Add NativeConfigDisabled flag to skip raw interface configuration on Darwin

network/interface.go

@@ -115,6 +115,10 @@ func FindUnusedUTUN() (string, error) {
 }
 
 func configureDarwin(interfaceName string, ip net.IP, ipNet *net.IPNet) error {
+	if NativeConfigDisabled {
+		return nil
+	}
+
 	logger.Info("Configuring darwin interface: %s", interfaceName)
 
 	prefix, _ := ipNet.Mask.Size()
@@ -246,6 +250,10 @@ func removeLinuxAddress(interfaceName string, ip net.IP, ipNet *net.IPNet) error
 }
 
 func removeDarwinAddress(interfaceName string, ip net.IP, ipNet *net.IPNet) error {
+	if NativeConfigDisabled {
+		return nil
+	}
+
 	prefix, _ := ipNet.Mask.Size()
 	ipStr := fmt.Sprintf("%s/%d", ip.String(), prefix)
 

network/route.go

@@ -32,6 +32,20 @@ const VPNRouteMetric = 9999
 // this to true (e.g. from a config value) before routes are added.
 var PreferLocalRoutes = false
 
+// NativeConfigDisabled, when true, skips the raw `ifconfig`/`route` subprocess
+// calls this package otherwise makes on darwin (configureDarwin,
+// removeDarwinAddress, DarwinAddRouteWithSource, DarwinRemoveRoute) while still
+// populating the JSON-facing NetworkSettings state. This must be set when the
+// TUN device's addresses/routes are instead owned by an external mechanism
+// that reconciles them independently - namely Apple's NetworkExtension
+// (NEPacketTunnelProvider.setTunnelNetworkSettings), which is the sole
+// sanctioned way to configure that virtual interface. Running our own
+// ifconfig/route commands in addition to NE applying its own settings was
+// observed to install two competing routes to the same destination (one via
+// NE's gatewayAddress-based route, one via our own `-ifa` route), so the two
+// mechanisms must be mutually exclusive rather than layered.
+var NativeConfigDisabled = false
+
 // DarwinAddRoute adds a route via the BSD routing table. Unlike Linux/Windows,
 // BSD's routing table has no per-route metric - preference between an
 // overlapping local route and this VPN route is instead resolved by
@@ -54,6 +68,9 @@ func DarwinAddRouteWithSource(destination string, gateway string, interfaceName
 	if runtime.GOOS != "darwin" {
 		return nil
 	}
+	if NativeConfigDisabled {
+		return nil
+	}
 
 	var args []string
 
@@ -87,6 +104,9 @@ func DarwinRemoveRoute(destination string) error {
 	if runtime.GOOS != "darwin" {
 		return nil
 	}
+	if NativeConfigDisabled {
+		return nil
+	}
 
 	cmd := exec.Command("route", "-q", "-n", "delete", "-inet", destination)
 	logger.Info("Running command: %v", cmd)