crypto/openssh/mux.c

   1 /* $OpenBSD: mux.c,v 1.7 2008/06/13 17:21:20 dtucker Exp $ */
   2 /*
   3  * Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
   4  *
   5  * Permission to use, copy, modify, and distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  16  */
  17
  18 /* ssh session multiplexing support */
  19
  20 #include "includes.h"
  21
  22 /*
  23  * TODO:
  24  *   1. partial reads in muxserver_accept_control (maybe make channels
  25  *      from accepted connections)
  26  *   2. Better signalling from master to slave, especially passing of
  27  *      error messages
  28  *   3. Better fall-back from mux slave error to new connection.
  29  *   3. Add/delete forwardings via slave
  30  *   4. ExitOnForwardingFailure (after #3 obviously)
  31  *   5. Maybe extension mechanisms for multi-X11/multi-agent forwarding
  32  *   6. Document the mux mini-protocol somewhere.
  33  *   7. Support ~^Z in mux slaves.
  34  *   8. Inspect or control sessions in master.
  35  *   9. If we ever support the "signal" channel request, send signals on
  36  *      sessions in master.
  37  */
  38
  39 #include <sys/types.h>
  40 #include <sys/param.h>
  41 #include <sys/stat.h>
  42 #include <sys/socket.h>
  43 #include <sys/un.h>
  44
  45 #include <errno.h>
  46 #include <fcntl.h>
  47 #include <signal.h>
  48 #include <stdarg.h>
  49 #include <stddef.h>
  50 #include <stdlib.h>
  51 #include <stdio.h>
  52 #include <string.h>
  53 #include <unistd.h>
  54 #ifdef HAVE_PATHS_H
  55 #include <paths.h>
  56 #endif
  57
  58 #ifdef HAVE_UTIL_H
  59 # include <util.h>
  60 #endif
  61
  62 #ifdef HAVE_LIBUTIL_H
  63 # include <libutil.h>
  64 #endif
  65
  66 #include "openbsd-compat/sys-queue.h"
  67 #include "xmalloc.h"
  68 #include "log.h"
  69 #include "ssh.h"
  70 #include "pathnames.h"
  71 #include "misc.h"
  72 #include "match.h"
  73 #include "buffer.h"
  74 #include "channels.h"
  75 #include "msg.h"
  76 #include "packet.h"
  77 #include "monitor_fdpass.h"
  78 #include "sshpty.h"
  79 #include "key.h"
  80 #include "readconf.h"
  81 #include "clientloop.h"
  82
  83 /* from ssh.c */
  84 extern int tty_flag;
  85 extern Options options;
  86 extern int stdin_null_flag;
  87 extern char *host;
  88 int subsystem_flag;
  89 extern Buffer command;
  90
  91 /* Context for session open confirmation callback */
  92 struct mux_session_confirm_ctx {
  93         int want_tty;
  94         int want_subsys;
  95         int want_x_fwd;
  96         int want_agent_fwd;
  97         Buffer cmd;
  98         char *term;
  99         struct termios tio;
 100         char **env;
 101 };
 102
 103 /* fd to control socket */
 104 int muxserver_sock = -1;
 105
 106 /* Multiplexing control command */
 107 u_int muxclient_command = 0;
 108
 109 /* Set when signalled. */
 110 static volatile sig_atomic_t muxclient_terminate = 0;
 111
 112 /* PID of multiplex server */
 113 static u_int muxserver_pid = 0;
 114
 115
 116 /* ** Multiplexing master support */
 117
 118 /* Prepare a mux master to listen on a Unix domain socket. */
 119 void
 120 muxserver_listen(void)
 121 {
 122         struct sockaddr_un addr;
 123         mode_t old_umask;
 124         int addr_len;
 125
 126         if (options.control_path == NULL ||
 127             options.control_master == SSHCTL_MASTER_NO)
 128                 return;
 129
 130         debug("setting up multiplex master socket");
 131
 132         memset(&addr, '\0', sizeof(addr));
 133         addr.sun_family = AF_UNIX;
 134         addr_len = offsetof(struct sockaddr_un, sun_path) +
 135             strlen(options.control_path) + 1;
 136
 137         if (strlcpy(addr.sun_path, options.control_path,
 138             sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
 139                 fatal("ControlPath too long");
 140
 141         if ((muxserver_sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
 142                 fatal("%s socket(): %s", __func__, strerror(errno));
 143
 144         old_umask = umask(0177);
 145         if (bind(muxserver_sock, (struct sockaddr *)&addr, addr_len) == -1) {
 146                 muxserver_sock = -1;
 147                 if (errno == EINVAL || errno == EADDRINUSE) {
 148                         error("ControlSocket %s already exists, "
 149                             "disabling multiplexing", options.control_path);
 150                         close(muxserver_sock);
 151                         muxserver_sock = -1;
 152                         xfree(options.control_path);
 153                         options.control_path = NULL;
 154                         options.control_master = SSHCTL_MASTER_NO;
 155                         return;
 156                 } else
 157                         fatal("%s bind(): %s", __func__, strerror(errno));
 158         }
 159         umask(old_umask);
 160
 161         if (listen(muxserver_sock, 64) == -1)
 162                 fatal("%s listen(): %s", __func__, strerror(errno));
 163
 164         set_nonblock(muxserver_sock);
 165 }
 166
 167 /* Callback on open confirmation in mux master for a mux client session. */
 168 static void
 169 mux_session_confirm(int id, void *arg)
 170 {
 171         struct mux_session_confirm_ctx *cctx = arg;
 172         const char *display;
 173         Channel *c;
 174         int i;
 175
 176         if (cctx == NULL)
 177                 fatal("%s: cctx == NULL", __func__);
 178         if ((c = channel_lookup(id)) == NULL)
 179                 fatal("%s: no channel for id %d", __func__, id);
 180
 181         display = getenv("DISPLAY");
 182         if (cctx->want_x_fwd && options.forward_x11 && display != NULL) {
 183                 char *proto, *data;
 184                 /* Get reasonable local authentication information. */
 185                 client_x11_get_proto(display, options.xauth_location,
 186                     options.forward_x11_trusted, &proto, &data);
 187                 /* Request forwarding with authentication spoofing. */
 188                 debug("Requesting X11 forwarding with authentication spoofing.");
 189                 x11_request_forwarding_with_spoofing(id, display, proto, data);
 190                 /* XXX wait for reply */
 191         }
 192
 193         if (cctx->want_agent_fwd && options.forward_agent) {
 194                 debug("Requesting authentication agent forwarding.");
 195                 channel_request_start(id, "auth-agent-req@openssh.com", 0);
 196                 packet_send();
 197         }
 198
 199         client_session2_setup(id, cctx->want_tty, cctx->want_subsys,
 200             cctx->term, &cctx->tio, c->rfd, &cctx->cmd, cctx->env);
 201
 202         c->open_confirm_ctx = NULL;
 203         buffer_free(&cctx->cmd);
 204         xfree(cctx->term);
 205         if (cctx->env != NULL) {
 206                 for (i = 0; cctx->env[i] != NULL; i++)
 207                         xfree(cctx->env[i]);
 208                 xfree(cctx->env);
 209         }
 210         xfree(cctx);
 211 }
 212
 213 /*
 214  * Accept a connection on the mux master socket and process the
 215  * client's request. Returns flag indicating whether mux master should
 216  * begin graceful close.
 217  */
 218 int
 219 muxserver_accept_control(void)
 220 {
 221         Buffer m;
 222         Channel *c;
 223         int client_fd, new_fd[3], ver, allowed, window, packetmax;
 224         socklen_t addrlen;
 225         struct sockaddr_storage addr;
 226         struct mux_session_confirm_ctx *cctx;
 227         char *cmd;
 228         u_int i, j, len, env_len, mux_command, flags, escape_char;
 229         uid_t euid;
 230         gid_t egid;
 231         int start_close = 0;
 232
 233         /*
 234          * Accept connection on control socket
 235          */
 236         memset(&addr, 0, sizeof(addr));
 237         addrlen = sizeof(addr);
 238         if ((client_fd = accept(muxserver_sock,
 239             (struct sockaddr*)&addr, &addrlen)) == -1) {
 240                 error("%s accept: %s", __func__, strerror(errno));
 241                 return 0;
 242         }
 243
 244         if (getpeereid(client_fd, &euid, &egid) < 0) {
 245                 error("%s getpeereid failed: %s", __func__, strerror(errno));
 246                 close(client_fd);
 247                 return 0;
 248         }
 249         if ((euid != 0) && (getuid() != euid)) {
 250                 error("control mode uid mismatch: peer euid %u != uid %u",
 251                     (u_int) euid, (u_int) getuid());
 252                 close(client_fd);
 253                 return 0;
 254         }
 255
 256         /* XXX handle asynchronously */
 257         unset_nonblock(client_fd);
 258
 259         /* Read command */
 260         buffer_init(&m);
 261         if (ssh_msg_recv(client_fd, &m) == -1) {
 262                 error("%s: client msg_recv failed", __func__);
 263                 close(client_fd);
 264                 buffer_free(&m);
 265                 return 0;
 266         }
 267         if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
 268                 error("%s: wrong client version %d", __func__, ver);
 269                 buffer_free(&m);
 270                 close(client_fd);
 271                 return 0;
 272         }
 273
 274         allowed = 1;
 275         mux_command = buffer_get_int(&m);
 276         flags = buffer_get_int(&m);
 277
 278         buffer_clear(&m);
 279
 280         switch (mux_command) {
 281         case SSHMUX_COMMAND_OPEN:
 282                 if (options.control_master == SSHCTL_MASTER_ASK ||
 283                     options.control_master == SSHCTL_MASTER_AUTO_ASK)
 284                         allowed = ask_permission("Allow shared connection "
 285                             "to %s? ", host);
 286                 /* continue below */
 287                 break;
 288         case SSHMUX_COMMAND_TERMINATE:
 289                 if (options.control_master == SSHCTL_MASTER_ASK ||
 290                     options.control_master == SSHCTL_MASTER_AUTO_ASK)
 291                         allowed = ask_permission("Terminate shared connection "
 292                             "to %s? ", host);
 293                 if (allowed)
 294                         start_close = 1;
 295                 /* FALLTHROUGH */
 296         case SSHMUX_COMMAND_ALIVE_CHECK:
 297                 /* Reply for SSHMUX_COMMAND_TERMINATE and ALIVE_CHECK */
 298                 buffer_clear(&m);
 299                 buffer_put_int(&m, allowed);
 300                 buffer_put_int(&m, getpid());
 301                 if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
 302                         error("%s: client msg_send failed", __func__);
 303                         close(client_fd);
 304                         buffer_free(&m);
 305                         return start_close;
 306                 }
 307                 buffer_free(&m);
 308                 close(client_fd);
 309                 return start_close;
 310         default:
 311                 error("Unsupported command %d", mux_command);
 312                 buffer_free(&m);
 313                 close(client_fd);
 314                 return 0;
 315         }
 316
 317         /* Reply for SSHMUX_COMMAND_OPEN */
 318         buffer_clear(&m);
 319         buffer_put_int(&m, allowed);
 320         buffer_put_int(&m, getpid());
 321         if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
 322                 error("%s: client msg_send failed", __func__);
 323                 close(client_fd);
 324                 buffer_free(&m);
 325                 return 0;
 326         }
 327
 328         if (!allowed) {
 329                 error("Refused control connection");
 330                 close(client_fd);
 331                 buffer_free(&m);
 332                 return 0;
 333         }
 334
 335         buffer_clear(&m);
 336         if (ssh_msg_recv(client_fd, &m) == -1) {
 337                 error("%s: client msg_recv failed", __func__);
 338                 close(client_fd);
 339                 buffer_free(&m);
 340                 return 0;
 341         }
 342         if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
 343                 error("%s: wrong client version %d", __func__, ver);
 344                 buffer_free(&m);
 345                 close(client_fd);
 346                 return 0;
 347         }
 348
 349         cctx = xcalloc(1, sizeof(*cctx));
 350         cctx->want_tty = (flags & SSHMUX_FLAG_TTY) != 0;
 351         cctx->want_subsys = (flags & SSHMUX_FLAG_SUBSYS) != 0;
 352         cctx->want_x_fwd = (flags & SSHMUX_FLAG_X11_FWD) != 0;
 353         cctx->want_agent_fwd = (flags & SSHMUX_FLAG_AGENT_FWD) != 0;
 354         cctx->term = buffer_get_string(&m, &len);
 355         escape_char = buffer_get_int(&m);
 356
 357         cmd = buffer_get_string(&m, &len);
 358         buffer_init(&cctx->cmd);
 359         buffer_append(&cctx->cmd, cmd, strlen(cmd));
 360
 361         env_len = buffer_get_int(&m);
 362         env_len = MIN(env_len, 4096);
 363         debug3("%s: receiving %d env vars", __func__, env_len);
 364         if (env_len != 0) {
 365                 cctx->env = xcalloc(env_len + 1, sizeof(*cctx->env));
 366                 for (i = 0; i < env_len; i++)
 367                         cctx->env[i] = buffer_get_string(&m, &len);
 368                 cctx->env[i] = NULL;
 369         }
 370
 371         debug2("%s: accepted tty %d, subsys %d, cmd %s", __func__,
 372             cctx->want_tty, cctx->want_subsys, cmd);
 373         xfree(cmd);
 374
 375         /* Gather fds from client */
 376         for(i = 0; i < 3; i++) {
 377                 if ((new_fd[i] = mm_receive_fd(client_fd)) == -1) {
 378                         error("%s: failed to receive fd %d from slave",
 379                             __func__, i);
 380                         for (j = 0; j < i; j++)
 381                                 close(new_fd[j]);
 382                         for (j = 0; j < env_len; j++)
 383                                 xfree(cctx->env[j]);
 384                         if (env_len > 0)
 385                                 xfree(cctx->env);
 386                         xfree(cctx->term);
 387                         buffer_free(&cctx->cmd);
 388                         close(client_fd);
 389                         xfree(cctx);
 390                         return 0;
 391                 }
 392         }
 393
 394         debug2("%s: got fds stdin %d, stdout %d, stderr %d", __func__,
 395             new_fd[0], new_fd[1], new_fd[2]);
 396
 397         /* Try to pick up ttymodes from client before it goes raw */
 398         if (cctx->want_tty && tcgetattr(new_fd[0], &cctx->tio) == -1)
 399                 error("%s: tcgetattr: %s", __func__, strerror(errno));
 400
 401         /* This roundtrip is just for synchronisation of ttymodes */
 402         buffer_clear(&m);
 403         if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
 404                 error("%s: client msg_send failed", __func__);
 405                 close(client_fd);
 406                 close(new_fd[0]);
 407                 close(new_fd[1]);
 408                 close(new_fd[2]);
 409                 buffer_free(&m);
 410                 xfree(cctx->term);
 411                 if (env_len != 0) {
 412                         for (i = 0; i < env_len; i++)
 413                                 xfree(cctx->env[i]);
 414                         xfree(cctx->env);
 415                 }
 416                 return 0;
 417         }
 418         buffer_free(&m);
 419
 420         /* enable nonblocking unless tty */
 421         if (!isatty(new_fd[0]))
 422                 set_nonblock(new_fd[0]);
 423         if (!isatty(new_fd[1]))
 424                 set_nonblock(new_fd[1]);
 425         if (!isatty(new_fd[2]))
 426                 set_nonblock(new_fd[2]);
 427
 428         set_nonblock(client_fd);
 429
 430         window = CHAN_SES_WINDOW_DEFAULT;
 431         packetmax = CHAN_SES_PACKET_DEFAULT;
 432         if (cctx->want_tty) {
 433                 window >>= 1;
 434                 packetmax >>= 1;
 435         }
 436
 437         c = channel_new("session", SSH_CHANNEL_OPENING,
 438             new_fd[0], new_fd[1], new_fd[2], window, packetmax,
 439             CHAN_EXTENDED_WRITE, "client-session", /*nonblock*/0);
 440
 441         c->ctl_fd = client_fd;
 442         if (cctx->want_tty && escape_char != 0xffffffff) {
 443                 channel_register_filter(c->self,
 444                     client_simple_escape_filter, NULL,
 445                     client_filter_cleanup,
 446                     client_new_escape_filter_ctx((int)escape_char));
 447         }
 448
 449         debug3("%s: channel_new: %d", __func__, c->self);
 450
 451         channel_send_open(c->self);
 452         channel_register_open_confirm(c->self, mux_session_confirm, cctx);
 453         return 0;
 454 }
 455
 456 /* ** Multiplexing client support */
 457
 458 /* Exit signal handler */
 459 static void
 460 control_client_sighandler(int signo)
 461 {
 462         muxclient_terminate = signo;
 463 }
 464
 465 /*
 466  * Relay signal handler - used to pass some signals from mux client to
 467  * mux master.
 468  */
 469 static void
 470 control_client_sigrelay(int signo)
 471 {
 472         int save_errno = errno;
 473
 474         if (muxserver_pid > 1)
 475                 kill(muxserver_pid, signo);
 476
 477         errno = save_errno;
 478 }
 479
 480 /* Check mux client environment variables before passing them to mux master. */
 481 static int
 482 env_permitted(char *env)
 483 {
 484         int i, ret;
 485         char name[1024], *cp;
 486
 487         if ((cp = strchr(env, '=')) == NULL || cp == env)
 488                 return (0);
 489         ret = snprintf(name, sizeof(name), "%.*s", (int)(cp - env), env);
 490         if (ret <= 0 || (size_t)ret >= sizeof(name))
 491                 fatal("env_permitted: name '%.100s...' too long", env);
 492
 493         for (i = 0; i < options.num_send_env; i++)
 494                 if (match_pattern(name, options.send_env[i]))
 495                         return (1);
 496
 497         return (0);
 498 }
 499
 500 /* Multiplex client main loop. */
 501 void
 502 muxclient(const char *path)
 503 {
 504         struct sockaddr_un addr;
 505         int i, r, fd, sock, exitval[2], num_env, addr_len;
 506         Buffer m;
 507         char *term;
 508         extern char **environ;
 509         u_int allowed, flags;
 510
 511         if (muxclient_command == 0)
 512                 muxclient_command = SSHMUX_COMMAND_OPEN;
 513
 514         switch (options.control_master) {
 515         case SSHCTL_MASTER_AUTO:
 516         case SSHCTL_MASTER_AUTO_ASK:
 517                 debug("auto-mux: Trying existing master");
 518                 /* FALLTHROUGH */
 519         case SSHCTL_MASTER_NO:
 520                 break;
 521         default:
 522                 return;
 523         }
 524
 525         memset(&addr, '\0', sizeof(addr));
 526         addr.sun_family = AF_UNIX;
 527         addr_len = offsetof(struct sockaddr_un, sun_path) +
 528             strlen(path) + 1;
 529
 530         if (strlcpy(addr.sun_path, path,
 531             sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
 532                 fatal("ControlPath too long");
 533
 534         if ((sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
 535                 fatal("%s socket(): %s", __func__, strerror(errno));
 536
 537         if (connect(sock, (struct sockaddr *)&addr, addr_len) == -1) {
 538                 if (muxclient_command != SSHMUX_COMMAND_OPEN) {
 539                         fatal("Control socket connect(%.100s): %s", path,
 540                             strerror(errno));
 541                 }
 542                 if (errno == ENOENT)
 543                         debug("Control socket \"%.100s\" does not exist", path);
 544                 else {
 545                         error("Control socket connect(%.100s): %s", path,
 546                             strerror(errno));
 547                 }
 548                 close(sock);
 549                 return;
 550         }
 551
 552         if (stdin_null_flag) {
 553                 if ((fd = open(_PATH_DEVNULL, O_RDONLY)) == -1)
 554                         fatal("open(/dev/null): %s", strerror(errno));
 555                 if (dup2(fd, STDIN_FILENO) == -1)
 556                         fatal("dup2: %s", strerror(errno));
 557                 if (fd > STDERR_FILENO)
 558                         close(fd);
 559         }
 560
 561         term = getenv("TERM");
 562
 563         flags = 0;
 564         if (tty_flag)
 565                 flags |= SSHMUX_FLAG_TTY;
 566         if (subsystem_flag)
 567                 flags |= SSHMUX_FLAG_SUBSYS;
 568         if (options.forward_x11)
 569                 flags |= SSHMUX_FLAG_X11_FWD;
 570         if (options.forward_agent)
 571                 flags |= SSHMUX_FLAG_AGENT_FWD;
 572
 573         signal(SIGPIPE, SIG_IGN);
 574
 575         buffer_init(&m);
 576
 577         /* Send our command to server */
 578         buffer_put_int(&m, muxclient_command);
 579         buffer_put_int(&m, flags);
 580         if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1) {
 581                 error("%s: msg_send", __func__);
 582  muxerr:
 583                 close(sock);
 584                 buffer_free(&m);
 585                 if (muxclient_command != SSHMUX_COMMAND_OPEN)
 586                         cleanup_exit(255);
 587                 logit("Falling back to non-multiplexed connection");
 588                 xfree(options.control_path);
 589                 options.control_path = NULL;
 590                 options.control_master = SSHCTL_MASTER_NO;
 591                 return;
 592         }
 593         buffer_clear(&m);
 594
 595         /* Get authorisation status and PID of controlee */
 596         if (ssh_msg_recv(sock, &m) == -1) {
 597                 error("%s: Did not receive reply from master", __func__);
 598                 goto muxerr;
 599         }
 600         if (buffer_get_char(&m) != SSHMUX_VER) {
 601                 error("%s: Master replied with wrong version", __func__);
 602                 goto muxerr;
 603         }
 604         if (buffer_get_int_ret(&allowed, &m) != 0) {
 605                 error("%s: bad server reply", __func__);
 606                 goto muxerr;
 607         }
 608         if (allowed != 1) {
 609                 error("Connection to master denied");
 610                 goto muxerr;
 611         }
 612         muxserver_pid = buffer_get_int(&m);
 613
 614         buffer_clear(&m);
 615
 616         switch (muxclient_command) {
 617         case SSHMUX_COMMAND_ALIVE_CHECK:
 618                 fprintf(stderr, "Master running (pid=%d)\r\n",
 619                     muxserver_pid);
 620                 exit(0);
 621         case SSHMUX_COMMAND_TERMINATE:
 622                 fprintf(stderr, "Exit request sent.\r\n");
 623                 exit(0);
 624         case SSHMUX_COMMAND_OPEN:
 625                 buffer_put_cstring(&m, term ? term : "");
 626                 if (options.escape_char == SSH_ESCAPECHAR_NONE)
 627                         buffer_put_int(&m, 0xffffffff);
 628                 else
 629                         buffer_put_int(&m, options.escape_char);
 630                 buffer_append(&command, "\0", 1);
 631                 buffer_put_cstring(&m, buffer_ptr(&command));
 632
 633                 if (options.num_send_env == 0 || environ == NULL) {
 634                         buffer_put_int(&m, 0);
 635                 } else {
 636                         /* Pass environment */
 637                         num_env = 0;
 638                         for (i = 0; environ[i] != NULL; i++) {
 639                                 if (env_permitted(environ[i]))
 640                                         num_env++; /* Count */
 641                         }
 642                         buffer_put_int(&m, num_env);
 643                 for (i = 0; environ[i] != NULL && num_env >= 0; i++) {
 644                                 if (env_permitted(environ[i])) {
 645                                         num_env--;
 646                                         buffer_put_cstring(&m, environ[i]);
 647                                 }
 648                         }
 649                 }
 650                 break;
 651         default:
 652                 fatal("unrecognised muxclient_command %d", muxclient_command);
 653         }
 654
 655         if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1) {
 656                 error("%s: msg_send", __func__);
 657                 goto muxerr;
 658         }
 659
 660         if (mm_send_fd(sock, STDIN_FILENO) == -1 ||
 661             mm_send_fd(sock, STDOUT_FILENO) == -1 ||
 662             mm_send_fd(sock, STDERR_FILENO) == -1) {
 663                 error("%s: send fds failed", __func__);
 664                 goto muxerr;
 665         }
 666
 667         /*
 668          * Mux errors are non-recoverable from this point as the master
 669          * has ownership of the session now.
 670          */
 671
 672         /* Wait for reply, so master has a chance to gather ttymodes */
 673         buffer_clear(&m);
 674         if (ssh_msg_recv(sock, &m) == -1)
 675                 fatal("%s: msg_recv", __func__);
 676         if (buffer_get_char(&m) != SSHMUX_VER)
 677                 fatal("%s: wrong version", __func__);
 678         buffer_free(&m);
 679
 680         signal(SIGHUP, control_client_sighandler);
 681         signal(SIGINT, control_client_sighandler);
 682         signal(SIGTERM, control_client_sighandler);
 683         signal(SIGWINCH, control_client_sigrelay);
 684
 685         if (tty_flag)
 686                 enter_raw_mode();
 687
 688         /*
 689          * Stick around until the controlee closes the client_fd.
 690          * Before it does, it is expected to write this process' exit
 691          * value (one int). This process must read the value and wait for
 692          * the closure of the client_fd; if this one closes early, the
 693          * multiplex master will terminate early too (possibly losing data).
 694          */
 695         exitval[0] = 0;
 696         for (i = 0; !muxclient_terminate && i < (int)sizeof(exitval);) {
 697                 r = read(sock, (char *)exitval + i, sizeof(exitval) - i);
 698                 if (r == 0) {
 699                         debug2("Received EOF from master");
 700                         break;
 701                 }
 702                 if (r == -1) {
 703                         if (errno == EINTR)
 704                                 continue;
 705                         fatal("%s: read %s", __func__, strerror(errno));
 706                 }
 707                 i += r;
 708         }
 709
 710         close(sock);
 711         leave_raw_mode();
 712         if (i > (int)sizeof(int))
 713                 fatal("%s: master returned too much data (%d > %lu)",
 714                     __func__, i, (u_long)sizeof(int));
 715         if (muxclient_terminate) {
 716                 debug2("Exiting on signal %d", muxclient_terminate);
 717                 exitval[0] = 255;
 718         } else if (i < (int)sizeof(int)) {
 719                 debug2("Control master terminated unexpectedly");
 720                 exitval[0] = 255;
 721         } else
 722                 debug2("Received exit status from master %d", exitval[0]);
 723
 724         if (tty_flag && options.log_level != SYSLOG_LEVEL_QUIET)
 725                 fprintf(stderr, "Shared connection to %s closed.\r\n", host);
 726
 727         exit(exitval[0]);
 728 }