Merge branch '2.0' into 2.1

7 files changed, 221 insertions, 90 deletions

diff --git a/demos/demo_simple.py b/demos/demo_simple.py
index 3a17988c..7ae3d8c8 100755..100644
--- a/demos/demo_simple.py
+++ b/demos/demo_simple.py
@@ -37,8 +37,10 @@ except ImportError:
 # setup logging
 paramiko.util.log_to_file('demo_simple.log')
 # Paramiko client configuration
-UseGSSAPI = True             # enable GSS-API / SSPI authentication
-DoGSSAPIKeyExchange = True
+UseGSSAPI = paramiko.GSS_AUTH_AVAILABLE             # enable "gssapi-with-mic" authentication, if supported by your python installation
+DoGSSAPIKeyExchange = paramiko.GSS_AUTH_AVAILABLE   # enable "gssapi-kex" key exchange, if supported by your python installation
+# UseGSSAPI = False
+# DoGSSAPIKeyExchange = False
 port = 22
 
 # get hostname
@@ -64,7 +66,7 @@ if username == '':
     username = input('Username [%s]: ' % default_username)
     if len(username) == 0:
         username = default_username
-if not UseGSSAPI or (not UseGSSAPI and not DoGSSAPIKeyExchange):
+if not UseGSSAPI and not DoGSSAPIKeyExchange:
     password = getpass.getpass('Password for %s@%s: ' % (username, hostname))
 
 
@@ -74,7 +76,7 @@ try:
     client.load_system_host_keys()
     client.set_missing_host_key_policy(paramiko.WarningPolicy())
     print('*** Connecting...')
-    if not UseGSSAPI or (not UseGSSAPI and not DoGSSAPIKeyExchange):
+    if not UseGSSAPI and not DoGSSAPIKeyExchange:
         client.connect(hostname, port, username, password)
     else:
         # SSPI works only with the FQDN of the target host
@@ -83,6 +85,7 @@ try:
             client.connect(hostname, port, username, gss_auth=UseGSSAPI,
                            gss_kex=DoGSSAPIKeyExchange)
         except Exception:
+            # traceback.print_exc()
             password = getpass.getpass('Password for %s@%s: ' % (username, hostname))
             client.connect(hostname, port, username, password)
 
diff --git a/paramiko/__init__.py b/paramiko/__init__.py
index 197f519a..01dc973c 100644
--- a/paramiko/__init__.py
+++ b/paramiko/__init__.py
@@ -34,7 +34,7 @@ from paramiko.client import (
     WarningPolicy,
 )
 from paramiko.auth_handler import AuthHandler
-from paramiko.ssh_gss import GSSAuth, GSS_AUTH_AVAILABLE
+from paramiko.ssh_gss import GSSAuth, GSS_AUTH_AVAILABLE, GSS_EXCEPTIONS
 from paramiko.channel import Channel, ChannelFile
 from paramiko.ssh_exception import (
     SSHException, PasswordRequiredException, BadAuthenticationType,
diff --git a/paramiko/auth_handler.py b/paramiko/auth_handler.py
index 33f01da6..24ada232 100644
--- a/paramiko/auth_handler.py
+++ b/paramiko/auth_handler.py
@@ -43,7 +43,7 @@ from paramiko.ssh_exception import (
     PartialAuthentication,
 )
 from paramiko.server import InteractiveQuery
-from paramiko.ssh_gss import GSSAuth
+from paramiko.ssh_gss import GSSAuth, GSS_EXCEPTIONS
 
 
 class AuthHandler (object):
@@ -262,19 +262,26 @@ class AuthHandler (object):
                     mech = m.get_string()
                     m = Message()
                     m.add_byte(cMSG_USERAUTH_GSSAPI_TOKEN)
-                    m.add_string(sshgss.ssh_init_sec_context(self.gss_host,
-                                                             mech,
-                                                             self.username,))
+                    try:
+                        m.add_string(sshgss.ssh_init_sec_context(
+                            self.gss_host,
+                            mech,
+                            self.username,))
+                    except GSS_EXCEPTIONS as e:
+                        return self._handle_local_gss_failure(e)
                     self.transport._send_message(m)
                     while True:
                         ptype, m = self.transport.packetizer.read_message()
                         if ptype == MSG_USERAUTH_GSSAPI_TOKEN:
                             srv_token = m.get_string()
-                            next_token = sshgss.ssh_init_sec_context(
-                                self.gss_host,
-                                mech,
-                                self.username,
-                                srv_token)
+                            try:
+                                next_token = sshgss.ssh_init_sec_context(
+                                    self.gss_host,
+                                    mech,
+                                    self.username,
+                                    srv_token)
+                            except GSS_EXCEPTIONS as e:
+                                return self._handle_local_gss_failure(e)
                             # After this step the GSSAPI should not return any
                             # token. If it does, we keep sending the token to
                             # the server until no more token is returned.
@@ -302,7 +309,7 @@ class AuthHandler (object):
                     maj_status = m.get_int()
                     min_status = m.get_int()
                     err_msg = m.get_string()
-                    m.get_string() # Lang tag - discarded
+                    m.get_string()  # Lang tag - discarded
                     raise SSHException("GSS-API Error:\nMajor Status: %s\n\
                                         Minor Status: %s\ \nError Message:\
                                          %s\n") % (str(maj_status),
@@ -395,7 +402,7 @@ class AuthHandler (object):
                 (self.auth_username != username)):
             self.transport._log(
                 WARNING,
-                'Auth rejected because the client attempted to change username in mid-flight' # noqa
+                'Auth rejected because the client attempted to change username in mid-flight'  # noqa
             )
             self._disconnect_no_more_auth()
             return
@@ -503,52 +510,16 @@ class AuthHandler (object):
             supported_mech = sshgss.ssh_gss_oids("server")
             # RFC 4462 says we are not required to implement GSS-API error
             # messages. See section 3.8 in http://www.ietf.org/rfc/rfc4462.txt
-            while True:
-                m = Message()
-                m.add_byte(cMSG_USERAUTH_GSSAPI_RESPONSE)
-                m.add_bytes(supported_mech)
-                self.transport._send_message(m)
-                ptype, m = self.transport.packetizer.read_message()
-                if ptype == MSG_USERAUTH_GSSAPI_TOKEN:
-                    client_token = m.get_string()
-                    # use the client token as input to establish a secure
-                    # context.
-                    try:
-                        token = sshgss.ssh_accept_sec_context(self.gss_host,
-                                                              client_token,
-                                                              username)
-                    except Exception:
-                        result = AUTH_FAILED
-                        self._send_auth_result(username, method, result)
-                        raise
-                    if token is not None:
-                        m = Message()
-                        m.add_byte(cMSG_USERAUTH_GSSAPI_TOKEN)
-                        m.add_string(token)
-                        self.transport._send_message(m)
-                else:
-                    result = AUTH_FAILED
-                    self._send_auth_result(username, method, result)
-                    return
-                # check MIC
-                ptype, m = self.transport.packetizer.read_message()
-                if ptype == MSG_USERAUTH_GSSAPI_MIC:
-                    break
-            mic_token = m.get_string()
-            try:
-                sshgss.ssh_check_mic(mic_token,
-                                     self.transport.session_id,
-                                     username)
-            except Exception:
-                result = AUTH_FAILED
-                self._send_auth_result(username, method, result)
-                raise
-            # TODO: Implement client credential saving.
-            # The OpenSSH server is able to create a TGT with the delegated
-            # client credentials, but this is not supported by GSS-API.
-            result = AUTH_SUCCESSFUL
-            self.transport.server_object.check_auth_gssapi_with_mic(
-                username, result)
+            m = Message()
+            m.add_byte(cMSG_USERAUTH_GSSAPI_RESPONSE)
+            m.add_bytes(supported_mech)
+            self.transport.auth_handler = GssapiWithMicAuthHandler(self,
+                                                                   sshgss)
+            self.transport._expected_packet = (MSG_USERAUTH_GSSAPI_TOKEN,
+                                               MSG_USERAUTH_REQUEST,
+                                               MSG_SERVICE_REQUEST)
+            self.transport._send_message(m)
+            return
         elif method == "gssapi-keyex" and gss_auth:
             mic_token = m.get_string()
             sshgss = self.transport.kexgss_ctxt
@@ -648,6 +619,17 @@ class AuthHandler (object):
         self._send_auth_result(
             self.auth_username, 'keyboard-interactive', result)
 
+    def _handle_local_gss_failure(self, e):
+        self.transport.saved_exception = e
+        self.transport._log(DEBUG, "GSSAPI failure: %s" % str(e))
+        self.transport._log(INFO, 'Authentication (%s) failed.' %
+                            self.auth_method)
+        self.authenticated = False
+        self.username = None
+        if self.auth_event is not None:
+            self.auth_event.set()
+        return
+
     _handler_table = {
         MSG_SERVICE_REQUEST: _parse_service_request,
         MSG_SERVICE_ACCEPT: _parse_service_accept,
@@ -658,3 +640,102 @@ class AuthHandler (object):
         MSG_USERAUTH_INFO_REQUEST: _parse_userauth_info_request,
         MSG_USERAUTH_INFO_RESPONSE: _parse_userauth_info_response,
     }
+
+
+class GssapiWithMicAuthHandler(object):
+    """A specialized Auth handler for gssapi-with-mic
+
+    During the GSSAPI token exchange we need a modified dispatch table,
+    because the packet type numbers are not unique.
+    """
+
+    method = "gssapi-with-mic"
+
+    def __init__(self, delegate, sshgss):
+        self._delegate = delegate
+        self.sshgss = sshgss
+
+    def abort(self):
+        self._restore_delegate_auth_handler()
+        return self._delegate.abort()
+
+    @property
+    def transport(self):
+        return self._delegate.transport
+
+    @property
+    def _send_auth_result(self):
+        return self._delegate._send_auth_result
+
+    @property
+    def auth_username(self):
+        return self._delegate.auth_username
+
+    @property
+    def gss_host(self):
+        return self._delegate.gss_host
+
+    def _restore_delegate_auth_handler(self):
+        self.transport.auth_handler = self._delegate
+
+    def _parse_userauth_gssapi_token(self, m):
+        client_token = m.get_string()
+        # use the client token as input to establish a secure
+        # context.
+        sshgss = self.sshgss
+        try:
+            token = sshgss.ssh_accept_sec_context(self.gss_host,
+                                                  client_token,
+                                                  self.auth_username)
+        except Exception as e:
+            self.transport.saved_exception = e
+            result = AUTH_FAILED
+            self._restore_delegate_auth_handler()
+            self._send_auth_result(self.auth_username, self.method, result)
+            raise
+        if token is not None:
+            m = Message()
+            m.add_byte(cMSG_USERAUTH_GSSAPI_TOKEN)
+            m.add_string(token)
+            self.transport._expected_packet = (MSG_USERAUTH_GSSAPI_TOKEN,
+                                               MSG_USERAUTH_GSSAPI_MIC,
+                                               MSG_USERAUTH_REQUEST)
+            self.transport._send_message(m)
+
+    def _parse_userauth_gssapi_mic(self, m):
+        mic_token = m.get_string()
+        sshgss = self.sshgss
+        username = self.auth_username
+        self._restore_delegate_auth_handler()
+        try:
+            sshgss.ssh_check_mic(mic_token,
+                                 self.transport.session_id,
+                                 username)
+        except Exception as e:
+            self.transport.saved_exception = e
+            result = AUTH_FAILED
+            self._send_auth_result(username, self.method, result)
+            raise
+        # TODO: Implement client credential saving.
+        # The OpenSSH server is able to create a TGT with the delegated
+        # client credentials, but this is not supported by GSS-API.
+        result = AUTH_SUCCESSFUL
+        self.transport.server_object.check_auth_gssapi_with_mic(username,
+                                                                result)
+        # okay, send result
+        self._send_auth_result(username, self.method, result)
+
+    def _parse_service_request(self, m):
+        self._restore_delegate_auth_handler()
+        return self._delegate._parse_service_request(m)
+
+    def _parse_userauth_request(self, m):
+        self._restore_delegate_auth_handler()
+        return self._delegate._parse_userauth_request(m)
+
+    _handler_table = {
+        MSG_SERVICE_REQUEST: _parse_service_request,
+        MSG_USERAUTH_REQUEST: _parse_userauth_request,
+        MSG_USERAUTH_GSSAPI_TOKEN: _parse_userauth_gssapi_token,
+        MSG_USERAUTH_GSSAPI_MIC: _parse_userauth_gssapi_mic,
+    }
diff --git a/paramiko/ssh_gss.py b/paramiko/ssh_gss.py
index 414485f9..b3c3f72b 100644
--- a/paramiko/ssh_gss.py
+++ b/paramiko/ssh_gss.py
@@ -33,34 +33,39 @@ import struct
 import os
 import sys
 
-"""
-:var bool GSS_AUTH_AVAILABLE:
-    Constraint that indicates if GSS-API / SSPI is available.
-"""
+
+#: A boolean constraint that indicates if GSS-API / SSPI is available.
 GSS_AUTH_AVAILABLE = True
 
+
+#: A tuple of the exception types used by the underlying GSSAPI implementation.
+GSS_EXCEPTIONS = ()
+
+
 from pyasn1.type.univ import ObjectIdentifier
 from pyasn1.codec.der import encoder, decoder
 
-from paramiko.common import MSG_USERAUTH_REQUEST
-from paramiko.ssh_exception import SSHException
 
-"""
-:var str _API: Constraint for the used API
-"""
+#: :var str _API: Constraint for the used API
 _API = "MIT"
 
 try:
     import gssapi
+    GSS_EXCEPTIONS = (gssapi.GSSException,)
 except (ImportError, OSError):
     try:
+        import pywintypes
         import sspicon
         import sspi
         _API = "SSPI"
+        GSS_EXCEPTIONS = (pywintypes.error,)
     except ImportError:
         GSS_AUTH_AVAILABLE = False
         _API = None
 
+from paramiko.common import MSG_USERAUTH_REQUEST
+from paramiko.ssh_exception import SSHException
+
 
 def GSSAuth(auth_method, gss_deleg_creds=True):
     """
@@ -345,9 +350,9 @@ class _SSH_GSSAPI(_SSH_GSSAuth):
         if self._username is not None:
             # server mode
             mic_field = self._ssh_build_mic(self._session_id,
-                                        self._username,
-                                        self._service,
-                                        self._auth_method)
+                                            self._username,
+                                            self._service,
+                                            self._auth_method)
             self._gss_srv_ctxt.verify_mic(mic_field, mic_token)
         else:
             # for key exchange with gssapi-keyex
@@ -438,9 +443,10 @@ class _SSH_SSPI(_SSH_GSSAuth):
                                                  targetspn=targ_name)
             error, token = self._gss_ctxt.authorize(recv_token)
             token = token[0].Buffer
-        except:
-            raise Exception("{0}, Target: {1}".format(sys.exc_info()[1],
-                                                      self._gss_host))
+        except pywintypes.error as e:
+            e.strerror += ", Target: {1}".format(e, self._gss_host)
+            raise
+
         if error == 0:
             """
             if the status is GSS_COMPLETE (error = 0) the context is fully
diff --git a/paramiko/transport.py b/paramiko/transport.py
index d26af833..7d5cde56 100644
--- a/paramiko/transport.py
+++ b/paramiko/transport.py
@@ -133,6 +133,11 @@ class Transport(threading.Thread, ClosingContextManager):
         'diffie-hellman-group-exchange-sha1',
         'diffie-hellman-group-exchange-sha256',
     )
+    _preferred_gsskex = (
+        'gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==',
+        'gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==',
+        'gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==',
+    )
     _preferred_compression = ('none',)
 
     _cipher_info = {
@@ -334,12 +339,7 @@ class Transport(threading.Thread, ClosingContextManager):
         self.gss_host = None
         if self.use_gss_kex:
             self.kexgss_ctxt = GSSAuth("gssapi-keyex", gss_deleg_creds)
-            self._preferred_kex = ('gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==',
-                                   'gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==',
-                                   'gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==',
-                                   'diffie-hellman-group-exchange-sha1',
-                                   'diffie-hellman-group14-sha1',
-                                   'diffie-hellman-group1-sha1')
+            self._preferred_kex = self._preferred_gsskex + self._preferred_kex
 
         # state used during negotiation
         self.kex_engine = None
@@ -1846,6 +1846,8 @@ class Transport(threading.Thread, ClosingContextManager):
                     ):
                         handler = self.auth_handler._handler_table[ptype]
                         handler(self.auth_handler, m)
+                        if len(self._expected_packet) > 0:
+                            continue
                     else:
                         self._log(WARNING, 'Oops, unhandled type %d' % ptype)
                         msg = Message()
diff --git a/sites/www/changelog.rst b/sites/www/changelog.rst
index 8665ee94..cac5a715 100644
--- a/sites/www/changelog.rst
+++ b/sites/www/changelog.rst
@@ -2,6 +2,14 @@
 Changelog
 =========
 
+* :bug:`1061` Clean up GSSAPI authentication procedures so they do not prevent
+  normal fallback to other authentication methods on failure. (In other words,
+  presence of GSSAPI functionality on a target server precluded use of _any_
+  other auth type if the user was unable to pass GSSAPI auth.) Patch via Anselm
+  Kruis.
+* :bug:`1060` Fix key exchange (kex) algorithm list for GSSAPI authentication;
+  previously, the list used solely out-of-date algorithms, and now contains
+  newer ones listed preferentially before the old. Credit: Anselm Kruis.
 * :bug:`1055` (also :issue:`1056`, :issue:`1057`, :issue:`1058`, :issue:`1059`)
   Fix up host-key checking in our GSSAPI support, which was previously using an
   incorrect API call. Thanks to Anselm Kruis for the patches.
diff --git a/tests/test_ssh_gss.py b/tests/test_ssh_gss.py
index 967b3b81..d8d05d2b 100644
--- a/tests/test_ssh_gss.py
+++ b/tests/test_ssh_gss.py
@@ -29,11 +29,13 @@ import unittest
 
 import paramiko
 
+from tests.util import test_path
+from tests.test_client import FINGERPRINTS
 
 class NullServer (paramiko.ServerInterface):
 
     def get_allowed_auths(self, username):
-        return 'gssapi-with-mic'
+        return 'gssapi-with-mic,publickey'
 
     def check_auth_gssapi_with_mic(self, username,
                                    gss_authenticated=paramiko.AUTH_FAILED,
@@ -45,6 +47,16 @@ class NullServer (paramiko.ServerInterface):
     def enable_auth_gssapi(self):
         return True
 
+    def check_auth_publickey(self, username, key):
+        try:
+            expected = FINGERPRINTS[key.get_name()]
+        except KeyError:
+            return paramiko.AUTH_FAILED
+        else:
+            if key.get_fingerprint() == expected:
+                return paramiko.AUTH_SUCCESSFUL
+        return paramiko.AUTH_FAILED
+
     def check_channel_request(self, kind, chanid):
         return paramiko.OPEN_SUCCEEDED
 
@@ -85,19 +97,21 @@ class GSSAuthTest(unittest.TestCase):
         server = NullServer()
         self.ts.start_server(self.event, server)
 
-    def test_1_gss_auth(self):
+    def _test_connection(self, **kwargs):
         """
-        Verify that Paramiko can handle SSHv2 GSS-API / SSPI authentication
-        (gssapi-with-mic) in client and server mode.
+        (Most) kwargs get passed directly into SSHClient.connect().
+
+        The exception is ... no exception yet
         """
         host_key = paramiko.RSAKey.from_private_key_file('tests/test_rsa.key')
         public_host_key = paramiko.RSAKey(data=host_key.asbytes())
 
         self.tc = paramiko.SSHClient()
-        self.tc.get_host_keys().add('[%s]:%d' % (self.hostname, self.port),
+        self.tc.set_missing_host_key_policy(paramiko.WarningPolicy())
+        self.tc.get_host_keys().add('[%s]:%d' % (self.addr, self.port),
                                     'ssh-rsa', public_host_key)
-        self.tc.connect(self.hostname, self.port, username=self.username,
-                        gss_auth=True)
+        self.tc.connect(hostname=self.addr, port=self.port, username=self.username, gss_host=self.hostname,
+                        gss_auth=True, **kwargs)
 
         self.event.wait(1.0)
         self.assert_(self.event.is_set())
@@ -120,3 +134,20 @@ class GSSAuthTest(unittest.TestCase):
         stdin.close()
         stdout.close()
         stderr.close()
+
+    def test_1_gss_auth(self):
+        """
+        Verify that Paramiko can handle SSHv2 GSS-API / SSPI authentication
+        (gssapi-with-mic) in client and server mode.
+        """
+        self._test_connection(allow_agent=False,
+                              look_for_keys=False)
+
+    def test_2_auth_trickledown(self):
+        """
+        Failed gssapi-with-mic auth doesn't prevent subsequent key auth from succeeding
+        """
+        self.hostname = "this_host_does_not_exists_and_causes_a_GSSAPI-exception"
+        self._test_connection(key_filename=[test_path('test_rsa.key')],
+                              allow_agent=False,
+                              look_for_keys=False)