lb: delete default routes as listed (RouteDel refuses a nil Dst)

RouteList returns a default route without Dst, and netlink's RouteDel
refuses a route with no Dst, Src or Gw. The egress unreachable table's
"unreachable default" could not be removed once installed: every later
pass failed there, before updating rules, so members stayed dropped after
their EgressService got a holder again (fail closed, but stuck). S1's
stale reply tables had the same latent fault. Both now delete through
delRoute, which spells the default destination out; the unreachable route
is compared by type alone, so it is not replaced on every pass.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UHXzGrsxfkGk8LmwrBbHNZ

lb/datapath.go

@@ -295,8 +295,7 @@ func (dp *Datapath) routes(holders []Holder) error {
 				return err
 			}
 			for _, rt := range routes {
-				rt := rt
-				if err := netlink.RouteDel(&rt); err != nil {
+				if err := delRoute(rt); err != nil {
 					return fmt.Errorf("removing stale route in table %d: %v", table, err)
 				}
 			}
@@ -324,3 +323,11 @@ func (dp *Datapath) routes(holders []Holder) error {
 	}
 	return nil
 }
+
+// delRoute deletes a route as RouteList returned it: a default route lists without Dst, which RouteDel refuses.
+func delRoute(rt netlink.Route) error {
+	if rt.Dst == nil {
+		rt.Dst = &net.IPNet{IP: net.IPv4zero, Mask: net.CIDRMask(0, 32)}
+	}
+	return netlink.RouteDel(&rt)
+}

lb/egress_datapath.go

@@ -213,11 +213,11 @@ func egressNet(e EgressDesired, self string, local Local) error {
 			return err
 		}
 		for _, rt := range routes {
-			if want != nil && rt.Type == want.Type && rt.LinkIndex == want.LinkIndex && rt.Gw.Equal(want.Gw) {
+			if want != nil && rt.Type == want.Type &&
+				(want.Type == unix.RTN_UNREACHABLE || rt.LinkIndex == want.LinkIndex && rt.Gw.Equal(want.Gw)) {
 				continue
 			}
-			rt := rt
-			if err := netlink.RouteDel(&rt); err != nil {
+			if err := delRoute(rt); err != nil {
 				return fmt.Errorf("removing stale route in table %d: %v", table, err)
 			}
 		}