Re: [PATCH nf] netfilter: restore default behavior for nf_conntrack_events

[Nicolas Dichtel <nicolas.dichtel@6wind.com>]

Le 05/06/2024 à 20:41, Pablo Neira Ayuso a écrit :
> On Wed, Jun 05, 2024 at 11:09:31AM +0200, Nicolas Dichtel wrote:
>> Le 05/06/2024 à 10:55, Florian Westphal a écrit :
>>> Nicolas Dichtel <nicolas.dichtel@6wind.com> wrote:
>>>> Since the below commit, there are regressions for legacy setups:
>>>> 1/ conntracks are created while there are no listener
>>>> 2/ a listener starts and dumps all conntracks to get the current state
>>>> 3/ conntracks deleted before the listener has started are not advertised
>>>>
>>>> This is problematic in containers, where conntracks could be created early.
>>>> This sysctl is part of unsafe sysctl and could not be changed easily in
>>>> some environments.
>>>>
>>>> Let's switch back to the legacy behavior.
>>>
>>> :-(
>>>
>>> Would it be possible to resolve this for containers by setting
>>> the container default to 1 if init_net had it changed to 1 at netns
>>> creation time?
>>
>> When we have access to the host, it is possible to allow the configuration of
>> this (unsafe) sysctl for the pod. But there are cases where we don't have access
>> to the host.
>>
>> https://docs.openshift.com/container-platform/4.9/nodes/containers/nodes-containers-sysctls.html#nodes-containers-sysctls-unsafe_nodes-containers-using
> 
> conntrack is enabled on-demand by the ruleset these days, such monitor
> process could be created _before_ the ruleset is loaded?
It's not so easy :) There are several modules in the system.

I understand it's "sad" to keep nf_conntrack_events=1, but this change breaks
the backward compatibility. A container migrated to a host with a recent kernel
is broken.
Usually, in the networking stack, sysctl are added to keep the legacy behavior
and enable new systems to use "modern" features. There are a lot of examples :)