Multiple vulnerabilities in bhyve device models

The HDA audio device model did not check for zero-length Buffer Descriptor List (BDL) entries when starting a stream. A zero-length entry caused an out-of-bounds read or write during DMA transfer processing. BDL fields were also subject to modification by the guest after validation.

A malicious guest can crash the bhyve process or potentially execute arbitrary code in the host userspace context running the virtual machine, subject to bhyve's Capsicum sandbox.