lib/controller/localdb/container_gateway.go

   1 // Copyright (C) The Arvados Authors. All rights reserved.
   2 //
   3 // SPDX-License-Identifier: AGPL-3.0
   4
   5 package localdb
   6
   7 import (
   8         "bufio"
   9         "bytes"
  10         "context"
  11         "crypto/hmac"
  12         "crypto/sha256"
  13         "crypto/subtle"
  14         "crypto/tls"
  15         "crypto/x509"
  16         "errors"
  17         "fmt"
  18         "io"
  19         "io/ioutil"
  20         "net"
  21         "net/http"
  22         "net/http/httputil"
  23         "net/url"
  24         "os"
  25         "strings"
  26
  27         "git.arvados.org/arvados.git/lib/controller/rpc"
  28         "git.arvados.org/arvados.git/lib/service"
  29         "git.arvados.org/arvados.git/lib/webdavfs"
  30         "git.arvados.org/arvados.git/sdk/go/arvados"
  31         "git.arvados.org/arvados.git/sdk/go/auth"
  32         "git.arvados.org/arvados.git/sdk/go/ctxlog"
  33         "git.arvados.org/arvados.git/sdk/go/httpserver"
  34         keepweb "git.arvados.org/arvados.git/services/keep-web"
  35         "github.com/hashicorp/yamux"
  36         "golang.org/x/net/webdav"
  37 )
  38
  39 var (
  40         forceProxyForTest       = false
  41         forceInternalURLForTest *arvados.URL
  42 )
  43
  44 // ContainerRequestLog returns a WebDAV handler that reads logs from
  45 // the indicated container request. It works by proxying the incoming
  46 // HTTP request to
  47 //
  48 //   - the container gateway, if there is an associated container that
  49 //     is running
  50 //
  51 //   - a different controller process, if there is a running container
  52 //     whose gateway is accessible through a tunnel to a different
  53 //     controller process
  54 //
  55 //   - keep-web, if saved logs exist and there is no gateway (or the
  56 //     associated container is finished)
  57 //
  58 //   - an empty-collection stub, if there is no gateway and no saved
  59 //     log
  60 //
  61 // For an incoming request
  62 //
  63 //      GET /arvados/v1/container_requests/{cr_uuid}/log/{c_uuid}{/c_log_path}
  64 //
  65 // The upstream request may be to {c_uuid}'s container gateway
  66 //
  67 //      GET /arvados/v1/container_requests/{cr_uuid}/log/{c_uuid}{/c_log_path}
  68 //      X-Webdav-Prefix: /arvados/v1/container_requests/{cr_uuid}/log/{c_uuid}
  69 //      X-Webdav-Source: /log
  70 //
  71 // ...or the upstream request may be to keep-web (where {cr_log_uuid}
  72 // is the container request log collection UUID)
  73 //
  74 //      GET /arvados/v1/container_requests/{cr_uuid}/log/{c_uuid}{/c_log_path}
  75 //      Host: {cr_log_uuid}.internal
  76 //      X-Webdav-Prefix: /arvados/v1/container_requests/{cr_uuid}/log
  77 //      X-Arvados-Container-Uuid: {c_uuid}
  78 //
  79 // ...or the request may be handled locally using an empty-collection
  80 // stub.
  81 func (conn *Conn) ContainerRequestLog(ctx context.Context, opts arvados.ContainerLogOptions) (http.Handler, error) {
  82         if opts.Method == "OPTIONS" && opts.Header.Get("Access-Control-Request-Method") != "" {
  83                 return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
  84                         if !keepweb.ServeCORSPreflight(w, opts.Header) {
  85                                 // Inconceivable.  We already checked
  86                                 // for the only condition where
  87                                 // ServeCORSPreflight returns false.
  88                                 httpserver.Error(w, "unhandled CORS preflight request", http.StatusInternalServerError)
  89                         }
  90                 }), nil
  91         }
  92         cr, err := conn.railsProxy.ContainerRequestGet(ctx, arvados.GetOptions{UUID: opts.UUID, Select: []string{"uuid", "container_uuid", "log_uuid"}})
  93         if err != nil {
  94                 if se := httpserver.HTTPStatusError(nil); errors.As(err, &se) && se.HTTPStatus() == http.StatusUnauthorized {
  95                         // Hint to WebDAV client that we accept HTTP basic auth.
  96                         return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
  97                                 w.Header().Set("Www-Authenticate", "Basic realm=\"collections\"")
  98                                 w.WriteHeader(http.StatusUnauthorized)
  99                         }), nil
 100                 }
 101                 return nil, err
 102         }
 103         ctr, err := conn.railsProxy.ContainerGet(ctx, arvados.GetOptions{UUID: cr.ContainerUUID, Select: []string{"uuid", "state", "gateway_address"}})
 104         if err != nil {
 105                 return nil, err
 106         }
 107         // .../log/{ctr.UUID} is a directory where the currently
 108         // assigned container's log data [will] appear (as opposed to
 109         // previous attempts in .../log/{previous_ctr_uuid}). Requests
 110         // that are outside that directory, and requests on a
 111         // non-running container, are proxied to keep-web instead of
 112         // going through the container gateway system.
 113         //
 114         // Side note: a depth>1 directory tree listing starting at
 115         // .../{cr_uuid}/log will only include subdirectories for
 116         // finished containers, i.e., will not include a subdirectory
 117         // with log data for a current (unfinished) container UUID.
 118         // In order to access live logs, a client must look up the
 119         // container_uuid field of the container request record, and
 120         // explicitly request a path under .../{cr_uuid}/log/{c_uuid}.
 121         if ctr.GatewayAddress == "" ||
 122                 (ctr.State != arvados.ContainerStateLocked && ctr.State != arvados.ContainerStateRunning) ||
 123                 !(opts.Path == "/"+ctr.UUID || strings.HasPrefix(opts.Path, "/"+ctr.UUID+"/")) {
 124                 return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 125                         conn.serveContainerRequestLogViaKeepWeb(opts, cr, w, r)
 126                 }), nil
 127         }
 128         dial, arpc, err := conn.findGateway(ctx, ctr, opts.NoForward)
 129         if err != nil {
 130                 return nil, err
 131         }
 132         if arpc != nil {
 133                 opts.NoForward = true
 134                 return arpc.ContainerRequestLog(ctx, opts)
 135         }
 136         return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 137                 r = r.WithContext(ctx)
 138                 var proxyReq *http.Request
 139                 var proxyErr error
 140                 var expectRespondAuth string
 141                 proxy := &httputil.ReverseProxy{
 142                         // Our custom Transport:
 143                         //
 144                         // - Uses a custom dialer to connect to the
 145                         // gateway (either directly or through a
 146                         // tunnel set up though ContainerTunnel)
 147                         //
 148                         // - Verifies the gateway's TLS certificate
 149                         // using X-Arvados-Authorization headers.
 150                         //
 151                         // This involves modifying the outgoing
 152                         // request header in DialTLSContext.
 153                         // (ReverseProxy certainly doesn't expect us
 154                         // to do this, but it works.)
 155                         Transport: &http.Transport{
 156                                 DialTLSContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
 157                                         tlsconn, requestAuth, respondAuth, err := dial()
 158                                         if err != nil {
 159                                                 return nil, err
 160                                         }
 161                                         proxyReq.Header.Set("X-Arvados-Authorization", requestAuth)
 162                                         expectRespondAuth = respondAuth
 163                                         return tlsconn, nil
 164                                 },
 165                         },
 166                         Director: func(r *http.Request) {
 167                                 // Scheme/host of incoming r.URL are
 168                                 // irrelevant now, and may even be
 169                                 // missing. Host is ignored by our
 170                                 // DialTLSContext, but we need a
 171                                 // generic syntactically correct URL
 172                                 // for net/http to work with.
 173                                 r.URL.Scheme = "https"
 174                                 r.URL.Host = "0.0.0.0:0"
 175                                 r.Header.Set("X-Arvados-Container-Gateway-Uuid", ctr.UUID)
 176                                 r.Header.Set("X-Webdav-Prefix", "/arvados/v1/container_requests/"+cr.UUID+"/log/"+ctr.UUID)
 177                                 r.Header.Set("X-Webdav-Source", "/log")
 178                                 proxyReq = r
 179                         },
 180                         ModifyResponse: func(resp *http.Response) error {
 181                                 if resp.Header.Get("X-Arvados-Authorization-Response") != expectRespondAuth {
 182                                         // Note this is how we detect
 183                                         // an attacker-in-the-middle.
 184                                         return httpserver.ErrorWithStatus(errors.New("bad X-Arvados-Authorization-Response header"), http.StatusBadGateway)
 185                                 }
 186                                 return nil
 187                         },
 188                         ErrorHandler: func(w http.ResponseWriter, r *http.Request, err error) {
 189                                 proxyErr = err
 190                         },
 191                 }
 192                 proxy.ServeHTTP(w, r)
 193                 if proxyErr == nil {
 194                         // proxy succeeded
 195                         return
 196                 }
 197                 // If proxying to the container gateway fails, it
 198                 // might be caused by a race where crunch-run exited
 199                 // after we decided (above) the log was not final.
 200                 // In that case we should proxy to keep-web.
 201                 ctr, err := conn.railsProxy.ContainerGet(ctx, arvados.GetOptions{
 202                         UUID:   ctr.UUID,
 203                         Select: []string{"uuid", "state", "gateway_address", "log"},
 204                 })
 205                 if err != nil {
 206                         // Lost access to the container record?
 207                         httpserver.Error(w, "error re-fetching container record: "+err.Error(), http.StatusServiceUnavailable)
 208                 } else if ctr.State == arvados.ContainerStateLocked || ctr.State == arvados.ContainerStateRunning {
 209                         // No race, proxyErr was the best we can do
 210                         httpserver.Error(w, "proxy error: "+proxyErr.Error(), http.StatusServiceUnavailable)
 211                 } else {
 212                         conn.serveContainerRequestLogViaKeepWeb(opts, cr, w, r)
 213                 }
 214         }), nil
 215 }
 216
 217 // serveContainerLogViaKeepWeb handles a request for saved container
 218 // log content by proxying to one of the configured keep-web servers.
 219 //
 220 // It tries to choose a keep-web server that is running on this host.
 221 func (conn *Conn) serveContainerRequestLogViaKeepWeb(opts arvados.ContainerLogOptions, cr arvados.ContainerRequest, w http.ResponseWriter, r *http.Request) {
 222         if cr.LogUUID == "" {
 223                 // Special case: if no log data exists yet, we serve
 224                 // an empty collection by ourselves instead of
 225                 // proxying to keep-web.
 226                 conn.serveEmptyDir("/arvados/v1/container_requests/"+cr.UUID+"/log", w, r)
 227                 return
 228         }
 229         myURL, _ := service.URLFromContext(r.Context())
 230         u := url.URL(myURL)
 231         myHostname := u.Hostname()
 232         var webdavBase arvados.URL
 233         var ok bool
 234         for webdavBase = range conn.cluster.Services.WebDAV.InternalURLs {
 235                 ok = true
 236                 u := url.URL(webdavBase)
 237                 if h := u.Hostname(); h == "127.0.0.1" || h == "0.0.0.0" || h == "::1" || h == myHostname {
 238                         // Prefer a keep-web service running on the
 239                         // same host as us. (If we don't find one, we
 240                         // pick one arbitrarily.)
 241                         break
 242                 }
 243         }
 244         if !ok {
 245                 httpserver.Error(w, "no internalURLs configured for WebDAV service", http.StatusInternalServerError)
 246                 return
 247         }
 248         proxy := &httputil.ReverseProxy{
 249                 Director: func(r *http.Request) {
 250                         r.URL.Scheme = webdavBase.Scheme
 251                         r.URL.Host = webdavBase.Host
 252                         // Outgoing Host header specifies the
 253                         // collection ID.
 254                         r.Host = cr.LogUUID + ".internal"
 255                         // We already checked permission on the
 256                         // container, so we can use a root token here
 257                         // instead of counting on the "access to log
 258                         // via container request and container"
 259                         // permission check, which can be racy when a
 260                         // request gets retried with a new container.
 261                         r.Header.Set("Authorization", "Bearer "+conn.cluster.SystemRootToken)
 262                         // We can't change r.URL.Path without
 263                         // confusing WebDAV (request body and response
 264                         // headers refer to the same paths) so we tell
 265                         // keep-web to map the log collection onto the
 266                         // containers/X/log/ namespace.
 267                         r.Header.Set("X-Webdav-Prefix", "/arvados/v1/container_requests/"+cr.UUID+"/log")
 268                         if len(opts.Path) >= 28 && opts.Path[6:13] == "-dz642-" {
 269                                 // "/arvados/v1/container_requests/{crUUID}/log/{cUUID}..."
 270                                 // proxies to
 271                                 // "/log for container {cUUID}..."
 272                                 r.Header.Set("X-Webdav-Prefix", "/arvados/v1/container_requests/"+cr.UUID+"/log/"+opts.Path[1:28])
 273                                 r.Header.Set("X-Webdav-Source", "/log for container "+opts.Path[1:28]+"/")
 274                         }
 275                 },
 276         }
 277         if conn.cluster.TLS.Insecure {
 278                 proxy.Transport = &http.Transport{
 279                         TLSClientConfig: &tls.Config{
 280                                 InsecureSkipVerify: conn.cluster.TLS.Insecure,
 281                         },
 282                 }
 283         }
 284         proxy.ServeHTTP(w, r)
 285 }
 286
 287 // serveEmptyDir handles read-only webdav requests as if there was an
 288 // empty collection rooted at the given path. It's equivalent to
 289 // proxying to an empty collection in keep-web, but avoids the extra
 290 // hop.
 291 func (conn *Conn) serveEmptyDir(path string, w http.ResponseWriter, r *http.Request) {
 292         wh := webdav.Handler{
 293                 Prefix:     path,
 294                 FileSystem: webdav.NewMemFS(),
 295                 LockSystem: webdavfs.NoLockSystem,
 296                 Logger: func(r *http.Request, err error) {
 297                         if err != nil && !os.IsNotExist(err) {
 298                                 ctxlog.FromContext(r.Context()).WithError(err).Info("webdav error on empty collection fs")
 299                         }
 300                 },
 301         }
 302         wh.ServeHTTP(w, r)
 303 }
 304
 305 // ContainerSSH returns a connection to the SSH server in the
 306 // appropriate crunch-run process on the worker node where the
 307 // specified container is running.
 308 //
 309 // If the returned error is nil, the caller is responsible for closing
 310 // sshconn.Conn.
 311 func (conn *Conn) ContainerSSH(ctx context.Context, opts arvados.ContainerSSHOptions) (sshconn arvados.ConnectionResponse, err error) {
 312         user, err := conn.railsProxy.UserGetCurrent(ctx, arvados.GetOptions{})
 313         if err != nil {
 314                 return sshconn, err
 315         }
 316         ctr, err := conn.railsProxy.ContainerGet(ctx, arvados.GetOptions{UUID: opts.UUID, Select: []string{"uuid", "state", "gateway_address", "interactive_session_started"}})
 317         if err != nil {
 318                 return sshconn, err
 319         }
 320         ctxRoot := auth.NewContext(ctx, &auth.Credentials{Tokens: []string{conn.cluster.SystemRootToken}})
 321         if !user.IsAdmin || !conn.cluster.Containers.ShellAccess.Admin {
 322                 if !conn.cluster.Containers.ShellAccess.User {
 323                         return sshconn, httpserver.ErrorWithStatus(errors.New("shell access is disabled in config"), http.StatusServiceUnavailable)
 324                 }
 325                 crs, err := conn.railsProxy.ContainerRequestList(ctxRoot, arvados.ListOptions{Limit: -1, Filters: []arvados.Filter{{"container_uuid", "=", opts.UUID}}})
 326                 if err != nil {
 327                         return sshconn, err
 328                 }
 329                 for _, cr := range crs.Items {
 330                         if cr.ModifiedByUserUUID != user.UUID {
 331                                 return sshconn, httpserver.ErrorWithStatus(errors.New("permission denied: container is associated with requests submitted by other users"), http.StatusForbidden)
 332                         }
 333                 }
 334                 if crs.ItemsAvailable != len(crs.Items) {
 335                         return sshconn, httpserver.ErrorWithStatus(errors.New("incomplete response while checking permission"), http.StatusInternalServerError)
 336                 }
 337         }
 338
 339         if ctr.State == arvados.ContainerStateQueued || ctr.State == arvados.ContainerStateLocked {
 340                 return sshconn, httpserver.ErrorWithStatus(fmt.Errorf("container is not running yet (state is %q)", ctr.State), http.StatusServiceUnavailable)
 341         } else if ctr.State != arvados.ContainerStateRunning {
 342                 return sshconn, httpserver.ErrorWithStatus(fmt.Errorf("container has ended (state is %q)", ctr.State), http.StatusGone)
 343         }
 344
 345         dial, arpc, err := conn.findGateway(ctx, ctr, opts.NoForward)
 346         if err != nil {
 347                 return sshconn, err
 348         }
 349         if arpc != nil {
 350                 opts.NoForward = true
 351                 return arpc.ContainerSSH(ctx, opts)
 352         }
 353
 354         tlsconn, requestAuth, respondAuth, err := dial()
 355         if err != nil {
 356                 return sshconn, err
 357         }
 358         bufr := bufio.NewReader(tlsconn)
 359         bufw := bufio.NewWriter(tlsconn)
 360
 361         u := url.URL{
 362                 Scheme: "http",
 363                 Host:   tlsconn.RemoteAddr().String(),
 364                 Path:   "/ssh",
 365         }
 366         postform := url.Values{
 367                 // uuid is only needed for older crunch-run versions
 368                 // (current version uses X-Arvados-* header below)
 369                 "uuid":           {opts.UUID},
 370                 "detach_keys":    {opts.DetachKeys},
 371                 "login_username": {opts.LoginUsername},
 372                 "no_forward":     {fmt.Sprintf("%v", opts.NoForward)},
 373         }
 374         postdata := postform.Encode()
 375         bufw.WriteString("POST " + u.String() + " HTTP/1.1\r\n")
 376         bufw.WriteString("Host: " + u.Host + "\r\n")
 377         bufw.WriteString("Upgrade: ssh\r\n")
 378         bufw.WriteString("X-Arvados-Container-Gateway-Uuid: " + opts.UUID + "\r\n")
 379         bufw.WriteString("X-Arvados-Authorization: " + requestAuth + "\r\n")
 380         bufw.WriteString("Content-Type: application/x-www-form-urlencoded\r\n")
 381         fmt.Fprintf(bufw, "Content-Length: %d\r\n", len(postdata))
 382         bufw.WriteString("\r\n")
 383         bufw.WriteString(postdata)
 384         bufw.Flush()
 385         resp, err := http.ReadResponse(bufr, &http.Request{Method: "POST"})
 386         if err != nil {
 387                 tlsconn.Close()
 388                 return sshconn, httpserver.ErrorWithStatus(fmt.Errorf("error reading http response from gateway: %w", err), http.StatusBadGateway)
 389         }
 390         defer resp.Body.Close()
 391         if resp.StatusCode != http.StatusSwitchingProtocols {
 392                 body, _ := ioutil.ReadAll(io.LimitReader(resp.Body, 1000))
 393                 tlsconn.Close()
 394                 return sshconn, httpserver.ErrorWithStatus(fmt.Errorf("unexpected status %s %q", resp.Status, body), http.StatusBadGateway)
 395         }
 396         if strings.ToLower(resp.Header.Get("Upgrade")) != "ssh" ||
 397                 strings.ToLower(resp.Header.Get("Connection")) != "upgrade" {
 398                 tlsconn.Close()
 399                 return sshconn, httpserver.ErrorWithStatus(errors.New("bad upgrade"), http.StatusBadGateway)
 400         }
 401         if resp.Header.Get("X-Arvados-Authorization-Response") != respondAuth {
 402                 tlsconn.Close()
 403                 return sshconn, httpserver.ErrorWithStatus(errors.New("bad X-Arvados-Authorization-Response header"), http.StatusBadGateway)
 404         }
 405
 406         if !ctr.InteractiveSessionStarted {
 407                 _, err = conn.railsProxy.ContainerUpdate(ctxRoot, arvados.UpdateOptions{
 408                         UUID: opts.UUID,
 409                         Attrs: map[string]interface{}{
 410                                 "interactive_session_started": true,
 411                         },
 412                 })
 413                 if err != nil {
 414                         tlsconn.Close()
 415                         return sshconn, httpserver.ErrorWithStatus(err, http.StatusInternalServerError)
 416                 }
 417         }
 418
 419         sshconn.Conn = tlsconn
 420         sshconn.Bufrw = &bufio.ReadWriter{Reader: bufr, Writer: bufw}
 421         sshconn.Logger = ctxlog.FromContext(ctx)
 422         sshconn.Header = http.Header{"Upgrade": {"ssh"}}
 423         return sshconn, nil
 424 }
 425
 426 // ContainerGatewayTunnel sets up a tunnel enabling us (controller) to
 427 // connect to the caller's (crunch-run's) gateway server.
 428 func (conn *Conn) ContainerGatewayTunnel(ctx context.Context, opts arvados.ContainerGatewayTunnelOptions) (resp arvados.ConnectionResponse, err error) {
 429         h := hmac.New(sha256.New, []byte(conn.cluster.SystemRootToken))
 430         fmt.Fprint(h, opts.UUID)
 431         authSecret := fmt.Sprintf("%x", h.Sum(nil))
 432         if subtle.ConstantTimeCompare([]byte(authSecret), []byte(opts.AuthSecret)) != 1 {
 433                 ctxlog.FromContext(ctx).Info("received incorrect auth_secret")
 434                 return resp, httpserver.ErrorWithStatus(errors.New("authentication error"), http.StatusUnauthorized)
 435         }
 436
 437         muxconn, clientconn := net.Pipe()
 438         tunnel, err := yamux.Server(muxconn, nil)
 439         if err != nil {
 440                 clientconn.Close()
 441                 return resp, httpserver.ErrorWithStatus(err, http.StatusInternalServerError)
 442         }
 443
 444         conn.gwTunnelsLock.Lock()
 445         if conn.gwTunnels == nil {
 446                 conn.gwTunnels = map[string]*yamux.Session{opts.UUID: tunnel}
 447         } else {
 448                 conn.gwTunnels[opts.UUID] = tunnel
 449         }
 450         conn.gwTunnelsLock.Unlock()
 451
 452         go func() {
 453                 <-tunnel.CloseChan()
 454                 conn.gwTunnelsLock.Lock()
 455                 if conn.gwTunnels[opts.UUID] == tunnel {
 456                         delete(conn.gwTunnels, opts.UUID)
 457                 }
 458                 conn.gwTunnelsLock.Unlock()
 459         }()
 460
 461         // Assuming we're acting as the backend of an http server,
 462         // lib/controller/router will call resp's ServeHTTP handler,
 463         // which upgrades the incoming http connection to a raw socket
 464         // and connects it to our yamux.Server through our net.Pipe().
 465         resp.Conn = clientconn
 466         resp.Bufrw = &bufio.ReadWriter{Reader: bufio.NewReader(&bytes.Buffer{}), Writer: bufio.NewWriter(&bytes.Buffer{})}
 467         resp.Logger = ctxlog.FromContext(ctx)
 468         resp.Header = http.Header{"Upgrade": {"tunnel"}}
 469         if u, ok := service.URLFromContext(ctx); ok {
 470                 resp.Header.Set("X-Arvados-Internal-Url", u.String())
 471         } else if forceInternalURLForTest != nil {
 472                 resp.Header.Set("X-Arvados-Internal-Url", forceInternalURLForTest.String())
 473         }
 474         return
 475 }
 476
 477 type gatewayDialer func() (conn net.Conn, requestAuth, respondAuth string, err error)
 478
 479 // findGateway figures out how to connect to ctr's gateway.
 480 //
 481 // If the gateway can be contacted directly or through a tunnel on
 482 // this instance, the first return value is a non-nil dialer.
 483 //
 484 // If the gateway is only accessible through a tunnel through a
 485 // different controller process, the second return value is a non-nil
 486 // *rpc.Conn for that controller.
 487 func (conn *Conn) findGateway(ctx context.Context, ctr arvados.Container, noForward bool) (gatewayDialer, *rpc.Conn, error) {
 488         conn.gwTunnelsLock.Lock()
 489         tunnel := conn.gwTunnels[ctr.UUID]
 490         conn.gwTunnelsLock.Unlock()
 491
 492         myURL, _ := service.URLFromContext(ctx)
 493
 494         if host, _, splitErr := net.SplitHostPort(ctr.GatewayAddress); splitErr == nil && host != "" && host != "127.0.0.1" {
 495                 // If crunch-run provided a GatewayAddress like
 496                 // "ipaddr:port", that means "ipaddr" is one of the
 497                 // external interfaces where the gateway is
 498                 // listening. In that case, it's the most
 499                 // reliable/direct option, so we use it even if a
 500                 // tunnel might also be available.
 501                 return func() (net.Conn, string, string, error) {
 502                         rawconn, err := (&net.Dialer{}).DialContext(ctx, "tcp", ctr.GatewayAddress)
 503                         if err != nil {
 504                                 return nil, "", "", httpserver.ErrorWithStatus(err, http.StatusServiceUnavailable)
 505                         }
 506                         return conn.dialGatewayTLS(ctx, ctr, rawconn)
 507                 }, nil, nil
 508         }
 509         if tunnel != nil && !(forceProxyForTest && !noForward) {
 510                 // If we can't connect directly, and the gateway has
 511                 // established a yamux tunnel with us, connect through
 512                 // the tunnel.
 513                 //
 514                 // ...except: forceProxyForTest means we are emulating
 515                 // a situation where the gateway has established a
 516                 // yamux tunnel with controller B, and the
 517                 // ContainerSSH request arrives at controller A. If
 518                 // noForward==false then we are acting as A, so
 519                 // we pretend not to have a tunnel, and fall through
 520                 // to the "tunurl" case below. If noForward==true
 521                 // then the client is A and we are acting as B, so we
 522                 // connect to our tunnel.
 523                 return func() (net.Conn, string, string, error) {
 524                         rawconn, err := tunnel.Open()
 525                         if err != nil {
 526                                 return nil, "", "", httpserver.ErrorWithStatus(err, http.StatusServiceUnavailable)
 527                         }
 528                         return conn.dialGatewayTLS(ctx, ctr, rawconn)
 529                 }, nil, nil
 530         }
 531         if tunurl := strings.TrimPrefix(ctr.GatewayAddress, "tunnel "); tunurl != ctr.GatewayAddress &&
 532                 tunurl != "" &&
 533                 tunurl != myURL.String() &&
 534                 !noForward {
 535                 // If crunch-run provided a GatewayAddress like
 536                 // "tunnel https://10.0.0.10:1010/", that means the
 537                 // gateway has established a yamux tunnel with the
 538                 // controller process at the indicated InternalURL
 539                 // (which isn't us, otherwise we would have had
 540                 // "tunnel != nil" above). We need to proxy through to
 541                 // the other controller process in order to use the
 542                 // tunnel.
 543                 for u := range conn.cluster.Services.Controller.InternalURLs {
 544                         if u.String() == tunurl {
 545                                 ctxlog.FromContext(ctx).Debugf("connecting to container gateway through other controller at %s", u)
 546                                 u := url.URL(u)
 547                                 return nil, rpc.NewConn(conn.cluster.ClusterID, &u, conn.cluster.TLS.Insecure, rpc.PassthroughTokenProvider), nil
 548                         }
 549                 }
 550                 ctxlog.FromContext(ctx).Warnf("container gateway provided a tunnel endpoint %s that is not one of Services.Controller.InternalURLs", tunurl)
 551                 return nil, nil, httpserver.ErrorWithStatus(errors.New("container gateway is running but tunnel endpoint is invalid"), http.StatusServiceUnavailable)
 552         }
 553         if ctr.GatewayAddress == "" {
 554                 return nil, nil, httpserver.ErrorWithStatus(errors.New("container is running but gateway is not available"), http.StatusServiceUnavailable)
 555         } else {
 556                 return nil, nil, httpserver.ErrorWithStatus(errors.New("container is running but tunnel is down"), http.StatusServiceUnavailable)
 557         }
 558 }
 559
 560 // dialGatewayTLS negotiates a TLS connection to a container gateway
 561 // over the given raw connection.
 562 func (conn *Conn) dialGatewayTLS(ctx context.Context, ctr arvados.Container, rawconn net.Conn) (*tls.Conn, string, string, error) {
 563         // crunch-run uses a self-signed / unverifiable TLS
 564         // certificate, so we use the following scheme to ensure we're
 565         // not talking to an attacker-in-the-middle.
 566         //
 567         // 1. Compute ctrKey = HMAC-SHA256(sysRootToken,ctrUUID) --
 568         // this will be the same ctrKey that a-d-c supplied to
 569         // crunch-run in the GatewayAuthSecret env var.
 570         //
 571         // 2. Compute requestAuth = HMAC-SHA256(ctrKey,serverCert) and
 572         // send it to crunch-run as the X-Arvados-Authorization
 573         // header, proving that we know ctrKey. (Note a MITM cannot
 574         // replay the proof to a real crunch-run server, because the
 575         // real crunch-run server would have a different cert.)
 576         //
 577         // 3. Compute respondAuth = HMAC-SHA256(ctrKey,requestAuth)
 578         // and ensure the server returns it in the
 579         // X-Arvados-Authorization-Response header, proving that the
 580         // server knows ctrKey.
 581         var requestAuth, respondAuth string
 582         tlsconn := tls.Client(rawconn, &tls.Config{
 583                 InsecureSkipVerify: true,
 584                 VerifyPeerCertificate: func(rawCerts [][]byte, verifiedChains [][]*x509.Certificate) error {
 585                         if len(rawCerts) == 0 {
 586                                 return errors.New("no certificate received, cannot compute authorization header")
 587                         }
 588                         h := hmac.New(sha256.New, []byte(conn.cluster.SystemRootToken))
 589                         fmt.Fprint(h, ctr.UUID)
 590                         authKey := fmt.Sprintf("%x", h.Sum(nil))
 591                         h = hmac.New(sha256.New, []byte(authKey))
 592                         h.Write(rawCerts[0])
 593                         requestAuth = fmt.Sprintf("%x", h.Sum(nil))
 594                         h.Reset()
 595                         h.Write([]byte(requestAuth))
 596                         respondAuth = fmt.Sprintf("%x", h.Sum(nil))
 597                         return nil
 598                 },
 599         })
 600         err := tlsconn.HandshakeContext(ctx)
 601         if err != nil {
 602                 return nil, "", "", httpserver.ErrorWithStatus(fmt.Errorf("TLS handshake failed: %w", err), http.StatusBadGateway)
 603         }
 604         if respondAuth == "" {
 605                 tlsconn.Close()
 606                 return nil, "", "", httpserver.ErrorWithStatus(errors.New("BUG: no respondAuth"), http.StatusInternalServerError)
 607         }
 608         return tlsconn, requestAuth, respondAuth, nil
 609 }