Commit message: ipv6: discard overlapping fragment

RFC5722 prohibits reassembling fragments when some data overlaps.

Bug spotted by Zhang Zuotao <zuotao.zhang@6wind.com>.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2012-4444
CWE: NVD-CWE-noinfo
Vulnerability description: The ip6_frag_queue function in net/ipv6/reassembly.c in the Linux kernel before 2.6.36 allows remote attackers to bypass intended network restrictions via overlapping IPv6 fragments.

Project: linux
File: reassembly.c

fq_find(struct net *net, __be32 id, struct in6_addr *src, struct in6_addr *dst)
{
	struct inet_frag_queue *q;
	struct ip6_create_arg arg;
	unsigned int hash;

	arg.id = id;
	arg.user = IP6_DEFRAG_LOCAL_DELIVER;
	arg.src = src;
	arg.dst = dst;

	read_lock(&ip6_frags.lock);
	hash = inet6_hash_frag(id, src, dst, ip6_frags.rnd);

	q = inet_frag_find(&net->ipv6.frags, &ip6_frags, &arg, hash);
	if (q == NULL)
		return NULL;

	return container_of(q, struct frag_queue, q);
}

Project: linux
File: reassembly.c

static __inline__ void fq_kill(struct frag_queue *fq)
{
	inet_frag_kill(&fq->q, &ip6_frags);
}

Project: linux
File: reassembly.c

static __inline__ void fq_put(struct frag_queue *fq)
{
	inet_frag_put(&fq->q, &ip6_frags);
}

Project: linux
File: reassembly.c

unsigned int inet6_hash_frag(__be32 id, const struct in6_addr *saddr,
			     const struct in6_addr *daddr, u32 rnd)
{
	u32 a, b, c;

	a = (__force u32)saddr->s6_addr32[0];
	b = (__force u32)saddr->s6_addr32[1];
	c = (__force u32)saddr->s6_addr32[2];

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

	a += (__force u32)saddr->s6_addr32[3];
	b += (__force u32)daddr->s6_addr32[0];
	c += (__force u32)daddr->s6_addr32[1];
	__jhash_mix(a, b, c);

	a += (__force u32)daddr->s6_addr32[2];
	b += (__force u32)daddr->s6_addr32[3];
	c += (__force u32)id;
	__jhash_mix(a, b, c);

	return c & (INETFRAGS_HASHSZ - 1);
}

Project: linux
File: reassembly.c

static void ip6_evictor(struct net *net, struct inet6_dev *idev)
{
	int evicted;

	evicted = inet_frag_evictor(&net->ipv6.frags, &ip6_frags);
	if (evicted)
		IP6_ADD_STATS_BH(net, idev, IPSTATS_MIB_REASMFAILS, evicted);
}

Project: linux
File: reassembly.c

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

	fq = container_of((struct inet_frag_queue *)data, struct frag_queue, q);

	spin_lock(&fq->q.lock);

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

	fq_kill(fq);

	net = container_of(fq->q.net, struct net, ipv6.frags);
	rcu_read_lock();
	dev = dev_get_by_index_rcu(net, fq->iif);
	if (!dev)
		goto out_rcu_unlock;

	IP6_INC_STATS_BH(net, __in6_dev_get(dev), IPSTATS_MIB_REASMTIMEOUT);
	IP6_INC_STATS_BH(net, __in6_dev_get(dev), IPSTATS_MIB_REASMFAILS);

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

	/*
	   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->q.fragments->dev = dev;
	icmpv6_send(fq->q.fragments, ICMPV6_TIME_EXCEED, ICMPV6_EXC_FRAGTIME, 0);
out_rcu_unlock:
	rcu_read_unlock();
out:
	spin_unlock(&fq->q.lock);
	fq_put(fq);
}

Project: linux
File: reassembly.c

 void ip6_frag_init(struct inet_frag_queue *q, void *a)
 {
 	struct frag_queue *fq = container_of(q, struct frag_queue, q);
	struct ip6_create_arg *arg = a;

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

Project: linux
File: reassembly.c

int ip6_frag_match(struct inet_frag_queue *q, void *a)
{
	struct frag_queue *fq;
	struct ip6_create_arg *arg = a;

	fq = container_of(q, struct frag_queue, q);
	return (fq->id == arg->id && fq->user == arg->user &&
			ipv6_addr_equal(&fq->saddr, arg->src) &&
			ipv6_addr_equal(&fq->daddr, arg->dst));
 }

Project: linux
File: reassembly.c

int ip6_frag_mem(struct net *net)
{
	return atomic_read(&net->ipv6.frags.mem);
}

Project: linux
File: reassembly.c

int ip6_frag_nqueues(struct net *net)
{
	return net->ipv6.frags.nqueues;
}

Project: linux
File: reassembly.c

static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
			  struct net_device *dev)
{
	struct net *net = container_of(fq->q.net, struct net, ipv6.frags);
	struct sk_buff *fp, *head = fq->q.fragments;
	int    payload_len;
	unsigned int nhoff;

	fq_kill(fq);

	/* Make the one we just received the head. */
	if (prev) {
		head = prev->next;
		fp = skb_clone(head, GFP_ATOMIC);

		if (!fp)
			goto out_oom;

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

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

		kfree_skb(fq->q.fragments);
		fq->q.fragments = head;
	}

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

	/* Unfragmented part is taken from the first segment. */
	payload_len = ((head->data - skb_network_header(head)) -
		       sizeof(struct ipv6hdr) + fq->q.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_has_frags(head)) {
		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_frag_list_init(head);
		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, &fq->q.net->mem);
	}

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

	skb_shinfo(head)->frag_list = head->next;
	skb_reset_transport_header(head);
	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;
	}
	atomic_sub(head->truesize, &fq->q.net->mem);

	head->next = NULL;
	head->dev = dev;
	head->tstamp = fq->q.stamp;
	ipv6_hdr(head)->payload_len = htons(payload_len);
	IP6CB(head)->nhoff = nhoff;

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

	rcu_read_lock();
	IP6_INC_STATS_BH(net, __in6_dev_get(dev), IPSTATS_MIB_REASMOKS);
	rcu_read_unlock();
	fq->q.fragments = NULL;
	fq->q.fragments_tail = 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:
	rcu_read_lock();
	IP6_INC_STATS_BH(net, __in6_dev_get(dev), IPSTATS_MIB_REASMFAILS);
	rcu_read_unlock();
	return -1;
}

Project: linux
File: reassembly.c

static int __net_init ip6_frags_ns_sysctl_register(struct net *net)
{
	struct ctl_table *table;
	struct ctl_table_header *hdr;

	table = ip6_frags_ns_ctl_table;
	if (!net_eq(net, &init_net)) {
		table = kmemdup(table, sizeof(ip6_frags_ns_ctl_table), GFP_KERNEL);
		if (table == NULL)
			goto err_alloc;

		table[0].data = &net->ipv6.frags.high_thresh;
		table[1].data = &net->ipv6.frags.low_thresh;
		table[2].data = &net->ipv6.frags.timeout;
	}

	hdr = register_net_sysctl_table(net, net_ipv6_ctl_path, table);
	if (hdr == NULL)
		goto err_reg;

	net->ipv6.sysctl.frags_hdr = hdr;
	return 0;

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

Project: linux
File: reassembly.c

static inline int ip6_frags_ns_sysctl_register(struct net *net)
{
	return 0;
}

Project: linux
File: reassembly.c

static void __net_exit ip6_frags_ns_sysctl_unregister(struct net *net)
{
	struct ctl_table *table;

	table = net->ipv6.sysctl.frags_hdr->ctl_table_arg;
	unregister_net_sysctl_table(net->ipv6.sysctl.frags_hdr);
	if (!net_eq(net, &init_net))
		kfree(table);
}

Project: linux
File: reassembly.c

static inline void ip6_frags_ns_sysctl_unregister(struct net *net)
{
}

Project: linux
File: reassembly.c

static int ip6_frags_sysctl_register(void)
{
	ip6_ctl_header = register_net_sysctl_rotable(net_ipv6_ctl_path,
			ip6_frags_ctl_table);
	return ip6_ctl_header == NULL ? -ENOMEM : 0;
}

Project: linux
File: reassembly.c

static inline int ip6_frags_sysctl_register(void)
{
	return 0;
}

Project: linux
File: reassembly.c

static void ip6_frags_sysctl_unregister(void)
{
	unregister_net_sysctl_table(ip6_ctl_header);
}

Project: linux
File: reassembly.c

static unsigned int ip6_hashfn(struct inet_frag_queue *q)
{
	struct frag_queue *fq;

	fq = container_of(q, struct frag_queue, q);
	return inet6_hash_frag(fq->id, &fq->saddr, &fq->daddr, ip6_frags.rnd);
}

Project: linux
File: reassembly.c

void ipv6_frag_exit(void)
{
	inet_frags_fini(&ip6_frags);
	ip6_frags_sysctl_unregister();
	unregister_pernet_subsys(&ip6_frags_ops);
	inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
}

Project: linux
File: reassembly.c

int __init ipv6_frag_init(void)
{
	int ret;

	ret = inet6_add_protocol(&frag_protocol, IPPROTO_FRAGMENT);
	if (ret)
		goto out;

	ret = ip6_frags_sysctl_register();
	if (ret)
		goto err_sysctl;

	ret = register_pernet_subsys(&ip6_frags_ops);
	if (ret)
		goto err_pernet;

	ip6_frags.hashfn = ip6_hashfn;
	ip6_frags.constructor = ip6_frag_init;
	ip6_frags.destructor = NULL;
	ip6_frags.skb_free = NULL;
	ip6_frags.qsize = sizeof(struct frag_queue);
	ip6_frags.match = ip6_frag_match;
	ip6_frags.frag_expire = ip6_frag_expire;
	ip6_frags.secret_interval = 10 * 60 * HZ;
	inet_frags_init(&ip6_frags);
out:
	return ret;

err_pernet:
	ip6_frags_sysctl_unregister();
err_sysctl:
	inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
	goto out;
}

Project: linux
File: reassembly.c

static int ipv6_frag_rcv(struct sk_buff *skb)
{
	struct frag_hdr *fhdr;
	struct frag_queue *fq;
	struct ipv6hdr *hdr = ipv6_hdr(skb);
	struct net *net = dev_net(skb_dst(skb)->dev);

	IP6_INC_STATS_BH(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMREQDS);

	/* Jumbo payload inhibits frag. header */
	if (hdr->payload_len==0)
		goto fail_hdr;

	if (!pskb_may_pull(skb, (skb_transport_offset(skb) +
				 sizeof(struct frag_hdr))))
		goto fail_hdr;

	hdr = ipv6_hdr(skb);
	fhdr = (struct frag_hdr *)skb_transport_header(skb);

	if (!(fhdr->frag_off & htons(0xFFF9))) {
		/* It is not a fragmented frame */
		skb->transport_header += sizeof(struct frag_hdr);
		IP6_INC_STATS_BH(net,
				 ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMOKS);

		IP6CB(skb)->nhoff = (u8 *)fhdr - skb_network_header(skb);
		return 1;
	}

	if (atomic_read(&net->ipv6.frags.mem) > net->ipv6.frags.high_thresh)
		ip6_evictor(net, ip6_dst_idev(skb_dst(skb)));

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

		spin_lock(&fq->q.lock);

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

		spin_unlock(&fq->q.lock);
		fq_put(fq);
		return ret;
	}

	IP6_INC_STATS_BH(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMFAILS);
	kfree_skb(skb);
	return -1;

fail_hdr:
	IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_INHDRERRORS);
	icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, skb_network_header_len(skb));
	return -1;
}

Project: linux
File: reassembly.c

static void __net_exit ipv6_frags_exit_net(struct net *net)
{
	ip6_frags_ns_sysctl_unregister(net);
	inet_frags_exit_net(&net->ipv6.frags, &ip6_frags);
}

Project: linux
File: reassembly.c

static int __net_init ipv6_frags_init_net(struct net *net)
{
	net->ipv6.frags.high_thresh = IPV6_FRAG_HIGH_THRESH;
	net->ipv6.frags.low_thresh = IPV6_FRAG_LOW_THRESH;
	net->ipv6.frags.timeout = IPV6_FRAG_TIMEOUT;

	inet_frags_init_net(&net->ipv6.frags);

	return ip6_frags_ns_sysctl_register(net);
}