contrib/tcp_wrappers/options.c

   1  /*
   2   * General skeleton for adding options to the access control language. The
   3   * features offered by this module are documented in the hosts_options(5)
   4   * manual page (source file: hosts_options.5, "nroff -man" format).
   5   *
   6   * Notes and warnings for those who want to add features:
   7   *
   8   * In case of errors, abort options processing and deny access. There are too
   9   * many irreversible side effects to make error recovery feasible. For
  10   * example, it makes no sense to continue after we have already changed the
  11   * userid.
  12   *
  13   * In case of errors, do not terminate the process: the routines might be
  14   * called from a long-running daemon that should run forever. Instead, call
  15   * tcpd_jump() which does a non-local goto back into the hosts_access()
  16   * routine.
  17   *
  18   * In case of severe errors, use clean_exit() instead of directly calling
  19   * exit(), or the inetd may loop on an UDP request.
  20   *
  21   * In verification mode (for example, with the "tcpdmatch" command) the
  22   * "dry_run" flag is set. In this mode, an option function should just "say"
  23   * what it is going to do instead of really doing it.
  24   *
  25   * Some option functions do not return (for example, the twist option passes
  26   * control to another program). In verification mode (dry_run flag is set)
  27   * such options should clear the "dry_run" flag to inform the caller of this
  28   * course of action.
  29   */
  30
  31 /* System libraries. */
  32
  33 #include <sys/types.h>
  34 #include <sys/param.h>
  35 #include <sys/socket.h>
  36 #include <sys/stat.h>
  37 #include <netinet/in.h>
  38 #include <netdb.h>
  39 #include <stdio.h>
  40 #include <unistd.h>
  41 #define SYSLOG_NAMES
  42 #include <syslog.h>
  43 #include <pwd.h>
  44 #include <grp.h>
  45 #include <ctype.h>
  46 #include <setjmp.h>
  47 #include <string.h>
  48 #include <stdlib.h>
  49
  50 #ifndef MAXPATHNAMELEN
  51 #define MAXPATHNAMELEN  BUFSIZ
  52 #endif
  53
  54 /* Local stuff. */
  55
  56 #include "tcpd.h"
  57
  58 /* Options runtime support. */
  59
  60 int     dry_run = 0;                    /* flag set in verification mode */
  61 extern jmp_buf tcpd_buf;                /* tcpd_jump() support */
  62
  63 /* Options parser support. */
  64
  65 static char whitespace_eq[] = "= \t\r\n";
  66 #define whitespace (whitespace_eq + 1)
  67
  68 static char *get_field();               /* chew :-delimited field off string */
  69 static char *chop_string();             /* strip leading and trailing blanks */
  70
  71 /* List of functions that implement the options. Add yours here. */
  72
  73 static void user_option();              /* execute "user name.group" option */
  74 static void group_option();             /* execute "group name" option */
  75 static void umask_option();             /* execute "umask mask" option */
  76 static void linger_option();            /* execute "linger time" option */
  77 static void keepalive_option();         /* execute "keepalive" option */
  78 static void spawn_option();             /* execute "spawn command" option */
  79 static void twist_option();             /* execute "twist command" option */
  80 static void rfc931_option();            /* execute "rfc931" option */
  81 static void setenv_option();            /* execute "setenv name value" */
  82 static void nice_option();              /* execute "nice" option */
  83 static void severity_option();          /* execute "severity value" */
  84 static void allow_option();             /* execute "allow" option */
  85 static void deny_option();              /* execute "deny" option */
  86 static void banners_option();           /* execute "banners path" option */
  87
  88 /* Structure of the options table. */
  89
  90 struct option {
  91     char   *name;                       /* keyword name, case is ignored */
  92     void  (*func) ();                   /* function that does the real work */
  93     int     flags;                      /* see below... */
  94 };
  95
  96 #define NEED_ARG        (1<<1)          /* option requires argument */
  97 #define USE_LAST        (1<<2)          /* option must be last */
  98 #define OPT_ARG         (1<<3)          /* option has optional argument */
  99 #define EXPAND_ARG      (1<<4)          /* do %x expansion on argument */
 100
 101 #define need_arg(o)     ((o)->flags & NEED_ARG)
 102 #define opt_arg(o)      ((o)->flags & OPT_ARG)
 103 #define permit_arg(o)   ((o)->flags & (NEED_ARG | OPT_ARG))
 104 #define use_last(o)     ((o)->flags & USE_LAST)
 105 #define expand_arg(o)   ((o)->flags & EXPAND_ARG)
 106
 107 /* List of known keywords. Add yours here. */
 108
 109 static struct option option_table[] = {
 110     { "user", user_option, NEED_ARG },
 111     { "group", group_option, NEED_ARG },
 112     { "umask", umask_option, NEED_ARG },
 113     { "linger", linger_option, NEED_ARG },
 114     { "keepalive", keepalive_option, 0 },
 115     { "spawn", spawn_option, NEED_ARG | EXPAND_ARG },
 116     { "twist", twist_option, NEED_ARG | EXPAND_ARG | USE_LAST },
 117     { "rfc931", rfc931_option, OPT_ARG },
 118     { "setenv", setenv_option, NEED_ARG | EXPAND_ARG },
 119     { "nice", nice_option, OPT_ARG },
 120     { "severity", severity_option, NEED_ARG },
 121     { "allow", allow_option, USE_LAST },
 122     { "deny", deny_option, USE_LAST },
 123     { "banners", banners_option, NEED_ARG },
 124     { .name = NULL },
 125 };
 126
 127 /* process_options - process access control options */
 128
 129 void    process_options(options, request)
 130 char   *options;
 131 struct request_info *request;
 132 {
 133     char   *key;
 134     char   *value;
 135     char   *curr_opt;
 136     char   *next_opt;
 137     struct option *op;
 138     char    bf[BUFSIZ];
 139
 140     for (curr_opt = get_field(options); curr_opt; curr_opt = next_opt) {
 141         next_opt = get_field((char *) 0);
 142
 143         /*
 144          * Separate the option into name and value parts. For backwards
 145          * compatibility we ignore exactly one '=' between name and value.
 146          */
 147         curr_opt = chop_string(curr_opt);
 148         if (*(value = curr_opt + strcspn(curr_opt, whitespace_eq))) {
 149             if (*value != '=') {
 150                 *value++ = 0;
 151                 value += strspn(value, whitespace);
 152             }
 153             if (*value == '=') {
 154                 *value++ = 0;
 155                 value += strspn(value, whitespace);
 156             }
 157         }
 158         if (*value == 0)
 159             value = 0;
 160         key = curr_opt;
 161
 162         /*
 163          * Disallow missing option names (and empty option fields).
 164          */
 165         if (*key == 0)
 166             tcpd_jump("missing option name");
 167
 168         /*
 169          * Lookup the option-specific info and do some common error checks.
 170          * Delegate option-specific processing to the specific functions.
 171          */
 172
 173         for (op = option_table; op->name && STR_NE(op->name, key); op++)
 174              /* VOID */ ;
 175         if (op->name == 0)
 176             tcpd_jump("bad option name: \"%s\"", key);
 177         if (!value && need_arg(op))
 178             tcpd_jump("option \"%s\" requires value", key);
 179         if (value && !permit_arg(op))
 180             tcpd_jump("option \"%s\" requires no value", key);
 181         if (next_opt && use_last(op))
 182             tcpd_jump("option \"%s\" must be at end", key);
 183         if (value && expand_arg(op))
 184             value = chop_string(percent_x(bf, sizeof(bf), value, request));
 185         if (hosts_access_verbose)
 186             syslog(LOG_DEBUG, "option:   %s %s", key, value ? value : "");
 187         (*(op->func)) (value, request);
 188     }
 189 }
 190
 191 /* allow_option - grant access */
 192
 193 /* ARGSUSED */
 194
 195 static void allow_option(value, request)
 196 char   *value;
 197 struct request_info *request;
 198 {
 199     longjmp(tcpd_buf, AC_PERMIT);
 200 }
 201
 202 /* deny_option - deny access */
 203
 204 /* ARGSUSED */
 205
 206 static void deny_option(value, request)
 207 char   *value;
 208 struct request_info *request;
 209 {
 210     longjmp(tcpd_buf, AC_DENY);
 211 }
 212
 213 /* banners_option - expand %<char>, terminate each line with CRLF */
 214
 215 static void banners_option(value, request)
 216 char   *value;
 217 struct request_info *request;
 218 {
 219     char    path[MAXPATHNAMELEN];
 220     char    ibuf[BUFSIZ];
 221     char    obuf[2 * BUFSIZ];
 222     struct stat st;
 223     int     ch;
 224     FILE   *fp;
 225
 226     sprintf(path, "%s/%s", value, eval_daemon(request));
 227     if ((fp = fopen(path, "r")) != 0) {
 228         while ((ch = fgetc(fp)) == 0)
 229             write(request->fd, "", 1);
 230         ungetc(ch, fp);
 231         while (fgets(ibuf, sizeof(ibuf) - 1, fp)) {
 232             if (split_at(ibuf, '\n'))
 233                 strcat(ibuf, "\r\n");
 234             percent_x(obuf, sizeof(obuf), ibuf, request);
 235             write(request->fd, obuf, strlen(obuf));
 236         }
 237         fclose(fp);
 238     } else if (stat(value, &st) < 0) {
 239         tcpd_warn("%s: %m", value);
 240     }
 241 }
 242
 243 /* group_option - switch group id */
 244
 245 /* ARGSUSED */
 246
 247 static void group_option(value, request)
 248 char   *value;
 249 struct request_info *request;
 250 {
 251     struct group *grp;
 252     struct group *getgrnam();
 253
 254     if ((grp = getgrnam(value)) == 0)
 255         tcpd_jump("unknown group: \"%s\"", value);
 256     endgrent();
 257
 258     if (dry_run == 0 && setgid(grp->gr_gid))
 259         tcpd_jump("setgid(%s): %m", value);
 260 }
 261
 262 /* user_option - switch user id */
 263
 264 /* ARGSUSED */
 265
 266 static void user_option(value, request)
 267 char   *value;
 268 struct request_info *request;
 269 {
 270     struct passwd *pwd;
 271     struct passwd *getpwnam();
 272     char   *group;
 273
 274     if ((group = split_at(value, '.')) != 0)
 275         group_option(group, request);
 276     if ((pwd = getpwnam(value)) == 0)
 277         tcpd_jump("unknown user: \"%s\"", value);
 278     endpwent();
 279
 280     if (dry_run == 0 && setuid(pwd->pw_uid))
 281         tcpd_jump("setuid(%s): %m", value);
 282 }
 283
 284 /* umask_option - set file creation mask */
 285
 286 /* ARGSUSED */
 287
 288 static void umask_option(value, request)
 289 char   *value;
 290 struct request_info *request;
 291 {
 292     unsigned mask;
 293     char    junk;
 294
 295     if (sscanf(value, "%o%c", &mask, &junk) != 1 || (mask & 0777) != mask)
 296         tcpd_jump("bad umask value: \"%s\"", value);
 297     (void) umask(mask);
 298 }
 299
 300 /* spawn_option - spawn a shell command and wait */
 301
 302 /* ARGSUSED */
 303
 304 static void spawn_option(value, request)
 305 char   *value;
 306 struct request_info *request;
 307 {
 308     if (dry_run == 0)
 309         shell_cmd(value);
 310 }
 311
 312 /* linger_option - set the socket linger time (Marc Boucher <marc@cam.org>) */
 313
 314 /* ARGSUSED */
 315
 316 static void linger_option(value, request)
 317 char   *value;
 318 struct request_info *request;
 319 {
 320     struct linger linger;
 321     char    junk;
 322
 323     if (sscanf(value, "%d%c", &linger.l_linger, &junk) != 1
 324         || linger.l_linger < 0)
 325         tcpd_jump("bad linger value: \"%s\"", value);
 326     if (dry_run == 0) {
 327         linger.l_onoff = (linger.l_linger != 0);
 328         if (setsockopt(request->fd, SOL_SOCKET, SO_LINGER, (char *) &linger,
 329                        sizeof(linger)) < 0)
 330             tcpd_warn("setsockopt SO_LINGER %d: %m", linger.l_linger);
 331     }
 332 }
 333
 334 /* keepalive_option - set the socket keepalive option */
 335
 336 /* ARGSUSED */
 337
 338 static void keepalive_option(value, request)
 339 char   *value;
 340 struct request_info *request;
 341 {
 342     static int on = 1;
 343
 344     if (dry_run == 0 && setsockopt(request->fd, SOL_SOCKET, SO_KEEPALIVE,
 345                                    (char *) &on, sizeof(on)) < 0)
 346         tcpd_warn("setsockopt SO_KEEPALIVE: %m");
 347 }
 348
 349 /* nice_option - set nice value */
 350
 351 /* ARGSUSED */
 352
 353 static void nice_option(value, request)
 354 char   *value;
 355 struct request_info *request;
 356 {
 357     int     niceval = 10;
 358     char    junk;
 359
 360     if (value != 0 && sscanf(value, "%d%c", &niceval, &junk) != 1)
 361         tcpd_jump("bad nice value: \"%s\"", value);
 362     if (dry_run == 0 && nice(niceval) < 0)
 363         tcpd_warn("nice(%d): %m", niceval);
 364 }
 365
 366 /* twist_option - replace process by shell command */
 367
 368 static void twist_option(value, request)
 369 char   *value;
 370 struct request_info *request;
 371 {
 372     char   *error;
 373
 374     if (dry_run != 0) {
 375         dry_run = 0;
 376     } else {
 377         if (resident > 0)
 378             tcpd_jump("twist option in resident process");
 379
 380         syslog(deny_severity, "twist %s to %s", eval_client(request), value);
 381
 382         /* Before switching to the shell, set up stdin, stdout and stderr. */
 383
 384 #define maybe_dup2(from, to) ((from == to) ? to : (close(to), dup(from)))
 385
 386         if (maybe_dup2(request->fd, 0) != 0 ||
 387             maybe_dup2(request->fd, 1) != 1 ||
 388             maybe_dup2(request->fd, 2) != 2) {
 389             error = "twist_option: dup: %m";
 390         } else {
 391             if (request->fd > 2)
 392                 close(request->fd);
 393             (void) execl("/bin/sh", "sh", "-c", value, (char *) 0);
 394             error = "twist_option: /bin/sh: %m";
 395         }
 396
 397         /* Something went wrong: we MUST terminate the process. */
 398
 399         tcpd_warn("%s", error);
 400         clean_exit(request);
 401     }
 402 }
 403
 404 /* rfc931_option - look up remote user name */
 405
 406 static void rfc931_option(value, request)
 407 char   *value;
 408 struct request_info *request;
 409 {
 410     int     timeout;
 411     char    junk;
 412
 413     if (value != 0) {
 414         if (sscanf(value, "%d%c", &timeout, &junk) != 1 || timeout <= 0)
 415             tcpd_jump("bad rfc931 timeout: \"%s\"", value);
 416         rfc931_timeout = timeout;
 417     }
 418     (void) eval_user(request);
 419 }
 420
 421 /* setenv_option - set environment variable */
 422
 423 /* ARGSUSED */
 424
 425 static void setenv_option(value, request)
 426 char   *value;
 427 struct request_info *request;
 428 {
 429     char   *var_value;
 430
 431     if (*(var_value = value + strcspn(value, whitespace)))
 432         *var_value++ = 0;
 433     if (setenv(chop_string(value), chop_string(var_value), 1))
 434         tcpd_jump("memory allocation failure");
 435 }
 436
 437 /* severity_map - lookup facility or severity value */
 438
 439 static int severity_map(table, name)
 440 CODE   *table;
 441 char   *name;
 442 {
 443     CODE *t;
 444
 445     for (t = table; t->c_name; t++)
 446         if (STR_EQ(t->c_name, name))
 447             return (t->c_val);
 448     tcpd_jump("bad syslog facility or severity: \"%s\"", name);
 449     /* NOTREACHED */
 450 }
 451
 452 /* severity_option - change logging severity for this event (Dave Mitchell) */
 453
 454 /* ARGSUSED */
 455
 456 static void severity_option(value, request)
 457 char   *value;
 458 struct request_info *request;
 459 {
 460     char   *level = split_at(value, '.');
 461
 462     allow_severity = deny_severity = level ?
 463         severity_map(facilitynames, value) | severity_map(prioritynames, level)
 464         : severity_map(prioritynames, value);
 465 }
 466
 467 /* get_field - return pointer to next field in string */
 468
 469 static char *get_field(string)
 470 char   *string;
 471 {
 472     static char *last = "";
 473     char   *src;
 474     char   *dst;
 475     char   *ret;
 476     int     ch;
 477
 478     /*
 479      * This function returns pointers to successive fields within a given
 480      * string. ":" is the field separator; warn if the rule ends in one. It
 481      * replaces a "\:" sequence by ":", without treating the result of
 482      * substitution as field terminator. A null argument means resume search
 483      * where the previous call terminated. This function destroys its
 484      * argument.
 485      *
 486      * Work from explicit source or from memory. While processing \: we
 487      * overwrite the input. This way we do not have to maintain buffers for
 488      * copies of input fields.
 489      */
 490
 491     src = dst = ret = (string ? string : last);
 492     if (src[0] == 0)
 493         return (0);
 494
 495     while ((ch = *src) != 0) {
 496         if (ch == ':') {
 497             if (*++src == 0)
 498                 tcpd_warn("rule ends in \":\"");
 499             break;
 500         }
 501         if (ch == '\\' && src[1] == ':')
 502             src++;
 503         *dst++ = *src++;
 504     }
 505     last = src;
 506     *dst = 0;
 507     return (ret);
 508 }
 509
 510 /* chop_string - strip leading and trailing blanks from string */
 511
 512 static char *chop_string(string)
 513 register char *string;
 514 {
 515     char   *start = 0;
 516     char   *end;
 517     char   *cp;
 518
 519     for (cp = string; *cp; cp++) {
 520         if (!isspace(*cp)) {
 521             if (start == 0)
 522                 start = cp;
 523             end = cp;
 524         }
 525     }
 526     return (start ? (end[1] = 0, start) : cp);
 527 }