[Samba] domain-free multi-user use cases

[Andrew Bartlett]

On Sat, 2021-10-23 at 20:31 -0700, Jeremy Allison via samba wrote:
> On Sat, Oct 23, 2021 at 07:43:01PM -0400, Eric Levy via samba wrote:
> > It seems the first scenario you describe is simply several users each
> > creating their own single-user mount, that is, several simultaneous
> > uses in class (1).
> > 
> > The second describes a Windows client, and it hasn't been explained
> > whether the same concept would transfer to a Linux client.
> > 
> > Can a Linux client mount (e.g. as root) a remote Samba share such that
> > files on the server owned by user1, user2, and so on, show
> > correspondingly on the client as owned by user1, user2, and so on?
> 
> man mount.cifs - options:
> 
>         multiuser
>                Map  user  accesses to individual credentials when accessing the
>                server. By default, CIFS mounts only use a single  set  of  user
>                credentials (the mount credentials) when accessing a share. With
>                this option, the client instead creates a new session  with  the
>                server using the user's credentials whenever a new user accesses
>                the mount.  Further accesses by that user will  also  use  those
>                credentials.  Because  the  kernel  cannot prompt for passwords,
>                multiuser mounts are limited to mounts using sec=  options  that
>                don't require passwords.
> 
>                With this change, it's feasible for the server to handle permis‐
>                sions enforcement, so this option also implies noperm . Further‐
>                more,  when  unix extensions aren't in use and the administrator
>                has not overridden ownership using the  uid=  or  gid=  options,
>                ownership  of  files  is presented as the current user accessing
>                the share.

One could imagine building a solution based on S4U2Proxy (constrained
delegation) to authorize one server to assert the identity of all the
users it holds.  That external to Samba tool (no need for us to be
involved) would just supply normal Kerberos tickets to the server for
each user, obtained with this protocol extension.

Of course, in this situation you would need an AD DC, thankfully we
have one built in!

Andrew Bartlett

-- 
Andrew Bartlett (he/him)        https://samba.org/~abartlet/
Samba Team Member (since 2001)  https://samba.org
Samba Developer, Catalyst IT    https://catalyst.net.nz/services/samba