CVE-2021-32845: Use of Uninitialized Resource

HyperKit is a toolkit for embedding hypervisor capabilities in an application. In versions 0.20210107 and prior of HyperKit, the implementation of `qnotify` at `pci_vtrnd_notify` fails to check the return value of `vq_getchain`. This leads to `struct iovec iov;` being uninitialized and used to read memory in `len = (int) read(sc->vrsc_fd, iov.iov_base, iov.iov_len);` when an attacker is able to make `vq_getchain` fail. This issue may lead to a guest crashing the host causing a denial of service and, under certain circumstance, memory corruption. This issue is fixed in commit 41272a980197917df8e58ff90642d14dec8fe948.