ipv6: Handle all fib6_nh in a nexthop in mtu updates

Use nexthop_for_each_fib6_nh to call fib6_nh_mtu_change for each
fib6_nh in a nexthop for rt6_mtu_change_route. For __ip6_rt_update_pmtu,
we need to find the nexthop that correlates to the device and gateway
in the rt6_info.
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -2679,10 +2679,31 @@ static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk,
 			rcu_read_unlock();
 			return;
 		}
-		res.nh = res.f6i->fib6_nh;
 		res.fib6_flags = res.f6i->fib6_flags;
 		res.fib6_type = res.f6i->fib6_type;
 
+		if (res.f6i->nh) {
+			struct fib6_nh_match_arg arg = {
+				.dev = dst->dev,
+				.gw = &rt6->rt6i_gateway,
+			};
+
+			nexthop_for_each_fib6_nh(res.f6i->nh,
+						 fib6_nh_find_match, &arg);
+
+			/* fib6_info uses a nexthop that does not have fib6_nh
+			 * using the dst->dev + gw. Should be impossible.
+			 */
+			if (!arg.match) {
+				rcu_read_unlock();
+				return;
+			}
+
+			res.nh = arg.match;
+		} else {
+			res.nh = res.f6i->fib6_nh;
+		}
+
 		nrt6 = ip6_rt_cache_alloc(&res, daddr, saddr);
 		if (nrt6) {
 			rt6_do_update_pmtu(nrt6, mtu);
@@ -4650,6 +4671,12 @@ static int rt6_mtu_change_route(struct fib6_info *f6i, void *p_arg)
 		return 0;
 
 	arg->f6i = f6i;
+	if (f6i->nh) {
+		/* fib6_nh_mtu_change only returns 0, so this is safe */
+		return nexthop_for_each_fib6_nh(f6i->nh, fib6_nh_mtu_change,
+						arg);
+	}
+
 	return fib6_nh_mtu_change(f6i->fib6_nh, arg);
 }