nfsd4: ignore WANT bits in open downgrade

commit c30e92df upstream.

We don't use WANT bits yet--and sending them can probably trigger a
BUG() further down.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/nfsd/nfs4state.c

@@ -3079,6 +3079,8 @@ nfsd4_open_downgrade(struct svc_rqst *rqstp,
 	if (!access_valid(od->od_share_access, cstate->minorversion)
 			|| !deny_valid(od->od_share_deny))
 		return nfserr_inval;
+	/* We don't yet support WANT bits: */
+	od->od_share_access &= NFS4_SHARE_ACCESS_MASK;
 
 	nfs4_lock_state();
 	if ((status = nfs4_preprocess_seqid_op(cstate,