Re: [Qemu-devel] NBD TLS support in QEMU

[Benoît Canet]

The Friday 05 Sep 2014 à 00:07:04 (+0200), Wouter Verhelst wrote :
> On Thu, Sep 04, 2014 at 04:19:17PM +0200, Benoît Canet wrote:
> > The Wednesday 03 Sep 2014 à 17:44:17 (+0100), Stefan Hajnoczi wrote :
> > > Hi,
> > > QEMU offers both NBD client and server functionality.  The NBD protocol
> > > runs unencrypted, which is a problem when the client and server
> > > communicate over an untrusted network.
> > > 
> > > The particular use case that prompted this mail is storage migration in
> > > OpenStack.  The goal is to encrypt the NBD connection between source and
> > > destination hosts during storage migration.
> > 
> > I agree this would be usefull.
> > 
> > > 
> > > I think we can integrate TLS into the NBD protocol as an optional flag.
> > > A quick web search does not reveal existing open source SSL/TLS NBD
> > > implementations.  I do see a VMware NBDSSL protocol but there is no
> > > specification so I guess it is proprietary.
> > > 
> > > The NBD protocol starts with a negotiation phase.  This would be the
> > > appropriate place to indicate that TLS will be used.  After client and
> > > server complete TLS setup the connection can continue as normal.
> > 
> > Prenegociating TLS look like we will accidentaly introduce some security 
> > hole.

I was thinking of the fallback to cleartext case.

As a regular developper I am afraid of doing something creative with
cryptography.

> 
> Can you elaborate on that? How would it be a security hole?
> 
> > Why not just using a dedicated port and let the TLS handshake happen 
> > normaly ?
> 
> Because STARTTLS(-like) protocols are much cleaner; no need to open two
> firewall ports. Also, when I made the request for a port number at IANA,
> I was told I wouldn't get another port for a "secure" variant -- which
> makes sense. As such, if the reference implementation is ever going to
> support TLS, it has to be in a way where it is negotiated at setup time.
> 
> SMTP can do this safely. So can LDAP. I'm sure we can come up with a
> safe way of negotiating TLS.
> 
> If you want to disallow nonencrypted communication, I'm sure it can be
> made possible to require TLS for (some of) your exports.
> 
> (my objections on userspace/kernelspace issues still stand, however)
> 
> -- 
> It is easy to love a country that is famous for chocolate and beer
> 
>   -- Barack Obama, speaking in Brussels, Belgium, 2014-03-26
>