be on a serial modem (speed <128Kbps). Excludes 9600bps as
	 * it is the default value adversized by pseudo-devices over ppp.
	 */
	if (ifp->if_type == IFT_PPP && slowlink_wsize > 0 && 
	    ifp->if_baudrate > 9600 && ifp->if_baudrate <= 128000) {
		tp->t_flags |= TF_SLOWLINK;
	}
	so = inp->inp_socket;

	taop = rmx_taop(rt->rt_rmx);
	/*
	 * Offer == -1 means that we didn't receive SYN yet,
	 * use cached value in that case;
	 */
	if (offer == -1)
		offer = taop->tao_mssopt;
	/*
	 * Offer == 0 means that there was no MSS on the SYN segment,
	 * in this case we use tcp_mssdflt.
	 */
	if (offer == 0)
		offer =
#if INET6
			isipv6 ? tcp_v6mssdflt :
#endif /* INET6 */
			tcp_mssdflt;
	else {
		/*
		 * Prevent DoS attack with too small MSS. Round up
		 * to at least minmss.
		 */
		offer = max(offer, tcp_minmss);
		/*
		 * Sanity check: make sure that maxopd will be large
		 * enough to allow some data on segments even is the
		 * all the option space is used (40bytes).  Otherwise
		 * funny things may happen in tcp_output.
		 */
		offer = max(offer, 64);
	}
	taop->tao_mssopt = offer;

	/*
	 * While we're here, check if there's an initial rtt
	 * or rttvar.  Convert from the route-table units
	 * to scaled multiples of the slow timeout timer.
	 */
	if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
		/*
		 * XXX the lock bit for RTT indicates that the value
		 * is also a minimum value; this is subject to time.
		 */
		if (rt->rt_rmx.rmx_locks & RTV_RTT)
			tp->t_rttmin = rtt / (RTM_RTTUNIT / PR_SLOWHZ);
		tp->t_srtt = rtt / (RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTT_SCALE));
		tcpstat.tcps_usedrtt++;
		if (rt->rt_rmx.rmx_rttvar) {
			tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
			    (RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTTVAR_SCALE));
			tcpstat.tcps_usedrttvar++;
		} else {
			/* default variation is +- 1 rtt */
			tp->t_rttvar =
			    tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
		}
		TCPT_RANGESET(tp->t_rxtcur,
			      ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
			      tp->t_rttmin, TCPTV_REXMTMAX);
	}
	/*
	 * if there's an mtu associated with the route, use it
	 * else, use the link mtu.
	 */
	if (rt->rt_rmx.rmx_mtu)
		mss = rt->rt_rmx.rmx_mtu - min_protoh;
	else
	{
		mss =
#if INET6
			(isipv6 ? nd_ifinfo[rt->rt_ifp->if_index].linkmtu :
#endif
			 ifp->if_mtu
#if INET6
			 )
#endif
			- min_protoh;
#if INET6
		if (isipv6) {
			if (!in6_localaddr(&inp->in6p_faddr))
				mss = min(mss, tcp_v6mssdflt);
		} else
#endif /* INET6 */
		if (!in_localaddr(inp->inp_faddr))
			mss = min(mss, tcp_mssdflt);
	}
	mss = min(mss, offer);
	/*
	 * maxopd stores the maximum length of data AND options
	 * in a segment; maxseg is the amount of data in a normal
	 * segment.  We need to store this value (maxopd) apart
	 * from maxseg, because now every segment carries options
	 * and thus we normally have somewhat less data in segments.
	 */
	tp->t_maxopd = mss;

	/*
	 * origoffer==-1 indicates, that no segments were received yet.
	 * In this case we just guess.
	 */
	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
	    (origoffer == -1 ||
	     (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
		mss -= TCPOLEN_TSTAMP_APPA;
	tp->t_maxseg = mss;

	/*
	 * If there's a pipesize (ie loopback), change the socket
	 * buffer to that size only if it's bigger than the current
	 * sockbuf size.  Make the socket buffers an integral
	 * number of mss units; if the mss is larger than
	 * the socket buffer, decrease the mss.
	 */
#if RTV_SPIPE
	bufsize = rt->rt_rmx.rmx_sendpipe;
	if (bufsize < so->so_snd.sb_hiwat)
#endif
		bufsize = so->so_snd.sb_hiwat;
	if (bufsize < mss)
		mss = bufsize;
	else {
		bufsize = roundup(bufsize, mss);
		if (bufsize > sb_max)
			bufsize = sb_max;
		(void)sbreserve(&so->so_snd, bufsize);
	}
	tp->t_maxseg = mss;

#if RTV_RPIPE
	bufsize = rt->rt_rmx.rmx_recvpipe;
	if (bufsize < so->so_rcv.sb_hiwat)
#endif
		bufsize = so->so_rcv.sb_hiwat;
	if (bufsize > mss) {
		bufsize = roundup(bufsize, mss);
		if (bufsize > sb_max)
			bufsize = sb_max;
		(void)sbreserve(&so->so_rcv, bufsize);
	}

	/*
	 * Set the slow-start flight size depending on whether this
	 * is a local network or not.
	 */
	if (
#if INET6
	    (isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
	    (!isipv6 &&
#endif
	     in_localaddr(inp->inp_faddr)
#if INET6
	     )
#endif
	    )
		tp->snd_cwnd = mss * ss_fltsz_local;
	else 
		tp->snd_cwnd = mss * ss_fltsz;

	if (rt->rt_rmx.rmx_ssthresh) {
		/*
		 * There's some sort of gateway or interface
		 * buffer limit on the path.  Use this to set
		 * the slow start threshhold, but set the
		 * threshold to no less than 2*mss.
		 */
		tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
		tcpstat.tcps_usedssthresh++;
	}
}

/*
 * Determine the MSS option to send on an outgoing SYN.
 */
int
tcp_mssopt(tp)
	struct tcpcb *tp;
{
	struct rtentry *rt;
	int mss;
#if INET6
	int isipv6;
	int min_protoh;
#endif

#if INET6
	isipv6 = ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
	min_protoh = isipv6 ? sizeof (struct ip6_hdr) + sizeof (struct tcphdr)
			    : sizeof (struct tcpiphdr);
#else
#define min_protoh  (sizeof (struct tcpiphdr))
#endif
#if INET6
	if (isipv6)
		rt = tcp_rtlookup6(tp->t_inpcb);
	else
#endif /* INET6 */
	rt = tcp_rtlookup(tp->t_inpcb);
	if (rt == NULL)
		return
#if INET6
			isipv6 ? tcp_v6mssdflt :
#endif /* INET6 */
			tcp_mssdflt;
	/*
	 * Slower link window correction:
	 * If a value is specificied for slowlink_wsize use it for PPP links
	 * believed to be on a serial modem (speed <128Kbps). Excludes 9600bps as
	 * it is the default value adversized by pseudo-devices over ppp.
	 */
	if (rt->rt_ifp->if_type == IFT_PPP && slowlink_wsize > 0 && 
	    rt->rt_ifp->if_baudrate > 9600 && rt->rt_ifp->if_baudrate <= 128000) {
		tp->t_flags |= TF_SLOWLINK;
	}

	if (rt->rt_rmx.rmx_mtu)
		mss =  rt->rt_rmx.rmx_mtu;
	else {
		mss =
#if INET6
			(isipv6 ? nd_ifinfo[rt->rt_ifp->if_index].linkmtu :
#endif
			 rt->rt_ifp->if_mtu
#if INET6
			 );
#endif
	}
	return (mss - min_protoh);
}

/*
 * On a partial ack arrives, force the retransmission of the
 * next unacknowledged segment.  Do not clear tp->t_dupacks.
 * By setting snd_nxt to ti_ack, this forces retransmission timer to
 * be started again.
 */
static void
tcp_newreno_partial_ack(tp, th)
	struct tcpcb *tp;
	struct tcphdr *th;
{
		tcp_seq onxt = tp->snd_nxt;
		u_long  ocwnd = tp->snd_cwnd;
		tp->t_timer[TCPT_REXMT] = 0;
		tp->t_rtttime = 0;
		tp->snd_nxt = th->th_ack;
		/*
		 * Set snd_cwnd to one segment beyond acknowledged offset
		 * (tp->snd_una has not yet been updated when this function 
		 *  is called)
		 */
		tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
		tp->t_flags |= TF_ACKNOW;
		(void) tcp_output(tp);
		tp->snd_cwnd = ocwnd;
		if (SEQ_GT(onxt, tp->snd_nxt))
			tp->snd_nxt = onxt;
		/*
		 * Partial window deflation.  Relies on fact that tp->snd_una
		 * not updated yet.
		 */
		tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg);
}

/*
 * Drop a random TCP connection that hasn't been serviced yet and
 * is eligible for discard.  There is a one in qlen chance that
 * we will return a null, saying that there are no dropable
 * requests.  In this case, the protocol specific code should drop
 * the new request.  This insures fairness.
 *
 * The listening TCP socket "head" must be locked
 */
static int
tcpdropdropablreq(struct socket *head)
{
	struct socket *so;
	unsigned int i, j, qlen;
	static int rnd;
	static struct timeval old_runtime;
	static unsigned int cur_cnt, old_cnt;
	struct timeval tv;
	struct inpcb *inp = NULL;
	struct tcpcb *tp;
	
	microtime(&tv);
	if ((i = (tv.tv_sec - old_runtime.tv_sec)) != 0) {
		old_runtime = tv;
		old_cnt = cur_cnt / i;
		cur_cnt = 0;
	}
	
	so = TAILQ_FIRST(&head->so_incomp);
	if (!so)
		return 0;
	
	qlen = head->so_incqlen;
	if (++cur_cnt > qlen || old_cnt > qlen) {
		rnd = (314159 * rnd + 66329) & 0xffff;
		j = ((qlen + 1) * rnd) >> 16;

		while (j-- && so)
			so = TAILQ_NEXT(so, so_list);
	}
	/* Find a connection that is not already closing */
	while (so) {
		inp = (struct inpcb *)so->so_pcb;
		
		if (in_pcb_checkstate(inp, WNT_ACQUIRE, 0) != WNT_STOPUSING)
			break;
		
		so = TAILQ_NEXT(so, so_list);
	}
	if (!so)
		return 0;
	
	head->so_incqlen--;
	head->so_qlen--;
	TAILQ_REMOVE(&head->so_incomp, so, so_list);
	tcp_unlock(head, 0, 0);

	/* Let's remove this connection from the incomplete list */
	tcp_lock(so, 1, 0);
	
	if (in_pcb_checkstate(inp, WNT_RELEASE, 1) == WNT_STOPUSING) {
		tcp_unlock(so, 1, 0);
		return 0;
	}
	
	so->so_head = NULL;
	so->so_usecount--;	/* No more held by so_head */

	/* 
	 * We do not want to lose track of the PCB right away in case we receive 
	 * more segments from the peer
	 */
	tp = sototcpcb(so);
	tp->t_flags |= TF_LQ_OVERFLOW;
	tp->t_state = TCPS_CLOSED;
	(void) tcp_output(tp);
	tcpstat.tcps_drops++;
	soisdisconnected(so);
	tcp_canceltimers(tp);
	add_to_time_wait(tp);
	
	tcp_unlock(so, 1, 0);
	tcp_lock(head, 0, 0);
	
	return 1;
	
}

static int
tcp_getstat SYSCTL_HANDLER_ARGS
{

	int error;

	if (req->oldptr == 0) {
		req->oldlen= (size_t)sizeof(struct tcpstat);
	}

	error = SYSCTL_OUT(req, &tcpstat, (size_t) req->oldlen);

        return (error);

}

SYSCTL_PROC(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RD, 0, 0,
    tcp_getstat, "S,tcpstat", "TCP statistics (struct tcpstat, netinet/tcp_var.h)");