ssh.c

   1 /*
   2  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   3  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   4  *                    All rights reserved
   5  * Ssh client program.  This program can be used to log into a remote machine.
   6  * The software supports strong authentication, encryption, and forwarding
   7  * of X11, TCP/IP, and authentication connections.
   8  *
   9  * As far as I am concerned, the code I have written for this software
  10  * can be used freely for any purpose.  Any derived versions of this
  11  * software must be clearly marked as such, and if the derived work is
  12  * incompatible with the protocol description in the RFC file, it must be
  13  * called by a name other than "ssh" or "Secure Shell".
  14  *
  15  * Copyright (c) 1999 Niels Provos.  All rights reserved.
  16  * Copyright (c) 2000, 2001, 2002, 2003 Markus Friedl.  All rights reserved.
  17  *
  18  * Modified to work with SSL by Niels Provos <provos@citi.umich.edu>
  19  * in Canada (German citizen).
  20  *
  21  * Redistribution and use in source and binary forms, with or without
  22  * modification, are permitted provided that the following conditions
  23  * are met:
  24  * 1. Redistributions of source code must retain the above copyright
  25  *    notice, this list of conditions and the following disclaimer.
  26  * 2. Redistributions in binary form must reproduce the above copyright
  27  *    notice, this list of conditions and the following disclaimer in the
  28  *    documentation and/or other materials provided with the distribution.
  29  *
  30  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  31  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  32  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  33  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  34  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  35  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  36  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  37  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  38  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  39  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  40  */
  41
  42 #include "includes.h"
  43 RCSID("$OpenBSD: ssh.c,v 1.264 2006/02/20 17:19:54 stevesk Exp $");
  44
  45 #include <sys/types.h>
  46 #ifdef HAVE_SYS_STAT_H
  47 # include <sys/stat.h>
  48 #endif
  49 #include <sys/resource.h>
  50 #include <sys/ioctl.h>
  51 #include <sys/un.h>
  52
  53 #include <paths.h>
  54
  55 #include <openssl/evp.h>
  56 #include <openssl/err.h>
  57
  58 #include "ssh.h"
  59 #include "ssh1.h"
  60 #include "ssh2.h"
  61 #include "compat.h"
  62 #include "cipher.h"
  63 #include "xmalloc.h"
  64 #include "packet.h"
  65 #include "buffer.h"
  66 #include "bufaux.h"
  67 #include "channels.h"
  68 #include "key.h"
  69 #include "authfd.h"
  70 #include "authfile.h"
  71 #include "pathnames.h"
  72 #include "dispatch.h"
  73 #include "clientloop.h"
  74 #include "log.h"
  75 #include "readconf.h"
  76 #include "sshconnect.h"
  77 #include "misc.h"
  78 #include "kex.h"
  79 #include "mac.h"
  80 #include "sshpty.h"
  81 #include "match.h"
  82 #include "msg.h"
  83 #include "monitor_fdpass.h"
  84 #include "uidswap.h"
  85
  86 #ifdef SMARTCARD
  87 #include "scard.h"
  88 #endif
  89
  90 extern char *__progname;
  91
  92 /* Flag indicating whether debug mode is on.  This can be set on the command line. */
  93 int debug_flag = 0;
  94
  95 /* Flag indicating whether a tty should be allocated */
  96 int tty_flag = 0;
  97 int no_tty_flag = 0;
  98 int force_tty_flag = 0;
  99
 100 /* don't exec a shell */
 101 int no_shell_flag = 0;
 102
 103 /*
 104  * Flag indicating that nothing should be read from stdin.  This can be set
 105  * on the command line.
 106  */
 107 int stdin_null_flag = 0;
 108
 109 /*
 110  * Flag indicating that ssh should fork after authentication.  This is useful
 111  * so that the passphrase can be entered manually, and then ssh goes to the
 112  * background.
 113  */
 114 int fork_after_authentication_flag = 0;
 115
 116 /*
 117  * General data structure for command line options and options configurable
 118  * in configuration files.  See readconf.h.
 119  */
 120 Options options;
 121
 122 /* optional user configfile */
 123 char *config = NULL;
 124
 125 /*
 126  * Name of the host we are connecting to.  This is the name given on the
 127  * command line, or the HostName specified for the user-supplied name in a
 128  * configuration file.
 129  */
 130 char *host;
 131
 132 /* socket address the host resolves to */
 133 struct sockaddr_storage hostaddr;
 134
 135 /* Private host keys. */
 136 Sensitive sensitive_data;
 137
 138 /* Original real UID. */
 139 uid_t original_real_uid;
 140 uid_t original_effective_uid;
 141
 142 /* command to be executed */
 143 Buffer command;
 144
 145 /* Should we execute a command or invoke a subsystem? */
 146 int subsystem_flag = 0;
 147
 148 /* # of replies received for global requests */
 149 static int client_global_request_id = 0;
 150
 151 /* pid of proxycommand child process */
 152 pid_t proxy_command_pid = 0;
 153
 154 /* fd to control socket */
 155 int control_fd = -1;
 156
 157 /* Multiplexing control command */
 158 static u_int mux_command = 0;
 159
 160 /* Only used in control client mode */
 161 volatile sig_atomic_t control_client_terminate = 0;
 162 u_int control_server_pid = 0;
 163
 164 /* Prints a help message to the user.  This function never returns. */
 165
 166 static void
 167 usage(void)
 168 {
 169         fprintf(stderr,
 170 "usage: ssh [-1246AaCfgkMNnqsTtVvXxY] [-b bind_address] [-c cipher_spec]\n"
 171 "           [-D [bind_address:]port] [-e escape_char] [-F configfile]\n"
 172 "           [-i identity_file] [-L [bind_address:]port:host:hostport]\n"
 173 "           [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port]\n"
 174 "           [-R [bind_address:]port:host:hostport] [-S ctl_path]\n"
 175 "           [-w tunnel:tunnel] [user@]hostname [command]\n"
 176         );
 177         exit(255);
 178 }
 179
 180 static int ssh_session(void);
 181 static int ssh_session2(void);
 182 static void load_public_identity_files(void);
 183 static void control_client(const char *path);
 184
 185 /*
 186  * Main program for the ssh client.
 187  */
 188 int
 189 main(int ac, char **av)
 190 {
 191         int i, opt, exit_status;
 192         char *p, *cp, *line, buf[256];
 193         struct stat st;
 194         struct passwd *pw;
 195         int dummy;
 196         extern int optind, optreset;
 197         extern char *optarg;
 198         struct servent *sp;
 199         Forward fwd;
 200
 201         /* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
 202         sanitise_stdfd();
 203
 204         __progname = ssh_get_progname(av[0]);
 205         init_rng();
 206
 207         /*
 208          * Save the original real uid.  It will be needed later (uid-swapping
 209          * may clobber the real uid).
 210          */
 211         original_real_uid = getuid();
 212         original_effective_uid = geteuid();
 213
 214         /*
 215          * Use uid-swapping to give up root privileges for the duration of
 216          * option processing.  We will re-instantiate the rights when we are
 217          * ready to create the privileged port, and will permanently drop
 218          * them when the port has been created (actually, when the connection
 219          * has been made, as we may need to create the port several times).
 220          */
 221         PRIV_END;
 222
 223 #ifdef HAVE_SETRLIMIT
 224         /* If we are installed setuid root be careful to not drop core. */
 225         if (original_real_uid != original_effective_uid) {
 226                 struct rlimit rlim;
 227                 rlim.rlim_cur = rlim.rlim_max = 0;
 228                 if (setrlimit(RLIMIT_CORE, &rlim) < 0)
 229                         fatal("setrlimit failed: %.100s", strerror(errno));
 230         }
 231 #endif
 232         /* Get user data. */
 233         pw = getpwuid(original_real_uid);
 234         if (!pw) {
 235                 logit("You don't exist, go away!");
 236                 exit(255);
 237         }
 238         /* Take a copy of the returned structure. */
 239         pw = pwcopy(pw);
 240
 241         /*
 242          * Set our umask to something reasonable, as some files are created
 243          * with the default umask.  This will make them world-readable but
 244          * writable only by the owner, which is ok for all files for which we
 245          * don't set the modes explicitly.
 246          */
 247         umask(022);
 248
 249         /* Initialize option structure to indicate that no values have been set. */
 250         initialize_options(&options);
 251
 252         /* Parse command-line arguments. */
 253         host = NULL;
 254
 255 again:
 256         while ((opt = getopt(ac, av,
 257             "1246ab:c:e:fgi:kl:m:no:p:qstvxACD:F:I:L:MNO:PR:S:TVw:XY")) != -1) {
 258                 switch (opt) {
 259                 case '1':
 260                         options.protocol = SSH_PROTO_1;
 261                         break;
 262                 case '2':
 263                         options.protocol = SSH_PROTO_2;
 264                         break;
 265                 case '4':
 266                         options.address_family = AF_INET;
 267                         break;
 268                 case '6':
 269                         options.address_family = AF_INET6;
 270                         break;
 271                 case 'n':
 272                         stdin_null_flag = 1;
 273                         break;
 274                 case 'f':
 275                         fork_after_authentication_flag = 1;
 276                         stdin_null_flag = 1;
 277                         break;
 278                 case 'x':
 279                         options.forward_x11 = 0;
 280                         break;
 281                 case 'X':
 282                         options.forward_x11 = 1;
 283                         break;
 284                 case 'Y':
 285                         options.forward_x11 = 1;
 286                         options.forward_x11_trusted = 1;
 287                         break;
 288                 case 'g':
 289                         options.gateway_ports = 1;
 290                         break;
 291                 case 'O':
 292                         if (strcmp(optarg, "check") == 0)
 293                                 mux_command = SSHMUX_COMMAND_ALIVE_CHECK;
 294                         else if (strcmp(optarg, "exit") == 0)
 295                                 mux_command = SSHMUX_COMMAND_TERMINATE;
 296                         else
 297                                 fatal("Invalid multiplex command.");
 298                         break;
 299                 case 'P':       /* deprecated */
 300                         options.use_privileged_port = 0;
 301                         break;
 302                 case 'a':
 303                         options.forward_agent = 0;
 304                         break;
 305                 case 'A':
 306                         options.forward_agent = 1;
 307                         break;
 308                 case 'k':
 309                         options.gss_deleg_creds = 0;
 310                         break;
 311                 case 'i':
 312                         if (stat(optarg, &st) < 0) {
 313                                 fprintf(stderr, "Warning: Identity file %s "
 314                                     "not accessible: %s.\n", optarg,
 315                                     strerror(errno));
 316                                 break;
 317                         }
 318                         if (options.num_identity_files >=
 319                             SSH_MAX_IDENTITY_FILES)
 320                                 fatal("Too many identity files specified "
 321                                     "(max %d)", SSH_MAX_IDENTITY_FILES);
 322                         options.identity_files[options.num_identity_files++] =
 323                             xstrdup(optarg);
 324                         break;
 325                 case 'I':
 326 #ifdef SMARTCARD
 327                         options.smartcard_device = xstrdup(optarg);
 328 #else
 329                         fprintf(stderr, "no support for smartcards.\n");
 330 #endif
 331                         break;
 332                 case 't':
 333                         if (tty_flag)
 334                                 force_tty_flag = 1;
 335                         tty_flag = 1;
 336                         break;
 337                 case 'v':
 338                         if (debug_flag == 0) {
 339                                 debug_flag = 1;
 340                                 options.log_level = SYSLOG_LEVEL_DEBUG1;
 341                         } else {
 342                                 if (options.log_level < SYSLOG_LEVEL_DEBUG3)
 343                                         options.log_level++;
 344                                 break;
 345                         }
 346                         /* FALLTHROUGH */
 347                 case 'V':
 348                         fprintf(stderr, "%s, %s\n",
 349                             SSH_RELEASE, SSLeay_version(SSLEAY_VERSION));
 350                         if (opt == 'V')
 351                                 exit(0);
 352                         break;
 353                 case 'w':
 354                         if (options.tun_open == -1)
 355                                 options.tun_open = SSH_TUNMODE_DEFAULT;
 356                         options.tun_local = a2tun(optarg, &options.tun_remote);
 357                         if (options.tun_local == SSH_TUNID_ERR) {
 358                                 fprintf(stderr, "Bad tun device '%s'\n", optarg);
 359                                 exit(255);
 360                         }
 361                         break;
 362                 case 'q':
 363                         options.log_level = SYSLOG_LEVEL_QUIET;
 364                         break;
 365                 case 'e':
 366                         if (optarg[0] == '^' && optarg[2] == 0 &&
 367                             (u_char) optarg[1] >= 64 &&
 368                             (u_char) optarg[1] < 128)
 369                                 options.escape_char = (u_char) optarg[1] & 31;
 370                         else if (strlen(optarg) == 1)
 371                                 options.escape_char = (u_char) optarg[0];
 372                         else if (strcmp(optarg, "none") == 0)
 373                                 options.escape_char = SSH_ESCAPECHAR_NONE;
 374                         else {
 375                                 fprintf(stderr, "Bad escape character '%s'.\n",
 376                                     optarg);
 377                                 exit(255);
 378                         }
 379                         break;
 380                 case 'c':
 381                         if (ciphers_valid(optarg)) {
 382                                 /* SSH2 only */
 383                                 options.ciphers = xstrdup(optarg);
 384                                 options.cipher = SSH_CIPHER_INVALID;
 385                         } else {
 386                                 /* SSH1 only */
 387                                 options.cipher = cipher_number(optarg);
 388                                 if (options.cipher == -1) {
 389                                         fprintf(stderr,
 390                                             "Unknown cipher type '%s'\n",
 391                                             optarg);
 392                                         exit(255);
 393                                 }
 394                                 if (options.cipher == SSH_CIPHER_3DES)
 395                                         options.ciphers = "3des-cbc";
 396                                 else if (options.cipher == SSH_CIPHER_BLOWFISH)
 397                                         options.ciphers = "blowfish-cbc";
 398                                 else
 399                                         options.ciphers = (char *)-1;
 400                         }
 401                         break;
 402                 case 'm':
 403                         if (mac_valid(optarg))
 404                                 options.macs = xstrdup(optarg);
 405                         else {
 406                                 fprintf(stderr, "Unknown mac type '%s'\n",
 407                                     optarg);
 408                                 exit(255);
 409                         }
 410                         break;
 411                 case 'M':
 412                         if (options.control_master == SSHCTL_MASTER_YES)
 413                                 options.control_master = SSHCTL_MASTER_ASK;
 414                         else
 415                                 options.control_master = SSHCTL_MASTER_YES;
 416                         break;
 417                 case 'p':
 418                         options.port = a2port(optarg);
 419                         if (options.port == 0) {
 420                                 fprintf(stderr, "Bad port '%s'\n", optarg);
 421                                 exit(255);
 422                         }
 423                         break;
 424                 case 'l':
 425                         options.user = optarg;
 426                         break;
 427
 428                 case 'L':
 429                         if (parse_forward(&fwd, optarg))
 430                                 add_local_forward(&options, &fwd);
 431                         else {
 432                                 fprintf(stderr,
 433                                     "Bad local forwarding specification '%s'\n",
 434                                     optarg);
 435                                 exit(255);
 436                         }
 437                         break;
 438
 439                 case 'R':
 440                         if (parse_forward(&fwd, optarg)) {
 441                                 add_remote_forward(&options, &fwd);
 442                         } else {
 443                                 fprintf(stderr,
 444                                     "Bad remote forwarding specification "
 445                                     "'%s'\n", optarg);
 446                                 exit(255);
 447                         }
 448                         break;
 449
 450                 case 'D':
 451                         cp = p = xstrdup(optarg);
 452                         memset(&fwd, '\0', sizeof(fwd));
 453                         fwd.connect_host = "socks";
 454                         if ((fwd.listen_host = hpdelim(&cp)) == NULL) {
 455                                 fprintf(stderr, "Bad dynamic forwarding "
 456                                     "specification '%.100s'\n", optarg);
 457                                 exit(255);
 458                         }
 459                         if (cp != NULL) {
 460                                 fwd.listen_port = a2port(cp);
 461                                 fwd.listen_host = cleanhostname(fwd.listen_host);
 462                         } else {
 463                                 fwd.listen_port = a2port(fwd.listen_host);
 464                                 fwd.listen_host = NULL;
 465                         }
 466
 467                         if (fwd.listen_port == 0) {
 468                                 fprintf(stderr, "Bad dynamic port '%s'\n",
 469                                     optarg);
 470                                 exit(255);
 471                         }
 472                         add_local_forward(&options, &fwd);
 473                         xfree(p);
 474                         break;
 475
 476                 case 'C':
 477                         options.compression = 1;
 478                         break;
 479                 case 'N':
 480                         no_shell_flag = 1;
 481                         no_tty_flag = 1;
 482                         break;
 483                 case 'T':
 484                         no_tty_flag = 1;
 485                         break;
 486                 case 'o':
 487                         dummy = 1;
 488                         line = xstrdup(optarg);
 489                         if (process_config_line(&options, host ? host : "",
 490                             line, "command-line", 0, &dummy) != 0)
 491                                 exit(255);
 492                         xfree(line);
 493                         break;
 494                 case 's':
 495                         subsystem_flag = 1;
 496                         break;
 497                 case 'S':
 498                         if (options.control_path != NULL)
 499                                 free(options.control_path);
 500                         options.control_path = xstrdup(optarg);
 501                         break;
 502                 case 'b':
 503                         options.bind_address = optarg;
 504                         break;
 505                 case 'F':
 506                         config = optarg;
 507                         break;
 508                 default:
 509                         usage();
 510                 }
 511         }
 512
 513         ac -= optind;
 514         av += optind;
 515
 516         if (ac > 0 && !host && **av != '-') {
 517                 if (strrchr(*av, '@')) {
 518                         p = xstrdup(*av);
 519                         cp = strrchr(p, '@');
 520                         if (cp == NULL || cp == p)
 521                                 usage();
 522                         options.user = p;
 523                         *cp = '\0';
 524                         host = ++cp;
 525                 } else
 526                         host = *av;
 527                 if (ac > 1) {
 528                         optind = optreset = 1;
 529                         goto again;
 530                 }
 531                 ac--, av++;
 532         }
 533
 534         /* Check that we got a host name. */
 535         if (!host)
 536                 usage();
 537
 538         SSLeay_add_all_algorithms();
 539         ERR_load_crypto_strings();
 540
 541         /* Initialize the command to execute on remote host. */
 542         buffer_init(&command);
 543
 544         /*
 545          * Save the command to execute on the remote host in a buffer. There
 546          * is no limit on the length of the command, except by the maximum
 547          * packet size.  Also sets the tty flag if there is no command.
 548          */
 549         if (!ac) {
 550                 /* No command specified - execute shell on a tty. */
 551                 tty_flag = 1;
 552                 if (subsystem_flag) {
 553                         fprintf(stderr,
 554                             "You must specify a subsystem to invoke.\n");
 555                         usage();
 556                 }
 557         } else {
 558                 /* A command has been specified.  Store it into the buffer. */
 559                 for (i = 0; i < ac; i++) {
 560                         if (i)
 561                                 buffer_append(&command, " ", 1);
 562                         buffer_append(&command, av[i], strlen(av[i]));
 563                 }
 564         }
 565
 566         /* Cannot fork to background if no command. */
 567         if (fork_after_authentication_flag && buffer_len(&command) == 0 && !no_shell_flag)
 568                 fatal("Cannot fork into background without a command to execute.");
 569
 570         /* Allocate a tty by default if no command specified. */
 571         if (buffer_len(&command) == 0)
 572                 tty_flag = 1;
 573
 574         /* Force no tty */
 575         if (no_tty_flag)
 576                 tty_flag = 0;
 577         /* Do not allocate a tty if stdin is not a tty. */
 578         if ((!isatty(fileno(stdin)) || stdin_null_flag) && !force_tty_flag) {
 579                 if (tty_flag)
 580                         logit("Pseudo-terminal will not be allocated because stdin is not a terminal.");
 581                 tty_flag = 0;
 582         }
 583
 584         /*
 585          * Initialize "log" output.  Since we are the client all output
 586          * actually goes to stderr.
 587          */
 588         log_init(av[0], options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level,
 589             SYSLOG_FACILITY_USER, 1);
 590
 591         /*
 592          * Read per-user configuration file.  Ignore the system wide config
 593          * file if the user specifies a config file on the command line.
 594          */
 595         if (config != NULL) {
 596                 if (!read_config_file(config, host, &options, 0))
 597                         fatal("Can't open user config file %.100s: "
 598                             "%.100s", config, strerror(errno));
 599         } else  {
 600                 snprintf(buf, sizeof buf, "%.100s/%.100s", pw->pw_dir,
 601                     _PATH_SSH_USER_CONFFILE);
 602                 (void)read_config_file(buf, host, &options, 1);
 603
 604                 /* Read systemwide configuration file after use config. */
 605                 (void)read_config_file(_PATH_HOST_CONFIG_FILE, host,
 606                     &options, 0);
 607         }
 608
 609         /* Fill configuration defaults. */
 610         fill_default_options(&options);
 611
 612         channel_set_af(options.address_family);
 613
 614         /* reinit */
 615         log_init(av[0], options.log_level, SYSLOG_FACILITY_USER, 1);
 616
 617         seed_rng();
 618
 619         if (options.user == NULL)
 620                 options.user = xstrdup(pw->pw_name);
 621
 622         if (options.hostname != NULL)
 623                 host = options.hostname;
 624
 625         /* force lowercase for hostkey matching */
 626         if (options.host_key_alias != NULL) {
 627                 for (p = options.host_key_alias; *p; p++)
 628                         if (isupper(*p))
 629                                 *p = tolower(*p);
 630         }
 631
 632         /* Get default port if port has not been set. */
 633         if (options.port == 0) {
 634                 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
 635                 options.port = sp ? ntohs(sp->s_port) : SSH_DEFAULT_PORT;
 636         }
 637
 638         if (options.proxy_command != NULL &&
 639             strcmp(options.proxy_command, "none") == 0)
 640                 options.proxy_command = NULL;
 641         if (options.control_path != NULL &&
 642             strcmp(options.control_path, "none") == 0)
 643                 options.control_path = NULL;
 644
 645         if (options.control_path != NULL) {
 646                 char me[NI_MAXHOST];
 647
 648                 if (gethostname(me, sizeof(me)) == -1)
 649                         fatal("gethostname: %s", strerror(errno));
 650                 snprintf(buf, sizeof(buf), "%d", options.port);
 651                 cp = tilde_expand_filename(options.control_path,
 652                     original_real_uid);
 653                 options.control_path = percent_expand(cp, "p", buf, "h", host,
 654                     "r", options.user, "l", me, (char *)NULL);
 655                 xfree(cp);
 656         }
 657         if (mux_command != 0 && options.control_path == NULL)
 658                 fatal("No ControlPath specified for \"-O\" command");
 659         if (options.control_path != NULL)
 660                 control_client(options.control_path);
 661
 662         /* Open a connection to the remote host. */
 663         if (ssh_connect(host, &hostaddr, options.port,
 664             options.address_family, options.connection_attempts,
 665 #ifdef HAVE_CYGWIN
 666             options.use_privileged_port,
 667 #else
 668             original_effective_uid == 0 && options.use_privileged_port,
 669 #endif
 670             options.proxy_command) != 0)
 671                 exit(255);
 672
 673         /*
 674          * If we successfully made the connection, load the host private key
 675          * in case we will need it later for combined rsa-rhosts
 676          * authentication. This must be done before releasing extra
 677          * privileges, because the file is only readable by root.
 678          * If we cannot access the private keys, load the public keys
 679          * instead and try to execute the ssh-keysign helper instead.
 680          */
 681         sensitive_data.nkeys = 0;
 682         sensitive_data.keys = NULL;
 683         sensitive_data.external_keysign = 0;
 684         if (options.rhosts_rsa_authentication ||
 685             options.hostbased_authentication) {
 686                 sensitive_data.nkeys = 3;
 687                 sensitive_data.keys = xmalloc(sensitive_data.nkeys *
 688                     sizeof(Key));
 689
 690                 PRIV_START;
 691                 sensitive_data.keys[0] = key_load_private_type(KEY_RSA1,
 692                     _PATH_HOST_KEY_FILE, "", NULL);
 693                 sensitive_data.keys[1] = key_load_private_type(KEY_DSA,
 694                     _PATH_HOST_DSA_KEY_FILE, "", NULL);
 695                 sensitive_data.keys[2] = key_load_private_type(KEY_RSA,
 696                     _PATH_HOST_RSA_KEY_FILE, "", NULL);
 697                 PRIV_END;
 698
 699                 if (options.hostbased_authentication == 1 &&
 700                     sensitive_data.keys[0] == NULL &&
 701                     sensitive_data.keys[1] == NULL &&
 702                     sensitive_data.keys[2] == NULL) {
 703                         sensitive_data.keys[1] = key_load_public(
 704                             _PATH_HOST_DSA_KEY_FILE, NULL);
 705                         sensitive_data.keys[2] = key_load_public(
 706                             _PATH_HOST_RSA_KEY_FILE, NULL);
 707                         sensitive_data.external_keysign = 1;
 708                 }
 709         }
 710         /*
 711          * Get rid of any extra privileges that we may have.  We will no
 712          * longer need them.  Also, extra privileges could make it very hard
 713          * to read identity files and other non-world-readable files from the
 714          * user's home directory if it happens to be on a NFS volume where
 715          * root is mapped to nobody.
 716          */
 717         if (original_effective_uid == 0) {
 718                 PRIV_START;
 719                 permanently_set_uid(pw);
 720         }
 721
 722         /*
 723          * Now that we are back to our own permissions, create ~/.ssh
 724          * directory if it doesn't already exist.
 725          */
 726         snprintf(buf, sizeof buf, "%.100s%s%.100s", pw->pw_dir, strcmp(pw->pw_dir, "/") ? "/" : "", _PATH_SSH_USER_DIR);
 727         if (stat(buf, &st) < 0)
 728                 if (mkdir(buf, 0700) < 0)
 729                         error("Could not create directory '%.200s'.", buf);
 730
 731         /* load options.identity_files */
 732         load_public_identity_files();
 733
 734         /* Expand ~ in known host file names. */
 735         /* XXX mem-leaks: */
 736         options.system_hostfile =
 737             tilde_expand_filename(options.system_hostfile, original_real_uid);
 738         options.user_hostfile =
 739             tilde_expand_filename(options.user_hostfile, original_real_uid);
 740         options.system_hostfile2 =
 741             tilde_expand_filename(options.system_hostfile2, original_real_uid);
 742         options.user_hostfile2 =
 743             tilde_expand_filename(options.user_hostfile2, original_real_uid);
 744
 745         signal(SIGPIPE, SIG_IGN); /* ignore SIGPIPE early */
 746
 747         /* Log into the remote system.  This never returns if the login fails. */
 748         ssh_login(&sensitive_data, host, (struct sockaddr *)&hostaddr, pw);
 749
 750         /* We no longer need the private host keys.  Clear them now. */
 751         if (sensitive_data.nkeys != 0) {
 752                 for (i = 0; i < sensitive_data.nkeys; i++) {
 753                         if (sensitive_data.keys[i] != NULL) {
 754                                 /* Destroys contents safely */
 755                                 debug3("clear hostkey %d", i);
 756                                 key_free(sensitive_data.keys[i]);
 757                                 sensitive_data.keys[i] = NULL;
 758                         }
 759                 }
 760                 xfree(sensitive_data.keys);
 761         }
 762         for (i = 0; i < options.num_identity_files; i++) {
 763                 if (options.identity_files[i]) {
 764                         xfree(options.identity_files[i]);
 765                         options.identity_files[i] = NULL;
 766                 }
 767                 if (options.identity_keys[i]) {
 768                         key_free(options.identity_keys[i]);
 769                         options.identity_keys[i] = NULL;
 770                 }
 771         }
 772
 773         exit_status = compat20 ? ssh_session2() : ssh_session();
 774         packet_close();
 775
 776         if (options.control_path != NULL && control_fd != -1)
 777                 unlink(options.control_path);
 778
 779         /*
 780          * Send SIGHUP to proxy command if used. We don't wait() in
 781          * case it hangs and instead rely on init to reap the child
 782          */
 783         if (proxy_command_pid > 1)
 784                 kill(proxy_command_pid, SIGHUP);
 785
 786         return exit_status;
 787 }
 788
 789 static void
 790 ssh_init_forwarding(void)
 791 {
 792         int success = 0;
 793         int i;
 794
 795         /* Initiate local TCP/IP port forwardings. */
 796         for (i = 0; i < options.num_local_forwards; i++) {
 797                 debug("Local connections to %.200s:%d forwarded to remote "
 798                     "address %.200s:%d",
 799                     (options.local_forwards[i].listen_host == NULL) ?
 800                     (options.gateway_ports ? "*" : "LOCALHOST") :
 801                     options.local_forwards[i].listen_host,
 802                     options.local_forwards[i].listen_port,
 803                     options.local_forwards[i].connect_host,
 804                     options.local_forwards[i].connect_port);
 805                 success += channel_setup_local_fwd_listener(
 806                     options.local_forwards[i].listen_host,
 807                     options.local_forwards[i].listen_port,
 808                     options.local_forwards[i].connect_host,
 809                     options.local_forwards[i].connect_port,
 810                     options.gateway_ports);
 811         }
 812         if (i > 0 && success == 0)
 813                 error("Could not request local forwarding.");
 814
 815         /* Initiate remote TCP/IP port forwardings. */
 816         for (i = 0; i < options.num_remote_forwards; i++) {
 817                 debug("Remote connections from %.200s:%d forwarded to "
 818                     "local address %.200s:%d",
 819                     (options.remote_forwards[i].listen_host == NULL) ?
 820                     "LOCALHOST" : options.remote_forwards[i].listen_host,
 821                     options.remote_forwards[i].listen_port,
 822                     options.remote_forwards[i].connect_host,
 823                     options.remote_forwards[i].connect_port);
 824                 channel_request_remote_forwarding(
 825                     options.remote_forwards[i].listen_host,
 826                     options.remote_forwards[i].listen_port,
 827                     options.remote_forwards[i].connect_host,
 828                     options.remote_forwards[i].connect_port);
 829         }
 830 }
 831
 832 static void
 833 check_agent_present(void)
 834 {
 835         if (options.forward_agent) {
 836                 /* Clear agent forwarding if we don't have an agent. */
 837                 if (!ssh_agent_present())
 838                         options.forward_agent = 0;
 839         }
 840 }
 841
 842 static int
 843 ssh_session(void)
 844 {
 845         int type;
 846         int interactive = 0;
 847         int have_tty = 0;
 848         struct winsize ws;
 849         char *cp;
 850         const char *display;
 851
 852         /* Enable compression if requested. */
 853         if (options.compression) {
 854                 debug("Requesting compression at level %d.", options.compression_level);
 855
 856                 if (options.compression_level < 1 || options.compression_level > 9)
 857                         fatal("Compression level must be from 1 (fast) to 9 (slow, best).");
 858
 859                 /* Send the request. */
 860                 packet_start(SSH_CMSG_REQUEST_COMPRESSION);
 861                 packet_put_int(options.compression_level);
 862                 packet_send();
 863                 packet_write_wait();
 864                 type = packet_read();
 865                 if (type == SSH_SMSG_SUCCESS)
 866                         packet_start_compression(options.compression_level);
 867                 else if (type == SSH_SMSG_FAILURE)
 868                         logit("Warning: Remote host refused compression.");
 869                 else
 870                         packet_disconnect("Protocol error waiting for compression response.");
 871         }
 872         /* Allocate a pseudo tty if appropriate. */
 873         if (tty_flag) {
 874                 debug("Requesting pty.");
 875
 876                 /* Start the packet. */
 877                 packet_start(SSH_CMSG_REQUEST_PTY);
 878
 879                 /* Store TERM in the packet.  There is no limit on the
 880                    length of the string. */
 881                 cp = getenv("TERM");
 882                 if (!cp)
 883                         cp = "";
 884                 packet_put_cstring(cp);
 885
 886                 /* Store window size in the packet. */
 887                 if (ioctl(fileno(stdin), TIOCGWINSZ, &ws) < 0)
 888                         memset(&ws, 0, sizeof(ws));
 889                 packet_put_int(ws.ws_row);
 890                 packet_put_int(ws.ws_col);
 891                 packet_put_int(ws.ws_xpixel);
 892                 packet_put_int(ws.ws_ypixel);
 893
 894                 /* Store tty modes in the packet. */
 895                 tty_make_modes(fileno(stdin), NULL);
 896
 897                 /* Send the packet, and wait for it to leave. */
 898                 packet_send();
 899                 packet_write_wait();
 900
 901                 /* Read response from the server. */
 902                 type = packet_read();
 903                 if (type == SSH_SMSG_SUCCESS) {
 904                         interactive = 1;
 905                         have_tty = 1;
 906                 } else if (type == SSH_SMSG_FAILURE)
 907                         logit("Warning: Remote host failed or refused to allocate a pseudo tty.");
 908                 else
 909                         packet_disconnect("Protocol error waiting for pty request response.");
 910         }
 911         /* Request X11 forwarding if enabled and DISPLAY is set. */
 912         display = getenv("DISPLAY");
 913         if (options.forward_x11 && display != NULL) {
 914                 char *proto, *data;
 915                 /* Get reasonable local authentication information. */
 916                 client_x11_get_proto(display, options.xauth_location,
 917                     options.forward_x11_trusted, &proto, &data);
 918                 /* Request forwarding with authentication spoofing. */
 919                 debug("Requesting X11 forwarding with authentication spoofing.");
 920                 x11_request_forwarding_with_spoofing(0, display, proto, data);
 921
 922                 /* Read response from the server. */
 923                 type = packet_read();
 924                 if (type == SSH_SMSG_SUCCESS) {
 925                         interactive = 1;
 926                 } else if (type == SSH_SMSG_FAILURE) {
 927                         logit("Warning: Remote host denied X11 forwarding.");
 928                 } else {
 929                         packet_disconnect("Protocol error waiting for X11 forwarding");
 930                 }
 931         }
 932         /* Tell the packet module whether this is an interactive session. */
 933         packet_set_interactive(interactive);
 934
 935         /* Request authentication agent forwarding if appropriate. */
 936         check_agent_present();
 937
 938         if (options.forward_agent) {
 939                 debug("Requesting authentication agent forwarding.");
 940                 auth_request_forwarding();
 941
 942                 /* Read response from the server. */
 943                 type = packet_read();
 944                 packet_check_eom();
 945                 if (type != SSH_SMSG_SUCCESS)
 946                         logit("Warning: Remote host denied authentication agent forwarding.");
 947         }
 948
 949         /* Initiate port forwardings. */
 950         ssh_init_forwarding();
 951
 952         /* If requested, let ssh continue in the background. */
 953         if (fork_after_authentication_flag)
 954                 if (daemon(1, 1) < 0)
 955                         fatal("daemon() failed: %.200s", strerror(errno));
 956
 957         /*
 958          * If a command was specified on the command line, execute the
 959          * command now. Otherwise request the server to start a shell.
 960          */
 961         if (buffer_len(&command) > 0) {
 962                 int len = buffer_len(&command);
 963                 if (len > 900)
 964                         len = 900;
 965                 debug("Sending command: %.*s", len, (u_char *)buffer_ptr(&command));
 966                 packet_start(SSH_CMSG_EXEC_CMD);
 967                 packet_put_string(buffer_ptr(&command), buffer_len(&command));
 968                 packet_send();
 969                 packet_write_wait();
 970         } else {
 971                 debug("Requesting shell.");
 972                 packet_start(SSH_CMSG_EXEC_SHELL);
 973                 packet_send();
 974                 packet_write_wait();
 975         }
 976
 977         /* Enter the interactive session. */
 978         return client_loop(have_tty, tty_flag ?
 979             options.escape_char : SSH_ESCAPECHAR_NONE, 0);
 980 }
 981
 982 static void
 983 ssh_subsystem_reply(int type, u_int32_t seq, void *ctxt)
 984 {
 985         int id, len;
 986
 987         id = packet_get_int();
 988         len = buffer_len(&command);
 989         if (len > 900)
 990                 len = 900;
 991         packet_check_eom();
 992         if (type == SSH2_MSG_CHANNEL_FAILURE)
 993                 fatal("Request for subsystem '%.*s' failed on channel %d",
 994                     len, (u_char *)buffer_ptr(&command), id);
 995 }
 996
 997 void
 998 client_global_request_reply_fwd(int type, u_int32_t seq, void *ctxt)
 999 {
1000         int i;
1001
1002         i = client_global_request_id++;
1003         if (i >= options.num_remote_forwards)
1004                 return;
1005         debug("remote forward %s for: listen %d, connect %s:%d",
1006             type == SSH2_MSG_REQUEST_SUCCESS ? "success" : "failure",
1007             options.remote_forwards[i].listen_port,
1008             options.remote_forwards[i].connect_host,
1009             options.remote_forwards[i].connect_port);
1010         if (type == SSH2_MSG_REQUEST_FAILURE)
1011                 logit("Warning: remote port forwarding failed for listen "
1012                     "port %d", options.remote_forwards[i].listen_port);
1013 }
1014
1015 static void
1016 ssh_control_listener(void)
1017 {
1018         struct sockaddr_un addr;
1019         mode_t old_umask;
1020         int addr_len;
1021
1022         if (options.control_path == NULL ||
1023             options.control_master == SSHCTL_MASTER_NO)
1024                 return;
1025
1026         debug("setting up multiplex master socket");
1027
1028         memset(&addr, '\0', sizeof(addr));
1029         addr.sun_family = AF_UNIX;
1030         addr_len = offsetof(struct sockaddr_un, sun_path) +
1031             strlen(options.control_path) + 1;
1032
1033         if (strlcpy(addr.sun_path, options.control_path,
1034             sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
1035                 fatal("ControlPath too long");
1036
1037         if ((control_fd = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
1038                 fatal("%s socket(): %s", __func__, strerror(errno));
1039
1040         old_umask = umask(0177);
1041         if (bind(control_fd, (struct sockaddr*)&addr, addr_len) == -1) {
1042                 control_fd = -1;
1043                 if (errno == EINVAL || errno == EADDRINUSE)
1044                         fatal("ControlSocket %s already exists",
1045                             options.control_path);
1046                 else
1047                         fatal("%s bind(): %s", __func__, strerror(errno));
1048         }
1049         umask(old_umask);
1050
1051         if (listen(control_fd, 64) == -1)
1052                 fatal("%s listen(): %s", __func__, strerror(errno));
1053
1054         set_nonblock(control_fd);
1055 }
1056
1057 /* request pty/x11/agent/tcpfwd/shell for channel */
1058 static void
1059 ssh_session2_setup(int id, void *arg)
1060 {
1061         extern char **environ;
1062         const char *display;
1063         int interactive = tty_flag;
1064
1065         display = getenv("DISPLAY");
1066         if (options.forward_x11 && display != NULL) {
1067                 char *proto, *data;
1068                 /* Get reasonable local authentication information. */
1069                 client_x11_get_proto(display, options.xauth_location,
1070                     options.forward_x11_trusted, &proto, &data);
1071                 /* Request forwarding with authentication spoofing. */
1072                 debug("Requesting X11 forwarding with authentication spoofing.");
1073                 x11_request_forwarding_with_spoofing(id, display, proto, data);
1074                 interactive = 1;
1075                 /* XXX wait for reply */
1076         }
1077
1078         check_agent_present();
1079         if (options.forward_agent) {
1080                 debug("Requesting authentication agent forwarding.");
1081                 channel_request_start(id, "auth-agent-req@openssh.com", 0);
1082                 packet_send();
1083         }
1084
1085         if (options.tun_open != SSH_TUNMODE_NO) {
1086                 Channel *c;
1087                 int fd;
1088
1089                 debug("Requesting tun.");
1090                 if ((fd = tun_open(options.tun_local,
1091                     options.tun_open)) >= 0) {
1092                         c = channel_new("tun", SSH_CHANNEL_OPENING, fd, fd, -1,
1093                             CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
1094                             0, "tun", 1);
1095                         c->datagram = 1;
1096 #if defined(SSH_TUN_FILTER)
1097                         if (options.tun_open == SSH_TUNMODE_POINTOPOINT)
1098                                 channel_register_filter(c->self, sys_tun_infilter,
1099                                     sys_tun_outfilter);
1100 #endif
1101                         packet_start(SSH2_MSG_CHANNEL_OPEN);
1102                         packet_put_cstring("tun@openssh.com");
1103                         packet_put_int(c->self);
1104                         packet_put_int(c->local_window_max);
1105                         packet_put_int(c->local_maxpacket);
1106                         packet_put_int(options.tun_open);
1107                         packet_put_int(options.tun_remote);
1108                         packet_send();
1109                 }
1110         }
1111
1112         client_session2_setup(id, tty_flag, subsystem_flag, getenv("TERM"),
1113             NULL, fileno(stdin), &command, environ, &ssh_subsystem_reply);
1114
1115         packet_set_interactive(interactive);
1116 }
1117
1118 /* open new channel for a session */
1119 static int
1120 ssh_session2_open(void)
1121 {
1122         Channel *c;
1123         int window, packetmax, in, out, err;
1124
1125         if (stdin_null_flag) {
1126                 in = open(_PATH_DEVNULL, O_RDONLY);
1127         } else {
1128                 in = dup(STDIN_FILENO);
1129         }
1130         out = dup(STDOUT_FILENO);
1131         err = dup(STDERR_FILENO);
1132
1133         if (in < 0 || out < 0 || err < 0)
1134                 fatal("dup() in/out/err failed");
1135
1136         /* enable nonblocking unless tty */
1137         if (!isatty(in))
1138                 set_nonblock(in);
1139         if (!isatty(out))
1140                 set_nonblock(out);
1141         if (!isatty(err))
1142                 set_nonblock(err);
1143
1144         window = CHAN_SES_WINDOW_DEFAULT;
1145         packetmax = CHAN_SES_PACKET_DEFAULT;
1146         if (tty_flag) {
1147                 window >>= 1;
1148                 packetmax >>= 1;
1149         }
1150         c = channel_new(
1151             "session", SSH_CHANNEL_OPENING, in, out, err,
1152             window, packetmax, CHAN_EXTENDED_WRITE,
1153             "client-session", /*nonblock*/0);
1154
1155         debug3("ssh_session2_open: channel_new: %d", c->self);
1156
1157         channel_send_open(c->self);
1158         if (!no_shell_flag)
1159                 channel_register_confirm(c->self, ssh_session2_setup, NULL);
1160
1161         return c->self;
1162 }
1163
1164 static int
1165 ssh_session2(void)
1166 {
1167         int id = -1;
1168
1169         /* XXX should be pre-session */
1170         ssh_init_forwarding();
1171         ssh_control_listener();
1172
1173         if (!no_shell_flag || (datafellows & SSH_BUG_DUMMYCHAN))
1174                 id = ssh_session2_open();
1175
1176         /* Execute a local command */
1177         if (options.local_command != NULL &&
1178             options.permit_local_command)
1179                 ssh_local_cmd(options.local_command);
1180
1181         /* If requested, let ssh continue in the background. */
1182         if (fork_after_authentication_flag)
1183                 if (daemon(1, 1) < 0)
1184                         fatal("daemon() failed: %.200s", strerror(errno));
1185
1186         return client_loop(tty_flag, tty_flag ?
1187             options.escape_char : SSH_ESCAPECHAR_NONE, id);
1188 }
1189
1190 static void
1191 load_public_identity_files(void)
1192 {
1193         char *filename;
1194         int i = 0;
1195         Key *public;
1196 #ifdef SMARTCARD
1197         Key **keys;
1198
1199         if (options.smartcard_device != NULL &&
1200             options.num_identity_files < SSH_MAX_IDENTITY_FILES &&
1201             (keys = sc_get_keys(options.smartcard_device, NULL)) != NULL ) {
1202                 int count = 0;
1203                 for (i = 0; keys[i] != NULL; i++) {
1204                         count++;
1205                         memmove(&options.identity_files[1], &options.identity_files[0],
1206                             sizeof(char *) * (SSH_MAX_IDENTITY_FILES - 1));
1207                         memmove(&options.identity_keys[1], &options.identity_keys[0],
1208                             sizeof(Key *) * (SSH_MAX_IDENTITY_FILES - 1));
1209                         options.num_identity_files++;
1210                         options.identity_keys[0] = keys[i];
1211                         options.identity_files[0] = sc_get_key_label(keys[i]);
1212                 }
1213                 if (options.num_identity_files > SSH_MAX_IDENTITY_FILES)
1214                         options.num_identity_files = SSH_MAX_IDENTITY_FILES;
1215                 i = count;
1216                 xfree(keys);
1217         }
1218 #endif /* SMARTCARD */
1219         for (; i < options.num_identity_files; i++) {
1220                 filename = tilde_expand_filename(options.identity_files[i],
1221                     original_real_uid);
1222                 public = key_load_public(filename, NULL);
1223                 debug("identity file %s type %d", filename,
1224                     public ? public->type : -1);
1225                 xfree(options.identity_files[i]);
1226                 options.identity_files[i] = filename;
1227                 options.identity_keys[i] = public;
1228         }
1229 }
1230
1231 static void
1232 control_client_sighandler(int signo)
1233 {
1234         control_client_terminate = signo;
1235 }
1236
1237 static void
1238 control_client_sigrelay(int signo)
1239 {
1240         if (control_server_pid > 1)
1241                 kill(control_server_pid, signo);
1242 }
1243
1244 static int
1245 env_permitted(char *env)
1246 {
1247         int i;
1248         char name[1024], *cp;
1249
1250         strlcpy(name, env, sizeof(name));
1251         if ((cp = strchr(name, '=')) == NULL)
1252                 return (0);
1253
1254         *cp = '\0';
1255
1256         for (i = 0; i < options.num_send_env; i++)
1257                 if (match_pattern(name, options.send_env[i]))
1258                         return (1);
1259
1260         return (0);
1261 }
1262
1263 static void
1264 control_client(const char *path)
1265 {
1266         struct sockaddr_un addr;
1267         int i, r, fd, sock, exitval, num_env, addr_len;
1268         Buffer m;
1269         char *term;
1270         extern char **environ;
1271         u_int  flags;
1272
1273         if (mux_command == 0)
1274                 mux_command = SSHMUX_COMMAND_OPEN;
1275
1276         switch (options.control_master) {
1277         case SSHCTL_MASTER_AUTO:
1278         case SSHCTL_MASTER_AUTO_ASK:
1279                 debug("auto-mux: Trying existing master");
1280                 /* FALLTHROUGH */
1281         case SSHCTL_MASTER_NO:
1282                 break;
1283         default:
1284                 return;
1285         }
1286
1287         memset(&addr, '\0', sizeof(addr));
1288         addr.sun_family = AF_UNIX;
1289         addr_len = offsetof(struct sockaddr_un, sun_path) +
1290             strlen(path) + 1;
1291
1292         if (strlcpy(addr.sun_path, path,
1293             sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
1294                 fatal("ControlPath too long");
1295
1296         if ((sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
1297                 fatal("%s socket(): %s", __func__, strerror(errno));
1298
1299         if (connect(sock, (struct sockaddr*)&addr, addr_len) == -1) {
1300                 if (mux_command != SSHMUX_COMMAND_OPEN) {
1301                         fatal("Control socket connect(%.100s): %s", path,
1302                             strerror(errno));
1303                 }
1304                 if (errno == ENOENT)
1305                         debug("Control socket \"%.100s\" does not exist", path);
1306                 else {
1307                         error("Control socket connect(%.100s): %s", path,
1308                             strerror(errno));
1309                 }
1310                 close(sock);
1311                 return;
1312         }
1313
1314         if (stdin_null_flag) {
1315                 if ((fd = open(_PATH_DEVNULL, O_RDONLY)) == -1)
1316                         fatal("open(/dev/null): %s", strerror(errno));
1317                 if (dup2(fd, STDIN_FILENO) == -1)
1318                         fatal("dup2: %s", strerror(errno));
1319                 if (fd > STDERR_FILENO)
1320                         close(fd);
1321         }
1322
1323         term = getenv("TERM");
1324
1325         flags = 0;
1326         if (tty_flag)
1327                 flags |= SSHMUX_FLAG_TTY;
1328         if (subsystem_flag)
1329                 flags |= SSHMUX_FLAG_SUBSYS;
1330         if (options.forward_x11)
1331                 flags |= SSHMUX_FLAG_X11_FWD;
1332         if (options.forward_agent)
1333                 flags |= SSHMUX_FLAG_AGENT_FWD;
1334
1335         buffer_init(&m);
1336
1337         /* Send our command to server */
1338         buffer_put_int(&m, mux_command);
1339         buffer_put_int(&m, flags);
1340         if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1)
1341                 fatal("%s: msg_send", __func__);
1342         buffer_clear(&m);
1343
1344         /* Get authorisation status and PID of controlee */
1345         if (ssh_msg_recv(sock, &m) == -1)
1346                 fatal("%s: msg_recv", __func__);
1347         if (buffer_get_char(&m) != SSHMUX_VER)
1348                 fatal("%s: wrong version", __func__);
1349         if (buffer_get_int(&m) != 1)
1350                 fatal("Connection to master denied");
1351         control_server_pid = buffer_get_int(&m);
1352
1353         buffer_clear(&m);
1354
1355         switch (mux_command) {
1356         case SSHMUX_COMMAND_ALIVE_CHECK:
1357                 fprintf(stderr, "Master running (pid=%d)\r\n",
1358                     control_server_pid);
1359                 exit(0);
1360         case SSHMUX_COMMAND_TERMINATE:
1361                 fprintf(stderr, "Exit request sent.\r\n");
1362                 exit(0);
1363         case SSHMUX_COMMAND_OPEN:
1364                 /* continue below */
1365                 break;
1366         default:
1367                 fatal("silly mux_command %d", mux_command);
1368         }
1369
1370         /* SSHMUX_COMMAND_OPEN */
1371         buffer_put_cstring(&m, term ? term : "");
1372         buffer_append(&command, "\0", 1);
1373         buffer_put_cstring(&m, buffer_ptr(&command));
1374
1375         if (options.num_send_env == 0 || environ == NULL) {
1376                 buffer_put_int(&m, 0);
1377         } else {
1378                 /* Pass environment */
1379                 num_env = 0;
1380                 for (i = 0; environ[i] != NULL; i++)
1381                         if (env_permitted(environ[i]))
1382                                 num_env++; /* Count */
1383
1384                 buffer_put_int(&m, num_env);
1385
1386                 for (i = 0; environ[i] != NULL && num_env >= 0; i++)
1387                         if (env_permitted(environ[i])) {
1388                                 num_env--;
1389                                 buffer_put_cstring(&m, environ[i]);
1390                         }
1391         }
1392
1393         if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1)
1394                 fatal("%s: msg_send", __func__);
1395
1396         mm_send_fd(sock, STDIN_FILENO);
1397         mm_send_fd(sock, STDOUT_FILENO);
1398         mm_send_fd(sock, STDERR_FILENO);
1399
1400         /* Wait for reply, so master has a chance to gather ttymodes */
1401         buffer_clear(&m);
1402         if (ssh_msg_recv(sock, &m) == -1)
1403                 fatal("%s: msg_recv", __func__);
1404         if (buffer_get_char(&m) != SSHMUX_VER)
1405                 fatal("%s: wrong version", __func__);
1406         buffer_free(&m);
1407
1408         signal(SIGHUP, control_client_sighandler);
1409         signal(SIGINT, control_client_sighandler);
1410         signal(SIGTERM, control_client_sighandler);
1411         signal(SIGWINCH, control_client_sigrelay);
1412
1413         if (tty_flag)
1414                 enter_raw_mode();
1415
1416         /* Stick around until the controlee closes the client_fd */
1417         exitval = 0;
1418         for (;!control_client_terminate;) {
1419                 r = read(sock, &exitval, sizeof(exitval));
1420                 if (r == 0) {
1421                         debug2("Received EOF from master");
1422                         break;
1423                 }
1424                 if (r > 0)
1425                         debug2("Received exit status from master %d", exitval);
1426                 if (r == -1 && errno != EINTR)
1427                         fatal("%s: read %s", __func__, strerror(errno));
1428         }
1429
1430         if (control_client_terminate)
1431                 debug2("Exiting on signal %d", control_client_terminate);
1432
1433         close(sock);
1434
1435         leave_raw_mode();
1436
1437         if (tty_flag && options.log_level != SYSLOG_LEVEL_QUIET)
1438                 fprintf(stderr, "Connection to master closed.\r\n");
1439
1440         exit(exitval);
1441 }