From e64f3f211ac03f270a2db476e01b34fd1d1c5301 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Tue, 12 Mar 2013 01:48:48 -0400
Subject: [PATCH] net: never use backlog > 65535

The system call takes an int, but the kernel stores it in a uint16.
At least one Linux system sets /proc/sys/net/core/somaxconn
to 262144, which ends up being 0 in the uint16. Avoid being tricked.

FreeBSD sources also store the backlog in a uint16.
Assume the problem is systemic and fix it everywhere.

Fixes #5030.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7480046
---
 src/pkg/net/sock_bsd.go     | 6 ++++++
 src/pkg/net/sock_linux.go   | 6 ++++++
 src/pkg/net/sock_windows.go | 1 +
 3 files changed, 13 insertions(+)

diff --git a/src/pkg/net/sock_bsd.go b/src/pkg/net/sock_bsd.go
index 3205f94047..d99349265e 100644
--- a/src/pkg/net/sock_bsd.go
+++ b/src/pkg/net/sock_bsd.go
@@ -27,5 +27,11 @@ func maxListenerBacklog() int {
 	if n == 0 || err != nil {
 		return syscall.SOMAXCONN
 	}
+	// FreeBSD stores the backlog in a uint16, as does Linux.
+	// Assume the other BSDs do too. Truncate number to avoid wrapping.
+	// See issue 5030.
+	if n > 1<<16-1 {
+		n = 1<<16 - 1
+	}
 	return int(n)
 }
diff --git a/src/pkg/net/sock_linux.go b/src/pkg/net/sock_linux.go
index 8bbd74ddc9..cc5ce153b3 100644
--- a/src/pkg/net/sock_linux.go
+++ b/src/pkg/net/sock_linux.go
@@ -21,5 +21,11 @@ func maxListenerBacklog() int {
 	if n == 0 || !ok {
 		return syscall.SOMAXCONN
 	}
+	// Linux stores the backlog in a uint16.
+	// Truncate number to avoid wrapping.
+	// See issue 5030.
+	if n > 1<<16-1 {
+		n = 1<<16 - 1
+	}
 	return n
 }
diff --git a/src/pkg/net/sock_windows.go b/src/pkg/net/sock_windows.go
index a77c48437f..41368d39e8 100644
--- a/src/pkg/net/sock_windows.go
+++ b/src/pkg/net/sock_windows.go
@@ -8,6 +8,7 @@ import "syscall"
 
 func maxListenerBacklog() int {
 	// TODO: Implement this
+	// NOTE: Never return a number bigger than 1<<16 - 1. See issue 5030.
 	return syscall.SOMAXCONN
 }