[Samba] Samba4 and NVSv4

Ritter, Marcel marcel.ritter at fau.de
Thu Jun 6 01:54:23 MDT 2013 

Hi Steve,

I guess you're running into the same problems I encountered:

Active Directory (and therefore Samba4) differs in some fields from basic MIT/heimdal Kerberos.
The only Service I ran into problems with this difference by now is NFS :-(

One reason for this is the different handling of ServicePrincipals and UserPrincipals.

If I recall things correctly the NFS server itself should be fine with a servicePrincipal, the NFS clients however refuse to work with SPNs and require separate UPNs (and therefore user objects) in AD/Samba4.
"net ads keytab add ..." only adds new SPNs to existing objects and does not create a new object/UPN (this could be done using windows' ktpass.exe or msktutil on linux).

Newer versions of nfs-utils  (>= 1.2.4) support the HOSTNAME$ format (treated like a UPN) used by Samba/Windows, which makes things easier (and could/should work out of the box with a keytab created by samba itself).

Let me know, if you need further help to track this issue down.

Bye,
   Marcel




-----Ursprüngliche Nachricht-----
Von: samba-bounces at lists.samba.org [mailto:samba-bounces at lists.samba.org] Im Auftrag von Steve Thompson
Gesendet: Mittwoch, 5. Juni 2013 23:58
An: samba at lists.samba.org; centos at centos.org
Betreff: [Samba] Samba4 and NVSv4

Short story: cannot get Kerberized NFSv4 to work. I've googled a great deal and cannot find where I have goofed (and there sure is a lot of misleading and just plain incorrect information out there), so would appreciate another pair of eyes. NFSv4 without Kerberos does work fine, as does ID mapping. We're using NFSv4 in production with sec=sys, but I'm not happy with that. My kerberized NFSv4 attempts are on a separate test cluster.

Longer story (sorry for the length):

All servers and clients are CentOS 6.4 with kernel 2.6.32-358.6.2.el6 and nfs-utils 1.2.3-36.el6; patches are up to date. NFSv4 servers are x86_64, clients are both x86_64 and i686. Two DC's are both i686, running Samba
4.0.5 with bind 9.91 + bind_dlz. Replication is good. All CentOS systems use sssd only and no winbind; this is also working (kinit, sudo, ssh, etc all good). Samba is at 3.6.9 on all systems except for the DC's.

Samba4 works; DNS works; Kerberos works; NFSv4 works with sec=sys.

I joined the clients to the domain ("TITAN.TEST.CORNELL.EDU") with:

   # net ads join -U Administrator ...
   # net ads testjoin

and created the nfs service principals (on the client and NFSv4 server)
with:

   # net ads keytab add nfs -U Administrator

This all works. I can see that the nfs service principals have been added; on the client abbott.test.cornell.edu, for example:

   # net ads keytab list | grep -i nfs
   2  DES cbc mode with CRC-32	nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU
   2  DES cbc mode with RSA-MD5  nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU
   2  ArcFour with HMAC/md5	nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU
   2  AES-128 CTS mode with 96-bit SHA-1 HMAC	nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU
   2  AES-256 CTS mode with 96-bit SHA-1 HMAC	nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU
   2  DES cbc mode with CRC-32	nfs/abbott at TITAN.TEST.CORNELL.EDU
   2  DES cbc mode with RSA-MD5	nfs/abbott at TITAN.TEST.CORNELL.EDU
   2  ArcFour with HMAC/md5	nfs/abbott at TITAN.TEST.CORNELL.EDU
   2  AES-128 CTS mode with 96-bit SHA-1 HMAC	nfs/abbott at TITAN.TEST.CORNELL.EDU
   2  AES-256 CTS mode with 96-bit SHA-1 HMAC	nfs/abbott at TITAN.TEST.CORNELL.EDU

and on one of the DC's:

   # ldbsearch cn=abbott | grep -i nfs
   servicePrincipalName: NFS/abbott
   servicePrincipalName: NFS/abbott.test.cornell.edu

and on the client "net ads search '(sAMAccountName=abbott$)'" also works, as does klist:

   # klist -ke | grep -i nfs
    2 nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU (des-cbc-crc)
    2 nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU (des-cbc-md5)
    2 nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU (arcfour-hmac)
    2 nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU (aes128-cts-hmac-sha1-96)
    2 nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU (aes256-cts-hmac-sha1-96)
    2 nfs/abbott at TITAN.TEST.CORNELL.EDU (des-cbc-crc)
    2 nfs/abbott at TITAN.TEST.CORNELL.EDU (des-cbc-md5)
    2 nfs/abbott at TITAN.TEST.CORNELL.EDU (arcfour-hmac)
    2 nfs/abbott at TITAN.TEST.CORNELL.EDU (aes128-cts-hmac-sha1-96)
    2 nfs/abbott at TITAN.TEST.CORNELL.EDU (aes256-cts-hmac-sha1-96)

In /etc/sysconfig/nfs, SECURE_NFS=yes on all clients and servers, and rpc.gssd and rpc.svcgssd are running (although no need for the latter on the clients). The NFSv4 server exports with sec=sys:krb5 (and as I said,
NFSv4 works fine without krb5, so I believe the exports file to be correct).

But when I try to mount, I get the catch-all error:

   # mount -t nfs4 -o sec=krb5 costello.test.cornell.edu:/data /mnt/tmp
   mount.nfs4: access denied by server while mounting costello.test.cornell.edu:/data

and in /var/log/messages on the same client:

Jun  5 17:11:13 abbott rpc.gssd[1439]: Success getting keytab entry for
 	'nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU'
Jun  5 17:11:13 abbott rpc.gssd[1439]: WARNING: Client
 	'nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU' not found in Kerberos
 	database while getting initial ticket for principal
 	'nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU' using keytab
 	'FILE:/etc/krb5.keytab'
Jun  5 17:11:13 abbott rpc.gssd[1439]: ERROR: No credentials found for connection to server costello.test.cornell.edu

With tcpdump I can see that the DC is contacted during the mount, but the
NFSv4 server is not. The log files on the NFSv4 server are silent.

I have tried (everything was restarted between tests); "no change" means that it still does not work and gives the same exact errors:

- verified that /etc/idmapd.conf on all systems has the same domains and
   realms. This works anyway with sec=sys.

- reduced the keytab to the DES enctypes for nfs/... on all systems; no
   change.

- used "allow_weak_crypto=true" in /etc/krb5.conf; no change.

- set default_tgs_enctypes and default_tkt_enctypes to "des-cbc-md5
   des-cbc-md4 des-cbc-crc" in /etc/krb5.conf; no change.

- tried adding the service principals on the DC with "samba-tool spn add"
   instead of "net ads keytab add" on the client, and then exporting the
   keytab to the client; no change.

- add the SPN "nfs/abbott.test.cornell.edu at TITAN.TEST.CORNELL.EDU" and
   "nfs/abbott at TITAN.TEST.CORNELL.EDU" in case the missing realm was a
   factor; no change.

- started rpc.gssd on the clients with the -l switch; no change.

- started rpc.svcgssd with the -n switch so that nfs/ service principals
   are in theory not required; no change.

I do not understand why rpc.gssd canot find the service principal, when it does exist in the database. I've probably missed out some other things that I have tried to no effect. Help!

Steve
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Steve Thompson                 E-mail:      smt AT vgersoft DOT com
Voyager Software LLC           Web:         http://www DOT vgersoft DOT com
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Ithaca, NY 14850
   "186,282 miles per second: it's not just a good idea, it's the law"
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