Re: Fedora 32 rpc.gssd misbehavior

[Robbie Harwood <rharwood@redhat.com>]

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Simo Sorce <simo@redhat.com> writes:

> On Wed, 2020-07-29 at 14:27 -0400, Chuck Lever wrote:
>> > On Jul 29, 2020, at 1:19 PM, Chuck Lever <chuck.lever@oracle.com> 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@klimt.ib.1015granger.net) does not match acceptor (nfs@klimt.ib).
>> >   kernel: NFS: NFSv4 callback contains invalid cred
>> > 
>> > I boosted gssd verbosity, and it says:
>> > 
>> >   rpc.gssd[986]: doing downcall: lifetime_rec=72226 acceptor=nfs@klimt.ib
>> > 
>> > 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.

Also, please try setting `qualify_shortname = ""`.  (I did update the
config file we ship with Fedora, but upstream's default turns that on.
This is a temporary workaround while we merge something better
upstream.)

Thanks,
--Robbie

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