[Freeipa-devel] global account lockout

Rich Megginson rmeggins at redhat.com
Mon Apr 7 18:47:25 UTC 2014

On 04/07/2014 12:31 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),

Ludwig has made some improvements with how 389 stores replication 
metadata for conflict resolution, but in this case it's not nearly enough.

> not lockout
> specific.
> Simo.

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