Re: [Qemu-devel] [PATCH 3/3] ui: fix VNC websockets TLS integration

[Daniel P. Berrange]

On Mon, Mar 16, 2015 at 01:17:16PM +0000, Alex Bennée wrote:
> 
> Daniel P. Berrange <address@hidden> writes:
> 
> > The way the websockets TLS code was integrated into the VNC server
> > made it insecure and essentially useless. The only time that the
> > websockets TLS support could be used is if the primary VNC server
> <snip>
> >
> > With this patch applied a number of things change
> >
> >  - TLS is not activated for websockets unless the 'tls' flag is
> >    actually given.
> >  - Non-TLS websockets connections are dropped if TLS is active
> >  - The client certificate is validated after handshake completes
> >    if the 'x509verify' flag is given
> >  - Separate VNC auth scheme is tracked for websockets server,
> >    since it makes no sense to try to use VeNCrypt over a TLS
> >    enabled websockets connection.
> >  - The separate "VncDisplayTLS ws_tls" field is dropped, since
> >    the auth setup ensures we can never have multiple TLS sessions.
> 
> I wonder if the mechanical changes to the tls field could be separated
> from the logic changes to the handling of authentication and certificate
> checking?

They are rather intertwined, because the need for this duplicated
TLS field was a result of the way auth was mishandled. So cleaning
up one implies cleaning up the other & vica-verca.

> > @@ -422,13 +417,6 @@ void vnc_tls_client_cleanup(struct VncState *vs)
> >          vs->tls.session = NULL;
> >      }
> >      g_free(vs->tls.dname);
> > -#ifdef CONFIG_VNC_WS
> > -    if (vs->ws_tls.session) {
> > -        gnutls_deinit(vs->ws_tls.session);
> > -        vs->ws_tls.session = NULL;
> > -    }
> > -    g_free(vs->ws_tls.dname);
> > -#endif /* CONFIG_VNC_WS */
> 
> I get we have added a bunch of exit cases earlier on that clean-up but
> what happens when we do a clean shutdown? Have we just leaked?

We deleted the vs->ws_tls field from the struct entirely, so there's
never any data to be leaked here.

> Perhaps the tls.session cleanup code should be in a shared function?

This is patch is a precursor to a major refactoring & cleanup of
the TLS code which will reduce code duplication significantly

   https://github.com/berrange/qemu/commits/qemu-io-channel-4

Regards,
Daniel
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