openssh bugs - Aug 2020 - [Bug 3203] New: Could default_ccache_name from krb5.conf be used for GSSAPI connections?

https://bugzilla.mindrot.org/show_bug.cgi?id=3203

            Bug ID: 3203
           Summary: Could default_ccache_name from krb5.conf be used for
                    GSSAPI connections?
           Product: Portable OpenSSH
           Version: 8.3p1
          Hardware: ix86
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: Kerberos support
          Assignee: unassigned-bugs at mindrot.org
          Reporter: toby at inf.ed.ac.uk

Hi there,

I'm filing this bug upstream as suggested in this ubuntu bug report:
https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/1889548

I'll recreate my original text from that ticket here:

"
ssh connections from a client with the following in ssh_config...

GSSAPIAuthentication yes
GSSAPIDelegateCredentials yes

... to an ubuntu 20.04 machine result in KRB5CCNAME being set to
'FILE:/tmp/krb5cc_[uid]_[random]' despite the following in
/etc/krb5.conf:

[libdefaults]
 ...
 default_ccache_name = KEYRING:persistent:%{uid}

This means that we cannot enforce a policy to use KEYRING ccaches
across our systems. Authentications which go via the pam stack (e.g.
login to the machine at the console or over ssh using a password) can
be configured to use a KEYRING ccache, via libpam-krb5 settings in
/etc/krb5.conf.

The FILE: setting seems to be hard-coded in the openssh code
(auth-krb5.c). It would be great if ssh(gssapi-with-mic) connections
either (a) set KRB5CCNAME to the default_ccache_name value, if set in
/etc/krb5.conf, or (b) didn't set KRB5CCNAME at all, so the system
default is used.
"

Redhat already patch for this, but they patch the upstream source quite
heavily (as do ubuntu, but in different ways).

I'm hoping to spend more time on getting a patch to do this on ubuntu,
but I suspect that wouldn't be of much use upstream.

Would there be interest in implementing this functionality upstream?

Thanks
Toby Blake
School of Informatics
University of Edinburgh

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3203

Jakub Jelen <jjelen at redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jjelen at redhat.com

--- Comment #1 from Jakub Jelen <jjelen at redhat.com> ---
We use several patches to do that in RHEL/Fedora and this was already
proposed in bug #2775, but without any feedback from OpenSSH
developers.

Feel free to use the patches we use (might need updating from version
posted in the bug). But note that there is still many people interested
in using per-session caches.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3203

--- Comment #2 from Toby Blake <toby at inf.ed.ac.uk> ---
(In reply to Jakub Jelen from comment #1)
> We use several patches to do that in RHEL/Fedora and this was
> already proposed in bug #2775, but without any feedback from OpenSSH
> developers.
> 
> Feel free to use the patches we use (might need updating from
> version posted in the bug). But note that there is still many people
> interested in using per-session caches.
Hi Jakub,

Thanks for the reply.  I've tried a (slightly reworked to get it to
apply) version of openssh-7.7p1-gssapi-new-unique.patch but it doesn't
seem to quite do what I want it to do, specifically it always gives me
a new unique ccache, rather than using e.g. KEYRING:persistent:%{uid}. 
It may be that in reworking it I've messed it up somewhat so I need to
find some time to look at it in more detail.

Cheers
Toby

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3203

--- Comment #3 from Jakub Jelen <jjelen at redhat.com> ---
Hi,
the current version we use in Fedora lives here so it could have gone
through some updates and fixes since 2 years ago:

https://src.fedoraproject.org/rpms/openssh/blob/master/f/openssh-7.7p1-gssapi-new-unique.patch

The new unique cache in the given collection is probably the most
sensible way of doing this. Or you suggest that you would like the new
login to override existing tickets in the ccache? Or you still see the
ccache in /tmp being used? What configuration did you try?

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3203

--- Comment #4 from Toby Blake <toby at inf.ed.ac.uk> ---
(In reply to Jakub Jelen from comment #3)
> Hi,
> the current version we use in Fedora lives here so it could have
> gone through some updates and fixes since 2 years ago:
> 
> https://src.fedoraproject.org/rpms/openssh/blob/master/f/openssh-7.
> 7p1-gssapi-new-unique.patch
Hi, this is the patch I've tried to rework for ubuntu.
> The new unique cache in the given collection is probably the most
> sensible way of doing this. Or you suggest that you would like the
> new login to override existing tickets in the ccache? Or you still
> see the ccache in /tmp being used? What configuration did you try?
What I'd like is to be able to set 

[libdefaults]
default_ccache_name = KEYRING:persistent:%{uid}

... in /etc/krb5.conf and for (gssapi) ssh connections to use this, in
the same way that I can set it for PAM connections.

This no doubt works under redhat (and indeed it works for us with
Scientific Linux 7.8 with the addition of a backported
openssh-7.5p1-gss-environment.patch, as discussed in
https://bugzilla.redhat.com/show_bug.cgi?id=1199363)

I think I need to look at the gssapi-new-unique patch again, with a
more complete understanding of the relevant code areas.  My reworking
of it is definitely not doing what it should do.

The biggest issue in getting this working is the divergent code bases
between redhat and ubuntu (in particular, I suspect, the gsskex patch).
 This is why I'd much prefer this issue to be fixed upstream.

Pending that, I'll look again at the the unique patch.

Cheers
Toby

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3203

Lars-Dominik Braun <ldb at leibniz-psychology.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ldb at leibniz-psychology.org

--- Comment #5 from Lars-Dominik Braun <ldb at leibniz-psychology.org> ---
Has there been any progress?

We?d also be interested in this feature. Our setup includes SSSD, which
provides a KCM: backend for ticket storage, but SSH keeps falling back
to KRB5CCNAME=FILE: when using an existing ticket to login.

Working around the issue is quite simple (because no pattern expansion
is needed) using pam_env and an entry in /etc/environment, which
overrides SSH?s default. Still, it?d be better if SSH respected
krb5.conf in the first place.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3203

Andreas Hasenack <andreas at canonical.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andreas at canonical.com

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3203

Pat Riehecky <riehecky at fnal.gov> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |riehecky at fnal.gov

--- Comment #6 from Pat Riehecky <riehecky at fnal.gov> ---
Echoing interest in this.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=3203

Bj??rn Jacke <bjoern at j3e.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bjoern at j3e.de

-- 
You are receiving this mail because:
You are watching the assignee of the bug.