Subject: Re: [PATCH 01/19] netfilter: move nf_conntrack initialize out of pernet operations

From: [email-masked] (Eric W. Biederman)
Date: Thu, 27 Dec 2012 22:00:23 -0800

canqun zhang <[email-masked]> writes:

> yes，Network namespaces in general can be cleaned up in any order，but
> when doing /etc/ini.d/iptables restart, the system need cleaning up
> all net namespace,and init_net should be cleanup lastly.init_net is
> the first namespace,other net namespace is copied for it ,and it is
> diuty for Initializing resources,so It in itself is special.

"other net namespaces is copied for it"  I don't have a clue what
you mean by that.  Every network namespace starts out in a default
state not in a copied state.

Nowhere else in the network stack does &init_net have the duty
of initializing or cleaning up resources.

That /etc/init.d/iptables restart removes modules in general is a little
dubious.  That /etc/init.d/iptables restart removes modules when there
are other existing network namespaces using those modules is down right
dangerous.  Dangerous in the anyone can ssh into the machine way.  I
suspect it has taken 5 years for this bug to show up because it is so
idiotic to remove code that someone else is using.

I won't argue that making it so that &init_net is the last network
namespace to go will solve this problem.  But I can't see how adding
the guarantee that &init_net will always be cleaned up last is a good
long term solution.

Removing the init_net special case gives a simpler mental model, and
less to learn and maintain about network namespaces.

Eric
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