NFSD: Fix CB_GETATTR status fix

Jeff says:

Now that I look, 1b3e26a is wrong. The patch on the ml was correct, but
the one that got committed is different. It should be:

    status = decode_cb_op_status(xdr, OP_CB_GETATTR, &cb->cb_status);
    if (unlikely(status || cb->cb_status))

If "status" is non-zero, decoding failed (usu. BADXDR), but we also want to
bail out and not decode the rest of the call if the decoded cb_status is
non-zero. That's not happening here, cb_seq_status has already been checked and
is non-zero, so this ends up trying to decode the rest of the CB_GETATTR reply
when it doesn't exist.

Reported-by: Jeff Layton <jlayton@kernel.org>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219737
Fixes: 1b3e26a ("NFSD: fix decoding in nfs4_xdr_dec_cb_getattr")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: chucklever

fs/nfsd/nfs4callback.c

@@ -679,7 +679,7 @@ static int nfs4_xdr_dec_cb_getattr(struct rpc_rqst *rqstp,
 		return status;
 
 	status = decode_cb_op_status(xdr, OP_CB_GETATTR, &cb->cb_status);
-	if (unlikely(status || cb->cb_seq_status))
+	if (unlikely(status || cb->cb_status))
 		return status;
 	if (xdr_stream_decode_uint32_array(xdr, bitmap, 3) < 0)
 		return -NFSERR_BAD_XDR;