Kerberos security flavors not tried in SETCLIENTID_CONFIRM client requests

Kerberos security flavors not tried in SETCLIENTID_CONFIRM client requests

[Jiri Horky]

Hello all,

(everything described below is from a client with 3.6.11-gentoo kernel).

When I mount a filesystem that is exported as follows:

/exports 
*(sec=krb5:krb5i:krb5p,rw,fsid=0,sync,no_subtree_check,no_root_squash,insecure,crossmnt)

without specifiying a security flavour on client, the mount will work. 
 From the tcpdump I can tell that the client tries AUTH_UNIX and 
AUTH_NULL flavours before succeeding with RPCSES_GSS. When I do a "ls" 
command in the mounted directory it works fine as well - this time 
clients uses RPCSES_GSS authentication right away.

The problems comes with "cat" command on a file, when the client calls 
SETCLIENID with AUTH_UNIX credentials and AUTH_NULL verifier, which 
successes but then call SETCLIENTID_CONFIRM again with just 
AUTH_UNIX/AUTH_NULL which results in NFS4ERR_WRONGSEC. The client tries 
to all the SETCLIENTID_CONFIRM multiple times, but it does not try 
Kerberos authentication. The WRONGSEC error is then propagated as EIO to 
the application.

I noticed patches from Chuck Level on 03/16/2013 which fix problems with 
security flavours handling but I am not sure whether they are supposed 
to fix thix particular problem as well. It would take me considerable 
amount of time to test it so I would appreciate if you could comment on 
that.

Regards
Jiri Horky

Re: Kerberos security flavors not tried in SETCLIENTID_CONFIRM client requests

[Myklebust, Trond]

On Thu, 2013-04-25 at 14:38 +0200, Jiri Horky wrote:
> Hello all,
> 
> (everything described below is from a client with 3.6.11-gentoo kernel).
> 
> When I mount a filesystem that is exported as follows:
> 
> /exports 
> *(sec=krb5:krb5i:krb5p,rw,fsid=0,sync,no_subtree_check,no_root_squash,insecure,crossmnt)
> 
> without specifiying a security flavour on client, the mount will work. 
>  From the tcpdump I can tell that the client tries AUTH_UNIX and 
> AUTH_NULL flavours before succeeding with RPCSES_GSS. When I do a "ls" 
> command in the mounted directory it works fine as well - this time 
> clients uses RPCSES_GSS authentication right away.
> 
> The problems comes with "cat" command on a file, when the client calls 
> SETCLIENID with AUTH_UNIX credentials and AUTH_NULL verifier, which 
> successes but then call SETCLIENTID_CONFIRM again with just 
> AUTH_UNIX/AUTH_NULL which results in NFS4ERR_WRONGSEC. The client tries 
> to all the SETCLIENTID_CONFIRM multiple times, but it does not try 
> Kerberos authentication. The WRONGSEC error is then propagated as EIO to 
> the application.
> 
> I noticed patches from Chuck Level on 03/16/2013 which fix problems with 
> security flavours handling but I am not sure whether they are supposed 
> to fix thix particular problem as well. It would take me considerable 
> amount of time to test it so I would appreciate if you could comment on 
> that.

That's not a client problem. You have a buggy server: NFS4ERR_WRONGSEC
is not listed as a valid error for SETCLIENTID or for
SETCLIENTID_CONFIRM in either RFC3530 or RFC3530bis.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com