Re: [libvirt] [PATCH v3] nwfilter: probe for inverted ctdir
On 03/27/2013 02:01 PM, Eric Blake wrote:
On 03/27/2013 10:30 AM, Laine Stump wrote:
> My opinion is that the patch we should apply should be a simple patch
> that just removes use of --ctdir. According to the netfilter developer
> who responded to the thread on libvirt-users, it doesn't add any extra
> security not already provided by conntrack:
>
> https://www.redhat.com/archives/libvirt-users/2013-March/msg00121.html
> https://www.redhat.com/archives/libvirt-users/2013-March/msg00128.html
>
> Not being an expert on netfilter internals, I can't dispute his claim.
>
> Does anyone else have an opinion?
What filters specifically caused the use of --ctdir, and are they broken
if we omit the use of --ctdir?
It depends on how you write the filters that the --ctdir is being used.
iirc: The effect of the --ctdir usage is that if one has an incoming
rule and and outgoing rule with the same IP address on the 'other' side
the check for an ESTABLISHED state is not enough to ACCEPT the traffic,
if one was to remove one of the rules while communication in both
directions was occurring and an immediate cut of the traffic in one way
was expected. The effect so far was that if the rule for the incoming
rule was removed it would cut the incoming traffic immediately while the
traffic in outgoing direction was uninterrupted. I think that if we
remove this now the traffic in both directions will continue. I will
verify tomorrow.
I don't quite understand the skepticism towards this patch (v3) that
tries to keep what is there right now.
Stefan