Esempio n. 1
0
// dialSsh is a helper that builds the transport layers and establishes the SSH connection.
// When additional dial configuration is used, DialStats are recorded and returned.
//
// The net.Conn return value is the value to be removed from pendingConns; additional
// layering (ThrottledConn, ActivityMonitoredConn) is applied, but this return value is the
// base dial conn. The *ActivityMonitoredConn return value is the layered conn passed into
// the ssh.Client.
func dialSsh(
	config *Config,
	pendingConns *common.Conns,
	serverEntry *protocol.ServerEntry,
	selectedProtocol,
	sessionId string) (*dialResult, error) {

	// The meek protocols tunnel obfuscated SSH. Obfuscated SSH is layered on top of SSH.
	// So depending on which protocol is used, multiple layers are initialized.

	useObfuscatedSsh := false
	var directTCPDialAddress string
	var meekConfig *MeekConfig
	var err error

	switch selectedProtocol {
	case protocol.TUNNEL_PROTOCOL_OBFUSCATED_SSH:
		useObfuscatedSsh = true
		directTCPDialAddress = fmt.Sprintf("%s:%d", serverEntry.IpAddress, serverEntry.SshObfuscatedPort)

	case protocol.TUNNEL_PROTOCOL_SSH:
		directTCPDialAddress = fmt.Sprintf("%s:%d", serverEntry.IpAddress, serverEntry.SshPort)

	default:
		useObfuscatedSsh = true
		meekConfig, err = initMeekConfig(config, serverEntry, selectedProtocol, sessionId)
		if err != nil {
			return nil, common.ContextError(err)
		}
	}

	NoticeConnectingServer(
		serverEntry.IpAddress,
		serverEntry.Region,
		selectedProtocol,
		directTCPDialAddress,
		meekConfig)

	// Use an asynchronous callback to record the resolved IP address when
	// dialing a domain name. Note that DialMeek doesn't immediately
	// establish any HTTPS connections, so the resolved IP address won't be
	// reported until during/after ssh session establishment (the ssh traffic
	// is meek payload). So don't Load() the IP address value until after that
	// has completed to ensure a result.
	var resolvedIPAddress atomic.Value
	resolvedIPAddress.Store("")
	setResolvedIPAddress := func(IPAddress string) {
		resolvedIPAddress.Store(IPAddress)
	}

	// Create the base transport: meek or direct connection
	dialConfig := &DialConfig{
		UpstreamProxyUrl:              config.UpstreamProxyUrl,
		UpstreamProxyCustomHeaders:    config.UpstreamProxyCustomHeaders,
		ConnectTimeout:                time.Duration(*config.TunnelConnectTimeoutSeconds) * time.Second,
		PendingConns:                  pendingConns,
		DeviceBinder:                  config.DeviceBinder,
		DnsServerGetter:               config.DnsServerGetter,
		UseIndistinguishableTLS:       config.UseIndistinguishableTLS,
		TrustedCACertificatesFilename: config.TrustedCACertificatesFilename,
		DeviceRegion:                  config.DeviceRegion,
		ResolvedIPCallback:            setResolvedIPAddress,
	}
	var dialConn net.Conn
	if meekConfig != nil {
		dialConn, err = DialMeek(meekConfig, dialConfig)
		if err != nil {
			return nil, common.ContextError(err)
		}
	} else {
		dialConn, err = DialTCP(directTCPDialAddress, dialConfig)
		if err != nil {
			return nil, common.ContextError(err)
		}
	}

	cleanupConn := dialConn
	defer func() {
		// Cleanup on error
		if cleanupConn != nil {
			cleanupConn.Close()
			pendingConns.Remove(cleanupConn)
		}
	}()

	// Activity monitoring is used to measure tunnel duration
	monitoredConn, err := common.NewActivityMonitoredConn(dialConn, 0, false, nil, nil)
	if err != nil {
		return nil, common.ContextError(err)
	}

	// Apply throttling (if configured)
	throttledConn := common.NewThrottledConn(monitoredConn, config.RateLimits)

	// Add obfuscated SSH layer
	var sshConn net.Conn = throttledConn
	if useObfuscatedSsh {
		sshConn, err = common.NewObfuscatedSshConn(
			common.OBFUSCATION_CONN_MODE_CLIENT, throttledConn, serverEntry.SshObfuscatedKey)
		if err != nil {
			return nil, common.ContextError(err)
		}
	}

	// Now establish the SSH session over the conn transport
	expectedPublicKey, err := base64.StdEncoding.DecodeString(serverEntry.SshHostKey)
	if err != nil {
		return nil, common.ContextError(err)
	}
	sshCertChecker := &ssh.CertChecker{
		HostKeyFallback: func(addr string, remote net.Addr, publicKey ssh.PublicKey) error {
			if !bytes.Equal(expectedPublicKey, publicKey.Marshal()) {
				return common.ContextError(errors.New("unexpected host public key"))
			}
			return nil
		},
	}

	sshPasswordPayload := &protocol.SSHPasswordPayload{
		SessionId:          sessionId,
		SshPassword:        serverEntry.SshPassword,
		ClientCapabilities: []string{protocol.CLIENT_CAPABILITY_SERVER_REQUESTS},
	}

	payload, err := json.Marshal(sshPasswordPayload)
	if err != nil {
		return nil, common.ContextError(err)
	}
	sshClientConfig := &ssh.ClientConfig{
		User: serverEntry.SshUsername,
		Auth: []ssh.AuthMethod{
			ssh.Password(string(payload)),
		},
		HostKeyCallback: sshCertChecker.CheckHostKey,
	}

	// The ssh session establishment (via ssh.NewClientConn) is wrapped
	// in a timeout to ensure it won't hang. We've encountered firewalls
	// that allow the TCP handshake to complete but then send a RST to the
	// server-side and nothing to the client-side, and if that happens
	// while ssh.NewClientConn is reading, it may wait forever. The timeout
	// closes the conn, which interrupts it.
	// Note: TCP handshake timeouts are provided by TCPConn, and session
	// timeouts *after* ssh establishment are provided by the ssh keep alive
	// in operate tunnel.
	// TODO: adjust the timeout to account for time-elapsed-from-start

	type sshNewClientResult struct {
		sshClient   *ssh.Client
		sshRequests <-chan *ssh.Request
		err         error
	}
	resultChannel := make(chan *sshNewClientResult, 2)
	if *config.TunnelConnectTimeoutSeconds > 0 {
		time.AfterFunc(time.Duration(*config.TunnelConnectTimeoutSeconds)*time.Second, func() {
			resultChannel <- &sshNewClientResult{nil, nil, errors.New("ssh dial timeout")}
		})
	}

	go func() {
		// The following is adapted from ssh.Dial(), here using a custom conn
		// The sshAddress is passed through to host key verification callbacks; we don't use it.
		sshAddress := ""
		sshClientConn, sshChannels, sshRequests, err := ssh.NewClientConn(
			sshConn, sshAddress, sshClientConfig)
		var sshClient *ssh.Client
		if err == nil {
			sshClient = ssh.NewClient(sshClientConn, sshChannels, nil)
		}
		resultChannel <- &sshNewClientResult{sshClient, sshRequests, err}
	}()

	result := <-resultChannel
	if result.err != nil {
		return nil, common.ContextError(result.err)
	}

	var dialStats *TunnelDialStats

	if dialConfig.UpstreamProxyUrl != "" || meekConfig != nil {
		dialStats = &TunnelDialStats{}

		if dialConfig.UpstreamProxyUrl != "" {

			// Note: UpstreamProxyUrl should have parsed correctly in the dial
			proxyURL, err := url.Parse(dialConfig.UpstreamProxyUrl)
			if err == nil {
				dialStats.UpstreamProxyType = proxyURL.Scheme
			}

			dialStats.UpstreamProxyCustomHeaderNames = make([]string, 0)
			for name, _ := range dialConfig.UpstreamProxyCustomHeaders {
				dialStats.UpstreamProxyCustomHeaderNames = append(dialStats.UpstreamProxyCustomHeaderNames, name)
			}
		}

		if meekConfig != nil {
			dialStats.MeekDialAddress = meekConfig.DialAddress
			dialStats.MeekResolvedIPAddress = resolvedIPAddress.Load().(string)
			dialStats.MeekSNIServerName = meekConfig.SNIServerName
			dialStats.MeekHostHeader = meekConfig.HostHeader
			dialStats.MeekTransformedHostName = meekConfig.TransformedHostName
		}

		NoticeConnectedTunnelDialStats(serverEntry.IpAddress, dialStats)
	}

	cleanupConn = nil

	// Note: dialConn may be used to close the underlying network connection
	// but should not be used to perform I/O as that would interfere with SSH
	// (and also bypasses throttling).

	return &dialResult{
			dialConn:      dialConn,
			monitoredConn: monitoredConn,
			sshClient:     result.sshClient,
			sshRequests:   result.sshRequests,
			dialStats:     dialStats},
		nil
}
Esempio n. 2
0
func (sshServer *sshServer) handleClient(tunnelProtocol string, clientConn net.Conn) {

	sshServer.registerAcceptedClient(tunnelProtocol)
	defer sshServer.unregisterAcceptedClient(tunnelProtocol)

	geoIPData := sshServer.support.GeoIPService.Lookup(
		common.IPAddressFromAddr(clientConn.RemoteAddr()))

	sshClient := newSshClient(sshServer, tunnelProtocol, geoIPData)

	// Set initial traffic rules, pre-handshake, based on currently known info.
	sshClient.setTrafficRules()

	// Wrap the base client connection with an ActivityMonitoredConn which will
	// terminate the connection if no data is received before the deadline. This
	// timeout is in effect for the entire duration of the SSH connection. Clients
	// must actively use the connection or send SSH keep alive requests to keep
	// the connection active. Writes are not considered reliable activity indicators
	// due to buffering.

	activityConn, err := common.NewActivityMonitoredConn(
		clientConn,
		SSH_CONNECTION_READ_DEADLINE,
		false,
		nil)
	if err != nil {
		clientConn.Close()
		log.WithContextFields(LogFields{"error": err}).Error("NewActivityMonitoredConn failed")
		return
	}
	clientConn = activityConn

	// Further wrap the connection in a rate limiting ThrottledConn.

	throttledConn := common.NewThrottledConn(clientConn, sshClient.rateLimits())
	clientConn = throttledConn

	// Run the initial [obfuscated] SSH handshake in a goroutine so we can both
	// respect shutdownBroadcast and implement a specific handshake timeout.
	// The timeout is to reclaim network resources in case the handshake takes
	// too long.

	type sshNewServerConnResult struct {
		conn     net.Conn
		sshConn  *ssh.ServerConn
		channels <-chan ssh.NewChannel
		requests <-chan *ssh.Request
		err      error
	}

	resultChannel := make(chan *sshNewServerConnResult, 2)

	if SSH_HANDSHAKE_TIMEOUT > 0 {
		time.AfterFunc(time.Duration(SSH_HANDSHAKE_TIMEOUT), func() {
			resultChannel <- &sshNewServerConnResult{err: errors.New("ssh handshake timeout")}
		})
	}

	go func(conn net.Conn) {
		sshServerConfig := &ssh.ServerConfig{
			PasswordCallback: sshClient.passwordCallback,
			AuthLogCallback:  sshClient.authLogCallback,
			ServerVersion:    sshServer.support.Config.SSHServerVersion,
		}
		sshServerConfig.AddHostKey(sshServer.sshHostKey)

		result := &sshNewServerConnResult{}

		// Wrap the connection in an SSH deobfuscator when required.

		if common.TunnelProtocolUsesObfuscatedSSH(tunnelProtocol) {
			// Note: NewObfuscatedSshConn blocks on network I/O
			// TODO: ensure this won't block shutdown
			conn, result.err = psiphon.NewObfuscatedSshConn(
				psiphon.OBFUSCATION_CONN_MODE_SERVER,
				conn,
				sshServer.support.Config.ObfuscatedSSHKey)
			if result.err != nil {
				result.err = common.ContextError(result.err)
			}
		}

		if result.err == nil {
			result.sshConn, result.channels, result.requests, result.err =
				ssh.NewServerConn(conn, sshServerConfig)
		}

		resultChannel <- result

	}(clientConn)

	var result *sshNewServerConnResult
	select {
	case result = <-resultChannel:
	case <-sshServer.shutdownBroadcast:
		// Close() will interrupt an ongoing handshake
		// TODO: wait for goroutine to exit before returning?
		clientConn.Close()
		return
	}

	if result.err != nil {
		clientConn.Close()
		// This is a Debug log due to noise. The handshake often fails due to I/O
		// errors as clients frequently interrupt connections in progress when
		// client-side load balancing completes a connection to a different server.
		log.WithContextFields(LogFields{"error": result.err}).Debug("handshake failed")
		return
	}

	sshClient.Lock()
	sshClient.sshConn = result.sshConn
	sshClient.activityConn = activityConn
	sshClient.throttledConn = throttledConn
	sshClient.Unlock()

	if !sshServer.registerEstablishedClient(sshClient) {
		clientConn.Close()
		log.WithContext().Warning("register failed")
		return
	}
	defer sshServer.unregisterEstablishedClient(sshClient.sessionID)

	sshClient.runClient(result.channels, result.requests)

	// Note: sshServer.unregisterClient calls sshClient.Close(),
	// which also closes underlying transport Conn.
}