mit-krb5 and heimdal binaries

Alexander Bokovoy ab at
Mon Mar 20 08:39:26 UTC 2023


On ma, 20 maalis 2023, Andrew Bartlett wrote:
> On Sun, 2023-03-19 at 09:29 +0200, Alexander Bokovoy via samba-
> technical wrote:
> > Hi,
> > 
> > 
> > I would be against a blended build against both MIT Kerberos and
> > Heimdal
> > Kerberos in a distribution. It is not going to bring you anything
> > good,
> > support wise.
> > 
> > Andreas and I have submitted a talk to SambaXP about MIT
> > Kerberos/Heimdal Kerberos-based Samba AD DC configurations, where
> > they
> > stand against each other and what are perspectives. In short, both
> > have
> > unique features that do not exist in the other variant and both are
> > close to being production-ready. We want to change the status for MIT
> > Kerberos-based build from experimental to production. Effectively,
> > actual decision for a version shipped in a particular distribution
> > would
> > need to be made by that distribution, of course.
> > 
> > Distributions need to take into account security releases, as Rowland
> > has pointed out as well. However, from my Fedora and RHEL experience,
> > this is not a problem with MIT Kerberos -- certainly not more than
> > with
> > Heimdal. It is pretty much a coordination question and I believe we
> > have
> > very good coordination on that front with MIT Kerberos and
> > distribution
> > maintainers.
> > 
> > If I was in Samba AD support for production deployments, I'd probably
> > go with deploying DCs in a containerized image way to isolate
> > completely
> > from the rest of the OS. There are few images already that provide
> > this
> > setup: [1] was presented at SambaXP by Michael Adam and other folks
> > now
> > from IBM Storage, [2] is older and also active one.
> > 
> > [1] 
> >
> > 
> > [2] 
> >
> Regarding the support and stability of a Samba AD Deployment based on
> MIT Kerberos, given the advances in testing over the past few years, I
> have, in 2023, no major concerns.  The features that are provided work
> and can be expected to operate in production without concern.
> The "experimental" designation is no longer correct, but it is not
> clear to me what different word we should apply instead, the closest I
> can come to is "unsupported".

Thanks. It is not 'unsupported', for sure, same way as linking against
system-built Heimdal Kerberos library is not considered 'unsupported'.

What should, perhaps, be defined is a matrix of features that are
expected to work. If somebody files a bug against Fedora with Samba
AD/MIT build or Samba upstream with a configuration that is expected to
work, it will be investigated and worked on -- pretty much like we
already do for years. This is definitely not an 'unsupported' state.
Given that Samba Team as the upstream project does not provide
commercial support in itself, this is best we do already. Commercial
support is provided by separate entities and I don't see why MIT
Kerberos build should be treated otherwise.

Right now we don't have this formalized in any in-tree document. The
wiki page says

Samba as an AD DC only supports:

 - The integrated LDAP server as AD back end. For details, see the
   frequently asked question (FAQ) Does Samba AD DCs Support OpenLDAP or
   Other LDAP Servers as Back End?
 - The Heimdal Kerberos Key Distribution Center (KDC).

   Samba provides experimental support for the MIT Kerberos KDC provided
   by your operating system if you run Samba 4.7 or later and has been
   built using the --with-system-mitkrb5 option. In other cases Samba
   uses the Heimdal KDC included in Samba. For further details about
   Samba using the MIT KDC, and why it is experimental see Running a
   Samba AD DC with MIT Kerberos KDC.  

>From this you don't get any state for system-provided Heimdal Kerberos
build as well. There are also no guidelines for distribution maintainers.

All this being said purely because we have a space for improvement, not
as a critique only. I can prepare a draft that describes guidelines to
distribution maintainers.

> Just as a distribution can and will ship a pre-release version of some
> software, to meet that distributions overall goals, Red Hat is free to
> ship the "experimental" MIT-based Samba AD DC, and provide the security
> support (in particular) for that configuration to its users.  Red Hat
> has the resources and ability to coordinate the release of patched
> Samba and a patched MIT Kerberos simultaneously if required, for
> example. 

Can we please stop assigning it all to 'Red Hat'? Same way as Canonical
or Catalyst IT are not driving decisions how Debian packaging of Samba
is done, Red Hat as a company is not involved in deciding Fedora's
packaging of Samba. Individuals are. I would prefer if our role would
be reflected in these discussions.

> However, things are different upstream.  I would suggest that, while
> vendoring has well documented costs (as seen when we got stuck on 'old
> Heimdal'), the choice to embed an copy of Heimdal has been a
> significant advantage to upstream Samba.  

So this is an entirely different discussion. You might want to create a
separate thread about it.

I am not even contesting the fact that embedded Heimdal usage is there.
When Tridge started Samba 4 work two decades ago, we did not have many
important elements of a rapid collaboration culture we have today.  At
that point it was great that we've got help from Love Astrand to make
Heimdal embeddable and used that to iterate quickly Kerberos
interoperability with Microsoft's Active Directory. At that point both
Heimdal and MIT Kerberos were a lot less active upstreams with regards
to advancing faster that goal. An irony and drama of git invention
should also not be forgotten.

It is normal for many upstreams to be able to build against different
versions or implementations of libraries they depend on. Sure, something
is marked as the primary one -- in case of Samba AD I would argue that
the primary supported variant is 'Samba AD built against an embedded
Heimdal Kerberos version'. However, this does not automatically
disqualify 'Samba AD built against a system-provided MIT Kerberos
version' or 'Samba AD built against a system-provided Heimdal Kerberos
version'. Making them supported is a task of the system provider
together with upstream -- to ensure that the specific target is viable
and usable. This is what we do with MIT build in Fedora since 2017 and
will do have a better standing once Fedora 39 is out due to krb5 1.20+

> As a current example, this is allowing Claims support to be added, with
> the KDC-side changes (to link the device and user) recorded in
> lorikeet-heimdal and proposed upstream but not required to be accepted
> at the time that the patches land in Samba.

Is this referencing a work being tracked in
> Likewise, security releases, which have been a significant burden of
> late, can be made from Samba master and directly consumed by our users.

Coordinating between upstreams is the only reasonable way going forward.
There is no way we wouldn't get burned out from vendoring-in everything.
It may work from time to time but a real answer is to build an ecosystem
around the area and deal with it altogether.

> I'm very sorry I won't be at SambaXP this year, as I would very much
> like to be part of the conversation around any changes we make here.
> It is not that the the current situation is ideal, but it has come with
> a number of significant advantages.

My aim is to not change that but rather enable what has been developed
over years. Current state of claiming 'experimental' has lived itself
out, in my opinion.

> In both cases the development process includes tests, and these tests
> are at least initially marked as knownfail for MIT Kerberos.  This is
> not as dire as it seems, because more then 50% of a Samba development
> task is tests, those supporting the MIT KDC are presented with a full
> set of tests and a list of know failures the address.  

Indeed. For the record, current set of tests not supported by
--with-system-mitkrb5 build:

$ cat selftest/skip_mit_kdc
# We do not support RODC yet

$ cat selftest/knownfail_mit_kdc_1_20 
# FAST tests
# Claims tests
# Group tests

Out of those the FAST tests should be fixed already. This leaves us with
SID compression. Claims work is being done by Joseph right now for
Heimdal KDC. As with the rest, my hope we can reuse a lot of this great
work, like we did in past. SID compression is something I was planning
to look at for MIT Kerberos myself.

> However that knownfail listing is the limit that the developers
> providing new Samba AD features and providing the security support are
> expected to provide.
> This last point is critical, as only one of these Kerberos
> implementations is funded, and currently the Kerberos distribution that
> the developers involved are funded to provide is Heimdal.
> This choice may of course change in the future, but as far as I see it
> it will always be one or the other.

So far, there is no real aim to drop one Kerberos implementation
upstream and stick to the other one. There is a good distributed effort
to cover both Heimdal and MIT Kerberos across multiple free software
directory services. The most important part is that this effort is used
to improve Kerberos testability and security everywhere, and this means
also a better base for Samba AD users.

/ Alexander Bokovoy

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