[Freeipa-users] Can mount NFS, but user only gets the permission question marks

Brendan Kearney bpk678 at gmail.com
Thu Feb 23 12:51:35 UTC 2017 

On 02/23/2017 07:32 AM, Kees Bakker wrote:
> On 22-02-17 17:33, Brendan Kearney wrote:
>> On 02/22/2017 10:26 AM, Kees Bakker wrote:
>>> On 22-02-17 14:05, Brendan Kearney wrote:
>>>> On 02/22/2017 05:23 AM, Kees Bakker wrote:
>>>>> On 21-02-17 19:49, Brendan Kearney wrote:
>>>>>> On 02/21/2017 10:57 AM, Kees Bakker wrote:
>>>>>>> Hey,
>>>>>>>
>>>>>>> Maybe one of the NFS users on this list could give me a hint what
>>>>>>> could be wrong. I'm not sure if it has any relation with FreeIPA/Kerberos.
>>>>>>>
>>>>>>> I've set up an NFS server and I can mount the NFS directory on my client. So, I'm
>>>>>>> guessing that setting up Kerberos principal was done correctly.
>>>>>>>
>>>>>>> However, only root can actually access the mounted contents. Any other user
>>>>>>> only sees question marks as shown below.
>>>>>>>
>>>>>>> The mount command is simple.
>>>>>>> $ sudo mount -v -t nfs srv1.example.com:/home /nfshome
>>>>>>> mount.nfs: timeout set for Tue Feb 21 16:36:39 2017
>>>>>>> mount.nfs: trying text-based options 'vers=4,addr=172.16.16.45,clientaddr=172.16.16.30'
>>>>>>>
>>>>>>> On the server side /etc/exports looks like this.
>>>>>>> /home        *(rw,sync,sec=krb5i,no_subtree_check)
>>>>>>>
>>>>>>> $ sudo mount |grep nfs
>>>>>>> srv1.example.com:/home on /nfshome type nfs4 (rw,relatime,vers=4.0,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=krb5i,clientaddr=172.16.16.30,local_lock=none,addr=172.16.16.45)
>>>>>>>
>>>>>>> $ sudo ls -ld /nfshome
>>>>>>> drwxr-xr-x 1 root root 72 feb 21 04:22 /nfshome
>>>>>>> $ sudo ls -l /nfshome
>>>>>>> total 0
>>>>>>> drwxr-xr-x 1 keesb  keesb  116 jan 27 12:56 keesb
>>>>>>>
>>>>>>> $ ls -l /nfshome
>>>>>>> ls: cannot access '/nfshome': Permission denied
>>>>>>> $ ls -l / | grep nfshome
>>>>>>> ls: cannot access '/nfshome': Permission denied
>>>>>>> d?????????   ? ?    ?       ?            ? nfshome
>>>>>>>
>>>>>> sec=krb* means that the user accessing the mount has to authenticate with a kerberos ticket, and has to be the user or in the group granted access to the share.  from the looks of things, the user did not authenticate, and that is why the permissions are question marks.  check the kerberos tickets that the user has (klist output).  Otherwise, the ownership might be user and group that the client machine does not recognize (think posix user/group that is not in sync between the NFS server and the client)
>>>>> Thanks for the reply.
>>>>>
>>>>> In this case the user _is_ authenticated.
>>>>> keesb at client1:~$ klist
>>>>> Ticket cache: KEYRING:persistent:60001:60001
>>>>> Default principal: keesb at EXAMPLE.COM
>>>>>
>>>>> Valid starting     Expires            Service principal
>>>>> 22-02-17 09:20:30  23-02-17 09:20:25  krbtgt/EXAMPLE.COM at EXAMPLE.COM
>>>> no, the user has a TGT.  a nfs/host.domain.tld at REALM ticket is needed to authenticate.
>>> (( I'm trying to catch up on the acronyms. TGT. Reading wikipedia now. ))
>>>
>>>>> What other grants could be needed? HBAC Rules?
>>>>>
>>>>> Do I need an nfs principal for the client? (I didn't think so, but many HOWTO's say so [2]. Anyway, it
>>>>> doesn't help to get access for the user.)
>>>> there are principals to create and keytabs to be updated on hte NFS sever, if not done already.
>>> I did create a principal for the NFS server (using ipa service-add) and
>>> add to the keytab on the NFS server (using ipa-getkeytab) ...
>>> root at srv1# klist -ke
>>> Keytab name: FILE:/etc/krb5.keytab
>>> KVNO Principal
>>> ---- --------------------------------------------------------------------------
>>>      1 host/srv1.example.com at EXAMPLE.COM (aes256-cts-hmac-sha1-96)
>>>      1 host/srv1.example.com at EXAMPLE.COM (aes128-cts-hmac-sha1-96)
>>>      1 nfs/srv1.example.com at EXAMPLE.COM (aes256-cts-hmac-sha1-96)
>>>      1 nfs/srv1.example.com at EXAMPLE.COM (aes128-cts-hmac-sha1-96)
>>>
>>> Is this what you mean?
>> yes, if that is done, the server side components should be done for kerberos.  have you set things up in /etc/idmapd.conf so your domain, REALM, etc are setup?
> I don't think that a change of idmapd.conf (on the NFS server) is needed because all host
> names are FQDN and everything is in one and the same REALM.
NFS needs to know how to map a user object to an ID and groups. 
identities established by kerberos do not directly translate to users.  
usually some sort of directory services are leveraged in order to 
accomplish this, though PAM and things like that can be used to.  by 
setting things in idmapd.conf, you are telling NFS who to translate 
kerberos identities into usernames, so ownership and permissions can be 
sync'd.
>
>>>>     then the user should be able to pull the ticket for auth.
>>> Sorry to ask, but how do I do that? On the client, I suppose, and by the user ??
>>>
>>> keesb at client1$ kinit nfs/srv1.example.com at EXAMPLE.COM
>>> Password for nfs/srv1.example.com at EXAMPLE.COM:
>>>
>>> But I don't have a password for that. Hmm.
>> there is no need to init on the client side, as long as the TGT is obtained.  you should never need to init the nfs/blah.. on the client side.
> OK
> So, it seems to me that all the basics are setup correctly. The mount succeeds. The user
> has a TGT and still the (non-root) user cannot even stat the mount point, nor the directory
> entry itself.
>
> What puzzles me is that root can see everything, also without a TGT.
the mount will succeed, but the user does not have access because NFS 
does not know who the user it.  it has an unassociated ID established by 
kerberos, but not a user.
>
>>>>> Furthermore, I'm guessing that the host principle which I got after ipa-client-install is
>>>>> good enough. (This [1] wiki suggests that I need to do a ipa-getkeytab for it, which I
>>>>> did not do.)
>>>>> # klist -ke
>>>>> Keytab name: FILE:/etc/krb5.keytab
>>>>> KVNO Principal
>>>>> ---- --------------------------------------------------------------------------
>>>>>       1 host/client1.example.com at EXAMPLE.COM (aes256-cts-hmac-sha1-96)
>>>>>       1 host/client1.example.com at EXAMPLE.COM (aes128-cts-hmac-sha1-96)
>>>>>
>>>>> [1] http://wiki.linux-nfs.org/wiki/index.php/NFS_and_FreeIPA
>>>>> [2] https://www.lisenet.com/2016/kerberised-nfs-server-on-rhel-7/
>>>> http://www.itp.uzh.ch/~dpotter/howto/kerberos
>>>>
added the thread back to the mailing list for the benefit of any who 
search on the subject.

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