[libvirt] [Qemu-devel] [RFC 0/5] block: File descriptor passing using -open-hook-fd

[Eric Blake]

On 05/01/2012 03:53 PM, Anthony Liguori wrote:

>> I think (correct me if I'm wrong) libvirt should be aware of any file
>> that qemu
>> asks it to open. So from a security point of view, libvirt can prevent
>> opening a
>> file if it isn't affiliated with the guest.
> 
> Right, libvirt can maintain a whitelist of files QEMU is allowed to open
> (which is already has because it needs to label these files).

Indeed.

>  The only
> complexity is that it's not a straight strcmp().  The path needs to be
> (carefully) broken into components with '.' and '..' handled
> appropriately.  But this shouldn't be that difficult to do.

Libvirt would probably canonicalize path names, both when sticking them
in the whitelist, and in validating the requests from qemu - agreed that
it's not difficult.

More importantly, libvirt needs to start tracking the backing chain of
any qcow2 or qed file as part of the domain XML; and operations like
'block-stream' would update not only the chain, but also the whitelist.
 In the drive-reopen case, this means that libvirt would have to be
careful when to change labeling - provide access to the new files before
drive-reopen, then revoke access to files after drive-reopen completes.
 In other words, having the -open-hook-fd client pass a command to
libvirt at the time it is closing an fd would help libvirt know when
qemu has quit using a file, which might make it easier to revoke SELinux
labels at that time.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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