[Freeipa-devel] global account lockout

Rich Megginson rmeggins at redhat.com
Mon Apr 7 20:28:04 UTC 2014

On 04/07/2014 01:00 PM, Simo Sorce wrote:
> 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.

I'm not sure what you mean.  The 389 conflict resolution strategy is 
"last-wins" already.  Or do you mean "for some cases, but not all cases"?

> Simo.

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