update go-git to v4.12.0 - fixes #7248 (#7249)

vendor/golang.org/x/crypto/ssh/client_auth.go

@@ -523,3 +523,117 @@ func (r *retryableAuthMethod) method() string {
 func RetryableAuthMethod(auth AuthMethod, maxTries int) AuthMethod {
 	return &retryableAuthMethod{authMethod: auth, maxTries: maxTries}
 }
+
+// GSSAPIWithMICAuthMethod is an AuthMethod with "gssapi-with-mic" authentication.
+// See RFC 4462 section 3
+// gssAPIClient is implementation of the GSSAPIClient interface, see the definition of the interface for details.
+// target is the server host you want to log in to.
+func GSSAPIWithMICAuthMethod(gssAPIClient GSSAPIClient, target string) AuthMethod {
+	if gssAPIClient == nil {
+		panic("gss-api client must be not nil with enable gssapi-with-mic")
+	}
+	return &gssAPIWithMICCallback{gssAPIClient: gssAPIClient, target: target}
+}
+
+type gssAPIWithMICCallback struct {
+	gssAPIClient GSSAPIClient
+	target       string
+}
+
+func (g *gssAPIWithMICCallback) auth(session []byte, user string, c packetConn, rand io.Reader) (authResult, []string, error) {
+	m := &userAuthRequestMsg{
+		User:    user,
+		Service: serviceSSH,
+		Method:  g.method(),
+	}
+	// The GSS-API authentication method is initiated when the client sends an SSH_MSG_USERAUTH_REQUEST.
+	// See RFC 4462 section 3.2.
+	m.Payload = appendU32(m.Payload, 1)
+	m.Payload = appendString(m.Payload, string(krb5OID))
+	if err := c.writePacket(Marshal(m)); err != nil {
+		return authFailure, nil, err
+	}
+	// The server responds to the SSH_MSG_USERAUTH_REQUEST with either an
+	// SSH_MSG_USERAUTH_FAILURE if none of the mechanisms are supported or
+	// with an SSH_MSG_USERAUTH_GSSAPI_RESPONSE.
+	// See RFC 4462 section 3.3.
+	// OpenSSH supports Kerberos V5 mechanism only for GSS-API authentication,so I don't want to check
+	// selected mech if it is valid.
+	packet, err := c.readPacket()
+	if err != nil {
+		return authFailure, nil, err
+	}
+	userAuthGSSAPIResp := &userAuthGSSAPIResponse{}
+	if err := Unmarshal(packet, userAuthGSSAPIResp); err != nil {
+		return authFailure, nil, err
+	}
+	// Start the loop into the exchange token.
+	// See RFC 4462 section 3.4.
+	var token []byte
+	defer g.gssAPIClient.DeleteSecContext()
+	for {
+		// Initiates the establishment of a security context between the application and a remote peer.
+		nextToken, needContinue, err := g.gssAPIClient.InitSecContext("host@"+g.target, token, false)
+		if err != nil {
+			return authFailure, nil, err
+		}
+		if len(nextToken) > 0 {
+			if err := c.writePacket(Marshal(&userAuthGSSAPIToken{
+				Token: nextToken,
+			})); err != nil {
+				return authFailure, nil, err
+			}
+		}
+		if !needContinue {
+			break
+		}
+		packet, err = c.readPacket()
+		if err != nil {
+			return authFailure, nil, err
+		}
+		switch packet[0] {
+		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 msgUserAuthGSSAPIError:
+			userAuthGSSAPIErrorResp := &userAuthGSSAPIError{}
+			if err := Unmarshal(packet, userAuthGSSAPIErrorResp); err != nil {
+				return authFailure, nil, err
+			}
+			return authFailure, nil, fmt.Errorf("GSS-API Error:\n"+
+				"Major Status: %d\n"+
+				"Minor Status: %d\n"+
+				"Error Message: %s\n", userAuthGSSAPIErrorResp.MajorStatus, userAuthGSSAPIErrorResp.MinorStatus,
+				userAuthGSSAPIErrorResp.Message)
+		case msgUserAuthGSSAPIToken:
+			userAuthGSSAPITokenReq := &userAuthGSSAPIToken{}
+			if err := Unmarshal(packet, userAuthGSSAPITokenReq); err != nil {
+				return authFailure, nil, err
+			}
+			token = userAuthGSSAPITokenReq.Token
+		}
+	}
+	// Binding Encryption Keys.
+	// See RFC 4462 section 3.5.
+	micField := buildMIC(string(session), user, "ssh-connection", "gssapi-with-mic")
+	micToken, err := g.gssAPIClient.GetMIC(micField)
+	if err != nil {
+		return authFailure, nil, err
+	}
+	if err := c.writePacket(Marshal(&userAuthGSSAPIMIC{
+		MIC: micToken,
+	})); err != nil {
+		return authFailure, nil, err
+	}
+	return handleAuthResponse(c)
+}
+
+func (g *gssAPIWithMICCallback) method() string {
+	return "gssapi-with-mic"
+}

vendor/golang.org/x/crypto/ssh/common.go

@@ -51,6 +51,13 @@ var supportedKexAlgos = []string{
 	kexAlgoDH14SHA1, kexAlgoDH1SHA1,
 }
 
+// serverForbiddenKexAlgos contains key exchange algorithms, that are forbidden
+// for the server half.
+var serverForbiddenKexAlgos = map[string]struct{}{
+	kexAlgoDHGEXSHA1:   {}, // server half implementation is only minimal to satisfy the automated tests
+	kexAlgoDHGEXSHA256: {}, // server half implementation is only minimal to satisfy the automated tests
+}
+
 // supportedHostKeyAlgos specifies the supported host-key algorithms (i.e. methods
 // of authenticating servers) in preference order.
 var supportedHostKeyAlgos = []string{

vendor/golang.org/x/crypto/ssh/kex.go

@@ -10,7 +10,9 @@ import (
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/subtle"
+	"encoding/binary"
 	"errors"
+	"fmt"
 	"io"
 	"math/big"
 
@@ -24,6 +26,12 @@ const (
 	kexAlgoECDH384          = "ecdh-sha2-nistp384"
 	kexAlgoECDH521          = "ecdh-sha2-nistp521"
 	kexAlgoCurve25519SHA256 = "curve25519-sha256@libssh.org"
+
+	// For the following kex only the client half contains a production
+	// ready implementation. The server half only consists of a minimal
+	// implementation to satisfy the automated tests.
+	kexAlgoDHGEXSHA1   = "diffie-hellman-group-exchange-sha1"
+	kexAlgoDHGEXSHA256 = "diffie-hellman-group-exchange-sha256"
 )
 
 // kexResult captures the outcome of a key exchange.
@@ -402,6 +410,8 @@ func init() {
 	kexAlgoMap[kexAlgoECDH384] = &ecdh{elliptic.P384()}
 	kexAlgoMap[kexAlgoECDH256] = &ecdh{elliptic.P256()}
 	kexAlgoMap[kexAlgoCurve25519SHA256] = &curve25519sha256{}
+	kexAlgoMap[kexAlgoDHGEXSHA1] = &dhGEXSHA{hashFunc: crypto.SHA1}
+	kexAlgoMap[kexAlgoDHGEXSHA256] = &dhGEXSHA{hashFunc: crypto.SHA256}
 }
 
 // curve25519sha256 implements the curve25519-sha256@libssh.org key
@@ -538,3 +548,242 @@ func (kex *curve25519sha256) Server(c packetConn, rand io.Reader, magics *handsh
 		Hash:      crypto.SHA256,
 	}, nil
 }
+
+// dhGEXSHA implements the diffie-hellman-group-exchange-sha1 and
+// diffie-hellman-group-exchange-sha256 key agreement protocols,
+// as described in RFC 4419
+type dhGEXSHA struct {
+	g, p     *big.Int
+	hashFunc crypto.Hash
+}
+
+const numMRTests = 64
+
+const (
+	dhGroupExchangeMinimumBits   = 2048
+	dhGroupExchangePreferredBits = 2048
+	dhGroupExchangeMaximumBits   = 8192
+)
+
+func (gex *dhGEXSHA) diffieHellman(theirPublic, myPrivate *big.Int) (*big.Int, error) {
+	if theirPublic.Sign() <= 0 || theirPublic.Cmp(gex.p) >= 0 {
+		return nil, fmt.Errorf("ssh: DH parameter out of bounds")
+	}
+	return new(big.Int).Exp(theirPublic, myPrivate, gex.p), nil
+}
+
+func (gex *dhGEXSHA) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) {
+	// Send GexRequest
+	kexDHGexRequest := kexDHGexRequestMsg{
+		MinBits:      dhGroupExchangeMinimumBits,
+		PreferedBits: dhGroupExchangePreferredBits,
+		MaxBits:      dhGroupExchangeMaximumBits,
+	}
+	if err := c.writePacket(Marshal(&kexDHGexRequest)); err != nil {
+		return nil, err
+	}
+
+	// Receive GexGroup
+	packet, err := c.readPacket()
+	if err != nil {
+		return nil, err
+	}
+
+	var kexDHGexGroup kexDHGexGroupMsg
+	if err = Unmarshal(packet, &kexDHGexGroup); err != nil {
+		return nil, err
+	}
+
+	// reject if p's bit length < dhGroupExchangeMinimumBits or > dhGroupExchangeMaximumBits
+	if kexDHGexGroup.P.BitLen() < dhGroupExchangeMinimumBits || kexDHGexGroup.P.BitLen() > dhGroupExchangeMaximumBits {
+		return nil, fmt.Errorf("ssh: server-generated gex p is out of range (%d bits)", kexDHGexGroup.P.BitLen())
+	}
+
+	gex.p = kexDHGexGroup.P
+	gex.g = kexDHGexGroup.G
+
+	// Check if p is safe by verifing that p and (p-1)/2 are primes
+	one := big.NewInt(1)
+	var pHalf = &big.Int{}
+	pHalf.Rsh(gex.p, 1)
+	if !gex.p.ProbablyPrime(numMRTests) || !pHalf.ProbablyPrime(numMRTests) {
+		return nil, fmt.Errorf("ssh: server provided gex p is not safe")
+	}
+
+	// Check if g is safe by verifing that g > 1 and g < p - 1
+	var pMinusOne = &big.Int{}
+	pMinusOne.Sub(gex.p, one)
+	if gex.g.Cmp(one) != 1 && gex.g.Cmp(pMinusOne) != -1 {
+		return nil, fmt.Errorf("ssh: server provided gex g is not safe")
+	}
+
+	// Send GexInit
+	x, err := rand.Int(randSource, pHalf)
+	if err != nil {
+		return nil, err
+	}
+	X := new(big.Int).Exp(gex.g, x, gex.p)
+	kexDHGexInit := kexDHGexInitMsg{
+		X: X,
+	}
+	if err := c.writePacket(Marshal(&kexDHGexInit)); err != nil {
+		return nil, err
+	}
+
+	// Receive GexReply
+	packet, err = c.readPacket()
+	if err != nil {
+		return nil, err
+	}
+
+	var kexDHGexReply kexDHGexReplyMsg
+	if err = Unmarshal(packet, &kexDHGexReply); err != nil {
+		return nil, err
+	}
+
+	kInt, err := gex.diffieHellman(kexDHGexReply.Y, x)
+	if err != nil {
+		return nil, err
+	}
+
+	// Check if k is safe by verifing that k > 1 and k < p - 1
+	if kInt.Cmp(one) != 1 && kInt.Cmp(pMinusOne) != -1 {
+		return nil, fmt.Errorf("ssh: derived k is not safe")
+	}
+
+	h := gex.hashFunc.New()
+	magics.write(h)
+	writeString(h, kexDHGexReply.HostKey)
+	binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMinimumBits))
+	binary.Write(h, binary.BigEndian, uint32(dhGroupExchangePreferredBits))
+	binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMaximumBits))
+	writeInt(h, gex.p)
+	writeInt(h, gex.g)
+	writeInt(h, X)
+	writeInt(h, kexDHGexReply.Y)
+	K := make([]byte, intLength(kInt))
+	marshalInt(K, kInt)
+	h.Write(K)
+
+	return &kexResult{
+		H:         h.Sum(nil),
+		K:         K,
+		HostKey:   kexDHGexReply.HostKey,
+		Signature: kexDHGexReply.Signature,
+		Hash:      gex.hashFunc,
+	}, nil
+}
+
+// Server half implementation of the Diffie Hellman Key Exchange with SHA1 and SHA256.
+//
+// This is a minimal implementation to satisfy the automated tests.
+func (gex *dhGEXSHA) Server(c packetConn, randSource io.Reader, magics *handshakeMagics, priv Signer) (result *kexResult, err error) {
+	// Receive GexRequest
+	packet, err := c.readPacket()
+	if err != nil {
+		return
+	}
+	var kexDHGexRequest kexDHGexRequestMsg
+	if err = Unmarshal(packet, &kexDHGexRequest); err != nil {
+		return
+	}
+
+	// smoosh the user's preferred size into our own limits
+	if kexDHGexRequest.PreferedBits > dhGroupExchangeMaximumBits {
+		kexDHGexRequest.PreferedBits = dhGroupExchangeMaximumBits
+	}
+	if kexDHGexRequest.PreferedBits < dhGroupExchangeMinimumBits {
+		kexDHGexRequest.PreferedBits = dhGroupExchangeMinimumBits
+	}
+	// fix min/max if they're inconsistent.  technically, we could just pout
+	// and hang up, but there's no harm in giving them the benefit of the
+	// doubt and just picking a bitsize for them.
+	if kexDHGexRequest.MinBits > kexDHGexRequest.PreferedBits {
+		kexDHGexRequest.MinBits = kexDHGexRequest.PreferedBits
+	}
+	if kexDHGexRequest.MaxBits < kexDHGexRequest.PreferedBits {
+		kexDHGexRequest.MaxBits = kexDHGexRequest.PreferedBits
+	}
+
+	// Send GexGroup
+	// This is the group called diffie-hellman-group14-sha1 in RFC
+	// 4253 and Oakley Group 14 in RFC 3526.
+	p, _ := new(big.Int).SetString("FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB9ED529077096966D670C354E4ABC9804F1746C08CA18217C32905E462E36CE3BE39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9DE2BCBF6955817183995497CEA956AE515D2261898FA051015728E5A8AACAA68FFFFFFFFFFFFFFFF", 16)
+	gex.p = p
+	gex.g = big.NewInt(2)
+
+	kexDHGexGroup := kexDHGexGroupMsg{
+		P: gex.p,
+		G: gex.g,
+	}
+	if err := c.writePacket(Marshal(&kexDHGexGroup)); err != nil {
+		return nil, err
+	}
+
+	// Receive GexInit
+	packet, err = c.readPacket()
+	if err != nil {
+		return
+	}
+	var kexDHGexInit kexDHGexInitMsg
+	if err = Unmarshal(packet, &kexDHGexInit); err != nil {
+		return
+	}
+
+	var pHalf = &big.Int{}
+	pHalf.Rsh(gex.p, 1)
+
+	y, err := rand.Int(randSource, pHalf)
+	if err != nil {
+		return
+	}
+
+	Y := new(big.Int).Exp(gex.g, y, gex.p)
+	kInt, err := gex.diffieHellman(kexDHGexInit.X, y)
+	if err != nil {
+		return nil, err
+	}
+
+	hostKeyBytes := priv.PublicKey().Marshal()
+
+	h := gex.hashFunc.New()
+	magics.write(h)
+	writeString(h, hostKeyBytes)
+	binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMinimumBits))
+	binary.Write(h, binary.BigEndian, uint32(dhGroupExchangePreferredBits))
+	binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMaximumBits))
+	writeInt(h, gex.p)
+	writeInt(h, gex.g)
+	writeInt(h, kexDHGexInit.X)
+	writeInt(h, Y)
+
+	K := make([]byte, intLength(kInt))
+	marshalInt(K, kInt)
+	h.Write(K)
+
+	H := h.Sum(nil)
+
+	// H is already a hash, but the hostkey signing will apply its
+	// own key-specific hash algorithm.
+	sig, err := signAndMarshal(priv, randSource, H)
+	if err != nil {
+		return nil, err
+	}
+
+	kexDHGexReply := kexDHGexReplyMsg{
+		HostKey:   hostKeyBytes,
+		Y:         Y,
+		Signature: sig,
+	}
+	packet = Marshal(&kexDHGexReply)
+
+	err = c.writePacket(packet)
+
+	return &kexResult{
+		H:         H,
+		K:         K,
+		HostKey:   hostKeyBytes,
+		Signature: sig,
+		Hash:      gex.hashFunc,
+	}, err
+}

vendor/golang.org/x/crypto/ssh/messages.go

@@ -97,6 +97,36 @@ type kexDHReplyMsg struct {
 	Signature []byte
 }
 
+// See RFC 4419, section 5.
+const msgKexDHGexGroup = 31
+
+type kexDHGexGroupMsg struct {
+	P *big.Int `sshtype:"31"`
+	G *big.Int
+}
+
+const msgKexDHGexInit = 32
+
+type kexDHGexInitMsg struct {
+	X *big.Int `sshtype:"32"`
+}
+
+const msgKexDHGexReply = 33
+
+type kexDHGexReplyMsg struct {
+	HostKey   []byte `sshtype:"33"`
+	Y         *big.Int
+	Signature []byte
+}
+
+const msgKexDHGexRequest = 34
+
+type kexDHGexRequestMsg struct {
+	MinBits      uint32 `sshtype:"34"`
+	PreferedBits uint32
+	MaxBits      uint32
+}
+
 // See RFC 4253, section 10.
 const msgServiceRequest = 5
 
@@ -275,6 +305,42 @@ type userAuthPubKeyOkMsg struct {
 	PubKey []byte
 }
 
+// See RFC 4462, section 3
+const msgUserAuthGSSAPIResponse = 60
+
+type userAuthGSSAPIResponse struct {
+	SupportMech []byte `sshtype:"60"`
+}
+
+const msgUserAuthGSSAPIToken = 61
+
+type userAuthGSSAPIToken struct {
+	Token []byte `sshtype:"61"`
+}
+
+const msgUserAuthGSSAPIMIC = 66
+
+type userAuthGSSAPIMIC struct {
+	MIC []byte `sshtype:"66"`
+}
+
+// See RFC 4462, section 3.9
+const msgUserAuthGSSAPIErrTok = 64
+
+type userAuthGSSAPIErrTok struct {
+	ErrorToken []byte `sshtype:"64"`
+}
+
+// See RFC 4462, section 3.8
+const msgUserAuthGSSAPIError = 65
+
+type userAuthGSSAPIError struct {
+	MajorStatus uint32 `sshtype:"65"`
+	MinorStatus uint32
+	Message     string
+	LanguageTag string
+}
+
 // typeTags returns the possible type bytes for the given reflect.Type, which
 // should be a struct. The possible values are separated by a '|' character.
 func typeTags(structType reflect.Type) (tags []byte) {
@@ -756,6 +822,14 @@ func decode(packet []byte) (interface{}, error) {
 		msg = new(channelRequestSuccessMsg)
 	case msgChannelFailure:
 		msg = new(channelRequestFailureMsg)
+	case msgUserAuthGSSAPIToken:
+		msg = new(userAuthGSSAPIToken)
+	case msgUserAuthGSSAPIMIC:
+		msg = new(userAuthGSSAPIMIC)
+	case msgUserAuthGSSAPIErrTok:
+		msg = new(userAuthGSSAPIErrTok)
+	case msgUserAuthGSSAPIError:
+		msg = new(userAuthGSSAPIError)
 	default:
 		return nil, unexpectedMessageError(0, packet[0])
 	}

vendor/golang.org/x/crypto/ssh/server.go

@@ -45,6 +45,20 @@ type Permissions struct {
 	Extensions map[string]string
 }
 
+type GSSAPIWithMICConfig struct {
+	// AllowLogin, must be set, is called when gssapi-with-mic
+	// authentication is selected (RFC 4462 section 3). The srcName is from the
+	// results of the GSS-API authentication. The format is username@DOMAIN.
+	// GSSAPI just guarantees to the server who the user is, but not if they can log in, and with what permissions.
+	// This callback is called after the user identity is established with GSSAPI to decide if the user can login with
+	// which permissions. If the user is allowed to login, it should return a nil error.
+	AllowLogin func(conn ConnMetadata, srcName string) (*Permissions, error)
+
+	// Server must be set. It's the implementation
+	// of the GSSAPIServer interface. See GSSAPIServer interface for details.
+	Server GSSAPIServer
+}
+
 // ServerConfig holds server specific configuration data.
 type ServerConfig struct {
 	// Config contains configuration shared between client and server.
@@ -99,6 +113,10 @@ type ServerConfig struct {
 	// 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
+
+	// GSSAPIWithMICConfig includes gssapi server and callback, which if both non-nil, is used
+	// when gssapi-with-mic authentication is selected (RFC 4462 section 3).
+	GSSAPIWithMICConfig *GSSAPIWithMICConfig
 }
 
 // AddHostKey adds a private key as a host key. If an existing host
@@ -175,6 +193,12 @@ func NewServerConn(c net.Conn, config *ServerConfig) (*ServerConn, <-chan NewCha
 	if fullConf.MaxAuthTries == 0 {
 		fullConf.MaxAuthTries = 6
 	}
+	// Check if the config contains any unsupported key exchanges
+	for _, kex := range fullConf.KeyExchanges {
+		if _, ok := serverForbiddenKexAlgos[kex]; ok {
+			return nil, nil, nil, fmt.Errorf("ssh: unsupported key exchange %s for server", kex)
+		}
+	}
 
 	s := &connection{
 		sshConn: sshConn{conn: c},
@@ -204,7 +228,9 @@ func (s *connection) serverHandshake(config *ServerConfig) (*Permissions, error)
 		return nil, errors.New("ssh: server has no host keys")
 	}
 
-	if !config.NoClientAuth && config.PasswordCallback == nil && config.PublicKeyCallback == nil && config.KeyboardInteractiveCallback == nil {
+	if !config.NoClientAuth && config.PasswordCallback == nil && config.PublicKeyCallback == nil &&
+		config.KeyboardInteractiveCallback == nil && (config.GSSAPIWithMICConfig == nil ||
+		config.GSSAPIWithMICConfig.AllowLogin == nil || config.GSSAPIWithMICConfig.Server == nil) {
 		return nil, errors.New("ssh: no authentication methods configured but NoClientAuth is also false")
 	}
 
@@ -295,6 +321,55 @@ func checkSourceAddress(addr net.Addr, sourceAddrs string) error {
 	return fmt.Errorf("ssh: remote address %v is not allowed because of source-address restriction", addr)
 }
 
+func gssExchangeToken(gssapiConfig *GSSAPIWithMICConfig, firstToken []byte, s *connection,
+	sessionID []byte, userAuthReq userAuthRequestMsg) (authErr error, perms *Permissions, err error) {
+	gssAPIServer := gssapiConfig.Server
+	defer gssAPIServer.DeleteSecContext()
+	var srcName string
+	for {
+		var (
+			outToken     []byte
+			needContinue bool
+		)
+		outToken, srcName, needContinue, err = gssAPIServer.AcceptSecContext(firstToken)
+		if err != nil {
+			return err, nil, nil
+		}
+		if len(outToken) != 0 {
+			if err := s.transport.writePacket(Marshal(&userAuthGSSAPIToken{
+				Token: outToken,
+			})); err != nil {
+				return nil, nil, err
+			}
+		}
+		if !needContinue {
+			break
+		}
+		packet, err := s.transport.readPacket()
+		if err != nil {
+			return nil, nil, err
+		}
+		userAuthGSSAPITokenReq := &userAuthGSSAPIToken{}
+		if err := Unmarshal(packet, userAuthGSSAPITokenReq); err != nil {
+			return nil, nil, err
+		}
+	}
+	packet, err := s.transport.readPacket()
+	if err != nil {
+		return nil, nil, err
+	}
+	userAuthGSSAPIMICReq := &userAuthGSSAPIMIC{}
+	if err := Unmarshal(packet, userAuthGSSAPIMICReq); err != nil {
+		return nil, nil, err
+	}
+	mic := buildMIC(string(sessionID), userAuthReq.User, userAuthReq.Service, userAuthReq.Method)
+	if err := gssAPIServer.VerifyMIC(mic, userAuthGSSAPIMICReq.MIC); err != nil {
+		return err, nil, nil
+	}
+	perms, authErr = gssapiConfig.AllowLogin(s, srcName)
+	return authErr, perms, nil
+}
+
 // ServerAuthError represents server authentication errors and is
 // sometimes returned by NewServerConn. It appends any authentication
 // errors that may occur, and is returned if all of the authentication
@@ -496,6 +571,49 @@ userAuthLoop:
 				authErr = candidate.result
 				perms = candidate.perms
 			}
+		case "gssapi-with-mic":
+			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)
 		}
@@ -522,6 +640,10 @@ userAuthLoop:
 		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")

vendor/golang.org/x/crypto/ssh/ssh_gss.go

@@ -0,0 +1,139 @@
+// 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 (
+	"encoding/asn1"
+	"errors"
+)
+
+var krb5OID []byte
+
+func init() {
+	krb5OID, _ = asn1.Marshal(krb5Mesh)
+}
+
+// GSSAPIClient provides the API to plug-in GSSAPI authentication for client logins.
+type GSSAPIClient interface {
+	// InitSecContext initiates the establishment of a security context for GSS-API between the
+	// ssh client and ssh server. Initially the token parameter should be specified as nil.
+	// The routine may return a outputToken which should be transferred to
+	// the ssh server, where the ssh server will present it to
+	// AcceptSecContext. If no token need be sent, InitSecContext will indicate this by setting
+	// needContinue to false. To complete the context
+	// establishment, one or more reply tokens may be required from the ssh
+	// server;if so, InitSecContext will return a needContinue which is true.
+	// In this case, InitSecContext should be called again when the
+	// reply token is received from the ssh server, passing the reply
+	// token to InitSecContext via the token parameters.
+	// See RFC 2743 section 2.2.1 and RFC 4462 section 3.4.
+	InitSecContext(target string, token []byte, isGSSDelegCreds bool) (outputToken []byte, needContinue bool, err error)
+	// GetMIC generates a cryptographic MIC for the SSH2 message, and places
+	// the MIC in a token for transfer to the ssh server.
+	// The contents of the MIC field are obtained by calling GSS_GetMIC()
+	// over the following, using the GSS-API context that was just
+	// established:
+	//  string    session identifier
+	//  byte      SSH_MSG_USERAUTH_REQUEST
+	//  string    user name
+	//  string    service
+	//  string    "gssapi-with-mic"
+	// See RFC 2743 section 2.3.1 and RFC 4462 3.5.
+	GetMIC(micFiled []byte) ([]byte, error)
+	// Whenever possible, it should be possible for
+	// DeleteSecContext() calls to be successfully processed even
+	// if other calls cannot succeed, thereby enabling context-related
+	// resources to be released.
+	// In addition to deleting established security contexts,
+	// gss_delete_sec_context must also be able to delete "half-built"
+	// security contexts resulting from an incomplete sequence of
+	// InitSecContext()/AcceptSecContext() calls.
+	// See RFC 2743 section 2.2.3.
+	DeleteSecContext() error
+}
+
+// GSSAPIServer provides the API to plug in GSSAPI authentication for server logins.
+type GSSAPIServer interface {
+	// AcceptSecContext allows a remotely initiated security context between the application
+	// and a remote peer to be established by the ssh client. The routine may return a
+	// outputToken which should be transferred to the ssh client,
+	// where the ssh client will present it to InitSecContext.
+	// If no token need be sent, AcceptSecContext will indicate this
+	// by setting the needContinue to false. To
+	// complete the context establishment, one or more reply tokens may be
+	// required from the ssh client. if so, AcceptSecContext
+	// will return a needContinue which is true, in which case it
+	// should be called again when the reply token is received from the ssh
+	// client, passing the token to AcceptSecContext via the
+	// token parameters.
+	// The srcName return value is the authenticated username.
+	// See RFC 2743 section 2.2.2 and RFC 4462 section 3.4.
+	AcceptSecContext(token []byte) (outputToken []byte, srcName string, needContinue bool, err error)
+	// VerifyMIC verifies that a cryptographic MIC, contained in the token parameter,
+	// fits the supplied message is received from the ssh client.
+	// See RFC 2743 section 2.3.2.
+	VerifyMIC(micField []byte, micToken []byte) error
+	// Whenever possible, it should be possible for
+	// DeleteSecContext() calls to be successfully processed even
+	// if other calls cannot succeed, thereby enabling context-related
+	// resources to be released.
+	// In addition to deleting established security contexts,
+	// gss_delete_sec_context must also be able to delete "half-built"
+	// security contexts resulting from an incomplete sequence of
+	// InitSecContext()/AcceptSecContext() calls.
+	// See RFC 2743 section 2.2.3.
+	DeleteSecContext() error
+}
+
+var (
+	// OpenSSH supports Kerberos V5 mechanism only for GSS-API authentication,
+	// so we also support the krb5 mechanism only.
+	// See RFC 1964 section 1.
+	krb5Mesh = asn1.ObjectIdentifier{1, 2, 840, 113554, 1, 2, 2}
+)
+
+// The GSS-API authentication method is initiated when the client sends an SSH_MSG_USERAUTH_REQUEST
+// See RFC 4462 section 3.2.
+type userAuthRequestGSSAPI struct {
+	N    uint32
+	OIDS []asn1.ObjectIdentifier
+}
+
+func parseGSSAPIPayload(payload []byte) (*userAuthRequestGSSAPI, error) {
+	n, rest, ok := parseUint32(payload)
+	if !ok {
+		return nil, errors.New("parse uint32 failed")
+	}
+	s := &userAuthRequestGSSAPI{
+		N:    n,
+		OIDS: make([]asn1.ObjectIdentifier, n),
+	}
+	for i := 0; i < int(n); i++ {
+		var (
+			desiredMech []byte
+			err         error
+		)
+		desiredMech, rest, ok = parseString(rest)
+		if !ok {
+			return nil, errors.New("parse string failed")
+		}
+		if rest, err = asn1.Unmarshal(desiredMech, &s.OIDS[i]); err != nil {
+			return nil, err
+		}
+
+	}
+	return s, nil
+}
+
+// See RFC 4462 section 3.6.
+func buildMIC(sessionID string, username string, service string, authMethod string) []byte {
+	out := make([]byte, 0, 0)
+	out = appendString(out, sessionID)
+	out = append(out, msgUserAuthRequest)
+	out = appendString(out, username)
+	out = appendString(out, service)
+	out = appendString(out, authMethod)
+	return out
+}