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
  44 #include <sys/types.h>
  45 #ifdef HAVE_SYS_STAT_H
  46 # include <sys/stat.h>
  47 #endif
  48 #include <sys/resource.h>
  49 #include <sys/ioctl.h>
  50 #include <sys/un.h>
  51
  52 #include <ctype.h>
  53 #ifdef HAVE_PATHS_H
  54 #include <paths.h>
  55 #endif
  56 #include <signal.h>
  57
  58 #include <openssl/evp.h>
  59 #include <openssl/err.h>
  60
  61 #include "ssh.h"
  62 #include "ssh1.h"
  63 #include "ssh2.h"
  64 #include "compat.h"
  65 #include "cipher.h"
  66 #include "xmalloc.h"
  67 #include "packet.h"
  68 #include "buffer.h"
  69 #include "bufaux.h"
  70 #include "channels.h"
  71 #include "key.h"
  72 #include "authfd.h"
  73 #include "authfile.h"
  74 #include "pathnames.h"
  75 #include "dispatch.h"
  76 #include "clientloop.h"
  77 #include "log.h"
  78 #include "readconf.h"
  79 #include "sshconnect.h"
  80 #include "misc.h"
  81 #include "kex.h"
  82 #include "mac.h"
  83 #include "sshpty.h"
  84 #include "match.h"
  85 #include "msg.h"
  86 #include "monitor_fdpass.h"
  87 #include "uidswap.h"
  88
  89 #ifdef SMARTCARD
  90 #include "scard.h"
  91 #endif
  92
  93 extern char *__progname;
  94
  95 /* Flag indicating whether debug mode is on.  This can be set on the command line. */
  96 int debug_flag = 0;
  97
  98 /* Flag indicating whether a tty should be allocated */
  99 int tty_flag = 0;
 100 int no_tty_flag = 0;
 101 int force_tty_flag = 0;
 102
 103 /* don't exec a shell */
 104 int no_shell_flag = 0;
 105
 106 /*
 107  * Flag indicating that nothing should be read from stdin.  This can be set
 108  * on the command line.
 109  */
 110 int stdin_null_flag = 0;
 111
 112 /*
 113  * Flag indicating that ssh should fork after authentication.  This is useful
 114  * so that the passphrase can be entered manually, and then ssh goes to the
 115  * background.
 116  */
 117 int fork_after_authentication_flag = 0;
 118
 119 /*
 120  * General data structure for command line options and options configurable
 121  * in configuration files.  See readconf.h.
 122  */
 123 Options options;
 124
 125 /* optional user configfile */
 126 char *config = NULL;
 127
 128 /*
 129  * Name of the host we are connecting to.  This is the name given on the
 130  * command line, or the HostName specified for the user-supplied name in a
 131  * configuration file.
 132  */
 133 char *host;
 134
 135 /* socket address the host resolves to */
 136 struct sockaddr_storage hostaddr;
 137
 138 /* Private host keys. */
 139 Sensitive sensitive_data;
 140
 141 /* Original real UID. */
 142 uid_t original_real_uid;
 143 uid_t original_effective_uid;
 144
 145 /* command to be executed */
 146 Buffer command;
 147
 148 /* Should we execute a command or invoke a subsystem? */
 149 int subsystem_flag = 0;
 150
 151 /* # of replies received for global requests */
 152 static int client_global_request_id = 0;
 153
 154 /* pid of proxycommand child process */
 155 pid_t proxy_command_pid = 0;
 156
 157 /* fd to control socket */
 158 int control_fd = -1;
 159
 160 /* Multiplexing control command */
 161 static u_int mux_command = 0;
 162
 163 /* Only used in control client mode */
 164 volatile sig_atomic_t control_client_terminate = 0;
 165 u_int control_server_pid = 0;
 166
 167 /* Prints a help message to the user.  This function never returns. */
 168
 169 static void
 170 usage(void)
 171 {
 172         fprintf(stderr,
 173 "usage: ssh [-1246AaCfgkMNnqsTtVvXxY] [-b bind_address] [-c cipher_spec]\n"
 174 "           [-D [bind_address:]port] [-e escape_char] [-F configfile]\n"
 175 "           [-i identity_file] [-L [bind_address:]port:host:hostport]\n"
 176 "           [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port]\n"
 177 "           [-R [bind_address:]port:host:hostport] [-S ctl_path]\n"
 178 "           [-w tunnel:tunnel] [user@]hostname [command]\n"
 179         );
 180         exit(255);
 181 }
 182
 183 static int ssh_session(void);
 184 static int ssh_session2(void);
 185 static void load_public_identity_files(void);
 186 static void control_client(const char *path);
 187
 188 /*
 189  * Main program for the ssh client.
 190  */
 191 int
 192 main(int ac, char **av)
 193 {
 194         int i, opt, exit_status;
 195         char *p, *cp, *line, buf[256];
 196         struct stat st;
 197         struct passwd *pw;
 198         int dummy;
 199         extern int optind, optreset;
 200         extern char *optarg;
 201         struct servent *sp;
 202         Forward fwd;
 203
 204         /* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
 205         sanitise_stdfd();
 206
 207         __progname = ssh_get_progname(av[0]);
 208         init_rng();
 209
 210         /*
 211          * Save the original real uid.  It will be needed later (uid-swapping
 212          * may clobber the real uid).
 213          */
 214         original_real_uid = getuid();
 215         original_effective_uid = geteuid();
 216
 217         /*
 218          * Use uid-swapping to give up root privileges for the duration of
 219          * option processing.  We will re-instantiate the rights when we are
 220          * ready to create the privileged port, and will permanently drop
 221          * them when the port has been created (actually, when the connection
 222          * has been made, as we may need to create the port several times).
 223          */
 224         PRIV_END;
 225
 226 #ifdef HAVE_SETRLIMIT
 227         /* If we are installed setuid root be careful to not drop core. */
 228         if (original_real_uid != original_effective_uid) {
 229                 struct rlimit rlim;
 230                 rlim.rlim_cur = rlim.rlim_max = 0;
 231                 if (setrlimit(RLIMIT_CORE, &rlim) < 0)
 232                         fatal("setrlimit failed: %.100s", strerror(errno));
 233         }
 234 #endif
 235         /* Get user data. */
 236         pw = getpwuid(original_real_uid);
 237         if (!pw) {
 238                 logit("You don't exist, go away!");
 239                 exit(255);
 240         }
 241         /* Take a copy of the returned structure. */
 242         pw = pwcopy(pw);
 243
 244         /*
 245          * Set our umask to something reasonable, as some files are created
 246          * with the default umask.  This will make them world-readable but
 247          * writable only by the owner, which is ok for all files for which we
 248          * don't set the modes explicitly.
 249          */
 250         umask(022);
 251
 252         /* Initialize option structure to indicate that no values have been set. */
 253         initialize_options(&options);
 254
 255         /* Parse command-line arguments. */
 256         host = NULL;
 257
 258  again:
 259         while ((opt = getopt(ac, av,
 260             "1246ab:c:e:fgi:kl:m:no:p:qstvxACD:F:I:L:MNO:PR:S:TVw:XY")) != -1) {
 261                 switch (opt) {
 262                 case '1':
 263                         options.protocol = SSH_PROTO_1;
 264                         break;
 265                 case '2':
 266                         options.protocol = SSH_PROTO_2;
 267                         break;
 268                 case '4':
 269                         options.address_family = AF_INET;
 270                         break;
 271                 case '6':
 272                         options.address_family = AF_INET6;
 273                         break;
 274                 case 'n':
 275                         stdin_null_flag = 1;
 276                         break;
 277                 case 'f':
 278                         fork_after_authentication_flag = 1;
 279                         stdin_null_flag = 1;
 280                         break;
 281                 case 'x':
 282                         options.forward_x11 = 0;
 283                         break;
 284                 case 'X':
 285                         options.forward_x11 = 1;
 286                         break;
 287                 case 'Y':
 288                         options.forward_x11 = 1;
 289                         options.forward_x11_trusted = 1;
 290                         break;
 291                 case 'g':
 292                         options.gateway_ports = 1;
 293                         break;
 294                 case 'O':
 295                         if (strcmp(optarg, "check") == 0)
 296                                 mux_command = SSHMUX_COMMAND_ALIVE_CHECK;
 297                         else if (strcmp(optarg, "exit") == 0)
 298                                 mux_command = SSHMUX_COMMAND_TERMINATE;
 299                         else
 300                                 fatal("Invalid multiplex command.");
 301                         break;
 302                 case 'P':       /* deprecated */
 303                         options.use_privileged_port = 0;
 304                         break;
 305                 case 'a':
 306                         options.forward_agent = 0;
 307                         break;
 308                 case 'A':
 309                         options.forward_agent = 1;
 310                         break;
 311                 case 'k':
 312                         options.gss_deleg_creds = 0;
 313                         break;
 314                 case 'i':
 315                         if (stat(optarg, &st) < 0) {
 316                                 fprintf(stderr, "Warning: Identity file %s "
 317                                     "not accessible: %s.\n", optarg,
 318                                     strerror(errno));
 319                                 break;
 320                         }
 321                         if (options.num_identity_files >=
 322                             SSH_MAX_IDENTITY_FILES)
 323                                 fatal("Too many identity files specified "
 324                                     "(max %d)", SSH_MAX_IDENTITY_FILES);
 325                         options.identity_files[options.num_identity_files++] =
 326                             xstrdup(optarg);
 327                         break;
 328                 case 'I':
 329 #ifdef SMARTCARD
 330                         options.smartcard_device = xstrdup(optarg);
 331 #else
 332                         fprintf(stderr, "no support for smartcards.\n");
 333 #endif
 334                         break;
 335                 case 't':
 336                         if (tty_flag)
 337                                 force_tty_flag = 1;
 338                         tty_flag = 1;
 339                         break;
 340                 case 'v':
 341                         if (debug_flag == 0) {
 342                                 debug_flag = 1;
 343                                 options.log_level = SYSLOG_LEVEL_DEBUG1;
 344                         } else {
 345                                 if (options.log_level < SYSLOG_LEVEL_DEBUG3)
 346                                         options.log_level++;
 347                                 break;
 348                         }
 349                         /* FALLTHROUGH */
 350                 case 'V':
 351                         fprintf(stderr, "%s, %s\n",
 352                             SSH_RELEASE, SSLeay_version(SSLEAY_VERSION));
 353                         if (opt == 'V')
 354                                 exit(0);
 355                         break;
 356                 case 'w':
 357                         if (options.tun_open == -1)
 358                                 options.tun_open = SSH_TUNMODE_DEFAULT;
 359                         options.tun_local = a2tun(optarg, &options.tun_remote);
 360                         if (options.tun_local == SSH_TUNID_ERR) {
 361                                 fprintf(stderr, "Bad tun device '%s'\n", optarg);
 362                                 exit(255);
 363                         }
 364                         break;
 365                 case 'q':
 366                         options.log_level = SYSLOG_LEVEL_QUIET;
 367                         break;
 368                 case 'e':
 369                         if (optarg[0] == '^' && optarg[2] == 0 &&
 370                             (u_char) optarg[1] >= 64 &&
 371                             (u_char) optarg[1] < 128)
 372                                 options.escape_char = (u_char) optarg[1] & 31;
 373                         else if (strlen(optarg) == 1)
 374                                 options.escape_char = (u_char) optarg[0];
 375                         else if (strcmp(optarg, "none") == 0)
 376                                 options.escape_char = SSH_ESCAPECHAR_NONE;
 377                         else {
 378                                 fprintf(stderr, "Bad escape character '%s'.\n",
 379                                     optarg);
 380                                 exit(255);
 381                         }
 382                         break;
 383                 case 'c':
 384                         if (ciphers_valid(optarg)) {
 385                                 /* SSH2 only */
 386                                 options.ciphers = xstrdup(optarg);
 387                                 options.cipher = SSH_CIPHER_INVALID;
 388                         } else {
 389                                 /* SSH1 only */
 390                                 options.cipher = cipher_number(optarg);
 391                                 if (options.cipher == -1) {
 392                                         fprintf(stderr,
 393                                             "Unknown cipher type '%s'\n",
 394                                             optarg);
 395                                         exit(255);
 396                                 }
 397                                 if (options.cipher == SSH_CIPHER_3DES)
 398                                         options.ciphers = "3des-cbc";
 399                                 else if (options.cipher == SSH_CIPHER_BLOWFISH)
 400                                         options.ciphers = "blowfish-cbc";
 401                                 else
 402                                         options.ciphers = (char *)-1;
 403                         }
 404                         break;
 405                 case 'm':
 406                         if (mac_valid(optarg))
 407                                 options.macs = xstrdup(optarg);
 408                         else {
 409                                 fprintf(stderr, "Unknown mac type '%s'\n",
 410                                     optarg);
 411                                 exit(255);
 412                         }
 413                         break;
 414                 case 'M':
 415                         if (options.control_master == SSHCTL_MASTER_YES)
 416                                 options.control_master = SSHCTL_MASTER_ASK;
 417                         else
 418                                 options.control_master = SSHCTL_MASTER_YES;
 419                         break;
 420                 case 'p':
 421                         options.port = a2port(optarg);
 422                         if (options.port == 0) {
 423                                 fprintf(stderr, "Bad port '%s'\n", optarg);
 424                                 exit(255);
 425                         }
 426                         break;
 427                 case 'l':
 428                         options.user = optarg;
 429                         break;
 430
 431                 case 'L':
 432                         if (parse_forward(&fwd, optarg))
 433                                 add_local_forward(&options, &fwd);
 434                         else {
 435                                 fprintf(stderr,
 436                                     "Bad local forwarding specification '%s'\n",
 437                                     optarg);
 438                                 exit(255);
 439                         }
 440                         break;
 441
 442                 case 'R':
 443                         if (parse_forward(&fwd, optarg)) {
 444                                 add_remote_forward(&options, &fwd);
 445                         } else {
 446                                 fprintf(stderr,
 447                                     "Bad remote forwarding specification "
 448                                     "'%s'\n", optarg);
 449                                 exit(255);
 450                         }
 451                         break;
 452
 453                 case 'D':
 454                         cp = p = xstrdup(optarg);
 455                         memset(&fwd, '\0', sizeof(fwd));
 456                         fwd.connect_host = "socks";
 457                         if ((fwd.listen_host = hpdelim(&cp)) == NULL) {
 458                                 fprintf(stderr, "Bad dynamic forwarding "
 459                                     "specification '%.100s'\n", optarg);
 460                                 exit(255);
 461                         }
 462                         if (cp != NULL) {
 463                                 fwd.listen_port = a2port(cp);
 464                                 fwd.listen_host = cleanhostname(fwd.listen_host);
 465                         } else {
 466                                 fwd.listen_port = a2port(fwd.listen_host);
 467                                 fwd.listen_host = NULL;
 468                         }
 469
 470                         if (fwd.listen_port == 0) {
 471                                 fprintf(stderr, "Bad dynamic port '%s'\n",
 472                                     optarg);
 473                                 exit(255);
 474                         }
 475                         add_local_forward(&options, &fwd);
 476                         xfree(p);
 477                         break;
 478
 479                 case 'C':
 480                         options.compression = 1;
 481                         break;
 482                 case 'N':
 483                         no_shell_flag = 1;
 484                         no_tty_flag = 1;
 485                         break;
 486                 case 'T':
 487                         no_tty_flag = 1;
 488                         break;
 489                 case 'o':
 490                         dummy = 1;
 491                         line = xstrdup(optarg);
 492                         if (process_config_line(&options, host ? host : "",
 493                             line, "command-line", 0, &dummy) != 0)
 494                                 exit(255);
 495                         xfree(line);
 496                         break;
 497                 case 's':
 498                         subsystem_flag = 1;
 499                         break;
 500                 case 'S':
 501                         if (options.control_path != NULL)
 502                                 free(options.control_path);
 503                         options.control_path = xstrdup(optarg);
 504                         break;
 505                 case 'b':
 506                         options.bind_address = optarg;
 507                         break;
 508                 case 'F':
 509                         config = optarg;
 510                         break;
 511                 default:
 512                         usage();
 513                 }
 514         }
 515
 516         ac -= optind;
 517         av += optind;
 518
 519         if (ac > 0 && !host && **av != '-') {
 520                 if (strrchr(*av, '@')) {
 521                         p = xstrdup(*av);
 522                         cp = strrchr(p, '@');
 523                         if (cp == NULL || cp == p)
 524                                 usage();
 525                         options.user = p;
 526                         *cp = '\0';
 527                         host = ++cp;
 528                 } else
 529                         host = *av;
 530                 if (ac > 1) {
 531                         optind = optreset = 1;
 532                         goto again;
 533                 }
 534                 ac--, av++;
 535         }
 536
 537         /* Check that we got a host name. */
 538         if (!host)
 539                 usage();
 540
 541         SSLeay_add_all_algorithms();
 542         ERR_load_crypto_strings();
 543
 544         /* Initialize the command to execute on remote host. */
 545         buffer_init(&command);
 546
 547         /*
 548          * Save the command to execute on the remote host in a buffer. There
 549          * is no limit on the length of the command, except by the maximum
 550          * packet size.  Also sets the tty flag if there is no command.
 551          */
 552         if (!ac) {
 553                 /* No command specified - execute shell on a tty. */
 554                 tty_flag = 1;
 555                 if (subsystem_flag) {
 556                         fprintf(stderr,
 557                             "You must specify a subsystem to invoke.\n");
 558                         usage();
 559                 }
 560         } else {
 561                 /* A command has been specified.  Store it into the buffer. */
 562                 for (i = 0; i < ac; i++) {
 563                         if (i)
 564                                 buffer_append(&command, " ", 1);
 565                         buffer_append(&command, av[i], strlen(av[i]));
 566                 }
 567         }
 568
 569         /* Cannot fork to background if no command. */
 570         if (fork_after_authentication_flag && buffer_len(&command) == 0 && !no_shell_flag)
 571                 fatal("Cannot fork into background without a command to execute.");
 572
 573         /* Allocate a tty by default if no command specified. */
 574         if (buffer_len(&command) == 0)
 575                 tty_flag = 1;
 576
 577         /* Force no tty */
 578         if (no_tty_flag)
 579                 tty_flag = 0;
 580         /* Do not allocate a tty if stdin is not a tty. */
 581         if ((!isatty(fileno(stdin)) || stdin_null_flag) && !force_tty_flag) {
 582                 if (tty_flag)
 583                         logit("Pseudo-terminal will not be allocated because stdin is not a terminal.");
 584                 tty_flag = 0;
 585         }
 586
 587         /*
 588          * Initialize "log" output.  Since we are the client all output
 589          * actually goes to stderr.
 590          */
 591         log_init(av[0], options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level,
 592             SYSLOG_FACILITY_USER, 1);
 593
 594         /*
 595          * Read per-user configuration file.  Ignore the system wide config
 596          * file if the user specifies a config file on the command line.
 597          */
 598         if (config != NULL) {
 599                 if (!read_config_file(config, host, &options, 0))
 600                         fatal("Can't open user config file %.100s: "
 601                             "%.100s", config, strerror(errno));
 602         } else  {
 603                 snprintf(buf, sizeof buf, "%.100s/%.100s", pw->pw_dir,
 604                     _PATH_SSH_USER_CONFFILE);
 605                 (void)read_config_file(buf, host, &options, 1);
 606
 607                 /* Read systemwide configuration file after use config. */
 608                 (void)read_config_file(_PATH_HOST_CONFIG_FILE, host,
 609                     &options, 0);
 610         }
 611
 612         /* Fill configuration defaults. */
 613         fill_default_options(&options);
 614
 615         channel_set_af(options.address_family);
 616
 617         /* reinit */
 618         log_init(av[0], options.log_level, SYSLOG_FACILITY_USER, 1);
 619
 620         seed_rng();
 621
 622         if (options.user == NULL)
 623                 options.user = xstrdup(pw->pw_name);
 624
 625         if (options.hostname != NULL)
 626                 host = options.hostname;
 627
 628         /* force lowercase for hostkey matching */
 629         if (options.host_key_alias != NULL) {
 630                 for (p = options.host_key_alias; *p; p++)
 631                         if (isupper(*p))
 632                                 *p = tolower(*p);
 633         }
 634
 635         /* Get default port if port has not been set. */
 636         if (options.port == 0) {
 637                 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
 638                 options.port = sp ? ntohs(sp->s_port) : SSH_DEFAULT_PORT;
 639         }
 640
 641         if (options.proxy_command != NULL &&
 642             strcmp(options.proxy_command, "none") == 0)
 643                 options.proxy_command = NULL;
 644         if (options.control_path != NULL &&
 645             strcmp(options.control_path, "none") == 0)
 646                 options.control_path = NULL;
 647
 648         if (options.control_path != NULL) {
 649                 char me[NI_MAXHOST];
 650
 651                 if (gethostname(me, sizeof(me)) == -1)
 652                         fatal("gethostname: %s", strerror(errno));
 653                 snprintf(buf, sizeof(buf), "%d", options.port);
 654                 cp = tilde_expand_filename(options.control_path,
 655                     original_real_uid);
 656                 options.control_path = percent_expand(cp, "p", buf, "h", host,
 657                     "r", options.user, "l", me, (char *)NULL);
 658                 xfree(cp);
 659         }
 660         if (mux_command != 0 && options.control_path == NULL)
 661                 fatal("No ControlPath specified for \"-O\" command");
 662         if (options.control_path != NULL)
 663                 control_client(options.control_path);
 664
 665         /* Open a connection to the remote host. */
 666         if (ssh_connect(host, &hostaddr, options.port,
 667             options.address_family, options.connection_attempts,
 668 #ifdef HAVE_CYGWIN
 669             options.use_privileged_port,
 670 #else
 671             original_effective_uid == 0 && options.use_privileged_port,
 672 #endif
 673             options.proxy_command) != 0)
 674                 exit(255);
 675
 676         /*
 677          * If we successfully made the connection, load the host private key
 678          * in case we will need it later for combined rsa-rhosts
 679          * authentication. This must be done before releasing extra
 680          * privileges, because the file is only readable by root.
 681          * If we cannot access the private keys, load the public keys
 682          * instead and try to execute the ssh-keysign helper instead.
 683          */
 684         sensitive_data.nkeys = 0;
 685         sensitive_data.keys = NULL;
 686         sensitive_data.external_keysign = 0;
 687         if (options.rhosts_rsa_authentication ||
 688             options.hostbased_authentication) {
 689                 sensitive_data.nkeys = 3;
 690                 sensitive_data.keys = xmalloc(sensitive_data.nkeys *
 691                     sizeof(Key));
 692
 693                 PRIV_START;
 694                 sensitive_data.keys[0] = key_load_private_type(KEY_RSA1,
 695                     _PATH_HOST_KEY_FILE, "", NULL);
 696                 sensitive_data.keys[1] = key_load_private_type(KEY_DSA,
 697                     _PATH_HOST_DSA_KEY_FILE, "", NULL);
 698                 sensitive_data.keys[2] = key_load_private_type(KEY_RSA,
 699                     _PATH_HOST_RSA_KEY_FILE, "", NULL);
 700                 PRIV_END;
 701
 702                 if (options.hostbased_authentication == 1 &&
 703                     sensitive_data.keys[0] == NULL &&
 704                     sensitive_data.keys[1] == NULL &&
 705                     sensitive_data.keys[2] == NULL) {
 706                         sensitive_data.keys[1] = key_load_public(
 707                             _PATH_HOST_DSA_KEY_FILE, NULL);
 708                         sensitive_data.keys[2] = key_load_public(
 709                             _PATH_HOST_RSA_KEY_FILE, NULL);
 710                         sensitive_data.external_keysign = 1;
 711                 }
 712         }
 713         /*
 714          * Get rid of any extra privileges that we may have.  We will no
 715          * longer need them.  Also, extra privileges could make it very hard
 716          * to read identity files and other non-world-readable files from the
 717          * user's home directory if it happens to be on a NFS volume where
 718          * root is mapped to nobody.
 719          */
 720         if (original_effective_uid == 0) {
 721                 PRIV_START;
 722                 permanently_set_uid(pw);
 723         }
 724
 725         /*
 726          * Now that we are back to our own permissions, create ~/.ssh
 727          * directory if it doesn't already exist.
 728          */
 729         snprintf(buf, sizeof buf, "%.100s%s%.100s", pw->pw_dir, strcmp(pw->pw_dir, "/") ? "/" : "", _PATH_SSH_USER_DIR);
 730         if (stat(buf, &st) < 0)
 731                 if (mkdir(buf, 0700) < 0)
 732                         error("Could not create directory '%.200s'.", buf);
 733
 734         /* load options.identity_files */
 735         load_public_identity_files();
 736
 737         /* Expand ~ in known host file names. */
 738         /* XXX mem-leaks: */
 739         options.system_hostfile =
 740             tilde_expand_filename(options.system_hostfile, original_real_uid);
 741         options.user_hostfile =
 742             tilde_expand_filename(options.user_hostfile, original_real_uid);
 743         options.system_hostfile2 =
 744             tilde_expand_filename(options.system_hostfile2, original_real_uid);
 745         options.user_hostfile2 =
 746             tilde_expand_filename(options.user_hostfile2, original_real_uid);
 747
 748         signal(SIGPIPE, SIG_IGN); /* ignore SIGPIPE early */
 749
 750         /* Log into the remote system.  This never returns if the login fails. */
 751         ssh_login(&sensitive_data, host, (struct sockaddr *)&hostaddr, pw);
 752
 753         /* We no longer need the private host keys.  Clear them now. */
 754         if (sensitive_data.nkeys != 0) {
 755                 for (i = 0; i < sensitive_data.nkeys; i++) {
 756                         if (sensitive_data.keys[i] != NULL) {
 757                                 /* Destroys contents safely */
 758                                 debug3("clear hostkey %d", i);
 759                                 key_free(sensitive_data.keys[i]);
 760                                 sensitive_data.keys[i] = NULL;
 761                         }
 762                 }
 763                 xfree(sensitive_data.keys);
 764         }
 765         for (i = 0; i < options.num_identity_files; i++) {
 766                 if (options.identity_files[i]) {
 767                         xfree(options.identity_files[i]);
 768                         options.identity_files[i] = NULL;
 769                 }
 770                 if (options.identity_keys[i]) {
 771                         key_free(options.identity_keys[i]);
 772                         options.identity_keys[i] = NULL;
 773                 }
 774         }
 775
 776         exit_status = compat20 ? ssh_session2() : ssh_session();
 777         packet_close();
 778
 779         if (options.control_path != NULL && control_fd != -1)
 780                 unlink(options.control_path);
 781
 782         /*
 783          * Send SIGHUP to proxy command if used. We don't wait() in
 784          * case it hangs and instead rely on init to reap the child
 785          */
 786         if (proxy_command_pid > 1)
 787                 kill(proxy_command_pid, SIGHUP);
 788
 789         return exit_status;
 790 }
 791
 792 static void
 793 ssh_init_forwarding(void)
 794 {
 795         int success = 0;
 796         int i;
 797
 798         /* Initiate local TCP/IP port forwardings. */
 799         for (i = 0; i < options.num_local_forwards; i++) {
 800                 debug("Local connections to %.200s:%d forwarded to remote "
 801                     "address %.200s:%d",
 802                     (options.local_forwards[i].listen_host == NULL) ?
 803                     (options.gateway_ports ? "*" : "LOCALHOST") :
 804                     options.local_forwards[i].listen_host,
 805                     options.local_forwards[i].listen_port,
 806                     options.local_forwards[i].connect_host,
 807                     options.local_forwards[i].connect_port);
 808                 success += channel_setup_local_fwd_listener(
 809                     options.local_forwards[i].listen_host,
 810                     options.local_forwards[i].listen_port,
 811                     options.local_forwards[i].connect_host,
 812                     options.local_forwards[i].connect_port,
 813                     options.gateway_ports);
 814         }
 815         if (i > 0 && success == 0)
 816                 error("Could not request local forwarding.");
 817
 818         /* Initiate remote TCP/IP port forwardings. */
 819         for (i = 0; i < options.num_remote_forwards; i++) {
 820                 debug("Remote connections from %.200s:%d forwarded to "
 821                     "local address %.200s:%d",
 822                     (options.remote_forwards[i].listen_host == NULL) ?
 823                     "LOCALHOST" : options.remote_forwards[i].listen_host,
 824                     options.remote_forwards[i].listen_port,
 825                     options.remote_forwards[i].connect_host,
 826                     options.remote_forwards[i].connect_port);
 827                 channel_request_remote_forwarding(
 828                     options.remote_forwards[i].listen_host,
 829                     options.remote_forwards[i].listen_port,
 830                     options.remote_forwards[i].connect_host,
 831                     options.remote_forwards[i].connect_port);
 832         }
 833 }
 834
 835 static void
 836 check_agent_present(void)
 837 {
 838         if (options.forward_agent) {
 839                 /* Clear agent forwarding if we don't have an agent. */
 840                 if (!ssh_agent_present())
 841                         options.forward_agent = 0;
 842         }
 843 }
 844
 845 static int
 846 ssh_session(void)
 847 {
 848         int type;
 849         int interactive = 0;
 850         int have_tty = 0;
 851         struct winsize ws;
 852         char *cp;
 853         const char *display;
 854
 855         /* Enable compression if requested. */
 856         if (options.compression) {
 857                 debug("Requesting compression at level %d.", options.compression_level);
 858
 859                 if (options.compression_level < 1 || options.compression_level > 9)
 860                         fatal("Compression level must be from 1 (fast) to 9 (slow, best).");
 861
 862                 /* Send the request. */
 863                 packet_start(SSH_CMSG_REQUEST_COMPRESSION);
 864                 packet_put_int(options.compression_level);
 865                 packet_send();
 866                 packet_write_wait();
 867                 type = packet_read();
 868                 if (type == SSH_SMSG_SUCCESS)
 869                         packet_start_compression(options.compression_level);
 870                 else if (type == SSH_SMSG_FAILURE)
 871                         logit("Warning: Remote host refused compression.");
 872                 else
 873                         packet_disconnect("Protocol error waiting for compression response.");
 874         }
 875         /* Allocate a pseudo tty if appropriate. */
 876         if (tty_flag) {
 877                 debug("Requesting pty.");
 878
 879                 /* Start the packet. */
 880                 packet_start(SSH_CMSG_REQUEST_PTY);
 881
 882                 /* Store TERM in the packet.  There is no limit on the
 883                    length of the string. */
 884                 cp = getenv("TERM");
 885                 if (!cp)
 886                         cp = "";
 887                 packet_put_cstring(cp);
 888
 889                 /* Store window size in the packet. */
 890                 if (ioctl(fileno(stdin), TIOCGWINSZ, &ws) < 0)
 891                         memset(&ws, 0, sizeof(ws));
 892                 packet_put_int(ws.ws_row);
 893                 packet_put_int(ws.ws_col);
 894                 packet_put_int(ws.ws_xpixel);
 895                 packet_put_int(ws.ws_ypixel);
 896
 897                 /* Store tty modes in the packet. */
 898                 tty_make_modes(fileno(stdin), NULL);
 899
 900                 /* Send the packet, and wait for it to leave. */
 901                 packet_send();
 902                 packet_write_wait();
 903
 904                 /* Read response from the server. */
 905                 type = packet_read();
 906                 if (type == SSH_SMSG_SUCCESS) {
 907                         interactive = 1;
 908                         have_tty = 1;
 909                 } else if (type == SSH_SMSG_FAILURE)
 910                         logit("Warning: Remote host failed or refused to allocate a pseudo tty.");
 911                 else
 912                         packet_disconnect("Protocol error waiting for pty request response.");
 913         }
 914         /* Request X11 forwarding if enabled and DISPLAY is set. */
 915         display = getenv("DISPLAY");
 916         if (options.forward_x11 && display != NULL) {
 917                 char *proto, *data;
 918                 /* Get reasonable local authentication information. */
 919                 client_x11_get_proto(display, options.xauth_location,
 920                     options.forward_x11_trusted, &proto, &data);
 921                 /* Request forwarding with authentication spoofing. */
 922                 debug("Requesting X11 forwarding with authentication spoofing.");
 923                 x11_request_forwarding_with_spoofing(0, display, proto, data);
 924
 925                 /* Read response from the server. */
 926                 type = packet_read();
 927                 if (type == SSH_SMSG_SUCCESS) {
 928                         interactive = 1;
 929                 } else if (type == SSH_SMSG_FAILURE) {
 930                         logit("Warning: Remote host denied X11 forwarding.");
 931                 } else {
 932                         packet_disconnect("Protocol error waiting for X11 forwarding");
 933                 }
 934         }
 935         /* Tell the packet module whether this is an interactive session. */
 936         packet_set_interactive(interactive);
 937
 938         /* Request authentication agent forwarding if appropriate. */
 939         check_agent_present();
 940
 941         if (options.forward_agent) {
 942                 debug("Requesting authentication agent forwarding.");
 943                 auth_request_forwarding();
 944
 945                 /* Read response from the server. */
 946                 type = packet_read();
 947                 packet_check_eom();
 948                 if (type != SSH_SMSG_SUCCESS)
 949                         logit("Warning: Remote host denied authentication agent forwarding.");
 950         }
 951
 952         /* Initiate port forwardings. */
 953         ssh_init_forwarding();
 954
 955         /* If requested, let ssh continue in the background. */
 956         if (fork_after_authentication_flag)
 957                 if (daemon(1, 1) < 0)
 958                         fatal("daemon() failed: %.200s", strerror(errno));
 959
 960         /*
 961          * If a command was specified on the command line, execute the
 962          * command now. Otherwise request the server to start a shell.
 963          */
 964         if (buffer_len(&command) > 0) {
 965                 int len = buffer_len(&command);
 966                 if (len > 900)
 967                         len = 900;
 968                 debug("Sending command: %.*s", len, (u_char *)buffer_ptr(&command));
 969                 packet_start(SSH_CMSG_EXEC_CMD);
 970                 packet_put_string(buffer_ptr(&command), buffer_len(&command));
 971                 packet_send();
 972                 packet_write_wait();
 973         } else {
 974                 debug("Requesting shell.");
 975                 packet_start(SSH_CMSG_EXEC_SHELL);
 976                 packet_send();
 977                 packet_write_wait();
 978         }
 979
 980         /* Enter the interactive session. */
 981         return client_loop(have_tty, tty_flag ?
 982             options.escape_char : SSH_ESCAPECHAR_NONE, 0);
 983 }
 984
 985 static void
 986 ssh_subsystem_reply(int type, u_int32_t seq, void *ctxt)
 987 {
 988         int id, len;
 989
 990         id = packet_get_int();
 991         len = buffer_len(&command);
 992         if (len > 900)
 993                 len = 900;
 994         packet_check_eom();
 995         if (type == SSH2_MSG_CHANNEL_FAILURE)
 996                 fatal("Request for subsystem '%.*s' failed on channel %d",
 997                     len, (u_char *)buffer_ptr(&command), id);
 998 }
 999
1000 void
1001 client_global_request_reply_fwd(int type, u_int32_t seq, void *ctxt)
1002 {
1003         int i;
1004
1005         i = client_global_request_id++;
1006         if (i >= options.num_remote_forwards)
1007                 return;
1008         debug("remote forward %s for: listen %d, connect %s:%d",
1009             type == SSH2_MSG_REQUEST_SUCCESS ? "success" : "failure",
1010             options.remote_forwards[i].listen_port,
1011             options.remote_forwards[i].connect_host,
1012             options.remote_forwards[i].connect_port);
1013         if (type == SSH2_MSG_REQUEST_FAILURE)
1014                 logit("Warning: remote port forwarding failed for listen "
1015                     "port %d", options.remote_forwards[i].listen_port);
1016 }
1017
1018 static void
1019 ssh_control_listener(void)
1020 {
1021         struct sockaddr_un addr;
1022         mode_t old_umask;
1023         int addr_len;
1024
1025         if (options.control_path == NULL ||
1026             options.control_master == SSHCTL_MASTER_NO)
1027                 return;
1028
1029         debug("setting up multiplex master socket");
1030
1031         memset(&addr, '\0', sizeof(addr));
1032         addr.sun_family = AF_UNIX;
1033         addr_len = offsetof(struct sockaddr_un, sun_path) +
1034             strlen(options.control_path) + 1;
1035
1036         if (strlcpy(addr.sun_path, options.control_path,
1037             sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
1038                 fatal("ControlPath too long");
1039
1040         if ((control_fd = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
1041                 fatal("%s socket(): %s", __func__, strerror(errno));
1042
1043         old_umask = umask(0177);
1044         if (bind(control_fd, (struct sockaddr*)&addr, addr_len) == -1) {
1045                 control_fd = -1;
1046                 if (errno == EINVAL || errno == EADDRINUSE)
1047                         fatal("ControlSocket %s already exists",
1048                             options.control_path);
1049                 else
1050                         fatal("%s bind(): %s", __func__, strerror(errno));
1051         }
1052         umask(old_umask);
1053
1054         if (listen(control_fd, 64) == -1)
1055                 fatal("%s listen(): %s", __func__, strerror(errno));
1056
1057         set_nonblock(control_fd);
1058 }
1059
1060 /* request pty/x11/agent/tcpfwd/shell for channel */
1061 static void
1062 ssh_session2_setup(int id, void *arg)
1063 {
1064         extern char **environ;
1065         const char *display;
1066         int interactive = tty_flag;
1067
1068         display = getenv("DISPLAY");
1069         if (options.forward_x11 && display != NULL) {
1070                 char *proto, *data;
1071                 /* Get reasonable local authentication information. */
1072                 client_x11_get_proto(display, options.xauth_location,
1073                     options.forward_x11_trusted, &proto, &data);
1074                 /* Request forwarding with authentication spoofing. */
1075                 debug("Requesting X11 forwarding with authentication spoofing.");
1076                 x11_request_forwarding_with_spoofing(id, display, proto, data);
1077                 interactive = 1;
1078                 /* XXX wait for reply */
1079         }
1080
1081         check_agent_present();
1082         if (options.forward_agent) {
1083                 debug("Requesting authentication agent forwarding.");
1084                 channel_request_start(id, "auth-agent-req@openssh.com", 0);
1085                 packet_send();
1086         }
1087
1088         if (options.tun_open != SSH_TUNMODE_NO) {
1089                 Channel *c;
1090                 int fd;
1091
1092                 debug("Requesting tun.");
1093                 if ((fd = tun_open(options.tun_local,
1094                     options.tun_open)) >= 0) {
1095                         c = channel_new("tun", SSH_CHANNEL_OPENING, fd, fd, -1,
1096                             CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
1097                             0, "tun", 1);
1098                         c->datagram = 1;
1099 #if defined(SSH_TUN_FILTER)
1100                         if (options.tun_open == SSH_TUNMODE_POINTOPOINT)
1101                                 channel_register_filter(c->self, sys_tun_infilter,
1102                                     sys_tun_outfilter);
1103 #endif
1104                         packet_start(SSH2_MSG_CHANNEL_OPEN);
1105                         packet_put_cstring("tun@openssh.com");
1106                         packet_put_int(c->self);
1107                         packet_put_int(c->local_window_max);
1108                         packet_put_int(c->local_maxpacket);
1109                         packet_put_int(options.tun_open);
1110                         packet_put_int(options.tun_remote);
1111                         packet_send();
1112                 }
1113         }
1114
1115         client_session2_setup(id, tty_flag, subsystem_flag, getenv("TERM"),
1116             NULL, fileno(stdin), &command, environ, &ssh_subsystem_reply);
1117
1118         packet_set_interactive(interactive);
1119 }
1120
1121 /* open new channel for a session */
1122 static int
1123 ssh_session2_open(void)
1124 {
1125         Channel *c;
1126         int window, packetmax, in, out, err;
1127
1128         if (stdin_null_flag) {
1129                 in = open(_PATH_DEVNULL, O_RDONLY);
1130         } else {
1131                 in = dup(STDIN_FILENO);
1132         }
1133         out = dup(STDOUT_FILENO);
1134         err = dup(STDERR_FILENO);
1135
1136         if (in < 0 || out < 0 || err < 0)
1137                 fatal("dup() in/out/err failed");
1138
1139         /* enable nonblocking unless tty */
1140         if (!isatty(in))
1141                 set_nonblock(in);
1142         if (!isatty(out))
1143                 set_nonblock(out);
1144         if (!isatty(err))
1145                 set_nonblock(err);
1146
1147         window = CHAN_SES_WINDOW_DEFAULT;
1148         packetmax = CHAN_SES_PACKET_DEFAULT;
1149         if (tty_flag) {
1150                 window >>= 1;
1151                 packetmax >>= 1;
1152         }
1153         c = channel_new(
1154             "session", SSH_CHANNEL_OPENING, in, out, err,
1155             window, packetmax, CHAN_EXTENDED_WRITE,
1156             "client-session", /*nonblock*/0);
1157
1158         debug3("ssh_session2_open: channel_new: %d", c->self);
1159
1160         channel_send_open(c->self);
1161         if (!no_shell_flag)
1162                 channel_register_confirm(c->self, ssh_session2_setup, NULL);
1163
1164         return c->self;
1165 }
1166
1167 static int
1168 ssh_session2(void)
1169 {
1170         int id = -1;
1171
1172         /* XXX should be pre-session */
1173         ssh_init_forwarding();
1174         ssh_control_listener();
1175
1176         if (!no_shell_flag || (datafellows & SSH_BUG_DUMMYCHAN))
1177                 id = ssh_session2_open();
1178
1179         /* Execute a local command */
1180         if (options.local_command != NULL &&
1181             options.permit_local_command)
1182                 ssh_local_cmd(options.local_command);
1183
1184         /* If requested, let ssh continue in the background. */
1185         if (fork_after_authentication_flag)
1186                 if (daemon(1, 1) < 0)
1187                         fatal("daemon() failed: %.200s", strerror(errno));
1188
1189         return client_loop(tty_flag, tty_flag ?
1190             options.escape_char : SSH_ESCAPECHAR_NONE, id);
1191 }
1192
1193 static void
1194 load_public_identity_files(void)
1195 {
1196         char *filename;
1197         int i = 0;
1198         Key *public;
1199 #ifdef SMARTCARD
1200         Key **keys;
1201
1202         if (options.smartcard_device != NULL &&
1203             options.num_identity_files < SSH_MAX_IDENTITY_FILES &&
1204             (keys = sc_get_keys(options.smartcard_device, NULL)) != NULL ) {
1205                 int count = 0;
1206                 for (i = 0; keys[i] != NULL; i++) {
1207                         count++;
1208                         memmove(&options.identity_files[1], &options.identity_files[0],
1209                             sizeof(char *) * (SSH_MAX_IDENTITY_FILES - 1));
1210                         memmove(&options.identity_keys[1], &options.identity_keys[0],
1211                             sizeof(Key *) * (SSH_MAX_IDENTITY_FILES - 1));
1212                         options.num_identity_files++;
1213                         options.identity_keys[0] = keys[i];
1214                         options.identity_files[0] = sc_get_key_label(keys[i]);
1215                 }
1216                 if (options.num_identity_files > SSH_MAX_IDENTITY_FILES)
1217                         options.num_identity_files = SSH_MAX_IDENTITY_FILES;
1218                 i = count;
1219                 xfree(keys);
1220         }
1221 #endif /* SMARTCARD */
1222         for (; i < options.num_identity_files; i++) {
1223                 filename = tilde_expand_filename(options.identity_files[i],
1224                     original_real_uid);
1225                 public = key_load_public(filename, NULL);
1226                 debug("identity file %s type %d", filename,
1227                     public ? public->type : -1);
1228                 xfree(options.identity_files[i]);
1229                 options.identity_files[i] = filename;
1230                 options.identity_keys[i] = public;
1231         }
1232 }
1233
1234 static void
1235 control_client_sighandler(int signo)
1236 {
1237         control_client_terminate = signo;
1238 }
1239
1240 static void
1241 control_client_sigrelay(int signo)
1242 {
1243         if (control_server_pid > 1)
1244                 kill(control_server_pid, signo);
1245 }
1246
1247 static int
1248 env_permitted(char *env)
1249 {
1250         int i;
1251         char name[1024], *cp;
1252
1253         strlcpy(name, env, sizeof(name));
1254         if ((cp = strchr(name, '=')) == NULL)
1255                 return (0);
1256
1257         *cp = '\0';
1258
1259         for (i = 0; i < options.num_send_env; i++)
1260                 if (match_pattern(name, options.send_env[i]))
1261                         return (1);
1262
1263         return (0);
1264 }
1265
1266 static void
1267 control_client(const char *path)
1268 {
1269         struct sockaddr_un addr;
1270         int i, r, fd, sock, exitval, num_env, addr_len;
1271         Buffer m;
1272         char *term;
1273         extern char **environ;
1274         u_int  flags;
1275
1276         if (mux_command == 0)
1277                 mux_command = SSHMUX_COMMAND_OPEN;
1278
1279         switch (options.control_master) {
1280         case SSHCTL_MASTER_AUTO:
1281         case SSHCTL_MASTER_AUTO_ASK:
1282                 debug("auto-mux: Trying existing master");
1283                 /* FALLTHROUGH */
1284         case SSHCTL_MASTER_NO:
1285                 break;
1286         default:
1287                 return;
1288         }
1289
1290         memset(&addr, '\0', sizeof(addr));
1291         addr.sun_family = AF_UNIX;
1292         addr_len = offsetof(struct sockaddr_un, sun_path) +
1293             strlen(path) + 1;
1294
1295         if (strlcpy(addr.sun_path, path,
1296             sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
1297                 fatal("ControlPath too long");
1298
1299         if ((sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
1300                 fatal("%s socket(): %s", __func__, strerror(errno));
1301
1302         if (connect(sock, (struct sockaddr*)&addr, addr_len) == -1) {
1303                 if (mux_command != SSHMUX_COMMAND_OPEN) {
1304                         fatal("Control socket connect(%.100s): %s", path,
1305                             strerror(errno));
1306                 }
1307                 if (errno == ENOENT)
1308                         debug("Control socket \"%.100s\" does not exist", path);
1309                 else {
1310                         error("Control socket connect(%.100s): %s", path,
1311                             strerror(errno));
1312                 }
1313                 close(sock);
1314                 return;
1315         }
1316
1317         if (stdin_null_flag) {
1318                 if ((fd = open(_PATH_DEVNULL, O_RDONLY)) == -1)
1319                         fatal("open(/dev/null): %s", strerror(errno));
1320                 if (dup2(fd, STDIN_FILENO) == -1)
1321                         fatal("dup2: %s", strerror(errno));
1322                 if (fd > STDERR_FILENO)
1323                         close(fd);
1324         }
1325
1326         term = getenv("TERM");
1327
1328         flags = 0;
1329         if (tty_flag)
1330                 flags |= SSHMUX_FLAG_TTY;
1331         if (subsystem_flag)
1332                 flags |= SSHMUX_FLAG_SUBSYS;
1333         if (options.forward_x11)
1334                 flags |= SSHMUX_FLAG_X11_FWD;
1335         if (options.forward_agent)
1336                 flags |= SSHMUX_FLAG_AGENT_FWD;
1337
1338         buffer_init(&m);
1339
1340         /* Send our command to server */
1341         buffer_put_int(&m, mux_command);
1342         buffer_put_int(&m, flags);
1343         if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1)
1344                 fatal("%s: msg_send", __func__);
1345         buffer_clear(&m);
1346
1347         /* Get authorisation status and PID of controlee */
1348         if (ssh_msg_recv(sock, &m) == -1)
1349                 fatal("%s: msg_recv", __func__);
1350         if (buffer_get_char(&m) != SSHMUX_VER)
1351                 fatal("%s: wrong version", __func__);
1352         if (buffer_get_int(&m) != 1)
1353                 fatal("Connection to master denied");
1354         control_server_pid = buffer_get_int(&m);
1355
1356         buffer_clear(&m);
1357
1358         switch (mux_command) {
1359         case SSHMUX_COMMAND_ALIVE_CHECK:
1360                 fprintf(stderr, "Master running (pid=%d)\r\n",
1361                     control_server_pid);
1362                 exit(0);
1363         case SSHMUX_COMMAND_TERMINATE:
1364                 fprintf(stderr, "Exit request sent.\r\n");
1365                 exit(0);
1366         case SSHMUX_COMMAND_OPEN:
1367                 /* continue below */
1368                 break;
1369         default:
1370                 fatal("silly mux_command %d", mux_command);
1371         }
1372
1373         /* SSHMUX_COMMAND_OPEN */
1374         buffer_put_cstring(&m, term ? term : "");
1375         buffer_append(&command, "\0", 1);
1376         buffer_put_cstring(&m, buffer_ptr(&command));
1377
1378         if (options.num_send_env == 0 || environ == NULL) {
1379                 buffer_put_int(&m, 0);
1380         } else {
1381                 /* Pass environment */
1382                 num_env = 0;
1383                 for (i = 0; environ[i] != NULL; i++)
1384                         if (env_permitted(environ[i]))
1385                                 num_env++; /* Count */
1386
1387                 buffer_put_int(&m, num_env);
1388
1389                 for (i = 0; environ[i] != NULL && num_env >= 0; i++)
1390                         if (env_permitted(environ[i])) {
1391                                 num_env--;
1392                                 buffer_put_cstring(&m, environ[i]);
1393                         }
1394         }
1395
1396         if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1)
1397                 fatal("%s: msg_send", __func__);
1398
1399         mm_send_fd(sock, STDIN_FILENO);
1400         mm_send_fd(sock, STDOUT_FILENO);
1401         mm_send_fd(sock, STDERR_FILENO);
1402
1403         /* Wait for reply, so master has a chance to gather ttymodes */
1404         buffer_clear(&m);
1405         if (ssh_msg_recv(sock, &m) == -1)
1406                 fatal("%s: msg_recv", __func__);
1407         if (buffer_get_char(&m) != SSHMUX_VER)
1408                 fatal("%s: wrong version", __func__);
1409         buffer_free(&m);
1410
1411         signal(SIGHUP, control_client_sighandler);
1412         signal(SIGINT, control_client_sighandler);
1413         signal(SIGTERM, control_client_sighandler);
1414         signal(SIGWINCH, control_client_sigrelay);
1415
1416         if (tty_flag)
1417                 enter_raw_mode();
1418
1419         /* Stick around until the controlee closes the client_fd */
1420         exitval = 0;
1421         for (;!control_client_terminate;) {
1422                 r = read(sock, &exitval, sizeof(exitval));
1423                 if (r == 0) {
1424                         debug2("Received EOF from master");
1425                         break;
1426                 }
1427                 if (r > 0)
1428                         debug2("Received exit status from master %d", exitval);
1429                 if (r == -1 && errno != EINTR)
1430                         fatal("%s: read %s", __func__, strerror(errno));
1431         }
1432
1433         if (control_client_terminate)
1434                 debug2("Exiting on signal %d", control_client_terminate);
1435
1436         close(sock);
1437
1438         leave_raw_mode();
1439
1440         if (tty_flag && options.log_level != SYSLOG_LEVEL_QUIET)
1441                 fprintf(stderr, "Connection to master closed.\r\n");
1442
1443         exit(exitval);
1444 }