netdev - NFS mounts failing when keytab present on client

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Date:   Tue, 27 Mar 2018 23:06:14 +0100 (BST)
From:   Michael Young <m.a.young@...ham.ac.uk>
To:     Eric Biggers <ebiggers@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
cc:     "J. Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...nel.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        linux-nfs@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: NFS mounts failing when keytab present on client

NFS mounts stopped working on one of my computers after a kernel update 
from 4.15.3 to 4.15.4. I traced the problem to the commit
[46e8d06e423c4f35eac7a8b677b713b3ec9b0684] crypto: hash - prevent using 
keyed hashes without setting key
and a later kernel with this patch reverted works normally.

The problem seems to be related to kerberos as the mount fails when the 
keytab is present, but works if I rename the keytab file. This is true 
even though the mount is with sec=sys . The mount should also work with 
sec=krb5 but that also fails in the same way. When the mount fails there 
are errors in dmesg like
[ 1232.522816] gss_marshal: gss_get_mic FAILED (851968)
[ 1232.522819] RPC: couldn't encode RPC header, exit EIO
[ 1232.522856] gss_marshal: gss_get_mic FAILED (851968)
[ 1232.522857] RPC: couldn't encode RPC header, exit EIO
[ 1232.522863] NFS: nfs4_discover_server_trunking unhandled error -5. 
Exiting with error EIO
[ 1232.525039] gss_marshal: gss_get_mic FAILED (851968)
[ 1232.525042] RPC: couldn't encode RPC header, exit EIO

 	Michael Young