linux-kernel - Re: [PATCH] netfilter: netns nf_conntrack: per-netns net.netfilter.nf_conntrack

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Message-Id: <20250408081712.54037-1-xiafei_xupt@163.com>
Date: Tue,  8 Apr 2025 16:17:12 +0800
From: lvxiafei <xiafei_xupt@....com>
To: fw@...len.de
Cc: coreteam@...filter.org,
	davem@...emloft.net,
	edumazet@...gle.com,
	horms@...nel.org,
	kadlec@...filter.org,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	lvxiafei@...setime.com,
	netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org,
	pabeni@...hat.com,
	pablo@...filter.org,
	xiafei_xupt@....com
Subject: Re: [PATCH] netfilter: netns nf_conntrack: per-netns net.netfilter.nf_conntrack_max sysctl

On Monday 2025-04-07 12:13, Florian Westphal wrote:
>lvxiafei <xiafei_xupt@....com> wrote:
>> The modification of nf_conntrack_max in one netns
>> should not affect the value in another one.
>
>nf_conntrack_max can only be changed in init_net.
>
>Given the check isn't removed:
>   /* Don't allow non-init_net ns to alter global sysctls */
>   if (!net_eq(&init_net, net)) {
>       table[NF_SYSCTL_CT_MAX].mode = 0444;
>
>... this patch seems untested?
>
>But, removing this check would allow any netns to consume
>arbitrary amount of kernel memory.
>
>How do you prevent this?

Yes, this check needs to be deleted
All netns share the original nf_conntrack_max. The nf_conntrack_max
limit does not limit the total ct_count of all netns. When it is changed
to a netns-level parameter, the default value is the same as the original
default value (=max_factor*nf_conntrack_htable_size), which is a global
(ancestral) limit, and kernel memory consumption is not affected.