Re: msgr2 protocol

[Gregory Farnum <gfarnum@redhat.com>]

On Thu, May 26, 2016 at 11:17 AM, Sage Weil <sweil@redhat.com> wrote:
> I wrote up a basic proposal for the new msgr2 protocol:
>
>         http://pad.ceph.com/p/msgr2
>
> It is pretty similar to the current protocol, with a few key changes:
>
> 1. The initial banner has a version number for protocl features supported
> and required.  This will allow optional behavior later.  The current
> protocol doesn't allow this (the banner string is fixed and has to match
> verbatim).
>
> 2. The auth handshake is a low-level msgr exchange now.  This more or less
> matches the MAuth and MAuthReply exchange with the mon.  Also, the
> authenticator/ticket presentation for established clients can be sent here
> as part of this exchange, instead of as part of the msg_connect and
> msg_connect_reply exchnage.
>
> 3. The identification of peers during connect is moved to the TAG_IDENT
> stage.  This way it could happen after authentication and/or encryption,
> if we like.  (Not sure it matters.)

Hmm, reading this through I'm actually confused about how we do
authentication before we identify ourselves.

Going back to the fast reconnects again (in which we allow a client to
submit all the reconnect data at once and submit a message without
waiting for a response from the server), we'd need to be able to
re-use the previous session key during the authentication phase but
for that to make any sense it would need to have supplied the
identifying cookie.

Were you thinking that with cephx, it would use the cluster key to
generate a "blind" session key, saying it's allowed to talk, and then
use that session key to do identification and share the cephx bundle?
-Greg


>
> 4. Signatures are a separate message now that follows the previous
> message.  If a message doesn't have a signature that follows, it is
> dropped.  Once authenticated we can sign all the other handshake exchanges
> (TAG_IDENT, etc.) as well as the messages themselves.
>
> 5. The reconnect behavior for stateful connections is a separate
> exchange. This keeps the stateless connections free of clutter.
>
> 6. A few changes in the auth_none and cephx integratoin will be needed.
> For example, all the current stubs assume that authentication happens over
> MAuth message and authorization happens in an authorizer blob in
> ceph_msg_connect.  Now both are part of TAG_AUTH_REQUEST, so we'll need to
> multiplex the cephx message blobs. Also, because the IDENT exchanges
> happens later, we may need to pass additional info in the auth handshake
> messages (like the peer type, or whatever else is needed).
>
> 7. Lots of messages can go either way, and I tried ot avoid a strict
> request/response model so that things could be pipelined, and we'd spend a
> minimal amount of time waiting for a response from the other end.  For
> example,
>
> C:
>  initiates connection
> S:
>  accepts connection
>  -> banner
>  -> TAG_AUTH_METHODS
> C:
>  -> banner
>  -> TAG_AUTH_SET_METHOD
>  -> TAG_AUTH_AUTH_REQUEST
> S:
>  -> TAG_AUTH_REPLY
> C:
>  -> TAG_ENCRYPT_BEGIN
>  -> TAG_IDENT
>  -> TAG_SIGNATURE
> S:
>  -> TAG_ENCRYPT_BEGIN
>  -> TAG_IDENT
>  -> TAG_SIGNATURE
> C:
>  -> TAG_START
>  -> TAG_SIGNATURE
>  -> TAG_MSG
>  -> TAG_SIGNATURE
>     ...
> S:
>  -> TAG_MSG
>  -> TAG_SIGNATURE
>     ...
>
> Comments, please!  The exhange is a bit less structured as far as who
> sends what message, with the idea that we could pipeline a lot of it, but
> it may end up being too ambiguous.  Let me know what you think...
>
> sage
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