mdw@git.distorted.org.uk Git - fwd/blob - fwd.c

   1 /* -*-c-*-
   2  *
   3  * Port forwarding thingy
   4  *
   5  * (c) 1999 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the `fwd' port forwarder.
  11  *
  12  * `fwd' is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * `fwd' is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with `fwd'; if not, write to the Free Software Foundation,
  24  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  25  */
  26
  27 #include "fwd.h"
  28
  29 /*----- Global variables --------------------------------------------------*/
  30
  31 sel_state *sel;                         /* Multiplexor for nonblocking I/O */
  32
  33 /*----- Static variables --------------------------------------------------*/
  34
  35 typedef struct conffile {
  36   struct conffile *next;
  37   char *name;
  38 } conffile;
  39
  40 static unsigned flags = 0;              /* Global state flags */
  41 static unsigned active = 0;             /* Number of active things */
  42 static conffile *conffiles = 0;         /* List of configuration files */
  43
  44 #define FW_SYSLOG 1u
  45 #define FW_QUIET 2u
  46 #define FW_SET 4u
  47
  48 /*----- Configuration parsing ---------------------------------------------*/
  49
  50 /* --- @parse@ --- *
  51  *
  52  * Arguments:   @scanner *sc@ = pointer to scanner definition
  53  *
  54  * Returns:     ---
  55  *
  56  * Use:         Parses a configuration file from the scanner.
  57  */
  58
  59 static source_ops *sources[] =
  60   { &xsource_ops, &fsource_ops, &ssource_ops, 0 };
  61 static target_ops *targets[] =
  62   { &xtarget_ops, &ftarget_ops, &starget_ops, 0 };
  63
  64 void parse(scanner *sc)
  65 {
  66   token(sc);
  67
  68   for (;;) {
  69     if (sc->t == CTOK_EOF)
  70       break;
  71     if (sc->t != CTOK_WORD)
  72       error(sc, "parse error, keyword expected");
  73
  74     /* --- Handle a forwarding request --- */
  75
  76     if (strcmp(sc->d.buf, "forward") == 0 ||
  77         strcmp(sc->d.buf, "fwd") == 0 ||
  78         strcmp(sc->d.buf, "from") == 0) {
  79       source *s;
  80       target *t;
  81
  82       token(sc);
  83
  84       /* --- Read a source description --- */
  85
  86       {
  87         source_ops **sops;
  88
  89         /* --- Try to find a source type which understands --- */
  90
  91         s = 0;
  92         for (sops = sources; *sops; sops++) {
  93           if ((s = (*sops)->read(sc)) != 0)
  94             goto found_source;
  95         }
  96         error(sc, "unknown source name `%s'", sc->d.buf);
  97
  98         /* --- Read any source-specific options --- */
  99
 100       found_source:
 101         if (sc->t == '{') {
 102           token(sc);
 103           while (sc->t == CTOK_WORD) {
 104             if (!s->ops->option || !s->ops->option(s, sc)) {
 105               error(sc, "unknown %s source option `%s'",
 106                     s->ops->name, sc->d.buf);
 107             }
 108             if (sc->t == ';')
 109               token(sc);
 110           }
 111           if (sc->t != '}')
 112             error(sc, "parse error, missing `}'");
 113           token(sc);
 114         }
 115       }
 116
 117       /* --- Read a destination description --- */
 118
 119       if (sc->t == CTOK_WORD && (strcmp(sc->d.buf, "to") == 0 ||
 120                                  strcmp(sc->d.buf, "->") == 0))
 121         token(sc);
 122
 123       {
 124         target_ops **tops;
 125
 126         /* --- Try to find a target which understands --- */
 127
 128         t = 0;
 129         for (tops = targets; *tops; tops++) {
 130           if ((t = (*tops)->read(sc)) != 0)
 131             goto found_target;
 132         }
 133         error(sc, "unknown target name `%s'", sc->d.buf);
 134
 135         /* --- Read any target-specific options --- */
 136
 137       found_target:
 138         if (sc->t == '{') {
 139           token(sc);
 140           while (sc->t == CTOK_WORD) {
 141             if (!t->ops->option || !t->ops->option(t, sc)) {
 142               error(sc, "unknown %s target option `%s'",
 143                     t->ops->name, sc->d.buf);
 144             }
 145             if (sc->t == ';')
 146               token(sc);
 147           }
 148           if (sc->t != '}')
 149             error(sc, "parse error, `}' expected");
 150           token(sc);
 151         }
 152       }
 153
 154       /* --- Combine the source and target --- */
 155
 156       s->ops->attach(s, sc, t);
 157       if (t->ops->confirm)
 158         t->ops->confirm(t);
 159     }
 160
 161     /* --- Include configuration from a file --- *
 162      *
 163      * Slightly tricky.  Scan the optional semicolon from the including
 164      * stream, not the included one.
 165      */
 166
 167     else if (strcmp(sc->d.buf, "include") == 0) {
 168       FILE *fp;
 169       dstr d = DSTR_INIT;
 170
 171       token(sc);
 172       conf_name(sc, '/', &d);
 173       if ((fp = fopen(d.buf, "r")) == 0)
 174         error(sc, "can't include `%s': %s", d.buf, strerror(errno));
 175       if (sc->t == ';')
 176         token(sc);
 177       pushback(sc);
 178       scan_push(sc, scan_file(fp, d.buf, 0));
 179       token(sc);
 180       dstr_destroy(&d);
 181       continue;                         /* Don't parse a trailing `;' */
 182     }
 183
 184     /* --- Other configuration is handled elsewhere --- */
 185
 186     else {
 187
 188       /* --- First try among the sources --- */
 189
 190       {
 191         source_ops **sops;
 192
 193         for (sops = sources; *sops; sops++) {
 194           if ((*sops)->option && (*sops)->option(0, sc))
 195             goto found_option;
 196         }
 197       }
 198
 199       /* --- Then try among the targets --- */
 200
 201       {
 202         target_ops **tops;
 203
 204         for (tops = targets; *tops; tops++) {
 205           if ((*tops)->option && (*tops)->option(0, sc))
 206             goto found_option;
 207         }
 208       }
 209
 210       /* --- Nobody wants the option --- */
 211
 212       error(sc, "unknown global option or prefix `%s'", sc->d.buf);
 213
 214     found_option:;
 215     }
 216
 217     if (sc->t == ';')
 218       token(sc);
 219   }
 220 }
 221
 222 /*----- General utility functions -----------------------------------------*/
 223
 224 /* --- @fw_log@ --- *
 225  *
 226  * Arguments:   @time_t t@ = when the connection occurred or (@-1@)
 227  *              @const char *fmt@ = format string to fill in
 228  *              @...@ = other arguments
 229  *
 230  * Returns:     ---
 231  *
 232  * Use:         Logs a connection.
 233  */
 234
 235 void fw_log(time_t t, const char *fmt, ...)
 236 {
 237   struct tm *tm;
 238   dstr d = DSTR_INIT;
 239   va_list ap;
 240
 241   if (flags & FW_QUIET)
 242     return;
 243
 244   if (t == NOW)
 245     t = time(0);
 246   tm = localtime(&t);
 247   DENSURE(&d, 64);
 248   d.len += strftime(d.buf, d.sz, "%Y-%m-%d %H:%M:%S %z ", tm);
 249   va_start(ap, fmt);
 250   dstr_vputf(&d, fmt, &ap);
 251   va_end(ap);
 252   if (flags & FW_SYSLOG)
 253     syslog(LOG_NOTICE, "%s", d.buf);
 254   else {
 255     DPUTC(&d, '\n');
 256     dstr_write(&d, stderr);
 257   }
 258   DDESTROY(&d);
 259 }
 260
 261 /* --- @fw_inc@, @fw_dec@ --- *
 262  *
 263  * Arguments:   ---
 264  *
 265  * Returns:     ---
 266  *
 267  * Use:         Increments or decrements the active thing count.  `fwd' won't
 268  *              quit while there are active things.
 269  */
 270
 271 void fw_inc(void) { flags |= FW_SET; active++; }
 272 void fw_dec(void) { if (active) active--; }
 273
 274 /* --- @fw_exit@ --- *
 275  *
 276  * Arguments:   ---
 277  *
 278  * Returns:     ---
 279  *
 280  * Use:         Exits when appropriate.
 281  */
 282
 283 static void fw_exit(void)
 284 {
 285   endpt_killall();
 286   source_killall();
 287 }
 288
 289 /* --- @fw_tidy@ --- *
 290  *
 291  * Arguments:   @int n@ = signal number
 292  *              @void *p@ = an uninteresting argument
 293  *
 294  * Returns:     ---
 295  *
 296  * Use:         Handles various signals and causes a clean tidy-up.
 297  */
 298
 299 static void fw_tidy(int n, void *p)
 300 {
 301   const char *sn = 0;
 302   switch (n) {
 303     case SIGTERM: sn = "SIGTERM"; break;
 304     case SIGINT: sn = "SIGINT"; break;
 305     default: abort();
 306   }
 307
 308   fw_log(NOW, "closing down gracefully on %s", sn);
 309   source_killall();
 310 }
 311
 312 /* --- @fw_die@ --- *
 313  *
 314  * Arguments:   @int n@ = signal number
 315  *              @void *p@ = an uninteresting argument
 316  *
 317  * Returns:     ---
 318  *
 319  * Use:         Handles various signals and causes an abrupt shutdown.
 320  */
 321
 322 static void fw_die(int n, void *p)
 323 {
 324   const char *sn = 0;
 325   switch (n) {
 326     case SIGQUIT: sn = "SIGQUIT"; break;
 327     default: abort();
 328   }
 329
 330   fw_log(NOW, "closing down abruptly on %s", sn);
 331   source_killall();
 332   endpt_killall();
 333 }
 334
 335 /* --- @fw_reload@ --- *
 336  *
 337  * Arguments:   @int n@ = a signal number
 338  *              @void *p@ = an uninteresting argument
 339  *
 340  * Returns:     ---
 341  *
 342  * Use:         Handles a hangup signal by re-reading configuration files.
 343  */
 344
 345 static void fw_reload(int n, void *p)
 346 {
 347   FILE *fp;
 348   scanner sc;
 349   conffile *cf;
 350
 351   assert(n == SIGHUP);
 352   if (!conffiles) {
 353     fw_log(NOW, "no configuration files to reload: ignoring SIGHUP");
 354     return;
 355   }
 356   fw_log(NOW, "reloading configuration files...");
 357   source_killall();
 358   scan_create(&sc);
 359   for (cf = conffiles; cf; cf = cf->next) {
 360     if ((fp = fopen(cf->name, "r")) == 0)
 361       fw_log(NOW, "error loading `%s': %s", cf->name, strerror(errno));
 362     else
 363       scan_add(&sc, scan_file(fp, cf->name, 0));
 364   }
 365   parse(&sc);
 366   fw_log(NOW, "... reload completed OK");
 367 }
 368
 369 /*----- Startup and options parsing ---------------------------------------*/
 370
 371 /* --- Standard GNU help options --- */
 372
 373 static void version(FILE *fp)
 374 {
 375   pquis(fp, "$ version " VERSION "\n");
 376 }
 377
 378 static void usage(FILE *fp)
 379 {
 380   pquis(fp, "Usage: $ [-dql] [-p PIDFILE] [-f FILE] [CONFIG-STMTS...]\n");
 381 }
 382
 383 static void help(FILE *fp)
 384 {
 385   version(fp);
 386   fputc('\n', fp);
 387   usage(fp);
 388   pquis(fp, "\n\
 389 An excessively full-featured port-forwarder, which subsumes large chunks\n\
 390 of the functionality of inetd, netcat, and normal cat.\n\
 391 \n\
 392 Configuration may be supplied in one or more configuration files, or on\n\
 393 the command line (or both).  If no `-f' option is present, and no\n\
 394 configuration is given on the command line, the standard input stream is\n\
 395 read.\n\
 396 \n\
 397 Configuration is free-form.  Comments begin with a `#' character and\n\
 398 continue to the end of the line.  Each command line argument is considered\n\
 399 to be a separate line.\n\
 400 \n\
 401 The grammar is fairly complicated.  For a summary, run `$ --grammar'.\n\
 402 For a summary of the various options, run `$ --options'.\n\
 403 \n\
 404 Options available are:\n\
 405 \n\
 406 Help options:\n\
 407   -h, --help           Display this help message.\n\
 408   -v, --version        Display the program's version number.\n\
 409   -u, --usage          Display a terse usage summary.\n\
 410 \n\
 411 Configuration summary:\n\
 412   -G, --grammar        Show a summary of the configuration language.\n\
 413   -O, --options        Show a summary of the source and target options.\n\
 414 \n\
 415 Other options:\n\
 416   -f, --file=FILE      Read configuration from a file.\n\
 417   -q, --quiet          Don't emit any logging information.\n\
 418   -d, --daemon         Fork into background after initializing.\n\
 419   -p, --pidfile=FILE   Write process-id to the named FILE.\n\
 420   -l, --syslog         Send log output to the system logger.\n\
 421   -s, --setuid=USER    Change uid to USER after initializing sources.\n\
 422   -g, --setgid=GRP     Change gid to GRP after initializing sources.\n\
 423 ");
 424 }
 425
 426 /* --- Other helpful options --- */
 427
 428 static void grammar(FILE *fp)
 429 {
 430   version(fp);
 431   fputs("\nGrammar summary\n\n", fp);
 432   fputs(grammar_text, fp);
 433 }
 434
 435 static void options(FILE *fp)
 436 {
 437   version(fp);
 438   fputs("\nOption summary\n\n", fp);
 439   fputs(option_text, fp);
 440 }
 441
 442 /* --- @main@ --- *
 443  *
 444  * Arguments:   @int argc@ = number of command line arguments
 445  *              @char *argv[]@ = vector of argument strings
 446  *
 447  * Returns:     ---
 448  *
 449  * Use:         Simple port-forwarding server.
 450  */
 451
 452 int main(int argc, char *argv[])
 453 {
 454   unsigned f = 0;
 455   sel_state sst;
 456   sig s_term, s_quit, s_int, s_hup;
 457   scanner sc;
 458   uid_t drop = -1;
 459   gid_t dropg = -1;
 460   const char *pidfile = 0;
 461   conffile *cf, **cff = &conffiles;
 462
 463 #define f_bogus 1u
 464 #define f_file 2u
 465 #define f_syslog 4u
 466 #define f_fork 8u
 467
 468   /* --- Initialize things --- */
 469
 470   ego(argv[0]);
 471   sel = &sst;
 472   sel_init(sel);
 473   sub_init();
 474   sig_init(sel);
 475   bres_init(sel);
 476   bres_exec(0);
 477   exec_init();
 478   fattr_init(&fattr_global);
 479   scan_create(&sc);
 480
 481   atexit(fw_exit);
 482
 483   /* --- Parse command line options --- */
 484
 485   for (;;) {
 486     static struct option opts[] = {
 487
 488       /* --- Standard GNU help options --- */
 489
 490       { "help",         0,              0,      'h' },
 491       { "version",      0,              0,      'v' },
 492       { "usage",        0,              0,      'u' },
 493
 494       /* --- Other help options --- */
 495
 496       { "grammar",      0,              0,      'G' },
 497       { "options",      0,              0,      'O' },
 498
 499       /* --- Other useful arguments --- */
 500
 501       { "file",         OPTF_ARGREQ,    0,      'f' },
 502       { "fork",         0,              0,      'd' },
 503       { "daemon",       0,              0,      'd' },
 504       { "pidfile",      OPTF_ARGREQ,    0,      'p' },
 505       { "syslog",       0,              0,      'l' },
 506       { "log",          0,              0,      'l' },
 507       { "quiet",        0,              0,      'q' },
 508       { "setuid",       OPTF_ARGREQ,    0,      's' },
 509       { "uid",          OPTF_ARGREQ,    0,      's' },
 510       { "setgid",       OPTF_ARGREQ,    0,      'g' },
 511       { "gid",          OPTF_ARGREQ,    0,      'g' },
 512
 513       /* --- Magic terminator --- */
 514
 515       { 0,              0,              0,      0 }
 516     };
 517     int i = mdwopt(argc, argv, "+hvu" "GO" "f:dp:lqs:g:", opts, 0, 0, 0);
 518
 519     if (i < 0)
 520       break;
 521     switch (i) {
 522       case 'h':
 523         help(stdout);
 524         exit(0);
 525         break;
 526       case 'v':
 527         version(stdout);
 528         exit(0);
 529         break;
 530       case 'u':
 531         usage(stdout);
 532         exit(0);
 533         break;
 534       case 'G':
 535         grammar(stdout);
 536         exit(0);
 537         break;
 538       case 'O':
 539         options(stdout);
 540         exit(0);
 541         break;
 542       case 'f':
 543         if (strcmp(optarg, "-") == 0)
 544           scan_add(&sc, scan_file(stdin, "<stdin>", SCF_NOCLOSE));
 545         else {
 546           FILE *fp;
 547           if ((fp = fopen(optarg, "r")) == 0)
 548             die(1, "couldn't open file `%s': %s", optarg, strerror(errno));
 549           cf = CREATE(conffile);
 550           cf->name = optarg;
 551           *cff = cf;
 552           cff = &cf->next;
 553           scan_add(&sc, scan_file(fp, optarg, 0));
 554         }
 555         f |= f_file;
 556         break;
 557       case 'd':
 558         f |= f_fork;
 559         break;
 560       case 'p':
 561         pidfile = optarg;
 562         break;
 563       case 'l':
 564         f |= f_syslog;
 565         break;
 566       case 'q':
 567         flags |= FW_QUIET;
 568         break;
 569       case 's':
 570         if (isdigit((unsigned char )optarg[0])) {
 571           char *q;
 572           drop = strtol(optarg, &q, 0);
 573           if (*q)
 574             die(1, "bad uid `%s'", optarg);
 575         } else {
 576           struct passwd *pw = getpwnam(optarg);
 577           if (!pw)
 578             die(1, "unknown user `%s'", optarg);
 579           drop = pw->pw_uid;
 580         }
 581         break;
 582       case 'g':
 583         if (isdigit((unsigned char )optarg[0])) {
 584           char *q;
 585           dropg = strtol(optarg, &q, 0);
 586           if (*q)
 587             die(1, "bad gid `%s'", optarg);
 588         } else {
 589           struct group *gr = getgrnam(optarg);
 590           if (!gr)
 591             die(1, "unknown group `%s'", optarg);
 592           dropg = gr->gr_gid;
 593         }
 594         break;
 595       default:
 596         f |= f_bogus;
 597         break;
 598     }
 599   }
 600
 601   if (f & f_bogus) {
 602     usage(stderr);
 603     exit(1);
 604   }
 605   *cff = 0;
 606
 607   /* --- Deal with the remaining arguments --- */
 608
 609   if (optind < argc)
 610     scan_add(&sc, scan_argv(argv + optind));
 611   else if (f & f_file)
 612     /* Cool */;
 613   else if (!isatty(STDIN_FILENO))
 614     scan_add(&sc, scan_file(stdin, "<stdin>", SCF_NOCLOSE));
 615   else {
 616     moan("no configuration given and stdin is a terminal.");
 617     moan("type `%s --help' for usage information.", QUIS);
 618     exit(1);
 619   }
 620
 621   /* --- Parse the configuration now gathered --- */
 622
 623   parse(&sc);
 624
 625   /* --- Set up some signal handlers --- *
 626    *
 627    * Don't enable @SIGINT@ if the caller already disabled it.
 628    */
 629
 630   {
 631     struct sigaction sa;
 632
 633     sig_add(&s_term, SIGTERM, fw_tidy, 0);
 634     sig_add(&s_quit, SIGQUIT, fw_die, 0);
 635     sigaction(SIGINT, 0, &sa);
 636     if (sa.sa_handler != SIG_IGN)
 637       sig_add(&s_int, SIGINT, fw_tidy, 0);
 638     sig_add(&s_hup, SIGHUP, fw_reload, 0);
 639   }
 640
 641   /* --- Fork into the background --- */
 642
 643   if (f & f_fork) {
 644     pid_t kid;
 645
 646     kid = fork();
 647     if (kid == -1)
 648       die(1, "couldn't fork: %s", strerror(errno));
 649     if (kid != 0)
 650       _exit(0);
 651
 652     close(0); close(1); close(2);
 653     if (chdir("/"))
 654       die(1, "couldn't change to root directory: %s", strerror(errno));
 655     setsid();
 656
 657     kid = fork();
 658     if (kid != 0)
 659       _exit(0);
 660   }
 661   if (pidfile) {
 662     FILE *fp = fopen(pidfile, "w");
 663     if (!fp) {
 664       die(EXIT_FAILURE, "couldn't create pidfile `%s': %s",
 665           pidfile, strerror(errno));
 666     }
 667     fprintf(fp, "%lu\n", (unsigned long)getpid());
 668     if (fflush(fp) || ferror(fp) || fclose(fp)) {
 669       die(EXIT_FAILURE, "couldn't write pidfile `%s': %s",
 670           pidfile, strerror(errno));
 671     }
 672   }
 673
 674   if (f & f_syslog) {
 675     flags |= FW_SYSLOG;
 676     openlog(QUIS, 0, LOG_DAEMON);
 677   }
 678
 679   /* --- Drop privileges --- */
 680
 681   if (drop != (uid_t)-1)
 682     privconn_split(sel);
 683 #ifdef HAVE_SETGROUPS
 684   if ((dropg != (gid_t)-1 && (setgid(dropg) || setgroups(1, &dropg))) ||
 685       (drop != (uid_t)-1 && setuid(drop)))
 686     die(1, "couldn't drop privileges: %s", strerror(errno));
 687 #else
 688   if ((dropg != (gid_t)-1 && setgid(dropg)) ||
 689       (drop != (uid_t)-1 && setuid(drop)))
 690     die(1, "couldn't drop privileges: %s", strerror(errno));
 691 #endif
 692
 693   /* --- Let rip --- */
 694
 695   if (!(flags & FW_SET))
 696     moan("nothing to do!");
 697   signal(SIGPIPE, SIG_IGN);
 698
 699   {
 700     int selerr = 0;
 701     while (active) {
 702       if (!sel_select(sel))
 703         selerr = 0;
 704       else if (errno != EINTR && errno != EAGAIN) {
 705         fw_log(NOW, "error from select: %s", strerror(errno));
 706         selerr++;
 707         if (selerr > 8) {
 708           fw_log(NOW, "too many consecutive select errors: bailing out");
 709           exit(EXIT_FAILURE);
 710         }
 711       }
 712     }
 713   }
 714
 715   return (0);
 716 }
 717
 718 /*----- That's all, folks -------------------------------------------------*/