net: ipv6: Fixup device for anycast routes during copy

Florian reported a breakage with anycast routes due to commit 4832c30d5458 ("net: ipv6: put host and anycast routes on device with address"). Prior to this commit anycast routes were added against the loopback device causing repetitive route entries with no insight into why they existed. e.g.:

  $ ip -6 ro ls  table local type anycast
  anycast 2001:db8:1:: dev lo proto kernel metric 0 pref medium
  anycast 2001:db8:2:: dev lo proto kernel metric 0 pref medium
  anycast fe80:: dev lo proto kernel metric 0 pref medium
  anycast fe80:: dev lo proto kernel metric 0 pref medium

The point of commit 4832c30d5458 is to add the routes using the device with the address which is causing the route to be added. e.g.,:

  $ ip -6 ro ls  table local type anycast
  anycast 2001:db8:1:: dev eth1 proto kernel metric 0 pref medium
  anycast 2001:db8:2:: dev eth2 proto kernel metric 0 pref medium
  anycast fe80:: dev eth2 proto kernel metric 0 pref medium
  anycast fe80:: dev eth1 proto kernel metric 0 pref medium

For traffic to work as it did before, the dst device needs to be switched to the loopback when the copy is created similar to local routes.

---
 net/ipv6/route.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 05eb7bc36156..1c29d9bcedc3 100644
@@ -1019,7 +1019,7 @@ static struct net_device *ip6_rt_get_dev_rcu(struct rt6_info *rt)
 {
 	struct net_device *dev = rt->dst.dev;
 
-	if (rt->rt6i_flags & RTF_LOCAL) {
+	if (rt->rt6i_flags & (RTF_LOCAL | RTF_ANYCAST)) {
 		/* for copies of local routes, dst->dev needs to be the
 		 * device if it is a master device, the master device if
 		 * device is enslaved, and the loopback as the default

2.11.0

From: David Ahern <[email protected]>
Date: Tue, 21 Nov 2017 07:08:57 -0800

Applied and queued up for -stable, thanks!