lib/crunchrun/container_gateway.go

   1 // Copyright (C) The Arvados Authors. All rights reserved.
   2 //
   3 // SPDX-License-Identifier: AGPL-3.0
   4
   5 package crunchrun
   6
   7 import (
   8         "context"
   9         "crypto/hmac"
  10         "crypto/rand"
  11         "crypto/rsa"
  12         "crypto/sha256"
  13         "crypto/tls"
  14         "fmt"
  15         "io"
  16         "net"
  17         "net/http"
  18         "net/url"
  19         "os"
  20         "os/exec"
  21         "strings"
  22         "sync"
  23         "syscall"
  24         "time"
  25
  26         "git.arvados.org/arvados.git/lib/controller/rpc"
  27         "git.arvados.org/arvados.git/lib/selfsigned"
  28         "git.arvados.org/arvados.git/lib/webdavfs"
  29         "git.arvados.org/arvados.git/sdk/go/arvados"
  30         "git.arvados.org/arvados.git/sdk/go/auth"
  31         "git.arvados.org/arvados.git/sdk/go/ctxlog"
  32         "git.arvados.org/arvados.git/sdk/go/httpserver"
  33         "github.com/creack/pty"
  34         "github.com/google/shlex"
  35         "github.com/hashicorp/yamux"
  36         "golang.org/x/crypto/ssh"
  37         "golang.org/x/net/webdav"
  38 )
  39
  40 type GatewayTarget interface {
  41         // Command that will execute cmd inside the container
  42         InjectCommand(ctx context.Context, detachKeys, username string, usingTTY bool, cmd []string) (*exec.Cmd, error)
  43
  44         // IP address inside container
  45         IPAddress() (string, error)
  46 }
  47
  48 type GatewayTargetStub struct{}
  49
  50 func (GatewayTargetStub) IPAddress() (string, error) { return "127.0.0.1", nil }
  51 func (GatewayTargetStub) InjectCommand(ctx context.Context, detachKeys, username string, usingTTY bool, cmd []string) (*exec.Cmd, error) {
  52         return exec.CommandContext(ctx, cmd[0], cmd[1:]...), nil
  53 }
  54
  55 type Gateway struct {
  56         ContainerUUID string
  57         // Caller should set Address to "", or "host:0" or "host:port"
  58         // where host is a known external IP address; port is a
  59         // desired port number to listen on; and ":0" chooses an
  60         // available dynamic port.
  61         //
  62         // If Address is "", Start() listens only on the loopback
  63         // interface (and changes Address to "127.0.0.1:port").
  64         // Otherwise it listens on all interfaces.
  65         //
  66         // If Address is "host:0", Start() updates Address to
  67         // "host:port".
  68         Address    string
  69         AuthSecret string
  70         Target     GatewayTarget
  71         Log        interface {
  72                 Printf(fmt string, args ...interface{})
  73         }
  74         // If non-nil, set up a ContainerGatewayTunnel, so that the
  75         // controller can connect to us even if our external IP
  76         // address is unknown or not routable from controller.
  77         ArvadosClient *arvados.Client
  78
  79         // When a tunnel is connected or reconnected, this func (if
  80         // not nil) will be called with the InternalURL of the
  81         // controller process at the other end of the tunnel.
  82         UpdateTunnelURL func(url string)
  83
  84         // Source for serving WebDAV requests with
  85         // X-Webdav-Source: /log
  86         LogCollection arvados.CollectionFileSystem
  87
  88         sshConfig   ssh.ServerConfig
  89         requestAuth string
  90         respondAuth string
  91 }
  92
  93 // Start starts an http server that allows authenticated clients to open an
  94 // interactive "docker exec" session and (in future) connect to tcp ports
  95 // inside the docker container.
  96 func (gw *Gateway) Start() error {
  97         gw.sshConfig = ssh.ServerConfig{
  98                 NoClientAuth: true,
  99                 PasswordCallback: func(c ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
 100                         if c.User() == "_" {
 101                                 return nil, nil
 102                         }
 103                         return nil, fmt.Errorf("cannot specify user %q via ssh client", c.User())
 104                 },
 105                 PublicKeyCallback: func(c ssh.ConnMetadata, pubKey ssh.PublicKey) (*ssh.Permissions, error) {
 106                         if c.User() == "_" {
 107                                 return &ssh.Permissions{
 108                                         Extensions: map[string]string{
 109                                                 "pubkey-fp": ssh.FingerprintSHA256(pubKey),
 110                                         },
 111                                 }, nil
 112                         }
 113                         return nil, fmt.Errorf("cannot specify user %q via ssh client", c.User())
 114                 },
 115         }
 116         pvt, err := rsa.GenerateKey(rand.Reader, 2048)
 117         if err != nil {
 118                 return err
 119         }
 120         err = pvt.Validate()
 121         if err != nil {
 122                 return err
 123         }
 124         signer, err := ssh.NewSignerFromKey(pvt)
 125         if err != nil {
 126                 return err
 127         }
 128         gw.sshConfig.AddHostKey(signer)
 129
 130         // Address (typically provided by arvados-dispatch-cloud) is
 131         // HOST:PORT where HOST is our IP address or hostname as seen
 132         // from arvados-controller, and PORT is either the desired
 133         // port where we should run our gateway server, or "0" if we
 134         // should choose an available port.
 135         extAddr := gw.Address
 136         // Generally we can't know which local interface corresponds
 137         // to an externally reachable IP address, so if we expect to
 138         // be reachable by external hosts, we listen on all
 139         // interfaces.
 140         listenHost := ""
 141         if extAddr == "" {
 142                 // If the dispatcher doesn't tell us our external IP
 143                 // address, controller will only be able to connect
 144                 // through the tunnel (see runTunnel), so our gateway
 145                 // server only needs to listen on the loopback
 146                 // interface.
 147                 extAddr = "127.0.0.1:0"
 148                 listenHost = "127.0.0.1"
 149         }
 150         extHost, extPort, err := net.SplitHostPort(extAddr)
 151         if err != nil {
 152                 return err
 153         }
 154         cert, err := selfsigned.CertGenerator{}.Generate()
 155         if err != nil {
 156                 return err
 157         }
 158         h := hmac.New(sha256.New, []byte(gw.AuthSecret))
 159         h.Write(cert.Certificate[0])
 160         gw.requestAuth = fmt.Sprintf("%x", h.Sum(nil))
 161         h.Reset()
 162         h.Write([]byte(gw.requestAuth))
 163         gw.respondAuth = fmt.Sprintf("%x", h.Sum(nil))
 164
 165         srv := &httpserver.Server{
 166                 Server: http.Server{
 167                         Handler: gw,
 168                         TLSConfig: &tls.Config{
 169                                 Certificates: []tls.Certificate{cert},
 170                         },
 171                 },
 172                 Addr: net.JoinHostPort(listenHost, extPort),
 173         }
 174         err = srv.Start()
 175         if err != nil {
 176                 return err
 177         }
 178         go func() {
 179                 err := srv.Wait()
 180                 gw.Log.Printf("gateway server stopped: %s", err)
 181         }()
 182         // Get the port number we are listening on (extPort might be
 183         // "0" or a port name, in which case this will be different).
 184         _, listenPort, err := net.SplitHostPort(srv.Addr)
 185         if err != nil {
 186                 return err
 187         }
 188         // When changing state to Running, the caller will want to set
 189         // gateway_address to a "HOST:PORT" that, if controller
 190         // connects to it, will reach this gateway server.
 191         //
 192         // The most likely thing to work is: HOST is our external
 193         // hostname/IP as provided by the caller
 194         // (arvados-dispatch-cloud) or 127.0.0.1 to indicate
 195         // non-tunnel connections aren't available; and PORT is the
 196         // port number we are listening on.
 197         gw.Address = net.JoinHostPort(extHost, listenPort)
 198         gw.Log.Printf("gateway server listening at %s", gw.Address)
 199         if gw.ArvadosClient != nil {
 200                 go gw.maintainTunnel(gw.Address)
 201         }
 202         return nil
 203 }
 204
 205 func (gw *Gateway) maintainTunnel(addr string) {
 206         for ; ; time.Sleep(5 * time.Second) {
 207                 err := gw.runTunnel(addr)
 208                 gw.Log.Printf("runTunnel: %s", err)
 209         }
 210 }
 211
 212 // runTunnel connects to controller and sets up a tunnel through
 213 // which controller can connect to the gateway server at the given
 214 // addr.
 215 func (gw *Gateway) runTunnel(addr string) error {
 216         ctx := auth.NewContext(context.Background(), auth.NewCredentials(gw.ArvadosClient.AuthToken))
 217         arpc := rpc.NewConn("", &url.URL{Scheme: "https", Host: gw.ArvadosClient.APIHost}, gw.ArvadosClient.Insecure, rpc.PassthroughTokenProvider)
 218         tun, err := arpc.ContainerGatewayTunnel(ctx, arvados.ContainerGatewayTunnelOptions{
 219                 UUID:       gw.ContainerUUID,
 220                 AuthSecret: gw.AuthSecret,
 221         })
 222         if err != nil {
 223                 return fmt.Errorf("error creating gateway tunnel: %w", err)
 224         }
 225         mux, err := yamux.Client(tun.Conn, nil)
 226         if err != nil {
 227                 return fmt.Errorf("error setting up mux client end: %s", err)
 228         }
 229         if url := tun.Header.Get("X-Arvados-Internal-Url"); url != "" && gw.UpdateTunnelURL != nil {
 230                 gw.UpdateTunnelURL(url)
 231         }
 232         for {
 233                 muxconn, err := mux.AcceptStream()
 234                 if err != nil {
 235                         return err
 236                 }
 237                 gw.Log.Printf("tunnel connection %d started", muxconn.StreamID())
 238                 go func() {
 239                         defer muxconn.Close()
 240                         gwconn, err := net.Dial("tcp", addr)
 241                         if err != nil {
 242                                 gw.Log.Printf("tunnel connection %d: error connecting to %s: %s", muxconn.StreamID(), addr, err)
 243                                 return
 244                         }
 245                         defer gwconn.Close()
 246                         var wg sync.WaitGroup
 247                         wg.Add(2)
 248                         go func() {
 249                                 defer wg.Done()
 250                                 _, err := io.Copy(gwconn, muxconn)
 251                                 if err != nil {
 252                                         gw.Log.Printf("tunnel connection %d: mux end: %s", muxconn.StreamID(), err)
 253                                 }
 254                                 gwconn.Close()
 255                         }()
 256                         go func() {
 257                                 defer wg.Done()
 258                                 _, err := io.Copy(muxconn, gwconn)
 259                                 if err != nil {
 260                                         gw.Log.Printf("tunnel connection %d: gateway end: %s", muxconn.StreamID(), err)
 261                                 }
 262                                 muxconn.Close()
 263                         }()
 264                         wg.Wait()
 265                         gw.Log.Printf("tunnel connection %d finished", muxconn.StreamID())
 266                 }()
 267         }
 268 }
 269
 270 var webdavMethod = map[string]bool{
 271         "GET":      true,
 272         "OPTIONS":  true,
 273         "PROPFIND": true,
 274 }
 275
 276 func (gw *Gateway) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 277         w.Header().Set("Vary", "X-Arvados-Authorization, X-Arvados-Container-Gateway-Uuid, X-Webdav-Prefix, X-Webdav-Source")
 278         reqUUID := req.Header.Get("X-Arvados-Container-Gateway-Uuid")
 279         if reqUUID == "" {
 280                 // older controller versions only send UUID as query param
 281                 req.ParseForm()
 282                 reqUUID = req.Form.Get("uuid")
 283         }
 284         if reqUUID != gw.ContainerUUID {
 285                 http.Error(w, fmt.Sprintf("misdirected request: meant for %q but received by crunch-run %q", reqUUID, gw.ContainerUUID), http.StatusBadGateway)
 286                 return
 287         }
 288         if req.Header.Get("X-Arvados-Authorization") != gw.requestAuth {
 289                 http.Error(w, "bad X-Arvados-Authorization header", http.StatusUnauthorized)
 290                 return
 291         }
 292         w.Header().Set("X-Arvados-Authorization-Response", gw.respondAuth)
 293         switch {
 294         case req.Method == "POST" && req.Header.Get("Upgrade") == "ssh":
 295                 gw.handleSSH(w, req)
 296         case req.Header.Get("X-Webdav-Source") == "/log":
 297                 if !webdavMethod[req.Method] {
 298                         http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
 299                         return
 300                 }
 301                 gw.handleLogsWebDAV(w, req)
 302         default:
 303                 http.Error(w, "path not found", http.StatusNotFound)
 304         }
 305 }
 306
 307 func (gw *Gateway) handleLogsWebDAV(w http.ResponseWriter, r *http.Request) {
 308         prefix := r.Header.Get("X-Webdav-Prefix")
 309         if !strings.HasPrefix(r.URL.Path, prefix) {
 310                 http.Error(w, "X-Webdav-Prefix header is not a prefix of the requested path", http.StatusBadRequest)
 311                 return
 312         }
 313         if gw.LogCollection == nil {
 314                 http.Error(w, "Not found", http.StatusNotFound)
 315                 return
 316         }
 317         wh := webdav.Handler{
 318                 Prefix: prefix,
 319                 FileSystem: &webdavfs.FS{
 320                         FileSystem:    gw.LogCollection,
 321                         Prefix:        "",
 322                         Writing:       false,
 323                         AlwaysReadEOF: r.Method == "PROPFIND",
 324                 },
 325                 LockSystem: webdavfs.NoLockSystem,
 326                 Logger:     gw.webdavLogger,
 327         }
 328         wh.ServeHTTP(w, r)
 329 }
 330
 331 func (gw *Gateway) webdavLogger(r *http.Request, err error) {
 332         if err != nil && !os.IsNotExist(err) {
 333                 ctxlog.FromContext(r.Context()).WithError(err).Info("error reported by webdav handler")
 334         } else {
 335                 ctxlog.FromContext(r.Context()).WithError(err).Debug("webdav request log")
 336         }
 337 }
 338
 339 // handleSSH connects to an SSH server that allows the caller to run
 340 // interactive commands as root (or any other desired user) inside the
 341 // container. The tunnel itself can only be created by an
 342 // authenticated caller, so the SSH server itself is wide open (any
 343 // password or key will be accepted).
 344 //
 345 // Requests must have path "/ssh" and the following headers:
 346 //
 347 // Connection: upgrade
 348 // Upgrade: ssh
 349 // X-Arvados-Target-Uuid: uuid of container
 350 // X-Arvados-Authorization: must match
 351 // hmac(AuthSecret,certfingerprint) (this prevents other containers
 352 // and shell nodes from connecting directly)
 353 //
 354 // Optional headers:
 355 //
 356 // X-Arvados-Detach-Keys: argument to "docker exec --detach-keys",
 357 // e.g., "ctrl-p,ctrl-q"
 358 // X-Arvados-Login-Username: argument to "docker exec --user": account
 359 // used to run command(s) inside the container.
 360 func (gw *Gateway) handleSSH(w http.ResponseWriter, req *http.Request) {
 361         req.ParseForm()
 362         detachKeys := req.Form.Get("detach_keys")
 363         username := req.Form.Get("login_username")
 364         if username == "" {
 365                 username = "root"
 366         }
 367         hj, ok := w.(http.Hijacker)
 368         if !ok {
 369                 http.Error(w, "ResponseWriter does not support connection upgrade", http.StatusInternalServerError)
 370                 return
 371         }
 372         netconn, _, err := hj.Hijack()
 373         if !ok {
 374                 http.Error(w, err.Error(), http.StatusInternalServerError)
 375                 return
 376         }
 377         defer netconn.Close()
 378         w.Header().Set("Connection", "upgrade")
 379         w.Header().Set("Upgrade", "ssh")
 380         netconn.Write([]byte("HTTP/1.1 101 Switching Protocols\r\n"))
 381         w.Header().Write(netconn)
 382         netconn.Write([]byte("\r\n"))
 383
 384         ctx := req.Context()
 385
 386         conn, newchans, reqs, err := ssh.NewServerConn(netconn, &gw.sshConfig)
 387         if err == io.EOF {
 388                 return
 389         } else if err != nil {
 390                 gw.Log.Printf("ssh.NewServerConn: %s", err)
 391                 return
 392         }
 393         defer conn.Close()
 394         go ssh.DiscardRequests(reqs)
 395         for newch := range newchans {
 396                 switch newch.ChannelType() {
 397                 case "direct-tcpip":
 398                         go gw.handleDirectTCPIP(ctx, newch)
 399                 case "session":
 400                         go gw.handleSession(ctx, newch, detachKeys, username)
 401                 default:
 402                         go newch.Reject(ssh.UnknownChannelType, fmt.Sprintf("unsupported channel type %q", newch.ChannelType()))
 403                 }
 404         }
 405 }
 406
 407 func (gw *Gateway) handleDirectTCPIP(ctx context.Context, newch ssh.NewChannel) {
 408         ch, reqs, err := newch.Accept()
 409         if err != nil {
 410                 gw.Log.Printf("accept direct-tcpip channel: %s", err)
 411                 return
 412         }
 413         defer ch.Close()
 414         go ssh.DiscardRequests(reqs)
 415
 416         // RFC 4254 7.2 (copy of channelOpenDirectMsg in
 417         // golang.org/x/crypto/ssh)
 418         var msg struct {
 419                 Raddr string
 420                 Rport uint32
 421                 Laddr string
 422                 Lport uint32
 423         }
 424         err = ssh.Unmarshal(newch.ExtraData(), &msg)
 425         if err != nil {
 426                 fmt.Fprintf(ch.Stderr(), "unmarshal direct-tcpip extradata: %s\n", err)
 427                 return
 428         }
 429         switch msg.Raddr {
 430         case "localhost", "0.0.0.0", "127.0.0.1", "::1", "::":
 431         default:
 432                 fmt.Fprintf(ch.Stderr(), "cannot forward to ports on %q, only localhost\n", msg.Raddr)
 433                 return
 434         }
 435
 436         dstaddr, err := gw.Target.IPAddress()
 437         if err != nil {
 438                 fmt.Fprintf(ch.Stderr(), "container has no IP address: %s\n", err)
 439                 return
 440         } else if dstaddr == "" {
 441                 fmt.Fprintf(ch.Stderr(), "container has no IP address\n")
 442                 return
 443         }
 444
 445         dst := net.JoinHostPort(dstaddr, fmt.Sprintf("%d", msg.Rport))
 446         tcpconn, err := net.Dial("tcp", dst)
 447         if err != nil {
 448                 fmt.Fprintf(ch.Stderr(), "%s: %s\n", dst, err)
 449                 return
 450         }
 451         go func() {
 452                 n, _ := io.Copy(ch, tcpconn)
 453                 ctxlog.FromContext(ctx).Debugf("tcpip: sent %d bytes\n", n)
 454                 ch.CloseWrite()
 455         }()
 456         n, _ := io.Copy(tcpconn, ch)
 457         ctxlog.FromContext(ctx).Debugf("tcpip: received %d bytes\n", n)
 458 }
 459
 460 func (gw *Gateway) handleSession(ctx context.Context, newch ssh.NewChannel, detachKeys, username string) {
 461         ch, reqs, err := newch.Accept()
 462         if err != nil {
 463                 gw.Log.Printf("error accepting session channel: %s", err)
 464                 return
 465         }
 466         defer ch.Close()
 467
 468         var pty0, tty0 *os.File
 469         // Where to send errors/messages for the client to see
 470         logw := io.Writer(ch.Stderr())
 471         // How to end lines when sending errors/messages to the client
 472         // (changes to \r\n when using a pty)
 473         eol := "\n"
 474         // Env vars to add to child process
 475         termEnv := []string(nil)
 476
 477         started := 0
 478         wantClose := make(chan struct{})
 479         for {
 480                 var req *ssh.Request
 481                 select {
 482                 case r, ok := <-reqs:
 483                         if !ok {
 484                                 return
 485                         }
 486                         req = r
 487                 case <-wantClose:
 488                         return
 489                 }
 490                 ok := false
 491                 switch req.Type {
 492                 case "shell", "exec":
 493                         if started++; started != 1 {
 494                                 // RFC 4254 6.5: "Only one of these
 495                                 // requests can succeed per channel."
 496                                 break
 497                         }
 498                         ok = true
 499                         var payload struct {
 500                                 Command string
 501                         }
 502                         ssh.Unmarshal(req.Payload, &payload)
 503                         execargs, err := shlex.Split(payload.Command)
 504                         if err != nil {
 505                                 fmt.Fprintf(logw, "error parsing supplied command: %s"+eol, err)
 506                                 return
 507                         }
 508                         if len(execargs) == 0 {
 509                                 execargs = []string{"/bin/bash", "-login"}
 510                         }
 511                         go func() {
 512                                 var resp struct {
 513                                         Status uint32
 514                                 }
 515                                 defer func() {
 516                                         ch.SendRequest("exit-status", false, ssh.Marshal(&resp))
 517                                         close(wantClose)
 518                                 }()
 519
 520                                 cmd, err := gw.Target.InjectCommand(ctx, detachKeys, username, tty0 != nil, execargs)
 521                                 if err != nil {
 522                                         fmt.Fprintln(ch.Stderr(), err)
 523                                         ch.CloseWrite()
 524                                         resp.Status = 1
 525                                         return
 526                                 }
 527                                 if tty0 != nil {
 528                                         cmd.Stdin = tty0
 529                                         cmd.Stdout = tty0
 530                                         cmd.Stderr = tty0
 531                                         go io.Copy(ch, pty0)
 532                                         go io.Copy(pty0, ch)
 533                                         // Send our own debug messages to tty as well.
 534                                         logw = tty0
 535                                 } else {
 536                                         // StdinPipe may seem
 537                                         // superfluous here, but it's
 538                                         // not: it causes cmd.Run() to
 539                                         // return when the subprocess
 540                                         // exits. Without it, Run()
 541                                         // waits for stdin to close,
 542                                         // which causes "ssh ... echo
 543                                         // ok" (with the client's
 544                                         // stdin connected to a
 545                                         // terminal or something) to
 546                                         // hang.
 547                                         stdin, err := cmd.StdinPipe()
 548                                         if err != nil {
 549                                                 fmt.Fprintln(ch.Stderr(), err)
 550                                                 ch.CloseWrite()
 551                                                 resp.Status = 1
 552                                                 return
 553                                         }
 554                                         go func() {
 555                                                 io.Copy(stdin, ch)
 556                                                 stdin.Close()
 557                                         }()
 558                                         cmd.Stdout = ch
 559                                         cmd.Stderr = ch.Stderr()
 560                                 }
 561                                 cmd.SysProcAttr = &syscall.SysProcAttr{
 562                                         Setctty: tty0 != nil,
 563                                         Setsid:  true,
 564                                 }
 565                                 cmd.Env = append(os.Environ(), termEnv...)
 566                                 err = cmd.Run()
 567                                 if exiterr, ok := err.(*exec.ExitError); ok {
 568                                         if status, ok := exiterr.Sys().(syscall.WaitStatus); ok {
 569                                                 resp.Status = uint32(status.ExitStatus())
 570                                         }
 571                                 } else if err != nil {
 572                                         // Propagate errors like `exec: "docker": executable file not found in $PATH`
 573                                         fmt.Fprintln(ch.Stderr(), err)
 574                                 }
 575                                 errClose := ch.CloseWrite()
 576                                 if resp.Status == 0 && (err != nil || errClose != nil) {
 577                                         resp.Status = 1
 578                                 }
 579                         }()
 580                 case "pty-req":
 581                         eol = "\r\n"
 582                         p, t, err := pty.Open()
 583                         if err != nil {
 584                                 fmt.Fprintf(ch.Stderr(), "pty failed: %s"+eol, err)
 585                                 break
 586                         }
 587                         defer p.Close()
 588                         defer t.Close()
 589                         pty0, tty0 = p, t
 590                         ok = true
 591                         var payload struct {
 592                                 Term string
 593                                 Cols uint32
 594                                 Rows uint32
 595                                 X    uint32
 596                                 Y    uint32
 597                         }
 598                         ssh.Unmarshal(req.Payload, &payload)
 599                         termEnv = []string{"TERM=" + payload.Term, "USE_TTY=1"}
 600                         err = pty.Setsize(pty0, &pty.Winsize{Rows: uint16(payload.Rows), Cols: uint16(payload.Cols), X: uint16(payload.X), Y: uint16(payload.Y)})
 601                         if err != nil {
 602                                 fmt.Fprintf(logw, "pty-req: setsize failed: %s"+eol, err)
 603                         }
 604                 case "window-change":
 605                         var payload struct {
 606                                 Cols uint32
 607                                 Rows uint32
 608                                 X    uint32
 609                                 Y    uint32
 610                         }
 611                         ssh.Unmarshal(req.Payload, &payload)
 612                         err := pty.Setsize(pty0, &pty.Winsize{Rows: uint16(payload.Rows), Cols: uint16(payload.Cols), X: uint16(payload.X), Y: uint16(payload.Y)})
 613                         if err != nil {
 614                                 fmt.Fprintf(logw, "window-change: setsize failed: %s"+eol, err)
 615                                 break
 616                         }
 617                         ok = true
 618                 case "env":
 619                         // TODO: implement "env"
 620                         // requests by setting env
 621                         // vars in the docker-exec
 622                         // command (not docker-exec's
 623                         // own environment, which
 624                         // would be a gaping security
 625                         // hole).
 626                 default:
 627                         // fmt.Fprintf(logw, "declined request %q on ssh channel"+eol, req.Type)
 628                 }
 629                 if req.WantReply {
 630                         req.Reply(ok, nil)
 631                 }
 632         }
 633 }