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

The Thursday 04 Sep 2014 à 15:34:59 (+0100), Daniel P. Berrange 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. > > Why not just using a dedicated port and let the TLS handshake happen normaly ? > > The mgmt app (libvirt in this case) chooses an arbitrary port when > telling QEMU to setup NBD, so we don't need to specify any alternate > port. I'd expect that libvirt just tell QEMU to enable NBD at both > ends, and we immediately do the TLS handshake upon opening the > connection. Only once TLS is established, should the NBD protocol > start running. IOW we don't need to modify the NBD protocol at all. > > If the mgmt app tells QEMU to enable TLS at one end and not the > other, the mgmt app gets what it deserves (a failed TLS handshake). > We certainly would not want QEMU to auto-negotiate and fallback > to plain text in this case. I agree.