On Fri, Sep 05, 2014 at 12:02:18AM +0200, Wouter Verhelst wrote: > [Cc: to nbd-general list added] > > On Wed, Sep 03, 2014 at 05:44:17PM +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've never given encrypted NBD high priority, since I don't think > encryption without authentication serves much purpose -- and I haven't > gotten around to adding authentication yet (for which I have plans; but > other things have priority).
While have an authentication layer like SASL wired into the NBD protocol would be nice, it shouldn't be considered a blocker / pre-requisite. It is pretty straightforward for the server to require x509 certificates from the client and validate those as a means of authentication. We've used that as an authentication mechanism in libvirt and VNC with success, though we did later add SASL integration as an option too. > > 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. > > > > Besides QEMU, the userspace NBD tools (http://nbd.sf.net/) can also be > > extended to support TLS. In this case the kernel needs a localhost > > socket and userspace handles TLS. > > That introduces a possibility for a deadlock, since now your network > socket isn't on the PF_MEMALLOC-protected socket anymore, which will > cause the kernel to throw away packets which are needed for your nbd > connection, in hopes of clearing some memory. > > I suppose you could theoretically do the encryption in kernel space. > Not convinced that trying TLS in kernel space is a good idea, though. > > I have heard of people using stunnel or the likes to pipe the NBD > protocol over a secure channel, with various levels of success. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
