Re: [libvirt-users] netfilter+libvirt=(smth got broken?)

[Eric Blake <eblake@redhat.com>]

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On 03/20/2013 08:30 PM, Pablo Neira Ayuso wrote:

>>
>> So apparently, netfilter's behaviour was indeed reversed at some
>> point, therefore libvirt stopped working properly.
> 
> --ctdir was broken and it was fixed in patch:

In other words, the kernel folks made a silent change in ABI.  Eww.

How can we reliably tell which kernels have the old behavior, and which
have the new, so that libvirt knows which sense to use?

> By looking at the changes you made:
> 
>> --A FI-vnet0 -p tcp -m tcp --sport 110 -m conntrack --ctstate
>> ESTABLISHED -m conntrack --ctdir ORIGINAL -j RETURN
>> +-A FI-vnet0 -p tcp -m tcp --sport 110 -m conntrack --ctstate
>> ESTABLISHED -m conntrack --ctdir REPLY -j RETURN
> 
> The first rule looks wrong to me indeed, traffic coming in the
> original direction will initiate the connection to destination port
> TCP/110. Therefore, your change is correct.

Correct for the new kernel interpretation, but we also want to support
use of libvirt with older kernels, preferably with a runtime check so
that a binary compiled on an older kernel will still work after a kernel
upgrade.

> 
> It's unfortunate nobody noticed this rule was incorrect so far (even
> if it was working).

It's also unfortunate that the kernel folks did a silent ABI change,
without offering any witness of which behavior is in operation.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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