control/controlclient: support lazy machine key generation

It's not done in the caller yet, but the controlclient does it now.

Updates #1573

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

control/controlclient/direct.go

@@ -63,7 +63,7 @@ type Direct struct {
 	logf                   logger.Logf
 	linkMon                *monitor.Mon // or nil
 	discoPubKey            tailcfg.DiscoKey
-	machinePrivKey         wgkey.Private
+	getMachinePrivKey      func() (wgkey.Private, error)
 	debugFlags             []string
 	keepSharerAndUserSplit bool
 
@@ -82,7 +82,7 @@ type Direct struct {
 
 type Options struct {
 	Persist              persist.Persist               // initial persistent data
-	MachinePrivateKey wgkey.Private     // the machine key to use
+	GetMachinePrivateKey func() (wgkey.Private, error) // returns the machine key to use
 	ServerURL            string                        // URL of the tailcontrol server
 	AuthKey              string                        // optional node auth key for auto registration
 	TimeNow              func() time.Time              // time.Now implementation used by Client
@@ -110,8 +110,8 @@ func NewDirect(opts Options) (*Direct, error) {
 	if opts.ServerURL == "" {
 		return nil, errors.New("controlclient.New: no server URL specified")
 	}
-	if opts.MachinePrivateKey.IsZero() {
+	if opts.GetMachinePrivateKey == nil {
-		return nil, errors.New("controlclient.New: no MachinePrivateKey specified")
+		return nil, errors.New("controlclient.New: no GetMachinePrivateKey specified")
 	}
 	opts.ServerURL = strings.TrimRight(opts.ServerURL, "/")
 	serverURL, err := url.Parse(opts.ServerURL)
@@ -147,7 +147,7 @@ func NewDirect(opts Options) (*Direct, error) {
 
 	c := &Direct{
 		httpc:                  httpc,
-		machinePrivKey:         opts.MachinePrivateKey,
+		getMachinePrivKey:      opts.GetMachinePrivateKey,
 		serverURL:              opts.ServerURL,
 		timeNow:                opts.TimeNow,
 		logf:                   opts.Logf,
@@ -301,8 +301,12 @@ func (c *Direct) doLogin(ctx context.Context, t *tailcfg.Oauth2Token, flags Logi
 	expired := c.expiry != nil && !c.expiry.IsZero() && c.expiry.Before(c.timeNow())
 	c.mu.Unlock()
 
-	if c.machinePrivKey.IsZero() {
+	machinePrivKey, err := c.getMachinePrivKey()
-		return false, "", errors.New("controlclient.Direct requires a machine private key")
+	if err != nil {
+		return false, "", fmt.Errorf("getMachinePrivKey: %w", err)
+	}
+	if machinePrivKey.IsZero() {
+		return false, "", errors.New("getMachinePrivKey returned zero key")
 	}
 
 	if expired {
@@ -370,7 +374,7 @@ func (c *Direct) doLogin(ctx context.Context, t *tailcfg.Oauth2Token, flags Logi
 	request.Auth.Provider = persist.Provider
 	request.Auth.LoginName = persist.LoginName
 	request.Auth.AuthKey = authKey
-	err = signRegisterRequest(&request, c.serverURL, c.serverKey, c.machinePrivKey.Public())
+	err = signRegisterRequest(&request, c.serverURL, c.serverKey, machinePrivKey.Public())
 	if err != nil {
 		// If signing failed, clear all related fields
 		request.SignatureType = tailcfg.SignatureNone
@@ -384,13 +388,13 @@ func (c *Direct) doLogin(ctx context.Context, t *tailcfg.Oauth2Token, flags Logi
 			c.logf("RegisterReq sign error: %v", err)
 		}
 	}
-	bodyData, err := encode(request, &serverKey, &c.machinePrivKey)
+	bodyData, err := encode(request, &serverKey, &machinePrivKey)
 	if err != nil {
 		return regen, url, err
 	}
 	body := bytes.NewReader(bodyData)
 
-	u := fmt.Sprintf("%s/machine/%s", c.serverURL, c.machinePrivKey.Public().HexString())
+	u := fmt.Sprintf("%s/machine/%s", c.serverURL, machinePrivKey.Public().HexString())
 	req, err := http.NewRequest("POST", u, body)
 	if err != nil {
 		return regen, url, err
@@ -408,8 +412,8 @@ func (c *Direct) doLogin(ctx context.Context, t *tailcfg.Oauth2Token, flags Logi
 			res.StatusCode, strings.TrimSpace(string(msg)))
 	}
 	resp := tailcfg.RegisterResponse{}
-	if err := decode(res, &resp, &serverKey, &c.machinePrivKey); err != nil {
+	if err := decode(res, &resp, &serverKey, &machinePrivKey); err != nil {
-		c.logf("error decoding RegisterResponse with server key %s and machine key %s: %v", serverKey, c.machinePrivKey.Public(), err)
+		c.logf("error decoding RegisterResponse with server key %s and machine key %s: %v", serverKey, machinePrivKey.Public(), err)
 		return regen, url, fmt.Errorf("register request: %v", err)
 	}
 	// Log without PII:
@@ -536,6 +540,14 @@ func (c *Direct) sendMapRequest(ctx context.Context, maxPolls int, cb func(*netm
 	everEndpoints := c.everEndpoints
 	c.mu.Unlock()
 
+	machinePrivKey, err := c.getMachinePrivKey()
+	if err != nil {
+		return fmt.Errorf("getMachinePrivKey: %w", err)
+	}
+	if machinePrivKey.IsZero() {
+		return errors.New("getMachinePrivKey returned zero key")
+	}
+
 	if persist.PrivateNodeKey.IsZero() {
 		return errors.New("privateNodeKey is zero")
 	}
@@ -593,7 +605,7 @@ func (c *Direct) sendMapRequest(ctx context.Context, maxPolls int, cb func(*netm
 		request.ReadOnly = true
 	}
 
-	bodyData, err := encode(request, &serverKey, &c.machinePrivKey)
+	bodyData, err := encode(request, &serverKey, &machinePrivKey)
 	if err != nil {
 		vlogf("netmap: encode: %v", err)
 		return err
@@ -602,7 +614,7 @@ func (c *Direct) sendMapRequest(ctx context.Context, maxPolls int, cb func(*netm
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
-	machinePubKey := tailcfg.MachineKey(c.machinePrivKey.Public())
+	machinePubKey := tailcfg.MachineKey(machinePrivKey.Public())
 	t0 := time.Now()
 	u := fmt.Sprintf("%s/machine/%s/map", serverURL, machinePubKey.HexString())
 
@@ -695,7 +707,7 @@ func (c *Direct) sendMapRequest(ctx context.Context, maxPolls int, cb func(*netm
 		vlogf("netmap: read body after %v", time.Since(t0).Round(time.Millisecond))
 
 		var resp tailcfg.MapResponse
-		if err := c.decodeMsg(msg, &resp); err != nil {
+		if err := c.decodeMsg(msg, &resp, &machinePrivKey); err != nil {
 			vlogf("netmap: decode error: %v")
 			return err
 		}
@@ -878,12 +890,12 @@ var debugMap, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_MAP"))
 
 var jsonEscapedZero = []byte(`\u0000`)
 
-func (c *Direct) decodeMsg(msg []byte, v interface{}) error {
+func (c *Direct) decodeMsg(msg []byte, v interface{}, machinePrivKey *wgkey.Private) error {
 	c.mu.Lock()
 	serverKey := c.serverKey
 	c.mu.Unlock()
 
-	decrypted, err := decryptMsg(msg, &serverKey, &c.machinePrivKey)
+	decrypted, err := decryptMsg(msg, &serverKey, machinePrivKey)
 	if err != nil {
 		return err
 	}
@@ -917,8 +929,8 @@ func (c *Direct) decodeMsg(msg []byte, v interface{}) error {
 
 }
 
-func decodeMsg(msg []byte, v interface{}, serverKey *wgkey.Key, mkey *wgkey.Private) error {
+func decodeMsg(msg []byte, v interface{}, serverKey *wgkey.Key, machinePrivKey *wgkey.Private) error {
-	decrypted, err := decryptMsg(msg, serverKey, mkey)
+	decrypted, err := decryptMsg(msg, serverKey, machinePrivKey)
 	if err != nil {
 		return err
 	}

control/controlclient/direct_test.go

@@ -103,7 +103,13 @@ func TestNewDirect(t *testing.T) {
 	if err != nil {
 		t.Error(err)
 	}
-	opts := Options{ServerURL: "https://example.com", MachinePrivateKey: key, Hostinfo: hi}
+	opts := Options{
+		ServerURL: "https://example.com",
+		Hostinfo:  hi,
+		GetMachinePrivateKey: func() (wgkey.Private, error) {
+			return key, nil
+		},
+	}
 	c, err := NewDirect(opts)
 	if err != nil {
 		t.Fatal(err)

ipn/ipnlocal/local.go

@@ -623,7 +623,12 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 		persistv = &persist.Persist{}
 	}
 	cli, err := controlclient.New(controlclient.Options{
-		MachinePrivateKey: machinePrivKey,
+		GetMachinePrivateKey: func() (wgkey.Private, error) {
+			// TODO(bradfitz): finish pushing this laziness further; see
+			// https://github.com/tailscale/tailscale/issues/1573
+			// For now this is only lazy-ified in controlclient.
+			return machinePrivKey, nil
+		},
 		Logf:            logger.WithPrefix(b.logf, "control: "),
 		Persist:         *persistv,
 		ServerURL:       b.serverURL,