mux.c

   1 /* $OpenBSD: mux.c,v 1.9 2010/01/09 05:04:24 djm 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 int force_tty_flag;
  86 extern Options options;
  87 extern int stdin_null_flag;
  88 extern char *host;
  89 extern int subsystem_flag;
  90 extern Buffer command;
  91
  92 /* Context for session open confirmation callback */
  93 struct mux_session_confirm_ctx {
  94         int want_tty;
  95         int want_subsys;
  96         int want_x_fwd;
  97         int want_agent_fwd;
  98         Buffer cmd;
  99         char *term;
 100         struct termios tio;
 101         char **env;
 102 };
 103
 104 /* fd to control socket */
 105 int muxserver_sock = -1;
 106
 107 /* Multiplexing control command */
 108 u_int muxclient_command = 0;
 109
 110 /* Set when signalled. */
 111 static volatile sig_atomic_t muxclient_terminate = 0;
 112
 113 /* PID of multiplex server */
 114 static u_int muxserver_pid = 0;
 115
 116
 117 /* ** Multiplexing master support */
 118
 119 /* Prepare a mux master to listen on a Unix domain socket. */
 120 void
 121 muxserver_listen(void)
 122 {
 123         struct sockaddr_un addr;
 124         mode_t old_umask;
 125         int addr_len;
 126
 127         if (options.control_path == NULL ||
 128             options.control_master == SSHCTL_MASTER_NO)
 129                 return;
 130
 131         debug("setting up multiplex master socket");
 132
 133         memset(&addr, '\0', sizeof(addr));
 134         addr.sun_family = AF_UNIX;
 135         addr_len = offsetof(struct sockaddr_un, sun_path) +
 136             strlen(options.control_path) + 1;
 137
 138         if (strlcpy(addr.sun_path, options.control_path,
 139             sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
 140                 fatal("ControlPath too long");
 141
 142         if ((muxserver_sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
 143                 fatal("%s socket(): %s", __func__, strerror(errno));
 144
 145         old_umask = umask(0177);
 146         if (bind(muxserver_sock, (struct sockaddr *)&addr, addr_len) == -1) {
 147                 muxserver_sock = -1;
 148                 if (errno == EINVAL || errno == EADDRINUSE) {
 149                         error("ControlSocket %s already exists, "
 150                             "disabling multiplexing", options.control_path);
 151                         close(muxserver_sock);
 152                         muxserver_sock = -1;
 153                         xfree(options.control_path);
 154                         options.control_path = NULL;
 155                         options.control_master = SSHCTL_MASTER_NO;
 156                         return;
 157                 } else
 158                         fatal("%s bind(): %s", __func__, strerror(errno));
 159         }
 160         umask(old_umask);
 161
 162         if (listen(muxserver_sock, 64) == -1)
 163                 fatal("%s listen(): %s", __func__, strerror(errno));
 164
 165         set_nonblock(muxserver_sock);
 166 }
 167
 168 /* Callback on open confirmation in mux master for a mux client session. */
 169 static void
 170 mux_session_confirm(int id, void *arg)
 171 {
 172         struct mux_session_confirm_ctx *cctx = arg;
 173         const char *display;
 174         Channel *c;
 175         int i;
 176
 177         if (cctx == NULL)
 178                 fatal("%s: cctx == NULL", __func__);
 179         if ((c = channel_lookup(id)) == NULL)
 180                 fatal("%s: no channel for id %d", __func__, id);
 181
 182         display = getenv("DISPLAY");
 183         if (cctx->want_x_fwd && options.forward_x11 && display != NULL) {
 184                 char *proto, *data;
 185                 /* Get reasonable local authentication information. */
 186                 client_x11_get_proto(display, options.xauth_location,
 187                     options.forward_x11_trusted, &proto, &data);
 188                 /* Request forwarding with authentication spoofing. */
 189                 debug("Requesting X11 forwarding with authentication spoofing.");
 190                 x11_request_forwarding_with_spoofing(id, display, proto, data);
 191                 /* XXX wait for reply */
 192         }
 193
 194         if (cctx->want_agent_fwd && options.forward_agent) {
 195                 debug("Requesting authentication agent forwarding.");
 196                 channel_request_start(id, "auth-agent-req@openssh.com", 0);
 197                 packet_send();
 198         }
 199
 200         client_session2_setup(id, cctx->want_tty, cctx->want_subsys,
 201             cctx->term, &cctx->tio, c->rfd, &cctx->cmd, cctx->env);
 202
 203         c->open_confirm_ctx = NULL;
 204         buffer_free(&cctx->cmd);
 205         xfree(cctx->term);
 206         if (cctx->env != NULL) {
 207                 for (i = 0; cctx->env[i] != NULL; i++)
 208                         xfree(cctx->env[i]);
 209                 xfree(cctx->env);
 210         }
 211         xfree(cctx);
 212 }
 213
 214 /*
 215  * Accept a connection on the mux master socket and process the
 216  * client's request. Returns flag indicating whether mux master should
 217  * begin graceful close.
 218  */
 219 int
 220 muxserver_accept_control(void)
 221 {
 222         Buffer m;
 223         Channel *c;
 224         int client_fd, new_fd[3], ver, allowed, window, packetmax;
 225         socklen_t addrlen;
 226         struct sockaddr_storage addr;
 227         struct mux_session_confirm_ctx *cctx;
 228         char *cmd;
 229         u_int i, j, len, env_len, mux_command, flags, escape_char;
 230         uid_t euid;
 231         gid_t egid;
 232         int start_close = 0;
 233
 234         /*
 235          * Accept connection on control socket
 236          */
 237         memset(&addr, 0, sizeof(addr));
 238         addrlen = sizeof(addr);
 239         if ((client_fd = accept(muxserver_sock,
 240             (struct sockaddr*)&addr, &addrlen)) == -1) {
 241                 error("%s accept: %s", __func__, strerror(errno));
 242                 return 0;
 243         }
 244
 245         if (getpeereid(client_fd, &euid, &egid) < 0) {
 246                 error("%s getpeereid failed: %s", __func__, strerror(errno));
 247                 close(client_fd);
 248                 return 0;
 249         }
 250         if ((euid != 0) && (getuid() != euid)) {
 251                 error("control mode uid mismatch: peer euid %u != uid %u",
 252                     (u_int) euid, (u_int) getuid());
 253                 close(client_fd);
 254                 return 0;
 255         }
 256
 257         /* XXX handle asynchronously */
 258         unset_nonblock(client_fd);
 259
 260         /* Read command */
 261         buffer_init(&m);
 262         if (ssh_msg_recv(client_fd, &m) == -1) {
 263                 error("%s: client msg_recv failed", __func__);
 264                 close(client_fd);
 265                 buffer_free(&m);
 266                 return 0;
 267         }
 268         if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
 269                 error("%s: wrong client version %d", __func__, ver);
 270                 buffer_free(&m);
 271                 close(client_fd);
 272                 return 0;
 273         }
 274
 275         allowed = 1;
 276         mux_command = buffer_get_int(&m);
 277         flags = buffer_get_int(&m);
 278
 279         buffer_clear(&m);
 280
 281         switch (mux_command) {
 282         case SSHMUX_COMMAND_OPEN:
 283                 if (options.control_master == SSHCTL_MASTER_ASK ||
 284                     options.control_master == SSHCTL_MASTER_AUTO_ASK)
 285                         allowed = ask_permission("Allow shared connection "
 286                             "to %s? ", host);
 287                 /* continue below */
 288                 break;
 289         case SSHMUX_COMMAND_TERMINATE:
 290                 if (options.control_master == SSHCTL_MASTER_ASK ||
 291                     options.control_master == SSHCTL_MASTER_AUTO_ASK)
 292                         allowed = ask_permission("Terminate shared connection "
 293                             "to %s? ", host);
 294                 if (allowed)
 295                         start_close = 1;
 296                 /* FALLTHROUGH */
 297         case SSHMUX_COMMAND_ALIVE_CHECK:
 298                 /* Reply for SSHMUX_COMMAND_TERMINATE and ALIVE_CHECK */
 299                 buffer_clear(&m);
 300                 buffer_put_int(&m, allowed);
 301                 buffer_put_int(&m, getpid());
 302                 if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
 303                         error("%s: client msg_send failed", __func__);
 304                         close(client_fd);
 305                         buffer_free(&m);
 306                         return start_close;
 307                 }
 308                 buffer_free(&m);
 309                 close(client_fd);
 310                 return start_close;
 311         default:
 312                 error("Unsupported command %d", mux_command);
 313                 buffer_free(&m);
 314                 close(client_fd);
 315                 return 0;
 316         }
 317
 318         /* Reply for SSHMUX_COMMAND_OPEN */
 319         buffer_clear(&m);
 320         buffer_put_int(&m, allowed);
 321         buffer_put_int(&m, getpid());
 322         if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
 323                 error("%s: client msg_send failed", __func__);
 324                 close(client_fd);
 325                 buffer_free(&m);
 326                 return 0;
 327         }
 328
 329         if (!allowed) {
 330                 error("Refused control connection");
 331                 close(client_fd);
 332                 buffer_free(&m);
 333                 return 0;
 334         }
 335
 336         buffer_clear(&m);
 337         if (ssh_msg_recv(client_fd, &m) == -1) {
 338                 error("%s: client msg_recv failed", __func__);
 339                 close(client_fd);
 340                 buffer_free(&m);
 341                 return 0;
 342         }
 343         if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
 344                 error("%s: wrong client version %d", __func__, ver);
 345                 buffer_free(&m);
 346                 close(client_fd);
 347                 return 0;
 348         }
 349
 350         cctx = xcalloc(1, sizeof(*cctx));
 351         cctx->want_tty = (flags & SSHMUX_FLAG_TTY) != 0;
 352         cctx->want_subsys = (flags & SSHMUX_FLAG_SUBSYS) != 0;
 353         cctx->want_x_fwd = (flags & SSHMUX_FLAG_X11_FWD) != 0;
 354         cctx->want_agent_fwd = (flags & SSHMUX_FLAG_AGENT_FWD) != 0;
 355         cctx->term = buffer_get_string(&m, &len);
 356         escape_char = buffer_get_int(&m);
 357
 358         cmd = buffer_get_string(&m, &len);
 359         buffer_init(&cctx->cmd);
 360         buffer_append(&cctx->cmd, cmd, strlen(cmd));
 361
 362         env_len = buffer_get_int(&m);
 363         env_len = MIN(env_len, 4096);
 364         debug3("%s: receiving %d env vars", __func__, env_len);
 365         if (env_len != 0) {
 366                 cctx->env = xcalloc(env_len + 1, sizeof(*cctx->env));
 367                 for (i = 0; i < env_len; i++)
 368                         cctx->env[i] = buffer_get_string(&m, &len);
 369                 cctx->env[i] = NULL;
 370         }
 371
 372         debug2("%s: accepted tty %d, subsys %d, cmd %s", __func__,
 373             cctx->want_tty, cctx->want_subsys, cmd);
 374         xfree(cmd);
 375
 376         /* Gather fds from client */
 377         for(i = 0; i < 3; i++) {
 378                 if ((new_fd[i] = mm_receive_fd(client_fd)) == -1) {
 379                         error("%s: failed to receive fd %d from slave",
 380                             __func__, i);
 381                         for (j = 0; j < i; j++)
 382                                 close(new_fd[j]);
 383                         for (j = 0; j < env_len; j++)
 384                                 xfree(cctx->env[j]);
 385                         if (env_len > 0)
 386                                 xfree(cctx->env);
 387                         xfree(cctx->term);
 388                         buffer_free(&cctx->cmd);
 389                         close(client_fd);
 390                         xfree(cctx);
 391                         return 0;
 392                 }
 393         }
 394
 395         debug2("%s: got fds stdin %d, stdout %d, stderr %d", __func__,
 396             new_fd[0], new_fd[1], new_fd[2]);
 397
 398         /* Try to pick up ttymodes from client before it goes raw */
 399         if (cctx->want_tty && tcgetattr(new_fd[0], &cctx->tio) == -1)
 400                 error("%s: tcgetattr: %s", __func__, strerror(errno));
 401
 402         /* This roundtrip is just for synchronisation of ttymodes */
 403         buffer_clear(&m);
 404         if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
 405                 error("%s: client msg_send failed", __func__);
 406                 close(client_fd);
 407                 close(new_fd[0]);
 408                 close(new_fd[1]);
 409                 close(new_fd[2]);
 410                 buffer_free(&m);
 411                 xfree(cctx->term);
 412                 if (env_len != 0) {
 413                         for (i = 0; i < env_len; i++)
 414                                 xfree(cctx->env[i]);
 415                         xfree(cctx->env);
 416                 }
 417                 return 0;
 418         }
 419         buffer_free(&m);
 420
 421         /* enable nonblocking unless tty */
 422         if (!isatty(new_fd[0]))
 423                 set_nonblock(new_fd[0]);
 424         if (!isatty(new_fd[1]))
 425                 set_nonblock(new_fd[1]);
 426         if (!isatty(new_fd[2]))
 427                 set_nonblock(new_fd[2]);
 428
 429         set_nonblock(client_fd);
 430
 431         window = CHAN_SES_WINDOW_DEFAULT;
 432         packetmax = CHAN_SES_PACKET_DEFAULT;
 433         if (cctx->want_tty) {
 434                 window >>= 1;
 435                 packetmax >>= 1;
 436         }
 437
 438         c = channel_new("session", SSH_CHANNEL_OPENING,
 439             new_fd[0], new_fd[1], new_fd[2], window, packetmax,
 440             CHAN_EXTENDED_WRITE, "client-session", /*nonblock*/0);
 441
 442         c->ctl_fd = client_fd;
 443         if (cctx->want_tty && escape_char != 0xffffffff) {
 444                 channel_register_filter(c->self,
 445                     client_simple_escape_filter, NULL,
 446                     client_filter_cleanup,
 447                     client_new_escape_filter_ctx((int)escape_char));
 448         }
 449
 450         debug3("%s: channel_new: %d", __func__, c->self);
 451
 452         channel_send_open(c->self);
 453         channel_register_open_confirm(c->self, mux_session_confirm, cctx);
 454         return 0;
 455 }
 456
 457 /* ** Multiplexing client support */
 458
 459 /* Exit signal handler */
 460 static void
 461 control_client_sighandler(int signo)
 462 {
 463         muxclient_terminate = signo;
 464 }
 465
 466 /*
 467  * Relay signal handler - used to pass some signals from mux client to
 468  * mux master.
 469  */
 470 static void
 471 control_client_sigrelay(int signo)
 472 {
 473         int save_errno = errno;
 474
 475         if (muxserver_pid > 1)
 476                 kill(muxserver_pid, signo);
 477
 478         errno = save_errno;
 479 }
 480
 481 /* Check mux client environment variables before passing them to mux master. */
 482 static int
 483 env_permitted(char *env)
 484 {
 485         int i, ret;
 486         char name[1024], *cp;
 487
 488         if ((cp = strchr(env, '=')) == NULL || cp == env)
 489                 return (0);
 490         ret = snprintf(name, sizeof(name), "%.*s", (int)(cp - env), env);
 491         if (ret <= 0 || (size_t)ret >= sizeof(name))
 492                 fatal("env_permitted: name '%.100s...' too long", env);
 493
 494         for (i = 0; i < options.num_send_env; i++)
 495                 if (match_pattern(name, options.send_env[i]))
 496                         return (1);
 497
 498         return (0);
 499 }
 500
 501 /* Multiplex client main loop. */
 502 void
 503 muxclient(const char *path)
 504 {
 505         struct sockaddr_un addr;
 506         int i, r, fd, sock, exitval[2], num_env, addr_len;
 507         Buffer m;
 508         char *term;
 509         extern char **environ;
 510         u_int allowed, flags;
 511
 512         if (muxclient_command == 0)
 513                 muxclient_command = SSHMUX_COMMAND_OPEN;
 514
 515         switch (options.control_master) {
 516         case SSHCTL_MASTER_AUTO:
 517         case SSHCTL_MASTER_AUTO_ASK:
 518                 debug("auto-mux: Trying existing master");
 519                 /* FALLTHROUGH */
 520         case SSHCTL_MASTER_NO:
 521                 break;
 522         default:
 523                 return;
 524         }
 525
 526         memset(&addr, '\0', sizeof(addr));
 527         addr.sun_family = AF_UNIX;
 528         addr_len = offsetof(struct sockaddr_un, sun_path) +
 529             strlen(path) + 1;
 530
 531         if (strlcpy(addr.sun_path, path,
 532             sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
 533                 fatal("ControlPath too long");
 534
 535         if ((sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
 536                 fatal("%s socket(): %s", __func__, strerror(errno));
 537
 538         if (connect(sock, (struct sockaddr *)&addr, addr_len) == -1) {
 539                 if (muxclient_command != SSHMUX_COMMAND_OPEN) {
 540                         fatal("Control socket connect(%.100s): %s", path,
 541                             strerror(errno));
 542                 }
 543                 if (errno == ENOENT)
 544                         debug("Control socket \"%.100s\" does not exist", path);
 545                 else {
 546                         error("Control socket connect(%.100s): %s", path,
 547                             strerror(errno));
 548                 }
 549                 close(sock);
 550                 return;
 551         }
 552
 553         if (stdin_null_flag) {
 554                 if ((fd = open(_PATH_DEVNULL, O_RDONLY)) == -1)
 555                         fatal("open(/dev/null): %s", strerror(errno));
 556                 if (dup2(fd, STDIN_FILENO) == -1)
 557                         fatal("dup2: %s", strerror(errno));
 558                 if (fd > STDERR_FILENO)
 559                         close(fd);
 560         }
 561
 562         term = getenv("TERM");
 563
 564         flags = 0;
 565         if (tty_flag)
 566                 flags |= SSHMUX_FLAG_TTY;
 567         if (subsystem_flag)
 568                 flags |= SSHMUX_FLAG_SUBSYS;
 569         if (options.forward_x11)
 570                 flags |= SSHMUX_FLAG_X11_FWD;
 571         if (options.forward_agent)
 572                 flags |= SSHMUX_FLAG_AGENT_FWD;
 573
 574         signal(SIGPIPE, SIG_IGN);
 575
 576         buffer_init(&m);
 577
 578         /* Send our command to server */
 579         buffer_put_int(&m, muxclient_command);
 580         buffer_put_int(&m, flags);
 581         if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1) {
 582                 error("%s: msg_send", __func__);
 583  muxerr:
 584                 close(sock);
 585                 buffer_free(&m);
 586                 if (muxclient_command != SSHMUX_COMMAND_OPEN)
 587                         cleanup_exit(255);
 588                 logit("Falling back to non-multiplexed connection");
 589                 xfree(options.control_path);
 590                 options.control_path = NULL;
 591                 options.control_master = SSHCTL_MASTER_NO;
 592                 return;
 593         }
 594         buffer_clear(&m);
 595
 596         /* Get authorisation status and PID of controlee */
 597         if (ssh_msg_recv(sock, &m) == -1) {
 598                 error("%s: Did not receive reply from master", __func__);
 599                 goto muxerr;
 600         }
 601         if (buffer_get_char(&m) != SSHMUX_VER) {
 602                 error("%s: Master replied with wrong version", __func__);
 603                 goto muxerr;
 604         }
 605         if (buffer_get_int_ret(&allowed, &m) != 0) {
 606                 error("%s: bad server reply", __func__);
 607                 goto muxerr;
 608         }
 609         if (allowed != 1) {
 610                 error("Connection to master denied");
 611                 goto muxerr;
 612         }
 613         muxserver_pid = buffer_get_int(&m);
 614
 615         buffer_clear(&m);
 616
 617         switch (muxclient_command) {
 618         case SSHMUX_COMMAND_ALIVE_CHECK:
 619                 fprintf(stderr, "Master running (pid=%d)\r\n",
 620                     muxserver_pid);
 621                 exit(0);
 622         case SSHMUX_COMMAND_TERMINATE:
 623                 fprintf(stderr, "Exit request sent.\r\n");
 624                 exit(0);
 625         case SSHMUX_COMMAND_OPEN:
 626                 buffer_put_cstring(&m, term ? term : "");
 627                 if (options.escape_char == SSH_ESCAPECHAR_NONE)
 628                         buffer_put_int(&m, 0xffffffff);
 629                 else
 630                         buffer_put_int(&m, options.escape_char);
 631                 buffer_append(&command, "\0", 1);
 632                 buffer_put_cstring(&m, buffer_ptr(&command));
 633
 634                 if (options.num_send_env == 0 || environ == NULL) {
 635                         buffer_put_int(&m, 0);
 636                 } else {
 637                         /* Pass environment */
 638                         num_env = 0;
 639                         for (i = 0; environ[i] != NULL; i++) {
 640                                 if (env_permitted(environ[i]))
 641                                         num_env++; /* Count */
 642                         }
 643                         buffer_put_int(&m, num_env);
 644                 for (i = 0; environ[i] != NULL && num_env >= 0; i++) {
 645                                 if (env_permitted(environ[i])) {
 646                                         num_env--;
 647                                         buffer_put_cstring(&m, environ[i]);
 648                                 }
 649                         }
 650                 }
 651                 break;
 652         default:
 653                 fatal("unrecognised muxclient_command %d", muxclient_command);
 654         }
 655
 656         if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1) {
 657                 error("%s: msg_send", __func__);
 658                 goto muxerr;
 659         }
 660
 661         if (mm_send_fd(sock, STDIN_FILENO) == -1 ||
 662             mm_send_fd(sock, STDOUT_FILENO) == -1 ||
 663             mm_send_fd(sock, STDERR_FILENO) == -1) {
 664                 error("%s: send fds failed", __func__);
 665                 goto muxerr;
 666         }
 667
 668         /*
 669          * Mux errors are non-recoverable from this point as the master
 670          * has ownership of the session now.
 671          */
 672
 673         /* Wait for reply, so master has a chance to gather ttymodes */
 674         buffer_clear(&m);
 675         if (ssh_msg_recv(sock, &m) == -1)
 676                 fatal("%s: msg_recv", __func__);
 677         if (buffer_get_char(&m) != SSHMUX_VER)
 678                 fatal("%s: wrong version", __func__);
 679         buffer_free(&m);
 680
 681         signal(SIGHUP, control_client_sighandler);
 682         signal(SIGINT, control_client_sighandler);
 683         signal(SIGTERM, control_client_sighandler);
 684         signal(SIGWINCH, control_client_sigrelay);
 685
 686         if (tty_flag)
 687                 enter_raw_mode(force_tty_flag);
 688
 689         /*
 690          * Stick around until the controlee closes the client_fd.
 691          * Before it does, it is expected to write this process' exit
 692          * value (one int). This process must read the value and wait for
 693          * the closure of the client_fd; if this one closes early, the
 694          * multiplex master will terminate early too (possibly losing data).
 695          */
 696         exitval[0] = 0;
 697         for (i = 0; !muxclient_terminate && i < (int)sizeof(exitval);) {
 698                 r = read(sock, (char *)exitval + i, sizeof(exitval) - i);
 699                 if (r == 0) {
 700                         debug2("Received EOF from master");
 701                         break;
 702                 }
 703                 if (r == -1) {
 704                         if (errno == EINTR)
 705                                 continue;
 706                         fatal("%s: read %s", __func__, strerror(errno));
 707                 }
 708                 i += r;
 709         }
 710
 711         close(sock);
 712         leave_raw_mode(force_tty_flag);
 713         if (i > (int)sizeof(int))
 714                 fatal("%s: master returned too much data (%d > %lu)",
 715                     __func__, i, (u_long)sizeof(int));
 716         if (muxclient_terminate) {
 717                 debug2("Exiting on signal %d", muxclient_terminate);
 718                 exitval[0] = 255;
 719         } else if (i < (int)sizeof(int)) {
 720                 debug2("Control master terminated unexpectedly");
 721                 exitval[0] = 255;
 722         } else
 723                 debug2("Received exit status from master %d", exitval[0]);
 724
 725         if (tty_flag && options.log_level != SYSLOG_LEVEL_QUIET)
 726                 fprintf(stderr, "Shared connection to %s closed.\r\n", host);
 727
 728         exit(exitval[0]);
 729 }