On 31.8.2016 12:42, Standa Laznicka wrote:
> On 08/30/2016 03:34 PM, Simo Sorce wrote:
>> On Tue, 2016-08-30 at 08:47 +0200, Standa Laznicka wrote:
>>> On 08/26/2016 05:37 PM, Simo Sorce wrote:
>>>> On Fri, 2016-08-26 at 11:26 -0400, Simo Sorce wrote:
>>>>> On Fri, 2016-08-26 at 18:09 +0300, Alexander Bokovoy wrote:
>>>>>> On Fri, 26 Aug 2016, Simo Sorce wrote:
>>>>>>> On Fri, 2016-08-26 at 12:39 +0200, Martin Basti wrote:
>>>>>>>>> I miss "why" part of "To be able to handle backward compatibility
>>>>>>>> with
>>>>>>>>> ease, a new object called ipaHBACRulev2 is introduced. " in the
>>>>>>>> design
>>>>>>>>> page. If the reason is the above - old client's should ignore time
>>>>>>>> rules
>>>>>>>>> then it has to be mentioned there. Otherwise I don't see a reason to
>>>>>>>>> introduce a new object type instead of extending the current.
>>>>>>>> How do you want to enforce HBAC rule that have set time from 10 to 14
>>>>>>>> everyday? With the same objectclass old clients will allow this HBAC
>>>>>>>> for
>>>>>>>> all day. Isn't this CVE?
>>>>>>> This is a discussion worth having.
>>>>>>> In general it is a CVE only if an authorization mechanism fails to work
>>>>>>> as advertised.
>>>>>>> If you make it clear that old clients *DO NOT* respect time rules then
>>>>>>> there is no CVE material, it is working as "described".
>>>>>>> The admins already have a way to not set those rules for older clients
>>>>>>> by simply grouping newer clients in a different host group and applying
>>>>>>> time rules only there.
>>>>>>> So the question really is: should we allow admins to apply an HBAC Rule
>>>>>>> potentially to older clients that do not understand it and will
>>>>>>> therefore allow access at any time of the day, or should we prevent it ?
>>>>>>> This is a hard question to answer and can go both ways.
>>>>>>> A time rule may be something that admins want to enforce at all cost or
>>>>>>> deny access. In this case a client that fails to handle it would be a
>>>>>>> problem.
>>>>>>> But it may be something that is just used for defense in depth and not a
>>>>>>> strictly hard requirement. In this case allowing older clients would
>>>>>>> make it an easy transition as you just set up the rule and the client
>>>>>>> will start enforcing the time when it is upgraded but work otherwise
>>>>>>> with the same rules.
>>>>>>> I am a bit conflicted on trying to decide what scenario we should
>>>>>>> target, but the second one appeals to me because host groups do already
>>>>>>> give admins a good way to apply rules to a specific set of hosts and
>>>>>>> exclude old clients w/o us making it a hard rule.
>>>>>>> OTOH if an admin does not understand this difference, they may be
>>>>>>> surprised to find out there are clients that do not honor it.
>>>>>>> Perhaps we could find a way to set a flag on the rule such that when set
>>>>>>> (and only when set) older clients get excluded by way of changing the
>>>>>>> objectlass or something else to similar effect.
>>>>>>> Open to discussion.
>>>>>> At this point using new object class becomes an attractive approach. We
>>>>>> don't have means to exclude HBAC rules other than applying them
>>>>>> per-host/hostgroup. We also have no deny rules.
>>>>>> I have another idea: what about enforcing time rules always to apply
>>>>>> per-host or per-hostgroup by default? Add --force option to override the
>>>>>> behavior but default to not allow --hostcat=all. This would raise
>>>>>> awareness and make sure admins are actually applying these rules with
>>>>>> intention.
>>>>> This sounds like a good idea, but it is not a silver bullet I am afraid.
>>>>> Simo.
>>>> I was thinking that for future proofing we could add a version field,
>>>> then reasoned more and realized that changing the object class is
>>>> basically the same thing.
>>>> There is only one big problem, ipaHBACRule is a STRUCTURAL objectclass.
>>>> (I know 389ds allows us to do an LDAPv3 illegal operation and change it,
>>>> but I do not like to depend on that behavoir).
>>>> Now looking into this I had an idea to solve the problem of legacy
>>>> clients without having to swap classes.
>>>> We can redefine the accessRuleType attribute to be a "capability" type.
>>>> Ie rules that have a timeAccess component will be of type
>>>> "allow_with_time" instead of just "allow".
>>>> Old clients are supposed to search with accessRuleType=allow (and I can
>>>> see that SSSD does that), so an older client will fail to get those
>>>> rules as they won't match.
>>>> New clients instead can recognize both types.
>>>> Also if we need a future extension we will simpy add a new access rule
>>>> type and we can have the same effect.
>>>> The nice thing is that accessRyleType is defined as multivalue (no
>>>> SINGLE in schema) so we may actually create compatible rules if we want
>>>> to.
>>>> Ie we could set both "allow" and "allow_with_time" on an object for
>>>> cases where the admin wants to enforce the time part only o newer client
>>>> but otherwise apply the rule to any client.
>>>> This should give us the best of all options at once.
>>>> Thoughts ?
>>>> Simo.
>>> Sorry to join the discussion so late, I was away yesterday.
>>> I have to say I too like this idea much better than fiddling with the
>>> objectClasses. Also, I believe that accessRuleType was originally
>>> actually used to distinguish newer version of HBAC rules from the older
>>> so we may just do this again and profit from its original purpose. To
>>> top it off, this change should be really easy to implement to what I
>>> currently have on SSSD side.
>>> I was just wondering - would you propose for every newly created rule to
>>> have the new accessRuleType set to "allow_with_time" or should the type
>>> change with addition of time rules to the HBAC rule as it does
>>> currently? Also, should the user be able to modify the type so that a
>>> rule with the new type is also visible for older clients (=> he could
>>> add "allow" to type anytime)?
>> Rules of type allow_with_time will not work on older clients, so we
>> should probably default to just the old "allow" schema.
>> I think in the first implementation the framework/cli/ui should not
>> emphasize this attribute but simply replace allow -> allow_with_time if
>> a time attribute is added.
>> In future we may give control of it and allow even to set multiple
>> values, after we discuss better if that should be done, and with ample
>> warnings to admins.
>> Also setting a time rule makes a rule incompatible with older clients so
>> we should spell it clearly in the CLI/UI with a warning message that
>> this rule will not apply at all to older clients.
>>> Thanks for your ideas, I am very happy with what you suggested here :)
>> Thank you.
>> Simo.
> So - can we all agree on a solution?
> I took an extra half an hour and created the accessRuleType solution on top of
> what I currently have, see patches attached to get the picture what the change
> would mean for what I currently have in
> https://github.com/stlaz/freeipa/tree/timerules_2 and
> https://github.com/stlaz/sssd/tree/freeipa-trac-547_2. Note that the sssd
> patch is really just to get a picture, it currently causes sssd_be to core
> dump, not sure why and don't want to waste time debugging it right now.
> I myself would in the end rather go for objectClasses implementation as new
> rules are not shown to old clients which seems correct as there's no confusion
> for admins who might scratch their heads at old clients with no idea why their
> HBAC rules don't apply otherwise.

+1, I agree with Standa and Martin Basti. Let me repeat myself:

I like the idea of "capabilities" in general but it needs proper design and
detailed specification first.

Given that we have to modify SSSD anyway, I would go for ipaHBACRulev2 object
class with clear definition of "capabilities" (without any obsolete cruft).

That should be future proof and without any negative/unforeseen impact to
existing clients + it matches what Jan Pazdziora plans to do for HBAC+URI.

Petr^2 Spacek

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