[Freeipa-devel] global account lockout

[Simo Sorce]

On Mon, 2014-04-07 at 14:47 -0400, Dmitri Pal wrote:
> On 04/07/2014 02:31 PM, Simo Sorce wrote:
> > On Mon, 2014-04-07 at 10:22 -0600, Rich Megginson wrote:
> >> On 04/07/2014 10:13 AM, Simo Sorce wrote:
> >>> On Mon, 2014-04-07 at 12:10 -0400, Simo Sorce wrote:
> >>>> On Mon, 2014-04-07 at 12:01 -0400, Simo Sorce wrote:
> >>>>> On Mon, 2014-04-07 at 11:26 -0400, Rob Crittenden wrote:
> >>>>>> Ludwig Krispenz wrote:
> >>>>>>> Hi,
> >>>>>>>
> >>>>>>> please review the following feature design. It introduces a global
> >>>>>>> account lockout, while trying to keep the replication traffic minimal.
> >>>>>>> In my opinion for a real global account lockout the basic lockout
> >>>>>>> attributes have to be replicated otherwise the benefit is minimal: an
> >>>>>>> attacker could perform (maxFailedcount -1) login attempts on every
> >>>>>>> server before the global lockout is set. But the design page describes
> >>>>>>> how it could be done if it should be implemented - maybe the side effect
> >>>>>>> that accounts could the be unlocked on any replica has its own benefit.
> >>>>>>>
> >>>>>>> http://www.freeipa.org/page/V4/Replicated_lockout
> >>>>>> One weakness with this is there is still a window for extra password
> >>>>>> attempts if one is clever, (m * (f-1))+1 to be exact, where m is the
> >>>>>> number of masters and f is the # of allowed failed logins.
> >>>>> Yes, but that is a problem that cannot be solved w/o full replication at
> >>>>> every authentication attempt.
> >>>>>
> >>>>> What we tried to achieve is a middle ground to at least ease
> >>>>> administration and still lock em up "earlier".
> >>>> Let me add that we "could" have yet another closer step by finding a way
> >>>> to replicate only failed attempts and not successful attempts in some
> >>>> case. Assuming a setup where most people do not fail to enter their
> >>>> password it would make for a decent compromise.
> >>>>
> >>>> That could be achieved by not storing lastsuccessful auth except when
> >>>> that is needed to clear failed logon attempts (ie when the failed logon
> >>>> counter is > 0)
> >>>>
> >>>> If we did that then we would not need a new attribute actually, as
> >>>> failed logins would always be replicated.
> >>>> However it would mean that last Successful auth would never be accurate
> >>>> on any server.
> >>>>
> >>>> Or perhaps we could have a local last successful auth and a global one
> >>>> by adding one new attribute, and keeping masking only the successful
> >>>> auth.
> >>>>
> >>>> The main issue about all these possibilities is how do we present them ?
> >>>> And how do we make a good default ?
> >>>>
> >>>> I think a good default is defined by these 2 characteristics:
> >>>> 1. lockouts can be dealt with on any replica w/o having the admin hunt
> >>>> down where a user is locked.
> >>>> 2. at least successful authentications will not cause replication storms
> >>>>
> >>>> If we can afford to cause replications on failed authentication by
> >>>> default, then we could open up replication for failedauth and
> >>>> failedcount attributes but still bar the successful auth attribute.
> >>>> Unlock would simply consist in forcibly setting failed count to 0 (which
> >>>> is replicated so it would unlock all servers).
> >>>> This would work w/o introducing new attributes and only with minimal
> >>>> logic changes in the KDC/pwd-extop plugins I think.
> >>> Sigh re[plying again to myself.
> >>> note that the main issue with replicating failed accounts is that you
> >>> can cause replication storms by simply probing all user accounts with
> >>> failed binds or AS requests. In some environments that may cause DoSs
> >>> (if you have slow/high latency links on which replication runs for
> >>> example).
> >>> So I think we should always give the option to turn off failed
> >>> date/count attributes replication, which in turn would mean we still
> >>> require a new attribute to replicate for when a user is finally locked
> >>> out on one of the servers or we fail requirement 1.
> >>>
> >>> Simo.
> >>>
> >> Another problem with keeping track of bind attributes in a replicated
> >> environment is the sheer size of the replication metadata.  Replicating
> >> 1 failed bind attempt might be 100kbytes or more data to all servers.
> >> We should have a way to perhaps say "only keep last N CSNs" or maybe
> >> even "don't keep CSNs for these attributes".
> > Yes, but this look a lot like general replication improvement (would
> > also be cool to have "better" conflict resolution), not lockout
> > specific.
> >
> > Simo.
> >
> My only comment is actually about conflict resolution. What would happen 
> if I attack (flood) two replicas at the same time beating the 
> replication. It would mean both servers would generate the global 
> attributes and try to replicate to each other. If the replicas are on 
> the edges of topology it might take some time and it might even happen 
> that admin already unlocked the account while the old lock is still 
> trying to propagate. IMO we need collisions resolution logic taken care 
> of first. I suspect that any real attack would lead to collisions and if 
> it would leave the deployment unstable even after the attack ended we lost.

Yes, this is a valid concern. We need a last-wins conflict resolution
strategy for some cases.

Simo.

-- 
Simo Sorce * Red Hat, Inc * New York