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

[Wouter Verhelst <w@uter.be>]

On Thu, Oct 02, 2014 at 03:50:57PM +0200, Wouter Verhelst wrote:
> On Thu, Oct 02, 2014 at 01:00:04PM +0200, Paolo Bonzini wrote:
> > Il 01/10/2014 22:23, Wouter Verhelst ha scritto:
> > > Hi,
> > > 
> > > On Fri, Sep 05, 2014 at 03:26:09PM +0200, Wouter Verhelst wrote:
> > >> Tunneling the entire protocol inside an SSL connection doesn't fix that;
> > >> if an attacker is able to hijack your TCP connections and change flags,
> > >> then this attacker is also able to hijack your TCP connection and
> > >> redirect it to a decrypting/encrypting proxy.
> > >>
> > >> I agree that preventing a possible SSL downgrade attack (and other forms
> > >> of MITM) should be high on the priority list, but "tunnel the whole
> > >> thing in SSL" doesn't do that.
> > > 
> > > So, having given this some thought, I wanted to come up with a spec just
> > > so that we had something we could all agree on. As part of that, I had a
> > > look at qemu-nbd, and noticed that it uses the "oldstyle" handshake
> > > protocol (on port 10809 by default -- ew, please don't do that).
> > 
> > Can you use new-style handshake with a single unnamed export?  Export
> > names are a useless complication for qemu-nbd.
> 
> Not currently, but I don't think you need that. You could have a default
> name, which would be used if no name was otherwise specified. It's not
> much of a stretch to make that name part of the protocol spec, either.

So. I think this makes sense, and as such changed the proto.txt file as
follows:

diff --git a/doc/proto.txt b/doc/proto.txt
index e0a4fb1..990d012 100644
--- a/doc/proto.txt
+++ b/doc/proto.txt
@@ -242,10 +242,13 @@ Option types
 * NBD_OPT_EXPORT_NAME (1)
   Choose the export which the client would like to use, and end option
   haggling. Data: name of the export, free-form UTF8 text (subject to
   limitations by server implementation). If the chosen export does not
   exist, the server closes the connection.
+  A special, "empty", name (i.e., the length field is zero and no name
+  is specified), is reserved for a "default" export, to be used in cases
+  where explicitly specifying an export name makes no sense.
 
 * NBD_OPT_ABORT (2)
   Abort negotiation and close the connection. Optional.
 
 * NBD_OPT_LIST (3)

That is, specify an empty name to specify a default.

Thoughts?

-- 
It is easy to love a country that is famous for chocolate and beer

  -- Barack Obama, speaking in Brussels, Belgium, 2014-03-26