CVE-2019-6974

En el kernel de Linux en versiones anteriores a la 4.20.8, kvm_ioctl_create_device en virt/kvm/kvm_main.c gestiona de manera incorrecta el conteo de referencias debido a una condición de carrera, lo que conduce a un uso de memoria previamente liberada.

A use-after-free vulnerability was found in the way the Linux kernel's KVM hypervisor implements its device control API. While creating a device via kvm_ioctl_create_device(), the device holds a reference to a VM object, later this reference is transferred to the caller's file descriptor table. If such file descriptor was to be closed, reference count to the VM object could become zero, potentially leading to a use-after-free issue. A user/process could use this flaw to crash the guest VM resulting in a denial of service issue or, potentially, gain privileged access to a system.

Linux kvm_ioctl_create_device() installs fd before taking reference.