bochs: Check extent_size header field (CVE-2014-0142) This fixes two possible division by zero crashes: In bochs_open() and in seek_to_sector(). Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>