Re: [PATCH] netfilter: netns nf_conntrack: per-netns net.netfilter.nf_conntrack_max sysctl

lvxiafei
2025-04-08T08:17:57Z

On Monday 2025-04-07 12:13, Florian Westphal wrote:
>lvxiafei <xiafei_xupt@163.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.