/
ssh_gocrypto.go
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/
ssh_gocrypto.go
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// Copyright 2013 Canonical Ltd.
// Licensed under the LGPLv3, see LICENCE file for details.
package ssh
import (
"bytes"
"fmt"
"io"
"io/ioutil"
"net"
"os"
"os/exec"
"os/user"
"strconv"
"strings"
"sync"
"time"
"github.com/juju/clock"
"github.com/juju/errors"
"github.com/juju/mutex"
"github.com/juju/utils"
"golang.org/x/crypto/ssh"
"golang.org/x/crypto/ssh/knownhosts"
"golang.org/x/crypto/ssh/terminal"
)
const sshDefaultPort = 22
// GoCryptoClient is an implementation of Client that
// uses the embedded go.crypto/ssh SSH client.
//
// GoCryptoClient is intentionally limited in the
// functionality that it enables, as it is currently
// intended to be used only for non-interactive command
// execution.
type GoCryptoClient struct {
signers []ssh.Signer
}
// NewGoCryptoClient creates a new GoCryptoClient.
//
// If no signers are specified, NewGoCryptoClient will
// use the private key generated by LoadClientKeys.
func NewGoCryptoClient(signers ...ssh.Signer) (*GoCryptoClient, error) {
return &GoCryptoClient{signers: signers}, nil
}
// Command implements Client.Command.
func (c *GoCryptoClient) Command(host string, command []string, options *Options) *Cmd {
shellCommand := utils.CommandString(command...)
signers := c.signers
if len(signers) == 0 {
signers = privateKeys()
}
user, host := splitUserHost(host)
port := sshDefaultPort
var proxyCommand []string
var knownHostsFile string
var strictHostKeyChecking StrictHostChecksOption
var hostKeyAlgorithms []string
if options != nil {
if options.port != 0 {
port = options.port
}
proxyCommand = options.proxyCommand
knownHostsFile = options.knownHostsFile
strictHostKeyChecking = options.strictHostKeyChecking
hostKeyAlgorithms = options.hostKeyAlgorithms
}
logger.Tracef(`running (equivalent of): ssh "%s@%s" -p %d '%s'`, user, host, port, shellCommand)
return &Cmd{impl: &goCryptoCommand{
signers: signers,
user: user,
addr: net.JoinHostPort(host, strconv.Itoa(port)),
command: shellCommand,
proxyCommand: proxyCommand,
knownHostsFile: knownHostsFile,
strictHostKeyChecking: strictHostKeyChecking,
hostKeyAlgorithms: hostKeyAlgorithms,
}}
}
// Copy implements Client.Copy.
//
// Copy is currently unimplemented, and will always return an error.
func (c *GoCryptoClient) Copy(args []string, options *Options) error {
return errors.Errorf("scp command is not implemented (OpenSSH scp not available in PATH)")
}
type goCryptoCommand struct {
signers []ssh.Signer
user string
addr string
command string
proxyCommand []string
knownHostsFile string
strictHostKeyChecking StrictHostChecksOption
hostKeyAlgorithms []string
stdin io.Reader
stdout io.Writer
stderr io.Writer
client *ssh.Client
sess *ssh.Session
}
var sshDial = ssh.Dial
var sshDialWithProxy = func(addr string, proxyCommand []string, config *ssh.ClientConfig) (*ssh.Client, error) {
if len(proxyCommand) == 0 {
return sshDial("tcp", addr, config)
}
// User has specified a proxy. Create a pipe and
// redirect the proxy command's stdin/stdout to it.
host, port, err := net.SplitHostPort(addr)
if err != nil {
host = addr
}
for i, arg := range proxyCommand {
arg = strings.Replace(arg, "%h", host, -1)
if port != "" {
arg = strings.Replace(arg, "%p", port, -1)
}
arg = strings.Replace(arg, "%r", config.User, -1)
proxyCommand[i] = arg
}
client, server := net.Pipe()
logger.Tracef(`executing proxy command %q`, proxyCommand)
cmd := exec.Command(proxyCommand[0], proxyCommand[1:]...)
cmd.Stdin = server
cmd.Stdout = server
cmd.Stderr = os.Stderr
if err := cmd.Start(); err != nil {
return nil, err
}
conn, chans, reqs, err := ssh.NewClientConn(client, addr, config)
if err != nil {
return nil, err
}
return ssh.NewClient(conn, chans, reqs), nil
}
func (c *goCryptoCommand) ensureSession() (*ssh.Session, error) {
if c.sess != nil {
return c.sess, nil
}
if len(c.signers) == 0 {
return nil, errors.Errorf("no private keys available")
}
if c.user == "" {
currentUser, err := user.Current()
if err != nil {
return nil, errors.Errorf("getting current user: %v", err)
}
c.user = currentUser.Username
}
config := &ssh.ClientConfig{
User: c.user,
HostKeyCallback: c.hostKeyCallback,
HostKeyAlgorithms: c.hostKeyAlgorithms,
Auth: []ssh.AuthMethod{
ssh.PublicKeysCallback(func() ([]ssh.Signer, error) {
return c.signers, nil
}),
},
}
client, err := sshDialWithProxy(c.addr, c.proxyCommand, config)
if err != nil {
return nil, err
}
sess, err := client.NewSession()
if err != nil {
client.Close()
return nil, err
}
c.client = client
c.sess = sess
c.sess.Stdin = WrapStdin(c.stdin)
c.sess.Stdout = c.stdout
c.sess.Stderr = c.stderr
return sess, nil
}
func (c *goCryptoCommand) Start() error {
sess, err := c.ensureSession()
if err != nil {
return err
}
if c.command == "" {
return sess.Shell()
}
return sess.Start(c.command)
}
func (c *goCryptoCommand) Close() error {
if c.sess == nil {
return nil
}
err0 := c.sess.Close()
err1 := c.client.Close()
if err0 == nil {
err0 = err1
}
c.sess = nil
c.client = nil
return err0
}
func (c *goCryptoCommand) Wait() error {
if c.sess == nil {
return errors.Errorf("command has not been started")
}
err := c.sess.Wait()
c.Close()
return err
}
func (c *goCryptoCommand) Kill() error {
if c.sess == nil {
return errors.Errorf("command has not been started")
}
return c.sess.Signal(ssh.SIGKILL)
}
func (c *goCryptoCommand) SetStdio(stdin io.Reader, stdout, stderr io.Writer) {
c.stdin = stdin
c.stdout = stdout
c.stderr = stderr
}
func (c *goCryptoCommand) StdinPipe() (io.WriteCloser, io.Reader, error) {
sess, err := c.ensureSession()
if err != nil {
return nil, nil, err
}
wc, err := sess.StdinPipe()
return wc, sess.Stdin, err
}
func (c *goCryptoCommand) StdoutPipe() (io.ReadCloser, io.Writer, error) {
sess, err := c.ensureSession()
if err != nil {
return nil, nil, err
}
wc, err := sess.StdoutPipe()
return ioutil.NopCloser(wc), sess.Stdout, err
}
func (c *goCryptoCommand) StderrPipe() (io.ReadCloser, io.Writer, error) {
sess, err := c.ensureSession()
if err != nil {
return nil, nil, err
}
wc, err := sess.StderrPipe()
return ioutil.NopCloser(wc), sess.Stderr, err
}
func (c *goCryptoCommand) hostKeyCallback(hostname string, remote net.Addr, key ssh.PublicKey) error {
knownHostsFile := c.knownHostsFile
if knownHostsFile == "" {
knownHostsFile = GoCryptoKnownHostsFile()
if knownHostsFile == "" {
return errors.New("known_hosts file not configured")
}
}
var printError func(string) error
term, cleanupTerm, err := getTerminal()
if err != nil {
return errors.Trace(err)
} else if term != nil {
defer cleanupTerm()
printError = func(message string) error {
_, err := fmt.Fprintln(term, message)
return err
}
} else {
printError = func(message string) error {
logger.Errorf("%s", message)
return nil
}
}
matched, err := checkHostKey(hostname, remote, key, knownHostsFile, printError)
if err != nil || matched {
return errors.Trace(err)
}
// We did not find a matching key, so what we do next depends on the
// strict host key checking configuration.
var warnAdd bool
switch c.strictHostKeyChecking {
case StrictHostChecksNo:
// Don't ask, just add.
warnAdd = true
case StrictHostChecksDefault, StrictHostChecksAsk:
message := fmt.Sprintf(`The authenticity of host '%s (%s)' can't be established.
%s key fingerprint is %s.
`,
hostname,
remote,
key.Type(),
ssh.FingerprintSHA256(key),
)
if term == nil {
// If we're not running in a terminal,
// we can't ask the user if they want
// to accept.
logger.Errorf("%s", message)
return errors.New("not running in a terminal, cannot prompt for verification")
}
// Prompt user, asking if they trust the key.
fmt.Fprint(term, message+"Are you sure you want to continue connecting (yes/no)? ")
for {
line, err := term.ReadLine()
if err != nil {
return errors.Trace(err)
}
var yes bool
switch strings.ToLower(line) {
case "yes":
yes = true
case "no":
return errors.New("Host key verification failed.")
default:
fmt.Fprint(term, "Please type 'yes' or 'no': ")
}
if yes {
break
}
}
default:
return errors.Errorf(
`no %s host key is known for %s and you have requested strict checking`,
key.Type(), hostname,
)
}
if knownHostsFile != os.DevNull {
// Make sure no other process modifies the file.
releaser, err := mutex.Acquire(mutex.Spec{
Name: "juju-ssh-client",
Clock: clock.WallClock,
Delay: time.Second,
})
if err != nil {
return errors.Trace(err)
}
defer releaser.Release()
// Write the file atomically, so the initial ReadAll above
// doesn't have to hold the mutex.
knownHostsData, err := ioutil.ReadFile(knownHostsFile)
if err != nil && !os.IsNotExist(err) {
return errors.Trace(err)
}
buf := bytes.NewBuffer(knownHostsData)
if len(knownHostsData) > 0 && !bytes.HasSuffix(knownHostsData, []byte("\n")) {
buf.WriteRune('\n')
}
buf.WriteString(knownhosts.Line([]string{hostname}, key))
buf.WriteRune('\n')
if err := utils.AtomicWriteFile(knownHostsFile, buf.Bytes(), 0600); err != nil {
return errors.Trace(err)
}
}
if warnAdd {
printError(fmt.Sprintf(
"Warning: permanently added '%s' (%s) to the list of known hosts.",
hostname, key.Type(),
))
}
return nil
}
type readLineWriter interface {
io.Writer
ReadLine() (string, error)
}
var getTerminal = func() (readLineWriter, func(), error) {
if fd := int(os.Stdin.Fd()); terminal.IsTerminal(fd) {
oldState, err := terminal.MakeRaw(fd)
if err != nil {
return nil, nil, errors.Trace(err)
}
cleanup := func() { terminal.Restore(fd, oldState) }
return terminal.NewTerminal(os.Stdin, ""), cleanup, nil
}
return nil, nil, nil
}
// checkHostKey checks the given (hostname, address, public key) tuple
// against the local known-hosts database, if it exists, and returns a
// boolean indicating whether a match was found, and any errors encountered.
func checkHostKey(
hostname string,
remote net.Addr,
key ssh.PublicKey,
knownHostsFile string,
printError func(string) error,
) (bool, error) {
// NOTE(axw) the knownhosts code is incomplete, but enough for
// our limited use cases. We do not support parsing a known_hosts
// file managed by OpenSSH (due to hashed hosts, etc.), but that
// is OK since this client exists only to support systems that
// do not have access to OpenSSH.
callback, err := knownhosts.New(knownHostsFile)
if err != nil {
if os.IsNotExist(err) {
// The known_hosts file does not exist.
return false, nil
}
return false, errors.Trace(err)
}
err = callback(hostname, remote, key)
switch err := err.(type) {
case nil:
// Known host with matching key.
return true, nil
case *knownhosts.KeyError:
if len(err.Want) == 0 {
// Unknown host.
return false, nil
}
head := fmt.Sprintf(`
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the %s key sent by the remote host is
%s.
Please contact your system administrator.
Add correct host key in %s to get rid of this message.
`[1:], key.Type(), ssh.FingerprintSHA256(key), knownHostsFile)
var typeKey *knownhosts.KnownKey
for i, knownKey := range err.Want {
if knownKey.Key.Type() == key.Type() {
typeKey = &err.Want[i]
}
}
var tail string
if typeKey != nil {
tail = fmt.Sprintf(
"Offending %s key in %s:%d",
typeKey.Key.Type(),
typeKey.Filename,
typeKey.Line,
)
} else {
tail = "Host was previously using different host key algorithms:"
for _, knownKey := range err.Want {
tail += fmt.Sprintf(
"\n - %s key in %s:%d",
knownKey.Key.Type(),
knownKey.Filename,
knownKey.Line,
)
}
}
if err := printError(head + tail); err != nil {
// Not being able to display the warning
// should be considered fatal.
return false, errors.Annotate(
err, "failed to print host key mismatch warning",
)
}
}
return false, errors.Trace(err)
}
func splitUserHost(s string) (user, host string) {
userHost := strings.SplitN(s, "@", 2)
if len(userHost) == 2 {
return userHost[0], userHost[1]
}
return "", userHost[0]
}
var (
goCryptoKnownHostsMutex sync.Mutex
goCryptoKnownHostsFile string
)
// GoCryptoKnownHostsFile returns the known_hosts file used
// by the golang.org/x/crypto/ssh-based client by default.
func GoCryptoKnownHostsFile() string {
goCryptoKnownHostsMutex.Lock()
defer goCryptoKnownHostsMutex.Unlock()
return goCryptoKnownHostsFile
}
// SetGoCryptoKnownHostsFile returns the known_hosts file used
// by the golang.org/x/crypto/ssh-based client.
func SetGoCryptoKnownHostsFile(file string) {
goCryptoKnownHostsMutex.Lock()
defer goCryptoKnownHostsMutex.Unlock()
goCryptoKnownHostsFile = file
}