Re: [libvirt] 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: > > C: NBD_OPT_PEEK_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 > NBD_OPT_STARTTLS: > > C: NBD_OPT_STARTTLS > 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, ...)