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

Thu Jun 19 13:36:47 UTC 2014

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 ??

we can have a sysaccount called named, like we did for kerberos before
we had the ipa-kdb driver.

Simo.

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