Stefano Stabellini writes ("[PATCH v2 for-4.6] libxl: handle read-only drives
with qemu-xen"):
> The current libxl code doesn't deal with read-only drives at all.
>
> Upstream QEMU and qemu-xen only support read-only cdrom drives: make
> sure to specify "readonly=on" for cdrom drives and return error in case
> the user requested a non-cdrom read-only drive.
Acked-by: Ian Jackson <ian.jack...@eu.citrix.com>
I have determined by experiment that cdroms are always marked
readonly. My qemu-dm opened a test iso, which I had expressed to be
passed as a cdrom, readonly.
So maybe the guest would be able to get qemu to write to it, but this
would just result in errors (or maybe a crash somewhere in qemu). I
was not able to easily persuade Linux to write to the cdrom device.
> - (gc,
> "if=ide,index=%d,media=cdrom,cache=writeback,id=ide-%i",
> - disk, dev_number);
> + (gc,
> "if=ide,index=%d,readonly=%s,media=cdrom,cache=writeback,id=ide-%i",
> + disk, disks[i].readwrite ? "off" : "on",
> dev_number);
I don't know what the effect of this would be on qemu iff
readwrite==0. I think it might be ineffective. But that is certainly
not a security problem.
I have just sent a draft of the advisory.
Ian.
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