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Re: [libvirt] Implementing VNC per VM access control lists



On 12/29/2010 11:45 AM, Neil Wilson wrote:
Hi,

At the moment SASL VNC authentication in libvirt allows any of the
userids to access any of the VNC consoles on a particular libvirt host.
There is a section in the qemu_command code marked "TODO: Support ACLs
later" and we would really like the ability to have per VM user
authorization to the VNC console from within libvirt.

Essentially the people who are accessing the VNC consoles are not
administrators and have no access to the Host server - so these ACLs
need to be completely based on a separate list of userids to any access
mechanism for the libvirtd itself.

Given that the VNC restrictions are enforced within qemu from the
monitor system, I'm presuming the authorization list is going to have to
be passed in via XML and be capable of being updated throughout the life
of a VM session. Unless there's another way of doing it...

What's the feeling about how this feature should be provided within
libvirt? 

One issue is probably around migration and the server (qemu-referenced) x509 certificates. If the certificates are embedded (rather than referenced) in the domain XML they will automatically migrate when the VM migrates, which is desirable. Otherwise migration becomes (again) problematic and layers above libvirt would have to take care of their migration.

The VNC session will still be lost due to the change of host and thus the IP address and the client user will need to learn about the new VNC port as well. 

Quoting from Qemu documentation webpage:

http://wiki.qemu.org/download/qemu-doc.html#vnc_005fsecurity

<quote>

3.10.3 With x509 certificates

The QEMU VNC server also implements the VeNCrypt extension allowing use of TLS for encryption of the session, and x509 certificates for authentication. The use of x509 certificates is strongly recommended, because TLS on its own is susceptible to man-in-the-middle attacks. Basic x509 certificate support provides a secure session, but no authentication. This allows any client to connect, and provides an encrypted session.

qemu [...OPTIONS...] -vnc :1,tls,x509=/etc/pki/qemu -monitor stdio

In the above example /etc/pki/qemu should contain at least three files, ca-cert.pem, server-cert.pem and server-key.pem. Unprivileged users will want to use a private directory, for example $HOME/.pki/qemu. NB the server-key.pem file should be protected with file mode 0600 to only be readable by the user owning it.

</quote>


It looks like the above mentioned 3 files would need to be embedded...

   Stefan



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