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Commit a5a81f0b authored by Paul Marks's avatar Paul Marks Committed by David S. Miller
Browse files

ipv6: Fix default route failover when CONFIG_IPV6_ROUTER_PREF=n 

I believe this commit from 2008 was incorrect:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=398bcbebb6f721ac308df1e3d658c0029bb74503



When CONFIG_IPV6_ROUTER_PREF is disabled, the kernel should follow
RFC4861 section 6.3.6: if no route is NUD_VALID, then traffic should be
sprayed across all routers (indirectly triggering NUD) until one of them
becomes NUD_VALID.

However, the following experiment demonstrates that this does not work:

1) Connect to an IPv6 network.
2) Change the router's MAC (and link-local) address.

The kernel will lock onto the first router and never try the new one, even
if the first becomes unreachable.  This patch fixes the problem by
allowing rt6_check_neigh() to return 0; if all routers return 0, then
rt6_select() will fall back to round-robin behavior.

This patch should have no effect when CONFIG_IPV6_ROUTER_PREF=y.

Note that rt6_check_neigh() is only used in a boolean context, so I've
changed its return type accordingly.

Signed-off-by: default avatarPaul Marks <pmarks@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5d097109

net/ipv6/route.c

+10 −14
Original line number Diff line number Diff line
@@ -544,35 +544,32 @@ static inline int rt6_check_dev(struct rt6_info *rt, int oif) 
	return 0;

}



static inline int rt6_check_neigh(struct rt6_info *rt)

static inline bool rt6_check_neigh(struct rt6_info *rt)

{

	struct neighbour *neigh;

	int m;

	bool ret = false;



	neigh = rt->n;

	if (rt->rt6i_flags & RTF_NONEXTHOP ||

	    !(rt->rt6i_flags & RTF_GATEWAY))

		m = 1;

		ret = true;

	else if (neigh) {

		read_lock_bh(&neigh->lock);

		if (neigh->nud_state & NUD_VALID)

			m = 2;

			ret = true;

#ifdef CONFIG_IPV6_ROUTER_PREF

		else if (neigh->nud_state & NUD_FAILED)

			m = 0;

		else if (!(neigh->nud_state & NUD_FAILED))

			ret = true;

#endif

		else

			m = 1;

		read_unlock_bh(&neigh->lock);

	} else

		m = 0;

	return m;

	}

	return ret;

}



static int rt6_score_route(struct rt6_info *rt, int oif,

			   int strict)

{

	int m, n;

	int m;



	m = rt6_check_dev(rt, oif);

	if (!m && (strict & RT6_LOOKUP_F_IFACE))
@@ -580,8 +577,7 @@ static int rt6_score_route(struct rt6_info *rt, int oif, 
#ifdef CONFIG_IPV6_ROUTER_PREF

	m |= IPV6_DECODE_PREF(IPV6_EXTRACT_PREF(rt->rt6i_flags)) << 2;

#endif

	n = rt6_check_neigh(rt);

	if (!n && (strict & RT6_LOOKUP_F_REACHABLE))

	if (!rt6_check_neigh(rt) && (strict & RT6_LOOKUP_F_REACHABLE))

		return -1;

	return m;

}