From 9166869e7e6530befddfd8bb46ff37436a38efc1 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Tue, 13 Sep 2022 07:35:13 +0200
Subject: tools/xenstore: fix deleting node in transaction

In case a node has been created in a transaction and it is later
deleted in the same transaction, the transaction will be terminated
with an error.

As this error is encountered only when handling the deleted node at
transaction finalization, the transaction will have been performed
partially and without updating the accounting information. This will
enable a malicious guest to create arbitrary number of nodes.

This is part of XSA-421 / CVE-2022-42325.

Reported-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>

diff --git a/tools/xenstore/xenstored_transaction.c b/tools/xenstore/xenstored_transaction.c
index 3e3eb47326cc..7ffe21bb5285 100644
--- a/tools/xenstore/xenstored_transaction.c
+++ b/tools/xenstore/xenstored_transaction.c
@@ -418,7 +418,13 @@ static int finalize_transaction(struct connection *conn,
 						   true);
 				talloc_free(data.dptr);
 			} else {
-				ret = do_tdb_delete(conn, &key, NULL);
+				/*
+				 * A node having been created and later deleted
+				 * in this transaction will have no generation
+				 * information stored.
+				 */
+				ret = (i->generation == NO_GENERATION)
+				      ? 0 : do_tdb_delete(conn, &key, NULL);
 			}
 			if (ret)
 				goto err;