[Freeipa-devel] Ticket #2866 - referential integrity in IPA

[Rich Megginson]

On 08/27/2012 02:27 PM, Martin Kosek wrote:
> On Mon, 2012-08-27 at 10:29 -0600, Rich Megginson wrote:
>> On 08/27/2012 10:24 AM, Martin Kosek wrote:
>>> On 08/17/2012 04:00 PM, Rich Megginson wrote:
>>>> On 08/17/2012 07:44 AM, Martin Kosek wrote:
>>>>> Hi guys,
>>>>>
>>>>> I am now investigating ticket #2866:
>>>>> https://fedorahosted.org/freeipa/ticket/2866
>>>>>
>>>>> And I am thinking about possible solutions for this problem. In a
>>>>> nutshell, we do not properly check referential integrity in some IPA
>>>>> objects where we keep one-way DN references to other objects, e.g. in
>>>>> - managedBy attribute for a host object
>>>>> - memberhost attribute for HBAC rule object
>>>>> - memberuser attribute for user object
>>>>> - memberallowcmd or memberdenycmd for SUDO command object (reported in
>>>>> #2866)
>>>>> ...
>>>>>
>>>>> Currently, I see 2 approaches to solve this:
>>>>> 1) Add relevant checks to our ipalib plugins where problematic
>>>>> operations with these operations are being executed (like we do for
>>>>> selinuxusermap's seealso attribute in HBAC plugin)
>>>>> This of course would not prevent direct LDAP deletes.
>>>>>
>>>>> 2) Implement a preop DS plugin that would hook to MODRDN and DELETE
>>>>> callbacks and check that this object's DN is not referenced in other
>>>>> objects. And if it does, it would reject such modification. Second
>>>>> option would be to delete the attribute value with now invalid
>>>>> reference. This would be probably  more suitable for example for
>>>>> references to user objects.
>>>>>
>>>>> Any comments to these possible approaches are welcome.
>>>>>
>>>>> Rich, do you think that as an alternative to these 2 approaches,
>>>>> memberOf plugin could be eventually modified to do this task?
>>>> This is very similar to the referential integrity plugin already in 389, except
>>>> instead of cleaning up references to moved and deleted entries, you want it to
>>>> prevent moving or deleting an entry if that entry is referenced by the
>>>> managedby/memberhost/memberuser/memberallowcmd/memberdenycmd of some other entry.
>>> I think that using or enhancing current DS referential integrity plugin will be
>>> the best and the most consistent way to go.
>>>
>>> We already use that plugin for some user attributes like "manager" or
>>> "secretary". seeAlso is already covered by default, so for example seeAlso
>>> attribute in SELinux usermap object referencing an HBAC rule will get removed
>>> when relevant HBAC rule is removed (I just checked that).
>>>
>>>> Note that the managed entry plugin (mep) already handles this for the managedby
>>>> attribute.
>>> I assume you are referencing "mepmanagedby" and "mepmanagedentry" attributes
>>> which then produce errors like this one:
>>>
>>> # ipa netgroup-del foo
>>> ipa: ERROR: Server is unwilling to perform: Deleting a managed entry is not
>>> allowed. It needs to be manually unlinked first.
>>>
>>> managedBy attribute used by hosts objects I had in mind seems to not be covered.
>>>
>>> But you are right, this is pretty much what I wanted. Though in case of MEP,
>>> there is a link in both referenced objects, but in our case, we have just the
>>> one-way link.
>>>
>>>> Are you already using the memberof plugin for
>>>> memberhost/memberuser/memberallowcmd/memberdenycmd?
>>>>
>>>> This doesn't seem like a job for memberof, this seems like more of a new check
>>>> for the referential integrity plugin.
>>>>
>>> I am now considering if current move/delete clean up already present in
>>> Referential Integrity plugin would not be sufficient for us.
>>>
>>> Rich, please correct me if I am wrong, but in that case, we would just need to
>>> add relevant attribute names
>>> (memberhost/memberuser/memberallowcmd/memberdenycmd...) to Referential
>>> Integrity plugin configuration as nsslapd-pluginarg7, nsslapd-pluginarg8, ...
>>> I wonder if there would be some performance issues if we add attributes to the
>>> list this way.
>> No, not if they are indexed for presence and equality.
>>
>> But referential integrity will not prevent deletion or moving entries -
>> it will delete/move references.
> I understand that. After some reconsideration, I think that cleaning up
> dangling references as postop should be OK for most of the referential
> attributes we use. But I would like a second opinion on that.
>
> So do I understand it correctly, that in case we want to go this way in
> IPA, the recommended approach DS-wise would be to:
> - add presence and equality indexes to IPA for the attributes we want to
> have checked for referential integrity
> - configure DS Referential Integrity plugin to check these attributes
>
> Or would it be better to wait on relevant DS changes you mentioned that
> Noriko is working on?

Also look at the Linked Attribute plugin - it may be able to do what you 
want right now - http://port389.org/wiki/Linked_Attributes_Design

>
> Thanks,
> Martin
>
>>> Rob, do you think that cleaning up the broken references during a DS postop
>>> instead of raising an preop error is OK for IPA references? I went through the
>>> referential attributes we use ("git grep LDAPAddMember") and I think it should
>>> be sufficient. We could cover some special cases with a query in our framework
>>> like you did in hbacrule-del.
>>>
>>> Martin
>