From 19f92a030ca6d772ab44b22ee6a01378a8cb32d4 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Wed, 30 Oct 2019 09:36:20 -0700
Subject: [PATCH] net: increase SOMAXCONN to 4096
SOMAXCONN is /proc/sys/net/core/somaxconn default value.
It has been defined as 128 more than 20 years ago.
Since it caps the listen() backlog values, the very small value has
caused numerous problems over the years, and many people had
to raise it on their hosts after beeing hit by problems.
Google has been using 1024 for at least 15 years, and we increased
this to 4096 after TCP listener rework has been completed, more than
4 years ago. We got no complain of this change breaking any
legacy application.
Many applications indeed setup a TCP listener with listen(fd, -1);
meaning they let the system select the backlog.
Raising SOMAXCONN lowers chance of the port being unavailable under
even small SYNFLOOD attack, and reduces possibilities of side channel
vulnerabilities.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Yue Cao <ycao009@ucr.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
Documentation/networking/ip-sysctl.txt | 4 ++--
include/linux/socket.h | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 49e95f438ed7..0e6653471c0e 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -207,8 +207,8 @@ TCP variables:
somaxconn - INTEGER
Limit of socket listen() backlog, known in userspace as SOMAXCONN.
- Defaults to 128. See also tcp_max_syn_backlog for additional tuning
- for TCP sockets.
+ Defaults to 4096. (Was 128 before linux-5.4)
+ See also tcp_max_syn_backlog for additional tuning for TCP sockets.
tcp_abort_on_overflow - BOOLEAN
If listening service is too slow to accept new connections,
diff --git a/include/linux/socket.h b/include/linux/socket.h
index fc0bed59fc84..4049d9755cf1 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -263,7 +263,7 @@ struct ucred {
#define PF_MAX AF_MAX
/* Maximum queue length specifiable by listen. */
-#define SOMAXCONN 128
+#define SOMAXCONN 4096
/* Flags we can use with send/ and recv.
Added those for 1003.1g not all are supported yet