client.go

/*
Copyright 2015 Gravitational, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package client

import (
	"bytes"
	"context"
	"encoding/json"
	"io"
	"io/ioutil"
	"net"
	"strings"
	"time"

	"github.com/gravitational/teleport/lib/auth"
	"github.com/gravitational/teleport/lib/defaults"
	"github.com/gravitational/teleport/lib/services"
	"github.com/gravitational/teleport/lib/sshutils/scp"
	"github.com/gravitational/teleport/lib/utils"

	log "github.com/Sirupsen/logrus"
	"github.com/gravitational/trace"
	"golang.org/x/crypto/ssh"
)

// ProxyClient implements ssh client to a teleport proxy
// It can provide list of nodes or connect to nodes
type ProxyClient struct {
	Client          *ssh.Client
	hostLogin       string
	proxyAddress    string
	hostKeyCallback utils.HostKeyCallback
	authMethod      ssh.AuthMethod
	siteName        string
}

// NodeClient implements ssh client to a ssh node (teleport or any regular ssh node)
// NodeClient can run shell and commands or upload and download files.
type NodeClient struct {
	Namespace string
	Client    *ssh.Client
	Proxy     *ProxyClient
}

// GetSites returns list of the "sites" (AKA teleport clusters) connected to the proxy
// Each site is returned as an instance of its auth server
//
func (proxy *ProxyClient) GetSites() ([]services.Site, error) {
	proxySession, err := proxy.Client.NewSession()
	if err != nil {
		return nil, trace.Wrap(err)
	}

	stdout := &bytes.Buffer{}
	reader, err := proxySession.StdoutPipe()
	if err != nil {
		return nil, trace.Wrap(err)
	}

	done := make(chan struct{})
	go func() {
		io.Copy(stdout, reader)
		close(done)
	}()

	if err := proxySession.RequestSubsystem("proxysites"); err != nil {
		return nil, trace.Wrap(err)
	}
	select {
	case <-done:
	case <-time.After(defaults.DefaultDialTimeout):
		return nil, trace.ConnectionProblem(nil, "timeout")
	}

	log.Debugf("[CLIENT] found clusters: %v", stdout.String())

	var sites []services.Site
	if err := json.Unmarshal(stdout.Bytes(), &sites); err != nil {
		return nil, trace.Wrap(err)
	}
	return sites, nil
}

// FindServersByLabels returns list of the nodes which have labels exactly matching
// the given label set.
//
// A server is matched when ALL labels match.
// If no labels are passed, ALL nodes are returned.
func (proxy *ProxyClient) FindServersByLabels(ctx context.Context, namespace string, labels map[string]string) ([]services.Server, error) {
	if namespace == "" {
		return nil, trace.BadParameter("missing parameter namespace")
	}
	nodes := make([]services.Server, 0)
	site, err := proxy.ConnectToSite(ctx, false)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	siteNodes, err := site.GetNodes(namespace)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	// look at every node on this site and see which ones match:
	for _, node := range siteNodes {
		if node.MatchAgainst(labels) {
			nodes = append(nodes, node)
		}
	}
	return nodes, nil
}

// ConnectToSite connects to the auth server of the given site via proxy.
// It returns connected and authenticated auth server client
//
// if 'quiet' is set to true, no errors will be printed to stdout, otherwise
// any connection errors are visible to a user.
func (proxy *ProxyClient) ConnectToSite(ctx context.Context, quiet bool) (auth.ClientI, error) {
	// get the current cluster:
	site, err := proxy.currentSite()
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// look at the certificate which we've received from the proxy and pick the 1st
	// valid principal to pass to the auth server
	authLogin := proxy.hostLogin
	certMethod, ok := proxy.authMethod.(*CertAuthMethod)
	if ok {
		if cert, ok := certMethod.Cert.PublicKey().(*ssh.Certificate); ok && len(cert.ValidPrincipals) > 0 {
			authLogin = cert.ValidPrincipals[0]
		}
	}

	// this connects us to the node which is an auth server for this site
	// note the addres we're using: "@sitename", which in practice looks like "@{site-global-id}"
	// the Teleport proxy interprets such address as a request to connec to the active auth server
	// of the named site
	nodeClient, err := proxy.ConnectToNode(ctx, "@"+site.Name, authLogin, quiet)
	if err != nil {
		log.Error(err)
		return nil, trace.Wrap(err)
	}
	// crate HTTP client to Auth API over SSH connection:
	sshDialer := func(network, addr string) (net.Conn, error) {
		return nodeClient.Client.Dial(network, addr)
	}
	clt, err := auth.NewClient("http://stub:0", sshDialer)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return clt, nil
}

// nodeName removes the port number from the hostname, if present
func nodeName(node string) string {
	n, _, err := net.SplitHostPort(node)
	if err != nil {
		return node
	}
	return n
}

// ConnectToNode connects to the ssh server via Proxy.
// It returns connected and authenticated NodeClient
func (proxy *ProxyClient) ConnectToNode(ctx context.Context, nodeAddress string, user string, quiet bool) (*NodeClient, error) {
	log.Infof("[CLIENT] connecting to node: %s", nodeAddress)

	// parse destination first:
	localAddr, err := utils.ParseAddr("tcp://" + proxy.proxyAddress)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	fakeAddr, err := utils.ParseAddr("tcp://" + nodeAddress)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// we have to try every auth method separatedly,
	// because go SSH will try only one (fist) auth method
	// of a given type, so if you have 2 different public keys
	// you have to try each one differently
	proxySession, err := proxy.Client.NewSession()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	proxyWriter, err := proxySession.StdinPipe()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	proxyReader, err := proxySession.StdoutPipe()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	proxyErr, err := proxySession.StderrPipe()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	err = proxySession.RequestSubsystem("proxy:" + nodeAddress)
	if err != nil {
		// read the stderr output from the failed SSH session and append
		// it to the end of our own message:
		serverErrorMsg, _ := ioutil.ReadAll(proxyErr)
		return nil, trace.Errorf("failed connecting to node %v. %s",
			nodeName(strings.Split(nodeAddress, "@")[0]), serverErrorMsg)
	}
	pipeNetConn := utils.NewPipeNetConn(
		proxyReader,
		proxyWriter,
		proxySession,
		localAddr,
		fakeAddr,
	)
	sshConfig := &ssh.ClientConfig{
		User:            user,
		Auth:            []ssh.AuthMethod{proxy.authMethod},
		HostKeyCallback: proxy.hostKeyCallback,
	}
	conn, chans, reqs, err := newClientConn(ctx, pipeNetConn, nodeAddress, sshConfig)
	if err != nil {
		if utils.IsHandshakeFailedError(err) {
			proxySession.Close()
			parts := strings.Split(nodeAddress, "@")
			hostname := parts[0]
			if len(hostname) == 0 && len(parts) > 1 {
				hostname = "cluster " + parts[1]
			}
			return nil, trace.Errorf(`access denied to %v connecting to %v`, user, nodeName(hostname))
		}
		return nil, trace.Wrap(err)
	}

	client := ssh.NewClient(conn, chans, reqs)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return &NodeClient{Client: client, Proxy: proxy, Namespace: defaults.Namespace}, nil
}

// newClientConn is a wrapper around ssh.NewClientConn
func newClientConn(ctx context.Context,
	conn net.Conn,
	nodeAddress string,
	config *ssh.ClientConfig) (ssh.Conn, <-chan ssh.NewChannel, <-chan *ssh.Request, error) {

	type response struct {
		conn   ssh.Conn
		chanCh <-chan ssh.NewChannel
		reqCh  <-chan *ssh.Request
		err    error
	}

	respCh := make(chan response, 1)
	go func() {
		conn, chans, reqs, err := ssh.NewClientConn(conn, nodeAddress, config)
		respCh <- response{conn, chans, reqs, err}
	}()

	select {
	case resp := <-respCh:
		if resp.err != nil {
			return nil, nil, nil, trace.Wrap(resp.err, "failed to connect to %q", nodeAddress)
		}
		return resp.conn, resp.chanCh, resp.reqCh, nil
	case <-ctx.Done():
		errClose := conn.Close()
		if errClose != nil {
			log.Error(errClose)
		}
		// drain the channel
		resp := <-respCh
		return nil, nil, nil, trace.ConnectionProblem(resp.err, "failed to connect to %q", nodeAddress)
	}
}

func (proxy *ProxyClient) Close() error {
	return proxy.Client.Close()
}

// Upload uploads local file(s) or to the remote server's destination path
func (client *NodeClient) Upload(srcPath, rDestPath string, recursive bool, stderr, progressWriter io.Writer) error {
	scpConf := scp.Command{
		Source:    true,
		Recursive: recursive,
		Target:    srcPath,
		Terminal:  progressWriter,
	}

	// "impersonate" scp to a server
	shellCmd := "/usr/bin/scp -t"
	if recursive {
		shellCmd += " -r"
	}
	shellCmd += " " + rDestPath
	return client.scp(scpConf, shellCmd, stderr)
}

// Download downloads file or dir from the remote server
func (client *NodeClient) Download(remoteSourcePath, localDestinationPath string, recursive bool, stderr, progressWriter io.Writer) error {
	scpConf := scp.Command{
		Sink:      true,
		Recursive: recursive,
		Target:    localDestinationPath,
		Terminal:  progressWriter,
	}

	// "impersonate" scp to a server
	shellCmd := "/usr/bin/scp -f"
	if recursive {
		shellCmd += " -r"
	}
	shellCmd += " " + remoteSourcePath
	return client.scp(scpConf, shellCmd, stderr)
}

// scp runs remote scp command(shellCmd) on the remote server and
// runs local scp handler using scpConf
func (client *NodeClient) scp(scpCommand scp.Command, shellCmd string, errWriter io.Writer) error {
	session, err := client.Client.NewSession()
	if err != nil {
		return trace.Wrap(err)
	}
	defer session.Close()

	stdin, err := session.StdinPipe()
	if err != nil {
		return trace.Wrap(err)
	}

	stdout, err := session.StdoutPipe()
	if err != nil {
		return trace.Wrap(err)
	}

	ch := utils.NewPipeNetConn(
		stdout,
		stdin,
		utils.MultiCloser(),
		&net.IPAddr{},
		&net.IPAddr{},
	)

	closeC := make(chan interface{}, 1)
	go func() {
		if err = scpCommand.Execute(ch); err != nil {
			log.Error(err)
		}
		stdin.Close()
		close(closeC)
	}()

	runErr := session.Run(shellCmd)
	if runErr != nil && err == nil {
		err = runErr
	}
	<-closeC
	if trace.IsEOF(err) {
		err = nil
	}
	return trace.Wrap(err)
}

// listenAndForward listens on a given socket and forwards all incoming connections
// to the given remote address via
func (client *NodeClient) listenAndForward(socket net.Listener, remoteAddr string) {
	defer socket.Close()
	defer client.Close()
	proxyConnection := func(incoming net.Conn) {
		defer incoming.Close()
		var (
			conn net.Conn
			err  error
		)
		log.Debugf("nodeClient.listenAndForward(%v -> %v) started", incoming.RemoteAddr(), remoteAddr)
		for attempt := 1; attempt <= 5; attempt++ {
			conn, err = client.Client.Dial("tcp", remoteAddr)
			if err != nil {
				log.Errorf("Connection attempt %v: %v", attempt, err)
				// failed to establish an outbound connection? try again:
				time.Sleep(time.Millisecond * time.Duration(100*attempt))
				continue
			}
			// connection established: continue:
			break
		}
		// permanent failure establishing connection
		if err != nil {
			log.Errorf("Failed to connect to node %v", remoteAddr)
			return
		}
		defer conn.Close()
		// start proxying:
		doneC := make(chan interface{}, 2)
		go func() {
			io.Copy(incoming, conn)
			doneC <- true
		}()
		go func() {
			io.Copy(conn, incoming)
			doneC <- true
		}()
		<-doneC
		<-doneC
		log.Debugf("nodeClient.listenAndForward(%v -> %v) exited", incoming.RemoteAddr(), remoteAddr)
	}
	// request processing loop: accept incoming requests to be connected to nodes
	// and proxy them to 'remoteAddr'
	for {
		incoming, err := socket.Accept()
		if err != nil {
			log.Error(err)
			break
		}
		go proxyConnection(incoming)
	}
}

func (client *NodeClient) Close() error {
	return client.Client.Close()
}

// currentSite returns the connection to the API of the current cluster
func (proxy *ProxyClient) currentSite() (*services.Site, error) {
	sites, err := proxy.GetSites()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	if len(sites) == 0 {
		return nil, trace.NotFound("no clusters registered")
	}
	if proxy.siteName == "" {
		return &sites[0], nil
	}
	for _, site := range sites {
		if site.Name == proxy.siteName {
			return &site, nil
		}
	}
	return nil, trace.NotFound("cluster %v not found", proxy.siteName)
}