ipv6: ignore null_entry in inet6_rtm_getroute() too

Like commit 1f17e2f ("net: ipv6: ignore null_entry on route dumps"),
we need to ignore null entry in inet6_rtm_getroute() too.

Return -ENETUNREACH here to sync with IPv4 behavior, as suggested by David.

Fixes: a1a22c1 ("net: ipv6: Keep nexthop of multipath route on admin down")
Reported-by: Dmitry Vyukov <[email protected]>
Cc: David Ahern <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
Acked-by: David Ahern <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: congwang

net/ipv6/route.c

@@ -3632,6 +3632,12 @@ static int inet6_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh)
 		rt = (struct rt6_info *)ip6_route_output(net, NULL, &fl6);
 	}
 
+	if (rt == net->ipv6.ip6_null_entry) {
+		err = rt->dst.error;
+		ip6_rt_put(rt);
+		goto errout;
+	}
+
 	skb = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
 	if (!skb) {
 		ip6_rt_put(rt);