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

[Simo Sorce]

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.

Simo.

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