ldap2.has_upg: Raise an error if the UPG definition is not found

The UPG Definition is always present in IPA; if it can not be read
it's usually caused by insufficient privileges.
Previously the code assumed the absence of the entry meant that
UPG is disabled. With granular read permissions, this would mean
that users that can add users but can't read UPG Definition would
add users without UPG, and the reason for that would not be very clear.
It is better to fail early if the definition can't be read.

Raise an error if the UPG Definition is not available. This makes
read access to it a prerequisite for adding users.

Part of the work for: https://fedorahosted.org/freeipa/ticket/3566

Reviewed-By: Martin Kosek <mkosek@redhat.com>

ipaserver/plugins/ldap2.py

@@ -28,7 +28,6 @@ Backend plugin for LDAP.
 # everything except the CrudBackend methods, where dn is part of the entry dict.
 
 import os
-import re
 import pwd
 
 import krbV
@@ -52,7 +51,7 @@ except ImportError:
         def __init__(self, criticality, authzId=None):
             LDAPControl.__init__(self, '1.3.6.1.4.1.42.2.27.9.5.2', criticality, authzId)
 
-from ipalib import api, errors
+from ipalib import api, errors, _
 from ipalib.crud import CrudBackend
 from ipalib.request import context
 
@@ -297,23 +296,28 @@ class ldap2(LDAPClient, CrudBackend):
 
     def has_upg(self):
         """Returns True/False whether User-Private Groups are enabled.
-           This is determined based on whether the UPG Template exists.
+
+        This is determined based on whether the UPG Definition's originfilter
+        contains "(objectclass=disable)".
+
+        If the UPG Definition or its originfilter is not readable,
+        an ACI error is raised.
         """
 
         upg_dn = DN(('cn', 'UPG Definition'), ('cn', 'Definitions'), ('cn', 'Managed Entries'),
                     ('cn', 'etc'), api.env.basedn)
 
         try:
-            upg_entry = self.conn.search_s(upg_dn, _ldap.SCOPE_BASE,
-                                           attrlist=['*'])[0]
-            disable_attr = '(objectclass=disable)'
-            if 'originfilter' in upg_entry:
-                org_filter = upg_entry['originfilter']
-                return not bool(re.search(r'%s' % disable_attr, org_filter[0]))
-            else:
-                return False
-        except _ldap.NO_SUCH_OBJECT, e:
-            return False
+            upg_entries = self.conn.search_s(upg_dn, _ldap.SCOPE_BASE,
+                                             attrlist=['*'])
+        except _ldap.NO_SUCH_OBJECT:
+            upg_entries = None
+        if not upg_entries or 'originfilter' not in upg_entries[0]:
+            raise errors.ACIError(info=_(
+                'Could not read UPG Definition originfilter. '
+                'Check your permissions.'))
+        org_filter = upg_entries[0].single_value['originfilter']
+        return '(objectclass=disable)' not in org_filter
 
     def get_effective_rights(self, dn, attrs_list):
         """Returns the rights the currently bound user has for the given DN.