[Freeipa-devel] LDAPI + autobind instead of Kerberos (for named)?

Thu Jun 19 14:05:26 UTC 2014

On 19.6.2014 16:02, Simo Sorce wrote:
> On Thu, 2014-06-19 at 16:41 +0300, Alexander Bokovoy wrote:
>> On Thu, 19 Jun 2014, Simo Sorce wrote:
>>> On Thu, 2014-06-19 at 14:13 +0300, Alexander Bokovoy wrote:
>>>> On Thu, 19 Jun 2014, Petr Spacek wrote:
>>>>> On 19.6.2014 11:02, Alexander Bokovoy wrote:
>>>>>> On Thu, 19 Jun 2014, Petr Spacek wrote:
>>>>>>> the thread "named's LDAP connection hangs" on freeipa-users list [1] opened
>>>>>>> question "Why do we use Kerberos for named<->DS connection? Named connects
>>>>>>> over LDAPI to local DS instance anyway."
>>>>>>>
>>>>>>> Maybe we can get rid of Kerberos for this particular connection and use
>>>>>>> autobind instead. It would make it more reliable and effective.
>>>>>>>
>>>>>>> As a side effect, named will be able to start even if KDC is down for some
>>>>>>> reason. It partially solves chicken-egg problem during IPA start-up.
>>>>>>>
>>>>>>> I wasn't around when it bind-dyndb-ldap was designed so I don't know
>>>>>>> historical reasons.
>>>>>> My primary worry is the fact that any break in named/bind-dyndb-ldap
>>>>>> could be then exploited to have access to all key material. In the case of
>>>>>> GSSAPI you are confined to whatever ACIs allow for dns/ principal.
>>>>> IMHO autobind maps uid+gid to a DN and normal ACIs apply after that so
>>>>> I don't see any difference from using SASL/GSSAPI/Kerberos.
>>>> My impression was that you wanted autobind to Directory Manager (root
>>>> autobind), this is what I don't want to support, for sure.
>>>>
>>>>>> Samba case goes further -- I specifically added GSSAPI bind to Samba
>>>>>> code LDAP code to allow splitting DCs and file servers while being able
>>>>>> to use the same ipasam module securely, in addition to the usual
>>>>>> ACI limitations.
>>>>> Named has only one function (i.e. DNS server with support for DNS
>>>>> updates). I don't think that there is meaningful separation.
>>>>>
>>>>>> For named what we could do is to have named+ldapi:// access mapped to
>>>>>> specific DN uidNumber=<named>+gidNumbe=<named>,cn=peercred,cn=external,cn=auth
>>>>> This is OpenLDAP-ism, right?
>>>> yes, this is what the client code reports. 389-ds server sees proper dn:
>>>>
>>>> # ipa service-mod DNS/ipa-01.t.vda.li at T.VDA.LI \
>>>>    --addattr=objectclass=posixgroup --addattr=objectclass=posixaccount \
>>>>    --setattr=cn=DNS/ipa-01.t.vda.li --setattr=uidNumber=25 \
>>>>    --setattr=gidNumber=25 --setattr=HomeDirectory=/var/named \
>>>>    --setattr=uid=named
>>>> -----------------------------------------------
>>>> Modified service "DNS/ipa-01.t.vda.li at T.VDA.LI"
>>>> -----------------------------------------------
>>>>    Principal: DNS/ipa-01.t.vda.li at T.VDA.LI
>>>>    Managed by: ipa-01.t.vda.li
>>>>
>>>> # su -l named -s /bin/bash -c 'ldapsearch -Y EXTERNAL -H ldapi://%2fvar%2frun%2fslapd-T-VDA-LI.socket cn=config '
>>>> SASL/EXTERNAL authentication started
>>>> SASL username: gidNumber=25+uidNumber=25,cn=peercred,cn=external,cn=auth
>>>> SASL SSF: 0
>>>> # extended LDIF
>>>> #
>>>> # LDAPv3
>>>> # base <dc=t,dc=vda,dc=li> (default) with scope subtree
>>>> # filter: cn=config
>>>> # requesting: ALL
>>>> #
>>>>
>>>> # search result
>>>> search: 2
>>>> result: 0 Success
>>>>
>>>> # numResponses: 1
>>>>
>>>> and here is what we see in the logs:
>>>> [19/Jun/2014:14:04:24 +0300] conn=177 AUTOBIND dn="krbprincipalname=dns/ipa-01.t.vda.li at t.vda.li,cn=services,cn=accounts,dc=t,dc=vda,dc=li"
>>>> [19/Jun/2014:14:04:24 +0300] conn=177 op=0 BIND dn="krbprincipalname=dns/ipa-01.t.vda.li at t.vda.li,cn=services,cn=accounts,dc=t,dc=vda,dc=li" method=sasl version=3 mech=EXTERNAL
>>>> [19/Jun/2014:14:04:24 +0300] conn=177 op=0 RESULT err=0 tag=97 nentries=0 etime=0 dn="krbprincipalname=dns/ipa-01.t.vda.li at t.vda.li,cn=services,cn=accounts,dc=t,dc=vda,dc=li"
>>>> [19/Jun/2014:14:04:24 +0300] conn=177 op=1 SRCH base="dc=t,dc=vda,dc=li" scope=2 filter="(cn=config)" attrs=ALL
>>>> [19/Jun/2014:14:04:24 +0300] conn=177 op=1 RESULT err=0 tag=101 nentries=0 etime=0
>>>> [19/Jun/2014:14:04:24 +0300] conn=177 op=2 UNBIND
>>>>
>>>>
>>>>>
>>>>>>    dn: krbprincipalname=dns/$master@$REALM,cn=services,cn=accounts,$SUFFIX
>>>>> This object already exists for every single DNS server, which is
>>>>> exactly the problem. Multiple servers are running under the same
>>>>> UID/GID pair on Fedora.
>>>> No, it is not a problem because there are multiple objects, one per
>>>> server.
>>>>
>>>>>> There is an issue of uid/gid being different on different platforms,
>>>>>> though but it is doable.
>>>>> I can see the problem with UID/GID mapping to multiple different
>>>>> principals. We can't remove these principals because they are used on
>>>>> server side for DNS updates.
>>>>>
>>>>> Maybe we can create autobind mapping objects in some non-replicated
>>>>> part of the tree. That would solve the problem with different UID/GIDs
>>>>> on different platforms and also mapping UID/GID mapping to multiple
>>>>> principals because one replica would see only one mapping object for
>>>>> given UID/GID.
>>>> No, I don't think we ever need to modify anything here apart from giving
>>>> posixgroup/posixaccount object classes to the DNS principal per server
>>>> and setting their properties.
>>>>
>>>> As you can see above, it simply works. I actually tested it with named
>>>> too, by setting
>>>>
>>>> diff -up /etc/named.conf.old /etc/named.conf
>>>> --- /etc/named.conf.old	2014-06-19 14:10:40.725934702 +0300
>>>> +++ /etc/named.conf	2014-06-19 14:10:58.432601624 +0300
>>>> @@ -45,7 +45,7 @@ dynamic-db "ipa" {
>>>>   	arg "base cn=dns, dc=t,dc=vda,dc=li";
>>>>   	arg "fake_mname ipa-01.t.vda.li.";
>>>>   	arg "auth_method sasl";
>>>> -	arg "sasl_mech GSSAPI";
>>>> -	arg "sasl_user DNS/ipa-01.t.vda.li";
>>>> +	arg "sasl_mech EXTERNAL";
>>>> +	arg "sasl_user named";
>>>>   	arg "serial_autoincrement yes";
>>>>   };
>>>>
>>>> and named successfully started, with 389-ds showing autobind to the same
>>>> krprincipalname=dns/... in the logs.
>>>
>>> why do we need to associate bind to dns/whatever ??
>> Because we already have ACIs given to dns/hostname to handle DNS
>> entries.
>
> Which are easy to change on upgrade.
>
>>> we can have a sysaccount called named, like we did for kerberos before
>>> we had the ipa-kdb driver.
>> A modification of DNS service with 'ipa service-mod' is all what we
>> need for single node case, I tried it.
>
> I do not like it at all, plus each server has a different object and
> they would all be duplicates. I prefer very much a single, passwordless
> special user in sysconfig, added to the same group that control access
> for the DNS tree.

We need to have the DNS principal for every replica anyway - for DNS updates. 
There is no way how to get rid of it without changes in GSS-TSIG protocol.

-- 
Petr^2 Spacek