ssh/client.go - crypto - Git at Google

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package ssh

 import (
 	"bytes"
 	"errors"
 	"fmt"
 	"net"
 	"os"
 	"sync"
 	"time"
 )

 // Client implements a traditional SSH client that supports shells,
 // subprocesses, TCP port/streamlocal forwarding and tunneled dialing.
 type Client struct {
 	Conn

 	handleForwardsOnce sync.Once // guards calling (*Client).handleForwards

 	forwards        forwardList // forwarded tcpip connections from the remote side
 	mu              sync.Mutex
 	channelHandlers map[string]chan NewChannel
 }

 // HandleChannelOpen returns a channel on which NewChannel requests
 // for the given type are sent. If the type already is being handled,
 // nil is returned. The channel is closed when the connection is closed.
 func (c *Client) HandleChannelOpen(channelType string) <-chan NewChannel {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	if c.channelHandlers == nil {
 		// The SSH channel has been closed.
 		c := make(chan NewChannel)
 		close(c)
 		return c
 	}

 	ch := c.channelHandlers[channelType]
 	if ch != nil {
 		return nil
 	}

 	ch = make(chan NewChannel, chanSize)
 	c.channelHandlers[channelType] = ch
 	return ch
 }

 // NewClient creates a Client on top of the given connection.
 func NewClient(c Conn, chans <-chan NewChannel, reqs <-chan *Request) *Client {
 	conn := &Client{
 		Conn:            c,
 		channelHandlers: make(map[string]chan NewChannel, 1),
 	}

 	go conn.handleGlobalRequests(reqs)
 	go conn.handleChannelOpens(chans)
 	go func() {
 		conn.Wait()
 		conn.forwards.closeAll()
 	}()
 	return conn
 }

 // NewClientConn establishes an authenticated SSH connection using c
 // as the underlying transport.  The Request and NewChannel channels
 // must be serviced or the connection will hang.
 func NewClientConn(c net.Conn, addr string, config *ClientConfig) (Conn, <-chan NewChannel, <-chan *Request, error) {
 	fullConf := *config
 	fullConf.SetDefaults()
 	if fullConf.HostKeyCallback == nil {
 		c.Close()
 		return nil, nil, nil, errors.New("ssh: must specify HostKeyCallback")
 	}

 	conn := &connection{
 		sshConn: sshConn{conn: c, user: fullConf.User},
 	}

 	if err := conn.clientHandshake(addr, &fullConf); err != nil {
 		c.Close()
 		return nil, nil, nil, fmt.Errorf("ssh: handshake failed: %v", err)
 	}
 	conn.mux = newMux(conn.transport)
 	return conn, conn.mux.incomingChannels, conn.mux.incomingRequests, nil
 }

 // clientHandshake performs the client side key exchange. See RFC 4253 Section
 // 7.
 func (c *connection) clientHandshake(dialAddress string, config *ClientConfig) error {
 	if config.ClientVersion != "" {
 		c.clientVersion = []byte(config.ClientVersion)
 	} else {
 		c.clientVersion = []byte(packageVersion)
 	}
 	var err error
 	c.serverVersion, err = exchangeVersions(c.sshConn.conn, c.clientVersion)
 	if err != nil {
 		return err
 	}

 	c.transport = newClientTransport(
 		newTransport(c.sshConn.conn, config.Rand, true /* is client */),
 		c.clientVersion, c.serverVersion, config, dialAddress, c.sshConn.RemoteAddr())
 	if err := c.transport.waitSession(); err != nil {
 		return err
 	}

 	c.sessionID = c.transport.getSessionID()
 	return c.clientAuthenticate(config)
 }

 // verifyHostKeySignature verifies the host key obtained in the key
 // exchange.
 func verifyHostKeySignature(hostKey PublicKey, algo string, result *kexResult) error {
 	sig, rest, ok := parseSignatureBody(result.Signature)
 	if len(rest) > 0 || !ok {
 		return errors.New("ssh: signature parse error")
 	}

 	// For keys, underlyingAlgo is exactly algo. For certificates,
 	// we have to look up the underlying key algorithm that SSH
 	// uses to evaluate signatures.
 	underlyingAlgo := algo
 	for sigAlgo, certAlgo := range certAlgoNames {
 		if certAlgo == algo {
 			underlyingAlgo = sigAlgo
 		}
 	}
 	if sig.Format != underlyingAlgo {
 		return fmt.Errorf("ssh: invalid signature algorithm %q, expected %q", sig.Format, underlyingAlgo)
 	}

 	return hostKey.Verify(result.H, sig)
 }

 // NewSession opens a new Session for this client. (A session is a remote
 // execution of a program.)
 func (c *Client) NewSession() (*Session, error) {
 	ch, in, err := c.OpenChannel("session", nil)
 	if err != nil {
 		return nil, err
 	}
 	return newSession(ch, in)
 }

 func (c *Client) handleGlobalRequests(incoming <-chan *Request) {
 	for r := range incoming {
 		// This handles keepalive messages and matches
 		// the behaviour of OpenSSH.
 		r.Reply(false, nil)
 	}
 }

 // handleChannelOpens channel open messages from the remote side.
 func (c *Client) handleChannelOpens(in <-chan NewChannel) {
 	for ch := range in {
 		c.mu.Lock()
 		handler := c.channelHandlers[ch.ChannelType()]
 		c.mu.Unlock()

 		if handler != nil {
 			handler <- ch
 		} else {
 			ch.Reject(UnknownChannelType, fmt.Sprintf("unknown channel type: %v", ch.ChannelType()))
 		}
 	}

 	c.mu.Lock()
 	for _, ch := range c.channelHandlers {
 		close(ch)
 	}
 	c.channelHandlers = nil
 	c.mu.Unlock()
 }

 // Dial starts a client connection to the given SSH server. It is a
 // convenience function that connects to the given network address,
 // initiates the SSH handshake, and then sets up a Client.  For access
 // to incoming channels and requests, use net.Dial with NewClientConn
 // instead.
 func Dial(network, addr string, config *ClientConfig) (*Client, error) {
 	conn, err := net.DialTimeout(network, addr, config.Timeout)
 	if err != nil {
 		return nil, err
 	}
 	c, chans, reqs, err := NewClientConn(conn, addr, config)
 	if err != nil {
 		return nil, err
 	}
 	return NewClient(c, chans, reqs), nil
 }

 // HostKeyCallback is the function type used for verifying server
 // keys.  A HostKeyCallback must return nil if the host key is OK, or
 // an error to reject it. It receives the hostname as passed to Dial
 // or NewClientConn. The remote address is the RemoteAddr of the
 // net.Conn underlying the SSH connection.
 type HostKeyCallback func(hostname string, remote net.Addr, key PublicKey) error

 // BannerCallback is the function type used for treat the banner sent by
 // the server. A BannerCallback receives the message sent by the remote server.
 type BannerCallback func(message string) error

 // A ClientConfig structure is used to configure a Client. It must not be
 // modified after having been passed to an SSH function.
 type ClientConfig struct {
 	// Config contains configuration that is shared between clients and
 	// servers.
 	Config

 	// User contains the username to authenticate as.
 	User string

 	// Auth contains possible authentication methods to use with the
 	// server. Only the first instance of a particular RFC 4252 method will
 	// be used during authentication.
 	Auth []AuthMethod

 	// HostKeyCallback is called during the cryptographic
 	// handshake to validate the server's host key. The client
 	// configuration must supply this callback for the connection
 	// to succeed. The functions InsecureIgnoreHostKey or
 	// FixedHostKey can be used for simplistic host key checks.
 	HostKeyCallback HostKeyCallback

 	// BannerCallback is called during the SSH dance to display a custom
 	// server's message. The client configuration can supply this callback to
 	// handle it as wished. The function BannerDisplayStderr can be used for
 	// simplistic display on Stderr.
 	BannerCallback BannerCallback

 	// ClientVersion contains the version identification string that will
 	// be used for the connection. If empty, a reasonable default is used.
 	ClientVersion string

 	// HostKeyAlgorithms lists the public key algorithms that the client will
 	// accept from the server for host key authentication, in order of
 	// preference. If empty, a reasonable default is used. Any
 	// string returned from a PublicKey.Type method may be used, or
 	// any of the CertAlgo and KeyAlgo constants.
 	HostKeyAlgorithms []string

 	// Timeout is the maximum amount of time for the TCP connection to establish.
 	//
 	// A Timeout of zero means no timeout.
 	Timeout time.Duration
 }

 // InsecureIgnoreHostKey returns a function that can be used for
 // ClientConfig.HostKeyCallback to accept any host key. It should
 // not be used for production code.
 func InsecureIgnoreHostKey() HostKeyCallback {
 	return func(hostname string, remote net.Addr, key PublicKey) error {
 		return nil
 	}
 }

 type fixedHostKey struct {
 	key PublicKey
 }

 func (f *fixedHostKey) check(hostname string, remote net.Addr, key PublicKey) error {
 	if f.key == nil {
 		return fmt.Errorf("ssh: required host key was nil")
 	}
 	if !bytes.Equal(key.Marshal(), f.key.Marshal()) {
 		return fmt.Errorf("ssh: host key mismatch")
 	}
 	return nil
 }

 // FixedHostKey returns a function for use in
 // ClientConfig.HostKeyCallback to accept only a specific host key.
 func FixedHostKey(key PublicKey) HostKeyCallback {
 	hk := &fixedHostKey{key}
 	return hk.check
 }

 // BannerDisplayStderr returns a function that can be used for
 // ClientConfig.BannerCallback to display banners on os.Stderr.
 func BannerDisplayStderr() BannerCallback {
 	return func(banner string) error {
 		_, err := os.Stderr.WriteString(banner)

 		return err
 	}
 }
	// Copyright 2011 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package ssh

	import (
	"bytes"
	"errors"
	"fmt"
	"net"
	"os"
	"sync"
	"time"
	)

	// Client implements a traditional SSH client that supports shells,
	// subprocesses, TCP port/streamlocal forwarding and tunneled dialing.
	type Client struct {
	Conn

	handleForwardsOnce sync.Once // guards calling (*Client).handleForwards

	forwards forwardList // forwarded tcpip connections from the remote side
	mu sync.Mutex
	channelHandlers map[string]chan NewChannel
	}

	// HandleChannelOpen returns a channel on which NewChannel requests
	// for the given type are sent. If the type already is being handled,
	// nil is returned. The channel is closed when the connection is closed.
	func (c *Client) HandleChannelOpen(channelType string) <-chan NewChannel {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.channelHandlers == nil {
	// The SSH channel has been closed.
	c := make(chan NewChannel)
	close(c)
	return c
	}

	ch := c.channelHandlers[channelType]
	if ch != nil {
	return nil
	}

	ch = make(chan NewChannel, chanSize)
	c.channelHandlers[channelType] = ch
	return ch
	}

	// NewClient creates a Client on top of the given connection.
	func NewClient(c Conn, chans <-chan NewChannel, reqs <-chan Request) Client {
	conn := &Client{
	Conn: c,
	channelHandlers: make(map[string]chan NewChannel, 1),
	}

	go conn.handleGlobalRequests(reqs)
	go conn.handleChannelOpens(chans)
	go func() {
	conn.Wait()
	conn.forwards.closeAll()
	}()
	return conn
	}

	// NewClientConn establishes an authenticated SSH connection using c
	// as the underlying transport. The Request and NewChannel channels
	// must be serviced or the connection will hang.
	func NewClientConn(c net.Conn, addr string, config ClientConfig) (Conn, <-chan NewChannel, <-chan Request, error) {
	fullConf := *config
	fullConf.SetDefaults()
	if fullConf.HostKeyCallback == nil {
	c.Close()
	return nil, nil, nil, errors.New("ssh: must specify HostKeyCallback")
	}

	conn := &connection{
	sshConn: sshConn{conn: c, user: fullConf.User},
	}

	if err := conn.clientHandshake(addr, &fullConf); err != nil {
	c.Close()
	return nil, nil, nil, fmt.Errorf("ssh: handshake failed: %v", err)
	}
	conn.mux = newMux(conn.transport)
	return conn, conn.mux.incomingChannels, conn.mux.incomingRequests, nil
	}

	// clientHandshake performs the client side key exchange. See RFC 4253 Section
	// 7.
	func (c connection) clientHandshake(dialAddress string, config ClientConfig) error {
	if config.ClientVersion != "" {
	c.clientVersion = []byte(config.ClientVersion)
	} else {
	c.clientVersion = []byte(packageVersion)
	}
	var err error
	c.serverVersion, err = exchangeVersions(c.sshConn.conn, c.clientVersion)
	if err != nil {
	return err
	}

	c.transport = newClientTransport(
	newTransport(c.sshConn.conn, config.Rand, true /* is client */),
	c.clientVersion, c.serverVersion, config, dialAddress, c.sshConn.RemoteAddr())
	if err := c.transport.waitSession(); err != nil {
	return err
	}

	c.sessionID = c.transport.getSessionID()
	return c.clientAuthenticate(config)
	}

	// verifyHostKeySignature verifies the host key obtained in the key
	// exchange.
	func verifyHostKeySignature(hostKey PublicKey, algo string, result *kexResult) error {
	sig, rest, ok := parseSignatureBody(result.Signature)
	if len(rest) > 0 \|\| !ok {
	return errors.New("ssh: signature parse error")
	}

	// For keys, underlyingAlgo is exactly algo. For certificates,
	// we have to look up the underlying key algorithm that SSH
	// uses to evaluate signatures.
	underlyingAlgo := algo
	for sigAlgo, certAlgo := range certAlgoNames {
	if certAlgo == algo {
	underlyingAlgo = sigAlgo
	}
	}
	if sig.Format != underlyingAlgo {
	return fmt.Errorf("ssh: invalid signature algorithm %q, expected %q", sig.Format, underlyingAlgo)
	}

	return hostKey.Verify(result.H, sig)
	}

	// NewSession opens a new Session for this client. (A session is a remote
	// execution of a program.)
	func (c Client) NewSession() (Session, error) {
	ch, in, err := c.OpenChannel("session", nil)
	if err != nil {
	return nil, err
	}
	return newSession(ch, in)
	}

	func (c Client) handleGlobalRequests(incoming <-chan Request) {
	for r := range incoming {
	// This handles keepalive messages and matches
	// the behaviour of OpenSSH.
	r.Reply(false, nil)
	}
	}

	// handleChannelOpens channel open messages from the remote side.
	func (c *Client) handleChannelOpens(in <-chan NewChannel) {
	for ch := range in {
	c.mu.Lock()
	handler := c.channelHandlers[ch.ChannelType()]
	c.mu.Unlock()

	if handler != nil {
	handler <- ch
	} else {
	ch.Reject(UnknownChannelType, fmt.Sprintf("unknown channel type: %v", ch.ChannelType()))
	}
	}

	c.mu.Lock()
	for _, ch := range c.channelHandlers {
	close(ch)
	}
	c.channelHandlers = nil
	c.mu.Unlock()
	}

	// Dial starts a client connection to the given SSH server. It is a
	// convenience function that connects to the given network address,
	// initiates the SSH handshake, and then sets up a Client. For access
	// to incoming channels and requests, use net.Dial with NewClientConn
	// instead.
	func Dial(network, addr string, config ClientConfig) (Client, error) {
	conn, err := net.DialTimeout(network, addr, config.Timeout)
	if err != nil {
	return nil, err
	}
	c, chans, reqs, err := NewClientConn(conn, addr, config)
	if err != nil {
	return nil, err
	}
	return NewClient(c, chans, reqs), nil
	}

	// HostKeyCallback is the function type used for verifying server
	// keys. A HostKeyCallback must return nil if the host key is OK, or
	// an error to reject it. It receives the hostname as passed to Dial
	// or NewClientConn. The remote address is the RemoteAddr of the
	// net.Conn underlying the SSH connection.
	type HostKeyCallback func(hostname string, remote net.Addr, key PublicKey) error

	// BannerCallback is the function type used for treat the banner sent by
	// the server. A BannerCallback receives the message sent by the remote server.
	type BannerCallback func(message string) error

	// A ClientConfig structure is used to configure a Client. It must not be
	// modified after having been passed to an SSH function.
	type ClientConfig struct {
	// Config contains configuration that is shared between clients and
	// servers.
	Config

	// User contains the username to authenticate as.
	User string

	// Auth contains possible authentication methods to use with the
	// server. Only the first instance of a particular RFC 4252 method will
	// be used during authentication.
	Auth []AuthMethod

	// HostKeyCallback is called during the cryptographic
	// handshake to validate the server's host key. The client
	// configuration must supply this callback for the connection
	// to succeed. The functions InsecureIgnoreHostKey or
	// FixedHostKey can be used for simplistic host key checks.
	HostKeyCallback HostKeyCallback

	// BannerCallback is called during the SSH dance to display a custom
	// server's message. The client configuration can supply this callback to
	// handle it as wished. The function BannerDisplayStderr can be used for
	// simplistic display on Stderr.
	BannerCallback BannerCallback

	// ClientVersion contains the version identification string that will
	// be used for the connection. If empty, a reasonable default is used.
	ClientVersion string

	// HostKeyAlgorithms lists the public key algorithms that the client will
	// accept from the server for host key authentication, in order of
	// preference. If empty, a reasonable default is used. Any
	// string returned from a PublicKey.Type method may be used, or
	// any of the CertAlgo and KeyAlgo constants.
	HostKeyAlgorithms []string

	// Timeout is the maximum amount of time for the TCP connection to establish.
	//
	// A Timeout of zero means no timeout.
	Timeout time.Duration
	}

	// InsecureIgnoreHostKey returns a function that can be used for
	// ClientConfig.HostKeyCallback to accept any host key. It should
	// not be used for production code.
	func InsecureIgnoreHostKey() HostKeyCallback {
	return func(hostname string, remote net.Addr, key PublicKey) error {
	return nil
	}
	}

	type fixedHostKey struct {
	key PublicKey
	}

	func (f *fixedHostKey) check(hostname string, remote net.Addr, key PublicKey) error {
	if f.key == nil {
	return fmt.Errorf("ssh: required host key was nil")
	}
	if !bytes.Equal(key.Marshal(), f.key.Marshal()) {
	return fmt.Errorf("ssh: host key mismatch")
	}
	return nil
	}

	// FixedHostKey returns a function for use in
	// ClientConfig.HostKeyCallback to accept only a specific host key.
	func FixedHostKey(key PublicKey) HostKeyCallback {
	hk := &fixedHostKey{key}
	return hk.check
	}

	// BannerDisplayStderr returns a function that can be used for
	// ClientConfig.BannerCallback to display banners on os.Stderr.
	func BannerDisplayStderr() BannerCallback {
	return func(banner string) error {
	_, err := os.Stderr.WriteString(banner)

	return err
	}
	}