Re: [Qemu-devel] [PATCH v4 4/8] nbd: Minimal structured read for server

[Eric Blake]

On 10/14/2017 08:01 PM, Eric Blake wrote:
> From: Vladimir Sementsov-Ogievskiy <address@hidden>
> 
> Minimal implementation of structured read: one structured reply chunk,
> no segmentation.
> Minimal structured error implementation: no text message.
> Support DF flag, but just ignore it, as there is no segmentation any
> way.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> Signed-off-by: Eric Blake <address@hidden>
> 

> +
> +            case NBD_OPT_STRUCTURED_REPLY:
> +                if (client->structured_reply) {
> +                    ret = nbd_negotiate_send_rep_err(
> +                        client->ioc, NBD_REP_ERR_INVALID, option, errp,
> +                        "structured reply already negotiated");
> +                } else {
> +                    ret = nbd_negotiate_send_rep(client->ioc, NBD_REP_ACK,
> +                                                 option, errp);
> +                }

Fails spectacularly if the client sent a non-zero length payload along
with the option, because we forgot to nbd_drop the payload, getting the
server out-of-sync with the client's next option request.  I'm
requesting clarification from the NBD list on how to best handle that
(presumably with NBD_REP_ERR_INVALID), and in the meantime will copy
what we do for NBD_OPT_LIST with unexpected payload.  It also made me
realize that we don't reject unexpected payload for NBD_OPT_STARTTLS; a
common helper function would make that easier, so guess what I'm adding
in v5 :)

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

signature.asc
Description: OpenPGP digital signature