/*      $OpenBSD: pf_norm.c,v 1.236 2025/07/07 02:28:50 jsg Exp $ */

/*
 * Copyright 2001 Niels Provos <provos@citi.umich.edu>
 * Copyright 2009 Henning Brauer <henning@openbsd.org>
 * Copyright 2011-2018 Alexander Bluhm <bluhm@openbsd.org>
 * 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 <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/pool.h>
#include <sys/syslog.h>
#include <sys/mutex.h>

#include <net/if.h>
#include <net/if_var.h>

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

#ifdef INET6
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet/icmp6.h>
#endif /* INET6 */

#include <net/pfvar.h>
#include <net/pfvar_priv.h>

struct pf_frent {
        TAILQ_ENTRY(pf_frent) fr_next;
        struct mbuf     *fe_m;
        u_int16_t        fe_hdrlen;     /* ipv4 header length with ip options
                                           ipv6, extension, fragment header */
        u_int16_t        fe_extoff;     /* last extension header offset or 0 */
        u_int16_t        fe_len;        /* fragment length */
        u_int16_t        fe_off;        /* fragment offset */
        u_int16_t        fe_mff;        /* more fragment flag */
};

RB_HEAD(pf_frag_tree, pf_fragment);
struct pf_frnode {
        struct pf_addr  fn_src;         /* ip source address */
        struct pf_addr  fn_dst;         /* ip destination address */
        sa_family_t     fn_af;          /* address family */
        u_int8_t        fn_proto;       /* protocol for fragments in fn_tree */
        u_int8_t        fn_direction;   /* pf packet direction */
        u_int32_t       fn_fragments;   /* number of entries in fn_tree */
        u_int32_t       fn_gen;         /* fr_gen of newest entry in fn_tree */

        RB_ENTRY(pf_frnode) fn_entry;
        struct pf_frag_tree fn_tree;    /* matching fragments, lookup by id */
};

struct pf_fragment {
        struct pf_frent *fr_firstoff[PF_FRAG_ENTRY_POINTS];
                                        /* pointers to queue element */
        u_int8_t        fr_entries[PF_FRAG_ENTRY_POINTS];
                                        /* count entries between pointers */
        RB_ENTRY(pf_fragment) fr_entry;
        TAILQ_ENTRY(pf_fragment) frag_next;
        TAILQ_HEAD(pf_fragq, pf_frent) fr_queue;
        u_int32_t       fr_id;          /* fragment id for reassemble */
        int32_t         fr_timeout;
        u_int32_t       fr_gen;         /* generation number (per pf_frnode) */
        u_int16_t       fr_maxlen;      /* maximum length of single fragment */
        u_int16_t       fr_holes;       /* number of holes in the queue */
        struct pf_frnode *fr_node;      /* ip src/dst/proto/af for fragments */
};

struct pf_fragment_tag {
        u_int16_t        ft_hdrlen;     /* header length of reassembled pkt */
        u_int16_t        ft_extoff;     /* last extension header offset or 0 */
        u_int16_t        ft_maxlen;     /* maximum fragment payload length */
};

TAILQ_HEAD(pf_fragqueue, pf_fragment)   pf_fragqueue;

static __inline int      pf_frnode_compare(struct pf_frnode *,
                            struct pf_frnode *);
RB_HEAD(pf_frnode_tree, pf_frnode)      pf_frnode_tree;
RB_PROTOTYPE(pf_frnode_tree, pf_frnode, fn_entry, pf_frnode_compare);
RB_GENERATE(pf_frnode_tree, pf_frnode, fn_entry, pf_frnode_compare);

static __inline int      pf_frag_compare(struct pf_fragment *,
                            struct pf_fragment *);
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_flush_fragments(void);
void                     pf_free_fragment(struct pf_fragment *);
struct pf_fragment      *pf_find_fragment(struct pf_frnode *, u_int32_t);
struct pf_frent         *pf_create_fragment(u_short *);
int                      pf_frent_holes(struct pf_frent *);
static inline int        pf_frent_index(struct pf_frent *);
int                      pf_frent_insert(struct pf_fragment *,
                            struct pf_frent *, struct pf_frent *);
void                     pf_frent_remove(struct pf_fragment *,
                            struct pf_frent *);
struct pf_frent         *pf_frent_previous(struct pf_fragment *,
                            struct pf_frent *);
struct pf_fragment      *pf_fillup_fragment(struct pf_frnode *, u_int32_t,
                            struct pf_frent *, u_short *);
struct mbuf             *pf_join_fragment(struct pf_fragment *);
int                      pf_reassemble(struct mbuf **, int, u_short *);
#ifdef INET6
int                      pf_reassemble6(struct mbuf **, struct ip6_frag *,
                            u_int16_t, u_int16_t, int, u_short *);
#endif /* INET6 */

/* Globals */
struct pool              pf_frent_pl, pf_frag_pl, pf_frnode_pl;
struct pool              pf_state_scrub_pl;

struct mutex             pf_frag_mtx;

#define PF_FRAG_LOCK_INIT()     mtx_init(&pf_frag_mtx, IPL_SOFTNET)

void
pf_normalize_init(void)
{
        pool_init(&pf_frent_pl, sizeof(struct pf_frent), 0,
            IPL_SOFTNET, 0, "pffrent", NULL);
        pool_init(&pf_frnode_pl, sizeof(struct pf_frnode), 0,
            IPL_SOFTNET, 0, "pffrnode", NULL);
        pool_init(&pf_frag_pl, sizeof(struct pf_fragment), 0,
            IPL_SOFTNET, 0, "pffrag", NULL);
        pool_init(&pf_state_scrub_pl, sizeof(struct pf_state_scrub), 0,
            IPL_SOFTNET, 0, "pfstscr", NULL);

        pool_sethiwat(&pf_frag_pl, PFFRAG_FRAG_HIWAT);
        pool_sethardlimit(&pf_frent_pl, PFFRAG_FRENT_HIWAT);

        TAILQ_INIT(&pf_fragqueue);

        PF_FRAG_LOCK_INIT();
}

static __inline int
pf_frnode_compare(struct pf_frnode *a, struct pf_frnode *b)
{
        int     diff;

        if ((diff = a->fn_proto - b->fn_proto) != 0)
                return (diff);
        if ((diff = a->fn_af - b->fn_af) != 0)
                return (diff);
        if ((diff = pf_addr_compare(&a->fn_src, &b->fn_src, a->fn_af)) != 0)
                return (diff);
        if ((diff = pf_addr_compare(&a->fn_dst, &b->fn_dst, a->fn_af)) != 0)
                return (diff);

        return (0);
}

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

        if ((diff = a->fr_id - b->fr_id) != 0)
                return (diff);

        return (0);
}

void
pf_purge_expired_fragments(void)
{
        struct pf_fragment      *frag;
        int32_t                  expire;

        PF_ASSERT_UNLOCKED();

        expire = getuptime() - pf_default_rule.timeout[PFTM_FRAG];

        PF_FRAG_LOCK();
        while ((frag = TAILQ_LAST(&pf_fragqueue, pf_fragqueue)) != NULL) {
                if (frag->fr_timeout > expire)
                        break;
                DPFPRINTF(LOG_NOTICE, "expiring %d(%p)", frag->fr_id, frag);
                pf_free_fragment(frag);
        }
        PF_FRAG_UNLOCK();
}

/*
 * Try to flush old fragments to make space for new ones
 */
void
pf_flush_fragments(void)
{
        struct pf_fragment      *frag;
        u_int                    goal;

        goal = pf_status.fragments * 9 / 10;
        DPFPRINTF(LOG_NOTICE, "trying to free > %u frents",
            pf_status.fragments - goal);
        while (goal < pf_status.fragments) {
                if ((frag = TAILQ_LAST(&pf_fragqueue, pf_fragqueue)) == NULL)
                        break;
                pf_free_fragment(frag);
        }
}

/*
 * Remove a fragment from the fragment queue, free its fragment entries,
 * and free the fragment itself.
 */
void
pf_free_fragment(struct pf_fragment *frag)
{
        struct pf_frent         *frent;
        struct pf_frnode        *frnode;

        frnode = frag->fr_node;
        RB_REMOVE(pf_frag_tree, &frnode->fn_tree, frag);
        KASSERT(frnode->fn_fragments >= 1);
        frnode->fn_fragments--;
        if (frnode->fn_fragments == 0) {
                KASSERT(RB_EMPTY(&frnode->fn_tree));
                RB_REMOVE(pf_frnode_tree, &pf_frnode_tree, frnode);
                pool_put(&pf_frnode_pl, frnode);
        }
        TAILQ_REMOVE(&pf_fragqueue, frag, frag_next);

        /* Free all fragment entries */
        while ((frent = TAILQ_FIRST(&frag->fr_queue)) != NULL) {
                TAILQ_REMOVE(&frag->fr_queue, frent, fr_next);
                pf_status.ncounters[NCNT_FRAG_REMOVALS]++;
                m_freem(frent->fe_m);
                pool_put(&pf_frent_pl, frent);
                pf_status.fragments--;
        }
        pool_put(&pf_frag_pl, frag);
}

struct pf_fragment *
pf_find_fragment(struct pf_frnode *key, u_int32_t id)
{
        struct pf_fragment      *frag, idkey;
        struct pf_frnode        *frnode;
        u_int32_t                stale;

        frnode = RB_FIND(pf_frnode_tree, &pf_frnode_tree, key);
        pf_status.ncounters[NCNT_FRAG_SEARCH]++;
        if (frnode == NULL)
                return (NULL);
        KASSERT(frnode->fn_fragments >= 1);
        idkey.fr_id = id;
        frag = RB_FIND(pf_frag_tree, &frnode->fn_tree, &idkey);
        if (frag == NULL)
                return (NULL);
        /*
         * Limit the number of fragments we accept for each (proto,src,dst,af)
         * combination (aka pf_frnode), so we can deal better with a high rate
         * of fragments.  Problem analysis is in RFC 4963.
         * Store the current generation for each pf_frnode in fn_gen and on
         * lookup discard 'stale' fragments (pf_fragment, based on the fr_gen
         * member).  Instead of adding another button interpret the pf fragment
         * timeout in multiples of 200 fragments.  This way the default of 60s
         * means: pf_fragment objects older than 60*200 = 12,000 generations
         * are considered stale.
         */
        stale = pf_default_rule.timeout[PFTM_FRAG] * PF_FRAG_STALE;
        if ((frnode->fn_gen - frag->fr_gen) >= stale) {
                DPFPRINTF(LOG_NOTICE, "stale fragment %d(%p), gen %u, num %u",
                    frag->fr_id, frag, frag->fr_gen, frnode->fn_fragments);
                pf_free_fragment(frag);
                return (NULL);
        }
        TAILQ_REMOVE(&pf_fragqueue, frag, frag_next);
        TAILQ_INSERT_HEAD(&pf_fragqueue, frag, frag_next);

        return (frag);
}

struct pf_frent *
pf_create_fragment(u_short *reason)
{
        struct pf_frent *frent;

        frent = pool_get(&pf_frent_pl, PR_NOWAIT);
        if (frent == NULL) {
                pf_flush_fragments();
                frent = pool_get(&pf_frent_pl, PR_NOWAIT);
                if (frent == NULL) {
                        REASON_SET(reason, PFRES_MEMORY);
                        return (NULL);
                }
        }
        pf_status.fragments++;

        return (frent);
}

/*
 * Calculate the additional holes that were created in the fragment
 * queue by inserting this fragment.  A fragment in the middle
 * creates one more hole by splitting.  For each connected side,
 * it loses one hole.
 * Fragment entry must be in the queue when calling this function.
 */
int
pf_frent_holes(struct pf_frent *frent)
{
        struct pf_frent *prev = TAILQ_PREV(frent, pf_fragq, fr_next);
        struct pf_frent *next = TAILQ_NEXT(frent, fr_next);
        int holes = 1;

        if (prev == NULL) {
                if (frent->fe_off == 0)
                        holes--;
        } else {
                KASSERT(frent->fe_off != 0);
                if (frent->fe_off == prev->fe_off + prev->fe_len)
                        holes--;
        }
        if (next == NULL) {
                if (!frent->fe_mff)
                        holes--;
        } else {
                KASSERT(frent->fe_mff);
                if (next->fe_off == frent->fe_off + frent->fe_len)
                        holes--;
        }
        return holes;
}

static inline int
pf_frent_index(struct pf_frent *frent)
{
        /*
         * We have an array of 16 entry points to the queue.  A full size
         * 65535 octet IP packet can have 8192 fragments.  So the queue
         * traversal length is at most 512 and at most 16 entry points are
         * checked.  We need 128 additional bytes on a 64 bit architecture.
         */
        CTASSERT(((u_int16_t)0xffff &~ 7) / (0x10000 / PF_FRAG_ENTRY_POINTS) ==
            16 - 1);
        CTASSERT(((u_int16_t)0xffff >> 3) / PF_FRAG_ENTRY_POINTS == 512 - 1);

        return frent->fe_off / (0x10000 / PF_FRAG_ENTRY_POINTS);
}

int
pf_frent_insert(struct pf_fragment *frag, struct pf_frent *frent,
    struct pf_frent *prev)
{
        CTASSERT(PF_FRAG_ENTRY_LIMIT <= 0xff);
        int index;

        /*
         * A packet has at most 65536 octets.  With 16 entry points, each one
         * spawns 4096 octets.  We limit these to 64 fragments each, which
         * means on average every fragment must have at least 64 octets.
         */
        index = pf_frent_index(frent);
        if (frag->fr_entries[index] >= PF_FRAG_ENTRY_LIMIT)
                return ENOBUFS;
        frag->fr_entries[index]++;

        if (prev == NULL) {
                TAILQ_INSERT_HEAD(&frag->fr_queue, frent, fr_next);
        } else {
                KASSERT(prev->fe_off + prev->fe_len <= frent->fe_off);
                TAILQ_INSERT_AFTER(&frag->fr_queue, prev, frent, fr_next);
        }
        pf_status.ncounters[NCNT_FRAG_INSERT]++;

        if (frag->fr_firstoff[index] == NULL) {
                KASSERT(prev == NULL || pf_frent_index(prev) < index);
                frag->fr_firstoff[index] = frent;
        } else {
                if (frent->fe_off < frag->fr_firstoff[index]->fe_off) {
                        KASSERT(prev == NULL || pf_frent_index(prev) < index);
                        frag->fr_firstoff[index] = frent;
                } else {
                        KASSERT(prev != NULL);
                        KASSERT(pf_frent_index(prev) == index);
                }
        }

        frag->fr_holes += pf_frent_holes(frent);

        return 0;
}

void
pf_frent_remove(struct pf_fragment *frag, struct pf_frent *frent)
{
#ifdef DIAGNOSTIC
        struct pf_frent *prev = TAILQ_PREV(frent, pf_fragq, fr_next);
#endif
        struct pf_frent *next = TAILQ_NEXT(frent, fr_next);
        int index;

        frag->fr_holes -= pf_frent_holes(frent);

        index = pf_frent_index(frent);
        KASSERT(frag->fr_firstoff[index] != NULL);
        if (frag->fr_firstoff[index]->fe_off == frent->fe_off) {
                if (next == NULL) {
                        frag->fr_firstoff[index] = NULL;
                } else {
                        KASSERT(frent->fe_off + frent->fe_len <= next->fe_off);
                        if (pf_frent_index(next) == index) {
                                frag->fr_firstoff[index] = next;
                        } else {
                                frag->fr_firstoff[index] = NULL;
                        }
                }
        } else {
                KASSERT(frag->fr_firstoff[index]->fe_off < frent->fe_off);
                KASSERT(prev != NULL);
                KASSERT(prev->fe_off + prev->fe_len <= frent->fe_off);
                KASSERT(pf_frent_index(prev) == index);
        }

        TAILQ_REMOVE(&frag->fr_queue, frent, fr_next);
        pf_status.ncounters[NCNT_FRAG_REMOVALS]++;

        KASSERT(frag->fr_entries[index] > 0);
        frag->fr_entries[index]--;
}

struct pf_frent *
pf_frent_previous(struct pf_fragment *frag, struct pf_frent *frent)
{
        struct pf_frent *prev, *next;
        int index;

        /*
         * If there are no fragments after frag, take the final one.  Assume
         * that the global queue is not empty.
         */
        prev = TAILQ_LAST(&frag->fr_queue, pf_fragq);
        KASSERT(prev != NULL);
        if (prev->fe_off <= frent->fe_off)
                return prev;
        /*
         * We want to find a fragment entry that is before frag, but still
         * close to it.  Find the first fragment entry that is in the same
         * entry point or in the first entry point after that.  As we have
         * already checked that there are entries behind frag, this will
         * succeed.
         */
        for (index = pf_frent_index(frent); index < PF_FRAG_ENTRY_POINTS;
            index++) {
                prev = frag->fr_firstoff[index];
                if (prev != NULL)
                        break;
        }
        KASSERT(prev != NULL);
        /*
         * In prev we may have a fragment from the same entry point that is
         * before frent, or one that is just one position behind frent.
         * In the latter case, we go back one step and have the predecessor.
         * There may be none if the new fragment will be the first one.
         */
        if (prev->fe_off > frent->fe_off) {
                prev = TAILQ_PREV(prev, pf_fragq, fr_next);
                if (prev == NULL)
                        return NULL;
                KASSERT(prev->fe_off <= frent->fe_off);
                return prev;
        }
        /*
         * In prev is the first fragment of the entry point.  The offset
         * of frag is behind it.  Find the closest previous fragment.
         */
        for (next = TAILQ_NEXT(prev, fr_next); next != NULL;
            next = TAILQ_NEXT(next, fr_next)) {
                if (next->fe_off > frent->fe_off)
                        break;
                prev = next;
        }
        return prev;
}

struct pf_fragment *
pf_fillup_fragment(struct pf_frnode *key, u_int32_t id,
    struct pf_frent *frent, u_short *reason)
{
        struct pf_frent         *after, *next, *prev;
        struct pf_fragment      *frag;
        struct pf_frnode        *frnode;
        u_int16_t                total;

        /* No empty fragments */
        if (frent->fe_len == 0) {
                DPFPRINTF(LOG_NOTICE, "bad fragment: len 0");
                goto bad_fragment;
        }

        /* All fragments are 8 byte aligned */
        if (frent->fe_mff && (frent->fe_len & 0x7)) {
                DPFPRINTF(LOG_NOTICE, "bad fragment: mff and len %d",
                    frent->fe_len);
                goto bad_fragment;
        }

        /* Respect maximum length, IP_MAXPACKET == IPV6_MAXPACKET */
        if (frent->fe_off + frent->fe_len > IP_MAXPACKET) {
                DPFPRINTF(LOG_NOTICE, "bad fragment: max packet %d",
                    frent->fe_off + frent->fe_len);
                goto bad_fragment;
        }

        DPFPRINTF(LOG_INFO, key->fn_af == AF_INET ?
            "reass frag %d @ %d-%d" : "reass frag %#08x @ %d-%d",
            id, frent->fe_off, frent->fe_off + frent->fe_len);

        /* Fully buffer all of the fragments in this fragment queue */
        frag = pf_find_fragment(key, id);

        /* Create a new reassembly queue for this packet */
        if (frag == NULL) {
                frag = pool_get(&pf_frag_pl, PR_NOWAIT);
                if (frag == NULL) {
                        pf_flush_fragments();
                        frag = pool_get(&pf_frag_pl, PR_NOWAIT);
                        if (frag == NULL) {
                                REASON_SET(reason, PFRES_MEMORY);
                                goto drop_fragment;
                        }
                }
                frnode = RB_FIND(pf_frnode_tree, &pf_frnode_tree, key);
                if (frnode == NULL) {
                        frnode = pool_get(&pf_frnode_pl, PR_NOWAIT);
                        if (frnode == NULL) {
                                pf_flush_fragments();
                                frnode = pool_get(&pf_frnode_pl, PR_NOWAIT);
                                if (frnode == NULL) {
                                        REASON_SET(reason, PFRES_MEMORY);
                                        pool_put(&pf_frag_pl, frag);
                                        goto drop_fragment;
                                }
                        }
                        *frnode = *key;
                        RB_INIT(&frnode->fn_tree);
                        frnode->fn_fragments = 0;
                        frnode->fn_gen = 0;
                }
                memset(frag->fr_firstoff, 0, sizeof(frag->fr_firstoff));
                memset(frag->fr_entries, 0, sizeof(frag->fr_entries));
                TAILQ_INIT(&frag->fr_queue);
                frag->fr_id = id;
                frag->fr_timeout = getuptime();
                frag->fr_gen = frnode->fn_gen++;
                frag->fr_maxlen = frent->fe_len;
                frag->fr_holes = 1;
                frag->fr_node = frnode;
                /* RB_INSERT cannot fail as pf_find_fragment() found nothing */
                RB_INSERT(pf_frag_tree, &frnode->fn_tree, frag);
                frnode->fn_fragments++;
                if (frnode->fn_fragments == 1)
                        RB_INSERT(pf_frnode_tree, &pf_frnode_tree, frnode);
                TAILQ_INSERT_HEAD(&pf_fragqueue, frag, frag_next);

                /* We do not have a previous fragment, cannot fail. */
                pf_frent_insert(frag, frent, NULL);

                return (frag);
        }

        KASSERT(!TAILQ_EMPTY(&frag->fr_queue));
        KASSERT(frag->fr_node);

        /* Remember maximum fragment len for refragmentation */
        if (frent->fe_len > frag->fr_maxlen)
                frag->fr_maxlen = frent->fe_len;

        /* Maximum data we have seen already */
        total = TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_off +
            TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_len;

        /* Non terminal fragments must have more fragments flag */
        if (frent->fe_off + frent->fe_len < total && !frent->fe_mff)
                goto free_ipv6_fragment;

        /* Check if we saw the last fragment already */
        if (!TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_mff) {
                if (frent->fe_off + frent->fe_len > total ||
                    (frent->fe_off + frent->fe_len == total && frent->fe_mff))
                        goto free_ipv6_fragment;
        } else {
                if (frent->fe_off + frent->fe_len == total && !frent->fe_mff)
                        goto free_ipv6_fragment;
        }

        /* Find neighbors for newly inserted fragment */
        prev = pf_frent_previous(frag, frent);
        if (prev == NULL) {
                after = TAILQ_FIRST(&frag->fr_queue);
                KASSERT(after != NULL);
        } else {
                after = TAILQ_NEXT(prev, fr_next);
        }

        if (prev != NULL && prev->fe_off + prev->fe_len > frent->fe_off) {
                u_int16_t       precut;

#ifdef INET6
                if (frag->fr_node->fn_af == AF_INET6)
                        goto free_ipv6_fragment;
#endif /* INET6 */

                precut = prev->fe_off + prev->fe_len - frent->fe_off;
                if (precut >= frent->fe_len) {
                        DPFPRINTF(LOG_NOTICE, "new frag overlapped");
                        goto drop_fragment;
                }
                DPFPRINTF(LOG_NOTICE, "frag head overlap %d", precut);
                m_adj(frent->fe_m, precut);
                frent->fe_off += precut;
                frent->fe_len -= precut;
        }

        for (; after != NULL && frent->fe_off + frent->fe_len > after->fe_off;
            after = next) {
                u_int16_t       aftercut;

#ifdef INET6
                if (frag->fr_node->fn_af == AF_INET6)
                        goto free_ipv6_fragment;
#endif /* INET6 */

                aftercut = frent->fe_off + frent->fe_len - after->fe_off;
                if (aftercut < after->fe_len) {
                        DPFPRINTF(LOG_NOTICE, "frag tail overlap %d", aftercut);
                        m_adj(after->fe_m, aftercut);
                        /* Fragment may switch queue as fe_off changes */
                        pf_frent_remove(frag, after);
                        after->fe_off += aftercut;
                        after->fe_len -= aftercut;
                        /* Insert into correct queue */
                        if (pf_frent_insert(frag, after, prev)) {
                                DPFPRINTF(LOG_WARNING,
                                    "fragment requeue limit exceeded");
                                m_freem(after->fe_m);
                                pool_put(&pf_frent_pl, after);
                                pf_status.fragments--;
                                /* There is not way to recover */
                                goto free_fragment;
                        }
                        break;
                }

                /* This fragment is completely overlapped, lose it */
                DPFPRINTF(LOG_NOTICE, "old frag overlapped");
                next = TAILQ_NEXT(after, fr_next);
                pf_frent_remove(frag, after);
                m_freem(after->fe_m);
                pool_put(&pf_frent_pl, after);
                pf_status.fragments--;
        }

        /* If part of the queue gets too long, there is not way to recover. */
        if (pf_frent_insert(frag, frent, prev)) {
                DPFPRINTF(LOG_WARNING, "fragment queue limit exceeded");
                goto free_fragment;
        }

        return (frag);

free_ipv6_fragment:
        if (frag->fr_node->fn_af == AF_INET)
                goto bad_fragment;
        /*
         * RFC 5722, Errata 3089:  When reassembling an IPv6 datagram, if one
         * or more its constituent fragments is determined to be an overlapping
         * fragment, the entire datagram (and any constituent fragments) MUST
         * be silently discarded.
         */
        DPFPRINTF(LOG_NOTICE, "flush overlapping fragments");
free_fragment:
        pf_free_fragment(frag);
bad_fragment:
        REASON_SET(reason, PFRES_FRAG);
drop_fragment:
        pool_put(&pf_frent_pl, frent);
        pf_status.fragments--;
        return (NULL);
}

struct mbuf *
pf_join_fragment(struct pf_fragment *frag)
{
        struct mbuf             *m, *m2;
        struct pf_frent         *frent;

        frent = TAILQ_FIRST(&frag->fr_queue);
        TAILQ_REMOVE(&frag->fr_queue, frent, fr_next);
        pf_status.ncounters[NCNT_FRAG_REMOVALS]++;

        m = frent->fe_m;
        /* Strip off any trailing bytes */
        if ((frent->fe_hdrlen + frent->fe_len) < m->m_pkthdr.len)
                m_adj(m, (frent->fe_hdrlen + frent->fe_len) - m->m_pkthdr.len);
        /* Magic from ip_input */
        m2 = m->m_next;
        m->m_next = NULL;
        m_cat(m, m2);
        pool_put(&pf_frent_pl, frent);
        pf_status.fragments--;

        while ((frent = TAILQ_FIRST(&frag->fr_queue)) != NULL) {
                TAILQ_REMOVE(&frag->fr_queue, frent, fr_next);
                pf_status.ncounters[NCNT_FRAG_REMOVALS]++;
                m2 = frent->fe_m;
                /* Strip off ip header */
                m_adj(m2, frent->fe_hdrlen);
                /* Strip off any trailing bytes */
                if (frent->fe_len < m2->m_pkthdr.len)
                        m_adj(m2, frent->fe_len - m2->m_pkthdr.len);
                pool_put(&pf_frent_pl, frent);
                pf_status.fragments--;
                m_removehdr(m2);
                m_cat(m, m2);
        }

        /* Remove from fragment queue */
        pf_free_fragment(frag);

        return (m);
}

int
pf_reassemble(struct mbuf **m0, int dir, u_short *reason)
{
        struct mbuf             *m = *m0;
        struct ip               *ip = mtod(m, struct ip *);
        struct pf_frent         *frent;
        struct pf_fragment      *frag;
        struct pf_frnode         key;
        u_int16_t                total, hdrlen;

        /* Get an entry for the fragment queue */
        if ((frent = pf_create_fragment(reason)) == NULL)
                return (PF_DROP);

        frent->fe_m = m;
        frent->fe_hdrlen = ip->ip_hl << 2;
        frent->fe_extoff = 0;
        frent->fe_len = ntohs(ip->ip_len) - (ip->ip_hl << 2);
        frent->fe_off = (ntohs(ip->ip_off) & IP_OFFMASK) << 3;
        frent->fe_mff = ntohs(ip->ip_off) & IP_MF;

        key.fn_src.v4 = ip->ip_src;
        key.fn_dst.v4 = ip->ip_dst;
        key.fn_af = AF_INET;
        key.fn_proto = ip->ip_p;
        key.fn_direction = dir;

        if ((frag = pf_fillup_fragment(&key, ip->ip_id, frent, reason))
            == NULL)
                return (PF_DROP);

        /* The mbuf is part of the fragment entry, no direct free or access */
        m = *m0 = NULL;

        if (frag->fr_holes) {
                DPFPRINTF(LOG_DEBUG, "frag %d, holes %d",
                    frag->fr_id, frag->fr_holes);
                return (PF_PASS);  /* drop because *m0 is NULL, no error */
        }

        /* We have all the data */
        frent = TAILQ_FIRST(&frag->fr_queue);
        KASSERT(frent != NULL);
        total = TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_off +
            TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_len;
        hdrlen = frent->fe_hdrlen;
        m = *m0 = pf_join_fragment(frag);
        frag = NULL;
        m_calchdrlen(m);

        ip = mtod(m, struct ip *);
        ip->ip_len = htons(hdrlen + total);
        ip->ip_off &= ~(IP_MF|IP_OFFMASK);

        if (hdrlen + total > IP_MAXPACKET) {
                DPFPRINTF(LOG_NOTICE, "drop: too big: %d", total);
                ip->ip_len = 0;
                REASON_SET(reason, PFRES_SHORT);
                /* PF_DROP requires a valid mbuf *m0 in pf_test() */
                return (PF_DROP);
        }

        DPFPRINTF(LOG_INFO, "complete: %p(%d)", m, ntohs(ip->ip_len));
        return (PF_PASS);
}

#ifdef INET6
int
pf_reassemble6(struct mbuf **m0, struct ip6_frag *fraghdr,
    u_int16_t hdrlen, u_int16_t extoff, int dir, u_short *reason)
{
        struct mbuf             *m = *m0;
        struct ip6_hdr          *ip6 = mtod(m, struct ip6_hdr *);
        struct m_tag            *mtag;
        struct pf_fragment_tag  *ftag;
        struct pf_frent         *frent;
        struct pf_fragment      *frag;
        struct pf_frnode         key;
        int                      off;
        u_int16_t                total, maxlen;
        u_int8_t                 proto;

        /* Get an entry for the fragment queue */
        if ((frent = pf_create_fragment(reason)) == NULL)
                return (PF_DROP);

        frent->fe_m = m;
        frent->fe_hdrlen = hdrlen;
        frent->fe_extoff = extoff;
        frent->fe_len = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) - hdrlen;
        frent->fe_off = ntohs(fraghdr->ip6f_offlg & IP6F_OFF_MASK);
        frent->fe_mff = fraghdr->ip6f_offlg & IP6F_MORE_FRAG;

        key.fn_src.v6 = ip6->ip6_src;
        key.fn_dst.v6 = ip6->ip6_dst;
        key.fn_af = AF_INET6;
        /* Only the first fragment's protocol is relevant */
        key.fn_proto = 0;
        key.fn_direction = dir;

        if ((frag = pf_fillup_fragment(&key, fraghdr->ip6f_ident, frent,
            reason)) == NULL)
                return (PF_DROP);

        /* The mbuf is part of the fragment entry, no direct free or access */
        m = *m0 = NULL;

        if (frag->fr_holes) {
                DPFPRINTF(LOG_DEBUG, "frag %#08x, holes %d",
                    frag->fr_id, frag->fr_holes);
                return (PF_PASS);  /* drop because *m0 is NULL, no error */
        }

        /* We have all the data */
        frent = TAILQ_FIRST(&frag->fr_queue);
        KASSERT(frent != NULL);
        extoff = frent->fe_extoff;
        maxlen = frag->fr_maxlen;
        total = TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_off +
            TAILQ_LAST(&frag->fr_queue, pf_fragq)->fe_len;
        hdrlen = frent->fe_hdrlen - sizeof(struct ip6_frag);
        m = *m0 = pf_join_fragment(frag);
        frag = NULL;

        /* Take protocol from first fragment header */
        if ((m = m_getptr(m, hdrlen + offsetof(struct ip6_frag, ip6f_nxt),
            &off)) == NULL)
                panic("%s: short frag mbuf chain", __func__);
        proto = *(mtod(m, caddr_t) + off);
        m = *m0;

        /* Delete frag6 header */
        if (frag6_deletefraghdr(m, hdrlen) != 0)
                goto fail;

        m_calchdrlen(m);

        if ((mtag = m_tag_get(PACKET_TAG_PF_REASSEMBLED, sizeof(struct
            pf_fragment_tag), M_NOWAIT)) == NULL)
                goto fail;
        ftag = (struct pf_fragment_tag *)(mtag + 1);
        ftag->ft_hdrlen = hdrlen;
        ftag->ft_extoff = extoff;
        ftag->ft_maxlen = maxlen;
        m_tag_prepend(m, mtag);

        ip6 = mtod(m, struct ip6_hdr *);
        ip6->ip6_plen = htons(hdrlen - sizeof(struct ip6_hdr) + total);
        if (extoff) {
                /* Write protocol into next field of last extension header */
                if ((m = m_getptr(m, extoff + offsetof(struct ip6_ext,
                    ip6e_nxt), &off)) == NULL)
                        panic("%s: short ext mbuf chain", __func__);
                *(mtod(m, caddr_t) + off) = proto;
                m = *m0;
        } else
                ip6->ip6_nxt = proto;

        if (hdrlen - sizeof(struct ip6_hdr) + total > IPV6_MAXPACKET) {
                DPFPRINTF(LOG_NOTICE, "drop: too big: %d", total);
                ip6->ip6_plen = 0;
                REASON_SET(reason, PFRES_SHORT);
                /* PF_DROP requires a valid mbuf *m0 in pf_test6() */
                return (PF_DROP);
        }

        DPFPRINTF(LOG_INFO, "complete: %p(%d)", m, ntohs(ip6->ip6_plen));
        return (PF_PASS);

fail:
        REASON_SET(reason, PFRES_MEMORY);
        /* PF_DROP requires a valid mbuf *m0 in pf_test6(), will free later */
        return (PF_DROP);
}

int
pf_refragment6(struct mbuf **m0, struct m_tag *mtag, struct sockaddr_in6 *dst,
    struct ifnet *ifp, struct rtentry *rt)
{
        struct mbuf             *m = *m0;
        struct mbuf_list         ml;
        struct pf_fragment_tag  *ftag = (struct pf_fragment_tag *)(mtag + 1);
        u_int32_t                mtu;
        u_int16_t                hdrlen, extoff, maxlen;
        u_int8_t                 proto;
        int                      error;

        hdrlen = ftag->ft_hdrlen;
        extoff = ftag->ft_extoff;
        maxlen = ftag->ft_maxlen;
        m_tag_delete(m, mtag);
        mtag = NULL;
        ftag = NULL;

        /* Checksum must be calculated for the whole packet */
        in6_proto_cksum_out(m, NULL);

        if (extoff) {
                int off;

                /* Use protocol from next field of last extension header */
                if ((m = m_getptr(m, extoff + offsetof(struct ip6_ext,
                    ip6e_nxt), &off)) == NULL)
                        panic("%s: short ext mbuf chain", __func__);
                proto = *(mtod(m, caddr_t) + off);
                *(mtod(m, caddr_t) + off) = IPPROTO_FRAGMENT;
                m = *m0;
        } else {
                struct ip6_hdr *hdr;

                hdr = mtod(m, struct ip6_hdr *);
                proto = hdr->ip6_nxt;
                hdr->ip6_nxt = IPPROTO_FRAGMENT;
        }

        /*
         * Maxlen may be less than 8 iff there was only a single
         * fragment.  As it was fragmented before, add a fragment
         * header also for a single fragment.  If total or maxlen
         * is less than 8, ip6_fragment() will return EMSGSIZE and
         * we drop the packet.
         */
        mtu = hdrlen + sizeof(struct ip6_frag) + maxlen;
        error = ip6_fragment(m, &ml, hdrlen, proto, mtu);
        *m0 = NULL;     /* ip6_fragment() has consumed original packet. */
        if (error) {
                DPFPRINTF(LOG_NOTICE, "refragment error %d", error);
                return (PF_DROP);
        }

        while ((m = ml_dequeue(&ml)) != NULL) {
                m->m_pkthdr.pf.flags |= PF_TAG_REFRAGMENTED;
                if (ifp == NULL) {
                        int flags = 0;

                        switch (atomic_load_int(&ip6_forwarding)) {
                        case 2:
                                SET(flags, IPV6_FORWARDING_IPSEC);
                                /* FALLTHROUGH */
                        case 1:
                                SET(flags, IPV6_FORWARDING);
                                break;
                        default:
                                ip6stat_inc(ip6s_cantforward);
                                return (PF_DROP);
                        }
                        ip6_forward(m, NULL, flags);
                } else if ((u_long)m->m_pkthdr.len <= ifp->if_mtu) {
                        ifp->if_output(ifp, m, sin6tosa(dst), rt);
                } else {
                        icmp6_error(m, ICMP6_PACKET_TOO_BIG, 0, ifp->if_mtu);
                }
        }

        return (PF_PASS);
}
#endif /* INET6 */

int
pf_normalize_ip(struct pf_pdesc *pd, u_short *reason)
{
        struct ip       *h = mtod(pd->m, struct ip *);
        u_int16_t        fragoff = (ntohs(h->ip_off) & IP_OFFMASK) << 3;
        u_int16_t        mff = (ntohs(h->ip_off) & IP_MF);

        if (!fragoff && !mff)
                goto no_fragment;

        /* Clear IP_DF if we're in no-df mode */
        if (pf_status.reass & PF_REASS_NODF && h->ip_off & htons(IP_DF))
                h->ip_off &= htons(~IP_DF);

        /* 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(LOG_NOTICE, "bad fragment: IP_DF");
                REASON_SET(reason, PFRES_FRAG);
                return (PF_DROP);
        }

        if (!pf_status.reass)
                return (PF_PASS);       /* no reassembly */

        /* Returns PF_DROP or m is NULL or completely reassembled mbuf */
        PF_FRAG_LOCK();
        if (pf_reassemble(&pd->m, pd->dir, reason) != PF_PASS) {
                PF_FRAG_UNLOCK();
                return (PF_DROP);
        }
        PF_FRAG_UNLOCK();
        if (pd->m == NULL)
                return (PF_PASS);  /* packet has been reassembled, no error */

        h = mtod(pd->m, struct ip *);

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

        return (PF_PASS);
}

#ifdef INET6
int
pf_normalize_ip6(struct pf_pdesc *pd, u_short *reason)
{
        struct ip6_frag          frag;

        if (pd->fragoff == 0)
                goto no_fragment;

        if (!pf_pull_hdr(pd->m, pd->fragoff, &frag, sizeof(frag), reason,
            AF_INET6))
                return (PF_DROP);

        if (!pf_status.reass)
                return (PF_PASS);       /* no reassembly */

        /* Returns PF_DROP or m is NULL or completely reassembled mbuf */
        PF_FRAG_LOCK();
        if (pf_reassemble6(&pd->m, &frag, pd->fragoff + sizeof(frag),
            pd->extoff, pd->dir, reason) != PF_PASS) {
                PF_FRAG_UNLOCK();
                return (PF_DROP);
        }
        PF_FRAG_UNLOCK();
        if (pd->m == NULL)
                return (PF_PASS);  /* packet has been reassembled, no error */

no_fragment:
        return (PF_PASS);
}
#endif /* INET6 */

struct pf_state_scrub *
pf_state_scrub_get(void)
{
        return (pool_get(&pf_state_scrub_pl, PR_NOWAIT | PR_ZERO));
}

void
pf_state_scrub_put(struct pf_state_scrub *scrub)
{
        pool_put(&pf_state_scrub_pl, scrub);
}

int
pf_normalize_tcp_alloc(struct pf_state_peer *src)
{
        src->scrub = pf_state_scrub_get();
        if (src->scrub == NULL)
                return (ENOMEM);

        return (0);
}

int
pf_normalize_tcp(struct pf_pdesc *pd)
{
        struct tcphdr   *th = &pd->hdr.tcp;
        u_short          reason;
        u_int8_t         flags;
        u_int            rewrite = 0;

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

                if (flags & TH_FIN)     /* XXX why clear instead of drop? */
                        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|TH_PUSH|TH_URG))
                        goto tcp_drop;
        }

        /* If flags changed, or reserved data set, then adjust */
        if (flags != th->th_flags || th->th_x2 != 0) {
                /* hack: set 4-bit th_x2 = 0 */
                u_int8_t *th_off = (u_int8_t*)(&th->th_ack+1);
                pf_patch_8(pd, th_off, th->th_off << 4, PF_HI);

                pf_patch_8(pd, &th->th_flags, flags, PF_LO);
                rewrite = 1;
        }

        /* Remove urgent pointer, if TH_URG is not set */
        if (!(flags & TH_URG) && th->th_urp) {
                pf_patch_16(pd, &th->th_urp, 0);
                rewrite = 1;
        }

        /* copy back packet headers if we sanitized */
        if (rewrite) {
                m_copyback(pd->m, pd->off, sizeof(*th), th, M_NOWAIT);
        }

        return (PF_PASS);

tcp_drop:
        REASON_SET(&reason, PFRES_NORM);
        return (PF_DROP);
}

int
pf_normalize_tcp_init(struct pf_pdesc *pd, struct pf_state_peer *src)
{
        struct tcphdr   *th = &pd->hdr.tcp;
        u_int32_t        tsval, tsecr;
        int              olen;
        u_int8_t         opts[MAX_TCPOPTLEN], *opt;


        KASSERT(src->scrub == NULL);

        if (pf_normalize_tcp_alloc(src) != 0)
                return (1);

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

        /*
         * 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);

        olen = (th->th_off << 2) - sizeof(*th);
        if (olen < TCPOLEN_TIMESTAMP || !pf_pull_hdr(pd->m,
            pd->off + sizeof(*th), opts, olen, NULL, pd->af))
                return (0);

        opt = opts;
        while ((opt = pf_find_tcpopt(opt, opts, olen,
                    TCPOPT_TIMESTAMP, TCPOLEN_TIMESTAMP)) != NULL) {

                src->scrub->pfss_flags |= PFSS_TIMESTAMP;
                src->scrub->pfss_ts_mod = arc4random();
                /* 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);

                opt += opt[1];
        }

        return (0);
}

void
pf_normalize_tcp_cleanup(struct pf_state *state)
{
        if (state->src.scrub)
                pool_put(&pf_state_scrub_pl, state->src.scrub);
        if (state->dst.scrub)
                pool_put(&pf_state_scrub_pl, state->dst.scrub);

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

int
pf_normalize_tcp_stateful(struct pf_pdesc *pd, u_short *reason,
    struct pf_state *state, struct pf_state_peer *src,
    struct pf_state_peer *dst, int *writeback)
{
        struct tcphdr   *th = &pd->hdr.tcp;
        struct timeval   uptime;
        u_int            tsval_from_last;
        u_int32_t        tsval, tsecr;
        int              copyback = 0;
        int              got_ts = 0;
        int              olen;
        u_int8_t         opts[MAX_TCPOPTLEN], *opt;

        KASSERT(src->scrub || dst->scrub);

        /*
         * 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) {
        case AF_INET:
                if (src->scrub) {
                        struct ip *h = mtod(pd->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;
#ifdef INET6
        case AF_INET6:
                if (src->scrub) {
                        struct ip6_hdr *h = mtod(pd->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 */
        default:
                unhandled_af(pd->af);
        }

        olen = (th->th_off << 2) - sizeof(*th);

        if (olen >= TCPOLEN_TIMESTAMP &&
            ((src->scrub && (src->scrub->pfss_flags & PFSS_TIMESTAMP)) ||
            (dst->scrub && (dst->scrub->pfss_flags & PFSS_TIMESTAMP))) &&
            pf_pull_hdr(pd->m, pd->off + sizeof(*th), opts, olen, NULL,
            pd->af)) {

                /* Modulate the timestamps.  Can be used for NAT detection, OS
                 * uptime determination or reboot detection.
                 */
                opt = opts;
                while ((opt = pf_find_tcpopt(opt, opts, olen,
                            TCPOPT_TIMESTAMP, TCPOLEN_TIMESTAMP)) != NULL) {

                        u_int8_t *ts = opt + 2;
                        u_int8_t *tsr = opt + 6;

                        if (got_ts) {
                                /* Huh?  Multiple timestamps!? */
                                if (pf_status.debug >= LOG_NOTICE) {
                                        log(LOG_NOTICE,
                                            "pf: %s: multiple TS??", __func__);
                                        pf_print_state(state);
                                        addlog("\n");
                                }
                                REASON_SET(reason, PFRES_TS);
                                return (PF_DROP);
                        }

                        memcpy(&tsval, ts, sizeof(u_int32_t));
                        memcpy(&tsecr, tsr, sizeof(u_int32_t));

                        /* modulate TS */
                        if (tsval && src->scrub &&
                            (src->scrub->pfss_flags & PFSS_TIMESTAMP)) {
                                /* tsval used further on */
                                tsval = ntohl(tsval);
                                pf_patch_32_unaligned(pd,
                                    ts, htonl(tsval + src->scrub->pfss_ts_mod),
                                    PF_ALGNMNT(ts - opts));
                                copyback = 1;
                        }

                        /* modulate TS reply if any (!0) */
                        if (tsecr && dst->scrub &&
                            (dst->scrub->pfss_flags & PFSS_TIMESTAMP)) {
                                /* tsecr used further on */
                                tsecr = ntohl(tsecr) - dst->scrub->pfss_ts_mod;
                                pf_patch_32_unaligned(pd,
                                    tsr, htonl(tsecr), PF_ALGNMNT(tsr - opts));
                                copyback = 1;
                        }

                        got_ts = 1;
                        opt += opt[1];
                }

                if (copyback) {
                        /* Copyback the options, caller copies back header */
                        *writeback = 1;
                        m_copyback(pd->m, pd->off + sizeof(*th), olen, opts, M_NOWAIT);
                }
        }


        /*
         * 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 ||
            getuptime() - state->creation > TS_MAX_CONN))  {
                if (pf_status.debug >= LOG_NOTICE) {
                        log(LOG_NOTICE, "pf: src idled out of PAWS ");
                        pf_print_state(state);
                        addlog("\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 >= LOG_NOTICE) {
                        log(LOG_NOTICE, "pf: dst idled out of PAWS ");
                        pf_print_state(state);
                        addlog("\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 */
                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(LOG_NOTICE, "Timestamp failed %c%c%c%c",
                            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(LOG_NOTICE, " tsval: %u  tsecr: %u  "
                            "+ticks: %u  idle: %llu.%06lus", tsval, tsecr,
                            tsval_from_last, (long long)delta_ts.tv_sec,
                            delta_ts.tv_usec);
                        DPFPRINTF(LOG_NOTICE, " src->tsval: %u  tsecr: %u",
                            src->scrub->pfss_tsval, src->scrub->pfss_tsecr);
                        DPFPRINTF(LOG_NOTICE, " dst->tsval: %u  tsecr: %u  "
                            "tsval0: %u", dst->scrub->pfss_tsval,
                            dst->scrub->pfss_tsecr, dst->scrub->pfss_tsval0);
                        if (pf_status.debug >= LOG_NOTICE) {
                                log(LOG_NOTICE, "pf: ");
                                pf_print_state(state);
                                pf_print_flags(th->th_flags);
                                addlog("\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 >= LOG_NOTICE) {
                                log(LOG_NOTICE,
                                    "pf: did not receive expected RFC1323 "
                                    "timestamp");
                                pf_print_state(state);
                                pf_print_flags(th->th_flags);
                                addlog("\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 >= LOG_NOTICE && dst->scrub &&
                            (dst->scrub->pfss_flags & PFSS_TIMESTAMP)) {
                                /* Don't warn if other host rejected RFC1323 */
                                log(LOG_NOTICE,
                                    "pf: broken RFC1323 stack did not "
                                    "timestamp data packet. Disabled PAWS "
                                    "security.");
                                pf_print_state(state);
                                pf_print_flags(th->th_flags);
                                addlog("\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_mss(struct pf_pdesc *pd, u_int16_t maxmss)
{
        int              olen, optsoff;
        u_int8_t         opts[MAX_TCPOPTLEN], *opt;

        olen = (pd->hdr.tcp.th_off << 2) - sizeof(struct tcphdr);
        optsoff = pd->off + sizeof(struct tcphdr);
        if (olen < TCPOLEN_MAXSEG ||
            !pf_pull_hdr(pd->m, optsoff, opts, olen, NULL, pd->af))
                return (0);

        opt = opts;
        while ((opt = pf_find_tcpopt(opt, opts, olen,
                    TCPOPT_MAXSEG, TCPOLEN_MAXSEG)) != NULL) {
                u_int16_t       mss;
                u_int8_t       *mssp = opt + 2;
                memcpy(&mss, mssp, sizeof(mss));
                if (ntohs(mss) > maxmss) {
                        size_t mssoffopts = mssp - opts;
                        pf_patch_16_unaligned(pd, &mss,
                            htons(maxmss), PF_ALGNMNT(mssoffopts));
                        m_copyback(pd->m, optsoff + mssoffopts,
                            sizeof(mss), &mss, M_NOWAIT);
                        m_copyback(pd->m, pd->off,
                            sizeof(struct tcphdr), &pd->hdr.tcp, M_NOWAIT);
                }

                opt += opt[1];
        }

        return (0);
}

void
pf_scrub(struct mbuf *m, u_int16_t flags, sa_family_t af, u_int8_t min_ttl,
    u_int8_t tos)
{
        struct ip               *h = mtod(m, struct ip *);
#ifdef INET6
        struct ip6_hdr          *h6 = mtod(m, struct ip6_hdr *);
#endif  /* INET6 */
        u_int16_t                old;

        /* Clear IP_DF if no-df was requested */
        if (flags & PFSTATE_NODF && af == AF_INET && h->ip_off & htons(IP_DF)) {
                old = h->ip_off;
                h->ip_off &= htons(~IP_DF);
                pf_cksum_fixup(&h->ip_sum, old, h->ip_off, 0);
        }

        /* Enforce a minimum ttl, may cause endless packet loops */
        if (min_ttl && af == AF_INET && h->ip_ttl < min_ttl) {
                old = h->ip_ttl;
                h->ip_ttl = min_ttl;
                pf_cksum_fixup(&h->ip_sum, old, h->ip_ttl, 0);
        }
#ifdef INET6
        if (min_ttl && af == AF_INET6 && h6->ip6_hlim < min_ttl)
                h6->ip6_hlim = min_ttl;
#endif  /* INET6 */

        /* Enforce tos */
        if (flags & PFSTATE_SETTOS) {
                if (af == AF_INET) {
                        /*
                         * ip_tos is 8 bit field at offset 1. Use 16 bit value
                         * at offset 0.
                         */
                        old = *(u_int16_t *)h;
                        h->ip_tos = tos | (h->ip_tos & IPTOS_ECN_MASK);
                        pf_cksum_fixup(&h->ip_sum, old, *(u_int16_t *)h, 0);
                }
#ifdef INET6
                if (af == AF_INET6) {
                        /* drugs are unable to explain such idiocy */
                        h6->ip6_flow &= ~htonl(0x0fc00000);
                        h6->ip6_flow |= htonl(((u_int32_t)tos) << 20);
                }
#endif  /* INET6 */
        }

        /* random-id, but not for fragments */
        if (flags & PFSTATE_RANDOMID && af == AF_INET &&
            !(h->ip_off & ~htons(IP_DF))) {
                old = h->ip_id;
                h->ip_id = htons(ip_randomid());
                pf_cksum_fixup(&h->ip_sum, old, h->ip_id, 0);
        }
}