inet: add RCU protection to inet->opt

We lack proper synchronization to manipulate inet->opt ip_options

Problem is ip_make_skb() calls ip_setup_cork() and
ip_setup_cork() possibly makes a copy of ipc->opt (struct ip_options),
without any protection against another thread manipulating inet->opt.

Another thread can change inet->opt pointer and free old one under us.

Use RCU to protect inet->opt (changed to inet->inet_opt).

Instead of handling atomic refcounts, just copy ip_options when
necessary, to avoid cache line dirtying.

We cant insert an rcu_head in struct ip_options since its included in
skb->cb[], so this patch is large because I had to introduce a new
ip_options_rcu structure.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
static void icmp_address_reply(struct sk_buff *skb)
{
	struct rtable *rt = skb_rtable(skb);
	struct net_device *dev = skb->dev;
	struct in_device *in_dev;
	struct in_ifaddr *ifa;

	if (skb->len < 4 || !(rt->rt_flags&RTCF_DIRECTSRC))
		return;

	in_dev = __in_dev_get_rcu(dev);
	if (!in_dev)
		return;

	if (in_dev->ifa_list &&
	    IN_DEV_LOG_MARTIANS(in_dev) &&
	    IN_DEV_FORWARD(in_dev)) {
		__be32 _mask, *mp;

		mp = skb_header_pointer(skb, 0, sizeof(_mask), &_mask);
		BUG_ON(mp == NULL);
		for (ifa = in_dev->ifa_list; ifa; ifa = ifa->ifa_next) {
			if (*mp == ifa->ifa_mask &&
			    inet_ifa_match(rt->rt_src, ifa))
				break;
		}
		if (!ifa && net_ratelimit()) {
			printk(KERN_INFO "Wrong address mask %pI4 from %s/%pI4\n",
			       mp, dev->name, &rt->rt_src);
		}
	}
}

static void icmp_address_reply(struct sk_buff *skb)
{
	struct rtable *rt = skb_rtable(skb);
	struct net_device *dev = skb->dev;
	struct in_device *in_dev;
	struct in_ifaddr *ifa;

	if (skb->len < 4 || !(rt->rt_flags&RTCF_DIRECTSRC))
		return;

	in_dev = __in_dev_get_rcu(dev);
	if (!in_dev)
		return;

	if (in_dev->ifa_list &&
	    IN_DEV_LOG_MARTIANS(in_dev) &&
	    IN_DEV_FORWARD(in_dev)) {
		__be32 _mask, *mp;

		mp = skb_header_pointer(skb, 0, sizeof(_mask), &_mask);
		BUG_ON(mp == NULL);
		for (ifa = in_dev->ifa_list; ifa; ifa = ifa->ifa_next) {
			if (*mp == ifa->ifa_mask &&
			    inet_ifa_match(rt->rt_src, ifa))
				break;
		}
		if (!ifa && net_ratelimit()) {
			printk(KERN_INFO "Wrong address mask %pI4 from %s/%pI4\n",
			       mp, dev->name, &rt->rt_src);
		}
	}
}
