harness-drone/vendor/code.google.com/p/go.crypto/ssh/client_auth.go
2015-09-29 18:21:17 -07:00

509 lines
14 KiB
Go

// 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 (
"errors"
"fmt"
"io"
"net"
)
// authenticate authenticates with the remote server. See RFC 4252.
func (c *ClientConn) authenticate() error {
// initiate user auth session
if err := c.transport.writePacket(marshal(msgServiceRequest, serviceRequestMsg{serviceUserAuth})); err != nil {
return err
}
packet, err := c.transport.readPacket()
if err != nil {
return err
}
var serviceAccept serviceAcceptMsg
if err := unmarshal(&serviceAccept, packet, msgServiceAccept); err != nil {
return err
}
// during the authentication phase the client first attempts the "none" method
// then any untried methods suggested by the server.
tried, remain := make(map[string]bool), make(map[string]bool)
for auth := ClientAuth(new(noneAuth)); auth != nil; {
ok, methods, err := auth.auth(c.transport.sessionID, c.config.User, c.transport, c.config.rand())
if err != nil {
return err
}
if ok {
// success
return nil
}
tried[auth.method()] = true
delete(remain, auth.method())
for _, meth := range methods {
if tried[meth] {
// if we've tried meth already, skip it.
continue
}
remain[meth] = true
}
auth = nil
for _, a := range c.config.Auth {
if remain[a.method()] {
auth = a
break
}
}
}
return fmt.Errorf("ssh: unable to authenticate, attempted methods %v, no supported methods remain", keys(tried))
}
func keys(m map[string]bool) (s []string) {
for k := range m {
s = append(s, k)
}
return
}
// HostKeyChecker represents a database of known server host keys.
type HostKeyChecker interface {
// Check is called during the handshake to check server's
// public key for unexpected changes. The hostKey argument is
// in SSH wire format. It can be parsed using
// ssh.ParsePublicKey. The address before DNS resolution is
// passed in the addr argument, so the key can also be checked
// against the hostname.
Check(addr string, remote net.Addr, algorithm string, hostKey []byte) error
}
// A ClientAuth represents an instance of an RFC 4252 authentication method.
type ClientAuth interface {
// auth authenticates user over transport t.
// Returns true if authentication is successful.
// If authentication is not successful, a []string of alternative
// method names is returned.
auth(session []byte, user string, p packetConn, rand io.Reader) (bool, []string, error)
// method returns the RFC 4252 method name.
method() string
}
// "none" authentication, RFC 4252 section 5.2.
type noneAuth int
func (n *noneAuth) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
if err := c.writePacket(marshal(msgUserAuthRequest, userAuthRequestMsg{
User: user,
Service: serviceSSH,
Method: "none",
})); err != nil {
return false, nil, err
}
return handleAuthResponse(c)
}
func (n *noneAuth) method() string {
return "none"
}
// "password" authentication, RFC 4252 Section 8.
type passwordAuth struct {
ClientPassword
}
func (p *passwordAuth) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
type passwordAuthMsg struct {
User string
Service string
Method string
Reply bool
Password string
}
pw, err := p.Password(user)
if err != nil {
return false, nil, err
}
if err := c.writePacket(marshal(msgUserAuthRequest, passwordAuthMsg{
User: user,
Service: serviceSSH,
Method: "password",
Reply: false,
Password: pw,
})); err != nil {
return false, nil, err
}
return handleAuthResponse(c)
}
func (p *passwordAuth) method() string {
return "password"
}
// A ClientPassword implements access to a client's passwords.
type ClientPassword interface {
// Password returns the password to use for user.
Password(user string) (password string, err error)
}
// ClientAuthPassword returns a ClientAuth using password authentication.
func ClientAuthPassword(impl ClientPassword) ClientAuth {
return &passwordAuth{impl}
}
// ClientKeyring implements access to a client key ring.
type ClientKeyring interface {
// Key returns the i'th Publickey, or nil if no key exists at i.
Key(i int) (key PublicKey, err error)
// Sign returns a signature of the given data using the i'th key
// and the supplied random source.
Sign(i int, rand io.Reader, data []byte) (sig []byte, err error)
}
// "publickey" authentication, RFC 4252 Section 7.
type publickeyAuth struct {
ClientKeyring
}
type publickeyAuthMsg struct {
User string
Service string
Method string
// HasSig indicates to the receiver packet that the auth request is signed and
// should be used for authentication of the request.
HasSig bool
Algoname string
Pubkey string
// Sig is defined as []byte so marshal will exclude it during validateKey
Sig []byte `ssh:"rest"`
}
func (p *publickeyAuth) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
// Authentication is performed in two stages. The first stage sends an
// enquiry to test if each key is acceptable to the remote. The second
// stage attempts to authenticate with the valid keys obtained in the
// first stage.
var index int
// a map of public keys to their index in the keyring
validKeys := make(map[int]PublicKey)
for {
key, err := p.Key(index)
if err != nil {
return false, nil, err
}
if key == nil {
// no more keys in the keyring
break
}
if ok, err := p.validateKey(key, user, c); ok {
validKeys[index] = key
} else {
if err != nil {
return false, nil, err
}
}
index++
}
// methods that may continue if this auth is not successful.
var methods []string
for i, key := range validKeys {
pubkey := MarshalPublicKey(key)
algoname := key.PublicKeyAlgo()
data := buildDataSignedForAuth(session, userAuthRequestMsg{
User: user,
Service: serviceSSH,
Method: p.method(),
}, []byte(algoname), pubkey)
sigBlob, err := p.Sign(i, rand, data)
if err != nil {
return false, nil, err
}
// manually wrap the serialized signature in a string
s := serializeSignature(key.PublicKeyAlgo(), sigBlob)
sig := make([]byte, stringLength(len(s)))
marshalString(sig, s)
msg := publickeyAuthMsg{
User: user,
Service: serviceSSH,
Method: p.method(),
HasSig: true,
Algoname: algoname,
Pubkey: string(pubkey),
Sig: sig,
}
p := marshal(msgUserAuthRequest, msg)
if err := c.writePacket(p); err != nil {
return false, nil, err
}
success, methods, err := handleAuthResponse(c)
if err != nil {
return false, nil, err
}
if success {
return success, methods, err
}
}
return false, methods, nil
}
// validateKey validates the key provided it is acceptable to the server.
func (p *publickeyAuth) validateKey(key PublicKey, user string, c packetConn) (bool, error) {
pubkey := MarshalPublicKey(key)
algoname := key.PublicKeyAlgo()
msg := publickeyAuthMsg{
User: user,
Service: serviceSSH,
Method: p.method(),
HasSig: false,
Algoname: algoname,
Pubkey: string(pubkey),
}
if err := c.writePacket(marshal(msgUserAuthRequest, msg)); err != nil {
return false, err
}
return p.confirmKeyAck(key, c)
}
func (p *publickeyAuth) confirmKeyAck(key PublicKey, c packetConn) (bool, error) {
pubkey := MarshalPublicKey(key)
algoname := key.PublicKeyAlgo()
for {
packet, err := c.readPacket()
if err != nil {
return false, err
}
switch packet[0] {
case msgUserAuthBanner:
// TODO(gpaul): add callback to present the banner to the user
case msgUserAuthPubKeyOk:
msg := userAuthPubKeyOkMsg{}
if err := unmarshal(&msg, packet, msgUserAuthPubKeyOk); err != nil {
return false, err
}
if msg.Algo != algoname || msg.PubKey != string(pubkey) {
return false, nil
}
return true, nil
case msgUserAuthFailure:
return false, nil
default:
return false, UnexpectedMessageError{msgUserAuthSuccess, packet[0]}
}
}
panic("unreachable")
}
func (p *publickeyAuth) method() string {
return "publickey"
}
// ClientAuthKeyring returns a ClientAuth using public key authentication.
func ClientAuthKeyring(impl ClientKeyring) ClientAuth {
return &publickeyAuth{impl}
}
// handleAuthResponse returns whether the preceding authentication request succeeded
// along with a list of remaining authentication methods to try next and
// an error if an unexpected response was received.
func handleAuthResponse(c packetConn) (bool, []string, error) {
for {
packet, err := c.readPacket()
if err != nil {
return false, nil, err
}
switch packet[0] {
case msgUserAuthBanner:
// TODO: add callback to present the banner to the user
case msgUserAuthFailure:
msg := userAuthFailureMsg{}
if err := unmarshal(&msg, packet, msgUserAuthFailure); err != nil {
return false, nil, err
}
return false, msg.Methods, nil
case msgUserAuthSuccess:
return true, nil, nil
case msgDisconnect:
return false, nil, io.EOF
default:
return false, nil, UnexpectedMessageError{msgUserAuthSuccess, packet[0]}
}
}
panic("unreachable")
}
// ClientAuthAgent returns a ClientAuth using public key authentication via
// an agent.
func ClientAuthAgent(agent *AgentClient) ClientAuth {
return ClientAuthKeyring(&agentKeyring{agent: agent})
}
// agentKeyring implements ClientKeyring.
type agentKeyring struct {
agent *AgentClient
keys []*AgentKey
}
func (kr *agentKeyring) Key(i int) (key PublicKey, err error) {
if kr.keys == nil {
if kr.keys, err = kr.agent.RequestIdentities(); err != nil {
return
}
}
if i >= len(kr.keys) {
return
}
return kr.keys[i].Key()
}
func (kr *agentKeyring) Sign(i int, rand io.Reader, data []byte) (sig []byte, err error) {
var key PublicKey
if key, err = kr.Key(i); err != nil {
return
}
if key == nil {
return nil, errors.New("ssh: key index out of range")
}
if sig, err = kr.agent.SignRequest(key, data); err != nil {
return
}
// Unmarshal the signature.
var ok bool
if _, sig, ok = parseString(sig); !ok {
return nil, errors.New("ssh: malformed signature response from agent")
}
if sig, _, ok = parseString(sig); !ok {
return nil, errors.New("ssh: malformed signature response from agent")
}
return sig, nil
}
// ClientKeyboardInteractive should prompt the user for the given
// questions.
type ClientKeyboardInteractive interface {
// Challenge should print the questions, optionally disabling
// echoing (eg. for passwords), and return all the answers.
// Challenge may be called multiple times in a single
// session. After successful authentication, the server may
// send a challenge with no questions, for which the user and
// instruction messages should be printed. RFC 4256 section
// 3.3 details how the UI should behave for both CLI and
// GUI environments.
Challenge(user, instruction string, questions []string, echos []bool) ([]string, error)
}
// ClientAuthKeyboardInteractive returns a ClientAuth using a
// prompt/response sequence controlled by the server.
func ClientAuthKeyboardInteractive(impl ClientKeyboardInteractive) ClientAuth {
return &keyboardInteractiveAuth{impl}
}
type keyboardInteractiveAuth struct {
ClientKeyboardInteractive
}
func (k *keyboardInteractiveAuth) method() string {
return "keyboard-interactive"
}
func (k *keyboardInteractiveAuth) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
type initiateMsg struct {
User string
Service string
Method string
Language string
Submethods string
}
if err := c.writePacket(marshal(msgUserAuthRequest, initiateMsg{
User: user,
Service: serviceSSH,
Method: "keyboard-interactive",
})); err != nil {
return false, nil, err
}
for {
packet, err := c.readPacket()
if err != nil {
return false, nil, err
}
// like handleAuthResponse, but with less options.
switch packet[0] {
case msgUserAuthBanner:
// TODO: Print banners during userauth.
continue
case msgUserAuthInfoRequest:
// OK
case msgUserAuthFailure:
var msg userAuthFailureMsg
if err := unmarshal(&msg, packet, msgUserAuthFailure); err != nil {
return false, nil, err
}
return false, msg.Methods, nil
case msgUserAuthSuccess:
return true, nil, nil
default:
return false, nil, UnexpectedMessageError{msgUserAuthInfoRequest, packet[0]}
}
var msg userAuthInfoRequestMsg
if err := unmarshal(&msg, packet, packet[0]); err != nil {
return false, nil, err
}
// Manually unpack the prompt/echo pairs.
rest := msg.Prompts
var prompts []string
var echos []bool
for i := 0; i < int(msg.NumPrompts); i++ {
prompt, r, ok := parseString(rest)
if !ok || len(r) == 0 {
return false, nil, errors.New("ssh: prompt format error")
}
prompts = append(prompts, string(prompt))
echos = append(echos, r[0] != 0)
rest = r[1:]
}
if len(rest) != 0 {
return false, nil, fmt.Errorf("ssh: junk following message %q", rest)
}
answers, err := k.Challenge(msg.User, msg.Instruction, prompts, echos)
if err != nil {
return false, nil, err
}
if len(answers) != len(prompts) {
return false, nil, errors.New("ssh: not enough answers from keyboard-interactive callback")
}
responseLength := 1 + 4
for _, a := range answers {
responseLength += stringLength(len(a))
}
serialized := make([]byte, responseLength)
p := serialized
p[0] = msgUserAuthInfoResponse
p = p[1:]
p = marshalUint32(p, uint32(len(answers)))
for _, a := range answers {
p = marshalString(p, []byte(a))
}
if err := c.writePacket(serialized); err != nil {
return false, nil, err
}
}
}