Re: [PATCH V6] netfilter: netns nf_conntrack: per-netns net.netfilter.nf_conntrack_max sysctl

Pablo Neira Ayuso
2025-05-22T19:24:58Z

On Tue, Apr 15, 2025 at 05:08:34PM +0800, lvxiafei wrote:
> diff --git a/Documentation/networking/nf_conntrack-sysctl.rst b/Documentation/networking/nf_conntrack-sysctl.rst
> index 238b66d0e059..6e7f17f5959a 100644
> --- a/Documentation/networking/nf_conntrack-sysctl.rst
> +++ b/Documentation/networking/nf_conntrack-sysctl.rst
> @@ -93,12 +93,29 @@ nf_conntrack_log_invalid - INTEGER
> Log invalid packets of a type specified by value.
>
> nf_conntrack_max - INTEGER
> - Maximum number of allowed connection tracking entries. 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.
> + - 0 - disabled (unlimited)

unlimited is too much, and the number of buckets is also global, how
does this work?

Is your goal to allow a netns to have larger table than netns? There
should be a cap for this.

> + - not 0 - enabled
> +
> + 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..594439b2f5a1 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 +359,17 @@ 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)
> +{
> +#if IS_ENABLED(CONFIG_NF_CONNTRACK)
> + 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);
> +#else
> + return 0;
> +#endif
> +}
> +
> int nf_ct_skb_network_trim(struct sk_buff *skb, int family);
> int nf_ct_handle_fragments(struct net *net, struct sk_buff *skb,
> u16 zone, u8 family, u8 *proto, u16 *mru);
> diff --git a/include/net/netns/conntrack.h b/include/net/netns/conntrack.h
> index bae914815aa3..d3fcd0b92b2d 100644
> --- a/include/net/netns/conntrack.h
> +++ b/include/net/netns/conntrack.h
> @@ -102,6 +102,7 @@ struct netns_ct {
> u8 sysctl_acct;
> u8 sysctl_tstamp;
> u8 sysctl_checksum;
> + unsigned int sysctl_max;
>
> struct ip_conntrack_stat __percpu *stat;
> struct nf_ct_event_notifier __rcu *nf_conntrack_event_cb;
> diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
> index 7f8b245e287a..a738564923ec 100644
> --- a/net/netfilter/nf_conntrack_core.c
> +++ b/net/netfilter/nf_conntrack_core.c
> @@ -202,8 +202,6 @@ static void nf_conntrack_all_unlock(void)
> unsigned int nf_conntrack_htable_size __read_mostly;
> EXPORT_SYMBOL_GPL(nf_conntrack_htable_size);
>
> -unsigned int nf_conntrack_max __read_mostly;
> -EXPORT_SYMBOL_GPL(nf_conntrack_max);
> seqcount_spinlock_t nf_conntrack_generation __read_mostly;
> static siphash_aligned_key_t nf_conntrack_hash_rnd;
>
> @@ -1498,7 +1496,7 @@ static bool gc_worker_can_early_drop(const struct nf_conn *ct)
>
> static void gc_worker(struct work_struct *work)
> {
> - unsigned int i, hashsz, nf_conntrack_max95 = 0;
> + unsigned int i, hashsz;
> u32 end_time, start_time = nfct_time_stamp;
> struct conntrack_gc_work *gc_work;
> unsigned int expired_count = 0;
> @@ -1509,8 +1507,6 @@ static void gc_worker(struct work_struct *work)
> gc_work = container_of(work, struct conntrack_gc_work, dwork.work);
>
> i = gc_work->next_bucket;
> - if (gc_work->early_drop)
> - nf_conntrack_max95 = nf_conntrack_max / 100u * 95u;
>
> if (i == 0) {
> gc_work->avg_timeout = GC_SCAN_INTERVAL_INIT;
> @@ -1538,6 +1534,7 @@ static void gc_worker(struct work_struct *work)
> }
>
> hlist_nulls_for_each_entry_rcu(h, n, &ct_hash[i], hnnode) {
> + unsigned int nf_conntrack_max95 = 0;
> struct nf_conntrack_net *cnet;
> struct net *net;
> long expires;
> @@ -1567,11 +1564,14 @@ static void gc_worker(struct work_struct *work)
> expires = clamp(nf_ct_expires(tmp), GC_SCAN_INTERVAL_MIN, GC_SCAN_INTERVAL_CLAMP);
> expires = (expires - (long)next_run) / ++count;
> next_run += expires;
> + net = nf_ct_net(tmp);
> +
> + if (gc_work->early_drop)
> + nf_conntrack_max95 = nf_conntrack_max(net) / 100u * 95u;
>
> if (nf_conntrack_max95 == 0 || gc_worker_skip_ct(tmp))
> continue;
>
> - net = nf_ct_net(tmp);
> cnet = nf_ct_pernet(net);
> if (atomic_read(&cnet->count) < nf_conntrack_max95)
> continue;
> @@ -1648,13 +1648,14 @@ __nf_conntrack_alloc(struct net *net,
> gfp_t gfp, u32 hash)
> {
> struct nf_conntrack_net *cnet = nf_ct_pernet(net);
> - unsigned int ct_count;
> + unsigned int ct_max, ct_count;
> struct nf_conn *ct;
>
> /* We don't want any race condition at early drop stage */
> ct_count = atomic_inc_return(&cnet->count);
> + ct_max = nf_conntrack_max(net);
>
> - if (nf_conntrack_max && unlikely(ct_count > nf_conntrack_max)) {
> + if (ct_max && unlikely(ct_count > ct_max)) {
> if (!early_drop(net, hash)) {
> if (!conntrack_gc_work.early_drop)
> conntrack_gc_work.early_drop = true;
> @@ -2650,7 +2651,7 @@ int nf_conntrack_init_start(void)
> if (!nf_conntrack_hash)
> return -ENOMEM;
>
> - nf_conntrack_max = max_factor * nf_conntrack_htable_size;
> + init_net.ct.sysctl_max = max_factor * nf_conntrack_htable_size;
>
> nf_conntrack_cachep = kmem_cache_create("nf_conntrack",
> sizeof(struct nf_conn),
> diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
> index 2cc0fde23344..73e6bb1e939b 100644
> --- a/net/netfilter/nf_conntrack_netlink.c
> +++ b/net/netfilter/nf_conntrack_netlink.c
> @@ -2608,7 +2608,7 @@ ctnetlink_stat_ct_fill_info(struct sk_buff *skb, u32 portid, u32 seq, u32 type,
> if (nla_put_be32(skb, CTA_STATS_GLOBAL_ENTRIES, htonl(nr_conntracks)))
> goto nla_put_failure;
>
> - if (nla_put_be32(skb, CTA_STATS_GLOBAL_MAX_ENTRIES, htonl(nf_conntrack_max)))
> + if (nla_put_be32(skb, CTA_STATS_GLOBAL_MAX_ENTRIES, htonl(nf_conntrack_max(net))))
> goto nla_put_failure;
>
> nlmsg_end(skb, nlh);
> diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
> index 2f666751c7e7..5db6df0e4eb3 100644
> --- a/net/netfilter/nf_conntrack_standalone.c
> +++ b/net/netfilter/nf_conntrack_standalone.c
> @@ -615,7 +615,7 @@ enum nf_ct_sysctl_index {
> static struct ctl_table nf_ct_sysctl_table[] = {
> [NF_SYSCTL_CT_MAX] = {
> .procname = "nf_conntrack_max",
> - .data = &nf_conntrack_max,
> + .data = &init_net.ct.sysctl_max,
> .maxlen = sizeof(int),
> .mode = 0644,
> .proc_handler = proc_dointvec_minmax,
> @@ -948,7 +948,7 @@ static struct ctl_table nf_ct_sysctl_table[] = {
> static struct ctl_table nf_ct_netfilter_table[] = {
> {
> .procname = "nf_conntrack_max",
> - .data = &nf_conntrack_max,
> + .data = &init_net.ct.sysctl_max,
> .maxlen = sizeof(int),
> .mode = 0644,
> .proc_handler = proc_dointvec_minmax,
> @@ -1063,6 +1063,7 @@ static int nf_conntrack_standalone_init_sysctl(struct net *net)
>
> table[NF_SYSCTL_CT_COUNT].data = &cnet->count;
> table[NF_SYSCTL_CT_CHECKSUM].data = &net->ct.sysctl_checksum;
> + table[NF_SYSCTL_CT_MAX].data = &net->ct.sysctl_max;
> table[NF_SYSCTL_CT_LOG_INVALID].data = &net->ct.sysctl_log_invalid;
> table[NF_SYSCTL_CT_ACCT].data = &net->ct.sysctl_acct;
> #ifdef CONFIG_NF_CONNTRACK_EVENTS
> @@ -1087,7 +1088,6 @@ static int nf_conntrack_standalone_init_sysctl(struct net *net)
>
> /* Don't allow non-init_net ns to alter global sysctls */
> if (!net_eq(&init_net, net)) {
> - table[NF_SYSCTL_CT_MAX].mode = 0444;
> table[NF_SYSCTL_CT_EXPECT_MAX].mode = 0444;
> table[NF_SYSCTL_CT_BUCKETS].mode = 0444;
> }
> @@ -1139,6 +1139,7 @@ static int nf_conntrack_pernet_init(struct net *net)
> int ret;
>
> net->ct.sysctl_checksum = 1;
> + net->ct.sysctl_max = init_net.ct.sysctl_max;
>
> ret = nf_conntrack_standalone_init_sysctl(net);
> if (ret < 0)
> --
> 2.40.1
>