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

Kees Bakker keesb at ghs.com
Fri Feb 24 08:33:10 UTC 2017 

On 23-02-17 15:39, Brendan Kearney wrote:
> On 02/23/2017 09:11 AM, Kees Bakker wrote:
>> On 23-02-17 13:51, Brendan Kearney wrote:
>>> 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.
>> Both the NFS server and the client are configured as FreeIPA client.
>> On the server the users are known (through PAM, SSSD). Only user
>> "ubuntu" is a local (/etc/passwd) user. All other users are defined on
>> the IPA server.
>>
>> root at srv1:~# ls -l /home
>> total 0
>> drwxr-xr-x 1 keesb  keesb  116 jan 27 12:56 keesb
>> drwxr-xr-x 1 ubuntu ubuntu 142 aug 17  2016 ubuntu
>> root at srv1:~# ls -ln /home
>> total 0
>> drwxr-xr-x 1 60001 60001 116 jan 27 12:56 keesb
>> drwxr-xr-x 1  1000  1000 142 aug 17  2016 ubuntu
>>
>> On the client, same story
>>
>> root at client1:~# ls -l /nfshome
>> total 0
>> drwxr-xr-x 1 keesb  keesb  116 jan 27 12:56 keesb
>> drwxr-xr-x 1 ubuntu  ubuntu  142 aug 17  2016 ubuntu
>> root at client1:~# ls -ln /nfshome
>> total 0
>> drwxr-xr-x 1 60001 60001 116 jan 27 12:56 keesb
>> drwxr-xr-x 1  1000  1000 142 aug 17  2016 ubuntu
>>
>>
>>
>>>>>>>      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.
>> Let's step back a little.
>>
>> On the NFS client, the user does an ls of / (that's where the mountpoint is). At the point
>> where ls reads the entry (through stat) for "nfshome" it gets (probably) EPERM.
>> And hence ls prints all the question marks. That leads me to believe that only the kernel
>> (on the NFS client) is involved at this point. I could be wrong but I don't think there is
>> any kerberos TGT involved.
>>
>>>>>>>> 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.
>>>
>>>
> run journalctl -fl on both the NFS server and the NFS client while trying to mount the share.  one of them should tell you something.

Nothing much. On the server I just see

    feb 23 15:47:34 srv1.example.com rpc.mountd[22742]: authenticated mount request from 172.16.16.39:678 for /home (/home)

The mount succeeds. Simple as that. Mounting is not the problem, I think.



>
> the mount operation will succeed, because any ACL set in the exports file is being met.  root likley has access because the uid/gid is common and local on both devices and therefore no mapping is needed.

OK. No problem with that.

>   your virtual user does not exist in either local user store, and therefore needs to be mapped.

No, no, the virtual user is present on both sides, because both NFS server and client are configured
as IPA client. That user can login on both systems. The uid/gid mapping is straightforward.

>   what does /etc/nsswitch.conf say for passwd, shadow and group?
>

On both server and client:
passwd:         compat sss
group:          compat sss
shadow:         compat sss

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