Commit a5a81f0b authored Dec 03, 2012 by Paul Marks Committed by David S. Miller Dec 03, 2012

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: Paul Marks <pmarks@google.com>
Signed-off-by: David 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;
		}

Admin message