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Re: [Nbd] spec, RFC: TLS support for NBD

On Sat, Oct 18, 2014 at 12:03:23AM +0200, Wouter Verhelst wrote:
> Hi all,
> (added rjones from nbdkit fame -- hi there)

[I'm happy to implement whatever you come up with, but I've added
Florian Weimer to CC who is part of Red Hat's product security group]

> So I think the following would make sense to allow TLS in NBD.
> This would extend the newstyle negotiation by adding two options (i.e.,
> client requests), one server reply, and one server error as well as
> extend one existing reply, in the following manner:
> - The two new commands are NBD_OPT_PEEK_EXPORT and NBD_OPT_STARTTLS. The
>   former would be used to verify if the server will do TLS for a given
>   export:
>   S: NBD_REP_SERVER, with an extra field after the export name
>      containing flags that describe the export (R/O vs R/W state,
>      whether TLS is allowed and/or required).
>   If the server indicates that TLS is allowed, the client may now issue
>   S: NBD_REP_STARTTLS # or NBD_REP_ERR_POLICY, if unwilling
>   C: <initiate TLS handshake>
>   Once the TLS handshake has completed, negotiation should continue over
>   the secure channel. The client should initiate that by sending an
>   NBD_OPT_* message.
> - The server may reply to any and all negotiation request with
>   NBD_REP_ERR_TLS_REQD if it does not want to do anything without TLS.
>   However, if at least one export is supported without encryption, the
>   server must not in any case use this reply.
> There is no command to "exit" TLS again. I don't think that makes sense,
> but I could be persuaded otherwise with sound technical arguments.
> Thoughts?
> (full spec (with numbers etc) exists as an (uncommitted) diff to
> doc/proto.txt on my laptop, ...)
> -- 
> It is easy to love a country that is famous for chocolate and beer
>   -- Barack Obama, speaking in Brussels, Belgium, 2014-03-26

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