| 1 | // Package sshtest is an in-process SSH server for exercising the remote |
| 2 | // module without a real sshd. It supports publickey and password auth, session |
| 3 | // exec with scripted responses, direct-tcpip (for -L forwards), tcpip-forward |
| 4 | // (for -R forwards), and an SFTP subsystem via pkg/sftp's server. It is |
| 5 | // test-only. |
| 6 | package sshtest |
| 7 | |
| 8 | import ( |
| 9 | "errors" |
| 10 | "fmt" |
| 11 | "io" |
| 12 | "net" |
| 13 | "sync" |
| 14 | "testing" |
| 15 | "time" |
| 16 | |
| 17 | "github.com/pkg/sftp" |
| 18 | "golang.org/x/crypto/ssh" |
| 19 | ) |
| 20 | |
| 21 | // Server is a running in-process SSH server. |
| 22 | type Server struct { |
| 23 | Addr string |
| 24 | HostKey ssh.Signer |
| 25 | config *ssh.ServerConfig |
| 26 | listener net.Listener |
| 27 | execFunc func(cmd string) (stdout string, stderr string, exit int) |
| 28 | sftpRoot string |
| 29 | enableSFT bool |
| 30 | |
| 31 | mu sync.Mutex |
| 32 | conns []net.Conn |
| 33 | listeners []net.Listener |
| 34 | wg sync.WaitGroup |
| 35 | |
| 36 | // stdinMu guards lastStdin, the session script the client streams after |
| 37 | // the exec request (models sshd's forwarding to the remote process's |
| 38 | // stdin). Test code reads it to assert the payload arrived intact. |
| 39 | stdinMu sync.Mutex |
| 40 | lastStdin []byte |
| 41 | } |
| 42 | |
| 43 | // Options configures a test server. |
| 44 | type Options struct { |
| 45 | // HostKeys, when non-empty, are offered by the server. The first key is |
| 46 | // also exposed as Server.HostKey. Empty generates one ed25519 key. |
| 47 | HostKeys []ssh.Signer |
| 48 | // Password, when non-empty, enables password auth accepting (any user, |
| 49 | // this password). |
| 50 | Password string |
| 51 | // AuthorizedKey, when set, enables publickey auth accepting this key. |
| 52 | AuthorizedKey ssh.PublicKey |
| 53 | // Exec handles `exec` requests; nil => a default echoing the command. |
| 54 | Exec func(cmd string) (stdout string, stderr string, exit int) |
| 55 | // SFTPRoot enables the SFTP subsystem rooted at this directory. |
| 56 | SFTPRoot string |
| 57 | } |
| 58 | |
| 59 | // Start launches a server on 127.0.0.1:0. |
| 60 | func Start(t *testing.T, opts Options) *Server { |
| 61 | t.Helper() |
| 62 | hostKeys := opts.HostKeys |
| 63 | if len(hostKeys) == 0 { |
| 64 | hostKey, err := generateHostKey() |
| 65 | if err != nil { |
| 66 | t.Fatalf("host key: %v", err) |
| 67 | } |
| 68 | hostKeys = []ssh.Signer{hostKey} |
| 69 | } |
| 70 | cfg := &ssh.ServerConfig{} |
| 71 | for _, hostKey := range hostKeys { |
| 72 | if hostKey == nil { |
| 73 | t.Fatal("host key must not be nil") |
| 74 | } |
| 75 | cfg.AddHostKey(hostKey) |
| 76 | } |
| 77 | if opts.Password != "" { |
| 78 | cfg.PasswordCallback = func(conn ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) { |
| 79 | if string(pass) == opts.Password { |
| 80 | return &ssh.Permissions{}, nil |
| 81 | } |
| 82 | return nil, errors.New("bad password") |
| 83 | } |
| 84 | } |
| 85 | if opts.AuthorizedKey != nil { |
| 86 | want := opts.AuthorizedKey.Marshal() |
| 87 | cfg.PublicKeyCallback = func(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) { |
| 88 | if string(key.Marshal()) == string(want) { |
| 89 | return &ssh.Permissions{}, nil |
| 90 | } |
| 91 | return nil, errors.New("unknown key") |
| 92 | } |
| 93 | } |
| 94 | if opts.Password == "" && opts.AuthorizedKey == nil { |
| 95 | cfg.NoClientAuth = true |
| 96 | } |
| 97 | |
| 98 | ln, err := net.Listen("tcp", "127.0.0.1:0") |
| 99 | if err != nil { |
| 100 | t.Fatalf("listen: %v", err) |
| 101 | } |
| 102 | s := &Server{ |
| 103 | Addr: ln.Addr().String(), |
| 104 | HostKey: hostKeys[0], |
| 105 | config: cfg, |
| 106 | listener: ln, |
| 107 | execFunc: opts.Exec, |
| 108 | sftpRoot: opts.SFTPRoot, |
| 109 | enableSFT: opts.SFTPRoot != "", |
| 110 | } |
| 111 | s.wg.Add(1) |
| 112 | go s.serve() |
| 113 | t.Cleanup(s.Close) |
| 114 | return s |
| 115 | } |
| 116 | |
| 117 | // Close stops the server and all active connections. |
| 118 | func (s *Server) Close() { |
| 119 | _ = s.listener.Close() |
| 120 | s.mu.Lock() |
| 121 | for _, c := range s.conns { |
| 122 | _ = c.Close() |
| 123 | } |
| 124 | for _, ln := range s.listeners { |
| 125 | _ = ln.Close() |
| 126 | } |
| 127 | s.conns = nil |
| 128 | s.listeners = nil |
| 129 | s.mu.Unlock() |
| 130 | s.wg.Wait() |
| 131 | } |
| 132 | |
| 133 | // DropConnections closes every currently-open client connection without |
| 134 | // stopping the server, simulating a network drop so a supervised Client must |
| 135 | // reconnect. |
| 136 | func (s *Server) DropConnections() { |
| 137 | s.mu.Lock() |
| 138 | conns := s.conns |
| 139 | s.conns = nil |
| 140 | s.mu.Unlock() |
| 141 | for _, c := range conns { |
| 142 | _ = c.Close() |
| 143 | } |
| 144 | } |
| 145 | |
| 146 | func (s *Server) serve() { |
| 147 | defer s.wg.Done() |
| 148 | for { |
| 149 | nConn, err := s.listener.Accept() |
| 150 | if err != nil { |
| 151 | return |
| 152 | } |
| 153 | s.mu.Lock() |
| 154 | s.conns = append(s.conns, nConn) |
| 155 | s.mu.Unlock() |
| 156 | s.wg.Go(func() { |
| 157 | s.handleConn(nConn) |
| 158 | }) |
| 159 | } |
| 160 | } |
| 161 | |
| 162 | func (s *Server) handleConn(nConn net.Conn) { |
| 163 | sshConn, chans, reqs, err := ssh.NewServerConn(nConn, s.config) |
| 164 | if err != nil { |
| 165 | return |
| 166 | } |
| 167 | defer sshConn.Close() |
| 168 | go s.handleGlobalRequests(sshConn, reqs) |
| 169 | for newCh := range chans { |
| 170 | switch newCh.ChannelType() { |
| 171 | case "session": |
| 172 | go s.handleSession(newCh) |
| 173 | case "direct-tcpip": |
| 174 | go s.handleDirectTCPIP(newCh) |
| 175 | default: |
| 176 | _ = newCh.Reject(ssh.UnknownChannelType, "unsupported") |
| 177 | } |
| 178 | } |
| 179 | } |
| 180 | |
| 181 | func (s *Server) handleGlobalRequests(conn *ssh.ServerConn, reqs <-chan *ssh.Request) { |
| 182 | for req := range reqs { |
| 183 | switch req.Type { |
| 184 | case "keepalive@openssh.com": |
| 185 | if req.WantReply { |
| 186 | _ = req.Reply(true, nil) |
| 187 | } |
| 188 | case "tcpip-forward": |
| 189 | s.handleTCPIPForward(conn, req) |
| 190 | case "cancel-tcpip-forward": |
| 191 | if req.WantReply { |
| 192 | _ = req.Reply(true, nil) |
| 193 | } |
| 194 | default: |
| 195 | if req.WantReply { |
| 196 | _ = req.Reply(false, nil) |
| 197 | } |
| 198 | } |
| 199 | } |
| 200 | } |
| 201 | |
| 202 | func (s *Server) handleSession(newCh ssh.NewChannel) { |
| 203 | ch, reqs, err := newCh.Accept() |
| 204 | if err != nil { |
| 205 | return |
| 206 | } |
| 207 | defer ch.Close() |
| 208 | for req := range reqs { |
| 209 | switch req.Type { |
| 210 | case "exec": |
| 211 | cmd := parseStringPayload(req.Payload) |
| 212 | // The client streams the script after the exec request; model the |
| 213 | // same ordering: wait for the first data frame, then run the |
| 214 | // handler. Reading until EOF would deadlock. |
| 215 | first := make(chan struct{}) |
| 216 | go func() { |
| 217 | buf := make([]byte, 64*1024) |
| 218 | n, _ := ch.Read(buf) |
| 219 | if n > 0 { |
| 220 | s.stdinMu.Lock() |
| 221 | s.lastStdin = append([]byte(nil), buf[:n]...) |
| 222 | s.stdinMu.Unlock() |
| 223 | } |
| 224 | close(first) |
| 225 | }() |
| 226 | if req.WantReply { |
| 227 | _ = req.Reply(true, nil) |
| 228 | } |
| 229 | select { |
| 230 | case <-first: |
| 231 | case <-time.After(500 * time.Millisecond): |
| 232 | } |
| 233 | s.runExec(ch, cmd) |
| 234 | return |
| 235 | case "subsystem": |
| 236 | name := parseStringPayload(req.Payload) |
| 237 | if name == "sftp" && s.enableSFT { |
| 238 | if req.WantReply { |
| 239 | _ = req.Reply(true, nil) |
| 240 | } |
| 241 | s.runSFTP(ch) |
| 242 | return |
| 243 | } |
| 244 | if req.WantReply { |
| 245 | _ = req.Reply(false, nil) |
| 246 | } |
| 247 | case "shell", "pty-req", "env": |
| 248 | if req.WantReply { |
| 249 | _ = req.Reply(true, nil) |
| 250 | } |
| 251 | default: |
| 252 | if req.WantReply { |
| 253 | _ = req.Reply(false, nil) |
| 254 | } |
| 255 | } |
| 256 | } |
| 257 | } |
| 258 | |
| 259 | // LastStdin returns the script streamed by the most recent exec request, |
| 260 | // once the session channel has closed (the same completion point a remote |
| 261 | // process observes). Test code polls it to assert the payload arrived intact. |
| 262 | func (s *Server) LastStdin() string { |
| 263 | s.stdinMu.Lock() |
| 264 | defer s.stdinMu.Unlock() |
| 265 | return string(s.lastStdin) |
| 266 | } |
| 267 | |
| 268 | func (s *Server) runExec(ch ssh.Channel, cmd string) { |
| 269 | stdout, stderr, exit := "", "", 0 |
| 270 | if s.execFunc != nil { |
| 271 | stdout, stderr, exit = s.execFunc(cmd) |
| 272 | } else { |
| 273 | stdout = cmd |
| 274 | } |
| 275 | _, _ = io.WriteString(ch, stdout) |
| 276 | if stderr != "" { |
| 277 | _, _ = io.WriteString(ch.Stderr(), stderr) |
| 278 | } |
| 279 | sendExitStatus(ch, exit) |
| 280 | } |
| 281 | |
| 282 | func (s *Server) runSFTP(ch ssh.Channel) { |
| 283 | var server *sftp.Server |
| 284 | var err error |
| 285 | if s.sftpRoot != "" { |
| 286 | server, err = sftp.NewServer(ch, sftp.WithServerWorkingDirectory(s.sftpRoot)) |
| 287 | } else { |
| 288 | server, err = sftp.NewServer(ch) |
| 289 | } |
| 290 | if err != nil { |
| 291 | return |
| 292 | } |
| 293 | _ = server.Serve() |
| 294 | _ = server.Close() |
| 295 | } |
| 296 | |
| 297 | // handleDirectTCPIP implements -L forwards: dial the requested target and |
| 298 | // splice. |
| 299 | func (s *Server) handleDirectTCPIP(newCh ssh.NewChannel) { |
| 300 | var payload struct { |
| 301 | HostToConnect string |
| 302 | PortToConnect uint32 |
| 303 | OriginatorHost string |
| 304 | OriginatorPort uint32 |
| 305 | } |
| 306 | if err := ssh.Unmarshal(newCh.ExtraData(), &payload); err != nil { |
| 307 | _ = newCh.Reject(ssh.ConnectionFailed, "bad payload") |
| 308 | return |
| 309 | } |
| 310 | target := net.JoinHostPort(payload.HostToConnect, fmt.Sprintf("%d", payload.PortToConnect)) |
| 311 | dst, err := net.Dial("tcp", target) |
| 312 | if err != nil { |
| 313 | _ = newCh.Reject(ssh.ConnectionFailed, err.Error()) |
| 314 | return |
| 315 | } |
| 316 | ch, reqs, err := newCh.Accept() |
| 317 | if err != nil { |
| 318 | _ = dst.Close() |
| 319 | return |
| 320 | } |
| 321 | go ssh.DiscardRequests(reqs) |
| 322 | splice(ch, dst) |
| 323 | } |
| 324 | |
| 325 | // handleTCPIPForward implements -R forwards: listen locally on the server and |
| 326 | // open a forwarded-tcpip channel back to the client for each accepted conn. |
| 327 | func (s *Server) handleTCPIPForward(conn *ssh.ServerConn, req *ssh.Request) { |
| 328 | var payload struct { |
| 329 | BindAddr string |
| 330 | BindPort uint32 |
| 331 | } |
| 332 | if err := ssh.Unmarshal(req.Payload, &payload); err != nil { |
| 333 | if req.WantReply { |
| 334 | _ = req.Reply(false, nil) |
| 335 | } |
| 336 | return |
| 337 | } |
| 338 | ln, err := net.Listen("tcp", net.JoinHostPort(payload.BindAddr, fmt.Sprintf("%d", payload.BindPort))) |
| 339 | if err != nil { |
| 340 | if req.WantReply { |
| 341 | _ = req.Reply(false, nil) |
| 342 | } |
| 343 | return |
| 344 | } |
| 345 | boundPort := uint32(ln.Addr().(*net.TCPAddr).Port) |
| 346 | s.mu.Lock() |
| 347 | s.listeners = append(s.listeners, ln) |
| 348 | s.mu.Unlock() |
| 349 | if req.WantReply { |
| 350 | _ = req.Reply(true, ssh.Marshal(struct{ Port uint32 }{boundPort})) |
| 351 | } |
| 352 | go func() { |
| 353 | for { |
| 354 | c, err := ln.Accept() |
| 355 | if err != nil { |
| 356 | return |
| 357 | } |
| 358 | go func() { |
| 359 | origPort := uint32(1) |
| 360 | if ta, ok := c.RemoteAddr().(*net.TCPAddr); ok && ta.Port > 0 { |
| 361 | origPort = uint32(ta.Port) |
| 362 | } |
| 363 | msg := struct { |
| 364 | ConnHost string |
| 365 | ConnPort uint32 |
| 366 | OrigHost string |
| 367 | OrigPort uint32 |
| 368 | }{payload.BindAddr, boundPort, "127.0.0.1", origPort} |
| 369 | ch, reqs, err := conn.OpenChannel("forwarded-tcpip", ssh.Marshal(msg)) |
| 370 | if err != nil { |
| 371 | _ = c.Close() |
| 372 | return |
| 373 | } |
| 374 | go ssh.DiscardRequests(reqs) |
| 375 | splice(ch, c) |
| 376 | }() |
| 377 | } |
| 378 | }() |
| 379 | } |
| 380 | |
| 381 | func splice(a io.ReadWriteCloser, b net.Conn) { |
| 382 | done := make(chan struct{}, 2) |
| 383 | go func() { _, _ = io.Copy(a, b); done <- struct{}{} }() |
| 384 | go func() { _, _ = io.Copy(b, a); done <- struct{}{} }() |
| 385 | <-done |
| 386 | _ = a.Close() |
| 387 | _ = b.Close() |
| 388 | } |
| 389 | |
| 390 | func parseStringPayload(p []byte) string { |
| 391 | if len(p) < 4 { |
| 392 | return "" |
| 393 | } |
| 394 | n := int(p[0])<<24 | int(p[1])<<16 | int(p[2])<<8 | int(p[3]) |
| 395 | if 4+n > len(p) { |
| 396 | return "" |
| 397 | } |
| 398 | return string(p[4 : 4+n]) |
| 399 | } |
| 400 | |
| 401 | func sendExitStatus(ch ssh.Channel, code int) { |
| 402 | _, _ = ch.SendRequest("exit-status", false, ssh.Marshal(struct{ Status uint32 }{uint32(code)})) |
| 403 | } |
| 404 |