[PATCH] Re: Loopback address to eth0 interface and rooting goes wrong

Hello

Gary < gary.manchon (at) gmail.com > found a problem where he was unable
to recover from a bad network interface configuration 
(ifconfig eth0 127.0.0.1), ref 
http://www.uwsg.iu.edu/hypermail/linux/net/0801.2/0009.html

This was confirmed by several people.

I suspect that the problem might be this code in net/ipv4/devinet.c ,
which sets ifa_scope to RT_SCOPE_HOST if you configure a loopback
address (127/8) on any interface.  I guess it's there to protect us from
sending packets with a loopback source address, which woulnd't look too
good:

static int inet_set_ifa(struct net_device *dev, struct in_ifaddr *ifa)
{
	struct in_device *in_dev = __in_dev_get_rtnl(dev);

	ASSERT_RTNL();

	if (!in_dev) {
		inet_free_ifa(ifa);
		return -ENOBUFS;
	}
	ipv4_devconf_setall(in_dev);
	if (ifa->ifa_dev != in_dev) {
		BUG_TRAP(!ifa->ifa_dev);
		in_dev_hold(in_dev);
		ifa->ifa_dev = in_dev;
	}
	if (LOOPBACK(ifa->ifa_local))
		ifa->ifa_scope = RT_SCOPE_HOST;
	return inet_insert_ifa(ifa);
}



The real problem is that there's never anything resetting this scope if
you change the address later.  This patch adds scope reset when changing
the address.