CVE-2022-23092

The implementation of lib9p's handling of RWALK messages was missing a bounds check needed when unpacking the message contents.  The missing check means that the receipt of a specially crafted message will cause lib9p to overwrite unrelated memory.

The bug can be triggered by a malicious bhyve guest kernel to overwrite memory in the bhyve(8) process.  This could potentially lead to user-mode code execution on the host, subject to bhyve's Capsicum sandbox.