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         "crypto/hmac"
   9         "crypto/rand"
  10         "crypto/rsa"
  11         "crypto/sha256"
  12         "crypto/tls"
  13         "fmt"
  14         "io"
  15         "net"
  16         "net/http"
  17         "net/url"
  18         "os"
  19         "os/exec"
  20         "strings"
  21         "sync"
  22         "syscall"
  23         "time"
  24
  25         "git.arvados.org/arvados.git/lib/controller/rpc"
  26         "git.arvados.org/arvados.git/lib/selfsigned"
  27         "git.arvados.org/arvados.git/lib/webdavfs"
  28         "git.arvados.org/arvados.git/sdk/go/arvados"
  29         "git.arvados.org/arvados.git/sdk/go/auth"
  30         "git.arvados.org/arvados.git/sdk/go/ctxlog"
  31         "git.arvados.org/arvados.git/sdk/go/httpserver"
  32         "github.com/creack/pty"
  33         "github.com/google/shlex"
  34         "github.com/hashicorp/yamux"
  35         "golang.org/x/crypto/ssh"
  36         "golang.org/x/net/context"
  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 at /arvados/v1/{uuid}/log/
  85         LogCollection arvados.CollectionFileSystem
  86
  87         sshConfig   ssh.ServerConfig
  88         requestAuth string
  89         respondAuth string
  90         logPath     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         gw.logPath = "/arvados/v1/containers/" + gw.ContainerUUID + "/log"
 166
 167         srv := &httpserver.Server{
 168                 Server: http.Server{
 169                         Handler: gw,
 170                         TLSConfig: &tls.Config{
 171                                 Certificates: []tls.Certificate{cert},
 172                         },
 173                 },
 174                 Addr: net.JoinHostPort(listenHost, extPort),
 175         }
 176         err = srv.Start()
 177         if err != nil {
 178                 return err
 179         }
 180         go func() {
 181                 err := srv.Wait()
 182                 gw.Log.Printf("gateway server stopped: %s", err)
 183         }()
 184         // Get the port number we are listening on (extPort might be
 185         // "0" or a port name, in which case this will be different).
 186         _, listenPort, err := net.SplitHostPort(srv.Addr)
 187         if err != nil {
 188                 return err
 189         }
 190         // When changing state to Running, the caller will want to set
 191         // gateway_address to a "HOST:PORT" that, if controller
 192         // connects to it, will reach this gateway server.
 193         //
 194         // The most likely thing to work is: HOST is our external
 195         // hostname/IP as provided by the caller
 196         // (arvados-dispatch-cloud) or 127.0.0.1 to indicate
 197         // non-tunnel connections aren't available; and PORT is the
 198         // port number we are listening on.
 199         gw.Address = net.JoinHostPort(extHost, listenPort)
 200         gw.Log.Printf("gateway server listening at %s", gw.Address)
 201         if gw.ArvadosClient != nil {
 202                 go gw.maintainTunnel(gw.Address)
 203         }
 204         return nil
 205 }
 206
 207 func (gw *Gateway) maintainTunnel(addr string) {
 208         for ; ; time.Sleep(5 * time.Second) {
 209                 err := gw.runTunnel(addr)
 210                 gw.Log.Printf("runTunnel: %s", err)
 211         }
 212 }
 213
 214 // runTunnel connects to controller and sets up a tunnel through
 215 // which controller can connect to the gateway server at the given
 216 // addr.
 217 func (gw *Gateway) runTunnel(addr string) error {
 218         ctx := auth.NewContext(context.Background(), auth.NewCredentials(gw.ArvadosClient.AuthToken))
 219         arpc := rpc.NewConn("", &url.URL{Scheme: "https", Host: gw.ArvadosClient.APIHost}, gw.ArvadosClient.Insecure, rpc.PassthroughTokenProvider)
 220         tun, err := arpc.ContainerGatewayTunnel(ctx, arvados.ContainerGatewayTunnelOptions{
 221                 UUID:       gw.ContainerUUID,
 222                 AuthSecret: gw.AuthSecret,
 223         })
 224         if err != nil {
 225                 return fmt.Errorf("error creating gateway tunnel: %s", err)
 226         }
 227         mux, err := yamux.Client(tun.Conn, nil)
 228         if err != nil {
 229                 return fmt.Errorf("error setting up mux client end: %s", err)
 230         }
 231         if url := tun.Header.Get("X-Arvados-Internal-Url"); url != "" && gw.UpdateTunnelURL != nil {
 232                 gw.UpdateTunnelURL(url)
 233         }
 234         for {
 235                 muxconn, err := mux.AcceptStream()
 236                 if err != nil {
 237                         return err
 238                 }
 239                 gw.Log.Printf("tunnel connection %d started", muxconn.StreamID())
 240                 go func() {
 241                         defer muxconn.Close()
 242                         gwconn, err := net.Dial("tcp", addr)
 243                         if err != nil {
 244                                 gw.Log.Printf("tunnel connection %d: error connecting to %s: %s", muxconn.StreamID(), addr, err)
 245                                 return
 246                         }
 247                         defer gwconn.Close()
 248                         var wg sync.WaitGroup
 249                         wg.Add(2)
 250                         go func() {
 251                                 defer wg.Done()
 252                                 _, err := io.Copy(gwconn, muxconn)
 253                                 if err != nil {
 254                                         gw.Log.Printf("tunnel connection %d: mux end: %s", muxconn.StreamID(), err)
 255                                 }
 256                                 gwconn.Close()
 257                         }()
 258                         go func() {
 259                                 defer wg.Done()
 260                                 _, err := io.Copy(muxconn, gwconn)
 261                                 if err != nil {
 262                                         gw.Log.Printf("tunnel connection %d: gateway end: %s", muxconn.StreamID(), err)
 263                                 }
 264                                 muxconn.Close()
 265                         }()
 266                         wg.Wait()
 267                         gw.Log.Printf("tunnel connection %d finished", muxconn.StreamID())
 268                 }()
 269         }
 270 }
 271
 272 var webdavMethod = map[string]bool{
 273         "GET":      true,
 274         "OPTIONS":  true,
 275         "PROPFIND": true,
 276 }
 277
 278 func (gw *Gateway) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 279         reqUUID := req.Header.Get("X-Arvados-Container-Gateway-Uuid")
 280         if reqUUID == "" {
 281                 // older controller versions only send UUID as query param
 282                 req.ParseForm()
 283                 reqUUID = req.Form.Get("uuid")
 284         }
 285         if reqUUID != gw.ContainerUUID {
 286                 http.Error(w, fmt.Sprintf("misdirected request: meant for %q but received by crunch-run %q", reqUUID, gw.ContainerUUID), http.StatusBadGateway)
 287                 return
 288         }
 289         if req.Header.Get("X-Arvados-Authorization") != gw.requestAuth {
 290                 http.Error(w, "bad X-Arvados-Authorization header", http.StatusUnauthorized)
 291                 return
 292         }
 293         w.Header().Set("X-Arvados-Authorization-Response", gw.respondAuth)
 294         switch {
 295         case req.Method == "POST" && req.Header.Get("Upgrade") == "ssh":
 296                 gw.handleSSH(w, req)
 297         case req.URL.Path == gw.logPath || strings.HasPrefix(req.URL.Path, gw.logPath):
 298                 if !webdavMethod[req.Method] {
 299                         http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
 300                         return
 301                 }
 302                 gw.handleLogsWebDAV(w, req)
 303         default:
 304                 http.Error(w, "path not found", http.StatusNotFound)
 305         }
 306 }
 307
 308 func (gw *Gateway) handleLogsWebDAV(w http.ResponseWriter, r *http.Request) {
 309         if gw.LogCollection == nil {
 310                 http.Error(w, "Not found", http.StatusNotFound)
 311                 return
 312         }
 313         wh := webdav.Handler{
 314                 Prefix: gw.logPath,
 315                 FileSystem: &webdavfs.FS{
 316                         FileSystem:    gw.LogCollection,
 317                         Prefix:        "",
 318                         Writing:       false,
 319                         AlwaysReadEOF: r.Method == "PROPFIND",
 320                 },
 321                 LockSystem: webdavfs.NoLockSystem,
 322                 Logger:     gw.webdavLogger,
 323         }
 324         wh.ServeHTTP(w, r)
 325 }
 326
 327 func (gw *Gateway) webdavLogger(r *http.Request, err error) {
 328         if err != nil {
 329                 ctxlog.FromContext(r.Context()).WithError(err).Error("error reported by webdav handler")
 330         }
 331 }
 332
 333 // handleSSH connects to an SSH server that allows the caller to run
 334 // interactive commands as root (or any other desired user) inside the
 335 // container. The tunnel itself can only be created by an
 336 // authenticated caller, so the SSH server itself is wide open (any
 337 // password or key will be accepted).
 338 //
 339 // Requests must have path "/ssh" and the following headers:
 340 //
 341 // Connection: upgrade
 342 // Upgrade: ssh
 343 // X-Arvados-Target-Uuid: uuid of container
 344 // X-Arvados-Authorization: must match
 345 // hmac(AuthSecret,certfingerprint) (this prevents other containers
 346 // and shell nodes from connecting directly)
 347 //
 348 // Optional headers:
 349 //
 350 // X-Arvados-Detach-Keys: argument to "docker exec --detach-keys",
 351 // e.g., "ctrl-p,ctrl-q"
 352 // X-Arvados-Login-Username: argument to "docker exec --user": account
 353 // used to run command(s) inside the container.
 354 func (gw *Gateway) handleSSH(w http.ResponseWriter, req *http.Request) {
 355         req.ParseForm()
 356         detachKeys := req.Form.Get("detach_keys")
 357         username := req.Form.Get("login_username")
 358         if username == "" {
 359                 username = "root"
 360         }
 361         hj, ok := w.(http.Hijacker)
 362         if !ok {
 363                 http.Error(w, "ResponseWriter does not support connection upgrade", http.StatusInternalServerError)
 364                 return
 365         }
 366         netconn, _, err := hj.Hijack()
 367         if !ok {
 368                 http.Error(w, err.Error(), http.StatusInternalServerError)
 369                 return
 370         }
 371         defer netconn.Close()
 372         w.Header().Set("Connection", "upgrade")
 373         w.Header().Set("Upgrade", "ssh")
 374         netconn.Write([]byte("HTTP/1.1 101 Switching Protocols\r\n"))
 375         w.Header().Write(netconn)
 376         netconn.Write([]byte("\r\n"))
 377
 378         ctx := req.Context()
 379
 380         conn, newchans, reqs, err := ssh.NewServerConn(netconn, &gw.sshConfig)
 381         if err == io.EOF {
 382                 return
 383         } else if err != nil {
 384                 gw.Log.Printf("ssh.NewServerConn: %s", err)
 385                 return
 386         }
 387         defer conn.Close()
 388         go ssh.DiscardRequests(reqs)
 389         for newch := range newchans {
 390                 switch newch.ChannelType() {
 391                 case "direct-tcpip":
 392                         go gw.handleDirectTCPIP(ctx, newch)
 393                 case "session":
 394                         go gw.handleSession(ctx, newch, detachKeys, username)
 395                 default:
 396                         go newch.Reject(ssh.UnknownChannelType, fmt.Sprintf("unsupported channel type %q", newch.ChannelType()))
 397                 }
 398         }
 399 }
 400
 401 func (gw *Gateway) handleDirectTCPIP(ctx context.Context, newch ssh.NewChannel) {
 402         ch, reqs, err := newch.Accept()
 403         if err != nil {
 404                 gw.Log.Printf("accept direct-tcpip channel: %s", err)
 405                 return
 406         }
 407         defer ch.Close()
 408         go ssh.DiscardRequests(reqs)
 409
 410         // RFC 4254 7.2 (copy of channelOpenDirectMsg in
 411         // golang.org/x/crypto/ssh)
 412         var msg struct {
 413                 Raddr string
 414                 Rport uint32
 415                 Laddr string
 416                 Lport uint32
 417         }
 418         err = ssh.Unmarshal(newch.ExtraData(), &msg)
 419         if err != nil {
 420                 fmt.Fprintf(ch.Stderr(), "unmarshal direct-tcpip extradata: %s\n", err)
 421                 return
 422         }
 423         switch msg.Raddr {
 424         case "localhost", "0.0.0.0", "127.0.0.1", "::1", "::":
 425         default:
 426                 fmt.Fprintf(ch.Stderr(), "cannot forward to ports on %q, only localhost\n", msg.Raddr)
 427                 return
 428         }
 429
 430         dstaddr, err := gw.Target.IPAddress()
 431         if err != nil {
 432                 fmt.Fprintf(ch.Stderr(), "container has no IP address: %s\n", err)
 433                 return
 434         } else if dstaddr == "" {
 435                 fmt.Fprintf(ch.Stderr(), "container has no IP address\n")
 436                 return
 437         }
 438
 439         dst := net.JoinHostPort(dstaddr, fmt.Sprintf("%d", msg.Rport))
 440         tcpconn, err := net.Dial("tcp", dst)
 441         if err != nil {
 442                 fmt.Fprintf(ch.Stderr(), "%s: %s\n", dst, err)
 443                 return
 444         }
 445         go func() {
 446                 n, _ := io.Copy(ch, tcpconn)
 447                 ctxlog.FromContext(ctx).Debugf("tcpip: sent %d bytes\n", n)
 448                 ch.CloseWrite()
 449         }()
 450         n, _ := io.Copy(tcpconn, ch)
 451         ctxlog.FromContext(ctx).Debugf("tcpip: received %d bytes\n", n)
 452 }
 453
 454 func (gw *Gateway) handleSession(ctx context.Context, newch ssh.NewChannel, detachKeys, username string) {
 455         ch, reqs, err := newch.Accept()
 456         if err != nil {
 457                 gw.Log.Printf("error accepting session channel: %s", err)
 458                 return
 459         }
 460         defer ch.Close()
 461
 462         var pty0, tty0 *os.File
 463         // Where to send errors/messages for the client to see
 464         logw := io.Writer(ch.Stderr())
 465         // How to end lines when sending errors/messages to the client
 466         // (changes to \r\n when using a pty)
 467         eol := "\n"
 468         // Env vars to add to child process
 469         termEnv := []string(nil)
 470
 471         started := 0
 472         wantClose := make(chan struct{})
 473         for {
 474                 var req *ssh.Request
 475                 select {
 476                 case r, ok := <-reqs:
 477                         if !ok {
 478                                 return
 479                         }
 480                         req = r
 481                 case <-wantClose:
 482                         return
 483                 }
 484                 ok := false
 485                 switch req.Type {
 486                 case "shell", "exec":
 487                         if started++; started != 1 {
 488                                 // RFC 4254 6.5: "Only one of these
 489                                 // requests can succeed per channel."
 490                                 break
 491                         }
 492                         ok = true
 493                         var payload struct {
 494                                 Command string
 495                         }
 496                         ssh.Unmarshal(req.Payload, &payload)
 497                         execargs, err := shlex.Split(payload.Command)
 498                         if err != nil {
 499                                 fmt.Fprintf(logw, "error parsing supplied command: %s"+eol, err)
 500                                 return
 501                         }
 502                         if len(execargs) == 0 {
 503                                 execargs = []string{"/bin/bash", "-login"}
 504                         }
 505                         go func() {
 506                                 var resp struct {
 507                                         Status uint32
 508                                 }
 509                                 defer func() {
 510                                         ch.SendRequest("exit-status", false, ssh.Marshal(&resp))
 511                                         close(wantClose)
 512                                 }()
 513
 514                                 cmd, err := gw.Target.InjectCommand(ctx, detachKeys, username, tty0 != nil, execargs)
 515                                 if err != nil {
 516                                         fmt.Fprintln(ch.Stderr(), err)
 517                                         ch.CloseWrite()
 518                                         resp.Status = 1
 519                                         return
 520                                 }
 521                                 if tty0 != nil {
 522                                         cmd.Stdin = tty0
 523                                         cmd.Stdout = tty0
 524                                         cmd.Stderr = tty0
 525                                         go io.Copy(ch, pty0)
 526                                         go io.Copy(pty0, ch)
 527                                         // Send our own debug messages to tty as well.
 528                                         logw = tty0
 529                                 } else {
 530                                         // StdinPipe may seem
 531                                         // superfluous here, but it's
 532                                         // not: it causes cmd.Run() to
 533                                         // return when the subprocess
 534                                         // exits. Without it, Run()
 535                                         // waits for stdin to close,
 536                                         // which causes "ssh ... echo
 537                                         // ok" (with the client's
 538                                         // stdin connected to a
 539                                         // terminal or something) to
 540                                         // hang.
 541                                         stdin, err := cmd.StdinPipe()
 542                                         if err != nil {
 543                                                 fmt.Fprintln(ch.Stderr(), err)
 544                                                 ch.CloseWrite()
 545                                                 resp.Status = 1
 546                                                 return
 547                                         }
 548                                         go func() {
 549                                                 io.Copy(stdin, ch)
 550                                                 stdin.Close()
 551                                         }()
 552                                         cmd.Stdout = ch
 553                                         cmd.Stderr = ch.Stderr()
 554                                 }
 555                                 cmd.SysProcAttr = &syscall.SysProcAttr{
 556                                         Setctty: tty0 != nil,
 557                                         Setsid:  true,
 558                                 }
 559                                 cmd.Env = append(os.Environ(), termEnv...)
 560                                 err = cmd.Run()
 561                                 if exiterr, ok := err.(*exec.ExitError); ok {
 562                                         if status, ok := exiterr.Sys().(syscall.WaitStatus); ok {
 563                                                 resp.Status = uint32(status.ExitStatus())
 564                                         }
 565                                 } else if err != nil {
 566                                         // Propagate errors like `exec: "docker": executable file not found in $PATH`
 567                                         fmt.Fprintln(ch.Stderr(), err)
 568                                 }
 569                                 errClose := ch.CloseWrite()
 570                                 if resp.Status == 0 && (err != nil || errClose != nil) {
 571                                         resp.Status = 1
 572                                 }
 573                         }()
 574                 case "pty-req":
 575                         eol = "\r\n"
 576                         p, t, err := pty.Open()
 577                         if err != nil {
 578                                 fmt.Fprintf(ch.Stderr(), "pty failed: %s"+eol, err)
 579                                 break
 580                         }
 581                         defer p.Close()
 582                         defer t.Close()
 583                         pty0, tty0 = p, t
 584                         ok = true
 585                         var payload struct {
 586                                 Term string
 587                                 Cols uint32
 588                                 Rows uint32
 589                                 X    uint32
 590                                 Y    uint32
 591                         }
 592                         ssh.Unmarshal(req.Payload, &payload)
 593                         termEnv = []string{"TERM=" + payload.Term, "USE_TTY=1"}
 594                         err = pty.Setsize(pty0, &pty.Winsize{Rows: uint16(payload.Rows), Cols: uint16(payload.Cols), X: uint16(payload.X), Y: uint16(payload.Y)})
 595                         if err != nil {
 596                                 fmt.Fprintf(logw, "pty-req: setsize failed: %s"+eol, err)
 597                         }
 598                 case "window-change":
 599                         var payload struct {
 600                                 Cols uint32
 601                                 Rows uint32
 602                                 X    uint32
 603                                 Y    uint32
 604                         }
 605                         ssh.Unmarshal(req.Payload, &payload)
 606                         err := pty.Setsize(pty0, &pty.Winsize{Rows: uint16(payload.Rows), Cols: uint16(payload.Cols), X: uint16(payload.X), Y: uint16(payload.Y)})
 607                         if err != nil {
 608                                 fmt.Fprintf(logw, "window-change: setsize failed: %s"+eol, err)
 609                                 break
 610                         }
 611                         ok = true
 612                 case "env":
 613                         // TODO: implement "env"
 614                         // requests by setting env
 615                         // vars in the docker-exec
 616                         // command (not docker-exec's
 617                         // own environment, which
 618                         // would be a gaping security
 619                         // hole).
 620                 default:
 621                         // fmt.Fprintf(logw, "declined request %q on ssh channel"+eol, req.Type)
 622                 }
 623                 if req.WantReply {
 624                         req.Reply(ok, nil)
 625                 }
 626         }
 627 }