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  • ip_fragment.c 20.79 KiB
    // SPDX-License-Identifier: GPL-2.0
    /*
     * 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 <waltje@uWalt.NL.Mugnet.ORG>
     *		Alan Cox <alan@lxorguk.ukuu.org.uk>
     *
     * 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>
    #include <net/l3mdev.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 const char ip_frag_cache_name[] = "ip4-frags";
    
    /* Describe an entry in the "incomplete datagrams" queue. */
    struct ipq {
    	struct inet_frag_queue q;
    
    	u8		ecn; /* RFC3168 support */
    	u16		max_df_size; /* largest frag with DF set seen */
    	int             iif;
    	unsigned int    rid;
    	struct inet_peer *peer;
    };
    
    static u8 ip4_frag_ecn(u8 tos)
    {
    	return 1 << (tos & INET_ECN_MASK);
    }
    
    static struct inet_frags ip4_frags;
    
    static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
    			 struct net_device *dev);
    
    
    static void ip4_frag_init(struct inet_frag_queue *q, const 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);
    
    	const struct frag_v4_compare_key *key = a;
    
    	q->key.v4 = *key;
    	qp->ecn = 0;
    	qp->peer = q->net->max_dist ?
    		inet_getpeer_v4(net->ipv4.peers, key->saddr, key->vif, 1) :
    		NULL;
    }
    
    static 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 void ipq_put(struct ipq *ipq)
    {
    	inet_frag_put(&ipq->q);
    }
    
    /* 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);
    }
    
    static bool frag_expire_skip_icmp(u32 user)
    {
    	return user == IP_DEFRAG_AF_PACKET ||
    	       ip_defrag_user_in_between(user, IP_DEFRAG_CONNTRACK_IN,
    					 __IP_DEFRAG_CONNTRACK_IN_END) ||
    	       ip_defrag_user_in_between(user, IP_DEFRAG_CONNTRACK_BRIDGE_IN,
    					 __IP_DEFRAG_CONNTRACK_BRIDGE_IN);
    }
    
    /*
     * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
     */
    static void ip_expire(struct timer_list *t)
    {
    	struct inet_frag_queue *frag = from_timer(frag, t, timer);
    	const struct iphdr *iph;
    	struct sk_buff *head;
    	struct net *net;
    	struct ipq *qp;
    	int err;
    
    	qp = container_of(frag, struct ipq, q);
    	net = container_of(qp->q.net, struct net, ipv4.frags);
    
    	rcu_read_lock();
    	spin_lock(&qp->q.lock);
    
    	if (qp->q.flags & INET_FRAG_COMPLETE)
    		goto out;
    
    	ipq_kill(qp);
    	__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
    
    	head = qp->q.fragments;
    
    	__IP_INC_STATS(net, IPSTATS_MIB_REASMTIMEOUT);
    
    	if (!(qp->q.flags & INET_FRAG_FIRST_IN) || !head)
    		goto out;
    
    	head->dev = dev_get_by_index_rcu(net, qp->iif);
    	if (!head->dev)
    		goto out;
    
    
    	/* skb has no dst, perform route lookup again */
    	iph = ip_hdr(head);
    	err = ip_route_input_noref(head, iph->daddr, iph->saddr,
    					   iph->tos, head->dev);
    	if (err)
    		goto out;
    
    	/* Only an end host needs to send an ICMP
    	 * "Fragment Reassembly Timeout" message, per RFC792.
    	 */
    	if (frag_expire_skip_icmp(qp->q.key.v4.user) &&
    	    (skb_rtable(head)->rt_type != RTN_LOCAL))
    		goto out;
    
    	skb_get(head);
    	spin_unlock(&qp->q.lock);
    	icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
    	kfree_skb(head);
    	goto out_rcu_unlock;
    
    out:
    	spin_unlock(&qp->q.lock);
    out_rcu_unlock:
    	rcu_read_unlock();
    	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 struct ipq *ip_find(struct net *net, struct iphdr *iph,
    			   u32 user, int vif)
    {
    	struct frag_v4_compare_key key = {
    		.saddr = iph->saddr,
    		.daddr = iph->daddr,
    		.user = user,
    		.vif = vif,
    		.id = iph->id,
    		.protocol = iph->protocol,
    	};
    	struct inet_frag_queue *q;
    
    	q = inet_frag_find(&net->ipv4.frags, &key);
    	if (!q)
    		return NULL;
    
    	return container_of(q, struct ipq, q);
    }
    
    /* Is the fragment too far ahead to be part of ipq? */
    static int ip_frag_too_far(struct ipq *qp)
    {
    	struct inet_peer *peer = qp->peer;
    	unsigned int max = qp->q.net->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(net, IPSTATS_MIB_REASMFAILS);
    	}
    
    	return rc;
    }
    
    static int ip_frag_reinit(struct ipq *qp)
    {
    	struct sk_buff *fp;
    	unsigned int sum_truesize = 0;
    
    	if (!mod_timer(&qp->q.timer, jiffies + qp->q.net->timeout)) {
    		refcount_inc(&qp->q.refcnt);
    		return -ETIMEDOUT;
    	}
    
    	fp = qp->q.fragments;
    	do {
    		struct sk_buff *xp = fp->next;
    
    		sum_truesize += fp->truesize;
    		kfree_skb(fp);
    		fp = xp;
    	} while (fp);
    	sub_frag_mem_limit(qp->q.net, sum_truesize);
    
    	qp->q.flags = 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;
    	unsigned int fragsize;
    	int flags, offset;
    	int ihl, end;
    	int err = -ENOENT;
    	u8 ecn;
    
    	if (qp->q.flags & 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 - skb_network_offset(skb) - 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.flags & INET_FRAG_LAST_IN) && end != qp->q.len))
    			goto err;
    		qp->q.flags |= 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.flags & INET_FRAG_LAST_IN)
    				goto err;
    			qp->q.len = end;
    		}
    	}
    	if (end == offset)
    		goto err;
    
    	err = -ENOMEM;
    	if (!pskb_pull(skb, skb_network_offset(skb) + ihl))
    		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 || prev->ip_defrag_offset < offset) {
    		next = NULL;
    		goto found;
    	}
    	prev = NULL;
    	for (next = qp->q.fragments; next != NULL; next = next->next) {
    		if (next->ip_defrag_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 = (prev->ip_defrag_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 && next->ip_defrag_offset < end) {
    		int i = end - next->ip_defrag_offset; /* overlap is 'i' bytes */
    
    		if (i < next->len) {
    			int delta = -next->truesize;
    
    			/* Eat head of the next overlapped fragment
    			 * and leave the loop. The next ones cannot overlap.
    			 */
    			if (!pskb_pull(next, i))
    				goto err;
    			delta += next->truesize;
    			if (delta)
    				add_frag_mem_limit(qp->q.net, delta);
    			next->ip_defrag_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;
    			sub_frag_mem_limit(qp->q.net, free_it->truesize);
    			kfree_skb(free_it);
    		}
    	}
    
    	/* Note : skb->ip_defrag_offset and skb->dev share the same location */
    	dev = skb->dev;
    	if (dev)
    		qp->iif = dev->ifindex;
    	/* Makes sure compiler wont do silly aliasing games */
    	barrier();
    	skb->ip_defrag_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;
    
    	qp->q.stamp = skb->tstamp;
    	qp->q.meat += skb->len;
    	qp->ecn |= ecn;
    	add_frag_mem_limit(qp->q.net, skb->truesize);
    	if (offset == 0)
    		qp->q.flags |= INET_FRAG_FIRST_IN;
    
    	fragsize = skb->len + ihl;
    
    	if (fragsize > qp->q.max_size)
    		qp->q.max_size = fragsize;
    
    	if (ip_hdr(skb)->frag_off & htons(IP_DF) &&
    	    fragsize > qp->max_df_size)
    		qp->max_df_size = fragsize;
    
    	if (qp->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
    	    qp->q.meat == qp->q.len) {
    		unsigned long orefdst = skb->_skb_refdst;
    
    		skb->_skb_refdst = 0UL;
    		err = ip_frag_reasm(qp, prev, dev);
    		skb->_skb_refdst = orefdst;
    		return err;
    	}
    
    	skb_dst_drop(skb);
    	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;
    	u8 ecn;
    
    	ipq_kill(qp);
    
    	ecn = ip_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);
    	WARN_ON(head->ip_defrag_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_unclone(head, 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;
    
    		clone = alloc_skb(0, GFP_ATOMIC);
    		if (!clone)
    			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;
    		add_frag_mem_limit(qp->q.net, clone->truesize);
    	}
    
    	skb_shinfo(head)->frag_list = head->next;
    	skb_push(head, head->data - skb_network_header(head));
    
    	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;
    	}
    	sub_frag_mem_limit(qp->q.net, head->truesize);
    
    	head->next = NULL;
    	head->dev = dev;
    	head->tstamp = qp->q.stamp;
    	IPCB(head)->frag_max_size = max(qp->max_df_size, qp->q.max_size);
    
    	iph = ip_hdr(head);
    	iph->tot_len = htons(len);
    	iph->tos |= ecn;
    
    	/* When we set IP_DF on a refragmented skb we must also force a
    	 * call to ip_fragment to avoid forwarding a DF-skb of size s while
    	 * original sender only sent fragments of size f (where f < s).
    	 *
    	 * We only set DF/IPSKB_FRAG_PMTU if such DF fragment was the largest
    	 * frag seen to avoid sending tiny DF-fragments in case skb was built
    	 * from one very small df-fragment and one large non-df frag.
    	 */
    	if (qp->max_df_size == qp->q.max_size) {
    		IPCB(head)->flags |= IPSKB_FRAG_PMTU;
    		iph->frag_off = htons(IP_DF);
    	} else {
    		iph->frag_off = 0;
    	}
    
    	ip_send_check(iph);
    
    	__IP_INC_STATS(net, IPSTATS_MIB_REASMOKS);
    	qp->q.fragments = NULL;
    	qp->q.fragments_tail = NULL;
    	return 0;
    
    out_nomem:
    	net_dbg_ratelimited("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->q.key.v4.saddr);
    out_fail:
    	__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
    	return err;
    }
    
    /* Process an incoming IP datagram fragment. */
    int ip_defrag(struct net *net, struct sk_buff *skb, u32 user)
    {
    	struct net_device *dev = skb->dev ? : skb_dst(skb)->dev;
    	int vif = l3mdev_master_ifindex_rcu(dev);
    	struct ipq *qp;
    
    	__IP_INC_STATS(net, IPSTATS_MIB_REASMREQDS);
    	skb_orphan(skb);
    
    	/* Lookup (or create) queue header */
    	qp = ip_find(net, ip_hdr(skb), user, vif);
    	if (qp) {
    		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(net, IPSTATS_MIB_REASMFAILS);
    	kfree_skb(skb);
    	return -ENOMEM;
    }
    EXPORT_SYMBOL(ip_defrag);
    
    struct sk_buff *ip_check_defrag(struct net *net, struct sk_buff *skb, u32 user)
    {
    	struct iphdr iph;
    	int netoff;
    	u32 len;
    
    	if (skb->protocol != htons(ETH_P_IP))
    		return skb;
    
    	netoff = skb_network_offset(skb);
    
    	if (skb_copy_bits(skb, netoff, &iph, sizeof(iph)) < 0)
    		return skb;
    
    	if (iph.ihl < 5 || iph.version != 4)
    		return skb;
    
    	len = ntohs(iph.tot_len);
    	if (skb->len < netoff + 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, netoff + iph.ihl * 4))
    				return skb;
    			if (pskb_trim_rcsum(skb, netoff + len))
    				return skb;
    			memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
    			if (ip_defrag(net, skb, user))
    				return NULL;
    			skb_clear_hash(skb);
    		}
    	}
    	return skb;
    }
    EXPORT_SYMBOL(ip_check_defrag);
    
    #ifdef CONFIG_SYSCTL
    static int dist_min;
    
    static struct ctl_table ip4_frags_ns_ctl_table[] = {
    	{
    		.procname	= "ipfrag_high_thresh",
    		.data		= &init_net.ipv4.frags.high_thresh,
    		.maxlen		= sizeof(unsigned long),
    		.mode		= 0644,
    		.proc_handler	= proc_doulongvec_minmax,
    		.extra1		= &init_net.ipv4.frags.low_thresh
    	},
    	{
    		.procname	= "ipfrag_low_thresh",
    		.data		= &init_net.ipv4.frags.low_thresh,
    		.maxlen		= sizeof(unsigned long),
    		.mode		= 0644,
    		.proc_handler	= proc_doulongvec_minmax,
    		.extra2		= &init_net.ipv4.frags.high_thresh
    	},
    	{
    		.procname	= "ipfrag_time",
    		.data		= &init_net.ipv4.frags.timeout,
    		.maxlen		= sizeof(int),
    		.mode		= 0644,
    		.proc_handler	= proc_dointvec_jiffies,
    	},
    	{
    		.procname	= "ipfrag_max_dist",
    		.data		= &init_net.ipv4.frags.max_dist,
    		.maxlen		= sizeof(int),
    		.mode		= 0644,
    		.proc_handler	= proc_dointvec_minmax,
    		.extra1		= &dist_min,
    	},
    	{ }
    };
    
    /* secret interval has been deprecated */
    static int ip4_frags_secret_interval_unused;
    static struct ctl_table ip4_frags_ctl_table[] = {
    	{
    		.procname	= "ipfrag_secret_interval",
    		.data		= &ip4_frags_secret_interval_unused,
    		.maxlen		= sizeof(int),
    		.mode		= 0644,
    		.proc_handler	= proc_dointvec_jiffies,
    	},
    	{ }
    };
    
    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)
    			goto err_alloc;
    
    		table[0].data = &net->ipv4.frags.high_thresh;
    		table[0].extra1 = &net->ipv4.frags.low_thresh;
    		table[0].extra2 = &init_net.ipv4.frags.high_thresh;
    		table[1].data = &net->ipv4.frags.low_thresh;
    		table[1].extra2 = &net->ipv4.frags.high_thresh;
    		table[2].data = &net->ipv4.frags.timeout;
    		table[3].data = &net->ipv4.frags.max_dist;
    	}
    
    	hdr = register_net_sysctl(net, "net/ipv4", table);
    	if (!hdr)
    		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 __init ip4_frags_ctl_register(void)
    {
    	register_net_sysctl(&init_net, "net/ipv4", ip4_frags_ctl_table);
    }
    #else
    static int ip4_frags_ns_ctl_register(struct net *net)
    {
    	return 0;
    }
    
    static void ip4_frags_ns_ctl_unregister(struct net *net)
    {
    }
    
    static void __init ip4_frags_ctl_register(void)
    {
    }
    #endif
    
    static int __net_init ipv4_frags_init_net(struct net *net)
    {
    	int res;
    
    	/* Fragment cache limits.
    	 *
    	 * The fragment memory accounting code, (tries to) account for
    	 * the real memory usage, by measuring both the size of frag
    	 * queue struct (inet_frag_queue (ipv4:ipq/ipv6:frag_queue))
    	 * and the SKB's truesize.
    	 *
    	 * A 64K fragment consumes 129736 bytes (44*2944)+200
    	 * (1500 truesize == 2944, sizeof(struct ipq) == 200)
    	 *
    	 * We will commit 4MB at one time. Should we cross that limit
    	 * we will prune down to 3MB, making room for approx 8 big 64K
    	 * fragments 8x128k.
    	 */
    	net->ipv4.frags.high_thresh = 4 * 1024 * 1024;
    	net->ipv4.frags.low_thresh  = 3 * 1024 * 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;
    
    	net->ipv4.frags.max_dist = 64;
    	net->ipv4.frags.f = &ip4_frags;
    
    	res = inet_frags_init_net(&net->ipv4.frags);
    	if (res < 0)
    		return res;
    	res = ip4_frags_ns_ctl_register(net);
    	if (res < 0)
    		inet_frags_exit_net(&net->ipv4.frags);
    	return res;
    }
    
    static void __net_exit ipv4_frags_exit_net(struct net *net)
    {
    	ip4_frags_ns_ctl_unregister(net);
    	inet_frags_exit_net(&net->ipv4.frags);
    }
    
    static struct pernet_operations ip4_frags_ops = {
    	.init = ipv4_frags_init_net,
    	.exit = ipv4_frags_exit_net,
    };
    
    
    static u32 ip4_key_hashfn(const void *data, u32 len, u32 seed)
    {
    	return jhash2(data,
    		      sizeof(struct frag_v4_compare_key) / sizeof(u32), seed);
    }
    
    static u32 ip4_obj_hashfn(const void *data, u32 len, u32 seed)
    {
    	const struct inet_frag_queue *fq = data;
    
    	return jhash2((const u32 *)&fq->key.v4,
    		      sizeof(struct frag_v4_compare_key) / sizeof(u32), seed);
    }
    
    static int ip4_obj_cmpfn(struct rhashtable_compare_arg *arg, const void *ptr)
    {
    	const struct frag_v4_compare_key *key = arg->key;
    	const struct inet_frag_queue *fq = ptr;
    
    	return !!memcmp(&fq->key, key, sizeof(*key));
    }
    
    static const struct rhashtable_params ip4_rhash_params = {
    	.head_offset		= offsetof(struct inet_frag_queue, node),
    	.key_offset		= offsetof(struct inet_frag_queue, key),
    	.key_len		= sizeof(struct frag_v4_compare_key),
    	.hashfn			= ip4_key_hashfn,
    	.obj_hashfn		= ip4_obj_hashfn,
    	.obj_cmpfn		= ip4_obj_cmpfn,
    	.automatic_shrinking	= true,
    };
    
    void __init ipfrag_init(void)
    {
    	ip4_frags.constructor = ip4_frag_init;
    	ip4_frags.destructor = ip4_frag_free;
    	ip4_frags.qsize = sizeof(struct ipq);
    	ip4_frags.frag_expire = ip_expire;
    	ip4_frags.frags_cache_name = ip_frag_cache_name;
    	ip4_frags.rhash_params = ip4_rhash_params;
    	if (inet_frags_init(&ip4_frags))
    		panic("IP: failed to allocate ip4_frags cache\n");
    	ip4_frags_ctl_register();
    	register_pernet_subsys(&ip4_frags_ops);
    }