CVE request: kernel: NLM: Don't hang forever on NLM unlock requests

[Eugene Teo <eugene () redhat com>]

NLM: Don't hang forever on NLM unlock requests

If the NLM daemon is killed on the NFS server, we can currently end up
hanging forever on an 'unlock' request, instead of aborting. Basically,
if the rpcbind request fails, or the server keeps returning garbage, we
really want to quit instead of retrying.

    Tested-by: Vasily Averin <vvs () sw ru>
    Signed-off-by: Trond Myklebust <Trond.Myklebust () netapp com>
    Cc: stable () kernel org

In English, it means that a local, unprivileged user could use the flock
system call on a NFS share to cause a denial of service.

https://bugzilla.redhat.com/show_bug.cgi?id=709393
http://git.kernel.org/linus/0b760113a3a155269a3fba93a409c640031dd68f

Thanks, Eugene