crypto/openssh/auth-options.c

   1 /* $OpenBSD: auth-options.c,v 1.74 2017/09/12 06:32:07 djm Exp $ */
   2 /*
   3  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   4  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   5  *                    All rights reserved
   6  * As far as I am concerned, the code I have written for this software
   7  * can be used freely for any purpose.  Any derived versions of this
   8  * software must be clearly marked as such, and if the derived work is
   9  * incompatible with the protocol description in the RFC file, it must be
  10  * called by a name other than "ssh" or "Secure Shell".
  11  */
  12
  13 #include "includes.h"
  14
  15 #include <sys/types.h>
  16
  17 #include <netdb.h>
  18 #include <pwd.h>
  19 #include <string.h>
  20 #include <stdio.h>
  21 #include <stdarg.h>
  22
  23 #include "openbsd-compat/sys-queue.h"
  24
  25 #include "key.h"        /* XXX for typedef */
  26 #include "buffer.h"     /* XXX for typedef */
  27 #include "xmalloc.h"
  28 #include "match.h"
  29 #include "ssherr.h"
  30 #include "log.h"
  31 #include "canohost.h"
  32 #include "packet.h"
  33 #include "sshbuf.h"
  34 #include "misc.h"
  35 #include "channels.h"
  36 #include "servconf.h"
  37 #include "sshkey.h"
  38 #include "auth-options.h"
  39 #include "hostfile.h"
  40 #include "auth.h"
  41
  42 /* Flags set authorized_keys flags */
  43 int no_port_forwarding_flag = 0;
  44 int no_agent_forwarding_flag = 0;
  45 int no_x11_forwarding_flag = 0;
  46 int no_pty_flag = 0;
  47 int no_user_rc = 0;
  48 int key_is_cert_authority = 0;
  49
  50 /* "command=" option. */
  51 char *forced_command = NULL;
  52
  53 /* "environment=" options. */
  54 struct envstring *custom_environment = NULL;
  55
  56 /* "tunnel=" option. */
  57 int forced_tun_device = -1;
  58
  59 /* "principals=" option. */
  60 char *authorized_principals = NULL;
  61
  62 extern ServerOptions options;
  63
  64 /* XXX refactor to be stateless */
  65
  66 void
  67 auth_clear_options(void)
  68 {
  69         struct ssh *ssh = active_state;         /* XXX */
  70
  71         no_agent_forwarding_flag = 0;
  72         no_port_forwarding_flag = 0;
  73         no_pty_flag = 0;
  74         no_x11_forwarding_flag = 0;
  75         no_user_rc = 0;
  76         key_is_cert_authority = 0;
  77         while (custom_environment) {
  78                 struct envstring *ce = custom_environment;
  79                 custom_environment = ce->next;
  80                 free(ce->s);
  81                 free(ce);
  82         }
  83         free(forced_command);
  84         forced_command = NULL;
  85         free(authorized_principals);
  86         authorized_principals = NULL;
  87         forced_tun_device = -1;
  88         channel_clear_permitted_opens(ssh);
  89 }
  90
  91 /*
  92  * Match flag 'opt' in *optsp, and if allow_negate is set then also match
  93  * 'no-opt'. Returns -1 if option not matched, 1 if option matches or 0
  94  * if negated option matches.
  95  * If the option or negated option matches, then *optsp is updated to
  96  * point to the first character after the option and, if 'msg' is not NULL
  97  * then a message based on it added via auth_debug_add().
  98  */
  99 static int
 100 match_flag(const char *opt, int allow_negate, char **optsp, const char *msg)
 101 {
 102         size_t opt_len = strlen(opt);
 103         char *opts = *optsp;
 104         int negate = 0;
 105
 106         if (allow_negate && strncasecmp(opts, "no-", 3) == 0) {
 107                 opts += 3;
 108                 negate = 1;
 109         }
 110         if (strncasecmp(opts, opt, opt_len) == 0) {
 111                 *optsp = opts + opt_len;
 112                 if (msg != NULL) {
 113                         auth_debug_add("%s %s.", msg,
 114                             negate ? "disabled" : "enabled");
 115                 }
 116                 return negate ? 0 : 1;
 117         }
 118         return -1;
 119 }
 120
 121 /*
 122  * return 1 if access is granted, 0 if not.
 123  * side effect: sets key option flags
 124  * XXX remove side effects; fill structure instead.
 125  */
 126 int
 127 auth_parse_options(struct passwd *pw, char *opts, const char *file,
 128     u_long linenum)
 129 {
 130         struct ssh *ssh = active_state;         /* XXX */
 131         const char *cp;
 132         int i, r;
 133
 134         /* reset options */
 135         auth_clear_options();
 136
 137         if (!opts)
 138                 return 1;
 139
 140         while (*opts && *opts != ' ' && *opts != '\t') {
 141                 if ((r = match_flag("cert-authority", 0, &opts, NULL)) != -1) {
 142                         key_is_cert_authority = r;
 143                         goto next_option;
 144                 }
 145                 if ((r = match_flag("restrict", 0, &opts, NULL)) != -1) {
 146                         auth_debug_add("Key is restricted.");
 147                         no_port_forwarding_flag = 1;
 148                         no_agent_forwarding_flag = 1;
 149                         no_x11_forwarding_flag = 1;
 150                         no_pty_flag = 1;
 151                         no_user_rc = 1;
 152                         goto next_option;
 153                 }
 154                 if ((r = match_flag("port-forwarding", 1, &opts,
 155                     "Port forwarding")) != -1) {
 156                         no_port_forwarding_flag = r != 1;
 157                         goto next_option;
 158                 }
 159                 if ((r = match_flag("agent-forwarding", 1, &opts,
 160                     "Agent forwarding")) != -1) {
 161                         no_agent_forwarding_flag = r != 1;
 162                         goto next_option;
 163                 }
 164                 if ((r = match_flag("x11-forwarding", 1, &opts,
 165                     "X11 forwarding")) != -1) {
 166                         no_x11_forwarding_flag = r != 1;
 167                         goto next_option;
 168                 }
 169                 if ((r = match_flag("pty", 1, &opts,
 170                     "PTY allocation")) != -1) {
 171                         no_pty_flag = r != 1;
 172                         goto next_option;
 173                 }
 174                 if ((r = match_flag("user-rc", 1, &opts,
 175                     "User rc execution")) != -1) {
 176                         no_user_rc = r != 1;
 177                         goto next_option;
 178                 }
 179                 cp = "command=\"";
 180                 if (strncasecmp(opts, cp, strlen(cp)) == 0) {
 181                         opts += strlen(cp);
 182                         free(forced_command);
 183                         forced_command = xmalloc(strlen(opts) + 1);
 184                         i = 0;
 185                         while (*opts) {
 186                                 if (*opts == '"')
 187                                         break;
 188                                 if (*opts == '\\' && opts[1] == '"') {
 189                                         opts += 2;
 190                                         forced_command[i++] = '"';
 191                                         continue;
 192                                 }
 193                                 forced_command[i++] = *opts++;
 194                         }
 195                         if (!*opts) {
 196                                 debug("%.100s, line %lu: missing end quote",
 197                                     file, linenum);
 198                                 auth_debug_add("%.100s, line %lu: missing end quote",
 199                                     file, linenum);
 200                                 free(forced_command);
 201                                 forced_command = NULL;
 202                                 goto bad_option;
 203                         }
 204                         forced_command[i] = '\0';
 205                         auth_debug_add("Forced command.");
 206                         opts++;
 207                         goto next_option;
 208                 }
 209                 cp = "principals=\"";
 210                 if (strncasecmp(opts, cp, strlen(cp)) == 0) {
 211                         opts += strlen(cp);
 212                         free(authorized_principals);
 213                         authorized_principals = xmalloc(strlen(opts) + 1);
 214                         i = 0;
 215                         while (*opts) {
 216                                 if (*opts == '"')
 217                                         break;
 218                                 if (*opts == '\\' && opts[1] == '"') {
 219                                         opts += 2;
 220                                         authorized_principals[i++] = '"';
 221                                         continue;
 222                                 }
 223                                 authorized_principals[i++] = *opts++;
 224                         }
 225                         if (!*opts) {
 226                                 debug("%.100s, line %lu: missing end quote",
 227                                     file, linenum);
 228                                 auth_debug_add("%.100s, line %lu: missing end quote",
 229                                     file, linenum);
 230                                 free(authorized_principals);
 231                                 authorized_principals = NULL;
 232                                 goto bad_option;
 233                         }
 234                         authorized_principals[i] = '\0';
 235                         auth_debug_add("principals: %.900s",
 236                             authorized_principals);
 237                         opts++;
 238                         goto next_option;
 239                 }
 240                 cp = "environment=\"";
 241                 if (strncasecmp(opts, cp, strlen(cp)) == 0) {
 242                         char *s;
 243                         struct envstring *new_envstring;
 244
 245                         opts += strlen(cp);
 246                         s = xmalloc(strlen(opts) + 1);
 247                         i = 0;
 248                         while (*opts) {
 249                                 if (*opts == '"')
 250                                         break;
 251                                 if (*opts == '\\' && opts[1] == '"') {
 252                                         opts += 2;
 253                                         s[i++] = '"';
 254                                         continue;
 255                                 }
 256                                 s[i++] = *opts++;
 257                         }
 258                         if (!*opts) {
 259                                 debug("%.100s, line %lu: missing end quote",
 260                                     file, linenum);
 261                                 auth_debug_add("%.100s, line %lu: missing end quote",
 262                                     file, linenum);
 263                                 free(s);
 264                                 goto bad_option;
 265                         }
 266                         s[i] = '\0';
 267                         opts++;
 268                         if (options.permit_user_env) {
 269                                 auth_debug_add("Adding to environment: "
 270                                     "%.900s", s);
 271                                 debug("Adding to environment: %.900s", s);
 272                                 new_envstring = xcalloc(1,
 273                                     sizeof(*new_envstring));
 274                                 new_envstring->s = s;
 275                                 new_envstring->next = custom_environment;
 276                                 custom_environment = new_envstring;
 277                                 s = NULL;
 278                         }
 279                         free(s);
 280                         goto next_option;
 281                 }
 282                 cp = "from=\"";
 283                 if (strncasecmp(opts, cp, strlen(cp)) == 0) {
 284                         const char *remote_ip = ssh_remote_ipaddr(ssh);
 285                         const char *remote_host = auth_get_canonical_hostname(
 286                             ssh, options.use_dns);
 287                         char *patterns = xmalloc(strlen(opts) + 1);
 288
 289                         opts += strlen(cp);
 290                         i = 0;
 291                         while (*opts) {
 292                                 if (*opts == '"')
 293                                         break;
 294                                 if (*opts == '\\' && opts[1] == '"') {
 295                                         opts += 2;
 296                                         patterns[i++] = '"';
 297                                         continue;
 298                                 }
 299                                 patterns[i++] = *opts++;
 300                         }
 301                         if (!*opts) {
 302                                 debug("%.100s, line %lu: missing end quote",
 303                                     file, linenum);
 304                                 auth_debug_add("%.100s, line %lu: missing end quote",
 305                                     file, linenum);
 306                                 free(patterns);
 307                                 goto bad_option;
 308                         }
 309                         patterns[i] = '\0';
 310                         opts++;
 311                         switch (match_host_and_ip(remote_host, remote_ip,
 312                             patterns)) {
 313                         case 1:
 314                                 free(patterns);
 315                                 /* Host name matches. */
 316                                 goto next_option;
 317                         case -1:
 318                                 debug("%.100s, line %lu: invalid criteria",
 319                                     file, linenum);
 320                                 auth_debug_add("%.100s, line %lu: "
 321                                     "invalid criteria", file, linenum);
 322                                 /* FALLTHROUGH */
 323                         case 0:
 324                                 free(patterns);
 325                                 logit("Authentication tried for %.100s with "
 326                                     "correct key but not from a permitted "
 327                                     "host (host=%.200s, ip=%.200s).",
 328                                     pw->pw_name, remote_host, remote_ip);
 329                                 auth_debug_add("Your host '%.200s' is not "
 330                                     "permitted to use this key for login.",
 331                                     remote_host);
 332                                 break;
 333                         }
 334                         /* deny access */
 335                         return 0;
 336                 }
 337                 cp = "permitopen=\"";
 338                 if (strncasecmp(opts, cp, strlen(cp)) == 0) {
 339                         char *host, *p;
 340                         int port;
 341                         char *patterns = xmalloc(strlen(opts) + 1);
 342
 343                         opts += strlen(cp);
 344                         i = 0;
 345                         while (*opts) {
 346                                 if (*opts == '"')
 347                                         break;
 348                                 if (*opts == '\\' && opts[1] == '"') {
 349                                         opts += 2;
 350                                         patterns[i++] = '"';
 351                                         continue;
 352                                 }
 353                                 patterns[i++] = *opts++;
 354                         }
 355                         if (!*opts) {
 356                                 debug("%.100s, line %lu: missing end quote",
 357                                     file, linenum);
 358                                 auth_debug_add("%.100s, line %lu: missing "
 359                                     "end quote", file, linenum);
 360                                 free(patterns);
 361                                 goto bad_option;
 362                         }
 363                         patterns[i] = '\0';
 364                         opts++;
 365                         p = patterns;
 366                         /* XXX - add streamlocal support */
 367                         host = hpdelim(&p);
 368                         if (host == NULL || strlen(host) >= NI_MAXHOST) {
 369                                 debug("%.100s, line %lu: Bad permitopen "
 370                                     "specification <%.100s>", file, linenum,
 371                                     patterns);
 372                                 auth_debug_add("%.100s, line %lu: "
 373                                     "Bad permitopen specification", file,
 374                                     linenum);
 375                                 free(patterns);
 376                                 goto bad_option;
 377                         }
 378                         host = cleanhostname(host);
 379                         if (p == NULL || (port = permitopen_port(p)) < 0) {
 380                                 debug("%.100s, line %lu: Bad permitopen port "
 381                                     "<%.100s>", file, linenum, p ? p : "");
 382                                 auth_debug_add("%.100s, line %lu: "
 383                                     "Bad permitopen port", file, linenum);
 384                                 free(patterns);
 385                                 goto bad_option;
 386                         }
 387                         if ((options.allow_tcp_forwarding & FORWARD_LOCAL) != 0)
 388                                 channel_add_permitted_opens(ssh, host, port);
 389                         free(patterns);
 390                         goto next_option;
 391                 }
 392                 cp = "tunnel=\"";
 393                 if (strncasecmp(opts, cp, strlen(cp)) == 0) {
 394                         char *tun = NULL;
 395                         opts += strlen(cp);
 396                         tun = xmalloc(strlen(opts) + 1);
 397                         i = 0;
 398                         while (*opts) {
 399                                 if (*opts == '"')
 400                                         break;
 401                                 tun[i++] = *opts++;
 402                         }
 403                         if (!*opts) {
 404                                 debug("%.100s, line %lu: missing end quote",
 405                                     file, linenum);
 406                                 auth_debug_add("%.100s, line %lu: missing end quote",
 407                                     file, linenum);
 408                                 free(tun);
 409                                 forced_tun_device = -1;
 410                                 goto bad_option;
 411                         }
 412                         tun[i] = '\0';
 413                         forced_tun_device = a2tun(tun, NULL);
 414                         free(tun);
 415                         if (forced_tun_device == SSH_TUNID_ERR) {
 416                                 debug("%.100s, line %lu: invalid tun device",
 417                                     file, linenum);
 418                                 auth_debug_add("%.100s, line %lu: invalid tun device",
 419                                     file, linenum);
 420                                 forced_tun_device = -1;
 421                                 goto bad_option;
 422                         }
 423                         auth_debug_add("Forced tun device: %d", forced_tun_device);
 424                         opts++;
 425                         goto next_option;
 426                 }
 427 next_option:
 428                 /*
 429                  * Skip the comma, and move to the next option
 430                  * (or break out if there are no more).
 431                  */
 432                 if (!*opts)
 433                         fatal("Bugs in auth-options.c option processing.");
 434                 if (*opts == ' ' || *opts == '\t')
 435                         break;          /* End of options. */
 436                 if (*opts != ',')
 437                         goto bad_option;
 438                 opts++;
 439                 /* Process the next option. */
 440         }
 441
 442         /* grant access */
 443         return 1;
 444
 445 bad_option:
 446         logit("Bad options in %.100s file, line %lu: %.50s",
 447             file, linenum, opts);
 448         auth_debug_add("Bad options in %.100s file, line %lu: %.50s",
 449             file, linenum, opts);
 450
 451         /* deny access */
 452         return 0;
 453 }
 454
 455 #define OPTIONS_CRITICAL        1
 456 #define OPTIONS_EXTENSIONS      2
 457 static int
 458 parse_option_list(struct sshbuf *oblob, struct passwd *pw,
 459     u_int which, int crit,
 460     int *cert_no_port_forwarding_flag,
 461     int *cert_no_agent_forwarding_flag,
 462     int *cert_no_x11_forwarding_flag,
 463     int *cert_no_pty_flag,
 464     int *cert_no_user_rc,
 465     char **cert_forced_command,
 466     int *cert_source_address_done)
 467 {
 468         struct ssh *ssh = active_state;         /* XXX */
 469         char *command, *allowed;
 470         const char *remote_ip;
 471         char *name = NULL;
 472         struct sshbuf *c = NULL, *data = NULL;
 473         int r, ret = -1, result, found;
 474
 475         if ((c = sshbuf_fromb(oblob)) == NULL) {
 476                 error("%s: sshbuf_fromb failed", __func__);
 477                 goto out;
 478         }
 479
 480         while (sshbuf_len(c) > 0) {
 481                 sshbuf_free(data);
 482                 data = NULL;
 483                 if ((r = sshbuf_get_cstring(c, &name, NULL)) != 0 ||
 484                     (r = sshbuf_froms(c, &data)) != 0) {
 485                         error("Unable to parse certificate options: %s",
 486                             ssh_err(r));
 487                         goto out;
 488                 }
 489                 debug3("found certificate option \"%.100s\" len %zu",
 490                     name, sshbuf_len(data));
 491                 found = 0;
 492                 if ((which & OPTIONS_EXTENSIONS) != 0) {
 493                         if (strcmp(name, "permit-X11-forwarding") == 0) {
 494                                 *cert_no_x11_forwarding_flag = 0;
 495                                 found = 1;
 496                         } else if (strcmp(name,
 497                             "permit-agent-forwarding") == 0) {
 498                                 *cert_no_agent_forwarding_flag = 0;
 499                                 found = 1;
 500                         } else if (strcmp(name,
 501                             "permit-port-forwarding") == 0) {
 502                                 *cert_no_port_forwarding_flag = 0;
 503                                 found = 1;
 504                         } else if (strcmp(name, "permit-pty") == 0) {
 505                                 *cert_no_pty_flag = 0;
 506                                 found = 1;
 507                         } else if (strcmp(name, "permit-user-rc") == 0) {
 508                                 *cert_no_user_rc = 0;
 509                                 found = 1;
 510                         }
 511                 }
 512                 if (!found && (which & OPTIONS_CRITICAL) != 0) {
 513                         if (strcmp(name, "force-command") == 0) {
 514                                 if ((r = sshbuf_get_cstring(data, &command,
 515                                     NULL)) != 0) {
 516                                         error("Unable to parse \"%s\" "
 517                                             "section: %s", name, ssh_err(r));
 518                                         goto out;
 519                                 }
 520                                 if (*cert_forced_command != NULL) {
 521                                         error("Certificate has multiple "
 522                                             "force-command options");
 523                                         free(command);
 524                                         goto out;
 525                                 }
 526                                 *cert_forced_command = command;
 527                                 found = 1;
 528                         }
 529                         if (strcmp(name, "source-address") == 0) {
 530                                 if ((r = sshbuf_get_cstring(data, &allowed,
 531                                     NULL)) != 0) {
 532                                         error("Unable to parse \"%s\" "
 533                                             "section: %s", name, ssh_err(r));
 534                                         goto out;
 535                                 }
 536                                 if ((*cert_source_address_done)++) {
 537                                         error("Certificate has multiple "
 538                                             "source-address options");
 539                                         free(allowed);
 540                                         goto out;
 541                                 }
 542                                 remote_ip = ssh_remote_ipaddr(ssh);
 543                                 result = addr_match_cidr_list(remote_ip,
 544                                     allowed);
 545                                 free(allowed);
 546                                 switch (result) {
 547                                 case 1:
 548                                         /* accepted */
 549                                         break;
 550                                 case 0:
 551                                         /* no match */
 552                                         logit("Authentication tried for %.100s "
 553                                             "with valid certificate but not "
 554                                             "from a permitted host "
 555                                             "(ip=%.200s).", pw->pw_name,
 556                                             remote_ip);
 557                                         auth_debug_add("Your address '%.200s' "
 558                                             "is not permitted to use this "
 559                                             "certificate for login.",
 560                                             remote_ip);
 561                                         goto out;
 562                                 case -1:
 563                                 default:
 564                                         error("Certificate source-address "
 565                                             "contents invalid");
 566                                         goto out;
 567                                 }
 568                                 found = 1;
 569                         }
 570                 }
 571
 572                 if (!found) {
 573                         if (crit) {
 574                                 error("Certificate critical option \"%s\" "
 575                                     "is not supported", name);
 576                                 goto out;
 577                         } else {
 578                                 logit("Certificate extension \"%s\" "
 579                                     "is not supported", name);
 580                         }
 581                 } else if (sshbuf_len(data) != 0) {
 582                         error("Certificate option \"%s\" corrupt "
 583                             "(extra data)", name);
 584                         goto out;
 585                 }
 586                 free(name);
 587                 name = NULL;
 588         }
 589         /* successfully parsed all options */
 590         ret = 0;
 591
 592  out:
 593         if (ret != 0 &&
 594             cert_forced_command != NULL &&
 595             *cert_forced_command != NULL) {
 596                 free(*cert_forced_command);
 597                 *cert_forced_command = NULL;
 598         }
 599         free(name);
 600         sshbuf_free(data);
 601         sshbuf_free(c);
 602         return ret;
 603 }
 604
 605 /*
 606  * Set options from critical certificate options. These supersede user key
 607  * options so this must be called after auth_parse_options().
 608  */
 609 int
 610 auth_cert_options(struct sshkey *k, struct passwd *pw, const char **reason)
 611 {
 612         int cert_no_port_forwarding_flag = 1;
 613         int cert_no_agent_forwarding_flag = 1;
 614         int cert_no_x11_forwarding_flag = 1;
 615         int cert_no_pty_flag = 1;
 616         int cert_no_user_rc = 1;
 617         char *cert_forced_command = NULL;
 618         int cert_source_address_done = 0;
 619
 620         *reason = "invalid certificate options";
 621
 622         /* Separate options and extensions for v01 certs */
 623         if (parse_option_list(k->cert->critical, pw,
 624             OPTIONS_CRITICAL, 1, NULL, NULL, NULL, NULL, NULL,
 625             &cert_forced_command,
 626             &cert_source_address_done) == -1)
 627                 return -1;
 628         if (parse_option_list(k->cert->extensions, pw,
 629             OPTIONS_EXTENSIONS, 0,
 630             &cert_no_port_forwarding_flag,
 631             &cert_no_agent_forwarding_flag,
 632             &cert_no_x11_forwarding_flag,
 633             &cert_no_pty_flag,
 634             &cert_no_user_rc,
 635             NULL, NULL) == -1)
 636                 return -1;
 637
 638         no_port_forwarding_flag |= cert_no_port_forwarding_flag;
 639         no_agent_forwarding_flag |= cert_no_agent_forwarding_flag;
 640         no_x11_forwarding_flag |= cert_no_x11_forwarding_flag;
 641         no_pty_flag |= cert_no_pty_flag;
 642         no_user_rc |= cert_no_user_rc;
 643         /*
 644          * Only permit both CA and key option forced-command if they match.
 645          * Otherwise refuse the certificate.
 646          */
 647         if (cert_forced_command != NULL && forced_command != NULL) {
 648                 if (strcmp(forced_command, cert_forced_command) == 0) {
 649                         free(forced_command);
 650                         forced_command = cert_forced_command;
 651                 } else {
 652                         *reason = "certificate and key options forced command "
 653                             "do not match";
 654                         free(cert_forced_command);
 655                         return -1;
 656                 }
 657         } else if (cert_forced_command != NULL)
 658                 forced_command = cert_forced_command;
 659         /* success */
 660         *reason = NULL;
 661         return 0;
 662 }
 663