[Freeipa-devel] [DESIGN][UPDATE] Time-Based HBAC Policies

[Jan Cholasta]

On 30.8.2016 08:47, 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.

Note that the resulting code will be exactly the same except for the 
attribute name - you won't be fiddling with objectClass but with 
attributeRuleType.

> 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.

The original purpose was to support deny rules, but they were deprecated.

> 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)?
>
> Thanks for your ideas, I am very happy with what you suggested here :)

TBH I'm not - I don't find adding hacks on top of obsolete deprecated 
stuff to be a particularly appealing solution to anything.

-- 
Jan Cholasta