From 32d2148835d28f5927daee2d1206c88ac343cfb3 Mon Sep 17 00:00:00 2001
From: Mathias Hall-Andersen <mathias@hall-andersen.dk>
Date: Sun, 16 Sep 2018 15:05:08 +0200
Subject: [PATCH] Fixed port overwrite issue on kernels without ipv6

Fixed an issue in CreateBind for Linux:
If ipv6 was not supported the error code would be
correctly identified as EAFNOSUPPORT and ipv4 binding attempted.
However the port would be set to 0,
which results in the subsequent create4 call requesting
a random port rather than the one provided to CreateBind.

This issue was identified by:
Kent Friis <leeloored@gmx.com>
---
 conn_linux.go | 48 +++++++++++++++++++++++++++++++++++-------------
 1 file changed, 35 insertions(+), 13 deletions(-)

diff --git a/conn_linux.go b/conn_linux.go
index db0e3a6..0849920 100644
--- a/conn_linux.go
+++ b/conn_linux.go
@@ -27,6 +27,10 @@ import (
 	"unsafe"
 )
 
+const (
+	FD_ERR = -1
+)
+
 type IPv4Source struct {
 	src     [4]byte
 	ifindex int32
@@ -126,6 +130,7 @@ func createNetlinkRouteSocket() (int, error) {
 func CreateBind(port uint16, device *Device) (*NativeBind, uint16, error) {
 	var err error
 	var bind NativeBind
+	var newPort uint16
 
 	bind.netlinkSock, err = createNetlinkRouteSocket()
 	if err != nil {
@@ -139,18 +144,35 @@ func CreateBind(port uint16, device *Device) (*NativeBind, uint16, error) {
 
 	go bind.routineRouteListener(device)
 
-	bind.sock6, port, err = create6(port)
-	if err != nil && err != syscall.EAFNOSUPPORT {
-		bind.netlinkCancel.Cancel()
-		return nil, 0, err
+	// attempt ipv6 bind, update port if succesful
+
+	bind.sock6, newPort, err = create6(port)
+	if err != nil {
+		if err != syscall.EAFNOSUPPORT {
+			bind.netlinkCancel.Cancel()
+			return nil, 0, err
+		}
+	} else {
+		port = newPort
 	}
 
-	bind.sock4, port, err = create4(port)
-	if err != nil && err != syscall.EAFNOSUPPORT {
-		bind.netlinkCancel.Cancel()
-		unix.Close(bind.sock6)
-		return nil, 0, err
+	// attempt ipv4 bind, update port if succesful
+
+	bind.sock4, newPort, err = create4(port)
+	if err != nil {
+		if err != syscall.EAFNOSUPPORT {
+			bind.netlinkCancel.Cancel()
+			unix.Close(bind.sock6)
+			return nil, 0, err
+		}
+	} else {
+		port = newPort
 	}
+
+	if bind.sock4 == FD_ERR && bind.sock6 == FD_ERR {
+		return nil, 0, errors.New("ipv4 and ipv6 not supported")
+	}
+
 	return &bind, port, nil
 }
 
@@ -334,7 +356,7 @@ func create4(port uint16) (int, uint16, error) {
 	)
 
 	if err != nil {
-		return -1, 0, err
+		return FD_ERR, 0, err
 	}
 
 	addr := unix.SockaddrInet4{
@@ -365,7 +387,7 @@ func create4(port uint16) (int, uint16, error) {
 		return unix.Bind(fd, &addr)
 	}(); err != nil {
 		unix.Close(fd)
-		return -1, 0, err
+		return FD_ERR, 0, err
 	}
 
 	return fd, uint16(addr.Port), err
@@ -382,7 +404,7 @@ func create6(port uint16) (int, uint16, error) {
 	)
 
 	if err != nil {
-		return -1, 0, err
+		return FD_ERR, 0, err
 	}
 
 	// set sockopts and bind
@@ -424,7 +446,7 @@ func create6(port uint16) (int, uint16, error) {
 
 	}(); err != nil {
 		unix.Close(fd)
-		return -1, 0, err
+		return FD_ERR, 0, err
 	}
 
 	return fd, uint16(addr.Port), err