ip_fragment.c

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/*
 * INET     An implementation of the TCP/IP protocol suite for the LINUX
 *      operating system.  INET is implemented using the  BSD Socket
 *      interface as the means of communication with the user level.
 *
 *      The IP fragmentation functionality.
 *
 * Authors: Fred N. van Kempen <[email protected]>
 *      Alan Cox <[email protected]>
 *
 * Fixes:
 *      Alan Cox    :   Split from ip.c , see ip_input.c for history.
 *      David S. Miller :   Begin massive cleanup...
 *      Andi Kleen  :   Add sysctls.
 *      xxxx        :   Overlapfrag bug.
 *      Ultima          :       ip_expire() kernel panic.
 *      Bill Hawes  :   Frag accounting and evictor fixes.
 *      John McDonald   :   0 length frag bug.
 *      Alexey Kuznetsov:   SMP races, threading, cleanup.
 *      Patrick McHardy :   LRU queue of frag heads for evictor.
 */

#define pr_fmt(fmt) "IPv4: " fmt

#include <linux/compiler.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/jiffies.h>
#include <linux/skbuff.h>
#include <linux/list.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <linux/netdevice.h>
#include <linux/jhash.h>
#include <linux/random.h>
#include <linux/slab.h>
#include <net/route.h>
#include <net/dst.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/checksum.h>
#include <net/inetpeer.h>
#include <net/inet_frag.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/inet.h>
#include <linux/netfilter_ipv4.h>
#include <net/inet_ecn.h>

/* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
 * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
 * as well. Or notify me, at least. --ANK
 */

static int sysctl_ipfrag_max_dist __read_mostly = 64;

struct ipfrag_skb_cb
{
    struct inet_skb_parm    h;
    int         offset;
};

#define FRAG_CB(skb)    ((struct ipfrag_skb_cb *)((skb)->cb))

/* Describe an entry in the "incomplete datagrams" queue. */
struct ipq {
    struct inet_frag_queue q;

    u32     user;
    __be32      saddr;
    __be32      daddr;
    __be16      id;
    u8      protocol;
    u8      ecn; /* RFC3168 support */
    int             iif;
    unsigned int    rid;
    struct inet_peer *peer;
};

/* RFC 3168 support :
 * We want to check ECN values of all fragments, do detect invalid combinations.
 * In ipq->ecn, we store the OR value of each ip4_frag_ecn() fragment value.
 */
#define IPFRAG_ECN_NOT_ECT  0x01 /* one frag had ECN_NOT_ECT */
#define IPFRAG_ECN_ECT_1    0x02 /* one frag had ECN_ECT_1 */
#define IPFRAG_ECN_ECT_0    0x04 /* one frag had ECN_ECT_0 */
#define IPFRAG_ECN_CE       0x08 /* one frag had ECN_CE */

static inline u8 ip4_frag_ecn(u8 tos)
{
    return 1 << (tos & INET_ECN_MASK);
}

/* Given the OR values of all fragments, apply RFC 3168 5.3 requirements
 * Value : 0xff if frame should be dropped.
 *         0 or INET_ECN_CE value, to be ORed in to final iph->tos field
 */
static const u8 ip4_frag_ecn_table[16] = {
    /* at least one fragment had CE, and others ECT_0 or ECT_1 */
    [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0]          = INET_ECN_CE,
    [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1]          = INET_ECN_CE,
    [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1]   = INET_ECN_CE,

    /* invalid combinations : drop frame */
    [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE] = 0xff,
    [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0] = 0xff,
    [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_1] = 0xff,
    [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
    [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0] = 0xff,
    [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1] = 0xff,
    [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
};

static struct inet_frags ip4_frags;

int ip_frag_nqueues(struct net *net)
{
    return net->ipv4.frags.nqueues;
}

int ip_frag_mem(struct net *net)
{
    return atomic_read(&net->ipv4.frags.mem);
}

static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
             struct net_device *dev);

struct ip4_create_arg {
    struct iphdr *iph;
    u32 user;
};

static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot)
{
    return jhash_3words((__force u32)id << 16 | prot,
                (__force u32)saddr, (__force u32)daddr,
                ip4_frags.rnd) & (INETFRAGS_HASHSZ - 1);
}

static unsigned int ip4_hashfn(struct inet_frag_queue *q)
{
    struct ipq *ipq;

    ipq = container_of(q, struct ipq, q);
    return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol);
}

static bool ip4_frag_match(struct inet_frag_queue *q, void *a)
{
    struct ipq *qp;
    struct ip4_create_arg *arg = a;

    qp = container_of(q, struct ipq, q);
    return  qp->id == arg->iph->id &&
        qp->saddr == arg->iph->saddr &&
        qp->daddr == arg->iph->daddr &&
        qp->protocol == arg->iph->protocol &&
        qp->user == arg->user;
}

/* Memory Tracking Functions. */
static void frag_kfree_skb(struct netns_frags *nf, struct sk_buff *skb)
{
    atomic_sub(skb->truesize, &nf->mem);
    kfree_skb(skb);
}

static void ip4_frag_init(struct inet_frag_queue *q, void *a)
{
    struct ipq *qp = container_of(q, struct ipq, q);
    struct netns_ipv4 *ipv4 = container_of(q->net, struct netns_ipv4,
                           frags);
    struct net *net = container_of(ipv4, struct net, ipv4);

    struct ip4_create_arg *arg = a;

    qp->protocol = arg->iph->protocol;
    qp->id = arg->iph->id;
    qp->ecn = ip4_frag_ecn(arg->iph->tos);
    qp->saddr = arg->iph->saddr;
    qp->daddr = arg->iph->daddr;
    qp->user = arg->user;
    qp->peer = sysctl_ipfrag_max_dist ?
        inet_getpeer_v4(net->ipv4.peers, arg->iph->saddr, 1) : NULL;
}

static __inline__ void ip4_frag_free(struct inet_frag_queue *q)
{
    struct ipq *qp;

    qp = container_of(q, struct ipq, q);
    if (qp->peer)
        inet_putpeer(qp->peer);
}


/* Destruction primitives. */

static __inline__ void ipq_put(struct ipq *ipq)
{
    inet_frag_put(&ipq->q, &ip4_frags);
}

/* Kill ipq entry. It is not destroyed immediately,
 * because caller (and someone more) holds reference count.
 */
static void ipq_kill(struct ipq *ipq)
{
    inet_frag_kill(&ipq->q, &ip4_frags);
}

/* Memory limiting on fragments.  Evictor trashes the oldest
 * fragment queue until we are back under the threshold.
 */
static void ip_evictor(struct net *net)
{
    int evicted;

    evicted = inet_frag_evictor(&net->ipv4.frags, &ip4_frags, false);
    if (evicted)
        IP_ADD_STATS_BH(net, IPSTATS_MIB_REASMFAILS, evicted);
}

/*
 * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
 */
static void ip_expire(unsigned long arg)
{
    struct ipq *qp;
    struct net *net;

    qp = container_of((struct inet_frag_queue *) arg, struct ipq, q);
    net = container_of(qp->q.net, struct net, ipv4.frags);

    spin_lock(&qp->q.lock);

    if (qp->q.last_in & INET_FRAG_COMPLETE)
        goto out;

    ipq_kill(qp);

    IP_INC_STATS_BH(net, IPSTATS_MIB_REASMTIMEOUT);
    IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);

    if ((qp->q.last_in & INET_FRAG_FIRST_IN) && qp->q.fragments != NULL) {
        struct sk_buff *head = qp->q.fragments;
        const struct iphdr *iph;
        int err;

        rcu_read_lock();
        head->dev = dev_get_by_index_rcu(net, qp->iif);
        if (!head->dev)
            goto out_rcu_unlock;

        /* skb dst is stale, drop it, and perform route lookup again */
        skb_dst_drop(head);
        iph = ip_hdr(head);
        err = ip_route_input_noref(head, iph->daddr, iph->saddr,
                       iph->tos, head->dev);
        if (err)
            goto out_rcu_unlock;

        /*
         * Only an end host needs to send an ICMP
         * "Fragment Reassembly Timeout" message, per RFC792.
         */
        if (qp->user == IP_DEFRAG_AF_PACKET ||
            (qp->user == IP_DEFRAG_CONNTRACK_IN &&
             skb_rtable(head)->rt_type != RTN_LOCAL))
            goto out_rcu_unlock;


        /* Send an ICMP "Fragment Reassembly Timeout" message. */
        icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
out_rcu_unlock:
        rcu_read_unlock();
    }
out:
    spin_unlock(&qp->q.lock);
    ipq_put(qp);
}

/* Find the correct entry in the "incomplete datagrams" queue for
 * this IP datagram, and create new one, if nothing is found.
 */
static inline struct ipq *ip_find(struct net *net, struct iphdr *iph, u32 user)
{
    struct inet_frag_queue *q;
    struct ip4_create_arg arg;
    unsigned int hash;

    arg.iph = iph;
    arg.user = user;

    read_lock(&ip4_frags.lock);
    hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);

    q = inet_frag_find(&net->ipv4.frags, &ip4_frags, &arg, hash);
    if (q == NULL)
        goto out_nomem;

    return container_of(q, struct ipq, q);

out_nomem:
    LIMIT_NETDEBUG(KERN_ERR pr_fmt("ip_frag_create: no memory left !\n"));
    return NULL;
}

/* Is the fragment too far ahead to be part of ipq? */
static inline int ip_frag_too_far(struct ipq *qp)
{
    struct inet_peer *peer = qp->peer;
    unsigned int max = sysctl_ipfrag_max_dist;
    unsigned int start, end;

    int rc;

    if (!peer || !max)
        return 0;

    start = qp->rid;
    end = atomic_inc_return(&peer->rid);
    qp->rid = end;

    rc = qp->q.fragments && (end - start) > max;

    if (rc) {
        struct net *net;

        net = container_of(qp->q.net, struct net, ipv4.frags);
        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
    }

    return rc;
}

static int ip_frag_reinit(struct ipq *qp)
{
    struct sk_buff *fp;

    if (!mod_timer(&qp->q.timer, jiffies + qp->q.net->timeout)) {
        atomic_inc(&qp->q.refcnt);
        return -ETIMEDOUT;
    }

    fp = qp->q.fragments;
    do {
        struct sk_buff *xp = fp->next;
        frag_kfree_skb(qp->q.net, fp);
        fp = xp;
    } while (fp);

    qp->q.last_in = 0;
    qp->q.len = 0;
    qp->q.meat = 0;
    qp->q.fragments = NULL;
    qp->q.fragments_tail = NULL;
    qp->iif = 0;
    qp->ecn = 0;

    return 0;
}

/* Add new segment to existing queue. */
static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
{
    struct sk_buff *prev, *next;
    struct net_device *dev;
    int flags, offset;
    int ihl, end;
    int err = -ENOENT;
    u8 ecn;

    if (qp->q.last_in & INET_FRAG_COMPLETE)
        goto err;

    if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
        unlikely(ip_frag_too_far(qp)) &&
        unlikely(err = ip_frag_reinit(qp))) {
        ipq_kill(qp);
        goto err;
    }

    ecn = ip4_frag_ecn(ip_hdr(skb)->tos);
    offset = ntohs(ip_hdr(skb)->frag_off);
    flags = offset & ~IP_OFFSET;
    offset &= IP_OFFSET;
    offset <<= 3;       /* offset is in 8-byte chunks */
    ihl = ip_hdrlen(skb);

    /* Determine the position of this fragment. */
    end = offset + skb->len - ihl;
    err = -EINVAL;

    /* Is this the final fragment? */
    if ((flags & IP_MF) == 0) {
        /* If we already have some bits beyond end
         * or have different end, the segment is corrupted.
         */
        if (end < qp->q.len ||
            ((qp->q.last_in & INET_FRAG_LAST_IN) && end != qp->q.len))
            goto err;
        qp->q.last_in |= INET_FRAG_LAST_IN;
        qp->q.len = end;
    } else {
        if (end&7) {
            end &= ~7;
            if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                skb->ip_summed = CHECKSUM_NONE;
        }
        if (end > qp->q.len) {
            /* Some bits beyond end -> corruption. */
            if (qp->q.last_in & INET_FRAG_LAST_IN)
                goto err;
            qp->q.len = end;
        }
    }
    if (end == offset)
        goto err;

    err = -ENOMEM;
    if (pskb_pull(skb, ihl) == NULL)
        goto err;

    err = pskb_trim_rcsum(skb, end - offset);
    if (err)
        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 = qp->q.fragments_tail;
    if (!prev || FRAG_CB(prev)->offset < offset) {
        next = NULL;
        goto found;
    }
    prev = NULL;
    for (next = qp->q.fragments; next != NULL; next = next->next) {
        if (FRAG_CB(next)->offset >= offset)
            break;  /* bingo! */
        prev = next;
    }

found:
    /* 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 = (FRAG_CB(prev)->offset + prev->len) - offset;

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

    err = -ENOMEM;

    while (next && FRAG_CB(next)->offset < end) {
        int i = end - FRAG_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;
            FRAG_CB(next)->offset += i;
            qp->q.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
                qp->q.fragments = next;

            qp->q.meat -= free_it->len;
            frag_kfree_skb(qp->q.net, free_it);
        }
    }

    FRAG_CB(skb)->offset = offset;

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

    dev = skb->dev;
    if (dev) {
        qp->iif = dev->ifindex;
        skb->dev = NULL;
    }
    qp->q.stamp = skb->tstamp;
    qp->q.meat += skb->len;
    qp->ecn |= ecn;
    atomic_add(skb->truesize, &qp->q.net->mem);
    if (offset == 0)
        qp->q.last_in |= INET_FRAG_FIRST_IN;

    if (ip_hdr(skb)->frag_off & htons(IP_DF) &&
        skb->len + ihl > qp->q.max_size)
        qp->q.max_size = skb->len + ihl;

    if (qp->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
        qp->q.meat == qp->q.len)
        return ip_frag_reasm(qp, prev, dev);

    write_lock(&ip4_frags.lock);
    list_move_tail(&qp->q.lru_list, &qp->q.net->lru_list);
    write_unlock(&ip4_frags.lock);
    return -EINPROGRESS;

err:
    kfree_skb(skb);
    return err;
}


/* Build a new IP datagram from all its fragments. */

static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
             struct net_device *dev)
{
    struct net *net = container_of(qp->q.net, struct net, ipv4.frags);
    struct iphdr *iph;
    struct sk_buff *fp, *head = qp->q.fragments;
    int len;
    int ihlen;
    int err;
    int sum_truesize;
    u8 ecn;

    ipq_kill(qp);

    ecn = ip4_frag_ecn_table[qp->ecn];
    if (unlikely(ecn == 0xff)) {
        err = -EINVAL;
        goto out_fail;
    }
    /* Make the one we just received the head. */
    if (prev) {
        head = prev->next;
        fp = skb_clone(head, GFP_ATOMIC);
        if (!fp)
            goto out_nomem;

        fp->next = head->next;
        if (!fp->next)
            qp->q.fragments_tail = fp;
        prev->next = fp;

        skb_morph(head, qp->q.fragments);
        head->next = qp->q.fragments->next;

        consume_skb(qp->q.fragments);
        qp->q.fragments = head;
    }

    WARN_ON(head == NULL);
    WARN_ON(FRAG_CB(head)->offset != 0);

    /* Allocate a new buffer for the datagram. */
    ihlen = ip_hdrlen(head);
    len = ihlen + qp->q.len;

    err = -E2BIG;
    if (len > 65535)
        goto out_oversize;

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

    /* 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_has_frag_list(head)) {
        struct sk_buff *clone;
        int i, plen = 0;

        if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
            goto out_nomem;
        clone->next = head->next;
        head->next = clone;
        skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
        skb_frag_list_init(head);
        for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
            plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
        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, &qp->q.net->mem);
    }

    skb_push(head, head->data - skb_network_header(head));

    sum_truesize = head->truesize;
    for (fp = head->next; fp;) {
        bool headstolen;
        int delta;
        struct sk_buff *next = fp->next;

        sum_truesize += fp->truesize;
        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);

        if (skb_try_coalesce(head, fp, &headstolen, &delta)) {
            kfree_skb_partial(fp, headstolen);
        } else {
            if (!skb_shinfo(head)->frag_list)
                skb_shinfo(head)->frag_list = fp;
            head->data_len += fp->len;
            head->len += fp->len;
            head->truesize += fp->truesize;
        }
        fp = next;
    }
    atomic_sub(sum_truesize, &qp->q.net->mem);

    head->next = NULL;
    head->dev = dev;
    head->tstamp = qp->q.stamp;
    IPCB(head)->frag_max_size = qp->q.max_size;

    iph = ip_hdr(head);
    /* max_size != 0 implies at least one fragment had IP_DF set */
    iph->frag_off = qp->q.max_size ? htons(IP_DF) : 0;
    iph->tot_len = htons(len);
    iph->tos |= ecn;
    IP_INC_STATS_BH(net, IPSTATS_MIB_REASMOKS);
    qp->q.fragments = NULL;
    qp->q.fragments_tail = NULL;
    return 0;

out_nomem:
    LIMIT_NETDEBUG(KERN_ERR pr_fmt("queue_glue: no memory for gluing queue %p\n"),
               qp);
    err = -ENOMEM;
    goto out_fail;
out_oversize:
    net_info_ratelimited("Oversized IP packet from %pI4\n", &qp->saddr);
out_fail:
    IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
    return err;
}

/* Process an incoming IP datagram fragment. */
int ip_defrag(struct sk_buff *skb, u32 user)
{
    struct ipq *qp;
    struct net *net;

    net = skb->dev ? dev_net(skb->dev) : dev_net(skb_dst(skb)->dev);
    IP_INC_STATS_BH(net, IPSTATS_MIB_REASMREQDS);

    /* Start by cleaning up the memory. */
    ip_evictor(net);

    /* Lookup (or create) queue header */
    if ((qp = ip_find(net, ip_hdr(skb), user)) != NULL) {
        int ret;

        spin_lock(&qp->q.lock);

        ret = ip_frag_queue(qp, skb);

        spin_unlock(&qp->q.lock);
        ipq_put(qp);
        return ret;
    }

    IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
    kfree_skb(skb);
    return -ENOMEM;
}
EXPORT_SYMBOL(ip_defrag);

struct sk_buff *ip_check_defrag(struct sk_buff *skb, u32 user)
{
    struct iphdr iph;
    u32 len;

    if (skb->protocol != htons(ETH_P_IP))
        return skb;

    if (!skb_copy_bits(skb, 0, &iph, sizeof(iph)))
        return skb;

    if (iph.ihl < 5 || iph.version != 4)
        return skb;

    len = ntohs(iph.tot_len);
    if (skb->len < len || len < (iph.ihl * 4))
        return skb;

    if (ip_is_fragment(&iph)) {
        skb = skb_share_check(skb, GFP_ATOMIC);
        if (skb) {
            if (!pskb_may_pull(skb, iph.ihl*4))
                return skb;
            if (pskb_trim_rcsum(skb, len))
                return skb;
            memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
            if (ip_defrag(skb, user))
                return NULL;
            skb->rxhash = 0;
        }
    }
    return skb;
}
EXPORT_SYMBOL(ip_check_defrag);

#ifdef CONFIG_SYSCTL
static int zero;

static struct ctl_table ip4_frags_ns_ctl_table[] = {
    {
        .procname   = "ipfrag_high_thresh",
        .data       = &init_net.ipv4.frags.high_thresh,
        .maxlen     = sizeof(int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec
    },
    {
        .procname   = "ipfrag_low_thresh",
        .data       = &init_net.ipv4.frags.low_thresh,
        .maxlen     = sizeof(int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec
    },
    {
        .procname   = "ipfrag_time",
        .data       = &init_net.ipv4.frags.timeout,
        .maxlen     = sizeof(int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec_jiffies,
    },
    { }
};

static struct ctl_table ip4_frags_ctl_table[] = {
    {
        .procname   = "ipfrag_secret_interval",
        .data       = &ip4_frags.secret_interval,
        .maxlen     = sizeof(int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec_jiffies,
    },
    {
        .procname   = "ipfrag_max_dist",
        .data       = &sysctl_ipfrag_max_dist,
        .maxlen     = sizeof(int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec_minmax,
        .extra1     = &zero
    },
    { }
};

static int __net_init ip4_frags_ns_ctl_register(struct net *net)
{
    struct ctl_table *table;
    struct ctl_table_header *hdr;

    table = ip4_frags_ns_ctl_table;
    if (!net_eq(net, &init_net)) {
        table = kmemdup(table, sizeof(ip4_frags_ns_ctl_table), GFP_KERNEL);
        if (table == NULL)
            goto err_alloc;

        table[0].data = &net->ipv4.frags.high_thresh;
        table[1].data = &net->ipv4.frags.low_thresh;
        table[2].data = &net->ipv4.frags.timeout;
    }

    hdr = register_net_sysctl(net, "net/ipv4", table);
    if (hdr == NULL)
        goto err_reg;

    net->ipv4.frags_hdr = hdr;
    return 0;

err_reg:
    if (!net_eq(net, &init_net))
        kfree(table);
err_alloc:
    return -ENOMEM;
}

static void __net_exit ip4_frags_ns_ctl_unregister(struct net *net)
{
    struct ctl_table *table;

    table = net->ipv4.frags_hdr->ctl_table_arg;
    unregister_net_sysctl_table(net->ipv4.frags_hdr);
    kfree(table);
}

static void ip4_frags_ctl_register(void)
{
    register_net_sysctl(&init_net, "net/ipv4", ip4_frags_ctl_table);
}
#else
static inline int ip4_frags_ns_ctl_register(struct net *net)
{
    return 0;
}

static inline void ip4_frags_ns_ctl_unregister(struct net *net)
{
}

static inline void ip4_frags_ctl_register(void)
{
}
#endif

static int __net_init ipv4_frags_init_net(struct net *net)
{
    /*
     * Fragment cache limits. We will commit 256K at one time. Should we
     * cross that limit we will prune down to 192K. This should cope with
     * even the most extreme cases without allowing an attacker to
     * measurably harm machine performance.
     */
    net->ipv4.frags.high_thresh = 256 * 1024;
    net->ipv4.frags.low_thresh = 192 * 1024;
    /*
     * Important NOTE! Fragment queue must be destroyed before MSL expires.
     * RFC791 is wrong proposing to prolongate timer each fragment arrival
     * by TTL.
     */
    net->ipv4.frags.timeout = IP_FRAG_TIME;

    inet_frags_init_net(&net->ipv4.frags);

    return ip4_frags_ns_ctl_register(net);
}

static void __net_exit ipv4_frags_exit_net(struct net *net)
{
    ip4_frags_ns_ctl_unregister(net);
    inet_frags_exit_net(&net->ipv4.frags, &ip4_frags);
}

static struct pernet_operations ip4_frags_ops = {
    .init = ipv4_frags_init_net,
    .exit = ipv4_frags_exit_net,
};

void __init ipfrag_init(void)
{
    ip4_frags_ctl_register();
    register_pernet_subsys(&ip4_frags_ops);
    ip4_frags.hashfn = ip4_hashfn;
    ip4_frags.constructor = ip4_frag_init;
    ip4_frags.destructor = ip4_frag_free;
    ip4_frags.skb_free = NULL;
    ip4_frags.qsize = sizeof(struct ipq);
    ip4_frags.match = ip4_frag_match;
    ip4_frags.frag_expire = ip_expire;
    ip4_frags.secret_interval = 10 * 60 * HZ;
    inet_frags_init(&ip4_frags);
}