Re: Fedora 32 rpc.gssd misbehavior

[Chuck Lever <chuck.lever@oracle.com>]

> On Jul 30, 2020, at 1:57 PM, Simo Sorce <simo@redhat.com> wrote:
> 
> On Thu, 2020-07-30 at 13:09 -0400, Chuck Lever wrote:
>>> On Jul 30, 2020, at 12:14 PM, Simo Sorce <simo@redhat.com> 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@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.
>> 
>> 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@klimt.ib.1015granger.net
> 
> Chuck,
> can you tell what does klimt.ib.1015granger.net resolve to (A names
> CNAMEs, not really interested in IP address)?

[root@manet ~]# dig klimt.ib.1015granger.net

; <<>> DiG 9.11.20-RedHat-9.11.20-1.fc32 <<>> klimt.ib.1015granger.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55806
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 0a7a07d8b06eedeab886314f5f230a8c6f752fe4a24c2f97 (good)
;; QUESTION SECTION:
;klimt.ib.1015granger.net.	IN	A

;; ANSWER SECTION:
klimt.ib.1015granger.net. 10800	IN	A	192.168.2.55

;; AUTHORITY SECTION:
ib.1015granger.net.	10800	IN	NS	gateway.1015granger.net.

;; ADDITIONAL SECTION:
gateway.1015granger.net. 10800	IN	A	192.168.1.1

;; Query time: 0 msec
;; SERVER: 192.168.1.1#53(192.168.1.1)
;; WHEN: Thu Jul 30 13:59:40 EDT 2020
;; MSG SIZE  rcvd: 135

[root@manet ~]#


> Also what ticket do you ultimately get in the ccache when this request
> is made ?

I'm not exactly sure what you're asking, but:

[root@manet ~]# klist FILE:/tmp/krb5ccmachine_1015GRANGER.NET
Ticket cache: FILE:/tmp/krb5ccmachine_1015GRANGER.NET
Default principal: host/manet.1015granger.net@1015GRANGER.NET

Valid starting       Expires              Service principal
07/30/2020 13:45:38  07/31/2020 13:45:38  krbtgt/1015GRANGER.NET@1015GRANGER.NET
	renew until 08/06/2020 13:45:38
[root@manet ~]#


--
Chuck Lever