diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 0a2474542309..acbe461e03ae 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -212,6 +212,25 @@ static char *savemem(struct nfsd4_compoundargs *argp, __be32 *p, int nbytes)
  * NFSv4 basic data type decoders
  */
 
+/*
+ * This helper handles variable-length opaques which belong to protocol
+ * elements that this implementation does not support.
+ */
+static __be32
+nfsd4_decode_ignored_string(struct nfsd4_compoundargs *argp, u32 maxlen)
+{
+	u32 len;
+
+	if (xdr_stream_decode_u32(argp->xdr, &len) < 0)
+		return nfserr_bad_xdr;
+	if (maxlen && len > maxlen)
+		return nfserr_bad_xdr;
+	if (!xdr_inline_decode(argp->xdr, len))
+		return nfserr_bad_xdr;
+
+	return nfs_ok;
+}
+
 static __be32
 nfsd4_decode_opaque(struct nfsd4_compoundargs *argp, struct xdr_netobj *o)
 {
@@ -645,87 +664,117 @@ nfsd4_decode_state_owner4(struct nfsd4_compoundargs *argp,
 	return nfsd4_decode_opaque(argp, owner);
 }
 
-static __be32 nfsd4_decode_cb_sec(struct nfsd4_compoundargs *argp, struct nfsd4_cb_sec *cbs)
+/* Defined in Appendix A of RFC 5531 */
+static __be32
+nfsd4_decode_authsys_parms(struct nfsd4_compoundargs *argp,
+			   struct nfsd4_cb_sec *cbs)
 {
-	DECODE_HEAD;
-	struct user_namespace *userns = nfsd_user_namespace(argp->rqstp);
-	u32 dummy, uid, gid;
-	char *machine_name;
-	int i;
-	int nr_secflavs;
+	u32 stamp, gidcount, uid, gid;
+	__be32 *p, status;
+
+	if (xdr_stream_decode_u32(argp->xdr, &stamp) < 0)
+		return nfserr_bad_xdr;
+	/* machine name */
+	status = nfsd4_decode_ignored_string(argp, 255);
+	if (status)
+		return status;
+	if (xdr_stream_decode_u32(argp->xdr, &uid) < 0)
+		return nfserr_bad_xdr;
+	if (xdr_stream_decode_u32(argp->xdr, &gid) < 0)
+		return nfserr_bad_xdr;
+	if (xdr_stream_decode_u32(argp->xdr, &gidcount) < 0)
+		return nfserr_bad_xdr;
+	if (gidcount > 16)
+		return nfserr_bad_xdr;
+	p = xdr_inline_decode(argp->xdr, gidcount << 2);
+	if (!p)
+		return nfserr_bad_xdr;
+	if (cbs->flavor == (u32)(-1)) {
+		struct user_namespace *userns = nfsd_user_namespace(argp->rqstp);
+
+		kuid_t kuid = make_kuid(userns, uid);
+		kgid_t kgid = make_kgid(userns, gid);
+		if (uid_valid(kuid) && gid_valid(kgid)) {
+			cbs->uid = kuid;
+			cbs->gid = kgid;
+			cbs->flavor = RPC_AUTH_UNIX;
+		} else {
+			dprintk("RPC_AUTH_UNIX with invalid uid or gid, ignoring!\n");
+		}
+	}
+
+	return nfs_ok;
+}
+
+static __be32
+nfsd4_decode_gss_cb_handles4(struct nfsd4_compoundargs *argp,
+			     struct nfsd4_cb_sec *cbs)
+{
+	__be32 status;
+	u32 service;
+
+	dprintk("RPC_AUTH_GSS callback secflavor not supported!\n");
+
+	if (xdr_stream_decode_u32(argp->xdr, &service) < 0)
+		return nfserr_bad_xdr;
+	if (service < RPC_GSS_SVC_NONE || service > RPC_GSS_SVC_PRIVACY)
+		return nfserr_bad_xdr;
+	/* gcbp_handle_from_server */
+	status = nfsd4_decode_ignored_string(argp, 0);
+	if (status)
+		return status;
+	/* gcbp_handle_from_client */
+	status = nfsd4_decode_ignored_string(argp, 0);
+	if (status)
+		return status;
+
+	return nfs_ok;
+}
+
+/* a counted array of callback_sec_parms4 items */
+static __be32
+nfsd4_decode_cb_sec(struct nfsd4_compoundargs *argp, struct nfsd4_cb_sec *cbs)
+{
+	u32 i, secflavor, nr_secflavs;
+	__be32 status;
 
 	/* callback_sec_params4 */
-	READ_BUF(4);
-	nr_secflavs = be32_to_cpup(p++);
+	if (xdr_stream_decode_u32(argp->xdr, &nr_secflavs) < 0)
+		return nfserr_bad_xdr;
 	if (nr_secflavs)
 		cbs->flavor = (u32)(-1);
 	else
 		/* Is this legal? Be generous, take it to mean AUTH_NONE: */
 		cbs->flavor = 0;
+
 	for (i = 0; i < nr_secflavs; ++i) {
-		READ_BUF(4);
-		dummy = be32_to_cpup(p++);
-		switch (dummy) {
+		if (xdr_stream_decode_u32(argp->xdr, &secflavor) < 0)
+			return nfserr_bad_xdr;
+		switch (secflavor) {
 		case RPC_AUTH_NULL:
-			/* Nothing to read */
+			/* void */
 			if (cbs->flavor == (u32)(-1))
 				cbs->flavor = RPC_AUTH_NULL;
 			break;
 		case RPC_AUTH_UNIX:
-			READ_BUF(8);
-			/* stamp */
-			dummy = be32_to_cpup(p++);
-
-			/* machine name */
-			dummy = be32_to_cpup(p++);
-			READ_BUF(dummy);
-			SAVEMEM(machine_name, dummy);
-
-			/* uid, gid */
-			READ_BUF(8);
-			uid = be32_to_cpup(p++);
-			gid = be32_to_cpup(p++);
-
-			/* more gids */
-			READ_BUF(4);
-			dummy = be32_to_cpup(p++);
-			READ_BUF(dummy * 4);
-			if (cbs->flavor == (u32)(-1)) {
-				kuid_t kuid = make_kuid(userns, uid);
-				kgid_t kgid = make_kgid(userns, gid);
-				if (uid_valid(kuid) && gid_valid(kgid)) {
-					cbs->uid = kuid;
-					cbs->gid = kgid;
-					cbs->flavor = RPC_AUTH_UNIX;
-				} else {
-					dprintk("RPC_AUTH_UNIX with invalid"
-						"uid or gid ignoring!\n");
-				}
-			}
+			status = nfsd4_decode_authsys_parms(argp, cbs);
+			if (status)
+				return status;
 			break;
 		case RPC_AUTH_GSS:
-			dprintk("RPC_AUTH_GSS callback secflavor "
-				"not supported!\n");
-			READ_BUF(8);
-			/* gcbp_service */
-			dummy = be32_to_cpup(p++);
-			/* gcbp_handle_from_server */
-			dummy = be32_to_cpup(p++);
-			READ_BUF(dummy);
-			p += XDR_QUADLEN(dummy);
-			/* gcbp_handle_from_client */
-			READ_BUF(4);
-			dummy = be32_to_cpup(p++);
-			READ_BUF(dummy);
+			status = nfsd4_decode_gss_cb_handles4(argp, cbs);
+			if (status)
+				return status;
 			break;
 		default:
-			dprintk("Illegal callback secflavor\n");
 			return nfserr_inval;
 		}
 	}
-	DECODE_TAIL;
+
+	return nfs_ok;
 }
 
+
 /*
  * NFSv4 operation argument decoders
  */
