qemu -- unchecked block read/write vulnerability

Ian Jackson reports on the debian-security mailinglist:

When a block device read or write request is made by the guest,
nothing checks that the request is within the range supported by
the backend, but the code in the backend typically assumes that
the request is sensible.
Depending on the backend, this can allow the guest to read
and write arbitrary memory locations in qemu, and possibly gain
control over the qemu process, escaping from the
emulation/virtualisation.