Xenstore: Guests can create orphaned Xenstore nodes

ISSUE DESCRIPTION

By creating multiple nodes inside a transaction resulting in an error, a malicious guest can create orphaned nodes in the Xenstore data base, as the cleanup after the error will not remove all nodes already created. When the transaction is committed after this situation, nodes without a valid parent can be made permanent in the data base.

IMPACT

A malicious guest can cause inconsistencies in the xenstored data base, resulting in unusual error responses or memory leaks in xenstored. This can finally cause Denial of Service situations or long running error recoveries of xenstored.

VULNERABLE SYSTEMS

Systems with Xen version 4.9 and newer running the C variant of Xenstore (xenstored or xenstore-stubdom) are vulnerable.
Systems using the Ocaml variant of Xenstore (oxenstored) are not vulnerable.