Subject: [PATCH V4] netfilter: netns nf_conntrack: per-netns net.netfilter.nf_conntrack_max sysctl

From: lvxiafei <[email-masked]>
Date: Sat, 12 Apr 2025 22:37:46 +0800

From: lvxiafei <[email-masked]>

Support net.netfilter.nf_conntrack_max settings per
netns, net.netfilter.nf_conntrack_max is used to more
flexibly limit the ct_count in different netns. The
default value belongs to the init_net limit.

After net.netfilter.nf_conntrack_max is set in different
netns, it is not allowed to be greater than the init_net
limit when working.

Signed-off-by: lvxiafei <[email-masked]>
---
 .../networking/nf_conntrack-sysctl.rst        | 29 +++++++++++++++----
 include/net/netfilter/nf_conntrack.h          |  8 ++++-
 include/net/netns/conntrack.h                 |  1 +
 net/netfilter/nf_conntrack_core.c             | 19 ++++++------
 net/netfilter/nf_conntrack_netlink.c          |  2 +-
 net/netfilter/nf_conntrack_standalone.c       |  5 ++--
 6 files changed, 44 insertions(+), 20 deletions(-)

diff --git a/Documentation/networking/nf_conntrack-sysctl.rst b/Documentation/networking/nf_conntrack-sysctl.rst
index 238b66d0e059..58aad49ea179 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)
+	- 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..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);
+}
+
 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..2f343842c2d9 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..8608aec88758 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,
@@ -1087,7 +1087,6 @@ 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;
 	}
-- 
2.40.1