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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


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