Merge branch 'upstream-linus' of master.kernel.org:/pub/scm/linux/kernel/git/jgarzik...

[deliverable/linux.git] / net / ipv6 / reassembly.c

/*
 *      IPv6 fragment reassembly
 *      Linux INET6 implementation 
 *
 *      Authors:
 *      Pedro Roque             <roque@di.fc.ul.pt>     
 *
 *      $Id: reassembly.c,v 1.26 2001/03/07 22:00:57 davem Exp $
 *
 *      Based on: net/ipv4/ip_fragment.c
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */

/* 
 *      Fixes:  
 *      Andi Kleen      Make it work with multiple hosts.
 *                      More RFC compliance.
 *
 *      Horst von Brand Add missing #include <linux/string.h>
 *      Alexey Kuznetsov        SMP races, threading, cleanup.
 *      Patrick McHardy         LRU queue of frag heads for evictor.
 *      Mitsuru KANDA @USAGI    Register inet6_protocol{}.
 *      David Stevens and
 *      YOSHIFUJI,H. @USAGI     Always remove fragment header to
 *                              calculate ICV correctly.
 */
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/jiffies.h>
#include <linux/net.h>
#include <linux/list.h>
#include <linux/netdevice.h>
#include <linux/in6.h>
#include <linux/ipv6.h>
#include <linux/icmpv6.h>
#include <linux/random.h>
#include <linux/jhash.h>

#include <net/sock.h>
#include <net/snmp.h>

#include <net/ipv6.h>
#include <net/protocol.h>
#include <net/transp_v6.h>
#include <net/rawv6.h>
#include <net/ndisc.h>
#include <net/addrconf.h>

int sysctl_ip6frag_high_thresh __read_mostly = 256*1024;
int sysctl_ip6frag_low_thresh __read_mostly = 192*1024;

int sysctl_ip6frag_time __read_mostly = IPV6_FRAG_TIMEOUT;

struct ip6frag_skb_cb
{
        struct inet6_skb_parm   h;
        int                     offset;
};

#define FRAG6_CB(skb)   ((struct ip6frag_skb_cb*)((skb)->cb))


/*
 *      Equivalent of ipv4 struct ipq
 */

struct frag_queue
{
        struct hlist_node       list;
        struct list_head lru_list;              /* lru list member      */

        __u32                   id;             /* fragment id          */
        struct in6_addr         saddr;
        struct in6_addr         daddr;

        spinlock_t              lock;
        atomic_t                refcnt;
        struct timer_list       timer;          /* expire timer         */
        struct sk_buff          *fragments;
        int                     len;
        int                     meat;
        int                     iif;
        struct timeval          stamp;
        unsigned int            csum;
        __u8                    last_in;        /* has first/last segment arrived? */
#define COMPLETE                4
#define FIRST_IN                2
#define LAST_IN                 1
        __u16                   nhoffset;
};

/* Hash table. */

#define IP6Q_HASHSZ     64

static struct hlist_head ip6_frag_hash[IP6Q_HASHSZ];
static DEFINE_RWLOCK(ip6_frag_lock);
static u32 ip6_frag_hash_rnd;
static LIST_HEAD(ip6_frag_lru_list);
int ip6_frag_nqueues = 0;

static __inline__ void __fq_unlink(struct frag_queue *fq)
{
        hlist_del(&fq->list);
        list_del(&fq->lru_list);
        ip6_frag_nqueues--;
}

static __inline__ void fq_unlink(struct frag_queue *fq)
{
        write_lock(&ip6_frag_lock);
        __fq_unlink(fq);
        write_unlock(&ip6_frag_lock);
}

/*
 * callers should be careful not to use the hash value outside the ipfrag_lock
 * as doing so could race with ipfrag_hash_rnd being recalculated.
 */
static unsigned int ip6qhashfn(u32 id, struct in6_addr *saddr,
                               struct in6_addr *daddr)
{
        u32 a, b, c;

        a = saddr->s6_addr32[0];
        b = saddr->s6_addr32[1];
        c = saddr->s6_addr32[2];

        a += JHASH_GOLDEN_RATIO;
        b += JHASH_GOLDEN_RATIO;
        c += ip6_frag_hash_rnd;
        __jhash_mix(a, b, c);

        a += saddr->s6_addr32[3];
        b += daddr->s6_addr32[0];
        c += daddr->s6_addr32[1];
        __jhash_mix(a, b, c);

        a += daddr->s6_addr32[2];
        b += daddr->s6_addr32[3];
        c += id;
        __jhash_mix(a, b, c);

        return c & (IP6Q_HASHSZ - 1);
}

static struct timer_list ip6_frag_secret_timer;
int sysctl_ip6frag_secret_interval __read_mostly = 10 * 60 * HZ;

static void ip6_frag_secret_rebuild(unsigned long dummy)
{
        unsigned long now = jiffies;
        int i;

        write_lock(&ip6_frag_lock);
        get_random_bytes(&ip6_frag_hash_rnd, sizeof(u32));
        for (i = 0; i < IP6Q_HASHSZ; i++) {
                struct frag_queue *q;
                struct hlist_node *p, *n;

                hlist_for_each_entry_safe(q, p, n, &ip6_frag_hash[i], list) {
                        unsigned int hval = ip6qhashfn(q->id,
                                                       &q->saddr,
                                                       &q->daddr);

                        if (hval != i) {
                                hlist_del(&q->list);

                                /* Relink to new hash chain. */
                                hlist_add_head(&q->list,
                                               &ip6_frag_hash[hval]);

                        }
                }
        }
        write_unlock(&ip6_frag_lock);

        mod_timer(&ip6_frag_secret_timer, now + sysctl_ip6frag_secret_interval);
}

atomic_t ip6_frag_mem = ATOMIC_INIT(0);

/* Memory Tracking Functions. */
static inline void frag_kfree_skb(struct sk_buff *skb, int *work)
{
        if (work)
                *work -= skb->truesize;
        atomic_sub(skb->truesize, &ip6_frag_mem);
        kfree_skb(skb);
}

static inline void frag_free_queue(struct frag_queue *fq, int *work)
{
        if (work)
                *work -= sizeof(struct frag_queue);
        atomic_sub(sizeof(struct frag_queue), &ip6_frag_mem);
        kfree(fq);
}

static inline struct frag_queue *frag_alloc_queue(void)
{
        struct frag_queue *fq = kzalloc(sizeof(struct frag_queue), GFP_ATOMIC);

        if(!fq)
                return NULL;
        atomic_add(sizeof(struct frag_queue), &ip6_frag_mem);
        return fq;
}

/* Destruction primitives. */

/* Complete destruction of fq. */
static void ip6_frag_destroy(struct frag_queue *fq, int *work)
{
        struct sk_buff *fp;

        BUG_TRAP(fq->last_in&COMPLETE);
        BUG_TRAP(del_timer(&fq->timer) == 0);

        /* Release all fragment data. */
        fp = fq->fragments;
        while (fp) {
                struct sk_buff *xp = fp->next;

                frag_kfree_skb(fp, work);
                fp = xp;
        }

        frag_free_queue(fq, work);
}

static __inline__ void fq_put(struct frag_queue *fq, int *work)
{
        if (atomic_dec_and_test(&fq->refcnt))
                ip6_frag_destroy(fq, work);
}

/* Kill fq entry. It is not destroyed immediately,
 * because caller (and someone more) holds reference count.
 */
static __inline__ void fq_kill(struct frag_queue *fq)
{
        if (del_timer(&fq->timer))
                atomic_dec(&fq->refcnt);

        if (!(fq->last_in & COMPLETE)) {
                fq_unlink(fq);
                atomic_dec(&fq->refcnt);
                fq->last_in |= COMPLETE;
        }
}

static void ip6_evictor(void)
{
        struct frag_queue *fq;
        struct list_head *tmp;
        int work;

        work = atomic_read(&ip6_frag_mem) - sysctl_ip6frag_low_thresh;
        if (work <= 0)
                return;

        while(work > 0) {
                read_lock(&ip6_frag_lock);
                if (list_empty(&ip6_frag_lru_list)) {
                        read_unlock(&ip6_frag_lock);
                        return;
                }
                tmp = ip6_frag_lru_list.next;
                fq = list_entry(tmp, struct frag_queue, lru_list);
                atomic_inc(&fq->refcnt);
                read_unlock(&ip6_frag_lock);

                spin_lock(&fq->lock);
                if (!(fq->last_in&COMPLETE))
                        fq_kill(fq);
                spin_unlock(&fq->lock);

                fq_put(fq, &work);
                IP6_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
        }
}

static void ip6_frag_expire(unsigned long data)
{
        struct frag_queue *fq = (struct frag_queue *) data;
        struct net_device *dev;

        spin_lock(&fq->lock);

        if (fq->last_in & COMPLETE)
                goto out;

        fq_kill(fq);

        IP6_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT);
        IP6_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);

        /* Don't send error if the first segment did not arrive. */
        if (!(fq->last_in&FIRST_IN) || !fq->fragments)
                goto out;

        dev = dev_get_by_index(fq->iif);
        if (!dev)
                goto out;

        /*
           But use as source device on which LAST ARRIVED
           segment was received. And do not use fq->dev
           pointer directly, device might already disappeared.
         */
        fq->fragments->dev = dev;
        icmpv6_send(fq->fragments, ICMPV6_TIME_EXCEED, ICMPV6_EXC_FRAGTIME, 0, dev);
        dev_put(dev);
out:
        spin_unlock(&fq->lock);
        fq_put(fq, NULL);
}

/* Creation primitives. */


static struct frag_queue *ip6_frag_intern(struct frag_queue *fq_in)
{
        struct frag_queue *fq;
        unsigned int hash;
#ifdef CONFIG_SMP
        struct hlist_node *n;
#endif

        write_lock(&ip6_frag_lock);
        hash = ip6qhashfn(fq_in->id, &fq_in->saddr, &fq_in->daddr);
#ifdef CONFIG_SMP
        hlist_for_each_entry(fq, n, &ip6_frag_hash[hash], list) {
                if (fq->id == fq_in->id && 
                    ipv6_addr_equal(&fq_in->saddr, &fq->saddr) &&
                    ipv6_addr_equal(&fq_in->daddr, &fq->daddr)) {
                        atomic_inc(&fq->refcnt);
                        write_unlock(&ip6_frag_lock);
                        fq_in->last_in |= COMPLETE;
                        fq_put(fq_in, NULL);
                        return fq;
                }
        }
#endif
        fq = fq_in;

        if (!mod_timer(&fq->timer, jiffies + sysctl_ip6frag_time))
                atomic_inc(&fq->refcnt);

        atomic_inc(&fq->refcnt);
        hlist_add_head(&fq->list, &ip6_frag_hash[hash]);
        INIT_LIST_HEAD(&fq->lru_list);
        list_add_tail(&fq->lru_list, &ip6_frag_lru_list);
        ip6_frag_nqueues++;
        write_unlock(&ip6_frag_lock);
        return fq;
}


static struct frag_queue *
ip6_frag_create(u32 id, struct in6_addr *src, struct in6_addr *dst)
{
        struct frag_queue *fq;

        if ((fq = frag_alloc_queue()) == NULL)
                goto oom;

        fq->id = id;
        ipv6_addr_copy(&fq->saddr, src);
        ipv6_addr_copy(&fq->daddr, dst);

        init_timer(&fq->timer);
        fq->timer.function = ip6_frag_expire;
        fq->timer.data = (long) fq;
        spin_lock_init(&fq->lock);
        atomic_set(&fq->refcnt, 1);

        return ip6_frag_intern(fq);

oom:
        IP6_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
        return NULL;
}

static __inline__ struct frag_queue *
fq_find(u32 id, struct in6_addr *src, struct in6_addr *dst)
{
        struct frag_queue *fq;
        struct hlist_node *n;
        unsigned int hash;

        read_lock(&ip6_frag_lock);
        hash = ip6qhashfn(id, src, dst);
        hlist_for_each_entry(fq, n, &ip6_frag_hash[hash], list) {
                if (fq->id == id && 
                    ipv6_addr_equal(src, &fq->saddr) &&
                    ipv6_addr_equal(dst, &fq->daddr)) {
                        atomic_inc(&fq->refcnt);
                        read_unlock(&ip6_frag_lock);
                        return fq;
                }
        }
        read_unlock(&ip6_frag_lock);

        return ip6_frag_create(id, src, dst);
}


static void ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb, 
                           struct frag_hdr *fhdr, int nhoff)
{
        struct sk_buff *prev, *next;
        int offset, end;

        if (fq->last_in & COMPLETE)
                goto err;

        offset = ntohs(fhdr->frag_off) & ~0x7;
        end = offset + (ntohs(skb->nh.ipv6h->payload_len) -
                        ((u8 *) (fhdr + 1) - (u8 *) (skb->nh.ipv6h + 1)));

        if ((unsigned int)end > IPV6_MAXPLEN) {
                IP6_INC_STATS_BH(IPSTATS_MIB_INHDRERRORS);
                icmpv6_param_prob(skb,ICMPV6_HDR_FIELD, (u8*)&fhdr->frag_off - skb->nh.raw);
                return;
        }

        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->csum = csum_sub(skb->csum,
                                     csum_partial(skb->nh.raw, (u8*)(fhdr+1)-skb->nh.raw, 0));

        /* Is this the final fragment? */
        if (!(fhdr->frag_off & htons(IP6_MF))) {
                /* If we already have some bits beyond end
                 * or have different end, the segment is corrupted.
                 */
                if (end < fq->len ||
                    ((fq->last_in & LAST_IN) && end != fq->len))
                        goto err;
                fq->last_in |= LAST_IN;
                fq->len = end;
        } else {
                /* Check if the fragment is rounded to 8 bytes.
                 * Required by the RFC.
                 */
                if (end & 0x7) {
                        /* RFC2460 says always send parameter problem in
                         * this case. -DaveM
                         */
                        IP6_INC_STATS_BH(IPSTATS_MIB_INHDRERRORS);
                        icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, 
                                          offsetof(struct ipv6hdr, payload_len));
                        return;
                }
                if (end > fq->len) {
                        /* Some bits beyond end -> corruption. */
                        if (fq->last_in & LAST_IN)
                                goto err;
                        fq->len = end;
                }
        }

        if (end == offset)
                goto err;

        /* Point into the IP datagram 'data' part. */
        if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data))
                goto err;
        
        if (pskb_trim_rcsum(skb, end - offset))
                goto err;

        /* Find out which fragments are in front and at the back of us
         * in the chain of fragments so far.  We must know where to put
         * this fragment, right?
         */
        prev = NULL;
        for(next = fq->fragments; next != NULL; next = next->next) {
                if (FRAG6_CB(next)->offset >= offset)
                        break;  /* bingo! */
                prev = next;
        }

        /* We found where to put this one.  Check for overlap with
         * preceding fragment, and, if needed, align things so that
         * any overlaps are eliminated.
         */
        if (prev) {
                int i = (FRAG6_CB(prev)->offset + prev->len) - offset;

                if (i > 0) {
                        offset += i;
                        if (end <= offset)
                                goto err;
                        if (!pskb_pull(skb, i))
                                goto err;
                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                                skb->ip_summed = CHECKSUM_NONE;
                }
        }

        /* Look for overlap with succeeding segments.
         * If we can merge fragments, do it.
         */
        while (next && FRAG6_CB(next)->offset < end) {
                int i = end - FRAG6_CB(next)->offset; /* overlap is 'i' bytes */

                if (i < next->len) {
                        /* Eat head of the next overlapped fragment
                         * and leave the loop. The next ones cannot overlap.
                         */
                        if (!pskb_pull(next, i))
                                goto err;
                        FRAG6_CB(next)->offset += i;    /* next fragment */
                        fq->meat -= i;
                        if (next->ip_summed != CHECKSUM_UNNECESSARY)
                                next->ip_summed = CHECKSUM_NONE;
                        break;
                } else {
                        struct sk_buff *free_it = next;

                        /* Old fragment is completely overridden with
                         * new one drop it.
                         */
                        next = next->next;

                        if (prev)
                                prev->next = next;
                        else
                                fq->fragments = next;

                        fq->meat -= free_it->len;
                        frag_kfree_skb(free_it, NULL);
                }
        }

        FRAG6_CB(skb)->offset = offset;

        /* Insert this fragment in the chain of fragments. */
        skb->next = next;
        if (prev)
                prev->next = skb;
        else
                fq->fragments = skb;

        if (skb->dev)
                fq->iif = skb->dev->ifindex;
        skb->dev = NULL;
        skb_get_timestamp(skb, &fq->stamp);
        fq->meat += skb->len;
        atomic_add(skb->truesize, &ip6_frag_mem);

        /* The first fragment.
         * nhoffset is obtained from the first fragment, of course.
         */
        if (offset == 0) {
                fq->nhoffset = nhoff;
                fq->last_in |= FIRST_IN;
        }
        write_lock(&ip6_frag_lock);
        list_move_tail(&fq->lru_list, &ip6_frag_lru_list);
        write_unlock(&ip6_frag_lock);
        return;

err:
        IP6_INC_STATS(IPSTATS_MIB_REASMFAILS);
        kfree_skb(skb);
}

/*
 *      Check if this packet is complete.
 *      Returns NULL on failure by any reason, and pointer
 *      to current nexthdr field in reassembled frame.
 *
 *      It is called with locked fq, and caller must check that
 *      queue is eligible for reassembly i.e. it is not COMPLETE,
 *      the last and the first frames arrived and all the bits are here.
 */
static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff **skb_in,
                          struct net_device *dev)
{
        struct sk_buff *fp, *head = fq->fragments;
        int    payload_len;
        unsigned int nhoff;

        fq_kill(fq);

        BUG_TRAP(head != NULL);
        BUG_TRAP(FRAG6_CB(head)->offset == 0);

        /* Unfragmented part is taken from the first segment. */
        payload_len = (head->data - head->nh.raw) - sizeof(struct ipv6hdr) + fq->len - sizeof(struct frag_hdr);
        if (payload_len > IPV6_MAXPLEN)
                goto out_oversize;

        /* Head of list must not be cloned. */
        if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
                goto out_oom;

        /* If the first fragment is fragmented itself, we split
         * it to two chunks: the first with data and paged part
         * and the second, holding only fragments. */
        if (skb_shinfo(head)->frag_list) {
                struct sk_buff *clone;
                int i, plen = 0;

                if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
                        goto out_oom;
                clone->next = head->next;
                head->next = clone;
                skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
                skb_shinfo(head)->frag_list = NULL;
                for (i=0; i<skb_shinfo(head)->nr_frags; i++)
                        plen += skb_shinfo(head)->frags[i].size;
                clone->len = clone->data_len = head->data_len - plen;
                head->data_len -= clone->len;
                head->len -= clone->len;
                clone->csum = 0;
                clone->ip_summed = head->ip_summed;
                atomic_add(clone->truesize, &ip6_frag_mem);
        }

        /* We have to remove fragment header from datagram and to relocate
         * header in order to calculate ICV correctly. */
        nhoff = fq->nhoffset;
        head->nh.raw[nhoff] = head->h.raw[0];
        memmove(head->head + sizeof(struct frag_hdr), head->head, 
                (head->data - head->head) - sizeof(struct frag_hdr));
        head->mac.raw += sizeof(struct frag_hdr);
        head->nh.raw += sizeof(struct frag_hdr);

        skb_shinfo(head)->frag_list = head->next;
        head->h.raw = head->data;
        skb_push(head, head->data - head->nh.raw);
        atomic_sub(head->truesize, &ip6_frag_mem);

        for (fp=head->next; fp; fp = fp->next) {
                head->data_len += fp->len;
                head->len += fp->len;
                if (head->ip_summed != fp->ip_summed)
                        head->ip_summed = CHECKSUM_NONE;
                else if (head->ip_summed == CHECKSUM_COMPLETE)
                        head->csum = csum_add(head->csum, fp->csum);
                head->truesize += fp->truesize;
                atomic_sub(fp->truesize, &ip6_frag_mem);
        }

        head->next = NULL;
        head->dev = dev;
        skb_set_timestamp(head, &fq->stamp);
        head->nh.ipv6h->payload_len = htons(payload_len);
        IP6CB(head)->nhoff = nhoff;

        *skb_in = head;

        /* Yes, and fold redundant checksum back. 8) */
        if (head->ip_summed == CHECKSUM_COMPLETE)
                head->csum = csum_partial(head->nh.raw, head->h.raw-head->nh.raw, head->csum);

        IP6_INC_STATS_BH(IPSTATS_MIB_REASMOKS);
        fq->fragments = NULL;
        return 1;

out_oversize:
        if (net_ratelimit())
                printk(KERN_DEBUG "ip6_frag_reasm: payload len = %d\n", payload_len);
        goto out_fail;
out_oom:
        if (net_ratelimit())
                printk(KERN_DEBUG "ip6_frag_reasm: no memory for reassembly\n");
out_fail:
        IP6_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
        return -1;
}

static int ipv6_frag_rcv(struct sk_buff **skbp)
{
        struct sk_buff *skb = *skbp; 
        struct net_device *dev = skb->dev;
        struct frag_hdr *fhdr;
        struct frag_queue *fq;
        struct ipv6hdr *hdr;

        hdr = skb->nh.ipv6h;

        IP6_INC_STATS_BH(IPSTATS_MIB_REASMREQDS);

        /* Jumbo payload inhibits frag. header */
        if (hdr->payload_len==0) {
                IP6_INC_STATS(IPSTATS_MIB_INHDRERRORS);
                icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, skb->h.raw-skb->nh.raw);
                return -1;
        }
        if (!pskb_may_pull(skb, (skb->h.raw-skb->data)+sizeof(struct frag_hdr))) {
                IP6_INC_STATS(IPSTATS_MIB_INHDRERRORS);
                icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, skb->h.raw-skb->nh.raw);
                return -1;
        }

        hdr = skb->nh.ipv6h;
        fhdr = (struct frag_hdr *)skb->h.raw;

        if (!(fhdr->frag_off & htons(0xFFF9))) {
                /* It is not a fragmented frame */
                skb->h.raw += sizeof(struct frag_hdr);
                IP6_INC_STATS_BH(IPSTATS_MIB_REASMOKS);

                IP6CB(skb)->nhoff = (u8*)fhdr - skb->nh.raw;
                return 1;
        }

        if (atomic_read(&ip6_frag_mem) > sysctl_ip6frag_high_thresh)
                ip6_evictor();

        if ((fq = fq_find(fhdr->identification, &hdr->saddr, &hdr->daddr)) != NULL) {
                int ret = -1;

                spin_lock(&fq->lock);

                ip6_frag_queue(fq, skb, fhdr, IP6CB(skb)->nhoff);

                if (fq->last_in == (FIRST_IN|LAST_IN) &&
                    fq->meat == fq->len)
                        ret = ip6_frag_reasm(fq, skbp, dev);

                spin_unlock(&fq->lock);
                fq_put(fq, NULL);
                return ret;
        }

        IP6_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
        kfree_skb(skb);
        return -1;
}

static struct inet6_protocol frag_protocol =
{
        .handler        =       ipv6_frag_rcv,
        .flags          =       INET6_PROTO_NOPOLICY,
};

void __init ipv6_frag_init(void)
{
        if (inet6_add_protocol(&frag_protocol, IPPROTO_FRAGMENT) < 0)
                printk(KERN_ERR "ipv6_frag_init: Could not register protocol\n");

        ip6_frag_hash_rnd = (u32) ((num_physpages ^ (num_physpages>>7)) ^
                                   (jiffies ^ (jiffies >> 6)));

        init_timer(&ip6_frag_secret_timer);
        ip6_frag_secret_timer.function = ip6_frag_secret_rebuild;
        ip6_frag_secret_timer.expires = jiffies + sysctl_ip6frag_secret_interval;
        add_timer(&ip6_frag_secret_timer);
}