trust: automatically resolve DNS trust conflicts for triangle trusts

For configuration where:
  - AD example.com trusts IPA at ipa.example.com
  - AD example.org trusts AD example.com
  - a trust is tried to be established between ipa.example.com and
    example.org,

there will be a trust topology conflict detected by example.org domain
controller because ipa.example.com DNS namespace overlaps with
example.com DNS namespace.

This type of trust topology conflict is documented in MS-ADTS 6.1.6.9.3.2
"Building Well-Formed msDS-TrustForestTrustInfo Message". A similar
conflict can arise for SID and NetBIOS namespaces. However, unlike SID
and NetBIOS namespaces, we can solve DNS namespace conflict
automatically if there are administrative credentials for example.org
available.

A manual sequence to solve the DNS namespace conflict is described in
https://msdn.microsoft.com/it-it/library/cc786254%28v=ws.10%29.aspx.
This sequence boils down to the following steps:

   1. As an administrator of the example.org, you need to add an
exclusion entry for ipa.example.com in the properties of the trust to
example.com
   2. Establish trust between ipa.example.com and example.org

It is important to add the exclusion entry before step 4 or there will
be conflict recorded which cannot be cleared easily right now due to a
combination of bugs in both IPA and Active Directory.

This patchset implements automated solution for the case when we have
access to the example.org's administrator credentials:

   1. Attempt to establish trust and update trust topology information.
   2. If trust topology conflict is detected as result of (1):
   2.1. Fetch trust topology infromation for the conflicting forest
        trust
   2.2. Add exclusion entry to our domain to the trust topology obtained
        in (2.1)
   2.3. Update trust topology for the conflicting forest trust
   3. Re-establish trust between ipa.example.com and example.org

We cannot do the same for shared secret trust and for external trust,
though:

   1. For shared secret trust we don't have administrative credentials
      in the forest reporting the conflict

   2. For the external trust we cannot set topology information due to
      MS-LSAD 3.1.4.7.16 because external trust is non-transitive by
      definition and thus setting topology information will fail.

To test this logic one can use two Samba AD forests with FreeIPA
using a sub-domain of one of them.

Fixes: https://fedorahosted.org/freeipa/ticket/6076
Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>

1 files changed, 192 insertions, 28 deletions

diff --git a/ipaserver/dcerpc.py b/ipaserver/dcerpc.py
index 19be6bf7a..a1c12f16a 100644
--- a/ipaserver/dcerpc.py
+++ b/ipaserver/dcerpc.py
@@ -1,7 +1,7 @@
 # Authors:
 #     Alexander Bokovoy <abokovoy@redhat.com>
 #
-# Copyright (C) 2011  Red Hat
+# Copyright (C) 2011-2016  Red Hat
 # see file 'COPYING' for use and warranty information
 #
 # Portions (C) Andrew Tridgell, Andrew Bartlett
@@ -140,6 +140,15 @@ pysss_type_key_translation_dict = {
     pysss_nss_idmap.ID_BOTH: 'both',
 }
 
+class TrustTopologyConflictSolved(Exception):
+    """
+    Internal trust error: raised when previously detected
+    trust topology conflict is automatically solved.
+
+    No separate errno is assigned as this error should
+    not be visible outside the dcerpc.py code.
+    """
+    pass
 
 def assess_dcerpc_exception(num=None, message=None):
     """
@@ -1087,34 +1096,165 @@ class TrustDomainInstance(object):
         info.entries = ftinfo_records
         return info
 
+    def clear_ftinfo_conflict(self, another_domain, cinfo):
+        """
+        Attempt to clean up the forest trust collisions
+
+        :param self: the forest we establish trust to
+        :param another_domain: a forest that establishes trust to 'self'
+        :param cinfo: lsa_ForestTrustCollisionInfo structure that contain
+                      set of of lsa_ForestTrustCollisionRecord structures
+        :raises: TrustTopologyConflictSolved, TrustTopologyConflictError
+
+        This code tries to perform intelligent job of going
+        over individual collisions and making exclusion entries
+        for affected IPA namespaces.
+
+        There are three possible conflict configurations:
+          - conflict of DNS namespace (TLN conflict, LSA_TLN_DISABLED_CONFLICT)
+          - conflict of SID namespace (LSA_SID_DISABLED_CONFLICT)
+          - conflict of NetBIOS namespace (LSA_NB_DISABLED_CONFLICT)
+
+        we only can handle TLN conflicts because (a) excluding SID namespace
+        is not possible and (b) excluding NetBIOS namespace not possible.
+        These two types of conflicts should result in trust-add CLI error
+
+        These conflicts can come from external source (another forest) or
+        from internal source (another domain in the same forest). We only
+        can fix the problems with another forest.
+
+        To resolve TLN conflict we need to do following:
+          1. Retrieve forest trust information for the forest we conflict on
+          2. Add an exclusion entry for IPA DNS namespace to it
+          3. Set forest trust information for the forest we conflict on
+          4. Re-try establishing trust to the original forest
+
+        This all can only be done under privileges of Active Directory admin
+        that can change forest trusts. If we cannot have those privileges,
+        the work has to be done manually in the Windows UI for
+        'Active Directory Domains and Trusts' by the administrator of the
+        original forest.
+        """
+
+        # List of entries for unsolved conflicts
+        result = []
+
+        trust_timestamp = long(time.time()*1e7+116444736000000000)
+
+        # Collision information contains entries for specific trusted domains
+        # we collide with. Look into TLN collisions and add a TLN exclusion
+        # entry to the specific domain trust.
+        root_logger.error("Attempt to solve forest trust topology conflicts")
+        for rec in cinfo.entries:
+            if rec.type == lsa.LSA_FOREST_TRUST_COLLISION_TDO:
+                dominfo = self._pipe.lsaRQueryForestTrustInformation(
+                                 self._policy_handle,
+                                 rec.name,
+                                 lsa.LSA_FOREST_TRUST_DOMAIN_INFO)
+
+                # Oops, we were unable to retrieve trust topology for this
+                # trusted domain (forest).
+                if not dominfo:
+                    result.append(rec)
+                    root_logger.error("Unable to resolve conflict for "
+                                      "DNS domain %s in the forest %s "
+                                      "for domain trust %s. Trust cannot "
+                                      "be established unless this conflict "
+                                      "is fixed manually."
+                                      % (another_domain.info['dns_domain'],
+                                         self.info['dns_domain'],
+                                         rec.name.string))
+                    continue
+
+                # Copy over the entries, extend with TLN exclusion
+                entries = []
+                for e in dominfo.entries:
+                    e1 = lsa.ForestTrustRecord()
+                    e1.type = e.type
+                    e1.flags = e.flags
+                    e1.time = e.time
+                    e1.forest_trust_data = e.forest_trust_data
+                    entries.append(e1)
+
+                # Create TLN exclusion record
+                record = lsa.ForestTrustRecord()
+                record.type = lsa.LSA_FOREST_TRUST_TOP_LEVEL_NAME_EX
+                record.flags = 0
+                record.time = trust_timestamp
+                record.forest_trust_data.string = \
+                    another_domain.info['dns_domain']
+                entries.append(record)
+
+                fti = lsa.ForestTrustInformation()
+                fti.count = len(entries)
+                fti.entries = entries
+
+                # Update the forest trust information now
+                ldname = lsa.StringLarge()
+                ldname.string = rec.name.string
+                cninfo = self._pipe.lsaRSetForestTrustInformation(
+                             self._policy_handle,
+                             ldname,
+                             lsa.LSA_FOREST_TRUST_DOMAIN_INFO,
+                             fti, 0)
+                if cninfo:
+                    result.append(rec)
+                    root_logger.error("When defining exception for DNS "
+                                      "domain %s in forest %s for "
+                                      "trusted forest %s, "
+                                      "got collision info back:\n%s"
+                                      % (another_domain.info['dns_domain'],
+                                         self.info['dns_domain'],
+                                         rec.name.string,
+                                         ndr_print(cninfo)))
+            else:
+                result.append(rec)
+                root_logger.error("Unable to resolve conflict for "
+                                  "DNS domain %s in the forest %s "
+                                  "for in-forest domain %s. Trust cannot "
+                                  "be established unless this conflict "
+                                  "is fixed manually."
+                                  % (another_domain.info['dns_domain'],
+                                     self.info['dns_domain'],
+                                     rec.name.string))
+
+        if len(result) == 0:
+            root_logger.error("Successfully solved all conflicts")
+            raise TrustTopologyConflictSolved()
+
+        # Otherwise, raise TrustTopologyConflictError() exception
+        domains = [x.name.string for x in result]
+        raise errors.TrustTopologyConflictError(
+                              target=self.info['dns_domain'],
+                              conflict=another_domain.info['dns_domain'],
+                              domains=domains)
+
+
+
     def update_ftinfo(self, another_domain):
         """
         Updates forest trust information in this forest corresponding
         to the another domain's information.
         """
-        try:
-            if another_domain.ftinfo_records:
-                ftinfo = self.generate_ftinfo(another_domain)
-                # Set forest trust information -- we do it only against AD DC as
-                # smbd already has the information about itself
-                ldname = lsa.StringLarge()
-                ldname.string = another_domain.info['dns_domain']
-                ftlevel = lsa.LSA_FOREST_TRUST_DOMAIN_INFO
-                # RSetForestTrustInformation returns collision information
-                # for trust topology
-                cinfo = self._pipe.lsaRSetForestTrustInformation(
-                            self._policy_handle,
-                            ldname,
-                            ftlevel,
-                            ftinfo, 0)
-                if cinfo:
-                    root_logger.error("When setting forest trust information, "
-                                      "got collision info back:\n%s"
-                                      % (ndr_print(cinfo)))
-        except RuntimeError as e:
-            # We can ignore the error here --
-            # setting up name suffix routes may fail
-            pass
+        if another_domain.ftinfo_records:
+            ftinfo = self.generate_ftinfo(another_domain)
+            # Set forest trust information -- we do it only against AD DC as
+            # smbd already has the information about itself
+            ldname = lsa.StringLarge()
+            ldname.string = another_domain.info['dns_domain']
+            ftlevel = lsa.LSA_FOREST_TRUST_DOMAIN_INFO
+            # RSetForestTrustInformation returns collision information
+            # for trust topology
+            cinfo = self._pipe.lsaRSetForestTrustInformation(
+                        self._policy_handle,
+                        ldname,
+                        ftlevel,
+                        ftinfo, 0)
+            if cinfo:
+                root_logger.error("When setting forest trust information, "
+                                  "got collision info back:\n%s"
+                                  % (ndr_print(cinfo)))
+                self.clear_ftinfo_conflict(another_domain, cinfo)
 
     def establish_trust(self, another_domain, trustdom_secret,
                         trust_type='bidirectional', trust_external=False):
@@ -1207,7 +1347,19 @@ class TrustDomainInstance(object):
                 root_logger.error(
                       'unable to set trust transitivity status: %s' % (str(e)))
 
-        if self.info['is_pdc'] or trust_external:
+        # Updating forest trust info may fail
+        # If it failed due to topology conflict, it may be fixed automatically
+        # update_ftinfo() will through exceptions in that case
+        # Note that MS-LSAD 3.1.4.7.16 says:
+        # -------------------------
+        # The server MUST also make sure that the trust attributes associated
+        # with the trusted domain object referenced by the TrustedDomainName
+        # parameter has the TRUST_ATTRIBUTE_FOREST_TRANSITIVE set.
+        # If the attribute is not present, the server MUST return
+        # STATUS_INVALID_PARAMETER.
+        # -------------------------
+        # Thus, we must not update forest trust info for the external trust
+        if self.info['is_pdc'] and not trust_external:
             self.update_ftinfo(another_domain)
 
     def verify_trust(self, another_domain):
@@ -1509,9 +1661,21 @@ class TrustDomainJoins(object):
         if not self.remote_domain.read_only:
             trustdom_pass = samba.generate_random_password(128, 128)
             self.get_realmdomains()
-            self.remote_domain.establish_trust(self.local_domain,
-                                               trustdom_pass,
-                                               trust_type, trust_external)
+
+            # Establishing trust may throw an exception for topology
+            # conflict. If it was solved, re-establish the trust again
+            # Otherwise let the CLI to display a message about the conflict
+            try:
+                self.remote_domain.establish_trust(self.local_domain,
+                                                   trustdom_pass,
+                                                   trust_type, trust_external)
+            except TrustTopologyConflictSolved as e:
+                # we solved topology conflict, retry again
+                self.remote_domain.establish_trust(self.local_domain,
+                                                   trustdom_pass,
+                                                   trust_type, trust_external)
+
+            # For local domain we don't set topology information
             self.local_domain.establish_trust(self.remote_domain,
                                               trustdom_pass,
                                               trust_type, trust_external)