diff options
Diffstat (limited to 'vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/ssh/server.go')
| -rw-r--r-- | vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/ssh/server.go | 580 |
1 files changed, 580 insertions, 0 deletions
diff --git a/vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/ssh/server.go b/vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/ssh/server.go new file mode 100644 index 000000000..148d2cb24 --- /dev/null +++ b/vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/ssh/server.go @@ -0,0 +1,580 @@ +// 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" + "net" + "strings" +) + +// The Permissions type holds fine-grained permissions that are +// specific to a user or a specific authentication method for a user. +// The Permissions value for a successful authentication attempt is +// available in ServerConn, so it can be used to pass information from +// the user-authentication phase to the application layer. +type Permissions struct { + // CriticalOptions indicate restrictions to the default + // permissions, and are typically used in conjunction with + // user certificates. The standard for SSH certificates + // defines "force-command" (only allow the given command to + // execute) and "source-address" (only allow connections from + // the given address). The SSH package currently only enforces + // the "source-address" critical option. It is up to server + // implementations to enforce other critical options, such as + // "force-command", by checking them after the SSH handshake + // is successful. In general, SSH servers should reject + // connections that specify critical options that are unknown + // or not supported. + CriticalOptions map[string]string + + // Extensions are extra functionality that the server may + // offer on authenticated connections. Lack of support for an + // extension does not preclude authenticating a user. Common + // extensions are "permit-agent-forwarding", + // "permit-X11-forwarding". The Go SSH library currently does + // not act on any extension, and it is up to server + // implementations to honor them. Extensions can be used to + // pass data from the authentication callbacks to the server + // application layer. + Extensions map[string]string +} + +// ServerConfig holds server specific configuration data. +type ServerConfig struct { + // Config contains configuration shared between client and server. + Config + + hostKeys []Signer + + // NoClientAuth is true if clients are allowed to connect without + // authenticating. + NoClientAuth bool + + // MaxAuthTries specifies the maximum number of authentication attempts + // permitted per connection. If set to a negative number, the number of + // attempts are unlimited. If set to zero, the number of attempts are limited + // to 6. + MaxAuthTries int + + // PasswordCallback, if non-nil, is called when a user + // attempts to authenticate using a password. + PasswordCallback func(conn ConnMetadata, password []byte) (*Permissions, error) + + // PublicKeyCallback, if non-nil, is called when a client + // offers a public key for authentication. It must return a nil error + // if the given public key can be used to authenticate the + // given user. For example, see CertChecker.Authenticate. A + // call to this function does not guarantee that the key + // offered is in fact used to authenticate. To record any data + // depending on the public key, store it inside a + // Permissions.Extensions entry. + PublicKeyCallback func(conn ConnMetadata, key PublicKey) (*Permissions, error) + + // KeyboardInteractiveCallback, if non-nil, is called when + // keyboard-interactive authentication is selected (RFC + // 4256). The client object's Challenge function should be + // used to query the user. The callback may offer multiple + // Challenge rounds. To avoid information leaks, the client + // should be presented a challenge even if the user is + // unknown. + KeyboardInteractiveCallback func(conn ConnMetadata, client KeyboardInteractiveChallenge) (*Permissions, error) + + // AuthLogCallback, if non-nil, is called to log all authentication + // attempts. + AuthLogCallback func(conn ConnMetadata, method string, err error) + + // ServerVersion is the version identification string to announce in + // the public handshake. + // If empty, a reasonable default is used. + // Note that RFC 4253 section 4.2 requires that this string start with + // "SSH-2.0-". + ServerVersion string + + // BannerCallback, if present, is called and the return string is sent to + // the client after key exchange completed but before authentication. + BannerCallback func(conn ConnMetadata) string +} + +// AddHostKey adds a private key as a host key. If an existing host +// key exists with the same algorithm, it is overwritten. Each server +// config must have at least one host key. +func (s *ServerConfig) AddHostKey(key Signer) { + for i, k := range s.hostKeys { + if k.PublicKey().Type() == key.PublicKey().Type() { + s.hostKeys[i] = key + return + } + } + + s.hostKeys = append(s.hostKeys, key) +} + +// cachedPubKey contains the results of querying whether a public key is +// acceptable for a user. +type cachedPubKey struct { + user string + pubKeyData []byte + result error + perms *Permissions +} + +const maxCachedPubKeys = 16 + +// pubKeyCache caches tests for public keys. Since SSH clients +// will query whether a public key is acceptable before attempting to +// authenticate with it, we end up with duplicate queries for public +// key validity. The cache only applies to a single ServerConn. +type pubKeyCache struct { + keys []cachedPubKey +} + +// get returns the result for a given user/algo/key tuple. +func (c *pubKeyCache) get(user string, pubKeyData []byte) (cachedPubKey, bool) { + for _, k := range c.keys { + if k.user == user && bytes.Equal(k.pubKeyData, pubKeyData) { + return k, true + } + } + return cachedPubKey{}, false +} + +// add adds the given tuple to the cache. +func (c *pubKeyCache) add(candidate cachedPubKey) { + if len(c.keys) < maxCachedPubKeys { + c.keys = append(c.keys, candidate) + } +} + +// ServerConn is an authenticated SSH connection, as seen from the +// server +type ServerConn struct { + Conn + + // If the succeeding authentication callback returned a + // non-nil Permissions pointer, it is stored here. + Permissions *Permissions +} + +// NewServerConn starts a new SSH server with c as the underlying +// transport. It starts with a handshake and, if the handshake is +// unsuccessful, it closes the connection and returns an error. The +// Request and NewChannel channels must be serviced, or the connection +// will hang. +func NewServerConn(c net.Conn, config *ServerConfig) (*ServerConn, <-chan NewChannel, <-chan *Request, error) { + fullConf := *config + fullConf.SetDefaults() + if fullConf.MaxAuthTries == 0 { + fullConf.MaxAuthTries = 6 + } + + s := &connection{ + sshConn: sshConn{conn: c}, + } + perms, err := s.serverHandshake(&fullConf) + if err != nil { + c.Close() + return nil, nil, nil, err + } + return &ServerConn{s, perms}, s.mux.incomingChannels, s.mux.incomingRequests, nil +} + +// signAndMarshal signs the data with the appropriate algorithm, +// and serializes the result in SSH wire format. +func signAndMarshal(k Signer, rand io.Reader, data []byte) ([]byte, error) { + sig, err := k.Sign(rand, data) + if err != nil { + return nil, err + } + + return Marshal(sig), nil +} + +// handshake performs key exchange and user authentication. +func (s *connection) serverHandshake(config *ServerConfig) (*Permissions, error) { + if len(config.hostKeys) == 0 { + return nil, errors.New("ssh: server has no host keys") + } + + if !config.NoClientAuth && config.PasswordCallback == nil && config.PublicKeyCallback == nil && config.KeyboardInteractiveCallback == nil { + return nil, errors.New("ssh: no authentication methods configured but NoClientAuth is also false") + } + + if config.ServerVersion != "" { + s.serverVersion = []byte(config.ServerVersion) + } else { + s.serverVersion = []byte(packageVersion) + } + var err error + s.clientVersion, err = exchangeVersions(s.sshConn.conn, s.serverVersion) + if err != nil { + return nil, err + } + + tr := newTransport(s.sshConn.conn, config.Rand, false /* not client */) + s.transport = newServerTransport(tr, s.clientVersion, s.serverVersion, config) + + if err := s.transport.waitSession(); err != nil { + return nil, err + } + + // We just did the key change, so the session ID is established. + s.sessionID = s.transport.getSessionID() + + var packet []byte + if packet, err = s.transport.readPacket(); err != nil { + return nil, err + } + + var serviceRequest serviceRequestMsg + if err = Unmarshal(packet, &serviceRequest); err != nil { + return nil, err + } + if serviceRequest.Service != serviceUserAuth { + return nil, errors.New("ssh: requested service '" + serviceRequest.Service + "' before authenticating") + } + serviceAccept := serviceAcceptMsg{ + Service: serviceUserAuth, + } + if err := s.transport.writePacket(Marshal(&serviceAccept)); err != nil { + return nil, err + } + + perms, err := s.serverAuthenticate(config) + if err != nil { + return nil, err + } + s.mux = newMux(s.transport) + return perms, err +} + +func isAcceptableAlgo(algo string) bool { + switch algo { + case KeyAlgoRSA, KeyAlgoDSA, KeyAlgoECDSA256, KeyAlgoECDSA384, KeyAlgoECDSA521, KeyAlgoED25519, + CertAlgoRSAv01, CertAlgoDSAv01, CertAlgoECDSA256v01, CertAlgoECDSA384v01, CertAlgoECDSA521v01: + return true + } + return false +} + +func checkSourceAddress(addr net.Addr, sourceAddrs string) error { + if addr == nil { + return errors.New("ssh: no address known for client, but source-address match required") + } + + tcpAddr, ok := addr.(*net.TCPAddr) + if !ok { + return fmt.Errorf("ssh: remote address %v is not an TCP address when checking source-address match", addr) + } + + for _, sourceAddr := range strings.Split(sourceAddrs, ",") { + if allowedIP := net.ParseIP(sourceAddr); allowedIP != nil { + if allowedIP.Equal(tcpAddr.IP) { + return nil + } + } else { + _, ipNet, err := net.ParseCIDR(sourceAddr) + if err != nil { + return fmt.Errorf("ssh: error parsing source-address restriction %q: %v", sourceAddr, err) + } + + if ipNet.Contains(tcpAddr.IP) { + return nil + } + } + } + + return fmt.Errorf("ssh: remote address %v is not allowed because of source-address restriction", addr) +} + +// ServerAuthError implements the error interface. It appends any authentication +// errors that may occur, and is returned if all of the authentication methods +// provided by the user failed to authenticate. +type ServerAuthError struct { + // Errors contains authentication errors returned by the authentication + // callback methods. + Errors []error +} + +func (l ServerAuthError) Error() string { + var errs []string + for _, err := range l.Errors { + errs = append(errs, err.Error()) + } + return "[" + strings.Join(errs, ", ") + "]" +} + +func (s *connection) serverAuthenticate(config *ServerConfig) (*Permissions, error) { + sessionID := s.transport.getSessionID() + var cache pubKeyCache + var perms *Permissions + + authFailures := 0 + var authErrs []error + +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 authFailures == 0 && config.BannerCallback != nil { + 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 := errors.New("no auth passed yet") + + 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 configubred") + 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) { + break + } + signedData := buildDataSignedForAuth(sessionID, userAuthReq, algoBytes, pubKeyData) + + if err := pubKey.Verify(signedData, sig); err != nil { + return nil, err + } + + authErr = candidate.result + perms = candidate.perms + } + 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 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 +} + +// sshClientKeyboardInteractive implements a ClientKeyboardInteractive by +// asking the client on the other side of a ServerConn. +type sshClientKeyboardInteractive struct { + *connection +} + +func (c *sshClientKeyboardInteractive) Challenge(user, instruction string, questions []string, echos []bool) (answers []string, err error) { + if len(questions) != len(echos) { + return nil, errors.New("ssh: echos and questions must have equal length") + } + + var prompts []byte + for i := range questions { + prompts = appendString(prompts, questions[i]) + prompts = appendBool(prompts, echos[i]) + } + + if err := c.transport.writePacket(Marshal(&userAuthInfoRequestMsg{ + Instruction: instruction, + NumPrompts: uint32(len(questions)), + Prompts: prompts, + })); err != nil { + return nil, err + } + + packet, err := c.transport.readPacket() + if err != nil { + return nil, err + } + if packet[0] != msgUserAuthInfoResponse { + return nil, unexpectedMessageError(msgUserAuthInfoResponse, packet[0]) + } + packet = packet[1:] + + n, packet, ok := parseUint32(packet) + if !ok || int(n) != len(questions) { + return nil, parseError(msgUserAuthInfoResponse) + } + + for i := uint32(0); i < n; i++ { + ans, rest, ok := parseString(packet) + if !ok { + return nil, parseError(msgUserAuthInfoResponse) + } + + answers = append(answers, string(ans)) + packet = rest + } + if len(packet) != 0 { + return nil, errors.New("ssh: junk at end of message") + } + + return answers, nil +} |