Re: [patch v8 3/7] nbd: check sock index in nbd_read_stat()

Eric Blake
2021-09-22T12:12:13Z

On Wed, Sep 22, 2021 at 05:22:07PM +0800, Ming Lei wrote:
>
> I think this one relies on nbd protocol between server and client, and
> does the protocol require both request and reply xmitted via same
> socket?

Yes, a reply must be transmitted on the same socket as the request
came over. This is because independent sockets are not required to
use distinct 64-bit handles, and there is no way for a server to tell
if independent clients are related to one another; sending a reply on
the wrong socket is thus not guaranteed to reach the intended client.
Thus, a compliant server will never send a reply over a different
socket than the original request, and if a client ever gets a reply
with a handle it was not expecting, then the server is buggy or
malicious.

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