mount: use sec= that was specified on the command line

When older servers return RPC_AUTH_NULL, it means the
rpc creds will be ignored. In that case use the sec=
that was specified instead of setting sec=null

Fixes Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1112983
Signed-off-by: Steve Dickson <steved@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/super.c

@@ -1684,21 +1684,29 @@ static int nfs_verify_authflavors(struct nfs_parsed_mount_data *args,
 {
 	rpc_authflavor_t flavor = RPC_AUTH_MAXFLAVOR;
 	unsigned int i;
+	int use_auth_null = false;
 
 	/*
 	 * If the sec= mount option is used, the specified flavor or AUTH_NULL
 	 * must be in the list returned by the server.
 	 *
 	 * AUTH_NULL has a special meaning when it's in the server list - it
 	 * means that the server will ignore the rpc creds, so any flavor
-	 * can be used.
+	 * can be used but still use the sec= that was specified.
 	 */
 	for (i = 0; i < count; i++) {
 		flavor = server_authlist[i];
 
-		if (nfs_auth_info_match(&args->auth_info, flavor) ||
-		    flavor == RPC_AUTH_NULL)
+		if (nfs_auth_info_match(&args->auth_info, flavor))
 			goto out;
+
+		if (flavor == RPC_AUTH_NULL)
+			use_auth_null = true;
+	}
+
+	if (use_auth_null) {
+		flavor = RPC_AUTH_NULL;
+		goto out;
 	}
 
 	dfprintk(MOUNT,