samba - Jan 2025 - odd UID behaviour in Linux hosts connected to Samba AD

Hi everyone,

I've been running into a small issue in the past few days after figuring 
out (or so I thought) how to properly map UIDs from AD to Linux clients so 
that they are identical across environments and work on both Linux and 
Windows boxes. Maybe I am doing something wrong.

I am wondering if someone could sched some light here.

My config is this:
- Two small VMs running Samba 4.20.z in AD mode.
- Several client endpoints.
- Several Linux (RHEL) AD clients configured to use winbind and acting as 
fileservers.
(# authselect select winbind --nobackup -f)

On one of these fileservers, here is what I am observing:

Right after booting a fileserver, I can 'id' a local user just fine and 
it's properly showing the local Linux groups:

# id raistlin
uid=1502(raistlin) gid=100(users) 
groups=3(sys),7(lp),10(wheel),11(cdrom),39(video),63(audio),100(users),197(system)

However, if I query the AD user related to that local user, things start 
going a -different- direction afterwards:

# id -a KRYNN_AD\\raistlin
uid=1502(KRYNN_AD\raistlin) gid=100(users)
groups=10001(BUILTIN\users),10000(BUILTIN\administrators),100(users)
This is coming from the

but then I the output of the -first- command changes and the extra groups 
are dropped and I can no longer query the local user:

# id -a raistlin
uid=1502(KRYNN_AD\raistlin) gid=100(users)
groups=10001(BUILTIN\users),10000(BUILTIN\administrators),100(users)

The above fileserver is running RHEL 8.10. The nsswitch configuration 
looks like this:

# grep winbind /etc/nsswitch.conf
passwd:     db files winbind systemd
group:      db files winbind systemd

the relevant samba configuration for the domain is this:
-------
security = ads
realm = AD.LASTHOME.SOLACE.KRYNN
vfs objects = acl_xattr
[....]
dedicated keytab file = /etc/krb5.keytab
kerberos method = secrets and keytab
template shell = /bin/bash
template homedir = /export/home/%U
idmap_ldb:use rfc2307 = yes
winbind use default domain = no
winbind refresh tickets = yes
winbind offline logon = yes
winbind enum groups = no
winbind enum users = no
winbind nss info = rfc2307
min domain uid = 1000
idmap config * : backend = tdb
idmap config * : range = 2000000-2999999
idmap config KRYNN_AD : backend = ad
idmap config KRYNN_AD : range = 1500-1999999
idmap config KRYNN_AD : schema_mode = rfc2307
idmap config KRYNN_AD : unix_nss_info = yes
idmap config KRYNN_AD : unix_primary_group = yes

While this 'works' as-is, I am a little concerned because of the 
following:
1) Why is the AD user taking precedence in NSS resolution even though 
winbind is listed later? (nsswitch.conf order shows it should hit the 
local user first). This also shows up while doing simple things such as 
'ls -l'.

the UID and GID in AD are coming from uidNumber and gidNumber which I have 
configured to match those of the local user.

2) the extra groups are dropped and it is causing issues to the local 
users when they login to the Linux workstations.

3) In this situation, is there a way to add the AD user to more groups on 
the Linux systems? Since winbind seems to be taking over, is that an 
attribute I could add in AD to add the missing groups?

Am I doing something totally wrong here? I admit I might have a knowledge 
gap on those topics. This is just my Home Lab and I am just trying to 
provide seamless Linux/Windows integration to just a few users..

Thank you for any help,

Vincent

On Thu, 16 Jan 2025 12:21:42 +0100 (CET)
"Vincent S. Cojot via samba" <samba at lists.samba.org> wrote:
> 
> Hi everyone,
> 
> I've been running into a small issue in the past few days after
> figuring out (or so I thought) how to properly map UIDs from AD to
> Linux clients so that they are identical across environments and work
> on both Linux and Windows boxes. Maybe I am doing something wrong.
> 
> I am wondering if someone could sched some light here.
> 
> My config is this:
> - Two small VMs running Samba 4.20.z in AD mode.
> - Several client endpoints.
> - Several Linux (RHEL) AD clients configured to use winbind and
> acting as fileservers.
> (# authselect select winbind --nobackup -f)
> 
> On one of these fileservers, here is what I am observing:
> 
> Right after booting a fileserver, I can 'id' a local user just fine
> and it's properly showing the local Linux groups:
Please define 'local user', if it is a user that is in /etc/passwd AND
in AD, you are doing it wrong.
> 
> # id raistlin
> uid=1502(raistlin) gid=100(users) 
>
groups=3(sys),7(lp),10(wheel),11(cdrom),39(video),63(audio),100(users),197(system)
> 
> However, if I query the AD user related to that local user, things
> start going a -different- direction afterwards:
> 
> # id -a KRYNN_AD\\raistlin
> uid=1502(KRYNN_AD\raistlin) gid=100(users)
> groups=10001(BUILTIN\users),10000(BUILTIN\administrators),100(users)
> This is coming from the
> 
> but then I the output of the -first- command changes and the extra
> groups are dropped and I can no longer query the local user:
> 
> # id -a raistlin
> uid=1502(KRYNN_AD\raistlin) gid=100(users)
> groups=10001(BUILTIN\users),10000(BUILTIN\administrators),100(users)
> 
> The above fileserver is running RHEL 8.10. The nsswitch configuration 
> looks like this:
> 
> # grep winbind /etc/nsswitch.conf
> passwd:     db files winbind systemd
> group:      db files winbind systemd
Hmm, what is the 'db' ?
> 
> the relevant samba configuration for the domain is this:
> -------
> security = ads
> realm = AD.LASTHOME.SOLACE.KRYNN
> vfs objects = acl_xattr
> [....]
> dedicated keytab file = /etc/krb5.keytab
> kerberos method = secrets and keytab
> template shell = /bin/bash
> template homedir = /export/home/%U
> idmap_ldb:use rfc2307 = yes
The above line is only used on a Samba AD DC.
> winbind use default domain = no
> winbind refresh tickets = yes
> winbind offline logon = yes
> winbind enum groups = no
> winbind enum users = no
> winbind nss info = rfc2307
That line is no longer required.
> min domain uid = 1000
> idmap config * : backend = tdb
> idmap config * : range = 2000000-2999999
I wish redhat would stop telling people to put the default domain above
the main domain and 999999 IDs is a bit much for the default domain,
something that is meant for the Well Known SIDs (there are less than
200 of those) and anything outside the main domain (so really '0').
> idmap config KRYNN_AD : backend = ad
> idmap config KRYNN_AD : range = 1500-1999999
> idmap config KRYNN_AD : schema_mode = rfc2307
> idmap config KRYNN_AD : unix_nss_info = yes
> idmap config KRYNN_AD : unix_primary_group = yes
I take it you have added rfc2307 attributes to AD.
> 
> While this 'works' as-is, I am a little concerned because of the 
> following:
> 1) Why is the AD user taking precedence in NSS resolution even though 
> winbind is listed later? (nsswitch.conf order shows it should hit the 
> local user first). This also shows up while doing simple things such
> as 'ls -l'.
Thing is, you shouldn't have local users and AD users with the same
name.
> 
> the UID and GID in AD are coming from uidNumber and gidNumber which I
> have configured to match those of the local user.
Yes, it really sounds like you are doing it wrong.
> 
> 2) the extra groups are dropped and it is causing issues to the local 
> users when they login to the Linux workstations.
Let me give you an example on my domain:

rowland at devstation:~$ grep 'rowland' /etc/passwd
rowland at devstation:~$ 

I am not in /etc/passwd, I am not a 'local user', so why does this work:

rowland at devstation:~$ id rowland
uid=11104(rowland) gid=10513(domain users) groups=10513(domain
users),102(netdev),1001(unixtest),11104(rowland),10512(domain
admins),12605(testgroup),10571(allowed rodc password replication
group),10572(denied rodc password replication
group),2001(BUILTIN\users),2000(BUILTIN\administrators)

It works because (using idmap_rid) winbind makes me a Unix user.
> 
> 3) In this situation, is there a way to add the AD user to more
> groups on the Linux systems? Since winbind seems to be taking over,
> is that an attribute I could add in AD to add the missing groups?
You can add AD users to local Unix groups, but a better way would be to
create groups in AD instead (not system groups, the ones with an ID
less than 1000)
> 
> Am I doing something totally wrong here?
It sounds like it.

Do you really need the rfc2307 attributes ?
Samba can map AD users to Unix IDs without them and Windows never uses
them.

Rowland