inet/ipf/ip_proxy.c

/*
 * Copyright (C) 1997-2003 by Darren Reed.
 *
 * See the IPFILTER.LICENCE file for details on licencing.
 *
 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#if defined(KERNEL) || defined(_KERNEL)
# undef KERNEL
# undef _KERNEL
# define        KERNEL  1
# define        _KERNEL 1
#endif
#include <sys/errno.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/file.h>
#if !defined(AIX)
# include <sys/fcntl.h>
#endif
#if !defined(_KERNEL) && !defined(__KERNEL__)
# include <stdio.h>
# include <string.h>
# include <stdlib.h>
# include <ctype.h>
# define _KERNEL
# ifdef __OpenBSD__
struct file;
# endif
# include <sys/uio.h>
# undef _KERNEL
#endif
#if !defined(linux)
# include <sys/protosw.h>
#endif
#include <sys/socket.h>
#if defined(_KERNEL)
# if !defined(__NetBSD__) && !defined(sun) && !defined(__osf__) && \
     !defined(__OpenBSD__) && !defined(__hpux) && !defined(__sgi) && \
     !defined(AIX)
#  include <sys/ctype.h>
# endif
# include <sys/systm.h>
# if !defined(__SVR4) && !defined(__svr4__)
#  include <sys/mbuf.h>
# endif
#endif
#if defined(_KERNEL) && (__FreeBSD_version >= 220000)
# include <sys/filio.h>
# include <sys/fcntl.h>
# if (__FreeBSD_version >= 300000) && !defined(IPFILTER_LKM)
#  include "opt_ipfilter.h"
# endif
#else
# include <sys/ioctl.h>
#endif
#if defined(__SVR4) || defined(__svr4__)
# include <sys/byteorder.h>
# ifdef _KERNEL
#  include <sys/dditypes.h>
#  include <sys/strsubr.h>
# endif
# include <sys/stream.h>
# include <sys/kmem.h>
# include <sys/pattr.h>
#endif
#if __FreeBSD__ > 2
# include <sys/queue.h>
#endif
#include <net/if.h>
#ifdef sun
# include <net/af.h>
#endif
#include <net/route.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#ifndef linux
# include <netinet/ip_var.h>
#endif
#include <netinet/tcp.h>
#include <netinet/udp.h>
#include <netinet/ip_icmp.h>
#include "netinet/ip_compat.h"
#include <netinet/tcpip.h>
#include "netinet/ipf_stack.h"
#include "netinet/ip_fil.h"
#include "netinet/ip_nat.h"
#include "netinet/ip_state.h"
#include "netinet/ip_proxy.h"
#if (__FreeBSD_version >= 300000)
# include <sys/malloc.h>
#endif

#include "netinet/ip_ftp_pxy.c"
#include "netinet/ip_rcmd_pxy.c"
# include "netinet/ip_pptp_pxy.c"
#if defined(_KERNEL)
# include "netinet/ip_irc_pxy.c"
# include "netinet/ip_raudio_pxy.c"
# include "netinet/ip_h323_pxy.c"
# include "netinet/ip_netbios_pxy.c"
#endif
#include "netinet/ip_ipsec_pxy.c"
#include "netinet/ip_rpcb_pxy.c"

/* END OF INCLUDES */

#if !defined(lint)
static const char rcsid[] = "@(#)$Id: ip_proxy.c,v 2.62.2.14 2005/06/18 02:41:33 darrenr Exp $";
#endif

static int appr_fixseqack __P((fr_info_t *, ip_t *, ap_session_t *, int ));

#define AP_SESS_SIZE    53

#if defined(_KERNEL)
int     ipf_proxy_debug = 0;
#else
int     ipf_proxy_debug = 2;
#endif

static aproxy_t lcl_ap_proxies[] = {
#ifdef  IPF_FTP_PROXY
    { NULL, "ftp", (char)IPPROTO_TCP, 0, 0, NULL, ippr_ftp_init, ippr_ftp_fini,
      ippr_ftp_new, NULL, ippr_ftp_in, ippr_ftp_out, NULL },
#endif
#ifdef  IPF_IRC_PROXY
    { NULL, "irc", (char)IPPROTO_TCP, 0, 0, NULL, ippr_irc_init, ippr_irc_fini,
      ippr_irc_new, NULL, NULL, ippr_irc_out, NULL, NULL },
#endif
#ifdef  IPF_RCMD_PROXY
    { NULL, "rcmd", (char)IPPROTO_TCP, 0, 0, NULL, ippr_rcmd_init, ippr_rcmd_fini,
      ippr_rcmd_new, NULL, ippr_rcmd_in, ippr_rcmd_out, NULL, NULL },
#endif
#ifdef  IPF_RAUDIO_PROXY
    { NULL, "raudio", (char)IPPROTO_TCP, 0, 0, NULL, ippr_raudio_init, ippr_raudio_fini,
      ippr_raudio_new, NULL, ippr_raudio_in, ippr_raudio_out, NULL, NULL },
#endif
#ifdef  IPF_MSNRPC_PROXY
    { NULL, "msnrpc", (char)IPPROTO_TCP, 0, 0, NULL, ippr_msnrpc_init, ippr_msnrpc_fini,
      ippr_msnrpc_new, NULL, ippr_msnrpc_in, ippr_msnrpc_out, NULL, NULL },
#endif
#ifdef  IPF_NETBIOS_PROXY
    { NULL, "netbios", (char)IPPROTO_UDP, 0, 0, NULL, ippr_netbios_init, ippr_netbios_fini,
      NULL, NULL, NULL, ippr_netbios_out, NULL, NULL },
#endif
#ifdef  IPF_IPSEC_PROXY
    { NULL, "ipsec", (char)IPPROTO_UDP, 0, 0, NULL,
      ippr_ipsec_init, ippr_ipsec_fini, ippr_ipsec_new, ippr_ipsec_del,
      ippr_ipsec_inout, ippr_ipsec_inout, ippr_ipsec_match, NULL },
#endif
#ifdef  IPF_PPTP_PROXY
    { NULL, "pptp", (char)IPPROTO_TCP, 0, 0, NULL,
      ippr_pptp_init, ippr_pptp_fini, ippr_pptp_new, ippr_pptp_del,
      ippr_pptp_inout, ippr_pptp_inout, NULL, NULL },
#endif
#ifdef  IPF_H323_PROXY
    { NULL, "h323", (char)IPPROTO_TCP, 0, 0, NULL, ippr_h323_init, ippr_h323_fini,
      ippr_h323_new, ippr_h323_del, ippr_h323_in, NULL, NULL },
    { NULL, "h245", (char)IPPROTO_TCP, 0, 0, NULL, NULL, NULL,
      ippr_h245_new, NULL, NULL, ippr_h245_out, NULL },
#endif
#ifdef  IPF_RPCB_PROXY
# if 0
    { NULL, "rpcbt", (char)IPPROTO_TCP, 0, 0, NULL,
      ippr_rpcb_init, ippr_rpcb_fini, ippr_rpcb_new, ippr_rpcb_del,
      ippr_rpcb_in, ippr_rpcb_out, NULL, NULL },
# endif
    { NULL, "rpcbu", (char)IPPROTO_UDP, 0, 0, NULL,
      ippr_rpcb_init, ippr_rpcb_fini, ippr_rpcb_new, ippr_rpcb_del,
      ippr_rpcb_in, ippr_rpcb_out, NULL, NULL },
#endif
    { NULL, "", '\0', 0, 0, NULL, NULL, NULL, NULL, NULL }
};

/*
 * Dynamically add a new kernel proxy.  Ensure that it is unique in the
 * collection compiled in and dynamically added.
 */
int appr_add(ap, ifs)
aproxy_t *ap;
ipf_stack_t *ifs;
{
    aproxy_t *a;

    for (a = ifs->ifs_ap_proxies; a->apr_p; a++)
        if ((a->apr_p == ap->apr_p) &&
            !strncmp(a->apr_label, ap->apr_label,
                 sizeof(ap->apr_label))) {
            if (ipf_proxy_debug > 1)
                printf("appr_add: %s/%d already present (B)\n",
                       a->apr_label, a->apr_p);
            return -1;
        }

    for (a = ifs->ifs_ap_proxylist; a->apr_p; a = a->apr_next)
        if ((a->apr_p == ap->apr_p) &&
            !strncmp(a->apr_label, ap->apr_label,
                 sizeof(ap->apr_label))) {
            if (ipf_proxy_debug > 1)
                printf("appr_add: %s/%d already present (D)\n",
                       a->apr_label, a->apr_p);
            return -1;
        }
    ap->apr_next = ifs->ifs_ap_proxylist;
    ifs->ifs_ap_proxylist = ap;
    if (ap->apr_init != NULL)
        return (*ap->apr_init)(&ap->apr_private, ifs);

    return 0;
}


/*
 * Check to see if the proxy this control request has come through for
 * exists, and if it does and it has a control function then invoke that
 * control function.
 */
int appr_ctl(ctl, ifs)
ap_ctl_t *ctl;
ipf_stack_t *ifs;
{
    aproxy_t *a;
    int error;

    a = appr_lookup(ctl->apc_p, ctl->apc_label, ifs);
    if (a == NULL) {
        if (ipf_proxy_debug > 1)
            printf("appr_ctl: can't find %s/%d\n",
                ctl->apc_label, ctl->apc_p);
        error = ESRCH;
    } else if (a->apr_ctl == NULL) {
        if (ipf_proxy_debug > 1)
            printf("appr_ctl: no ctl function for %s/%d\n",
                ctl->apc_label, ctl->apc_p);
        error = ENXIO;
    } else {
        error = (*a->apr_ctl)(a, ctl, a->apr_private);
        if ((error != 0) && (ipf_proxy_debug > 1))
            printf("appr_ctl: %s/%d ctl error %d\n",
                a->apr_label, a->apr_p, error);
    }
    return error;
}


/*
 * Delete a proxy that has been added dynamically from those available.
 * If it is in use, return 1 (do not destroy NOW), not in use 0 or -1
 * if it cannot be matched.
 */
int appr_del(ap, ifs)
aproxy_t *ap;
ipf_stack_t *ifs;
{
    aproxy_t *a, **app;

    for (app = &ifs->ifs_ap_proxylist; ((a = *app) != NULL);
         app = &a->apr_next)
        if (a == ap) {
            a->apr_flags |= APR_DELETE;
            *app = a->apr_next;
            if (ap->apr_ref != 0) {
                if (ipf_proxy_debug > 2)
                    printf("appr_del: orphaning %s/%d\n",
                        ap->apr_label, ap->apr_p);
                return 1;
            }
            return 0;
        }
    if (ipf_proxy_debug > 1)
        printf("appr_del: proxy %lx not found\n", (u_long)ap);
    return -1;
}


/*
 * Return 1 if the packet is a good match against a proxy, else 0.
 */
int appr_ok(fin, tcp, nat)
fr_info_t *fin;
tcphdr_t *tcp;
ipnat_t *nat;
{
    aproxy_t *apr = nat->in_apr;
    u_short dport = nat->in_dport;

    if ((apr == NULL) || (apr->apr_flags & APR_DELETE) ||
        (fin->fin_p != apr->apr_p))
        return 0;
    if ((tcp == NULL) && dport)
        return 0;
    return 1;
}


int appr_ioctl(data, cmd, mode, ifs)
caddr_t data;
ioctlcmd_t cmd;
int mode;
ipf_stack_t *ifs;
{
    ap_ctl_t ctl;
    caddr_t ptr;
    int error;

    mode = mode;    /* LINT */

    switch (cmd)
    {
    case SIOCPROXY :
        error = BCOPYIN(data, &ctl, sizeof(ctl));
        if (error != 0)
            return EFAULT;

        ptr = NULL;

        if (ctl.apc_dsize > 0) {
            KMALLOCS(ptr, caddr_t, ctl.apc_dsize);
            if (ptr == NULL)
                error = ENOMEM;
            else {
                error = copyinptr(ctl.apc_data, ptr,
                          ctl.apc_dsize);
                if (error == 0)
                    ctl.apc_data = ptr;
            }
        } else {
            ctl.apc_data = NULL;
            error = 0;
        }

        if (error == 0)
            error = appr_ctl(&ctl, ifs);

        if ((ctl.apc_dsize > 0) && (ptr != NULL) &&
            (ctl.apc_data == ptr)) {
            KFREES(ptr, ctl.apc_dsize);
        }
        break;

    default :
        error = EINVAL;
    }
    return error;
}


/*
 * If a proxy has a match function, call that to do extended packet
 * matching.
 */
int appr_match(fin, nat)
fr_info_t *fin;
nat_t *nat;
{
    aproxy_t *apr;
    ipnat_t *ipn;
    int result;

    ipn = nat->nat_ptr;
    if (ipf_proxy_debug > 8)
        printf("appr_match(%lx,%lx) aps %lx ptr %lx\n",
            (u_long)fin, (u_long)nat, (u_long)nat->nat_aps,
            (u_long)ipn);

    if ((fin->fin_flx & (FI_SHORT|FI_BAD)) != 0) {
        if (ipf_proxy_debug > 0)
            printf("appr_match: flx 0x%x (BAD|SHORT)\n",
                fin->fin_flx);
        return -1;
    }

    apr = ipn->in_apr;
    if ((apr == NULL) || (apr->apr_flags & APR_DELETE)) {
        if (ipf_proxy_debug > 0)
            printf("appr_match:apr %lx apr_flags 0x%x\n",
                (u_long)apr, apr ? apr->apr_flags : 0);
        return -1;
    }

    if (apr->apr_match != NULL) {
        result = (*apr->apr_match)(fin, nat->nat_aps, nat, apr->apr_private);
        if (result != 0) {
            if (ipf_proxy_debug > 4)
                printf("appr_match: result %d\n", result);
            return -1;
        }
    }
    return 0;
}


/*
 * Allocate a new application proxy structure and fill it in with the
 * relevant details.  call the init function once complete, prior to
 * returning.
 */
int appr_new(fin, nat)
fr_info_t *fin;
nat_t *nat;
{
    register ap_session_t *aps;
    aproxy_t *apr;
    ipf_stack_t *ifs = fin->fin_ifs;

    if (ipf_proxy_debug > 8)
        printf("appr_new(%lx,%lx) \n", (u_long)fin, (u_long)nat);

    if ((nat->nat_ptr == NULL) || (nat->nat_aps != NULL)) {
        if (ipf_proxy_debug > 0)
            printf("appr_new: nat_ptr %lx nat_aps %lx\n",
                (u_long)nat->nat_ptr, (u_long)nat->nat_aps);
        return -1;
    }

    apr = nat->nat_ptr->in_apr;

    if ((apr->apr_flags & APR_DELETE) ||
        (fin->fin_p != apr->apr_p)) {
        if (ipf_proxy_debug > 2)
            printf("appr_new: apr_flags 0x%x p %d/%d\n",
                apr->apr_flags, fin->fin_p, apr->apr_p);
        return -1;
    }

    KMALLOC(aps, ap_session_t *);
    if (!aps) {
        if (ipf_proxy_debug > 0)
            printf("appr_new: malloc failed (%lu)\n",
                (u_long)sizeof(ap_session_t));
        return -1;
    }

    bzero((char *)aps, sizeof(*aps));
    aps->aps_p = fin->fin_p;
    aps->aps_data = NULL;
    aps->aps_apr = apr;
    aps->aps_psiz = 0;
    if (apr->apr_new != NULL)
        if ((*apr->apr_new)(fin, aps, nat, apr->apr_private) == -1) {
            if ((aps->aps_data != NULL) && (aps->aps_psiz != 0)) {
                KFREES(aps->aps_data, aps->aps_psiz);
            }
            KFREE(aps);
            if (ipf_proxy_debug > 2)
                printf("appr_new: new(%lx) failed\n",
                    (u_long)apr->apr_new);
            return -1;
        }
    aps->aps_nat = nat;
    aps->aps_next = ifs->ifs_ap_sess_list;
    ifs->ifs_ap_sess_list = aps;
    nat->nat_aps = aps;

    return 0;
}


/*
 * Check to see if a packet should be passed through an active proxy routine
 * if one has been setup for it.  We don't need to check the checksum here if
 * IPFILTER_CKSUM is defined because if it is, a failed check causes FI_BAD
 * to be set.
 */
int appr_check(fin, nat)
fr_info_t *fin;
nat_t *nat;
{
#if SOLARIS && defined(_KERNEL) && (SOLARIS2 >= 6) && defined(ICK_VALID)
    mb_t *m;
    int dosum = 1;
#endif
    tcphdr_t *tcp = NULL;
    udphdr_t *udp = NULL;
    void *tcpudp = NULL;
    u_short *csump;
    ap_session_t *aps;
    aproxy_t *apr;
    ip_t *ip;
    short rv;
    int err;
#if !defined(_KERNEL) || defined(MENTAT) || defined(__sgi)
    u_32_t s1, s2, sd;
#endif
    ipf_stack_t *ifs = fin->fin_ifs;

#if SOLARIS && defined(_KERNEL) && (SOLARIS2 >= 6)
    net_handle_t net_data_p;
    if (fin->fin_v == 4)
        net_data_p = ifs->ifs_ipf_ipv4;
    else
        net_data_p = ifs->ifs_ipf_ipv6;
#endif

    if (fin->fin_flx & FI_BAD) {
        if (ipf_proxy_debug > 0)
            printf("appr_check: flx 0x%x (BAD)\n", fin->fin_flx);
        return -1;
    }

#ifndef IPFILTER_CKSUM
    if ((fin->fin_out == 0) && (fr_checkl4sum(fin) == -1)) {
        if (ipf_proxy_debug > 0)
            printf("appr_check: l4 checksum failure %d\n",
                fin->fin_p);
        if (fin->fin_p == IPPROTO_TCP)
            ifs->ifs_frstats[fin->fin_out].fr_tcpbad++;
        return -1;
    }
#endif

    aps = nat->nat_aps;
    if ((aps != NULL) && (aps->aps_p == fin->fin_p)) {
        /*
         * If there is data in this packet to be proxied then try and
         * get it all into the one buffer, else drop it.
         */
#if defined(MENTAT) || defined(HAVE_M_PULLDOWN)
        if ((fin->fin_dlen > 0) && !(fin->fin_flx & FI_COALESCE))
            if (fr_coalesce(fin) == -1) {
                if (ipf_proxy_debug > 0)
                    printf("appr_check: fr_coalesce failed %x\n", fin->fin_flx);
                return -1;
            }
#endif
        ip = fin->fin_ip;

        switch (fin->fin_p)
        {
        case IPPROTO_TCP :
            tcp = (tcphdr_t *)fin->fin_dp;

#if SOLARIS && defined(_KERNEL) && (SOLARIS2 >= 6) && defined(ICK_VALID)
            m = fin->fin_qfm;
            if (dohwcksum && (m->b_ick_flag == ICK_VALID))
                dosum = 0;
#endif
            /*
             * Don't bother the proxy with these...or in fact,
             * should we free up proxy stuff when seen?
             */
            if ((fin->fin_tcpf & TH_RST) != 0)
                break;
            /*FALLTHROUGH*/
        case IPPROTO_UDP :
            udp = (udphdr_t *)fin->fin_dp;
            break;
        default :
            break;
        }

        apr = aps->aps_apr;
        err = 0;
        if (fin->fin_out != 0) {
            if (apr->apr_outpkt != NULL)
                err = (*apr->apr_outpkt)(fin, aps, nat, apr->apr_private);
        } else {
            if (apr->apr_inpkt != NULL)
                err = (*apr->apr_inpkt)(fin, aps, nat, apr->apr_private);
        }

        rv = APR_EXIT(err);
        if (((ipf_proxy_debug > 0) && (rv != 0)) ||
            (ipf_proxy_debug > 8))
            printf("appr_check: out %d err %x rv %d\n",
                fin->fin_out, err, rv);
        if (rv == 1)
            return -1;

        if (rv == 2) {
            appr_free(apr);
            nat->nat_aps = NULL;
            return -1;
        }

        /*
         * If err != 0 then the data size of the packet has changed
         * so we need to recalculate the header checksums for the
         * packet.
         * inbound packets always need to be adjusted.
         */
#if !defined(_KERNEL) || defined(MENTAT) || defined(__sgi)
        if (err != 0) {
            short adjlen = err & 0xffff;

            s1 = LONG_SUM(ip->ip_len - adjlen);
            s2 = LONG_SUM(ip->ip_len);
            CALC_SUMD(s1, s2, sd);
            sd = (sd & 0xffff) + (sd >> 16);
            if (!fin->fin_out ||
                !NET_IS_HCK_L3_FULL(net_data_p, fin->fin_m))
                fix_outcksum(&ip->ip_sum, sd);
        }
#endif

        /*
         * For TCP packets, we may need to adjust the sequence and
         * acknowledgement numbers to reflect changes in size of the
         * data stream.
         *
         * For both TCP and UDP, recalculate the layer 4 checksum in
         * software checksum case, as we can't tell if data has been
         * changed or not.
         */
        if (tcp != NULL) {
            tcpudp = tcp;
            csump = &tcp->th_sum;
            (void) appr_fixseqack(fin, ip, aps, APR_INC(err));
        } else if (udp != NULL) {
            tcpudp = udp;
            csump = &udp->uh_sum;
        }

        if (tcpudp) {
#if SOLARIS && defined(_KERNEL) && (SOLARIS2 >= 6) && defined(MENTAT)
            if (!fin->fin_out) {
                /*
                 * We are incapable of adjusting partial hcksum
                 * result for inbound packets here, as the
                 * partial hcksum calculation range might not
                 * cover the whole payload, and the payload data
                 * might be changed by proxy.
                 */
                DB_CKSUMFLAGS(fin->fin_m) &= ~HCK_PARTIALCKSUM;

                /* Inbound packets always need recalculation. */
                *csump = fr_cksum(fin->fin_qfm, ip,
                          fin->fin_p, tcpudp);
            } else if (NET_IS_HCK_L4_PART(net_data_p, fin->fin_m)) {
                if (err != 0) {
                    DB_CKSUMEND(fin->fin_m) += (short)err;
                    fix_incksum(csump, sd);
                }
            } else if (!NET_IS_HCK_L4_FULL(net_data_p, fin->fin_m))
                *csump = fr_cksum(fin->fin_qfm, ip,
                          fin->fin_p, tcpudp);
#else
            *csump = fr_cksum(fin->fin_m, ip, fin->fin_p, tcpudp);
#endif
        }
        aps->aps_bytes += fin->fin_plen;
        aps->aps_pkts++;
        return 1;
    }
    return 0;
}


/*
 * Search for an proxy by the protocol it is being used with and its name.
 */
aproxy_t *appr_lookup(pr, name, ifs)
u_int pr;
char *name;
ipf_stack_t *ifs;
{
    aproxy_t *ap;

    if (ipf_proxy_debug > 8)
        printf("appr_lookup(%d,%s)\n", pr, name);

    for (ap = ifs->ifs_ap_proxies; ap->apr_p; ap++)
        if ((ap->apr_p == pr) &&
            !strncmp(name, ap->apr_label, sizeof(ap->apr_label))) {
            ap->apr_ref++;
            return ap;
        }

    for (ap = ifs->ifs_ap_proxylist; ap; ap = ap->apr_next)
        if ((ap->apr_p == pr) &&
            !strncmp(name, ap->apr_label, sizeof(ap->apr_label))) {
            ap->apr_ref++;
            return ap;
        }
    if (ipf_proxy_debug > 2)
        printf("appr_lookup: failed for %d/%s\n", pr, name);
    return NULL;
}


void appr_free(ap)
aproxy_t *ap;
{
    ap->apr_ref--;
}


void aps_free(aps, ifs)
ap_session_t *aps;
ipf_stack_t *ifs;
{
    ap_session_t *a, **ap;
    aproxy_t *apr;

    if (!aps)
        return;

    for (ap = &ifs->ifs_ap_sess_list; ((a = *ap) != NULL); ap = &a->aps_next)
        if (a == aps) {
            *ap = a->aps_next;
            break;
        }

    apr = aps->aps_apr;
    if ((apr != NULL) && (apr->apr_del != NULL))
        (*apr->apr_del)(aps, apr->apr_private, ifs);

    if ((aps->aps_data != NULL) && (aps->aps_psiz != 0))
        KFREES(aps->aps_data, aps->aps_psiz);
    KFREE(aps);
}


/*
 * returns 2 if ack or seq number in TCP header is changed, returns 0 otherwise
 */
static int appr_fixseqack(fin, ip, aps, inc)
fr_info_t *fin;
ip_t *ip;
ap_session_t *aps;
int inc;
{
    int sel, ch = 0, out, nlen;
    u_32_t seq1, seq2;
    tcphdr_t *tcp;
    short inc2;

    tcp = (tcphdr_t *)fin->fin_dp;
    out = fin->fin_out;
    /*
     * ip_len has already been adjusted by 'inc'.
     */
    nlen = ip->ip_len;
    nlen -= (IP_HL(ip) << 2) + (TCP_OFF(tcp) << 2);

    inc2 = inc;
    inc = (int)inc2;

    if (out != 0) {
        seq1 = (u_32_t)ntohl(tcp->th_seq);
        sel = aps->aps_sel[out];

        /* switch to other set ? */
        if ((aps->aps_seqmin[!sel] > aps->aps_seqmin[sel]) &&
            (seq1 > aps->aps_seqmin[!sel])) {
            if (ipf_proxy_debug > 7)
                printf("proxy out switch set seq %d -> %d %x > %x\n",
                    sel, !sel, seq1,
                    aps->aps_seqmin[!sel]);
            sel = aps->aps_sel[out] = !sel;
        }

        if (aps->aps_seqoff[sel]) {
            seq2 = aps->aps_seqmin[sel] - aps->aps_seqoff[sel];
            if (seq1 > seq2) {
                seq2 = aps->aps_seqoff[sel];
                seq1 += seq2;
                tcp->th_seq = htonl(seq1);
                ch = 1;
            }
        }

        if (inc && (seq1 > aps->aps_seqmin[!sel])) {
            aps->aps_seqmin[sel] = seq1 + nlen - 1;
            aps->aps_seqoff[sel] = aps->aps_seqoff[sel] + inc;
            if (ipf_proxy_debug > 7)
                printf("proxy seq set %d at %x to %d + %d\n",
                    sel, aps->aps_seqmin[sel],
                    aps->aps_seqoff[sel], inc);
        }

        /***/

        seq1 = ntohl(tcp->th_ack);
        sel = aps->aps_sel[1 - out];

        /* switch to other set ? */
        if ((aps->aps_ackmin[!sel] > aps->aps_ackmin[sel]) &&
            (seq1 > aps->aps_ackmin[!sel])) {
            if (ipf_proxy_debug > 7)
                printf("proxy out switch set ack %d -> %d %x > %x\n",
                    sel, !sel, seq1,
                    aps->aps_ackmin[!sel]);
            sel = aps->aps_sel[1 - out] = !sel;
        }

        if (aps->aps_ackoff[sel] && (seq1 > aps->aps_ackmin[sel])) {
            seq2 = aps->aps_ackoff[sel];
            tcp->th_ack = htonl(seq1 - seq2);
            ch = 1;
        }
    } else {
        seq1 = ntohl(tcp->th_seq);
        sel = aps->aps_sel[out];

        /* switch to other set ? */
        if ((aps->aps_ackmin[!sel] > aps->aps_ackmin[sel]) &&
            (seq1 > aps->aps_ackmin[!sel])) {
            if (ipf_proxy_debug > 7)
                printf("proxy in switch set ack %d -> %d %x > %x\n",
                    sel, !sel, seq1, aps->aps_ackmin[!sel]);
            sel = aps->aps_sel[out] = !sel;
        }

        if (aps->aps_ackoff[sel]) {
            seq2 = aps->aps_ackmin[sel] - aps->aps_ackoff[sel];
            if (seq1 > seq2) {
                seq2 = aps->aps_ackoff[sel];
                seq1 += seq2;
                tcp->th_seq = htonl(seq1);
                ch = 1;
            }
        }

        if (inc && (seq1 > aps->aps_ackmin[!sel])) {
            aps->aps_ackmin[!sel] = seq1 + nlen - 1;
            aps->aps_ackoff[!sel] = aps->aps_ackoff[sel] + inc;

            if (ipf_proxy_debug > 7)
                printf("proxy ack set %d at %x to %d + %d\n",
                    !sel, aps->aps_seqmin[!sel],
                    aps->aps_seqoff[sel], inc);
        }

        /***/

        seq1 = ntohl(tcp->th_ack);
        sel = aps->aps_sel[1 - out];

        /* switch to other set ? */
        if ((aps->aps_seqmin[!sel] > aps->aps_seqmin[sel]) &&
            (seq1 > aps->aps_seqmin[!sel])) {
            if (ipf_proxy_debug > 7)
                printf("proxy in switch set seq %d -> %d %x > %x\n",
                    sel, !sel, seq1, aps->aps_seqmin[!sel]);
            sel = aps->aps_sel[1 - out] = !sel;
        }

        if (aps->aps_seqoff[sel] != 0) {
            if (ipf_proxy_debug > 7)
                printf("sel %d seqoff %d seq1 %x seqmin %x\n",
                    sel, aps->aps_seqoff[sel], seq1,
                    aps->aps_seqmin[sel]);
            if (seq1 > aps->aps_seqmin[sel]) {
                seq2 = aps->aps_seqoff[sel];
                tcp->th_ack = htonl(seq1 - seq2);
                ch = 1;
            }
        }
    }

    if (ipf_proxy_debug > 8)
        printf("appr_fixseqack: seq %x ack %x\n",
            ntohl(tcp->th_seq), ntohl(tcp->th_ack));
    return ch ? 2 : 0;
}


/*
 * Initialise hook for kernel application proxies.
 * Call the initialise routine for all the compiled in kernel proxies.
 */
int appr_init(ifs)
ipf_stack_t *ifs;
{
    aproxy_t *ap;
    int err =  0;

    /* Since the refcnt is used we make a copy of lcl_ap_proxies */
    KMALLOCS(ifs->ifs_ap_proxies, aproxy_t *, sizeof (lcl_ap_proxies));
    bcopy(lcl_ap_proxies, ifs->ifs_ap_proxies, sizeof (lcl_ap_proxies));

    for (ap = ifs->ifs_ap_proxies; ap->apr_p; ap++) {
        if (ap->apr_init != NULL) {
            err = (*ap->apr_init)(&ap->apr_private, ifs);
            if (err != 0)
                break;
        }
    }
    return 0;
}


/*
 * Unload hook for kernel application proxies.
 * Call the finialise routine for all the compiled in kernel proxies.
 */
void appr_unload(ifs)
ipf_stack_t *ifs;
{
    aproxy_t *ap;
    if(ifs->ifs_ap_proxies == NULL)
        return;

    for (ap = ifs->ifs_ap_proxies; ap->apr_p; ap++)
        if (ap->apr_fini != NULL)
            (*ap->apr_fini)(&ap->apr_private, ifs);
    for (ap = ifs->ifs_ap_proxylist; ap; ap = ap->apr_next)
        if (ap->apr_fini != NULL)
            (*ap->apr_fini)(&ap->apr_private, ifs);

    KFREES(ifs->ifs_ap_proxies, sizeof (lcl_ap_proxies));
    ifs->ifs_ap_proxies = NULL;
}