> On Jul 30, 2020, at 12:14 PM, Simo Sorce <simo@xxxxxxxxxx> wrote:
>
> On Wed, 2020-07-29 at 14:27 -0400, Chuck Lever wrote:
>>> On Jul 29, 2020, at 1:19 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>>
>>> Hi!
>>>
>>> I recently updated my test systems from EL7 to Fedora 32, and
>>> NFSv4.0 with Kerberos has stopped working.
>>>
>>> I mount with "klimt.ib" as before. The client workload stops
>>> dead when the server tries to perform its first CB_RECALL.
>>>
>>> I added some client instrumentation:
>>>
>>> kernel: NFSv4: Callback principal (nfs@xxxxxxxxxxxxxxxxxxxxxxxx) does not match acceptor (nfs@xxxxxxxx).
>>> kernel: NFS: NFSv4 callback contains invalid cred
>>>
>>> I boosted gssd verbosity, and it says:
>>>
>>> rpc.gssd[986]: doing downcall: lifetime_rec=72226 acceptor=nfs@xxxxxxxx
>>>
>>> But it knows the full hostname for the server:
>>>
>>> rpc.gssd[986]: Full hostname for 'klimt.ib' is 'klimt.ib.1015granger.net'
>>>
>>>
>>> The acceptor appears to come from the Kerberos library. Shouldn't
>>> it be canonicalized? If so, should the Kerberos library do it, or
>>> should gssd? Since this behavior appeared after an upgrade, I
>>> suspect a Kerberos library regression. But it could be config-
>>> related, since both systems were re-imaged from the ground up.
>>>
>>> Also noticing some other problems on the server (missing hostname
>>> strings in debug messages, sssd_kcm infinite loops, and gssd
>>> sending garbage to the client after the NULL request that
>>> establishes the callback context).
>>>
>>> But let's look at the client acceptor problem first.
>>
>> I believe I found the problem.
>>
>> 8bffe8c5ec1a ("gssd: add /etc/nfs.conf support") added a number of gssd config
>> options to /etc/nfs.conf, including "avoid-dns". The default setting of avoid-
>> dns is 1. When I set this option on my client system explicitly to 0, NFSv4.0
>> with Kerberos works again.
>>
>> Is there a reason the default setting is 1?
>>
>
> Now that you mention DNS, this may be an interaction between a new
> default in Fedora 32 and how your environment is setup re DNS.
>
> In F32 we changed the option dns_canonicalize_hostname from 'true' to
> 'fallback'.
> This is a transitional state to eventually move it to 'false' at some
> point in the future.
>
> What it changes in practice is that it will first try the name passed
> in *as is* and only as a fallback try a CNAME if the name passed is not
> resolved as an A name. If you have principals in the KDC for both
> names, but you do not have keys in the keytab for both, you can have
> transitional issues.
>
> Additionally we discovered a bug that causes non qualified names to
> fail resolution with the 'fallback' option.
> If your name in the principal is really not qualified it will try to
> qualify it anyway, so if your principal is literally nfs/foo@FOO
> libgssapi may try to use nfs/foo.my.domdain@FOO, where "my.domain" is
> what is defined in resolv.conf search path.
>
> We are trying to address this regression.
>
> So try to set dns_canonicalize_hostname to true to see if that may
> influence your issue. If so, please let me know, as we still need to
> address this where possible.
I set avoid-dns to 1 and dns_canonicalize_hostname to true. The
workload hang is not reproducible, and the acceptor is fully qualified.
rpc.gssd[965]: doing downcall: lifetime_rec=86338 acceptor=nfs@xxxxxxxxxxxxxxxxxxxxxxxx
--
Chuck Lever
