Who should be the owner of newly created files when the creator is in the local Administrators group

Richard Sharpe realrichardsharpe at gmail.com
Mon Apr 30 08:26:28 MDT 2012

On Sun, Apr 29, 2012 at 10:39 AM, simo <idra at samba.org> wrote:
> On Sat, 2012-04-28 at 21:52 -0700, Richard Sharpe wrote:
>> Hi folks,
>> Here http://technet.microsoft.com/en-us/library/cc781716%28v=WS.10%29.aspx
>> it says:
>> "Note
>>     When users who are members of the local Administrators group
>> access objects on Windows Server 2003, the Default Owner field in the
>> user's access token contains the SID for the Administrators group, not
>> the SID for the user. A similar rule applies to users who access
>> objects in Active Directory. If the user is a member of the Domain
>> Admins group, the Default Owner field in the user's access token
>> contains the SID for the Domain Admins group. In both cases, objects
>> that the user creates or takes ownership of are owned by the group,
>> not by the individual user."
>> This suggests that we currently do the wrong thing, I think, when we
>> create a file and the creator is in the local Administrators group.
> The problem is that in Posix, groups cannot own files.
> Around the first time I put my hands in Idmap (2002/3 ?) I had a
> discussion with Tridge and Jeremy about changing samba to always
> allocate both a uid and a gid for any SID for 2 simple reasons:
> 1) It allows us to avoid resolving the SID at allocation time if we do
> not want to as we do not need anymore to check what it is.
> 2) It would allow groups to own files by using the "Group's UID".
> At that time it wasn't accepted as an idea, so samba 3.x never gained
> this ability.
> Fast forward to samba 4 and now there is IDMAP_BOTH, which is
> essentially that proposal come true :-)
> Unfortunately we still do not support IDMAP_BOTH in samba 3.
> Point is that it is an incompatible change, that you cannot turn on
> implicitly in existing installations.
> That said I do support this method, so much so that in FreeIPA I also by
> default merged the id space, long ago, and effectively only have a
> unified ID space in the default install, as it makes it easier to handle
> personal user groups w/o polluting the tree with real fully featured
> groups.
> So long story short, yes we should do what is suggested there, but
> before we can do it, we need to add the option to use IDMAP_BOTH in the
> File server, optionally. The ACL code needs to be changed to understand
> IDMAP_BOTH and Winbindd also need to be changed so that a direct lookup
> of a UID beloging to a Group returns an actual disabled user with the
> same name of the group, the same ID, but no password, no home, no shell,
> and an indicator in the Gecos that this is actually a group. We should
> never returns these entries in enumerations though. As they are not real
> users and you do not want to pollute user's lists in those installations
> that want to be able to list users and groups.

Well, if acl_xattr (or even acl_tdb) is in use, we do not care at all
about POSIX groups.

So, from my perspective, modules/vfs_acl_common.c can get it right and
things will be fine.

Richard Sharpe

More information about the samba-technical mailing list