[Freeipa-devel] global account lockout

[Simo Sorce]

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.

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