linux-kernel - Re: [PATCH v2] netfilter: Make xt_cgroup independent from net

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Message-ID: <iy3wkjdtudq4m763oji7bhj6w7bj2pdst7sbtahtwgcjrhpx6i@a4cy47mlcnqf>
Date: Mon, 24 Mar 2025 19:01:14 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Pablo Neira Ayuso <pablo@...filter.org>
Cc: netfilter-devel@...r.kernel.org, coreteam@...filter.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Jozsef Kadlecsik <kadlec@...filter.org>, "David S . Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, cgroups@...r.kernel.org, 
	Jan Engelhardt <ej@...i.de>, Florian Westphal <fw@...len.de>
Subject: Re: [PATCH v2] netfilter: Make xt_cgroup independent from net_cls

On Mon, Mar 24, 2025 at 05:49:09PM +0100, Pablo Neira Ayuso <pablo@...filter.org> wrote:
> If !CONFIG_CGROUP_NET_CLASSID, then no classid matching is possible.
> 
> So why allow a rule to match on cgroup with classid == 0?

It is conservative approach to supposed users who may have filtering
rules with classid=0 but never mkdir any net_cls group. Only those who
eventually need to mkdir would realize there's nowhere to mkdir on (with
!CONFIG_CGROUP_NET_CLASSID). Admittedly, I have no idea if this helps to
5% of net_cls users or 0.05% or 0%. Do you have any insights into that?

> Maybe simply do this instead?
> 
> static bool possible_classid(u32 classid)
> {
>        return IS_ENABLED(CONFIG_CGROUP_NET_CLASSID);
> }

Yes, if the above carefulness is unnecessary, I'd like to accompany this
with complete removal of sock_cgroup_classid() function then (to have it
compile-checked that it's really impossible to compare any classids w/o
CONFIG_CGROUP_NET_CLASSID).

Thanks,
Michal

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