/*      $OpenBSD: pf_norm.c,v 1.113 2008/05/07 07:07:29 markus Exp $ */

/*
 * Copyright (c) 2010 The DragonFly Project.  All rights reserved.
 *
 * Copyright 2001 Niels Provos <provos@citi.umich.edu>
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 */

#include "opt_inet.h"
#include "opt_inet6.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/filio.h>
#include <sys/fcntl.h>
#include <sys/malloc.h>
#include <sys/socket.h>
#include <sys/kernel.h>
#include <sys/time.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/if_types.h>
#include <net/bpf.h>
#include <net/route.h>
#include <net/pf/if_pflog.h>

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_seq.h>
#include <netinet/udp.h>
#include <netinet/ip_icmp.h>

#ifdef INET6
#include <netinet/ip6.h>
#endif /* INET6 */

#include <net/pf/pfvar.h>

#define PFFRAG_SEENLAST 0x0001          /* Seen the last fragment for this */
#define PFFRAG_NOBUFFER 0x0002          /* Non-buffering fragment cache */
#define PFFRAG_DROP     0x0004          /* Drop all fragments */
#define BUFFER_FRAGMENTS(fr)    (!((fr)->fr_flags & PFFRAG_NOBUFFER))


TAILQ_HEAD(pf_fragqueue, pf_fragment)   *pf_fragqueue;
TAILQ_HEAD(pf_cachequeue, pf_fragment)  *pf_cachequeue;

static __inline int      pf_frag_compare(struct pf_fragment *,
                            struct pf_fragment *);
RB_HEAD(pf_frag_tree, pf_fragment)      *pf_frag_tree,
                                        *pf_cache_tree;
RB_PROTOTYPE(pf_frag_tree, pf_fragment, fr_entry, pf_frag_compare);
RB_GENERATE(pf_frag_tree, pf_fragment, fr_entry, pf_frag_compare);

/* Private prototypes */
void                     pf_ip2key(struct pf_fragment *, struct ip *);
void                     pf_remove_fragment(struct pf_fragment *);
void                     pf_flush_fragments(void);
void                     pf_free_fragment(struct pf_fragment *);
struct pf_fragment      *pf_find_fragment(struct ip *, struct pf_frag_tree *);
struct mbuf             *pf_reassemble(struct mbuf **, struct pf_fragment **,
                            struct pf_frent *, int);
struct mbuf             *pf_fragcache(struct mbuf **, struct ip*,
                            struct pf_fragment **, int, int, int *);
int                      pf_normalize_tcpopt(struct pf_rule *, struct mbuf *,
                            struct tcphdr *, int, sa_family_t);

#define DPFPRINTF(x) do {                               \
        if (pf_status.debug >= PF_DEBUG_MISC) {         \
                kprintf("%s: ", __func__);              \
                kprintf x ;                             \
        }                                               \
} while(0)

static MALLOC_DEFINE(M_PFFRAGPL, "pffrag", "pf fragment pool list");
static MALLOC_DEFINE(M_PFCACHEPL, "pffrcache", "pf fragment cache pool list");
static MALLOC_DEFINE(M_PFFRENTPL, "pffrent", "pf frent pool list");
static MALLOC_DEFINE(M_PFCENTPL, "pffrcent", "pf fragment cent pool list");
static MALLOC_DEFINE(M_PFSTATESCRUBPL, "pfstatescrub", "pf state scrub pool list");

/* Globals */
struct malloc_type       *pf_frent_pl, *pf_frag_pl, *pf_cache_pl, *pf_cent_pl;
struct malloc_type       *pf_state_scrub_pl;
int                      pf_nfrents, pf_ncache;

void
pf_normalize_init(void)
{
        int n;

        /* XXX
        pool_sethiwat(&pf_frag_pl, PFFRAG_FRAG_HIWAT);
        pool_sethardlimit(&pf_frent_pl, PFFRAG_FRENT_HIWAT, NULL, 0);
        pool_sethardlimit(&pf_cache_pl, PFFRAG_FRCACHE_HIWAT, NULL, 0);
        pool_sethardlimit(&pf_cent_pl, PFFRAG_FRCENT_HIWAT, NULL, 0);
        */

        /*
         * pcpu queues and trees
         */
        pf_fragqueue = kmalloc(sizeof(*pf_fragqueue) * ncpus,
                                M_PF, M_WAITOK | M_ZERO);
        pf_cachequeue = kmalloc(sizeof(*pf_cachequeue) * ncpus,
                                M_PF, M_WAITOK | M_ZERO);
        pf_frag_tree = kmalloc(sizeof(*pf_frag_tree) * ncpus,
                                M_PF, M_WAITOK | M_ZERO);
        pf_cache_tree = kmalloc(sizeof(*pf_cache_tree) * ncpus,
                                M_PF, M_WAITOK | M_ZERO);

        for (n = 0; n < ncpus; ++n) {
                TAILQ_INIT(&pf_fragqueue[n]);
                TAILQ_INIT(&pf_cachequeue[n]);
                RB_INIT(&pf_frag_tree[n]);
                RB_INIT(&pf_cache_tree[n]);
        }
}

void
pf_normalize_unload(void)
{
        kfree(pf_fragqueue, M_PF);
        kfree(pf_cachequeue, M_PF);
        kfree(pf_frag_tree, M_PF);
        kfree(pf_cache_tree, M_PF);
}

static __inline int
pf_frag_compare(struct pf_fragment *a, struct pf_fragment *b)
{
        int     diff;

        if ((diff = a->fr_id - b->fr_id))
                return (diff);
        else if ((diff = a->fr_p - b->fr_p))
                return (diff);
        else if (a->fr_src.s_addr < b->fr_src.s_addr)
                return (-1);
        else if (a->fr_src.s_addr > b->fr_src.s_addr)
                return (1);
        else if (a->fr_dst.s_addr < b->fr_dst.s_addr)
                return (-1);
        else if (a->fr_dst.s_addr > b->fr_dst.s_addr)
                return (1);
        return (0);
}

void
pf_purge_expired_fragments(void)
{
        struct pf_fragment *frag;
        u_int32_t expire;
        int cpu = mycpu->gd_cpuid;

        expire = time_second - pf_default_rule.timeout[PFTM_FRAG];

        while ((frag = TAILQ_LAST(&pf_fragqueue[cpu], pf_fragqueue)) != NULL) {
                KASSERT((BUFFER_FRAGMENTS(frag)),
                        ("BUFFER_FRAGMENTS(frag) == 0: %s", __func__));
                if (frag->fr_timeout > expire)
                        break;

                DPFPRINTF(("expiring %d(%p)\n", frag->fr_id, frag));
                pf_free_fragment(frag);
        }

        while ((frag = TAILQ_LAST(&pf_cachequeue[cpu], pf_cachequeue)) != NULL) {
                KASSERT((!BUFFER_FRAGMENTS(frag)),
                        ("BUFFER_FRAGMENTS(frag) != 0: %s", __func__));
                if (frag->fr_timeout > expire)
                        break;

                DPFPRINTF(("expiring %d(%p)\n", frag->fr_id, frag));
                pf_free_fragment(frag);
                KASSERT((TAILQ_EMPTY(&pf_cachequeue[cpu]) ||
                    TAILQ_LAST(&pf_cachequeue[cpu], pf_cachequeue) != frag),
                    ("!(TAILQ_EMPTY() || TAILQ_LAST() == farg): %s",
                    __func__));
        }
}

/*
 * Try to flush old fragments to make space for new ones
 */

void
pf_flush_fragments(void)
{
        struct pf_fragment *frag;
        int goal;
        int cpu = mycpu->gd_cpuid;

        goal = pf_nfrents * 9 / 10;
        DPFPRINTF(("trying to free > %d frents\n",
            pf_nfrents - goal));
        while (goal < pf_nfrents) {
                frag = TAILQ_LAST(&pf_fragqueue[cpu], pf_fragqueue);
                if (frag == NULL)
                        break;
                pf_free_fragment(frag);
        }


        goal = pf_ncache * 9 / 10;
        DPFPRINTF(("trying to free > %d cache entries\n",
            pf_ncache - goal));
        while (goal < pf_ncache) {
                frag = TAILQ_LAST(&pf_cachequeue[cpu], pf_cachequeue);
                if (frag == NULL)
                        break;
                pf_free_fragment(frag);
        }
}

/* Frees the fragments and all associated entries */

void
pf_free_fragment(struct pf_fragment *frag)
{
        struct pf_frent         *frent;
        struct pf_frcache       *frcache;

        /* Free all fragments */
        if (BUFFER_FRAGMENTS(frag)) {
                for (frent = LIST_FIRST(&frag->fr_queue); frent;
                    frent = LIST_FIRST(&frag->fr_queue)) {
                        LIST_REMOVE(frent, fr_next);

                        m_freem(frent->fr_m);
                        kfree(frent, M_PFFRENTPL);
                        pf_nfrents--;
                }
        } else {
                for (frcache = LIST_FIRST(&frag->fr_cache); frcache;
                    frcache = LIST_FIRST(&frag->fr_cache)) {
                        LIST_REMOVE(frcache, fr_next);

                        KASSERT((LIST_EMPTY(&frag->fr_cache) ||
                            LIST_FIRST(&frag->fr_cache)->fr_off >
                            frcache->fr_end),
                            ("! (LIST_EMPTY() || LIST_FIRST()->fr_off >"
                             " frcache->fr_end): %s", __func__));

                        kfree(frcache, M_PFCENTPL);
                        pf_ncache--;
                }
        }

        pf_remove_fragment(frag);
}

void
pf_ip2key(struct pf_fragment *key, struct ip *ip)
{
        key->fr_p = ip->ip_p;
        key->fr_id = ip->ip_id;
        key->fr_src.s_addr = ip->ip_src.s_addr;
        key->fr_dst.s_addr = ip->ip_dst.s_addr;
}

struct pf_fragment *
pf_find_fragment(struct ip *ip, struct pf_frag_tree *tree)
{
        struct pf_fragment       key;
        struct pf_fragment      *frag;
        int cpu = mycpu->gd_cpuid;

        pf_ip2key(&key, ip);

        frag = RB_FIND(pf_frag_tree, tree, &key);
        if (frag != NULL) {
                /* XXX Are we sure we want to update the timeout? */
                frag->fr_timeout = time_second;
                if (BUFFER_FRAGMENTS(frag)) {
                        TAILQ_REMOVE(&pf_fragqueue[cpu], frag, frag_next);
                        TAILQ_INSERT_HEAD(&pf_fragqueue[cpu], frag, frag_next);
                } else {
                        TAILQ_REMOVE(&pf_cachequeue[cpu], frag, frag_next);
                        TAILQ_INSERT_HEAD(&pf_cachequeue[cpu], frag, frag_next);
                }
        }

        return (frag);
}

/* Removes a fragment from the fragment queue and frees the fragment */

void
pf_remove_fragment(struct pf_fragment *frag)
{
        int cpu = mycpu->gd_cpuid;

        if (BUFFER_FRAGMENTS(frag)) {
                RB_REMOVE(pf_frag_tree, &pf_frag_tree[cpu], frag);
                TAILQ_REMOVE(&pf_fragqueue[cpu], frag, frag_next);
                kfree(frag, M_PFFRAGPL);
        } else {
                RB_REMOVE(pf_frag_tree, &pf_cache_tree[cpu], frag);
                TAILQ_REMOVE(&pf_cachequeue[cpu], frag, frag_next);
                kfree(frag, M_PFCACHEPL);
        }
}

#define FR_IP_OFF(fr)   ((ntohs((fr)->fr_ip->ip_off) & IP_OFFMASK) << 3)

struct mbuf *
pf_reassemble(struct mbuf **m0, struct pf_fragment **frag,
    struct pf_frent *frent, int mff)
{
        struct mbuf     *m = *m0, *m2;
        struct pf_frent *frea, *next;
        struct pf_frent *frep = NULL;
        struct ip       *ip = frent->fr_ip;
        int             hlen = ip->ip_hl << 2;
        u_int16_t       off = (ntohs(ip->ip_off) & IP_OFFMASK) << 3;
        u_int16_t       ip_len = ntohs(ip->ip_len) - hlen;
        u_int16_t       max = ip_len + off;
        int             cpu = mycpu->gd_cpuid;

        KASSERT((*frag == NULL || BUFFER_FRAGMENTS(*frag)),
            ("! (*frag == NULL || BUFFER_FRAGMENTS(*frag)): %s", __func__));

        /* Strip off ip header */
        m->m_data += hlen;
        m->m_len -= hlen;

        /* Create a new reassembly queue for this packet */
        if (*frag == NULL) {
                *frag = kmalloc(sizeof(struct pf_fragment),
                                M_PFFRAGPL, M_NOWAIT);
                if (*frag == NULL) {
                        pf_flush_fragments();
                        *frag = kmalloc(sizeof(struct pf_fragment),
                                        M_PFFRAGPL, M_NOWAIT);
                        if (*frag == NULL)
                                goto drop_fragment;
                }

                (*frag)->fr_flags = 0;
                (*frag)->fr_max = 0;
                (*frag)->fr_src = frent->fr_ip->ip_src;
                (*frag)->fr_dst = frent->fr_ip->ip_dst;
                (*frag)->fr_p = frent->fr_ip->ip_p;
                (*frag)->fr_id = frent->fr_ip->ip_id;
                (*frag)->fr_timeout = time_second;
                LIST_INIT(&(*frag)->fr_queue);

                RB_INSERT(pf_frag_tree, &pf_frag_tree[cpu], *frag);
                TAILQ_INSERT_HEAD(&pf_fragqueue[cpu], *frag, frag_next);

                /* We do not have a previous fragment */
                frep = NULL;
                goto insert;
        }

        /*
         * Find a fragment after the current one:
         *  - off contains the real shifted offset.
         */
        LIST_FOREACH(frea, &(*frag)->fr_queue, fr_next) {
                if (FR_IP_OFF(frea) > off)
                        break;
                frep = frea;
        }

        KASSERT((frep != NULL || frea != NULL),
            ("!(frep != NULL || frea != NULL): %s", __func__));

        /*
         * Merge with previous fragment by cutting the start of
         * the current packet.
         */
        if (frep != NULL &&
            (FR_IP_OFF(frep) + ntohs(frep->fr_ip->ip_len) -
             frep->fr_ip->ip_hl * 4) > off)
        {
                u_int16_t       precut;

                precut = FR_IP_OFF(frep) + ntohs(frep->fr_ip->ip_len) -
                         frep->fr_ip->ip_hl * 4 - off;
                if (precut >= ip_len)
                        goto drop_fragment;
                m_adj(frent->fr_m, precut);
                DPFPRINTF(("overlap -%d\n", precut));
                /* Enforce 8 byte boundaries */
                ip->ip_off = htons(ntohs(ip->ip_off) + (precut >> 3));
                off = (ntohs(ip->ip_off) & IP_OFFMASK) << 3;
                ip_len -= precut;
                ip->ip_len = htons(ip_len + hlen);
        }

        /*
         * Cut or delete overlapping later fragments.
         */
        for (; frea != NULL && ip_len + off > FR_IP_OFF(frea);
            frea = next)
        {
                u_int16_t       aftercut;

                aftercut = ip_len + off - FR_IP_OFF(frea);
                DPFPRINTF(("adjust overlap %d\n", aftercut));
                if (aftercut < (ntohs(frea->fr_ip->ip_len) -
                                frea->fr_ip->ip_hl * 4))
                {
                        frea->fr_ip->ip_len =
                            htons(ntohs(frea->fr_ip->ip_len) - aftercut +
                                  frea->fr_ip->ip_hl * 4);
                        frea->fr_ip->ip_off =
                            htons(ntohs(frea->fr_ip->ip_off) + (aftercut >> 3));
                        m_adj(frea->fr_m, aftercut);
                        break;
                }

                /* This fragment is completely overlapped, lose it */
                next = LIST_NEXT(frea, fr_next);
                m_freem(frea->fr_m);
                LIST_REMOVE(frea, fr_next);
                kfree(frea, M_PFFRENTPL);
                pf_nfrents--;
        }

 insert:
        /* Update maximum data size */
        if ((*frag)->fr_max < max)
                (*frag)->fr_max = max;
        /* This is the last segment */
        if (!mff)
                (*frag)->fr_flags |= PFFRAG_SEENLAST;

        if (frep == NULL)
                LIST_INSERT_HEAD(&(*frag)->fr_queue, frent, fr_next);
        else
                LIST_INSERT_AFTER(frep, frent, fr_next);

        /* Check if we are completely reassembled */
        if (!((*frag)->fr_flags & PFFRAG_SEENLAST))
                return (NULL);

        /* Check if we have all the data */
        off = 0;
        for (frep = LIST_FIRST(&(*frag)->fr_queue); frep; frep = next) {
                next = LIST_NEXT(frep, fr_next);

                off += ntohs(frep->fr_ip->ip_len) - frep->fr_ip->ip_hl * 4;
                if (off < (*frag)->fr_max &&
                    (next == NULL || FR_IP_OFF(next) != off))
                {
                        DPFPRINTF(("missing fragment at %d, next %d, max %d\n",
                            off, next == NULL ? -1 : FR_IP_OFF(next),
                            (*frag)->fr_max));
                        return (NULL);
                }
        }
        DPFPRINTF(("%d < %d?\n", off, (*frag)->fr_max));
        if (off < (*frag)->fr_max)
                return (NULL);

        /* We have all the data */
        frent = LIST_FIRST(&(*frag)->fr_queue);
        KASSERT((frent != NULL), ("frent == NULL: %s", __func__));
        if ((frent->fr_ip->ip_hl << 2) + off > IP_MAXPACKET) {
                DPFPRINTF(("drop: too big: %d\n", off));
                pf_free_fragment(*frag);
                *frag = NULL;
                return (NULL);
        }
        next = LIST_NEXT(frent, fr_next);

        /* Magic from ip_input */
        ip = frent->fr_ip;
        m = frent->fr_m;
        m2 = m->m_next;
        m->m_next = NULL;
        m_cat(m, m2);
        kfree(frent, M_PFFRENTPL);
        pf_nfrents--;
        for (frent = next; frent != NULL; frent = next) {
                next = LIST_NEXT(frent, fr_next);

                m2 = frent->fr_m;
                kfree(frent, M_PFFRENTPL);
                pf_nfrents--;
                m_cat(m, m2);
        }

        ip->ip_src = (*frag)->fr_src;
        ip->ip_dst = (*frag)->fr_dst;

        /* Remove from fragment queue */
        pf_remove_fragment(*frag);
        *frag = NULL;

        hlen = ip->ip_hl << 2;
        ip->ip_len = htons(off + hlen);
        ip->ip_off &= htons(IP_DF);
        m->m_len += hlen;
        m->m_data -= hlen;

        /* some debugging cruft by sklower, below, will go away soon */
        /* XXX this should be done elsewhere */
        if (m->m_flags & M_PKTHDR) {
                int plen = 0;
                for (m2 = m; m2; m2 = m2->m_next)
                        plen += m2->m_len;
                m->m_pkthdr.len = plen;
        }

#if 0
        kprintf("reassembly complete: len=%u\n", ntohs(ip->ip_len));
        kprintf("ip_src=%08x dst=%08x tos=%u p=%u off=%u len=%u\n",
                ip->ip_src.s_addr, ip->ip_dst.s_addr, ip->ip_tos, ip->ip_p,
                ntohs(ip->ip_off), ntohs(ip->ip_len));
#endif

        DPFPRINTF(("complete: %p(%d)\n", m, ntohs(ip->ip_len)));
        return (m);

 drop_fragment:
        /* Oops - fail safe - drop packet */
        kfree(frent, M_PFFRENTPL);
        pf_nfrents--;
        m_freem(m);
        return (NULL);
}

struct mbuf *
pf_fragcache(struct mbuf **m0, struct ip *h, struct pf_fragment **frag, int mff,
    int drop, int *nomem)
{
        struct mbuf     *m = *m0;
        struct pf_frcache *frp, *fra, *cur = NULL;
        int             ip_len = ntohs(h->ip_len) - (h->ip_hl << 2);
        u_int16_t       off = (ntohs(h->ip_off) & IP_OFFMASK) << 3;
        u_int16_t       max = ip_len + off;
        int             hosed = 0;
        int             cpu = mycpu->gd_cpuid;

        KASSERT((*frag == NULL || !BUFFER_FRAGMENTS(*frag)),
            ("!(*frag == NULL || !BUFFER_FRAGMENTS(*frag)): %s", __func__));

        /* Create a new range queue for this packet */
        if (*frag == NULL) {
                *frag = kmalloc(sizeof(struct pf_fragment), M_PFCACHEPL, M_NOWAIT);
                if (*frag == NULL) {
                        pf_flush_fragments();
                        *frag = kmalloc(sizeof(struct pf_fragment), M_PFCACHEPL, M_NOWAIT);
                        if (*frag == NULL)
                                goto no_mem;
                }

                /* Get an entry for the queue */
                cur = kmalloc(sizeof(struct pf_frcache), M_PFCENTPL, M_NOWAIT);
                if (cur == NULL) {
                        kfree(*frag, M_PFCACHEPL);
                        *frag = NULL;
                        goto no_mem;
                }
                pf_ncache++;

                (*frag)->fr_flags = PFFRAG_NOBUFFER;
                (*frag)->fr_max = 0;
                (*frag)->fr_src = h->ip_src;
                (*frag)->fr_dst = h->ip_dst;
                (*frag)->fr_p = h->ip_p;
                (*frag)->fr_id = h->ip_id;
                (*frag)->fr_timeout = time_second;

                cur->fr_off = off;
                cur->fr_end = max;
                LIST_INIT(&(*frag)->fr_cache);
                LIST_INSERT_HEAD(&(*frag)->fr_cache, cur, fr_next);

                RB_INSERT(pf_frag_tree, &pf_cache_tree[cpu], *frag);
                TAILQ_INSERT_HEAD(&pf_cachequeue[cpu], *frag, frag_next);

                DPFPRINTF(("fragcache[%d]: new %d-%d\n", h->ip_id, off, max));

                goto pass;
        }

        /*
         * Find a fragment after the current one:
         *  - off contains the real shifted offset.
         */
        frp = NULL;
        LIST_FOREACH(fra, &(*frag)->fr_cache, fr_next) {
                if (fra->fr_off > off)
                        break;
                frp = fra;
        }

        KASSERT((frp != NULL || fra != NULL),
            ("!(frp != NULL || fra != NULL): %s", __func__));

        if (frp != NULL) {
                int     precut;

                precut = frp->fr_end - off;
                if (precut >= ip_len) {
                        /* Fragment is entirely a duplicate */
                        DPFPRINTF(("fragcache[%d]: dead (%d-%d) %d-%d\n",
                            h->ip_id, frp->fr_off, frp->fr_end, off, max));
                        goto drop_fragment;
                }
                if (precut == 0) {
                        /* They are adjacent.  Fixup cache entry */
                        DPFPRINTF(("fragcache[%d]: adjacent (%d-%d) %d-%d\n",
                            h->ip_id, frp->fr_off, frp->fr_end, off, max));
                        frp->fr_end = max;
                } else if (precut > 0) {
                        /* The first part of this payload overlaps with a
                         * fragment that has already been passed.
                         * Need to trim off the first part of the payload.
                         * But to do so easily, we need to create another
                         * mbuf to throw the original header into.
                         */

                        DPFPRINTF(("fragcache[%d]: chop %d (%d-%d) %d-%d\n",
                            h->ip_id, precut, frp->fr_off, frp->fr_end, off,
                            max));

                        off += precut;
                        max -= precut;
                        /* Update the previous frag to encompass this one */
                        frp->fr_end = max;

                        if (!drop) {
                                /* XXX Optimization opportunity
                                 * This is a very heavy way to trim the payload.
                                 * we could do it much faster by diddling mbuf
                                 * internals but that would be even less legible
                                 * than this mbuf magic.  For my next trick,
                                 * I'll pull a rabbit out of my laptop.
                                 */
                                *m0 = m_dup(m, M_NOWAIT);
                                /* From KAME Project : We have missed this! */
                                m_adj(*m0, (h->ip_hl << 2) -
                                    (*m0)->m_pkthdr.len);
                                if (*m0 == NULL)
                                        goto no_mem;
                                KASSERT(((*m0)->m_next == NULL),
                                    ("(*m0)->m_next != NULL: %s",
                                    __func__));
                                m_adj(m, precut + (h->ip_hl << 2));
                                m_cat(*m0, m);
                                m = *m0;
                                if (m->m_flags & M_PKTHDR) {
                                        int plen = 0;
                                        struct mbuf *t;
                                        for (t = m; t; t = t->m_next)
                                                plen += t->m_len;
                                        m->m_pkthdr.len = plen;
                                }


                                h = mtod(m, struct ip *);

                                KASSERT(((int)m->m_len ==
                                    ntohs(h->ip_len) - precut),
                                    ("m->m_len != h->ip_len - precut: %s",
                                    __func__));
                                h->ip_off = htons(ntohs(h->ip_off) +
                                                  (precut >> 3));
                                h->ip_len = htons(ntohs(h->ip_len) - precut);
                        } else {
                                hosed++;
                        }
                } else {
                        /* There is a gap between fragments */

                        DPFPRINTF(("fragcache[%d]: gap %d (%d-%d) %d-%d\n",
                            h->ip_id, -precut, frp->fr_off, frp->fr_end, off,
                            max));

                        cur = kmalloc(sizeof(struct pf_frcache), M_PFCENTPL, M_NOWAIT);
                        if (cur == NULL)
                                goto no_mem;
                        pf_ncache++;

                        cur->fr_off = off;
                        cur->fr_end = max;
                        LIST_INSERT_AFTER(frp, cur, fr_next);
                }
        }

        if (fra != NULL) {
                int     aftercut;
                int     merge = 0;

                aftercut = max - fra->fr_off;
                if (aftercut == 0) {
                        /* Adjacent fragments */
                        DPFPRINTF(("fragcache[%d]: adjacent %d-%d (%d-%d)\n",
                            h->ip_id, off, max, fra->fr_off, fra->fr_end));
                        fra->fr_off = off;
                        merge = 1;
                } else if (aftercut > 0) {
                        /* Need to chop off the tail of this fragment */
                        DPFPRINTF(("fragcache[%d]: chop %d %d-%d (%d-%d)\n",
                            h->ip_id, aftercut, off, max, fra->fr_off,
                            fra->fr_end));
                        fra->fr_off = off;
                        max -= aftercut;

                        merge = 1;

                        if (!drop) {
                                m_adj(m, -aftercut);
                                if (m->m_flags & M_PKTHDR) {
                                        int plen = 0;
                                        struct mbuf *t;
                                        for (t = m; t; t = t->m_next)
                                                plen += t->m_len;
                                        m->m_pkthdr.len = plen;
                                }
                                h = mtod(m, struct ip *);
                                KASSERT(((int)m->m_len ==
                                         ntohs(h->ip_len) - aftercut),
                                    ("m->m_len != h->ip_len - aftercut: %s",
                                    __func__));
                                h->ip_len = htons(ntohs(h->ip_len) - aftercut);
                        } else {
                                hosed++;
                        }
                } else if (frp == NULL) {
                        /* There is a gap between fragments */
                        DPFPRINTF(("fragcache[%d]: gap %d %d-%d (%d-%d)\n",
                            h->ip_id, -aftercut, off, max, fra->fr_off,
                            fra->fr_end));

                        cur = kmalloc(sizeof(struct pf_frcache), M_PFCENTPL, M_NOWAIT);
                        if (cur == NULL)
                                goto no_mem;
                        pf_ncache++;

                        cur->fr_off = off;
                        cur->fr_end = max;
                        LIST_INSERT_BEFORE(fra, cur, fr_next);
                }


                /* Need to glue together two separate fragment descriptors */
                if (merge) {
                        if (cur && fra->fr_off <= cur->fr_end) {
                                /* Need to merge in a previous 'cur' */
                                DPFPRINTF(("fragcache[%d]: adjacent(merge "
                                    "%d-%d) %d-%d (%d-%d)\n",
                                    h->ip_id, cur->fr_off, cur->fr_end, off,
                                    max, fra->fr_off, fra->fr_end));
                                fra->fr_off = cur->fr_off;
                                LIST_REMOVE(cur, fr_next);
                                kfree(cur, M_PFCENTPL);
                                pf_ncache--;
                                cur = NULL;

                        } else if (frp && fra->fr_off <= frp->fr_end) {
                                /* Need to merge in a modified 'frp' */
                                KASSERT((cur == NULL), ("cur != NULL: %s",
                                    __func__));
                                DPFPRINTF(("fragcache[%d]: adjacent(merge "
                                    "%d-%d) %d-%d (%d-%d)\n",
                                    h->ip_id, frp->fr_off, frp->fr_end, off,
                                    max, fra->fr_off, fra->fr_end));
                                fra->fr_off = frp->fr_off;
                                LIST_REMOVE(frp, fr_next);
                                kfree(frp, M_PFCENTPL);
                                pf_ncache--;
                                frp = NULL;

                        }
                }
        }

        if (hosed) {
                /*
                 * We must keep tracking the overall fragment even when
                 * we're going to drop it anyway so that we know when to
                 * free the overall descriptor.  Thus we drop the frag late.
                 */
                goto drop_fragment;
        }


 pass:
        /* Update maximum data size */
        if ((*frag)->fr_max < max)
                (*frag)->fr_max = max;

        /* This is the last segment */
        if (!mff)
                (*frag)->fr_flags |= PFFRAG_SEENLAST;

        /* Check if we are completely reassembled */
        if (((*frag)->fr_flags & PFFRAG_SEENLAST) &&
            LIST_FIRST(&(*frag)->fr_cache)->fr_off == 0 &&
            LIST_FIRST(&(*frag)->fr_cache)->fr_end == (*frag)->fr_max) {
                /* Remove from fragment queue */
                DPFPRINTF(("fragcache[%d]: done 0-%d\n", h->ip_id,
                    (*frag)->fr_max));
                pf_free_fragment(*frag);
                *frag = NULL;
        }

        return (m);

 no_mem:
        *nomem = 1;

        /* Still need to pay attention to !IP_MF */
        if (!mff && *frag != NULL)
                (*frag)->fr_flags |= PFFRAG_SEENLAST;

        m_freem(m);
        return (NULL);

 drop_fragment:

        /* Still need to pay attention to !IP_MF */
        if (!mff && *frag != NULL)
                (*frag)->fr_flags |= PFFRAG_SEENLAST;

        if (drop) {
                /* This fragment has been deemed bad.  Don't reass */
                if (((*frag)->fr_flags & PFFRAG_DROP) == 0)
                        DPFPRINTF(("fragcache[%d]: dropping overall fragment\n",
                            h->ip_id));
                (*frag)->fr_flags |= PFFRAG_DROP;
        }

        m_freem(m);
        return (NULL);
}

int
pf_normalize_ip(struct mbuf **m0, int dir, struct pfi_kif *kif, u_short *reason,
    struct pf_pdesc *pd)
{
        struct mbuf     *m = *m0;
        struct pf_rule  *r;
        struct pf_frent *frent;
        struct pf_fragment *frag = NULL;
        struct ip       *h = mtod(m, struct ip *);
        int             mff = (h->ip_off & htons(IP_MF));
        int             hlen = h->ip_hl << 2;
        u_int16_t       fragoff = (ntohs(h->ip_off) & IP_OFFMASK) << 3;
        u_int16_t       max;
        int             ip_len;
        int             tag = -1;
        int             cpu = mycpu->gd_cpuid;

        r = TAILQ_FIRST(pf_main_ruleset.rules[PF_RULESET_SCRUB].active.ptr);
        while (r != NULL) {
                r->evaluations++;
                if (pfi_kif_match(r->kif, kif) == r->ifnot)
                        r = r->skip[PF_SKIP_IFP].ptr;
                else if (r->direction && r->direction != dir)
                        r = r->skip[PF_SKIP_DIR].ptr;
                else if (r->af && r->af != AF_INET)
                        r = r->skip[PF_SKIP_AF].ptr;
                else if (r->proto && r->proto != h->ip_p)
                        r = r->skip[PF_SKIP_PROTO].ptr;
                else if (PF_MISMATCHAW(&r->src.addr,
                    (struct pf_addr *)&h->ip_src.s_addr, AF_INET,
                    r->src.neg, kif))
                        r = r->skip[PF_SKIP_SRC_ADDR].ptr;
                else if (PF_MISMATCHAW(&r->dst.addr,
                    (struct pf_addr *)&h->ip_dst.s_addr, AF_INET,
                    r->dst.neg, NULL))
                        r = r->skip[PF_SKIP_DST_ADDR].ptr;
                else if (r->match_tag && !pf_match_tag(m, r, &tag))
                        r = TAILQ_NEXT(r, entries);
                else
                        break;
        }

        if (r == NULL || r->action == PF_NOSCRUB)
                return (PF_PASS);
        else {
                r->packets[dir == PF_OUT]++;
                r->bytes[dir == PF_OUT] += pd->tot_len;
        }

        /* Check for illegal packets */
        if (hlen < (int)sizeof(struct ip))
                goto drop;

        if (hlen > ntohs(h->ip_len))
                goto drop;

        /* Clear IP_DF if the rule uses the no-df option */
        if ((r->rule_flag & PFRULE_NODF) && (h->ip_off & htons(IP_DF))) {
                u_int16_t ip_off = h->ip_off;   /* network byte order */

                h->ip_off &= ~htons(IP_DF);
                h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_off, h->ip_off, 0);
        }

        /* We will need other tests here */
        if (!fragoff && !mff)
                goto no_fragment;

        /* A fragment; rehash required. */
        m->m_flags &= ~M_HASH;

        /* We're dealing with a fragment now. Don't allow fragments
         * with IP_DF to enter the cache. If the flag was cleared by
         * no-df above, fine. Otherwise drop it.
         */
        if (h->ip_off & htons(IP_DF)) {
                DPFPRINTF(("IP_DF\n"));
                goto bad;
        }

        ip_len = ntohs(h->ip_len) - hlen;

        /* All fragments are 8 byte aligned */
        if (mff && (ip_len & 0x7)) {
                DPFPRINTF(("mff and %d\n", ip_len));
                goto bad;
        }

        /* Respect maximum length */
        if (fragoff + ip_len > IP_MAXPACKET) {
                DPFPRINTF(("max packet %d\n", fragoff + ip_len));
                goto bad;
        }
        max = fragoff + ip_len;

        if ((r->rule_flag & (PFRULE_FRAGCROP|PFRULE_FRAGDROP)) == 0) {
                /* Fully buffer all of the fragments */

                frag = pf_find_fragment(h, &pf_frag_tree[cpu]);

                /* Check if we saw the last fragment already */
                if (frag != NULL && (frag->fr_flags & PFFRAG_SEENLAST) &&
                    max > frag->fr_max)
                        goto bad;

                /* Get an entry for the fragment queue */
                frent = kmalloc(sizeof(struct pf_frent), M_PFFRENTPL, M_NOWAIT);
                if (frent == NULL) {
                        REASON_SET(reason, PFRES_MEMORY);
                        return (PF_DROP);
                }
                pf_nfrents++;
                frent->fr_ip = h;
                frent->fr_m = m;

                /* Might return a completely reassembled mbuf, or NULL */
                DPFPRINTF(("reass frag %d @ %d-%d\n", h->ip_id, fragoff, max));
                *m0 = m = pf_reassemble(m0, &frag, frent, mff);

                if (m == NULL)
                        return (PF_DROP);

                if (frag != NULL && (frag->fr_flags & PFFRAG_DROP))
                        goto drop;

                h = mtod(m, struct ip *);
        } else {
                /* non-buffering fragment cache (drops or masks overlaps) */
                int     nomem = 0;

                if (dir == PF_OUT && m->m_pkthdr.pf.flags & PF_TAG_FRAGCACHE) {
                        /*
                         * Already passed the fragment cache in the
                         * input direction.  If we continued, it would
                         * appear to be a dup and would be dropped.
                         */
                        goto fragment_pass;
                }

                frag = pf_find_fragment(h, &pf_cache_tree[cpu]);

                /* Check if we saw the last fragment already */
                if (frag != NULL && (frag->fr_flags & PFFRAG_SEENLAST) &&
                    max > frag->fr_max) {
                        if (r->rule_flag & PFRULE_FRAGDROP)
                                frag->fr_flags |= PFFRAG_DROP;
                        goto bad;
                }

                *m0 = m = pf_fragcache(m0, h, &frag, mff,
                    (r->rule_flag & PFRULE_FRAGDROP) ? 1 : 0, &nomem);
                if (m == NULL) {
                        if (nomem)
                                goto no_mem;
                        goto drop;
                }

                if (dir == PF_IN)
                        m->m_pkthdr.pf.flags |= PF_TAG_FRAGCACHE;

                if (frag != NULL && (frag->fr_flags & PFFRAG_DROP))
                        goto drop;
                goto fragment_pass;
        }

 no_fragment:
        /* At this point, only IP_DF is allowed in ip_off */
        if (h->ip_off & ~htons(IP_DF)) {
                u_int16_t ip_off = h->ip_off;   /* network byte order */

                h->ip_off &= htons(IP_DF);
                h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_off, h->ip_off, 0);
        }

        /* Enforce a minimum ttl, may cause endless packet loops */
        if (r->min_ttl && h->ip_ttl < r->min_ttl) {
                u_int16_t ip_ttl = h->ip_ttl;

                h->ip_ttl = r->min_ttl;
                h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_ttl, h->ip_ttl, 0);
        }

        /* Enforce tos */
        if (r->rule_flag & PFRULE_SET_TOS) {
                u_int16_t       ov, nv;

                ov = *(u_int16_t *)h;
                h->ip_tos = r->set_tos;
                nv = *(u_int16_t *)h;

                h->ip_sum = pf_cksum_fixup(h->ip_sum, ov, nv, 0);
        }

        if (r->rule_flag & PFRULE_RANDOMID) {
                u_int16_t ip_id = h->ip_id;

                h->ip_id = ip_randomid();
                h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_id, h->ip_id, 0);
        }
        if ((r->rule_flag & (PFRULE_FRAGCROP|PFRULE_FRAGDROP)) == 0)
                pd->flags |= PFDESC_IP_REAS;

        return (PF_PASS);

 fragment_pass:
        /* Enforce a minimum ttl, may cause endless packet loops */
        if (r->min_ttl && h->ip_ttl < r->min_ttl) {
                u_int16_t ip_ttl = h->ip_ttl;

                h->ip_ttl = r->min_ttl;
                h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_ttl, h->ip_ttl, 0);
        }
        /* Enforce tos */
        if (r->rule_flag & PFRULE_SET_TOS) {
                u_int16_t       ov, nv;

                ov = *(u_int16_t *)h;
                h->ip_tos = r->set_tos;
                nv = *(u_int16_t *)h;

                h->ip_sum = pf_cksum_fixup(h->ip_sum, ov, nv, 0);
        }
        if ((r->rule_flag & (PFRULE_FRAGCROP|PFRULE_FRAGDROP)) == 0)
                pd->flags |= PFDESC_IP_REAS;
        return (PF_PASS);

 no_mem:
        REASON_SET(reason, PFRES_MEMORY);
        if (r != NULL && r->log)
                PFLOG_PACKET(kif, h, m, AF_INET, dir, *reason, r, NULL, NULL, pd);
        return (PF_DROP);

 drop:
        REASON_SET(reason, PFRES_NORM);
        if (r != NULL && r->log)
                PFLOG_PACKET(kif, h, m, AF_INET, dir, *reason, r, NULL, NULL, pd);
        return (PF_DROP);

 bad:
        DPFPRINTF(("dropping bad fragment\n"));

        /* Free associated fragments */
        if (frag != NULL)
                pf_free_fragment(frag);

        REASON_SET(reason, PFRES_FRAG);
        if (r != NULL && r->log)
                PFLOG_PACKET(kif, h, m, AF_INET, dir, *reason, r, NULL, NULL, pd);

        return (PF_DROP);
}

#ifdef INET6
int
pf_normalize_ip6(struct mbuf **m0, int dir, struct pfi_kif *kif,
    u_short *reason, struct pf_pdesc *pd)
{
        struct mbuf             *m = *m0;
        struct pf_rule          *r;
        struct ip6_hdr          *h = mtod(m, struct ip6_hdr *);
        int                      off;
        struct ip6_ext           ext;
        struct ip6_opt           opt;
        struct ip6_opt_jumbo     jumbo;
        struct ip6_frag          frag;
        u_int32_t                jumbolen = 0, plen;
        u_int16_t                fragoff = 0;
        int                      optend;
        int                      ooff;
        u_int8_t                 proto;
        int                      terminal;

        r = TAILQ_FIRST(pf_main_ruleset.rules[PF_RULESET_SCRUB].active.ptr);
        while (r != NULL) {
                r->evaluations++;
                if (pfi_kif_match(r->kif, kif) == r->ifnot)
                        r = r->skip[PF_SKIP_IFP].ptr;
                else if (r->direction && r->direction != dir)
                        r = r->skip[PF_SKIP_DIR].ptr;
                else if (r->af && r->af != AF_INET6)
                        r = r->skip[PF_SKIP_AF].ptr;
#if 0 /* header chain! */
                else if (r->proto && r->proto != h->ip6_nxt)
                        r = r->skip[PF_SKIP_PROTO].ptr;
#endif
                else if (PF_MISMATCHAW(&r->src.addr,
                    (struct pf_addr *)&h->ip6_src, AF_INET6,
                    r->src.neg, kif))
                        r = r->skip[PF_SKIP_SRC_ADDR].ptr;
                else if (PF_MISMATCHAW(&r->dst.addr,
                    (struct pf_addr *)&h->ip6_dst, AF_INET6,
                    r->dst.neg, NULL))
                        r = r->skip[PF_SKIP_DST_ADDR].ptr;
                else
                        break;
        }

        if (r == NULL || r->action == PF_NOSCRUB)
                return (PF_PASS);
        else {
                r->packets[dir == PF_OUT]++;
                r->bytes[dir == PF_OUT] += pd->tot_len;
        }

        /* Check for illegal packets */
        if (sizeof(struct ip6_hdr) + IPV6_MAXPACKET < m->m_pkthdr.len)
                goto drop;

        off = sizeof(struct ip6_hdr);
        proto = h->ip6_nxt;
        terminal = 0;
        do {
                switch (proto) {
                case IPPROTO_FRAGMENT:
                        goto fragment;
                        break;
                case IPPROTO_AH:
                case IPPROTO_ROUTING:
                case IPPROTO_DSTOPTS:
                        if (!pf_pull_hdr(m, off, &ext, sizeof(ext), NULL,
                            NULL, AF_INET6))
                                goto shortpkt;
                        if (proto == IPPROTO_AH)
                                off += (ext.ip6e_len + 2) * 4;
                        else
                                off += (ext.ip6e_len + 1) * 8;
                        proto = ext.ip6e_nxt;
                        break;
                case IPPROTO_HOPOPTS:
                        if (!pf_pull_hdr(m, off, &ext, sizeof(ext), NULL,
                            NULL, AF_INET6))
                                goto shortpkt;
                        optend = off + (ext.ip6e_len + 1) * 8;
                        ooff = off + sizeof(ext);
                        do {
                                if (!pf_pull_hdr(m, ooff, &opt.ip6o_type,
                                    sizeof(opt.ip6o_type), NULL, NULL,
                                    AF_INET6))
                                        goto shortpkt;
                                if (opt.ip6o_type == IP6OPT_PAD1) {
                                        ooff++;
                                        continue;
                                }
                                if (!pf_pull_hdr(m, ooff, &opt, sizeof(opt),
                                    NULL, NULL, AF_INET6))
                                        goto shortpkt;
                                if (ooff + sizeof(opt) + opt.ip6o_len > optend)
                                        goto drop;
                                switch (opt.ip6o_type) {
                                case IP6OPT_JUMBO:
                                        if (h->ip6_plen != 0)
                                                goto drop;
                                        if (!pf_pull_hdr(m, ooff, &jumbo,
                                            sizeof(jumbo), NULL, NULL,
                                            AF_INET6))
                                                goto shortpkt;
                                        memcpy(&jumbolen, jumbo.ip6oj_jumbo_len,
                                            sizeof(jumbolen));
                                        jumbolen = ntohl(jumbolen);
                                        if (jumbolen <= IPV6_MAXPACKET)
                                                goto drop;
                                        if (sizeof(struct ip6_hdr) + jumbolen !=
                                            m->m_pkthdr.len)
                                                goto drop;
                                        break;
                                default:
                                        break;
                                }
                                ooff += sizeof(opt) + opt.ip6o_len;
                        } while (ooff < optend);

                        off = optend;
                        proto = ext.ip6e_nxt;
                        break;
                default:
                        terminal = 1;
                        break;
                }
        } while (!terminal);

        /* jumbo payload option must be present, or plen > 0 */
        if (ntohs(h->ip6_plen) == 0)
                plen = jumbolen;
        else
                plen = ntohs(h->ip6_plen);
        if (plen == 0)
                goto drop;
        if (sizeof(struct ip6_hdr) + plen > m->m_pkthdr.len)
                goto shortpkt;

        /* Enforce a minimum ttl, may cause endless packet loops */
        if (r->min_ttl && h->ip6_hlim < r->min_ttl)
                h->ip6_hlim = r->min_ttl;

        return (PF_PASS);

 fragment:
        if (ntohs(h->ip6_plen) == 0 || jumbolen)
                goto drop;
        plen = ntohs(h->ip6_plen);

        if (!pf_pull_hdr(m, off, &frag, sizeof(frag), NULL, NULL, AF_INET6))
                goto shortpkt;
        fragoff = ntohs(frag.ip6f_offlg & IP6F_OFF_MASK);
        if (fragoff + (plen - off - sizeof(frag)) > IPV6_MAXPACKET)
                goto badfrag;

        /* do something about it */
        /* remember to set pd->flags |= PFDESC_IP_REAS */
        return (PF_PASS);

 shortpkt:
        REASON_SET(reason, PFRES_SHORT);
        if (r != NULL && r->log)
                PFLOG_PACKET(kif, h, m, AF_INET6, dir, *reason, r, NULL, NULL, pd);
        return (PF_DROP);

 drop:
        REASON_SET(reason, PFRES_NORM);
        if (r != NULL && r->log)
                PFLOG_PACKET(kif, h, m, AF_INET6, dir, *reason, r, NULL, NULL, pd);
        return (PF_DROP);

 badfrag:
        REASON_SET(reason, PFRES_FRAG);
        if (r != NULL && r->log)
                PFLOG_PACKET(kif, h, m, AF_INET6, dir, *reason, r, NULL, NULL, pd);
        return (PF_DROP);
}
#endif /* INET6 */

int
pf_normalize_tcp(int dir, struct pfi_kif *kif, struct mbuf *m, int ipoff,
    int off, void *h, struct pf_pdesc *pd)
{
        struct pf_rule  *r, *rm = NULL;
        struct tcphdr   *th = pd->hdr.tcp;
        int              rewrite = 0;
        u_short          reason;
        u_int8_t         flags;
        sa_family_t      af = pd->af;

        r = TAILQ_FIRST(pf_main_ruleset.rules[PF_RULESET_SCRUB].active.ptr);
        while (r != NULL) {
                r->evaluations++;
                if (pfi_kif_match(r->kif, kif) == r->ifnot)
                        r = r->skip[PF_SKIP_IFP].ptr;
                else if (r->direction && r->direction != dir)
                        r = r->skip[PF_SKIP_DIR].ptr;
                else if (r->af && r->af != af)
                        r = r->skip[PF_SKIP_AF].ptr;
                else if (r->proto && r->proto != pd->proto)
                        r = r->skip[PF_SKIP_PROTO].ptr;
                else if (PF_MISMATCHAW(&r->src.addr, pd->src, af,
                    r->src.neg, kif))
                        r = r->skip[PF_SKIP_SRC_ADDR].ptr;
                else if (r->src.port_op && !pf_match_port(r->src.port_op,
                            r->src.port[0], r->src.port[1], th->th_sport))
                        r = r->skip[PF_SKIP_SRC_PORT].ptr;
                else if (PF_MISMATCHAW(&r->dst.addr, pd->dst, af,
                    r->dst.neg, NULL))
                        r = r->skip[PF_SKIP_DST_ADDR].ptr;
                else if (r->dst.port_op && !pf_match_port(r->dst.port_op,
                            r->dst.port[0], r->dst.port[1], th->th_dport))
                        r = r->skip[PF_SKIP_DST_PORT].ptr;
                else if (r->os_fingerprint != PF_OSFP_ANY && !pf_osfp_match(
                            pf_osfp_fingerprint(pd, m, off, th),
                            r->os_fingerprint))
                        r = TAILQ_NEXT(r, entries);
                else {
                        rm = r;
                        break;
                }
        }

        if (rm == NULL || rm->action == PF_NOSCRUB)
                return (PF_PASS);
        else {
                r->packets[dir == PF_OUT]++;
                r->bytes[dir == PF_OUT] += pd->tot_len;
        }

        if (rm->rule_flag & PFRULE_REASSEMBLE_TCP)
                pd->flags |= PFDESC_TCP_NORM;

        flags = th->th_flags;
        if (flags & TH_SYN) {
                /* Illegal packet */
                if (flags & TH_RST)
                        goto tcp_drop;

                if (flags & TH_FIN)
                        flags &= ~TH_FIN;
        } else {
                /* Illegal packet */
                if (!(flags & (TH_ACK|TH_RST)))
                        goto tcp_drop;
        }

        if (!(flags & TH_ACK)) {
                /* These flags are only valid if ACK is set */
                if ((flags & TH_FIN) || (flags & TH_PUSH) || (flags & TH_URG))
                        goto tcp_drop;
        }

        /* Check for illegal header length */
        if (th->th_off < (sizeof(struct tcphdr) >> 2))
                goto tcp_drop;

        /* If flags changed, or reserved data set, then adjust */
        if (flags != th->th_flags || th->th_x2 != 0) {
                u_int16_t       ov, nv;

                ov = *(u_int16_t *)(&th->th_ack + 1);
                th->th_flags = flags;
                th->th_x2 = 0;
                nv = *(u_int16_t *)(&th->th_ack + 1);

                th->th_sum = pf_cksum_fixup(th->th_sum, ov, nv, 0);
                rewrite = 1;
        }

        /* Remove urgent pointer, if TH_URG is not set */
        if (!(flags & TH_URG) && th->th_urp) {
                th->th_sum = pf_cksum_fixup(th->th_sum, th->th_urp, 0, 0);
                th->th_urp = 0;
                rewrite = 1;
        }

        /* Process options */
        if (r->max_mss && pf_normalize_tcpopt(r, m, th, off, pd->af))
                rewrite = 1;

        /* copy back packet headers if we sanitized */
        if (rewrite)
                m_copyback(m, off, sizeof(*th), th);

        return (PF_PASS);

 tcp_drop:
        REASON_SET(&reason, PFRES_NORM);
        if (rm != NULL && r->log)
                PFLOG_PACKET(kif, h, m, AF_INET, dir, reason, r, NULL, NULL, pd);
        return (PF_DROP);
}

int
pf_normalize_tcp_init(struct mbuf *m, int off, struct pf_pdesc *pd,
    struct tcphdr *th, struct pf_state_peer *src, struct pf_state_peer *dst)
{
        u_int32_t tsval, tsecr;
        u_int8_t hdr[60];
        u_int8_t *opt;

        KASSERT((src->scrub == NULL),
            ("pf_normalize_tcp_init: src->scrub != NULL"));

        src->scrub = kmalloc(sizeof(struct pf_state_scrub), M_PFSTATESCRUBPL,
            M_NOWAIT | M_ZERO);
        if (src->scrub == NULL)
                return (1);

        switch (pd->af) {
#ifdef INET
        case AF_INET: {
                struct ip *h = mtod(m, struct ip *);
                src->scrub->pfss_ttl = h->ip_ttl;
                break;
        }
#endif /* INET */
#ifdef INET6
        case AF_INET6: {
                struct ip6_hdr *h = mtod(m, struct ip6_hdr *);
                src->scrub->pfss_ttl = h->ip6_hlim;
                break;
        }
#endif /* INET6 */
        }


        /*
         * All normalizations below are only begun if we see the start of
         * the connections.  They must all set an enabled bit in pfss_flags
         */
        if ((th->th_flags & TH_SYN) == 0)
                return (0);


        if (th->th_off > (sizeof(struct tcphdr) >> 2) && src->scrub &&
            pf_pull_hdr(m, off, hdr, th->th_off << 2, NULL, NULL, pd->af)) {
                /* Diddle with TCP options */
                int hlen;
                opt = hdr + sizeof(struct tcphdr);
                hlen = (th->th_off << 2) - sizeof(struct tcphdr);
                while (hlen >= TCPOLEN_TIMESTAMP) {
                        switch (*opt) {
                        case TCPOPT_EOL:        /* FALLTHROUGH */
                        case TCPOPT_NOP:
                                opt++;
                                hlen--;
                                break;
                        case TCPOPT_TIMESTAMP:
                                if (opt[1] >= TCPOLEN_TIMESTAMP) {
                                        src->scrub->pfss_flags |=
                                            PFSS_TIMESTAMP;
                                        src->scrub->pfss_ts_mod = karc4random();

                                        /* note PFSS_PAWS not set yet */
                                        memcpy(&tsval, &opt[2],
                                            sizeof(u_int32_t));
                                        memcpy(&tsecr, &opt[6],
                                            sizeof(u_int32_t));
                                        src->scrub->pfss_tsval0 = ntohl(tsval);
                                        src->scrub->pfss_tsval = ntohl(tsval);
                                        src->scrub->pfss_tsecr = ntohl(tsecr);
                                        getmicrouptime(&src->scrub->pfss_last);
                                }
                                /* FALLTHROUGH */
                        default:
                                hlen -= MAX(opt[1], 2);
                                opt += MAX(opt[1], 2);
                                break;
                        }
                }
        }

        return (0);
}

void
pf_normalize_tcp_cleanup(struct pf_state *state)
{
        if (state->src.scrub)
                kfree(state->src.scrub, M_PFSTATESCRUBPL);
        if (state->dst.scrub)
                kfree(state->dst.scrub, M_PFSTATESCRUBPL);

        /* Someday... flush the TCP segment reassembly descriptors. */
}

int
pf_normalize_tcp_stateful(struct mbuf *m, int off, struct pf_pdesc *pd,
    u_short *reason, struct tcphdr *th, struct pf_state *state,
    struct pf_state_peer *src, struct pf_state_peer *dst, int *writeback)
{
        struct timeval uptime;
        u_int32_t tsval, tsecr;
        u_int tsval_from_last;
        u_int8_t hdr[60];
        u_int8_t *opt;
        int copyback = 0;
        int got_ts = 0;

        KASSERT((src->scrub || dst->scrub),
            ("pf_normalize_tcp_statefull: src->scrub && dst->scrub!"));

        tsval = 0;      /* avoid gcc complaint */
        tsecr = 0;      /* avoid gcc complaint */

        /*
         * Enforce the minimum TTL seen for this connection.  Negate a common
         * technique to evade an intrusion detection system and confuse
         * firewall state code.
         */
        switch (pd->af) {
#ifdef INET
        case AF_INET: {
                if (src->scrub) {
                        struct ip *h = mtod(m, struct ip *);
                        if (h->ip_ttl > src->scrub->pfss_ttl)
                                src->scrub->pfss_ttl = h->ip_ttl;
                        h->ip_ttl = src->scrub->pfss_ttl;
                }
                break;
        }
#endif /* INET */
#ifdef INET6
        case AF_INET6: {
                if (src->scrub) {
                        struct ip6_hdr *h = mtod(m, struct ip6_hdr *);
                        if (h->ip6_hlim > src->scrub->pfss_ttl)
                                src->scrub->pfss_ttl = h->ip6_hlim;
                        h->ip6_hlim = src->scrub->pfss_ttl;
                }
                break;
        }
#endif /* INET6 */
        }

        if (th->th_off > (sizeof(struct tcphdr) >> 2) &&
            ((src->scrub && (src->scrub->pfss_flags & PFSS_TIMESTAMP)) ||
            (dst->scrub && (dst->scrub->pfss_flags & PFSS_TIMESTAMP))) &&
            pf_pull_hdr(m, off, hdr, th->th_off << 2, NULL, NULL, pd->af)) {
                /* Diddle with TCP options */
                int hlen;
                opt = hdr + sizeof(struct tcphdr);
                hlen = (th->th_off << 2) - sizeof(struct tcphdr);
                while (hlen >= TCPOLEN_TIMESTAMP) {
                        switch (*opt) {
                        case TCPOPT_EOL:        /* FALLTHROUGH */
                        case TCPOPT_NOP:
                                opt++;
                                hlen--;
                                break;
                        case TCPOPT_TIMESTAMP:
                                /* Modulate the timestamps.  Can be used for
                                 * NAT detection, OS uptime determination or
                                 * reboot detection.
                                 */

                                if (got_ts) {
                                        /* Huh?  Multiple timestamps!? */
                                        if (pf_status.debug >= PF_DEBUG_MISC) {
                                                DPFPRINTF(("multiple TS??"));
                                                pf_print_state(state);
                                                kprintf("\n");
                                        }
                                        REASON_SET(reason, PFRES_TS);
                                        return (PF_DROP);
                                }
                                if (opt[1] >= TCPOLEN_TIMESTAMP) {
                                        memcpy(&tsval, &opt[2],
                                            sizeof(u_int32_t));
                                        if (tsval && src->scrub &&
                                            (src->scrub->pfss_flags &
                                            PFSS_TIMESTAMP)) {
                                                tsval = ntohl(tsval);
                                                pf_change_a(&opt[2],
                                                    &th->th_sum,
                                                    htonl(tsval +
                                                    src->scrub->pfss_ts_mod),
                                                    0);
                                                copyback = 1;
                                        }

                                        /* Modulate TS reply iff valid (!0) */
                                        memcpy(&tsecr, &opt[6],
                                            sizeof(u_int32_t));
                                        if (tsecr && dst->scrub &&
                                            (dst->scrub->pfss_flags &
                                            PFSS_TIMESTAMP)) {
                                                tsecr = ntohl(tsecr)
                                                    - dst->scrub->pfss_ts_mod;
                                                pf_change_a(&opt[6],
                                                    &th->th_sum, htonl(tsecr),
                                                    0);
                                                copyback = 1;
                                        }
                                        got_ts = 1;
                                }
                                /* FALLTHROUGH */
                        default:
                                hlen -= MAX(opt[1], 2);
                                opt += MAX(opt[1], 2);
                                break;
                        }
                }
                if (copyback) {
                        /* Copyback the options, caller copys back header */
                        *writeback = 1;
                        m_copyback(m, off + sizeof(struct tcphdr),
                            (th->th_off << 2) - sizeof(struct tcphdr),
                            hdr + sizeof(struct tcphdr));
                }
        }


        /*
         * Must invalidate PAWS checks on connections idle for too long.
         * The fastest allowed timestamp clock is 1ms.  That turns out to
         * be about 24 days before it wraps.  XXX Right now our lowerbound
         * TS echo check only works for the first 12 days of a connection
         * when the TS has exhausted half its 32bit space
         */
#define TS_MAX_IDLE     (24*24*60*60)
#define TS_MAX_CONN     (12*24*60*60)   /* XXX remove when better tsecr check */

        getmicrouptime(&uptime);
        if (src->scrub && (src->scrub->pfss_flags & PFSS_PAWS) &&
            (uptime.tv_sec - src->scrub->pfss_last.tv_sec > TS_MAX_IDLE ||
            time_second - state->creation > TS_MAX_CONN))  {
                if (pf_status.debug >= PF_DEBUG_MISC) {
                        DPFPRINTF(("src idled out of PAWS\n"));
                        pf_print_state(state);
                        kprintf("\n");
                }
                src->scrub->pfss_flags = (src->scrub->pfss_flags & ~PFSS_PAWS)
                    | PFSS_PAWS_IDLED;
        }
        if (dst->scrub && (dst->scrub->pfss_flags & PFSS_PAWS) &&
            uptime.tv_sec - dst->scrub->pfss_last.tv_sec > TS_MAX_IDLE) {
                if (pf_status.debug >= PF_DEBUG_MISC) {
                        DPFPRINTF(("dst idled out of PAWS\n"));
                        pf_print_state(state);
                        kprintf("\n");
                }
                dst->scrub->pfss_flags = (dst->scrub->pfss_flags & ~PFSS_PAWS)
                    | PFSS_PAWS_IDLED;
        }

        if (got_ts && src->scrub && dst->scrub &&
            (src->scrub->pfss_flags & PFSS_PAWS) &&
            (dst->scrub->pfss_flags & PFSS_PAWS)) {
                /* Validate that the timestamps are "in-window".
                 * RFC1323 describes TCP Timestamp options that allow
                 * measurement of RTT (round trip time) and PAWS
                 * (protection against wrapped sequence numbers).  PAWS
                 * gives us a set of rules for rejecting packets on
                 * long fat pipes (packets that were somehow delayed
                 * in transit longer than the time it took to send the
                 * full TCP sequence space of 4Gb).  We can use these
                 * rules and infer a few others that will let us treat
                 * the 32bit timestamp and the 32bit echoed timestamp
                 * as sequence numbers to prevent a blind attacker from
                 * inserting packets into a connection.
                 *
                 * RFC1323 tells us:
                 *  - The timestamp on this packet must be greater than
                 *    or equal to the last value echoed by the other
                 *    endpoint.  The RFC says those will be discarded
                 *    since it is a dup that has already been acked.
                 *    This gives us a lowerbound on the timestamp.
                 *        timestamp >= other last echoed timestamp
                 *  - The timestamp will be less than or equal to
                 *    the last timestamp plus the time between the
                 *    last packet and now.  The RFC defines the max
                 *    clock rate as 1ms.  We will allow clocks to be
                 *    up to 10% fast and will allow a total difference
                 *    or 30 seconds due to a route change.  And this
                 *    gives us an upperbound on the timestamp.
                 *        timestamp <= last timestamp + max ticks
                 *    We have to be careful here.  Windows will send an
                 *    initial timestamp of zero and then initialize it
                 *    to a random value after the 3whs; presumably to
                 *    avoid a DoS by having to call an expensive RNG
                 *    during a SYN flood.  Proof MS has at least one
                 *    good security geek.
                 *
                 *  - The TCP timestamp option must also echo the other
                 *    endpoints timestamp.  The timestamp echoed is the
                 *    one carried on the earliest unacknowledged segment
                 *    on the left edge of the sequence window.  The RFC
                 *    states that the host will reject any echoed
                 *    timestamps that were larger than any ever sent.
                 *    This gives us an upperbound on the TS echo.
                 *        tescr <= largest_tsval
                 *  - The lowerbound on the TS echo is a little more
                 *    tricky to determine.  The other endpoint's echoed
                 *    values will not decrease.  But there may be
                 *    network conditions that re-order packets and
                 *    cause our view of them to decrease.  For now the
                 *    only lowerbound we can safely determine is that
                 *    the TS echo will never be less than the original
                 *    TS.  XXX There is probably a better lowerbound.
                 *    Remove TS_MAX_CONN with better lowerbound check.
                 *        tescr >= other original TS
                 *
                 * It is also important to note that the fastest
                 * timestamp clock of 1ms will wrap its 32bit space in
                 * 24 days.  So we just disable TS checking after 24
                 * days of idle time.  We actually must use a 12d
                 * connection limit until we can come up with a better
                 * lowerbound to the TS echo check.
                 */
                struct timeval delta_ts;
                int ts_fudge;


                /*
                 * PFTM_TS_DIFF is how many seconds of leeway to allow
                 * a host's timestamp.  This can happen if the previous
                 * packet got delayed in transit for much longer than
                 * this packet.
                 */
                if ((ts_fudge = state->rule.ptr->timeout[PFTM_TS_DIFF]) == 0)
                        ts_fudge = pf_default_rule.timeout[PFTM_TS_DIFF];


                /* Calculate max ticks since the last timestamp */
#define TS_MAXFREQ      1100            /* RFC max TS freq of 1Khz + 10% skew */
#define TS_MICROSECS    1000000         /* microseconds per second */
#ifndef timersub
#define timersub(tvp, uvp, vvp)                                         \
        do {                                                            \
                (vvp)->tv_sec = (tvp)->tv_sec - (uvp)->tv_sec;          \
                (vvp)->tv_usec = (tvp)->tv_usec - (uvp)->tv_usec;       \
                if ((vvp)->tv_usec < 0) {                               \
                        (vvp)->tv_sec--;                                \
                        (vvp)->tv_usec += 1000000;                      \
                }                                                       \
        } while (0)
#endif

                timersub(&uptime, &src->scrub->pfss_last, &delta_ts);
                tsval_from_last = (delta_ts.tv_sec + ts_fudge) * TS_MAXFREQ;
                tsval_from_last += delta_ts.tv_usec / (TS_MICROSECS/TS_MAXFREQ);


                if ((src->state >= TCPS_ESTABLISHED &&
                    dst->state >= TCPS_ESTABLISHED) &&
                    (SEQ_LT(tsval, dst->scrub->pfss_tsecr) ||
                    SEQ_GT(tsval, src->scrub->pfss_tsval + tsval_from_last) ||
                    (tsecr && (SEQ_GT(tsecr, dst->scrub->pfss_tsval) ||
                    SEQ_LT(tsecr, dst->scrub->pfss_tsval0))))) {
                        /* Bad RFC1323 implementation or an insertion attack.
                         *
                         * - Solaris 2.6 and 2.7 are known to send another ACK
                         *   after the FIN,FIN|ACK,ACK closing that carries
                         *   an old timestamp.
                         */

                        DPFPRINTF(("Timestamp failed %c%c%c%c\n",
                            SEQ_LT(tsval, dst->scrub->pfss_tsecr) ? '0' : ' ',
                            SEQ_GT(tsval, src->scrub->pfss_tsval +
                            tsval_from_last) ? '1' : ' ',
                            SEQ_GT(tsecr, dst->scrub->pfss_tsval) ? '2' : ' ',
                            SEQ_LT(tsecr, dst->scrub->pfss_tsval0)? '3' : ' '));
                        DPFPRINTF((" tsval: %u  tsecr: %u  +ticks: %u  "
                            "idle: %lus %lums\n",
                            tsval, tsecr, tsval_from_last, delta_ts.tv_sec,
                            delta_ts.tv_usec / 1000));
                        DPFPRINTF((" src->tsval: %u  tsecr: %u\n",
                            src->scrub->pfss_tsval, src->scrub->pfss_tsecr));
                        DPFPRINTF((" dst->tsval: %u  tsecr: %u  tsval0: %u"
                            "\n", dst->scrub->pfss_tsval,
                            dst->scrub->pfss_tsecr, dst->scrub->pfss_tsval0));
                        if (pf_status.debug >= PF_DEBUG_MISC) {
                                pf_print_state(state);
                                pf_print_flags(th->th_flags);
                                kprintf("\n");
                        }
                        REASON_SET(reason, PFRES_TS);
                        return (PF_DROP);
                }

                /* XXX I'd really like to require tsecr but it's optional */

        } else if (!got_ts && (th->th_flags & TH_RST) == 0 &&
            ((src->state == TCPS_ESTABLISHED && dst->state == TCPS_ESTABLISHED)
            || pd->p_len > 0 || (th->th_flags & TH_SYN)) &&
            src->scrub && dst->scrub &&
            (src->scrub->pfss_flags & PFSS_PAWS) &&
            (dst->scrub->pfss_flags & PFSS_PAWS)) {
                /* Didn't send a timestamp.  Timestamps aren't really useful
                 * when:
                 *  - connection opening or closing (often not even sent).
                 *    but we must not let an attacker to put a FIN on a
                 *    data packet to sneak it through our ESTABLISHED check.
                 *  - on a TCP reset.  RFC suggests not even looking at TS.
                 *  - on an empty ACK.  The TS will not be echoed so it will
                 *    probably not help keep the RTT calculation in sync and
                 *    there isn't as much danger when the sequence numbers
                 *    got wrapped.  So some stacks don't include TS on empty
                 *    ACKs :-(
                 *
                 * To minimize the disruption to mostly RFC1323 conformant
                 * stacks, we will only require timestamps on data packets.
                 *
                 * And what do ya know, we cannot require timestamps on data
                 * packets.  There appear to be devices that do legitimate
                 * TCP connection hijacking.  There are HTTP devices that allow
                 * a 3whs (with timestamps) and then buffer the HTTP request.
                 * If the intermediate device has the HTTP response cache, it
                 * will spoof the response but not bother timestamping its
                 * packets.  So we can look for the presence of a timestamp in
                 * the first data packet and if there, require it in all future
                 * packets.
                 */

                if (pd->p_len > 0 && (src->scrub->pfss_flags & PFSS_DATA_TS)) {
                        /*
                         * Hey!  Someone tried to sneak a packet in.  Or the
                         * stack changed its RFC1323 behavior?!?!
                         */
                        if (pf_status.debug >= PF_DEBUG_MISC) {
                                DPFPRINTF(("Did not receive expected RFC1323 "
                                    "timestamp\n"));
                                pf_print_state(state);
                                pf_print_flags(th->th_flags);
                                kprintf("\n");
                        }
                        REASON_SET(reason, PFRES_TS);
                        return (PF_DROP);
                }
        }


        /*
         * We will note if a host sends his data packets with or without
         * timestamps.  And require all data packets to contain a timestamp
         * if the first does.  PAWS implicitly requires that all data packets be
         * timestamped.  But I think there are middle-man devices that hijack
         * TCP streams immediately after the 3whs and don't timestamp their
         * packets (seen in a WWW accelerator or cache).
         */
        if (pd->p_len > 0 && src->scrub && (src->scrub->pfss_flags &
            (PFSS_TIMESTAMP|PFSS_DATA_TS|PFSS_DATA_NOTS)) == PFSS_TIMESTAMP) {
                if (got_ts)
                        src->scrub->pfss_flags |= PFSS_DATA_TS;
                else {
                        src->scrub->pfss_flags |= PFSS_DATA_NOTS;
                        if (pf_status.debug >= PF_DEBUG_MISC && dst->scrub &&
                            (dst->scrub->pfss_flags & PFSS_TIMESTAMP)) {
                                /* Don't warn if other host rejected RFC1323 */
                                DPFPRINTF(("Broken RFC1323 stack did not "
                                    "timestamp data packet. Disabled PAWS "
                                    "security.\n"));
                                pf_print_state(state);
                                pf_print_flags(th->th_flags);
                                kprintf("\n");
                        }
                }
        }


        /*
         * Update PAWS values
         */
        if (got_ts && src->scrub && PFSS_TIMESTAMP == (src->scrub->pfss_flags &
            (PFSS_PAWS_IDLED|PFSS_TIMESTAMP))) {
                getmicrouptime(&src->scrub->pfss_last);
                if (SEQ_GEQ(tsval, src->scrub->pfss_tsval) ||
                    (src->scrub->pfss_flags & PFSS_PAWS) == 0)
                        src->scrub->pfss_tsval = tsval;

                if (tsecr) {
                        if (SEQ_GEQ(tsecr, src->scrub->pfss_tsecr) ||
                            (src->scrub->pfss_flags & PFSS_PAWS) == 0)
                                src->scrub->pfss_tsecr = tsecr;

                        if ((src->scrub->pfss_flags & PFSS_PAWS) == 0 &&
                            (SEQ_LT(tsval, src->scrub->pfss_tsval0) ||
                            src->scrub->pfss_tsval0 == 0)) {
                                /* tsval0 MUST be the lowest timestamp */
                                src->scrub->pfss_tsval0 = tsval;
                        }

                        /* Only fully initialized after a TS gets echoed */
                        if ((src->scrub->pfss_flags & PFSS_PAWS) == 0)
                                src->scrub->pfss_flags |= PFSS_PAWS;
                }
        }

        /* I have a dream....  TCP segment reassembly.... */
        return (0);
}

int
pf_normalize_tcpopt(struct pf_rule *r, struct mbuf *m, struct tcphdr *th,
    int off, sa_family_t af)
{
        u_int16_t       *mss;
        int              thoff;
        int              opt, cnt, optlen = 0;
        int              rewrite = 0;
        u_char           opts[TCP_MAXOLEN];
        u_char          *optp = opts;

        thoff = th->th_off << 2;
        cnt = thoff - sizeof(struct tcphdr);

        if (cnt > 0 && !pf_pull_hdr(m, off + sizeof(*th), opts, cnt,
            NULL, NULL, af))
                return (rewrite);

        for (; cnt > 0; cnt -= optlen, optp += optlen) {
                opt = optp[0];
                if (opt == TCPOPT_EOL)
                        break;
                if (opt == TCPOPT_NOP)
                        optlen = 1;
                else {
                        if (cnt < 2)
                                break;
                        optlen = optp[1];
                        if (optlen < 2 || optlen > cnt)
                                break;
                }
                switch (opt) {
                case TCPOPT_MAXSEG:
                        mss = (u_int16_t *)(optp + 2);
                        if ((ntohs(*mss)) > r->max_mss) {
                                th->th_sum = pf_cksum_fixup(th->th_sum,
                                    *mss, htons(r->max_mss), 0);
                                *mss = htons(r->max_mss);
                                rewrite = 1;
                        }
                        break;
                default:
                        break;
                }
        }

        if (rewrite)
                m_copyback(m, off + sizeof(*th), thoff - sizeof(*th), opts);

        return (rewrite);
}