nfsd4: disallow ALLOCATE with special stateids

nfsd4: disallow ALLOCATE with special stateids

commit 5ba4a25ab7b13be528b23f85182f4d09cf7f71ad upstream.

vfs_fallocate will hit a NULL dereference if the client tries an
ALLOCATE or DEALLOCATE with a special stateid.  Fix that.  (We also
depend on the open to have broken any conflicting leases or delegations
for us.)

(If it turns out we need to allow special stateid's then we could do a
temporary open here in the special-stateid case, as we do for read and
write.  For now I'm assuming it's not necessary.)

Fixes: 95d871f03cae "nfsd: Add ALLOCATE support"
Cc: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>