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tunnel.go
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tunnel.go
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package main
import (
"errors"
"flag"
"io"
"io/ioutil"
"log"
"net"
"net/http"
"net/http/httputil"
"strings"
"sync"
"time"
"golang.org/x/crypto/ssh"
)
type tcpipForward struct {
Host string
Port uint32
}
type tcpipForwardSuccess struct {
Port uint32
}
type cancelTCPIPForward struct {
Host string
Port uint32
}
type forwardedTCPIP struct {
Host string
Port uint32
OriginHost string
OriginPort uint32
}
type chanConn struct {
Chan ssh.Channel
}
func (c *chanConn) Read(b []byte) (int, error) {
return c.Chan.Read(b)
}
func (c *chanConn) Write(b []byte) (int, error) {
return c.Chan.Write(b)
}
func (c *chanConn) Close() error {
return c.Chan.Close()
}
func (c *chanConn) LocalAddr() net.Addr {
panic("chanConn: LocalAddr")
}
func (c *chanConn) RemoteAddr() net.Addr {
panic("chanConn: RemoteAddr")
}
func (c *chanConn) SetDeadline(t time.Time) error {
return nil
}
func (c *chanConn) SetReadDeadline(t time.Time) error {
return nil
}
func (c *chanConn) SetWriteDeadline(t time.Time) error {
return nil
}
func isDomainName(s string) bool {
// Very loose validation to exclude port numbers. Only for lowercase strings.
for _, r := range s {
if (r < 'a' || r > 'z') && (r < '0' || r > '9') && r != '-' && r != '.' {
return false
}
}
return true
}
type Server struct {
SSHAddr string
HTTPAddr string
SSHConfig *ssh.ServerConfig
hosts sync.Map
}
func (s *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
t, ok := s.hosts.Load(strings.ToLower(req.Host))
if !ok {
w.Header().Set("Content-Type", "text/html")
w.WriteHeader(http.StatusNotFound)
io.WriteString(w, `<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>tunnel</center>
</body>
</html>`)
return
}
proxy := httputil.ReverseProxy{
Director: director,
Transport: t.(http.RoundTripper),
}
proxy.ServeHTTP(w, req)
}
func director(req *http.Request) {
req.URL.Scheme = "http"
host := strings.ToLower(req.Host)
req.URL.Host = host
req.Host = host
if _, ok := req.Header["User-Agent"]; !ok {
req.Header.Set("User-Agent", "")
}
}
func (s *Server) transport(conn *ssh.ServerConn, host string) http.RoundTripper {
dial := func(network, addr string) (net.Conn, error) {
if network != "tcp" && network != "tcp4" && network != "tcp6" {
panic("invalid network in dial")
}
host_, serv, err := net.SplitHostPort(addr)
if err != nil {
return nil, err
}
if host_ != strings.ToLower(host) {
panic("invalid host in dial")
}
port, err := net.LookupPort(network, serv)
if err != nil {
return nil, err
}
if port != 80 {
panic("invalid port in dial")
}
payload := forwardedTCPIP{Host: host, Port: 80, OriginHost: "0.0.0.0", OriginPort: 0}
ch, reqs, err := conn.OpenChannel("forwarded-tcpip", ssh.Marshal(&payload))
if err != nil {
return nil, err
}
go ssh.DiscardRequests(reqs)
return &chanConn{ch}, nil
}
return &http.Transport{Dial: dial}
}
func (s *Server) serveSSH(l net.Listener) error {
for {
rw, err := l.Accept()
if err != nil {
log.Print(err)
continue
}
go func() {
conn, chans, reqs, err := ssh.NewServerConn(rw, s.SSHConfig)
if err != nil {
log.Print(err)
return
}
hosts := make(map[string]struct{})
for reqs != nil && chans != nil {
select {
case req, ok := <-reqs:
if !ok {
reqs = nil
continue
}
if req.Type == "tcpip-forward" {
var payload tcpipForward
if err := ssh.Unmarshal(req.Payload, &payload); err != nil {
req.Reply(false, nil)
continue
}
host := strings.ToLower(payload.Host)
if !isDomainName(host) || payload.Port != 0 && payload.Port != 80 {
req.Reply(false, nil)
continue
}
transport := s.transport(conn, payload.Host)
if _, ok := s.hosts.LoadOrStore(host, transport); ok {
req.Reply(false, nil)
continue
}
hosts[host] = struct{}{}
replyPayload := tcpipForwardSuccess{Port: 80}
req.Reply(true, ssh.Marshal(&replyPayload))
} else if req.Type == "cancel-tcpip-forward" {
var payload cancelTCPIPForward
if err := ssh.Unmarshal(req.Payload, &payload); err != nil {
req.Reply(false, nil)
continue
}
host := strings.ToLower(payload.Host)
if payload.Port != 80 {
req.Reply(false, nil)
continue
}
if _, ok := hosts[host]; ok {
req.Reply(false, nil)
continue
}
s.hosts.Delete(payload.Host)
delete(hosts, payload.Host)
req.Reply(true, nil)
} else {
req.Reply(false, nil)
}
case ch, ok := <-chans:
if !ok {
chans = nil
continue
}
ch.Reject(ssh.UnknownChannelType, "no incoming channels accepted")
}
}
for host := range hosts {
s.hosts.Delete(host)
}
}()
}
}
func (s *Server) serveHTTP(l net.Listener) error {
return http.Serve(l, s)
}
func (s *Server) Serve(sshL net.Listener, httpL net.Listener) error {
sshError := make(chan error, 1)
httpError := make(chan error, 1)
go func() {
sshError <- s.serveSSH(sshL)
}()
go func() {
httpError <- s.serveHTTP(httpL)
}()
select {
case e := <-sshError:
return e
case e := <-httpError:
return e
}
}
func (s *Server) ListenAndServe() error {
sshAddr := s.SSHAddr
if sshAddr == "" {
sshAddr = ":ssh"
}
sshL, err := net.Listen("tcp", sshAddr)
if err != nil {
return err
}
defer sshL.Close() // FIXME multiple close?
httpAddr := s.HTTPAddr
if httpAddr == "" {
httpAddr = ":http"
}
httpL, err := net.Listen("tcp", httpAddr)
if err != nil {
return err
}
defer httpL.Close() // FIXME multiple close?
return s.Serve(sshL, httpL)
}
func main() {
sshAddrPtr := flag.String("bind-ssh", "", "bind address for the SSH server")
httpAddrPtr := flag.String("bind-http", "", "bind address for the HTTP server")
hostKeyPtr := flag.String("host-key", "./ssh_host_key", "host key file")
authKeysPtr := flag.String("authorized-keys", "./authorized_keys", "authorized keys file")
flag.Parse()
server := &Server{SSHAddr: *sshAddrPtr, HTTPAddr: *httpAddrPtr}
authKeys := make(map[string]struct{})
authKeysBytes, err := ioutil.ReadFile(*authKeysPtr)
if err != nil {
log.Fatal(err)
}
for len(authKeysBytes) > 0 {
key, _, _, rest, err := ssh.ParseAuthorizedKey(authKeysBytes)
if err != nil {
log.Print(err)
} else {
authKeys[string(key.Marshal())] = struct{}{}
}
authKeysBytes = rest
}
server.SSHConfig = &ssh.ServerConfig{
PublicKeyCallback: func(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
if _, ok := authKeys[string(key.Marshal())]; ok {
return nil, nil
}
return nil, errors.New("unknown public key")
},
}
privateBytes, err := ioutil.ReadFile(*hostKeyPtr)
if err != nil {
log.Fatal(err)
}
private, err := ssh.ParsePrivateKey(privateBytes)
if err != nil {
log.Fatal(err)
}
server.SSHConfig.AddHostKey(private)
log.Fatal(server.ListenAndServe())
}