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/*
* Copyright (c) 2015, Yawning Angel <yawning at torproject dot org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
// Package socks5 implements a SOCKS 5 server and the required pluggable
// transport specific extensions. For more information see RFC 1928 and RFC
// 1929.
//
// Notes:
// * GSSAPI authentication, is NOT supported.
// * Only the CONNECT command is supported.
// * The authentication provided by the client is always accepted as it is
// used as a channel to pass information rather than for authentication for
// pluggable transports.
package socks5
import (
"bufio"
"bytes"
"fmt"
"io"
"net"
"syscall"
"time"
"git.torproject.org/pluggable-transports/goptlib.git"
)
const (
version = 0x05
rsv = 0x00
cmdConnect = 0x01
atypIPv4 = 0x01
atypDomainName = 0x03
atypIPv6 = 0x04
authNoneRequired = 0x00
authUsernamePassword = 0x02
authNoAcceptableMethods = 0xff
requestTimeout = 5 * time.Second
)
// ReplyCode is a SOCKS 5 reply code.
type ReplyCode byte
// The various SOCKS 5 reply codes from RFC 1928.
const (
ReplySucceeded ReplyCode = iota
ReplyGeneralFailure
ReplyConnectionNotAllowed
ReplyNetworkUnreachable
ReplyHostUnreachable
ReplyConnectionRefused
ReplyTTLExpired
ReplyCommandNotSupported
ReplyAddressNotSupported
)
// Version returns a string suitable to be included in a call to Cmethod.
func Version() string {
return "socks5"
}
// ErrorToReplyCode converts an error to the "best" reply code.
func ErrorToReplyCode(err error) ReplyCode {
opErr, ok := err.(*net.OpError)
if !ok {
return ReplyGeneralFailure
}
errno, ok := opErr.Err.(syscall.Errno)
if !ok {
return ReplyGeneralFailure
}
switch errno {
case syscall.EADDRNOTAVAIL:
return ReplyAddressNotSupported
case syscall.ETIMEDOUT:
return ReplyTTLExpired
case syscall.ENETUNREACH:
return ReplyNetworkUnreachable
case syscall.EHOSTUNREACH:
return ReplyHostUnreachable
case syscall.ECONNREFUSED, syscall.ECONNRESET:
return ReplyConnectionRefused
default:
return ReplyGeneralFailure
}
}
// Request describes a SOCKS 5 request.
type Request struct {
Target string
Args pt.Args
rw *bufio.ReadWriter
}
// Handshake attempts to handle a incoming client handshake over the provided
// connection and receive the SOCKS5 request. The routine handles sending
// appropriate errors if applicable, but will not close the connection.
func Handshake(conn net.Conn) (*Request, error) {
// Arm the handshake timeout.
var err error
if err = conn.SetDeadline(time.Now().Add(requestTimeout)); err != nil {
return nil, err
}
defer func() {
// Disarm the handshake timeout, only propagate the error if
// the handshake was successful.
nerr := conn.SetDeadline(time.Time{})
if err == nil {
err = nerr
}
}()
req := new(Request)
req.rw = bufio.NewReadWriter(bufio.NewReader(conn), bufio.NewWriter(conn))
// Negotiate the protocol version and authentication method.
var method byte
if method, err = req.negotiateAuth(); err != nil {
return nil, err
}
// Authenticate if neccecary.
if err = req.authenticate(method); err != nil {
return nil, err
}
// Read the client command.
if err = req.readCommand(); err != nil {
return nil, err
}
return req, err
}
// Reply sends a SOCKS5 reply to the corresponding request. The BND.ADDR and
// BND.PORT fields are always set to an address/port corresponding to
// "0.0.0.0:0".
func (req *Request) Reply(code ReplyCode) error {
// The server sends a reply message.
// uint8_t ver (0x05)
// uint8_t rep
// uint8_t rsv (0x00)
// uint8_t atyp
// uint8_t bnd_addr[]
// uint16_t bnd_port
var resp [4 + 4 + 2]byte
resp[0] = version
resp[1] = byte(code)
resp[2] = rsv
resp[3] = atypIPv4
if _, err := req.rw.Write(resp[:]); err != nil {
return err
}
return req.flushBuffers()
}
func (req *Request) negotiateAuth() (byte, error) {
// The client sends a version identifier/selection message.
// uint8_t ver (0x05)
// uint8_t nmethods (>= 1).
// uint8_t methods[nmethods]
var err error
if err = req.readByteVerify("version", version); err != nil {
return 0, err
}
// Read the number of methods, and the methods.
var nmethods byte
method := byte(authNoAcceptableMethods)
if nmethods, err = req.readByte(); err != nil {
return method, err
}
var methods []byte
if methods, err = req.readBytes(int(nmethods)); err != nil {
return 0, err
}
// Pick the best authentication method, prioritizing authenticating
// over not if both options are present.
if bytes.IndexByte(methods, authUsernamePassword) != -1 {
method = authUsernamePassword
} else if bytes.IndexByte(methods, authNoneRequired) != -1 {
method = authNoneRequired
}
// The server sends a method selection message.
// uint8_t ver (0x05)
// uint8_t method
msg := []byte{version, method}
if _, err = req.rw.Write(msg); err != nil {
return 0, err
}
return method, req.flushBuffers()
}
func (req *Request) authenticate(method byte) error {
switch method {
case authNoneRequired:
// No authentication required.
case authUsernamePassword:
if err := req.authRFC1929(); err != nil {
return err
}
case authNoAcceptableMethods:
return fmt.Errorf("no acceptable authentication methods")
default:
// This should never happen as only supported auth methods should be
// negotiated.
return fmt.Errorf("negotiated unsupported method 0x%02x", method)
}
return req.flushBuffers()
}
func (req *Request) readCommand() error {
// The client sends the request details.
// uint8_t ver (0x05)
// uint8_t cmd
// uint8_t rsv (0x00)
// uint8_t atyp
// uint8_t dst_addr[]
// uint16_t dst_port
var err error
if err = req.readByteVerify("version", version); err != nil {
req.Reply(ReplyGeneralFailure)
return err
}
if err = req.readByteVerify("command", cmdConnect); err != nil {
req.Reply(ReplyCommandNotSupported)
return err
}
if err = req.readByteVerify("reserved", rsv); err != nil {
req.Reply(ReplyGeneralFailure)
return err
}
// Read the destination address/port.
var atyp byte
var host string
if atyp, err = req.readByte(); err != nil {
req.Reply(ReplyGeneralFailure)
return err
}
switch atyp {
case atypIPv4:
var addr []byte
if addr, err = req.readBytes(net.IPv4len); err != nil {
req.Reply(ReplyGeneralFailure)
return err
}
host = net.IPv4(addr[0], addr[1], addr[2], addr[3]).String()
case atypDomainName:
var alen byte
if alen, err = req.readByte(); err != nil {
req.Reply(ReplyGeneralFailure)
return err
}
if alen == 0 {
req.Reply(ReplyGeneralFailure)
return fmt.Errorf("domain name with 0 length")
}
var addr []byte
if addr, err = req.readBytes(int(alen)); err != nil {
req.Reply(ReplyGeneralFailure)
return err
}
host = string(addr)
case atypIPv6:
var rawAddr []byte
if rawAddr, err = req.readBytes(net.IPv6len); err != nil {
req.Reply(ReplyGeneralFailure)
return err
}
addr := make(net.IP, net.IPv6len)
copy(addr[:], rawAddr[:])
host = fmt.Sprintf("[%s]", addr.String())
default:
req.Reply(ReplyAddressNotSupported)
return fmt.Errorf("unsupported address type 0x%02x", atyp)
}
var rawPort []byte
if rawPort, err = req.readBytes(2); err != nil {
req.Reply(ReplyGeneralFailure)
return err
}
port := int(rawPort[0])<<8 | int(rawPort[1])
req.Target = fmt.Sprintf("%s:%d", host, port)
return req.flushBuffers()
}
func (req *Request) flushBuffers() error {
if err := req.rw.Flush(); err != nil {
return err
}
if req.rw.Reader.Buffered() > 0 {
return fmt.Errorf("read buffer has %d bytes of trailing data", req.rw.Reader.Buffered())
}
return nil
}
func (req *Request) readByte() (byte, error) {
return req.rw.ReadByte()
}
func (req *Request) readByteVerify(descr string, expected byte) error {
val, err := req.rw.ReadByte()
if err != nil {
return err
}
if val != expected {
return fmt.Errorf("message field '%s' was 0x%02x (expected 0x%02x)", descr, val, expected)
}
return nil
}
func (req *Request) readBytes(n int) ([]byte, error) {
b := make([]byte, n)
if _, err := io.ReadFull(req.rw, b); err != nil {
return nil, err
}
return b, nil
}
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