NFSv4.0 fix client reference leak in callback

If there is an error during processing of a callback message, it leads
to refrence leak on the client structure and eventually an unclean
superblock.
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/callback_xdr.c

@@ -883,16 +883,21 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp)
 
 	if (hdr_arg.minorversion == 0) {
 		cps.clp = nfs4_find_client_ident(SVC_NET(rqstp), hdr_arg.cb_ident);
-		if (!cps.clp || !check_gss_callback_principal(cps.clp, rqstp))
+		if (!cps.clp || !check_gss_callback_principal(cps.clp, rqstp)) {
+			if (cps.clp)
+				nfs_put_client(cps.clp);
 			goto out_invalidcred;
+		}
 	}
 
 	cps.minorversion = hdr_arg.minorversion;
 	hdr_res.taglen = hdr_arg.taglen;
 	hdr_res.tag = hdr_arg.tag;
-	if (encode_compound_hdr_res(&xdr_out, &hdr_res) != 0)
+	if (encode_compound_hdr_res(&xdr_out, &hdr_res) != 0) {
+		if (cps.clp)
+			nfs_put_client(cps.clp);
 		return rpc_system_err;
-
+	}
 	while (status == 0 && nops != hdr_arg.nops) {
 		status = process_op(nops, rqstp, &xdr_in,
 				    rqstp->rq_argp, &xdr_out, rqstp->rq_resp,