SUNRPC: Don't recognize RPC_AUTH_MAXFLAVOR

RPC_AUTH_MAXFLAVOR is an invalid flavor, on purpose.  Don't allow
any processing whatsoever if a caller passes it to rpcauth_create()
or rpcauth_get_gssinfo().
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/auth.c

@@ -82,7 +82,7 @@ MODULE_PARM_DESC(auth_hashtable_size, "RPC credential cache hashtable size");
 
 static u32
 pseudoflavor_to_flavor(u32 flavor) {
-	if (flavor >= RPC_AUTH_MAXFLAVOR)
+	if (flavor > RPC_AUTH_MAXFLAVOR)
 		return RPC_AUTH_GSS;
 	return flavor;
 }
@@ -173,6 +173,9 @@ rpcauth_get_gssinfo(rpc_authflavor_t pseudoflavor, struct rpcsec_gss_info *info)
 	const struct rpc_authops *ops;
 	int result;
 
+	if (flavor >= RPC_AUTH_MAXFLAVOR)
+		return -EINVAL;
+
 	ops = auth_flavors[flavor];
 	if (ops == NULL)
 		request_module("rpc-auth-%u", flavor);