| // 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" |
| ) |
| |
| type authResult int |
| |
| const ( |
| authFailure authResult = iota |
| authPartialSuccess |
| authSuccess |
| ) |
| |
| // 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 == authSuccess { |
| // success |
| return nil |
| } else if ok == authFailure { |
| 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) (authResult, []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) (authResult, []string, error) { |
| if err := c.writePacket(Marshal(&userAuthRequestMsg{ |
| User: user, |
| Service: serviceSSH, |
| Method: "none", |
| })); err != nil { |
| return authFailure, 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) (authResult, []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 authFailure, nil, err |
| } |
| |
| if err := c.writePacket(Marshal(&passwordAuthMsg{ |
| User: user, |
| Service: serviceSSH, |
| Method: cb.method(), |
| Reply: false, |
| Password: pw, |
| })); err != nil { |
| return authFailure, 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) (authResult, []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 authFailure, nil, err |
| } |
| var methods []string |
| for _, signer := range signers { |
| ok, err := validateKey(signer.PublicKey(), user, c) |
| if err != nil { |
| return authFailure, 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 authFailure, 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 authFailure, nil, err |
| } |
| var success authResult |
| success, methods, err = handleAuthResponse(c) |
| if err != nil { |
| return authFailure, 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 == authSuccess || !containsMethod(methods, cb.method()) { |
| return success, methods, err |
| } |
| } |
| |
| return authFailure, 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: |
| if err := handleBannerResponse(c, packet); err != nil { |
| return false, err |
| } |
| 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) (authResult, []string, error) { |
| for { |
| packet, err := c.readPacket() |
| if err != nil { |
| return authFailure, nil, err |
| } |
| |
| switch packet[0] { |
| case msgUserAuthBanner: |
| if err := handleBannerResponse(c, packet); err != nil { |
| return authFailure, nil, err |
| } |
| case msgUserAuthFailure: |
| var msg userAuthFailureMsg |
| if err := Unmarshal(packet, &msg); err != nil { |
| return authFailure, nil, err |
| } |
| if msg.PartialSuccess { |
| return authPartialSuccess, msg.Methods, nil |
| } |
| return authFailure, msg.Methods, nil |
| case msgUserAuthSuccess: |
| return authSuccess, nil, nil |
| default: |
| return authFailure, nil, unexpectedMessageError(msgUserAuthSuccess, packet[0]) |
| } |
| } |
| } |
| |
| func handleBannerResponse(c packetConn, packet []byte) error { |
| var msg userAuthBannerMsg |
| if err := Unmarshal(packet, &msg); err != nil { |
| return err |
| } |
| |
| transport, ok := c.(*handshakeTransport) |
| if !ok { |
| return nil |
| } |
| |
| if transport.bannerCallback != nil { |
| return transport.bannerCallback(msg.Message) |
| } |
| |
| return nil |
| } |
| |
| // 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 an 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) (authResult, []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 authFailure, nil, err |
| } |
| |
| for { |
| packet, err := c.readPacket() |
| if err != nil { |
| return authFailure, nil, err |
| } |
| |
| // like handleAuthResponse, but with less options. |
| switch packet[0] { |
| case msgUserAuthBanner: |
| if err := handleBannerResponse(c, packet); err != nil { |
| return authFailure, nil, err |
| } |
| continue |
| case msgUserAuthInfoRequest: |
| // OK |
| case msgUserAuthFailure: |
| var msg userAuthFailureMsg |
| if err := Unmarshal(packet, &msg); err != nil { |
| return authFailure, nil, err |
| } |
| if msg.PartialSuccess { |
| return authPartialSuccess, msg.Methods, nil |
| } |
| return authFailure, msg.Methods, nil |
| case msgUserAuthSuccess: |
| return authSuccess, nil, nil |
| default: |
| return authFailure, nil, unexpectedMessageError(msgUserAuthInfoRequest, packet[0]) |
| } |
| |
| var msg userAuthInfoRequestMsg |
| if err := Unmarshal(packet, &msg); err != nil { |
| return authFailure, 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 authFailure, 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 authFailure, nil, errors.New("ssh: extra data following keyboard-interactive pairs") |
| } |
| |
| answers, err := cb(msg.User, msg.Instruction, prompts, echos) |
| if err != nil { |
| return authFailure, nil, err |
| } |
| |
| if len(answers) != len(prompts) { |
| return authFailure, 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 authFailure, nil, err |
| } |
| } |
| } |
| |
| type retryableAuthMethod struct { |
| authMethod AuthMethod |
| maxTries int |
| } |
| |
| func (r *retryableAuthMethod) auth(session []byte, user string, c packetConn, rand io.Reader) (ok authResult, 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 != authFailure || err != nil { // either success, partial 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} |
| } |