Re: [PATCH V5] netfilter: netns nf_conntrack: per-netns net.netfilter.nf_conntrack_max sysctl

Florian Westphal
2025-04-13T09:08:22Z

lvxiafei <xiafei_xupt@163.com> wrote:
> + Maximum number of allowed connection tracking entries per netns. This value
> + is set to nf_conntrack_buckets by default.
> +
> + Note that connection tracking entries are added to the table twice -- once
> + for the original direction and once for the reply direction (i.e., with
> + the reversed address). This means that with default settings a maxed-out
> + table will have a average hash chain length of 2, not 1.
> +
> + The limit of other netns cannot be greater than init_net netns.
> + +----------------+-------------+----------------+
> + | init_net netns | other netns | limit behavior |
> + +----------------+-------------+----------------+
> + | 0 | 0 | unlimited |
> + +----------------+-------------+----------------+
> + | 0 | not 0 | other |
> + +----------------+-------------+----------------+
> + | not 0 | 0 | init_net |
> + +----------------+-------------+----------------+
> + | not 0 | not 0 | min |
> + +----------------+-------------+----------------+
>
> nf_conntrack_tcp_be_liberal - BOOLEAN
> - 0 - disabled (default)
> diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
> index 3f02a45773e8..062e67b9a5d7 100644
> --- a/include/net/netfilter/nf_conntrack.h
> +++ b/include/net/netfilter/nf_conntrack.h
> @@ -320,7 +320,6 @@ int nf_conntrack_hash_resize(unsigned int hashsize);
> extern struct hlist_nulls_head *nf_conntrack_hash;
> extern unsigned int nf_conntrack_htable_size;
> extern seqcount_spinlock_t nf_conntrack_generation;
> -extern unsigned int nf_conntrack_max;
>
> /* must be called with rcu read lock held */
> static inline void
> @@ -360,6 +359,13 @@ static inline struct nf_conntrack_net *nf_ct_pernet(const struct net *net)
> return net_generic(net, nf_conntrack_net_id);
> }
>
> +static inline unsigned int nf_conntrack_max(const struct net *net)
> +{
> + return likely(init_net.ct.sysctl_max && net->ct.sysctl_max) ?
> + min(init_net.ct.sysctl_max, net->ct.sysctl_max) :
> + max(init_net.ct.sysctl_max, net->ct.sysctl_max);
> +}

Is there a reason you did not follow my suggstion in
https://lore.kernel.org/netdev/20250410105352.GB6272@breakpoint.cc/

to disable net->ct.sysctl_max == 0 for non init netns?

You could then make this

if (likely(init_net.ct.sysctl_max))
return min(init_net.ct.sysctl_max, net->ct.sysctl_max);

return net->ct.sysctl_max;

... or am i missing something?

Aside from that (and the needed #IS_ENABLED() guard) this change looks
good to me.