[Freeipa-devel] #4534: SSSD deref processing fail when entryusn can be read and objectclass doesn't
thierry bordaz
tbordaz at redhat.com
Fri Sep 12 08:27:19 UTC 2014
On 09/11/2014 10:24 PM, Martin Kosek wrote:
> On 09/11/2014 08:49 PM, Simo Sorce wrote:
>> On Thu, 2014-09-11 at 20:28 +0200, Martin Kosek wrote:
>>> On 09/11/2014 05:37 PM, Simo Sorce wrote:
>>>> On Thu, 2014-09-11 at 17:03 +0200, Martin Kosek wrote:
>>>>> Hello,
>>>>>
>>>>> We have another important issue to resolve. Current FreeIPA 4.0.2
>>>>> ACI settings
>>>>> cause older SSSD clients to fail as they get returned an LDAP
>>>>> deref call
>>>>> results without objectclass attribute and just with entryusn
>>>>> attribute. Details
>>>>> in https://fedorahosted.org/freeipa/ticket/4534. While I agree
>>>>> SSSD should be
>>>>> more tolerant in this case, it still breaks old clients which we
>>>>> should prevent.
>>>>>
>>>>> There are 2 ways how to fix I currently see:
>>>>>
>>>>> 1) Return objectclass for any entry, just like we do with
>>>>> operational attributes
>>>>>
>>>>> This would include adding "objectclass" to "System: Read Timestamp
>>>>> and USN
>>>>> Operational Attributes". However, I am rather cautious about this
>>>>> approach as
>>>>> even though objectclass does not usually carry a secret
>>>>> information, we could
>>>>> still leak some information about our DIT to unprivileged user.
>>>>
>>>> Our DIT is public and known, I see no problem.
>>>
>>> I rather meant the LDAP tree and it's contents (custom groups, sudo
>>> rules,
>>> roles, ...).
>>>
>>> I did one more test and found out we cannot do this as it would
>>> undermine the
>>> ACIs we have right now. As soon as objectclass is allowed globally,
>>> ldapsearch
>>> returns every object even if no other attribute is returned:
>>>
>>> # ldapsearch -h `hostname` -Y GSSAPI -b
>>> cn=pbac,dc=mkosek-fedora20,dc=test
>>> SASL/GSSAPI authentication started
>>> SASL username: host/ipa.mkosek-fedora20.test at MKOSEK-FEDORA20.TEST
>>> SASL SSF: 56
>>> SASL data security layer installed.
>>> ...
>>> # User Administrators, privileges, pbac, mkosek-fedora20.test
>>> dn: cn=User
>>> Administrators,cn=privileges,cn=pbac,dc=mkosek-fedora20,dc=test
>>> objectClass: top
>>> objectClass: groupofnames
>>> objectClass: nestedgroup
>>> ...
>>>
>>> It would not show any more info before that, but even the list of
>>> permissions,
>>> privileges and roles along with it's names is a leaked information.
>>>
>>>
>>>>> 2) Show objectclass+operational attributes in our Read ACIs
>>>>> Other way I see is to update *all* our Read permissions allowing
>>>>> reading
>>>>> objectclass attribute and also allow the chosen LDAP operational
>>>>> attribute.
>>>>> This would let the LDAP caller to always get either all these
>>>>> discussed
>>>>> attributes but none at all.
>>>>>
>>>>>
>>>>> Do we want to do this? Any other (better) idea how to approach it?
>>>>
>>>> I honestly am not sure I understand the distinction between 1 and
>>>> 2, can
>>>> you provide the actual ACIs or a behavior example ?
>>>>
>>>> Simo.
>>>
>>> Currently, our ACI allows reading entryusn in any LDAP entry. So
>>> user (SSSD)
>>> running LDAP deref call gets entryusn from object it does not have a
>>> read
>>> access to:
>>>
>>> # ldapsearch -h `hostname` -Y GSSAPI -b
>>> uid=admin,cn=users,cn=accounts,dc=mkosek-fedora20,dc=test -E
>>> 'deref=memberof:objectclass,entryusn'
>>> SASL/GSSAPI authentication started
>>> SASL username: host/ipa.mkosek-fedora20.test at MKOSEK-FEDORA20.TEST
>>> SASL SSF: 56
>>> SASL data security layer installed.
>>> ...
>>> # memberof: <entryusn=845>;cn=replication
>>> administrators,cn=privileges,cn=pba
>>> c,dc=mkosek-fedora20,dc=test
>>>
>>> # memberof: <entryusn=75>;cn=add replication
>>> agreements,cn=permissions,cn=pba
>>> c,dc=mkosek-fedora20,dc=test
>>> ...
>>>
>>> This confuses SSSD (sees entryusn but does not see objectclass
>>> attribute) + may
>>> give out some information we do not want to give out. Fortunately, bare
>>> ldapsearch does not show anything:
>>>
>>> # ldapsearch -h `hostname` -Y GSSAPI -b "cn=replication
>>> administrators,cn=privileges,cn=pbac,dc=mkosek-fedora20,dc=test"
>>> entryusn
>>> SASL/GSSAPI authentication started
>>> SASL username: host/ipa.mkosek-fedora20.test at MKOSEK-FEDORA20.TEST
>>> SASL SSF: 56
>>> SASL data security layer installed.
>>> # extended LDIF
>>> #
>>> # LDAPv3
>>> # base <cn=replication
>>> administrators,cn=privileges,cn=pbac,dc=mkosek-fedora20,dc=test>
>>> with scope subtree
>>> # filter: (objectclass=*)
>>> # requesting: entryusn
>>> #
>>>
>>> # search result
>>> search: 4
>>> result: 0 Success
>>>
>>> # numResponses: 1
>>>
>>>
>>> The idea behind Option 1 was to add ACI to allow reading objectclass
>>> attribute
>>> globally, for our entire tree. (as noted above, not an option).
>>>
>>> The idea behind Option 2 was to:
>>> - remove global ACI allowing reading entryusn (System: Read
>>> Timestamp and USN
>>> Operational Attributes)
>>> - update all our Read permissions to allow entryusn
>>>
>>> Then for example, if user (SSSD) is allowed to read RBAC role
>>> objects, he would
>>> not be able to read either objectclass or entryusn attributes. This
>>> means users
>>> would be only allowed to read entryusn for objects that they can
>>> really read
>>> (i.e. for objects where they can read at least objectclass).
>>>
>>> Did that clarify the options?
>>>
>>> Of course, there is still option 3) to close as wontfix and let
>>> older SSSDs be
>>> incompatible with FreeIPA 4.0+.
>>
>> No, 3 is definitely not on the table, I would rather do 1, but I guess 2
>> is the only good way for now ?
>>
>> Simo.
>
> Yeah - 1) would be easy to implement, but it would be a step back in
> our ACI model (global allowing ACI again...).
>
> Something based on 2) is the only approach that I have in mind right
> now and that would work. It also looks as the right thing to do as
> then with changing visibility of objects by our permission system,
> visibility of entryusn would change too.
>
> Programatically it should not be difficult to do, we could add these
> attributes by default to all read permissions which have allow
> objectclass attribute so we would not have to update all our read
> permissions by hand...
Hello,
I was thinking to an other option that is looking more as a hack. It
is to relax the aci checking (for a given list of attributes) in
deref plugin.
For example, if a user has access to at least one of the requested
attribute (e.g. entryusn), in the deref req, then the derefenced
entry could be returned with additional attributes (given in the
deref plugin config.: 'objectclass', 'cn').
I honestly do not like this option but in case changing aci
definitions is too risky/complex it is an option.
regards
thierry
> '
> Martin
>
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