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

[Martin Kosek]

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?

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
>