[Freeipa-devel] Managed permission versioning

Petr Viktorin pviktori at redhat.com
Wed Apr 23 12:14:27 UTC 2014

On 04/23/2014 01:55 PM, Petr Spacek wrote:
> On 21.4.2014 14:48, Simo Sorce wrote:
>> On Mon, 2014-04-21 at 08:39 -0400, Rob Crittenden wrote:
>>> Simo Sorce wrote:
>>>> On Thu, 2014-04-17 at 18:25 -0400, Rob Crittenden wrote:
>>>>> Simo Sorce wrote:
>>>>>> On Thu, 2014-04-17 at 15:00 -0400, Rob Crittenden wrote:
>>>>>>> Simo Sorce wrote:
>>>>>>>> On Thu, 2014-04-17 at 15:48 +0200, Martin Kosek wrote:
>>>>>>>>> I would like to discuss more on the managed read permissions
>>>>>>>>> upgrades [1].
>>>>>>>>> Right now, we simply merge an old permission with the new one,
>>>>>>>>> making sure that
>>>>>>>>> we only add new attributes instead of just replacing them, to
>>>>>>>>> prevent a managed
>>>>>>>>> permission to be spoiled by a lower FreeIPA server version
>>>>>>>>> which runs an updates.
>>>>>>>>> I was thinking about it some more and seems to me we could run
>>>>>>>>> in problems when
>>>>>>>>> we for example find out that some permission is too relaxed and
>>>>>>>>> we want to
>>>>>>>>> remove some default attribute. Or when we want to update the
>>>>>>>>> permission filter.
>>>>>>>>> Or when object has anonymous and authenticated permission and
>>>>>>>>> we want to move
>>>>>>>>> attribute from anonymous to authenticated permission.
>>>>>>>>> Changes like this can happen, especially in the first release
>>>>>>>>> and we do not
>>>>>>>>> have means to address them. What about simply versioning the
>>>>>>>>> permissions as we
>>>>>>>>> do with our configs? I.e.
>>>>>>>>> 1) Introduce new MUST numeric attribute ipaPermVersion
>>>>>>>>> 2) Add 'version' field to managed permissions:
>>>>>>>>>         managed_permissions = {
>>>>>>>>>             'System: Read Roles': {
>>>>>>>>>                 'version': 1,
>>>>>>>>>                 'replaces_global_anonymous_aci': True,
>>>>>>>>>                 'ipapermbindruletype': 'permission',
>>>>>>>>>                 'ipapermright': {'read', 'search', 'compare'},
>>>>>>>>>                 'ipapermdefaultattr': {
>>>>>>>>>                     'businesscategory', 'cn', 'description',
>>>>>>>>> 'member', 'memberof',
>>>>>>>>>                     'o', 'objectclass', 'ou', 'owner', 'seealso',
>>>>>>>>>                 },
>>>>>>>>>                 'default_privileges': {'RBAC Readers'},
>>>>>>>>>             },
>>>>>>>>>         }
>>>>>>>>> 3) Modify updater to only update the permission if it's version
>>>>>>>>> is higher than
>>>>>>>>> the one in LDAP. In that case, it should simply replace the
>>>>>>>>> managed permission
>>>>>>>>> attributes with the new one, no merging (except the attributes
>>>>>>>>> that we allow
>>>>>>>>> users to change).
>>>>>>>>> When we want to change the permission, we simply do the
>>>>>>>>> changes, bump the
>>>>>>>>> version and we are done and we do not need to fear some older
>>>>>>>>> FreeIPA will
>>>>>>>>> overwrite it. That of course assumes that the versioning would
>>>>>>>>> be available
>>>>>>>>> from FreeIPA 4.0.
>>>>>>>>> Makes sense?
>>>>>>>>> [1] http://www.freeipa.org/page/V3/Managed_Read_permissions
>>>>>>>> Uhmm, yes, and no, let me explain.
>>>>>>>> What you say *does* make sense, but you are being too focused :-)
>>>>>>>> The upgrade issue is not limited to permissions, but affects
>>>>>>>> everything.
>>>>>>>> I think that what we need is to add a "ipa schema version"
>>>>>>>> attribute
>>>>>>>> somewhere in cn=etc, and then always check this number in the
>>>>>>>> updater
>>>>>>>> script. if this number is higher than what we know we
>>>>>>>> immediately stop
>>>>>>>> and do not perform updates that affect anything but our own
>>>>>>>> server data.
>>>>>>>> This will protect the whole tree from unintentional changes
>>>>>>>> caused by an
>>>>>>>> older replica.
>>>>>>>> Makes sense ?
>>>>>>> This could lead to new features not working. Those features would
>>>>>>> rely
>>>>>>> on containers, ACIs, etc to exist but they wouldn't if the updates
>>>>>>> aren't run.
>>>>>> Sorry I don't get this, if they are new features, then the version
>>>>>> will
>>>>>> be "older" and the update *will* run and at the end raise the
>>>>>> version.
>>>>>> We just prevent old updates from running and current updates from
>>>>>> running multiple times, for the shared tree.
>>>>>> Do we depend on having updates run multiple times for the data in the
>>>>>> shared tree ?
>>>>>> Note that I am not saying that all updates should stop, any update
>>>>>> for
>>>>>> cn=config would still need to be run on each server (although
>>>>>> setting a
>>>>>> version there too would probably be beneficial).
>>>>> Ok, so the update runs, adds data, which gets replicated out to
>>>>> potentially old servers, and we're at the place you said we
>>>>> wouldn't be.
>>>> I am not following you, the aim here is not to avoid replicating new
>>>> data to old server, the aim is that if you update the rpm of an older
>>>> replica and the rpm runs the ldap updater with the *old* code, we do
>>>> not
>>>> end up with that updater *undoing* what a more recent update did.
>>>>> Updates are all loaded and sorted so that all changes to a given DN
>>>>> should be applied at once, so it isn't like applying a old update
>>>>> and a
>>>>> new update are two separate operations. In fact, it would likely be a
>>>>> no-op in the case that they have already been applied.
>>>>> Do you have any examples to clarify your concerns? I'm not
>>>>> following you.
>>>> Sure at some point version freeipa version 4.2 is released and it
>>>> has an
>>>> update that changes a default object so that now attribute 'foo' is
>>>> added, this is done through the updater.
>>>> Later on we release freeipa version 5.0 and we realize we will have
>>>> again to remove attribute 'foo' because we never really needed it, plus
>>>> if it is still there it causes issues to new feature XYZ.
>>>> The admin installs 5.0 and all are happy, then a week later he runs a
>>>> simply yum update on th eolder replicas still running 4.2 and 4.2.1 is
>>>> available, and gets installed and ... bah the 4.2.1 updater re-adds
>>>> attribute 'foo' back ... and 5.0 servers are now broken.
>>>> If we have an updater version field when the 4.2.1 update goes on it
>>>> will see that all updates that were necessary (and more) have already
>>>> been added and just quits.
>>> Ok, this won't happen in a modify case. When changing data we only
>>> change a known existing value, so exact match is required.
>>> The only risk is in adding and deleting data.
>>> So if we delete a permission named "Do cool stuff" in 5.0 and that was
>>> something previously added in 4.2 then yeah, re-running the 4.2 updates
>>> will re-apply the data. Similarly deletes would always be applied.
>>> I would not be keen on adding a global version value though, as we've
>>> had issues with updates in the past where re-running the updater would
>>> fix things. This would short circuit that.
>> Well we could allow the updater to run on "same version" values, this
>> would preserve this ability while still blocking older updaters.
>> Besides modifies can be affected too, say we have default value of 10,
>> we change it to 20 in 4.2 then change it back to 10 in 5.0 as we found
>> an issue with the new value. If you run 4.2 updater it puts it back to
>> 20.
>> All cases of flipping values are also affected.
>>> Something more fine-grained might work but carries its own problems.
>> I think in this case we really want a domain level version, as the tree
>> is shared and we want updates to be consistent, so the update need to be
>> applied in full or not at all IMO.
>> We do have some fine-grained approach as we will have a separate version
>> for he shared tree than the cn=config tree (and I guess another one for
>> the CA tree).
>> Each tree is a Silo, and should have its own tree version.
> IMHO more granular "versions" would be handy. Specifically for DNSSEC,
> we need to somehow distinguish old installation with centralized key
> management from new installation with distributed key management and
> different key storage etc. etc.
> Maybe we can invent some generic mechanism for "component versioning"?
> (Recall Dogtag 9 vs. 10 ...)

I don't like this idea. With very granular versioning we'd need to 
correctly identify which part each particular update belongs to and what 
happens when components of various versions are mixed. And we couldn't 
hope to test all the combinations. Making this into a generic mechanism 
now, with just a few very different current uses, sounds dangerously 

I'd like to see something very simple: only update if stored version <= 
current API version; store current API version at end of update.
The bugs will be much easier to identify that way.

Of course this supposes a monolithic IPA and e.g. isn't very friendly to 
external plugins, but I don't think we can design a good story for 
external plugins without actually writing some first. Let's do something 
simple and iterate later.


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