wireguard-go-bridge: account for network changes

Everytime the network changes, we need to recreate the UDP socket,
because the ephemeral listen port is tied to the old physical interface.
As well, we need to re-set the IP addresses for each endpoint, so that
they're passed to getaddrinfo and are then resolved using DNS46.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

wireguard-go-bridge/src/api-ios.go

@@ -25,6 +25,8 @@ import (
 	"os/signal"
 	"runtime"
 	"strings"
+	"syscall"
+	"time"
 	"unsafe"
 )
 
@@ -46,12 +48,54 @@ func (l *CLogger) Write(p []byte) (int, error) {
 	return len(p), nil
 }
 
-var tunnelHandles map[int32]*Device
+type DeviceState struct {
+	device            *Device
+	logger            *Logger
+	endpointsTimer    *time.Timer
+	endpointsSettings string
+}
+
+var tunnelHandles map[int32]*DeviceState
+
+func listenForRouteChanges() {
+	//TODO: replace with NWPathMonitor
+	data := make([]byte, os.Getpagesize())
+	routeSocket, err := unix.Socket(unix.AF_ROUTE, unix.SOCK_RAW, unix.AF_UNSPEC)
+	if err != nil {
+		return
+	}
+	for {
+		n, err := unix.Read(routeSocket, data)
+		if err != nil {
+			if errno, ok := err.(syscall.Errno); ok && errno == syscall.EINTR {
+				continue
+			}
+			return
+		}
+
+		if n < 4 {
+			continue
+		}
+		for _, deviceState := range tunnelHandles {
+			if deviceState.endpointsTimer == nil {
+				deviceState.endpointsTimer = time.AfterFunc(time.Second, func() {
+					deviceState.endpointsTimer = nil
+					bufferedSettings := bufio.NewReadWriter(bufio.NewReader(strings.NewReader(deviceState.endpointsSettings)), bufio.NewWriter(ioutil.Discard))
+					deviceState.logger.Info.Println("Setting endpoints for re-resolution due to network change")
+					err := ipcSetOperation(deviceState.device, bufferedSettings)
+					if err != nil {
+						deviceState.logger.Error.Println(err)
+					}
+				})
+			}
+		}
+	}
+}
 
 func init() {
 	versionString = C.CString(WireGuardGoVersion)
 	roamingDisabled = true
-	tunnelHandles = make(map[int32]*Device)
+	tunnelHandles = make(map[int32]*DeviceState)
 	signals := make(chan os.Signal)
 	signal.Notify(signals, unix.SIGUSR2)
 	go func() {
@@ -67,6 +111,7 @@ func init() {
 			}
 		}
 	}()
+	go listenForRouteChanges()
 }
 
 //export wgSetLogger
@@ -74,6 +119,32 @@ func wgSetLogger(loggerFn uintptr) {
 	loggerFunc = unsafe.Pointer(loggerFn)
 }
 
+func extractEndpointFromSettings(settings string) string {
+	var b strings.Builder
+	pubkey := ""
+	endpoint := ""
+	listenPort := "listen_port=0"
+	for _, line := range strings.Split(settings, "\n") {
+		if strings.HasPrefix(line, "listen_port=") {
+			listenPort = line
+		} else if strings.HasPrefix(line, "public_key=") {
+			if pubkey != "" && endpoint != "" {
+				b.WriteString(pubkey + "\n" + endpoint + "\n")
+			}
+			pubkey = line
+		} else if strings.HasPrefix(line, "endpoint=") {
+			endpoint = line
+		} else if line == "remove=true" {
+			pubkey = ""
+			endpoint = ""
+		}
+	}
+	if pubkey != "" && endpoint != "" {
+		b.WriteString(pubkey + "\n" + endpoint + "\n")
+	}
+	return listenPort + "\n" + b.String()
+}
+
 //export wgTurnOn
 func wgTurnOn(ifnameRef string, settings string, tunFd int32) int32 {
 	interfaceName := string([]byte(ifnameRef))
@@ -113,18 +184,27 @@ func wgTurnOn(ifnameRef string, settings string, tunFd int32) int32 {
 	if i == math.MaxInt32 {
 		return -1
 	}
-	tunnelHandles[i] = device
+	tunnelHandles[i] = &DeviceState{
+		device:            device,
+		logger:            logger,
+		endpointsSettings: extractEndpointFromSettings(settings),
+	}
 	return i
 }
 
 //export wgTurnOff
 func wgTurnOff(tunnelHandle int32) {
-	device, ok := tunnelHandles[tunnelHandle]
+	deviceState, ok := tunnelHandles[tunnelHandle]
 	if !ok {
 		return
 	}
 	delete(tunnelHandles, tunnelHandle)
-	device.Close()
+	t := deviceState.endpointsTimer
+	if t != nil {
+		deviceState.endpointsTimer = nil
+		t.Stop()
+	}
+	deviceState.device.Close()
 }
 
 //export wgVersion