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         "os"
  18         "os/exec"
  19         "sync"
  20         "syscall"
  21
  22         "git.arvados.org/arvados.git/lib/selfsigned"
  23         "git.arvados.org/arvados.git/sdk/go/ctxlog"
  24         "git.arvados.org/arvados.git/sdk/go/httpserver"
  25         "github.com/creack/pty"
  26         "github.com/google/shlex"
  27         "golang.org/x/crypto/ssh"
  28         "golang.org/x/net/context"
  29 )
  30
  31 type GatewayTarget interface {
  32         // Command that will execute cmd inside the container
  33         InjectCommand(ctx context.Context, detachKeys, username string, usingTTY bool, cmd []string) (*exec.Cmd, error)
  34
  35         // IP address inside container
  36         IPAddress() (string, error)
  37 }
  38
  39 type Gateway struct {
  40         ContainerUUID string
  41         Address       string // listen host:port; if port=0, Start() will change it to the selected port
  42         AuthSecret    string
  43         Target        GatewayTarget
  44         Log           interface {
  45                 Printf(fmt string, args ...interface{})
  46         }
  47
  48         sshConfig   ssh.ServerConfig
  49         requestAuth string
  50         respondAuth string
  51 }
  52
  53 // Start starts an http server that allows authenticated clients to open an
  54 // interactive "docker exec" session and (in future) connect to tcp ports
  55 // inside the docker container.
  56 func (gw *Gateway) Start() error {
  57         gw.sshConfig = ssh.ServerConfig{
  58                 NoClientAuth: true,
  59                 PasswordCallback: func(c ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
  60                         if c.User() == "_" {
  61                                 return nil, nil
  62                         }
  63                         return nil, fmt.Errorf("cannot specify user %q via ssh client", c.User())
  64                 },
  65                 PublicKeyCallback: func(c ssh.ConnMetadata, pubKey ssh.PublicKey) (*ssh.Permissions, error) {
  66                         if c.User() == "_" {
  67                                 return &ssh.Permissions{
  68                                         Extensions: map[string]string{
  69                                                 "pubkey-fp": ssh.FingerprintSHA256(pubKey),
  70                                         },
  71                                 }, nil
  72                         }
  73                         return nil, fmt.Errorf("cannot specify user %q via ssh client", c.User())
  74                 },
  75         }
  76         pvt, err := rsa.GenerateKey(rand.Reader, 2048)
  77         if err != nil {
  78                 return err
  79         }
  80         err = pvt.Validate()
  81         if err != nil {
  82                 return err
  83         }
  84         signer, err := ssh.NewSignerFromKey(pvt)
  85         if err != nil {
  86                 return err
  87         }
  88         gw.sshConfig.AddHostKey(signer)
  89
  90         // Address (typically provided by arvados-dispatch-cloud) is
  91         // HOST:PORT where HOST is our IP address or hostname as seen
  92         // from arvados-controller, and PORT is either the desired
  93         // port where we should run our gateway server, or "0" if we
  94         // should choose an available port.
  95         host, port, err := net.SplitHostPort(gw.Address)
  96         if err != nil {
  97                 return err
  98         }
  99         cert, err := selfsigned.CertGenerator{}.Generate()
 100         if err != nil {
 101                 return err
 102         }
 103         h := hmac.New(sha256.New, []byte(gw.AuthSecret))
 104         h.Write(cert.Certificate[0])
 105         gw.requestAuth = fmt.Sprintf("%x", h.Sum(nil))
 106         h.Reset()
 107         h.Write([]byte(gw.requestAuth))
 108         gw.respondAuth = fmt.Sprintf("%x", h.Sum(nil))
 109
 110         srv := &httpserver.Server{
 111                 Server: http.Server{
 112                         Handler: http.HandlerFunc(gw.handleSSH),
 113                         TLSConfig: &tls.Config{
 114                                 Certificates: []tls.Certificate{cert},
 115                         },
 116                 },
 117                 Addr: ":" + port,
 118         }
 119         err = srv.Start()
 120         if err != nil {
 121                 return err
 122         }
 123         // Get the port number we are listening on (the port might be
 124         // "0" or a port name, in which case this will be different).
 125         _, port, err = net.SplitHostPort(srv.Addr)
 126         if err != nil {
 127                 return err
 128         }
 129         // When changing state to Running, we will set
 130         // gateway_address to "HOST:PORT" where HOST is our
 131         // external hostname/IP as provided by arvados-dispatch-cloud,
 132         // and PORT is the port number we ended up listening on.
 133         gw.Address = net.JoinHostPort(host, port)
 134         return nil
 135 }
 136
 137 // handleSSH connects to an SSH server that allows the caller to run
 138 // interactive commands as root (or any other desired user) inside the
 139 // container. The tunnel itself can only be created by an
 140 // authenticated caller, so the SSH server itself is wide open (any
 141 // password or key will be accepted).
 142 //
 143 // Requests must have path "/ssh" and the following headers:
 144 //
 145 // Connection: upgrade
 146 // Upgrade: ssh
 147 // X-Arvados-Target-Uuid: uuid of container
 148 // X-Arvados-Authorization: must match
 149 // hmac(AuthSecret,certfingerprint) (this prevents other containers
 150 // and shell nodes from connecting directly)
 151 //
 152 // Optional headers:
 153 //
 154 // X-Arvados-Detach-Keys: argument to "docker exec --detach-keys",
 155 // e.g., "ctrl-p,ctrl-q"
 156 // X-Arvados-Login-Username: argument to "docker exec --user": account
 157 // used to run command(s) inside the container.
 158 func (gw *Gateway) handleSSH(w http.ResponseWriter, req *http.Request) {
 159         // In future we'll handle browser traffic too, but for now the
 160         // only traffic we expect is an SSH tunnel from
 161         // (*lib/controller/localdb.Conn)ContainerSSH()
 162         if req.Method != "GET" || req.Header.Get("Upgrade") != "ssh" {
 163                 http.Error(w, "path not found", http.StatusNotFound)
 164                 return
 165         }
 166         if want := req.Header.Get("X-Arvados-Target-Uuid"); want != gw.ContainerUUID {
 167                 http.Error(w, fmt.Sprintf("misdirected request: meant for %q but received by crunch-run %q", want, gw.ContainerUUID), http.StatusBadGateway)
 168                 return
 169         }
 170         if req.Header.Get("X-Arvados-Authorization") != gw.requestAuth {
 171                 http.Error(w, "bad X-Arvados-Authorization header", http.StatusUnauthorized)
 172                 return
 173         }
 174         detachKeys := req.Header.Get("X-Arvados-Detach-Keys")
 175         username := req.Header.Get("X-Arvados-Login-Username")
 176         if username == "" {
 177                 username = "root"
 178         }
 179         hj, ok := w.(http.Hijacker)
 180         if !ok {
 181                 http.Error(w, "ResponseWriter does not support connection upgrade", http.StatusInternalServerError)
 182                 return
 183         }
 184         netconn, _, err := hj.Hijack()
 185         if !ok {
 186                 http.Error(w, err.Error(), http.StatusInternalServerError)
 187                 return
 188         }
 189         defer netconn.Close()
 190         w.Header().Set("Connection", "upgrade")
 191         w.Header().Set("Upgrade", "ssh")
 192         w.Header().Set("X-Arvados-Authorization-Response", gw.respondAuth)
 193         netconn.Write([]byte("HTTP/1.1 101 Switching Protocols\r\n"))
 194         w.Header().Write(netconn)
 195         netconn.Write([]byte("\r\n"))
 196
 197         ctx := req.Context()
 198
 199         conn, newchans, reqs, err := ssh.NewServerConn(netconn, &gw.sshConfig)
 200         if err != nil {
 201                 gw.Log.Printf("ssh.NewServerConn: %s", err)
 202                 return
 203         }
 204         defer conn.Close()
 205         go ssh.DiscardRequests(reqs)
 206         for newch := range newchans {
 207                 switch newch.ChannelType() {
 208                 case "direct-tcpip":
 209                         go gw.handleDirectTCPIP(ctx, newch)
 210                 case "session":
 211                         go gw.handleSession(ctx, newch, detachKeys, username)
 212                 default:
 213                         go newch.Reject(ssh.UnknownChannelType, fmt.Sprintf("unsupported channel type %q", newch.ChannelType()))
 214                 }
 215         }
 216 }
 217
 218 func (gw *Gateway) handleDirectTCPIP(ctx context.Context, newch ssh.NewChannel) {
 219         ch, reqs, err := newch.Accept()
 220         if err != nil {
 221                 gw.Log.Printf("accept direct-tcpip channel: %s", err)
 222                 return
 223         }
 224         defer ch.Close()
 225         go ssh.DiscardRequests(reqs)
 226
 227         // RFC 4254 7.2 (copy of channelOpenDirectMsg in
 228         // golang.org/x/crypto/ssh)
 229         var msg struct {
 230                 Raddr string
 231                 Rport uint32
 232                 Laddr string
 233                 Lport uint32
 234         }
 235         err = ssh.Unmarshal(newch.ExtraData(), &msg)
 236         if err != nil {
 237                 fmt.Fprintf(ch.Stderr(), "unmarshal direct-tcpip extradata: %s\n", err)
 238                 return
 239         }
 240         switch msg.Raddr {
 241         case "localhost", "0.0.0.0", "127.0.0.1", "::1", "::":
 242         default:
 243                 fmt.Fprintf(ch.Stderr(), "cannot forward to ports on %q, only localhost\n", msg.Raddr)
 244                 return
 245         }
 246
 247         dstaddr, err := gw.Target.IPAddress()
 248         if err != nil {
 249                 fmt.Fprintf(ch.Stderr(), "container has no IP address: %s\n", err)
 250                 return
 251         } else if dstaddr == "" {
 252                 fmt.Fprintf(ch.Stderr(), "container has no IP address\n")
 253                 return
 254         }
 255
 256         dst := net.JoinHostPort(dstaddr, fmt.Sprintf("%d", msg.Rport))
 257         tcpconn, err := net.Dial("tcp", dst)
 258         if err != nil {
 259                 fmt.Fprintf(ch.Stderr(), "%s: %s\n", dst, err)
 260                 return
 261         }
 262         go func() {
 263                 n, _ := io.Copy(ch, tcpconn)
 264                 ctxlog.FromContext(ctx).Debugf("tcpip: sent %d bytes\n", n)
 265                 ch.CloseWrite()
 266         }()
 267         n, _ := io.Copy(tcpconn, ch)
 268         ctxlog.FromContext(ctx).Debugf("tcpip: received %d bytes\n", n)
 269 }
 270
 271 func (gw *Gateway) handleSession(ctx context.Context, newch ssh.NewChannel, detachKeys, username string) {
 272         ch, reqs, err := newch.Accept()
 273         if err != nil {
 274                 gw.Log.Printf("accept session channel: %s", err)
 275                 return
 276         }
 277         var pty0, tty0 *os.File
 278         // Where to send errors/messages for the client to see
 279         logw := io.Writer(ch.Stderr())
 280         // How to end lines when sending errors/messages to the client
 281         // (changes to \r\n when using a pty)
 282         eol := "\n"
 283         // Env vars to add to child process
 284         termEnv := []string(nil)
 285         for req := range reqs {
 286                 ok := false
 287                 switch req.Type {
 288                 case "shell", "exec":
 289                         ok = true
 290                         var payload struct {
 291                                 Command string
 292                         }
 293                         ssh.Unmarshal(req.Payload, &payload)
 294                         execargs, err := shlex.Split(payload.Command)
 295                         if err != nil {
 296                                 fmt.Fprintf(logw, "error parsing supplied command: %s"+eol, err)
 297                                 return
 298                         }
 299                         if len(execargs) == 0 {
 300                                 execargs = []string{"/bin/bash", "-login"}
 301                         }
 302                         go func() {
 303                                 var resp struct {
 304                                         Status uint32
 305                                 }
 306                                 defer func() {
 307                                         ch.SendRequest("exit-status", false, ssh.Marshal(&resp))
 308                                         ch.Close()
 309                                 }()
 310
 311                                 cmd, err := gw.Target.InjectCommand(ctx, detachKeys, username, tty0 != nil, execargs)
 312                                 if err != nil {
 313                                         fmt.Fprintln(ch.Stderr(), err)
 314                                         ch.CloseWrite()
 315                                         resp.Status = 1
 316                                         return
 317                                 }
 318                                 cmd.Stdin = ch
 319                                 cmd.Stdout = ch
 320                                 cmd.Stderr = ch.Stderr()
 321                                 if tty0 != nil {
 322                                         cmd.Stdin = tty0
 323                                         cmd.Stdout = tty0
 324                                         cmd.Stderr = tty0
 325                                         var wg sync.WaitGroup
 326                                         defer wg.Wait()
 327                                         wg.Add(2)
 328                                         go func() { io.Copy(ch, pty0); wg.Done() }()
 329                                         go func() { io.Copy(pty0, ch); wg.Done() }()
 330                                         // Send our own debug messages to tty as well.
 331                                         logw = tty0
 332                                 }
 333                                 cmd.SysProcAttr = &syscall.SysProcAttr{
 334                                         Setctty: tty0 != nil,
 335                                         Setsid:  true,
 336                                 }
 337                                 cmd.Env = append(os.Environ(), termEnv...)
 338                                 err = cmd.Run()
 339                                 if exiterr, ok := err.(*exec.ExitError); ok {
 340                                         if status, ok := exiterr.Sys().(syscall.WaitStatus); ok {
 341                                                 resp.Status = uint32(status.ExitStatus())
 342                                         }
 343                                 } else if err != nil {
 344                                         // Propagate errors like `exec: "docker": executable file not found in $PATH`
 345                                         fmt.Fprintln(ch.Stderr(), err)
 346                                 }
 347                                 errClose := ch.CloseWrite()
 348                                 if resp.Status == 0 && (err != nil || errClose != nil) {
 349                                         resp.Status = 1
 350                                 }
 351                         }()
 352                 case "pty-req":
 353                         eol = "\r\n"
 354                         p, t, err := pty.Open()
 355                         if err != nil {
 356                                 fmt.Fprintf(ch.Stderr(), "pty failed: %s"+eol, err)
 357                                 break
 358                         }
 359                         defer p.Close()
 360                         defer t.Close()
 361                         pty0, tty0 = p, t
 362                         ok = true
 363                         var payload struct {
 364                                 Term string
 365                                 Cols uint32
 366                                 Rows uint32
 367                                 X    uint32
 368                                 Y    uint32
 369                         }
 370                         ssh.Unmarshal(req.Payload, &payload)
 371                         termEnv = []string{"TERM=" + payload.Term, "USE_TTY=1"}
 372                         err = pty.Setsize(pty0, &pty.Winsize{Rows: uint16(payload.Rows), Cols: uint16(payload.Cols), X: uint16(payload.X), Y: uint16(payload.Y)})
 373                         if err != nil {
 374                                 fmt.Fprintf(logw, "pty-req: setsize failed: %s"+eol, err)
 375                         }
 376                 case "window-change":
 377                         var payload struct {
 378                                 Cols uint32
 379                                 Rows uint32
 380                                 X    uint32
 381                                 Y    uint32
 382                         }
 383                         ssh.Unmarshal(req.Payload, &payload)
 384                         err := pty.Setsize(pty0, &pty.Winsize{Rows: uint16(payload.Rows), Cols: uint16(payload.Cols), X: uint16(payload.X), Y: uint16(payload.Y)})
 385                         if err != nil {
 386                                 fmt.Fprintf(logw, "window-change: setsize failed: %s"+eol, err)
 387                                 break
 388                         }
 389                         ok = true
 390                 case "env":
 391                         // TODO: implement "env"
 392                         // requests by setting env
 393                         // vars in the docker-exec
 394                         // command (not docker-exec's
 395                         // own environment, which
 396                         // would be a gaping security
 397                         // hole).
 398                 default:
 399                         // fmt.Fprintf(logw, "declining %q req"+eol, req.Type)
 400                 }
 401                 if req.WantReply {
 402                         req.Reply(ok, nil)
 403                 }
 404         }
 405 }