ipv6: Set nexthop flags upon carrier change

Similar to IPv4, when the carrier of a netdev changes we should toggle
the 'linkdown' flag on all the nexthops using it as their nexthop
device.

This will later allow us to test for the presence of this flag during
route lookup and dump.

Up until commit 4832c30d ("net: ipv6: put host and anycast routes on
device with address") host and anycast routes used the loopback netdev
as their nexthop device and thus were not marked with the 'linkdown'
flag. The patch preserves this behavior and allows one to ping the local
address even when the nexthop device does not have a carrier and the
'ignore_routes_with_linkdown' sysctl is set.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_route.h

@@ -170,6 +170,7 @@ void rt6_remove_prefsrc(struct inet6_ifaddr *ifp);
 void rt6_clean_tohost(struct net *net, struct in6_addr *gateway);
 void rt6_sync_up(struct net_device *dev, unsigned int nh_flags);
 void rt6_disable_ip(struct net_device *dev, unsigned long event);
+void rt6_sync_down_dev(struct net_device *dev, unsigned long event);
 
 static inline const struct rt6_info *skb_rt6_info(const struct sk_buff *skb)
 {

net/ipv6/addrconf.c

@@ -3438,6 +3438,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 		} else if (event == NETDEV_CHANGE) {
 			if (!addrconf_link_ready(dev)) {
 				/* device is still not ready. */
+				rt6_sync_down_dev(dev, event);
 				break;
 			}
 
@@ -3449,6 +3450,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 					 * multicast snooping switches
 					 */
 					ipv6_mc_up(idev);
+					rt6_sync_up(dev, RTNH_F_LINKDOWN);
 					break;
 				}
 				idev->if_flags |= IF_READY;

net/ipv6/route.c

@@ -3498,18 +3498,29 @@ static int fib6_ifdown(struct rt6_info *rt, void *p_arg)
 	const struct net_device *dev = arg->dev;
 	const struct net *net = dev_net(dev);
 
-	if (rt->dst.dev == dev &&
-	    rt != net->ipv6.ip6_null_entry &&
-	    (rt->rt6i_nsiblings == 0 || netdev_unregistering(dev) ||
-	     !rt->rt6i_idev->cnf.ignore_routes_with_linkdown)) {
-		rt->rt6i_nh_flags |= (RTNH_F_DEAD | RTNH_F_LINKDOWN);
+	if (rt->dst.dev != dev || rt == net->ipv6.ip6_null_entry)
+		return 0;
+
+	switch (arg->event) {
+	case NETDEV_UNREGISTER:
 		return -1;
+	case NETDEV_DOWN:
+		if (rt->rt6i_nsiblings == 0 ||
+		    !rt->rt6i_idev->cnf.ignore_routes_with_linkdown)
+			return -1;
+		rt->rt6i_nh_flags |= RTNH_F_DEAD;
+		/* fall through */
+	case NETDEV_CHANGE:
+		if (rt->rt6i_flags & (RTF_LOCAL | RTF_ANYCAST))
+			break;
+		rt->rt6i_nh_flags |= RTNH_F_LINKDOWN;
+		break;
 	}
 
 	return 0;
 }
 
-static void rt6_sync_down_dev(struct net_device *dev, unsigned long event)
+void rt6_sync_down_dev(struct net_device *dev, unsigned long event)
 {
 	struct arg_netdev_event arg = {
 		.dev = dev,