Qemu-kvm: 'qemu-img info' leads to host file read/write

A flaw was found in the QEMU disk image utility (qemu-img) 'info' command. A specially crafted image file containing a `json:{}` value describing block devices in QMP could cause the qemu-img process on the host to consume large amounts of memory or CPU time, leading to denial of service or read/write to an existing external file.