add a customized ssh dialer that will timeout

pkg/ssh/ssh.go

@@ -111,7 +111,7 @@ func makeSSHTunnel(user string, signer ssh.Signer, host string) (*SSHTunnel, err
 
 func (s *SSHTunnel) Open() error {
 	var err error
-	s.client, err = realTimeoutDialer.Dial("tcp", net.JoinHostPort(s.Host, s.SSHPort), s.Config)
+	s.client, err = defaultTimeoutDialer.Dial("tcp", net.JoinHostPort(s.Host, s.SSHPort), s.Config)
 	tunnelOpenCounter.Inc()
 	if err != nil {
 		tunnelOpenFailCounter.Inc()
@@ -154,21 +154,9 @@ type sshDialer interface {
 	Dial(network, addr string, config *ssh.ClientConfig) (*ssh.Client, error)
 }
 
-// Real implementation of sshDialer
-type realSSHDialer struct{}
-
-var _ sshDialer = &realSSHDialer{}
-
-func (d *realSSHDialer) Dial(network, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
-	return ssh.Dial(network, addr, config)
-}
-
-// timeoutDialer wraps an sshDialer with a timeout around Dial(). The golang
+// timeoutDialer implements a Dial() method that will timeout. The golang
 // ssh library can hang indefinitely inside the Dial() call (see issue #23835).
-// Wrapping all Dial() calls with a conservative timeout provides safety against
-// getting stuck on that.
 type timeoutDialer struct {
-	dialer  sshDialer
 	timeout time.Duration
 }
 
@@ -176,30 +164,32 @@ type timeoutDialer struct {
 // seconds). This timeout is only intended to catch otherwise uncaught hangs.
 const sshDialTimeout = 150 * time.Second
 
-var realTimeoutDialer sshDialer = &timeoutDialer{&realSSHDialer{}, sshDialTimeout}
+var defaultTimeoutDialer sshDialer = &timeoutDialer{sshDialTimeout}
 
 func (d *timeoutDialer) Dial(network, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
-	var client *ssh.Client
-	errCh := make(chan error, 1)
-	go func() {
-		defer runtime.HandleCrash()
-		var err error
-		client, err = d.dialer.Dial(network, addr, config)
-		errCh <- err
-	}()
-	select {
-	case err := <-errCh:
-		return client, err
-	case <-time.After(d.timeout):
-		return nil, fmt.Errorf("timed out dialing %s:%s", network, addr)
+	conn, err := net.Dial(network, addr)
+	if err != nil {
+		return nil, err
 	}
+	conn.SetDeadline(time.Now().Add(d.timeout))
+	// set to 0 so that conn will not time out after Dial.
+	defer func() {
+		conn.SetDeadline(time.Time{})
+	}()
+	// if conn times out, the NewClientConn will close it, so we will not end up
+	// with hanging goroutines or open file descriptors.
+	c, chans, reqs, err := ssh.NewClientConn(conn, addr, config)
+	if err != nil {
+		return nil, err
+	}
+	return ssh.NewClient(c, chans, reqs), nil
 }
 
 // RunSSHCommand returns the stdout, stderr, and exit code from running cmd on
 // host as specific user, along with any SSH-level error.
 // If user=="", it will default (like SSH) to os.Getenv("USER")
 func RunSSHCommand(cmd, user, host string, signer ssh.Signer) (string, string, int, error) {
-	return runSSHCommand(realTimeoutDialer, cmd, user, host, signer, true)
+	return runSSHCommand(defaultTimeoutDialer, cmd, user, host, signer, true)
 }
 
 // Internal implementation of runSSHCommand, for testing

pkg/ssh/ssh_test.go

@@ -329,38 +329,49 @@ func TestSSHUser(t *testing.T) {
 
 }
 
-type slowDialer struct {
-	delay time.Duration
-	err   error
-}
-
-func (s *slowDialer) Dial(network, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
-	time.Sleep(s.delay)
-	if s.err != nil {
-		return nil, s.err
-	}
-	return &ssh.Client{}, nil
-}
-
 func TestTimeoutDialer(t *testing.T) {
 	testCases := []struct {
-		delay             time.Duration
 		timeout           time.Duration
-		err               error
 		expectedErrString string
 	}{
-		// delay > timeout should cause ssh.Dial to timeout.
-		{1 * time.Second, 0, nil, "timed out dialing"},
-		// delay < timeout should return the result of the call to the dialer.
-		{0, 1 * time.Second, nil, ""},
-		{0, 1 * time.Second, fmt.Errorf("test dial error"), "test dial error"},
+		// should cause ssh.Dial to timeout.
+		{0, "i/o timeout"},
+		// should succeed
+		{1 * time.Second, ""},
 	}
 	for _, tc := range testCases {
-		dialer := &timeoutDialer{&slowDialer{tc.delay, tc.err}, tc.timeout}
-		_, err := dialer.Dial("tcp", "addr:port", &ssh.ClientConfig{})
+		// setup
+		private, _, err := GenerateKey(2048)
+		if err != nil {
+			t.Errorf("unexpected error: %v", err)
+			t.FailNow()
+		}
+		server, err := runTestSSHServer("foo", "bar")
+		if err != nil {
+			t.Errorf("unexpected error: %v", err)
+			t.FailNow()
+		}
+		privateData := EncodePrivateKey(private)
+		tunnel, err := NewSSHTunnelFromBytes("foo", privateData, server.Host)
+		if err != nil {
+			t.Errorf("unexpected error: %v", err)
+			t.FailNow()
+		}
+		tunnel.SSHPort = server.Port
+
+		// test the dialer
+		dialer := &timeoutDialer{tc.timeout}
+		client, err := dialer.Dial("tcp", net.JoinHostPort(tunnel.Host, tunnel.SSHPort), tunnel.Config)
 		if len(tc.expectedErrString) == 0 && err != nil ||
 			!strings.Contains(fmt.Sprint(err), tc.expectedErrString) {
 			t.Errorf("Expected error to contain %q; got %v", tc.expectedErrString, err)
 		}
+		if len(tc.expectedErrString) == 0 {
+			// verify the connection doesn't timeout after the handshake is done.
+			time.Sleep(tc.timeout + 1*time.Second)
+			if _, _, err := client.OpenChannel("direct-tcpip", nil); err != nil {
+				t.Errorf("unexpected error %v", err)
+			}
+		}
 	}
 }