Handle exceptions when establishing trusts

Translate exceptions produced by DCERPC bindings when establishing trusts.
There are two types of errors that may be produced by DCERPC bindings:
- RuntimeError with a text (RuntimeError('NT_STATUS_OBJECT_NAME_NOT_FOUND')
- RuntimeError with a numeric code and 'friendly' message

Error codes could have two prefixes:
  - NT error codes, start with NT_STATUS_ prefix
  - Windows error codes, start with WERR_ prefix

Full list of errors is available in Samba source code:
  libcli/util/ntstatus.h: NT_STATUS error codes
  libcli/util/werror.h: Windows error codes

Majority of errors returned when dealing with trusts are of NT_STATUS type,
these also include all typical POSIX errors mapped to corresponding NT errors.

Unfortunately, in the textual RuntimeError case very little can be done to
get better clarification of the error. More error paths will need to be added
as they will be discovered -- DCERPC error messaging is complex.

https://fedorahosted.org/freeipa/ticket/2868

ipaserver/dcerpc.py

@@ -28,6 +28,7 @@ from ipalib.parameters import Enum
 from ipalib import Command
 from ipalib import errors
 from ipapython import ipautil
+from ipapython.ipa_log_manager import *
 from ipaserver.install import installutils
 
 import os, string, struct, copy
@@ -49,6 +50,31 @@ The code in this module relies heavily on samba4-python package
 and Samba4 python bindings.
 """)
 
+access_denied_error =  errors.ACIError(info='CIFS server denied your credentials')
+dcerpc_error_codes = {
+    -1073741823: errors.RemoteRetrieveError(reason='communication with CIFS server was unsuccessful'),
+    -1073741790: access_denied_error,
+    -1073741715: access_denied_error,
+    -1073741614: access_denied_error,
+    -1073741603: errors.ValidationError(name='AD domain controller', error='unsupported functional level'),
+}
+
+dcerpc_error_messages = {
+    "NT_STATUS_OBJECT_NAME_NOT_FOUND": errors.NotFound(reason='Cannot find specified domain or server name'),
+    "NT_STATUS_INVALID_PARAMETER_MIX": errors.RequirementError(name='At least the domain or IP address should be specified'),
+}
+
+def assess_dcerpc_exception(num=None,message=None):
+    """
+    Takes error returned by Samba bindings and converts it into
+    an IPA error class.
+    """
+    if num and num in dcerpc_error_codes:
+        return dcerpc_error_codes[num]
+    if message and message in dcerpc_error_messages:
+        return dcerpc_error_messages[message]
+    return errors.RemoteRetrieveError(reason='CIFS server communication error: code "%s", message "%s" (both may be "None")' % (num, message))
+
 class ExtendedDNControl(_ldap.controls.RequestControl):
     def __init__(self):
         self.controlType = "1.2.840.113556.1.4.529"
@@ -151,8 +177,8 @@ class TrustDomainInstance(object):
        try:
            result = lsa.lsarpc(binding, self.parm, self.creds)
            return result
-       except:
+       except RuntimeError, (num, message):
-           return None
+           raise assess_dcerpc_exception(num=num, message=message)
 
     def __init_lsa_pipe(self, remote_host):
         """
@@ -168,13 +194,21 @@ class TrustDomainInstance(object):
         if self._pipe:
             return
 
+        attempts = 0
         bindings = self.__gen_lsa_bindings(remote_host)
         for binding in bindings:
+            try:
                 self._pipe = self.__gen_lsa_connection(binding)
                 if self._pipe:
                     break
+            except errors.ACIError, e:
+                attempts = attempts + 1
+
+        if self._pipe is None and attempts == len(bindings):
+            raise errors.ACIError(info='CIFS server %s denied your credentials' % (remote_host))
+
         if self._pipe is None:
-            raise errors.RequirementError(name='Working LSA pipe')
+            raise errors.RemoteRetrieveError(reason='Cannot establish LSA connection to %s. Is CIFS server running?' % (remote_host))
 
     def __gen_lsa_bindings(self, remote_host):
         """
@@ -195,10 +229,14 @@ class TrustDomainInstance(object):
         When retrieving DC information anonymously, we can't get SID of the domain
         """
         netrc = net.Net(creds=self.creds, lp=self.parm)
+        try:
             if discover_srv:
                 result = netrc.finddc(domain=remote_host, flags=nbt.NBT_SERVER_LDAP | nbt.NBT_SERVER_DS)
             else:
                 result = netrc.finddc(address=remote_host, flags=nbt.NBT_SERVER_LDAP | nbt.NBT_SERVER_DS)
+        except RuntimeError, e:
+            raise assess_dcerpc_exception(message=str(e))
+
         if not result:
             return False
         self.info['name'] = unicode(result.domain_name)
@@ -217,7 +255,7 @@ class TrustDomainInstance(object):
             result = res['defaultNamingContext'][0]
             self.info['dns_hostname'] = res['dnsHostName'][0]
         except _ldap.LDAPError, e:
-            print "LDAP error when connecting to %s: %s" % (unicode(result.pdc_name), str(e))
+            root_logger.error("LDAP error when connecting to %s: %s" % (unicode(result.pdc_name), str(e)))
 
         if result:
            self.info['sid'] = self.parse_naming_context(result)
@@ -232,8 +270,12 @@ class TrustDomainInstance(object):
 
         objectAttribute = lsa.ObjectAttribute()
         objectAttribute.sec_qos = lsa.QosInfo()
+        try:
             self._policy_handle = self._pipe.OpenPolicy2(u"", objectAttribute, security.SEC_FLAG_MAXIMUM_ALLOWED)
             result = self._pipe.QueryInfoPolicy2(self._policy_handle, lsa.LSA_POLICY_INFO_DNS)
+        except RuntimeError, (num, message):
+            raise assess_dcerpc_exception(num=num, message=message)
+
         self.info['name'] = unicode(result.name.string)
         self.info['dns_domain'] = unicode(result.dns_domain.string)
         self.info['dns_forest'] = unicode(result.dns_forest.string)
@@ -315,9 +357,12 @@ class TrustDomainInstance(object):
             dname.string = another_domain.info['dns_domain']
             res = self._pipe.QueryTrustedDomainInfoByName(self._policy_handle, dname, lsa.LSA_TRUSTED_DOMAIN_INFO_FULL_INFO)
             self._pipe.DeleteTrustedDomain(self._policy_handle, res.info_ex.sid)
-        except:
+        except RuntimeError, e:
             pass
+        try:
             self._pipe.CreateTrustedDomainEx2(self._policy_handle, info, self.auth_info, security.SEC_STD_DELETE)
+        except RuntimeError, (num, message):
+            raise assess_dcerpc_exception(num=num, message=message)
 
 class TrustDomainJoins(object):
     def __init__(self, api):