Fix Windows DNS interface configuration

Author: sjmiller609

lib/instances/restore.go

@@ -487,6 +487,12 @@ func reconfigureGuestNetworkConfig(ctx context.Context, stored *StoredMetadata,
 	if err != nil {
 		return err
 	}
+	if isWindowsPlatform(stored.Platform) {
+		cfg.dns, err = parseWindowsDNSServers(netConfig.DNS)
+		if err != nil {
+			return err
+		}
+	}
 
 	dialer, err := hypervisor.NewVsockDialer(stored.HypervisorType, stored.VsockSocket, stored.VsockCID)
 	if err != nil {
@@ -570,15 +576,19 @@ func guestNetworkReconfigureConfig(netConfig *network.NetworkConfig) (*guestNetw
 	if err != nil {
 		return nil, err
 	}
+	return &guestNetworkConfig{ip: ip, mac: mac, gateway: gateway, prefix: prefix}, nil
+}
+
+func parseWindowsDNSServers(value string) ([]string, error) {
 	var dns []string
-	for _, server := range strings.FieldsFunc(netConfig.DNS, func(r rune) bool { return r == ',' || r == ' ' }) {
+	for _, server := range strings.FieldsFunc(value, func(r rune) bool { return r == ',' || r == ' ' }) {
 		server = strings.TrimSpace(server)
 		if net.ParseIP(server).To4() == nil {
-			return nil, fmt.Errorf("invalid DNS server %q", server)
+			return nil, fmt.Errorf("invalid Windows DNS server %q", server)
 		}
 		dns = append(dns, server)
 	}
-	return &guestNetworkConfig{ip: ip, mac: mac, gateway: gateway, dns: dns, prefix: prefix}, nil
+	return dns, nil
 }
 
 func guestNetworkReconfigureCommand(alloc *network.Allocation) (string, error) {

lib/instances/restore_egress_test.go

@@ -30,19 +30,20 @@ func TestNetworkConfigFromAllocation_PreservesDNS(t *testing.T) {
 	assert.Equal(t, alloc.TAPDevice, cfg.TAPDevice)
 }
 
-func TestGuestNetworkReconfigureConfigParsesDNS(t *testing.T) {
+func TestWindowsDNSServerParsingDoesNotAffectLinuxConfig(t *testing.T) {
 	t.Parallel()
 
-	cfg, err := guestNetworkReconfigureConfig(&network.NetworkConfig{
-		IP: "10.102.146.62", MAC: "02:00:00:85:17:c8", Gateway: "10.102.0.1", Netmask: "255.255.0.0", DNS: "1.1.1.1, 8.8.8.8",
-	})
+	dns, err := parseWindowsDNSServers("1.1.1.1, 8.8.8.8")
 	require.NoError(t, err)
-	assert.Equal(t, []string{"1.1.1.1", "8.8.8.8"}, cfg.dns)
+	assert.Equal(t, []string{"1.1.1.1", "8.8.8.8"}, dns)
+	_, err = parseWindowsDNSServers("2606:4700:4700::1111")
+	require.ErrorContains(t, err, "invalid Windows DNS server")
 
-	_, err = guestNetworkReconfigureConfig(&network.NetworkConfig{
-		IP: "10.102.146.62", MAC: "02:00:00:85:17:c8", Gateway: "10.102.0.1", Netmask: "255.255.0.0", DNS: "not-an-address",
+	cfg, err := guestNetworkReconfigureConfig(&network.NetworkConfig{
+		IP: "10.102.146.62", MAC: "02:00:00:85:17:c8", Gateway: "10.102.0.1", Netmask: "255.255.0.0", DNS: "2606:4700:4700::1111",
 	})
-	require.ErrorContains(t, err, "invalid DNS server")
+	require.NoError(t, err)
+	assert.Empty(t, cfg.dns)
 }
 
 func TestGuestNetworkReconfigureCommand_AppliesAllocatedMAC(t *testing.T) {

lib/instances/windows_networking_integration_linux_test.go

@@ -9,6 +9,7 @@ import (
 	"net"
 	"os"
 	"os/exec"
+	"strings"
 	"testing"
 	"time"
 
@@ -83,8 +84,11 @@ func assertWindowsNetworkReady(t *testing.T, ctx context.Context, manager *manag
 
 	dialer, err := manager.GetVsockDialer(ctx, instanceID)
 	require.NoError(t, err)
+	allocation, err := manager.networkManager.GetAllocation(ctx, instanceID)
+	require.NoError(t, err)
+	expectedDNS := strings.Join(strings.FieldsFunc(allocation.DNS, func(r rune) bool { return r == ',' || r == ' ' }), ",")
 	var stdout, stderr bytes.Buffer
-	command := fmt.Sprintf("$a=Get-NetIPAddress -AddressFamily IPv4 | Where-Object IPAddress -eq '%s'; if (-not $a) { exit 20 }; [System.Net.Dns]::GetHostAddresses('example.com') | Out-Null; [Console]::Out.Write($a.IPAddress)", expectedIP)
+	command := fmt.Sprintf("$a=Get-NetIPAddress -AddressFamily IPv4 | Where-Object IPAddress -eq '%s'; if (-not $a) { exit 20 }; $dns=@((Get-DnsClientServerAddress -InterfaceIndex $a.InterfaceIndex -AddressFamily IPv4).ServerAddresses); if (($dns -join ',') -ne '%s') { exit 21 }; [System.Net.Dns]::GetHostAddresses('example.com') | Out-Null; [Console]::Out.Write($a.IPAddress)", expectedIP, expectedDNS)
 	exit, err := guest.ExecIntoInstance(ctx, dialer, guest.ExecOptions{
 		Command: []string{"powershell.exe", "-NoProfile", "-NonInteractive", "-Command", command},
 		Stdout:  &stdout,

lib/system/guest_agent/network_windows.go

@@ -17,12 +17,10 @@ import (
 )
 
 const (
-	addressFamilyIPv4       = 2
-	gaaFlagIncludePrefixes  = 0x10
-	dnsSettingsVersion1     = 1
-	dnsSettingNameServer    = 0x2
-	windowsErrorBufferLarge = syscall.Errno(111)
-	windowsErrorNotFound    = syscall.Errno(1168)
+	addressFamilyIPv4      = 2
+	gaaFlagIncludePrefixes = 0x10
+	dnsSettingsVersion1    = 1
+	dnsSettingNameServer   = 0x2
 )
 
 var (
@@ -35,6 +33,7 @@ var (
 	createForwardEntryProc       = ipHelperDLL.NewProc("CreateIpForwardEntry2")
 	deleteForwardEntryProc       = ipHelperDLL.NewProc("DeleteIpForwardEntry2")
 	setInterfaceDNSSettingsProc  = ipHelperDLL.NewProc("SetInterfaceDnsSettings")
+	convertInterfaceLuidProc     = ipHelperDLL.NewProc("ConvertInterfaceLuidToGuid")
 )
 
 type dnsInterfaceSettings struct {
@@ -80,18 +79,18 @@ func (s *guestServer) ReconfigureNetwork(ctx context.Context, req *pb.Reconfigur
 		return nil, err
 	}
 	if len(req.DnsServers) > 0 {
-		if err := configureWindowsDNS(adapter.NetworkGUID, req.DnsServers); err != nil {
+		if err := configureWindowsDNS(adapter.InterfaceGUID, req.DnsServers); err != nil {
 			return nil, err
 		}
 	}
 	return &pb.ReconfigureNetworkResponse{}, nil
 }
 
 type windowsAdapterInfo struct {
-	Luid        uint64
-	Index       uint32
-	NetworkGUID windows.GUID
-	IPv4        []net.IP
+	Luid          uint64
+	Index         uint32
+	InterfaceGUID windows.GUID
+	IPv4          []net.IP
 }
 
 func waitForWindowsAdapter(ctx context.Context, mac net.HardwareAddr, name string) (*windowsAdapterInfo, error) {
@@ -119,7 +118,7 @@ func findWindowsAdapter(mac net.HardwareAddr, name string) (*windowsAdapterInfo,
 		buffer := make([]byte, size)
 		first := (*windows.IpAdapterAddresses)(unsafe.Pointer(&buffer[0]))
 		err := windows.GetAdaptersAddresses(addressFamilyIPv4, gaaFlagIncludePrefixes, 0, first, &size)
-		if err == windowsErrorBufferLarge {
+		if err == windows.ERROR_BUFFER_OVERFLOW {
 			continue
 		}
 		if err != nil {
@@ -129,7 +128,13 @@ func findWindowsAdapter(mac net.HardwareAddr, name string) (*windowsAdapterInfo,
 			physical := net.HardwareAddr(adapter.PhysicalAddress[:adapter.PhysicalAddressLength])
 			friendlyName := windows.UTF16PtrToString(adapter.FriendlyName)
 			if strings.EqualFold(physical.String(), mac.String()) && (name == "" || strings.EqualFold(name, friendlyName)) {
-				result := &windowsAdapterInfo{Luid: adapter.Luid, Index: adapter.IfIndex, NetworkGUID: adapter.NetworkGuid}
+				result := &windowsAdapterInfo{Luid: adapter.Luid, Index: adapter.IfIndex}
+				if code, _, _ := convertInterfaceLuidProc.Call(
+					uintptr(unsafe.Pointer(&result.Luid)),
+					uintptr(unsafe.Pointer(&result.InterfaceGUID)),
+				); code != 0 {
+					return nil, fmt.Errorf("convert Windows interface LUID to GUID: %w", syscall.Errno(code))
+				}
 				for address := adapter.FirstUnicastAddress; address != nil; address = address.Next {
 					if ipv4 := address.Address.IP().To4(); ipv4 != nil {
 						result.IPv4 = append(result.IPv4, append(net.IP(nil), ipv4...))
@@ -149,7 +154,7 @@ func configureWindowsAddresses(adapter *windowsAdapterInfo, ipv4 net.IP, prefix
 		row.InterfaceLuid = adapter.Luid
 		row.InterfaceIndex = adapter.Index
 		copyRawIPv4(unsafe.Pointer(&row.Address), address)
-		if code, _, _ := deleteUnicastAddressProc.Call(uintptr(unsafe.Pointer(&row))); code != 0 && syscall.Errno(code) != windowsErrorNotFound {
+		if code, _, _ := deleteUnicastAddressProc.Call(uintptr(unsafe.Pointer(&row))); code != 0 && syscall.Errno(code) != windows.ERROR_NOT_FOUND {
 			return fmt.Errorf("delete Windows IPv4 address: %w", syscall.Errno(code))
 		}
 	}
@@ -164,7 +169,7 @@ func configureWindowsAddresses(adapter *windowsAdapterInfo, ipv4 net.IP, prefix
 			destination := (*windows.RawSockaddrInet4)(unsafe.Pointer(&route.DestinationPrefix.Prefix))
 			if route.InterfaceLuid == adapter.Luid && route.DestinationPrefix.PrefixLength == 0 && destination.Addr == [4]byte{} {
 				row := route
-				if code, _, _ := deleteForwardEntryProc.Call(uintptr(unsafe.Pointer(&row))); code != 0 && syscall.Errno(code) != windowsErrorNotFound {
+				if code, _, _ := deleteForwardEntryProc.Call(uintptr(unsafe.Pointer(&row))); code != 0 && syscall.Errno(code) != windows.ERROR_NOT_FOUND {
 					return fmt.Errorf("delete Windows default route: %w", syscall.Errno(code))
 				}
 			}