netdev - [PATCH net-next 2/3] netfilter: conntrack: disable 0 value for conntrack

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Message-ID: <20251030121954.29175-3-fw@strlen.de>
Date: Thu, 30 Oct 2025 13:19:53 +0100
From: Florian Westphal <fw@...len.de>
To: <netdev@...r.kernel.org>
Cc: Paolo Abeni <pabeni@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	<netfilter-devel@...r.kernel.org>,
	pablo@...filter.org
Subject: [PATCH net-next 2/3] netfilter: conntrack: disable 0 value for conntrack_max setting

Undocumented historical artifact inherited from ip_conntrack.
If value is 0, then no limit is applied at all, conntrack table
can grow to huge value, only limited by size of conntrack hashes and
the kernel-internal upper limit on the hash chain lengths.

This feature makes no sense; users can just set
conntrack_max=2147483647 (INT_MAX).

Disallow a 0 value.  This will make it slightly easier to allow
per-netns constraints for this value in a future patch.

Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/netfilter/nf_conntrack_core.c       | 2 +-
 net/netfilter/nf_conntrack_standalone.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 344f88295976..0b95f226f211 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1668,7 +1668,7 @@ __nf_conntrack_alloc(struct net *net,
 	/* We don't want any race condition at early drop stage */
 	ct_count = atomic_inc_return(&cnet->count);
 
-	if (nf_conntrack_max && unlikely(ct_count > nf_conntrack_max)) {
+	if (unlikely(ct_count > nf_conntrack_max)) {
 		if (!early_drop(net, hash)) {
 			if (!conntrack_gc_work.early_drop)
 				conntrack_gc_work.early_drop = true;
diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 708b79380f04..207b240b14e5 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -648,7 +648,7 @@ static struct ctl_table nf_ct_sysctl_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= SYSCTL_ZERO,
+		.extra1		= SYSCTL_ONE,
 		.extra2		= SYSCTL_INT_MAX,
 	},
 	[NF_SYSCTL_CT_COUNT] = {
@@ -929,7 +929,7 @@ static struct ctl_table nf_ct_netfilter_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= SYSCTL_ZERO,
+		.extra1		= SYSCTL_ONE,
 		.extra2		= SYSCTL_INT_MAX,
 	},
 };
-- 
2.51.0