krb5 library missing functions for collections

[Simo Sorce]

On Tue, 2019-07-23 at 14:09 +0000, Charles Hedrick wrote:
> Maybe there’s a path through the code that I didn’t find. But it ends
> up failing if the credential isn’t username at DOMAIN. There’s an
> explicit test. I don’t see why it couldn't specify that in the first
> place.
> 
> I think if you want a local user joe to access NFS as jdoe at REALM,
> you’d want to set up that mapping somewhere. I haven’t checked this
> in the code, but I’d expect it in a krb5.conf mapping, .k5identity,
> and/or idmap. I doubt you want NFS to use whatever random ticket may
> be in the default cache for the uid making the access. As far as I
> can tell it doesn’t actually do that now.

Actually this is how NFS is supposed to work, it will pick the first
valid credential, but it is possible a later change broke it.

.k5identity is also an option but as a way to select a non-default
principal, if you have only one krbtgt regardless of what it is I
expect an NFS mount to try to use that credential.

Simo.

> > On Jul 23, 2019, at 9:35 AM, Simo Sorce <simo at redhat.com> wrote:
> > 
> > On Mon, 2019-07-22 at 20:10 +0000, Charles Hedrick wrote:
> > > The problem is that the code in rpc.gssd works as followers:
> > > 
> > > * get the default credential from the collection
> > > * fail unless it’s username at DOMAIN
> > > 
> > > If you replace the initial step by code telling it explicitly to get 
> > > username at DOMAIN then it works just fine, assuming that the user
> > > actually has such a credential. Which they will. GSSAPI is perfectly
> > > capable of looking for a specific credential if you tell it to. It’s
> > > just that the code doesn’t do it that way. To avoid building my own
> > > copy of rpc.gssd, I use a loadable library to interpose code around
> > > GSSAPI that supplies the right argument.
> > 
> > rpc.gssd does this because it cannot know what the right credential
> > name is in all situations.
> > 
> > In very controlled environments it is indeed username + @REALM and the
> > realm is known, but in other cases it is not.
> > For example a personal laptop where the username is 'joe' and no
> > default realm is set and someone doing kinit jdoe at WORK.REALM then
> > walking into an NFS mount.
> > 
> > I guess the nfs-utils folks may accept a patch to rpc.gssd where an
> > option can be given to assume a specific form for the user's principal
> > name to look for, but that can't be the default as it would break
> > current uses.
> > 
> > HTH,
> > Simo.
> > 
> > -- 
> > Simo Sorce
> > RHEL Crypto Team
> > Red Hat, Inc
> > 
> > 
> > 
> > 
> 
> 

-- 
Simo Sorce
RHEL Crypto Team
Red Hat, Inc