[ 3.5.y.z extended stable ] Patch "net: check net.core.somaxconn sysctl values" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Fri Sep 20 19:33:43 UTC 2013

This is a note to let you know that I have just added a patch titled

    net: check net.core.somaxconn sysctl values

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From b2821adcfb163d7d1ea506e65a277620cd5d1018 Mon Sep 17 00:00:00 2001
From: Roman Gushchin <klamm at yandex-team.ru>
Date: Fri, 2 Aug 2013 18:36:40 +0400
Subject: [PATCH] net: check net.core.somaxconn sysctl values

commit 5f671d6b4ec3e6d66c2a868738af2cdea09e7509 upstream.

It's possible to assign an invalid value to the net.core.somaxconn
sysctl variable, because there is no checks at all.

The sk_max_ack_backlog field of the sock structure is defined as
unsigned short. Therefore, the backlog argument in inet_listen()
shouldn't exceed USHRT_MAX. The backlog argument in the listen() syscall
is truncated to the somaxconn value. So, the somaxconn value shouldn't
exceed 65535 (USHRT_MAX).
Also, negative values of somaxconn are meaningless.

$ sysctl -w net.core.somaxconn=256
net.core.somaxconn = 256
$ sysctl -w net.core.somaxconn=65536
net.core.somaxconn = 65536
$ sysctl -w net.core.somaxconn=-100
net.core.somaxconn = -100

$ sysctl -w net.core.somaxconn=256
net.core.somaxconn = 256
$ sysctl -w net.core.somaxconn=65536
error: "Invalid argument" setting key "net.core.somaxconn"
$ sysctl -w net.core.somaxconn=-100
error: "Invalid argument" setting key "net.core.somaxconn"

Based on a prior patch from Changli Gao.

Signed-off-by: Roman Gushchin <klamm at yandex-team.ru>
Reported-by: Changli Gao <xiaosuo at gmail.com>
Suggested-by: Eric Dumazet <edumazet at google.com>
Acked-by: Eric Dumazet <edumazet at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
[ luis: backported to 3.5: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 net/core/sysctl_net_core.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index a7c3684..df0dafe 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -20,6 +20,9 @@
 #include <net/sock.h>
 #include <net/net_ratelimit.h>

+static int zero = 0;
+static int ushort_max = USHRT_MAX;
 #ifdef CONFIG_RPS
 static int rps_sock_flow_sysctl(ctl_table *table, int write,
 				void __user *buffer, size_t *lenp, loff_t *ppos)
@@ -198,7 +201,9 @@ static struct ctl_table netns_core_table[] = {
 		.data		= &init_net.core.sysctl_somaxconn,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec
+		.extra1		= &zero,
+		.extra2		= &ushort_max,
+		.proc_handler	= proc_dointvec_minmax
 	{ }

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