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
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 Sorce * Red Hat, Inc * New York

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