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// Copyright 2019 Path Network, Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"bytes"
"encoding/binary"
"flag"
"fmt"
"io"
"log"
"net"
"strings"
"syscall"
)
var listenAddr string
var targetAddr4 string
var targetAddr6 string
func init() {
flag.StringVar(&listenAddr, "l", "0.0.0.0:8443", "Adress the proxy listens on")
flag.StringVar(&targetAddr4, "4", "127.0.0.1:443", "Address to which IPv4 TCP traffic will be forwarded to")
flag.StringVar(&targetAddr6, "6", "[::1]:443", "Address to which IPv6 TCP traffic will be forwarded to")
flag.IntVar(&mark, "mark", 0, "The mark that will be set on outbound packets")
flag.StringVar(&allowedSubnetsPath, "allowed-subnets", "", "Path to a file that contains allowed subnets of the proxy servers")
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}
func readRemoteAddrPROXYv2(conn net.Conn, ctrlBuf []byte) (net.Addr, net.Addr, []byte, error) {
if (ctrlBuf[12] >> 4) != 2 {
return nil, nil, nil, fmt.Errorf("unknown protocol version %d", ctrlBuf[12]>>4)
}
if ctrlBuf[12]&0xFF > 1 {
return nil, nil, nil, fmt.Errorf("unknown command %d", ctrlBuf[12]&0xFF)
}
if ctrlBuf[12]&0xFF == 1 && ctrlBuf[13] != 0x11 && ctrlBuf[13] != 0x21 {
return nil, nil, nil, fmt.Errorf("invalid family/protocol %d/%d", ctrlBuf[13]>>4, ctrlBuf[13]&0xFF)
}
var dataLen uint16
reader := bytes.NewReader(ctrlBuf[14:16])
if err := binary.Read(reader, binary.BigEndian, &dataLen); err != nil {
return nil, nil, nil, fmt.Errorf("failed to decode address data length: %s", err.Error())
}
if ctrlBuf[12]&0xFF == 1 { // LOCAL
return conn.RemoteAddr(), conn.LocalAddr(), ctrlBuf[16+dataLen:], nil
}
var sport, dport uint16
if ctrlBuf[13] == 0x11 { // IPv4
reader = bytes.NewReader(ctrlBuf[24:])
} else {
reader = bytes.NewReader(ctrlBuf[48:])
}
if err := binary.Read(reader, binary.BigEndian, &sport); err != nil {
return nil, nil, nil, fmt.Errorf("failed to decode source TCP port: %s", err.Error())
}
if err := binary.Read(reader, binary.BigEndian, &dport); err != nil {
return nil, nil, nil, fmt.Errorf("failed to decode destination TCP port: %s", err.Error())
}
if ctrlBuf[13] == 0x11 { // TCP over IPv4
srcIP := net.IPv4(ctrlBuf[16], ctrlBuf[17], ctrlBuf[18], ctrlBuf[19])
dstIP := net.IPv4(ctrlBuf[20], ctrlBuf[21], ctrlBuf[22], ctrlBuf[23])
return &net.TCPAddr{IP: srcIP, Port: int(sport)}, &net.TCPAddr{IP: dstIP, Port: int(dport)}, ctrlBuf[16+dataLen:], nil
}
return &net.TCPAddr{IP: ctrlBuf[16:32], Port: int(sport)}, &net.TCPAddr{IP: ctrlBuf[32:48], Port: int(dport)}, ctrlBuf[16+dataLen:], nil
}
func readRemoteAddrPROXYv1(conn net.Conn, ctrlBuf []byte) (net.Addr, net.Addr, []byte, error) {
str := string(ctrlBuf)
if idx := strings.Index(str, "\r\n"); idx >= 0 {
var protocol, src, dst string
var sport, dport int
n, err := fmt.Sscanf(str, "PROXY %s", &protocol)
if err != nil {
return nil, nil, nil, err
}
if n != 1 {
return nil, nil, nil, fmt.Errorf("failed to decode elements")
}
if protocol == "UNKNOWN" {
return conn.RemoteAddr(), conn.LocalAddr(), ctrlBuf[idx+2:], nil
}
if protocol != "TCP4" && protocol != "TCP6" {
return nil, nil, nil, fmt.Errorf("unknown protocol %s", protocol)
}
n, err = fmt.Sscanf(str, "PROXY %s %s %s %d %d", &protocol, &src, &dst, &sport, &dport)
if err != nil {
return nil, nil, nil, err
}
if n != 5 {
return nil, nil, nil, fmt.Errorf("failed to decode elements")
}
srcIP := net.ParseIP(src)
if srcIP == nil {
return nil, nil, nil, fmt.Errorf("failed to parse source IP address %s", src)
}
dstIP := net.ParseIP(dst)
if dstIP == nil {
return nil, nil, nil, fmt.Errorf("failed to parse destination IP address %s", dst)
}
return &net.TCPAddr{IP: srcIP, Port: sport}, &net.TCPAddr{IP: dstIP, Port: dport}, ctrlBuf[idx+2:], nil
}
return nil, nil, nil, fmt.Errorf("did not find \\r\\n in first data segment")
}
func readRemoteAddr(conn net.Conn) (net.Addr, net.Addr, []byte, error) {
buf := make([]byte, 108)
n, err := conn.Read(buf)
if err != nil {
return nil, nil, nil, fmt.Errorf("failed to read header: %s", err.Error())
}
if n >= 16 && bytes.Equal(buf[:13], []byte{0x0D, 0x0A, 0x0D, 0x0A, 0x00, 0x0D, 0x0A, 0x51, 0x55, 0x49, 0x54, 0x0A}) {
saddr, daddr, rest, err := readRemoteAddrPROXYv2(conn, buf[:n])
if err != nil {
return nil, nil, nil, fmt.Errorf("failed to parse PROXY v2 header: %s", err.Error())
}
return saddr, daddr, rest, err
}
if n >= 8 && bytes.Equal(buf[:5], []byte("PROXY")) {
saddr, daddr, rest, err := readRemoteAddrPROXYv1(conn, buf[:n])
if err != nil {
return nil, nil, nil, fmt.Errorf("failed to parse PROXY v1 header: %s", err.Error())
}
return saddr, daddr, rest, err
}
return nil, nil, nil, fmt.Errorf("PROXY header missing")
}
func dialUpstreamControl(sport int) func(string, string, syscall.RawConn) error {
return func(network, address string, c syscall.RawConn) error {
var syscallErr error
err := c.Control(func(fd uintptr) {
syscallErr = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_TCP, syscall.TCP_SYNCNT, 2)
if syscallErr != nil {
syscallErr = fmt.Errorf("setsockopt(IPPROTO_TCP, TCP_SYNCTNT, 2): %s", syscallErr.Error())
return
}
syscallErr = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IP_TRANSPARENT, 1)
if syscallErr != nil {
syscallErr = fmt.Errorf("setsockopt(IPPROTO_IP, IP_TRANSPARENT, 1): %s", syscallErr.Error())
return
}
syscallErr = syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
if syscallErr != nil {
syscallErr = fmt.Errorf("setsockopt(SOL_SOCKET, SO_REUSEADDR, 1): %s", syscallErr.Error())
return
}
if sport == 0 {
ipBindAddressNoPort := 24
syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, ipBindAddressNoPort, 1)
}
if mark != 0 {
syscallErr = syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_MARK, mark)
if syscallErr != nil {
syscallErr = fmt.Errorf("setsockopt(SOL_SOCK, SO_MARK, %d): %s", mark, syscallErr.Error())
return
}
}
if network == "tcp6" {
syscallErr = syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IPV6_V6ONLY, 0)
if syscallErr != nil {
syscallErr = fmt.Errorf("setsockopt(IPPROTO_IP, IPV6_ONLY, 0): %s", syscallErr.Error())
return
}
}
})
if err != nil {
return err
}
return syscallErr
}
}
func copyData(dst net.Conn, src net.Conn, ch chan<- error) {
_, err := io.Copy(dst, src)
ch <- err
}
func checkOriginAllowed(conn net.Conn) bool {
if len(allowedSubnets) == 0 {
return true
}
addr := conn.RemoteAddr().(*net.TCPAddr)
for _, ipNet := range allowedSubnets {
if ipNet.Contains(addr.IP) {
return true
}
}
return false
}
func handleConnection(conn net.Conn) {
defer conn.Close()
if !checkOriginAllowed(conn) {
log.Printf("Disallowed connection from %s", conn.RemoteAddr().String())
return
}
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saddr, _, restBytes, err := readRemoteAddr(conn)
if err != nil {
log.Printf("Failed to parse PROXY data from %s: %s", conn.RemoteAddr().String(), err.Error())
return
}
targetAddr := targetAddr6
if strings.ContainsRune(saddr.String(), '.') { // poor man's ipv6 check - golang makes it unnecessarily hard
targetAddr = targetAddr4
}
dialer := net.Dialer{LocalAddr: saddr, Control: dialUpstreamControl(saddr.(*net.TCPAddr).Port)}
upstreamConn, err := dialer.Dial("tcp", targetAddr)
if err != nil {
log.Printf("Failed to establish upstream connection %s -> %s (PROXY %s -> %s): %s",
conn.RemoteAddr().String(), conn.LocalAddr().String(), saddr.String(), targetAddr, err.Error())
return
}
if err := conn.(*net.TCPConn).SetNoDelay(true); err != nil {
log.Printf("Failed to set nodelay on upstream connection %s -> %s (PROXY %s -> %s): %s",
conn.RemoteAddr().String(), conn.LocalAddr().String(), saddr.String(), targetAddr, err.Error())
}
if err := upstreamConn.(*net.TCPConn).SetNoDelay(true); err != nil {
log.Printf("Failed to set nodelay on upstream connection %s -> %s (PROXY %s -> %s): %s",
conn.RemoteAddr().String(), conn.LocalAddr().String(), saddr.String(), targetAddr, err.Error())
}
defer upstreamConn.Close()
for len(restBytes) > 0 {
n, err := conn.Write(restBytes)
if err != nil {
log.Printf("Failed to write data to upstream connection %s -> %s (PROXY %s -> %s): %s",
conn.RemoteAddr().String(), conn.LocalAddr().String(), saddr.String(), targetAddr, err.Error())
return
}
restBytes = restBytes[n:]
}
outErr := make(chan error, 2)
go copyData(upstreamConn, conn, outErr)
go copyData(conn, upstreamConn, outErr)
err = <-outErr
if err != nil {
log.Printf("Connection %s -> %s (PROXY %s -> %s): %s",
conn.RemoteAddr().String(), conn.LocalAddr().String(), saddr.String(), targetAddr, err.Error())
}
}
func loadAllowedSubnets() error {
file, err := os.Open(allowedSubnetsPath)
if err != nil {
return err
}
defer file.Close()
scanner := bufio.NewScanner(file)
for scanner.Scan() {
_, ipNet, err := net.ParseCIDR(scanner.Text())
if err != nil {
return err
}
allowedSubnets = append(allowedSubnets, ipNet)
}
return nil
}
func main() {
flag.Parse()
if allowedSubnetsPath != "" {
if err := loadAllowedSubnets(); err != nil {
log.Fatalf("Failed to load allowed subnets file: %s", err.Error())
}
}
ln, err := net.Listen("tcp", listenAddr)
if err != nil {
log.Fatalf("Failed to bind to %s: %s\n", listenAddr, err.Error())
}
for {
conn, err := ln.Accept()
if err != nil {
log.Fatalf("Failed to accept new connection: %s\n", err.Error())
}
go handleConnection(conn)
}
}