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

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Message-ID: <20250407101352.GA10818@breakpoint.cc>
Date: Mon, 7 Apr 2025 12:13:52 +0200
From: Florian Westphal <fw@...len.de>
To: lvxiafei <xiafei_xupt@....com>
Cc: "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>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>,
	lvxiafei <lvxiafei@...setime.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org
Subject: Re: [PATCH] netfilter: netns nf_conntrack: per-netns
 net.netfilter.nf_conntrack_max sysctl

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?