net: Compute protocol sequence numbers and fragment IDs using MD5.

Computers have become a lot faster since we compromised on the
partial MD4 hash which we use currently for performance reasons.

MD5 is a much safer choice, and is inline with both RFC1948 and
other ISS generators (OpenBSD, Solaris, etc.)

Furthermore, only having 24-bits of the sequence number be truly
unpredictable is a very serious limitation.  So the periodic
regeneration and 8-bit counter have been removed.  We compute and
use a full 32-bit sequence number.

For ipv6, DCCP was found to use a 32-bit truncated initial sequence
number (it needs 43-bits) and that is fixed here as well.

Reported-by: Dan Kaminsky <dan@doxpara.com>
Tested-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>
void ip_rt_get_source(u8 *addr, struct sk_buff *skb, struct rtable *rt)
{
	__be32 src;

	if (rt_is_output_route(rt))
		src = ip_hdr(skb)->saddr;
	else {
		struct fib_result res;
		struct flowi4 fl4;
		struct iphdr *iph;

		iph = ip_hdr(skb);

		memset(&fl4, 0, sizeof(fl4));
		fl4.daddr = iph->daddr;
		fl4.saddr = iph->saddr;
		fl4.flowi4_tos = RT_TOS(iph->tos);
		fl4.flowi4_oif = rt->dst.dev->ifindex;
		fl4.flowi4_iif = skb->dev->ifindex;
		fl4.flowi4_mark = skb->mark;

		rcu_read_lock();
		if (fib_lookup(dev_net(rt->dst.dev), &fl4, &res) == 0)
			src = FIB_RES_PREFSRC(dev_net(rt->dst.dev), res);
		else
			src = inet_select_addr(rt->dst.dev, rt->rt_gateway,
					RT_SCOPE_UNIVERSE);
		rcu_read_unlock();
	}
	memcpy(addr, &src, 4);
}

void ip_rt_get_source(u8 *addr, struct sk_buff *skb, struct rtable *rt)
{
	__be32 src;

	if (rt_is_output_route(rt))
		src = ip_hdr(skb)->saddr;
	else {
		struct fib_result res;
		struct flowi4 fl4;
		struct iphdr *iph;

		iph = ip_hdr(skb);

		memset(&fl4, 0, sizeof(fl4));
		fl4.daddr = iph->daddr;
		fl4.saddr = iph->saddr;
		fl4.flowi4_tos = RT_TOS(iph->tos);
		fl4.flowi4_oif = rt->dst.dev->ifindex;
		fl4.flowi4_iif = skb->dev->ifindex;
		fl4.flowi4_mark = skb->mark;

		rcu_read_lock();
		if (fib_lookup(dev_net(rt->dst.dev), &fl4, &res) == 0)
			src = FIB_RES_PREFSRC(dev_net(rt->dst.dev), res);
		else
			src = inet_select_addr(rt->dst.dev, rt->rt_gateway,
					RT_SCOPE_UNIVERSE);
		rcu_read_unlock();
	}
	memcpy(addr, &src, 4);
}
