On Mon, Aug 27, 2018 at 05:18:01PM -0600, Erinn Looney-Triggs wrote:

I have a system that is joined to an AD domain via SSSD, it was happily running samba and serving shares using either kerberos or password authentication, with the update to Samba 4.7.1 in the RHEL 7.5 release, all of that stopped working.

samba config file:

[global]   log level = 5

password server = *   realm = AD.EXAMPLE.COM   encrypt passwords = yes   kerberos method = system keytab   workgroup = AD   server string = %h samba   security = ADS   map to guest = Bad User   interfaces =  <valid IP>   hosts allow = <valid IP blocks>   load printers = no   passdb backend = tdbsam   dns proxy = no   max log size = 5000   bind interfaces only = no

restrict anonymous = 2

#============================ Share Definitions

[images]     comment = example images     path = /var/eng/     guest ok = no     printable = no     write list =     create mask = 0664     directory mask = 0775     read only = no     valid users = +valid-example-group     force group =     browseable = yes

Now samba will not even start without either libwbclient or sssd-libwbclient installed with the above configuration. After installing sssd-libwbclient and modifying valid users to:

valid users = AD\valid-example-group

kerberos based connections will work just fine. However password based connections for windows systems that are not AD joined, or smbclient without kerberos, does not work. I believe this is falling back to NTLM and NTLM is simply not supported by SSSD correct?

Oddly, what used to work, with basically a call to getgrnam() no longer works in 4.7.1 release of samba and there seems to be no mention that I can find as to why. Any thoughts?

It looks an awful lot like, if we need to support both krb and password based connections we will need to use winbind, correct? Or is there another way to make this thing work? If I have to use winbind it looks like I need to use 'net ads join' or 'realm join --client-software=winbind' but it then seems to me that the system will be joined to the AD twice, once to use SSSD, and once for winbind is this correct? Is there a way to make winbind and SSSD work together?

Further it looks like, according to this: https://bugzilla.redhat.com/show_bug.cgi?id=1558560 that RHEL 7.6 with Samba 4.8.1 will require winbind to be running period. I believe that statement to be a bit of an oversimplification because sssd-libwbclient should still work, or am I misunderstanding?

Any guidance here would be great, this seems to be a fairly murky area, or my google fu is weak.

Yes, if you want to use password authentication (NTLM) you have to run winbind with recent versions of Samba. The reason is that some old fallback code was removed from the smbd binary mainly for security reasons and to simplify the code in general.

If you only need Kerberos authentication sssd-libwbclient can still be used.

For all other cases where winbind must be running install Samba's libwbclient and I would recommend to use SSSD's idmap plugin for Samba/Winbind, see man idmap_sss for details.

Since idmap_sss is read-only from the winbind perspective it is recommend to have a read-write plugin as well so that the actual imap config for smb.conf might look like:

idmap config * : backend", "tdb" idmap config * : range", "10000-99999"

idmap config MYDOMAIN : backend = sss idmap config MYDOMAIN : range = 200000-2147483647

If you have a forest with multiple domains you should add a configuration for each domain with suitable ranges.

This way both SSSD and Winbind will talk to AD with the same credentials but SSSD still does all system authentication (no need to add pam_winbind to the PAM configuration) and user group lookup. Winbind will only serve the needs of smbd and other direct users of libwbclient but gets all information about idmapping from SSSD so that both Winbind and SSSD will always use the same UIDs and GIDs for the same AD object.

HTH

bye, Sumit

-Erinn

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