On 30.08.2016 11:51, Standa Laznicka wrote:
On 08/30/2016 09:34 AM, Standa Laznicka wrote:
On 08/30/2016 09:23 AM, Alexander Bokovoy wrote:
On Tue, 30 Aug 2016, Jan Cholasta wrote:
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.
I do realize that (even though I touched this in my first question) but this solution seems a bit cleaner to me.

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.
It is just an attribute. Reusing an attribute that is not used anymore
for anything else is not a bad thing. The original solution may be
deprecated but the schema is in place and will be almost forever, so
using otherwise unused but present schema is just fine.

+1, why not to use it if there's no other use for it anyway.

Actually, I gave it a further thought - the problem with using accessRuleType for this purpose would be that even the new rules that older clients can't evaluate correctly would be displayed/listed in WebUI/hbacrule-find results. I do not think this should happen, it is confusing.

I should also say explicitly that I do NOT think that if a time rule is set for an HBAC rule this HBAC rule should still be taken into account during evaluation on an old client. To base the decision whether to allow/not-allow access purely on a client version is just wrong.


I agree, we should not mix this on old clients, I like the most the original proposal with switching objeclasses

Martin^2

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