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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     Roman Kapl <roman.kapl@sysgo.com>,
        "David S . Miller" <davem@davemloft.net>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.4 077/167] net: move somaxconn init from sysctl
 code
Thread-Topic: [PATCH AUTOSEL for 4.4 077/167] net: move somaxconn init from
 sysctl code
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Date:   Mon, 19 Mar 2018 16:06:58 +0000
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From: Roman Kapl <roman.kapl@sysgo.com>

[ Upstream commit 7c3f1875c66fbc19762760097cabc91849ea0bbb ]

The default value for somaxconn is set in sysctl_core_net_init(), but this
function is not called when kernel is configured without CONFIG_SYSCTL.

This results in the kernel not being able to accept TCP connections,
because the backlog has zero size. Usually, the user ends up with:
"TCP: request_sock_TCP: Possible SYN flooding on port 7. Dropping request. =
 Check SNMP counters."
If SYN cookies are not enabled the connection is rejected.

Before ef547f2ac16 (tcp: remove max_qlen_log), the effects were less
severe, because the backlog was always at least eight slots long.

Signed-off-by: Roman Kapl <roman.kapl@sysgo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 net/core/net_namespace.c   | 19 +++++++++++++++++++
 net/core/sysctl_net_core.c |  2 --
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index b5c351d2830b..ccd20669ac00 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -310,6 +310,25 @@ static __net_init int setup_net(struct net *net, struc=
t user_namespace *user_ns)
 	goto out;
 }
=20
+static int __net_init net_defaults_init_net(struct net *net)
+{
+	net->core.sysctl_somaxconn =3D SOMAXCONN;
+	return 0;
+}
+
+static struct pernet_operations net_defaults_ops =3D {
+	.init =3D net_defaults_init_net,
+};
+
+static __init int net_defaults_init(void)
+{
+	if (register_pernet_subsys(&net_defaults_ops))
+		panic("Cannot initialize net default settings");
+
+	return 0;
+}
+
+core_initcall(net_defaults_init);
=20
 #ifdef CONFIG_NET_NS
 static struct kmem_cache *net_cachep;
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 6578a0a2f708..32898247d8bf 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -429,8 +429,6 @@ static __net_init int sysctl_core_net_init(struct net *=
net)
 {
 	struct ctl_table *tbl;
=20
-	net->core.sysctl_somaxconn =3D SOMAXCONN;
-
 	tbl =3D netns_core_table;
 	if (!net_eq(net, &init_net)) {
 		tbl =3D kmemdup(tbl, sizeof(netns_core_table), GFP_KERNEL);
--=20
2.14.1