in ssh/server.go [398:665]
func (s *connection) serverAuthenticate(config *ServerConfig) (*Permissions, error) {
sessionID := s.transport.getSessionID()
var cache pubKeyCache
var perms *Permissions
authFailures := 0
var authErrs []error
var displayedBanner bool
userAuthLoop:
for {
if authFailures >= config.MaxAuthTries && config.MaxAuthTries > 0 {
discMsg := &disconnectMsg{
Reason: 2,
Message: "too many authentication failures",
}
if err := s.transport.writePacket(Marshal(discMsg)); err != nil {
return nil, err
}
return nil, discMsg
}
var userAuthReq userAuthRequestMsg
if packet, err := s.transport.readPacket(); err != nil {
if err == io.EOF {
return nil, &ServerAuthError{Errors: authErrs}
}
return nil, err
} else if err = Unmarshal(packet, &userAuthReq); err != nil {
return nil, err
}
if userAuthReq.Service != serviceSSH {
return nil, errors.New("ssh: client attempted to negotiate for unknown service: " + userAuthReq.Service)
}
s.user = userAuthReq.User
if !displayedBanner && config.BannerCallback != nil {
displayedBanner = true
msg := config.BannerCallback(s)
if msg != "" {
bannerMsg := &userAuthBannerMsg{
Message: msg,
}
if err := s.transport.writePacket(Marshal(bannerMsg)); err != nil {
return nil, err
}
}
}
perms = nil
authErr := ErrNoAuth
switch userAuthReq.Method {
case "none":
if config.NoClientAuth {
authErr = nil
}
// allow initial attempt of 'none' without penalty
if authFailures == 0 {
authFailures--
}
case "password":
if config.PasswordCallback == nil {
authErr = errors.New("ssh: password auth not configured")
break
}
payload := userAuthReq.Payload
if len(payload) < 1 || payload[0] != 0 {
return nil, parseError(msgUserAuthRequest)
}
payload = payload[1:]
password, payload, ok := parseString(payload)
if !ok || len(payload) > 0 {
return nil, parseError(msgUserAuthRequest)
}
perms, authErr = config.PasswordCallback(s, password)
case "keyboard-interactive":
if config.KeyboardInteractiveCallback == nil {
authErr = errors.New("ssh: keyboard-interactive auth not configured")
break
}
prompter := &sshClientKeyboardInteractive{s}
perms, authErr = config.KeyboardInteractiveCallback(s, prompter.Challenge)
case "publickey":
if config.PublicKeyCallback == nil {
authErr = errors.New("ssh: publickey auth not configured")
break
}
payload := userAuthReq.Payload
if len(payload) < 1 {
return nil, parseError(msgUserAuthRequest)
}
isQuery := payload[0] == 0
payload = payload[1:]
algoBytes, payload, ok := parseString(payload)
if !ok {
return nil, parseError(msgUserAuthRequest)
}
algo := string(algoBytes)
if !isAcceptableAlgo(algo) {
authErr = fmt.Errorf("ssh: algorithm %q not accepted", algo)
break
}
pubKeyData, payload, ok := parseString(payload)
if !ok {
return nil, parseError(msgUserAuthRequest)
}
pubKey, err := ParsePublicKey(pubKeyData)
if err != nil {
return nil, err
}
candidate, ok := cache.get(s.user, pubKeyData)
if !ok {
candidate.user = s.user
candidate.pubKeyData = pubKeyData
candidate.perms, candidate.result = config.PublicKeyCallback(s, pubKey)
if candidate.result == nil && candidate.perms != nil && candidate.perms.CriticalOptions != nil && candidate.perms.CriticalOptions[sourceAddressCriticalOption] != "" {
candidate.result = checkSourceAddress(
s.RemoteAddr(),
candidate.perms.CriticalOptions[sourceAddressCriticalOption])
}
cache.add(candidate)
}
if isQuery {
// The client can query if the given public key
// would be okay.
if len(payload) > 0 {
return nil, parseError(msgUserAuthRequest)
}
if candidate.result == nil {
okMsg := userAuthPubKeyOkMsg{
Algo: algo,
PubKey: pubKeyData,
}
if err = s.transport.writePacket(Marshal(&okMsg)); err != nil {
return nil, err
}
continue userAuthLoop
}
authErr = candidate.result
} else {
sig, payload, ok := parseSignature(payload)
if !ok || len(payload) > 0 {
return nil, parseError(msgUserAuthRequest)
}
// Ensure the public key algo and signature algo
// are supported. Compare the private key
// algorithm name that corresponds to algo with
// sig.Format. This is usually the same, but
// for certs, the names differ.
if !isAcceptableAlgo(sig.Format) {
authErr = fmt.Errorf("ssh: algorithm %q not accepted", sig.Format)
break
}
signedData := buildDataSignedForAuth(sessionID, userAuthReq, algoBytes, pubKeyData)
if err := pubKey.Verify(signedData, sig); err != nil {
return nil, err
}
authErr = candidate.result
perms = candidate.perms
}
case "gssapi-with-mic":
if config.GSSAPIWithMICConfig == nil {
authErr = errors.New("ssh: gssapi-with-mic auth not configured")
break
}
gssapiConfig := config.GSSAPIWithMICConfig
userAuthRequestGSSAPI, err := parseGSSAPIPayload(userAuthReq.Payload)
if err != nil {
return nil, parseError(msgUserAuthRequest)
}
// OpenSSH supports Kerberos V5 mechanism only for GSS-API authentication.
if userAuthRequestGSSAPI.N == 0 {
authErr = fmt.Errorf("ssh: Mechanism negotiation is not supported")
break
}
var i uint32
present := false
for i = 0; i < userAuthRequestGSSAPI.N; i++ {
if userAuthRequestGSSAPI.OIDS[i].Equal(krb5Mesh) {
present = true
break
}
}
if !present {
authErr = fmt.Errorf("ssh: GSSAPI authentication must use the Kerberos V5 mechanism")
break
}
// Initial server response, see RFC 4462 section 3.3.
if err := s.transport.writePacket(Marshal(&userAuthGSSAPIResponse{
SupportMech: krb5OID,
})); err != nil {
return nil, err
}
// Exchange token, see RFC 4462 section 3.4.
packet, err := s.transport.readPacket()
if err != nil {
return nil, err
}
userAuthGSSAPITokenReq := &userAuthGSSAPIToken{}
if err := Unmarshal(packet, userAuthGSSAPITokenReq); err != nil {
return nil, err
}
authErr, perms, err = gssExchangeToken(gssapiConfig, userAuthGSSAPITokenReq.Token, s, sessionID,
userAuthReq)
if err != nil {
return nil, err
}
default:
authErr = fmt.Errorf("ssh: unknown method %q", userAuthReq.Method)
}
authErrs = append(authErrs, authErr)
if config.AuthLogCallback != nil {
config.AuthLogCallback(s, userAuthReq.Method, authErr)
}
if authErr == nil {
break userAuthLoop
}
authFailures++
var failureMsg userAuthFailureMsg
if config.PasswordCallback != nil {
failureMsg.Methods = append(failureMsg.Methods, "password")
}
if config.PublicKeyCallback != nil {
failureMsg.Methods = append(failureMsg.Methods, "publickey")
}
if config.KeyboardInteractiveCallback != nil {
failureMsg.Methods = append(failureMsg.Methods, "keyboard-interactive")
}
if config.GSSAPIWithMICConfig != nil && config.GSSAPIWithMICConfig.Server != nil &&
config.GSSAPIWithMICConfig.AllowLogin != nil {
failureMsg.Methods = append(failureMsg.Methods, "gssapi-with-mic")
}
if len(failureMsg.Methods) == 0 {
return nil, errors.New("ssh: no authentication methods configured but NoClientAuth is also false")
}
if err := s.transport.writePacket(Marshal(&failureMsg)); err != nil {
return nil, err
}
}
if err := s.transport.writePacket([]byte{msgUserAuthSuccess}); err != nil {
return nil, err
}
return perms, nil
}