+++ /dev/null
-// 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"
- "io"
-)
-
-// clientAuthenticate authenticates with the remote server. See RFC 4252.
-func (c *connection) clientAuthenticate(config *ClientConfig) error {
- // initiate user auth session
- if err := c.transport.writePacket(Marshal(&serviceRequestMsg{serviceUserAuth})); err != nil {
- return err
- }
- packet, err := c.transport.readPacket()
- if err != nil {
- return err
- }
- var serviceAccept serviceAcceptMsg
- if err := Unmarshal(packet, &serviceAccept); err != nil {
- return err
- }
-
- // during the authentication phase the client first attempts the "none" method
- // then any untried methods suggested by the server.
- tried := make(map[string]bool)
- var lastMethods []string
-
- sessionID := c.transport.getSessionID()
- for auth := AuthMethod(new(noneAuth)); auth != nil; {
- ok, methods, err := auth.auth(sessionID, config.User, c.transport, config.Rand)
- if err != nil {
- return err
- }
- if ok {
- // success
- return nil
- }
- tried[auth.method()] = true
- if methods == nil {
- methods = lastMethods
- }
- lastMethods = methods
-
- auth = nil
-
- findNext:
- for _, a := range config.Auth {
- candidateMethod := a.method()
- if tried[candidateMethod] {
- continue
- }
- for _, meth := range methods {
- if meth == candidateMethod {
- auth = a
- break findNext
- }
- }
- }
- }
- return fmt.Errorf("ssh: unable to authenticate, attempted methods %v, no supported methods remain", keys(tried))
-}
-
-func keys(m map[string]bool) []string {
- s := make([]string, 0, len(m))
-
- for key := range m {
- s = append(s, key)
- }
- return s
-}
-
-// An AuthMethod represents an instance of an RFC 4252 authentication method.
-type AuthMethod 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. If the slice is nil, it will be ignored
- // and the previous set of possible methods will be reused.
- 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(&userAuthRequestMsg{
- User: user,
- Service: serviceSSH,
- Method: "none",
- })); err != nil {
- return false, nil, err
- }
-
- return handleAuthResponse(c)
-}
-
-func (n *noneAuth) method() string {
- return "none"
-}
-
-// passwordCallback is an AuthMethod that fetches the password through
-// a function call, e.g. by prompting the user.
-type passwordCallback func() (password string, err error)
-
-func (cb passwordCallback) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
- type passwordAuthMsg struct {
- User string `sshtype:"50"`
- Service string
- Method string
- Reply bool
- Password string
- }
-
- pw, err := cb()
- // REVIEW NOTE: is there a need to support skipping a password attempt?
- // The program may only find out that the user doesn't have a password
- // when prompting.
- if err != nil {
- return false, nil, err
- }
-
- if err := c.writePacket(Marshal(&passwordAuthMsg{
- User: user,
- Service: serviceSSH,
- Method: cb.method(),
- Reply: false,
- Password: pw,
- })); err != nil {
- return false, nil, err
- }
-
- return handleAuthResponse(c)
-}
-
-func (cb passwordCallback) method() string {
- return "password"
-}
-
-// Password returns an AuthMethod using the given password.
-func Password(secret string) AuthMethod {
- return passwordCallback(func() (string, error) { return secret, nil })
-}
-
-// PasswordCallback returns an AuthMethod that uses a callback for
-// fetching a password.
-func PasswordCallback(prompt func() (secret string, err error)) AuthMethod {
- return passwordCallback(prompt)
-}
-
-type publickeyAuthMsg struct {
- User string `sshtype:"50"`
- 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 []byte
- // Sig is tagged with "rest" so Marshal will exclude it during
- // validateKey
- Sig []byte `ssh:"rest"`
-}
-
-// publicKeyCallback is an AuthMethod that uses a set of key
-// pairs for authentication.
-type publicKeyCallback func() ([]Signer, error)
-
-func (cb publicKeyCallback) method() string {
- return "publickey"
-}
-
-func (cb publicKeyCallback) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
- // Authentication is performed by sending an enquiry to test if a key is
- // acceptable to the remote. If the key is acceptable, the client will
- // attempt to authenticate with the valid key. If not the client will repeat
- // the process with the remaining keys.
-
- signers, err := cb()
- if err != nil {
- return false, nil, err
- }
- var methods []string
- for _, signer := range signers {
- ok, err := validateKey(signer.PublicKey(), user, c)
- if err != nil {
- return false, nil, err
- }
- if !ok {
- continue
- }
-
- pub := signer.PublicKey()
- pubKey := pub.Marshal()
- sign, err := signer.Sign(rand, buildDataSignedForAuth(session, userAuthRequestMsg{
- User: user,
- Service: serviceSSH,
- Method: cb.method(),
- }, []byte(pub.Type()), pubKey))
- if err != nil {
- return false, nil, err
- }
-
- // manually wrap the serialized signature in a string
- s := Marshal(sign)
- sig := make([]byte, stringLength(len(s)))
- marshalString(sig, s)
- msg := publickeyAuthMsg{
- User: user,
- Service: serviceSSH,
- Method: cb.method(),
- HasSig: true,
- Algoname: pub.Type(),
- PubKey: pubKey,
- Sig: sig,
- }
- p := Marshal(&msg)
- if err := c.writePacket(p); err != nil {
- return false, nil, err
- }
- var success bool
- success, methods, err = handleAuthResponse(c)
- if err != nil {
- return false, nil, err
- }
-
- // If authentication succeeds or the list of available methods does not
- // contain the "publickey" method, do not attempt to authenticate with any
- // other keys. According to RFC 4252 Section 7, the latter can occur when
- // additional authentication methods are required.
- if success || !containsMethod(methods, cb.method()) {
- return success, methods, err
- }
- }
-
- return false, methods, nil
-}
-
-func containsMethod(methods []string, method string) bool {
- for _, m := range methods {
- if m == method {
- return true
- }
- }
-
- return false
-}
-
-// validateKey validates the key provided is acceptable to the server.
-func validateKey(key PublicKey, user string, c packetConn) (bool, error) {
- pubKey := key.Marshal()
- msg := publickeyAuthMsg{
- User: user,
- Service: serviceSSH,
- Method: "publickey",
- HasSig: false,
- Algoname: key.Type(),
- PubKey: pubKey,
- }
- if err := c.writePacket(Marshal(&msg)); err != nil {
- return false, err
- }
-
- return confirmKeyAck(key, c)
-}
-
-func confirmKeyAck(key PublicKey, c packetConn) (bool, error) {
- pubKey := key.Marshal()
- algoname := key.Type()
-
- 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:
- var msg userAuthPubKeyOkMsg
- if err := Unmarshal(packet, &msg); err != nil {
- return false, err
- }
- if msg.Algo != algoname || !bytes.Equal(msg.PubKey, pubKey) {
- return false, nil
- }
- return true, nil
- case msgUserAuthFailure:
- return false, nil
- default:
- return false, unexpectedMessageError(msgUserAuthSuccess, packet[0])
- }
- }
-}
-
-// PublicKeys returns an AuthMethod that uses the given key
-// pairs.
-func PublicKeys(signers ...Signer) AuthMethod {
- return publicKeyCallback(func() ([]Signer, error) { return signers, nil })
-}
-
-// PublicKeysCallback returns an AuthMethod that runs the given
-// function to obtain a list of key pairs.
-func PublicKeysCallback(getSigners func() (signers []Signer, err error)) AuthMethod {
- return publicKeyCallback(getSigners)
-}
-
-// 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:
- var msg userAuthFailureMsg
- if err := Unmarshal(packet, &msg); err != nil {
- return false, nil, err
- }
- return false, msg.Methods, nil
- case msgUserAuthSuccess:
- return true, nil, nil
- default:
- return false, nil, unexpectedMessageError(msgUserAuthSuccess, packet[0])
- }
- }
-}
-
-// KeyboardInteractiveChallenge should print questions, optionally
-// disabling echoing (e.g. 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.
-type KeyboardInteractiveChallenge func(user, instruction string, questions []string, echos []bool) (answers []string, err error)
-
-// KeyboardInteractive returns a AuthMethod using a prompt/response
-// sequence controlled by the server.
-func KeyboardInteractive(challenge KeyboardInteractiveChallenge) AuthMethod {
- return challenge
-}
-
-func (cb KeyboardInteractiveChallenge) method() string {
- return "keyboard-interactive"
-}
-
-func (cb KeyboardInteractiveChallenge) auth(session []byte, user string, c packetConn, rand io.Reader) (bool, []string, error) {
- type initiateMsg struct {
- User string `sshtype:"50"`
- Service string
- Method string
- Language string
- Submethods string
- }
-
- if err := c.writePacket(Marshal(&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(packet, &msg); 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(packet, &msg); 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, errors.New("ssh: extra data following keyboard-interactive pairs")
- }
-
- answers, err := cb(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
- }
- }
-}
-
-type retryableAuthMethod struct {
- authMethod AuthMethod
- maxTries int
-}
-
-func (r *retryableAuthMethod) auth(session []byte, user string, c packetConn, rand io.Reader) (ok bool, methods []string, err error) {
- for i := 0; r.maxTries <= 0 || i < r.maxTries; i++ {
- ok, methods, err = r.authMethod.auth(session, user, c, rand)
- if ok || err != nil { // either success or error terminate
- return ok, methods, err
- }
- }
- return ok, methods, err
-}
-
-func (r *retryableAuthMethod) method() string {
- return r.authMethod.method()
-}
-
-// RetryableAuthMethod is a decorator for other auth methods enabling them to
-// be retried up to maxTries before considering that AuthMethod itself failed.
-// If maxTries is <= 0, will retry indefinitely
-//
-// This is useful for interactive clients using challenge/response type
-// authentication (e.g. Keyboard-Interactive, Password, etc) where the user
-// could mistype their response resulting in the server issuing a
-// SSH_MSG_USERAUTH_FAILURE (rfc4252 #8 [password] and rfc4256 #3.4
-// [keyboard-interactive]); Without this decorator, the non-retryable
-// AuthMethod would be removed from future consideration, and never tried again
-// (and so the user would never be able to retry their entry).
-func RetryableAuthMethod(auth AuthMethod, maxTries int) AuthMethod {
- return &retryableAuthMethod{authMethod: auth, maxTries: maxTries}
-}
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