Guests can trigger deadlock in Linux netback driver

ISSUE DESCRIPTION

The patch for XSA-392 introduced another issue which might result in a deadlock when trying to free the SKB of a packet dropped due to the XSA-392 handling (CVE-2022-42328).
Additionally when dropping packages for other reasons the same deadlock could occur in case of netpoll being active for the interface the xen-netback driver is connected to (CVE-2022-42329).

IMPACT

A malicious guest could cause Denial of Service (DoS) of the host via the paravirtualized network interface.

VULNERABLE SYSTEMS

All systems using the Linux kernel based network backend xen-netback are vulnerable.