libexec/rshd/rshd.c

   1 /*-
   2  * Copyright (c) 1988, 1989, 1992, 1993, 1994
   3  *      The Regents of the University of California.  All rights reserved.
   4  * Copyright (c) 2002 Networks Associates Technology, Inc.
   5  * All rights reserved.
   6  *
   7  * Portions of this software were developed for the FreeBSD Project by
   8  * ThinkSec AS and NAI Labs, the Security Research Division of Network
   9  * Associates, Inc.  under DARPA/SPAWAR contract N66001-01-C-8035
  10  * ("CBOSS"), as part of the DARPA CHATS research program.
  11  *
  12  * Redistribution and use in source and binary forms, with or without
  13  * modification, are permitted provided that the following conditions
  14  * are met:
  15  * 1. Redistributions of source code must retain the above copyright
  16  *    notice, this list of conditions and the following disclaimer.
  17  * 2. Redistributions in binary form must reproduce the above copyright
  18  *    notice, this list of conditions and the following disclaimer in the
  19  *    documentation and/or other materials provided with the distribution.
  20  * 3. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  */
  36
  37 #ifndef lint
  38 static const char copyright[] =
  39 "@(#) Copyright (c) 1988, 1989, 1992, 1993, 1994\n\
  40         The Regents of the University of California.  All rights reserved.\n";
  41 #endif /* not lint */
  42
  43 #ifndef lint
  44 #if 0
  45 static const char sccsid[] = "@(#)rshd.c        8.2 (Berkeley) 4/6/94";
  46 #endif
  47 #endif /* not lint */
  48
  49 #include <sys/cdefs.h>
  50 __FBSDID("$FreeBSD$");
  51
  52 /*
  53  * remote shell server:
  54  *      [port]\0
  55  *      ruser\0
  56  *      luser\0
  57  *      command\0
  58  *      data
  59  */
  60 #include <sys/param.h>
  61 #include <sys/ioctl.h>
  62 #include <sys/time.h>
  63 #include <sys/socket.h>
  64
  65 #include <netinet/in_systm.h>
  66 #include <netinet/in.h>
  67 #include <netinet/ip.h>
  68 #include <netinet/tcp.h>
  69 #include <arpa/inet.h>
  70 #include <netdb.h>
  71
  72 #include <err.h>
  73 #include <errno.h>
  74 #include <fcntl.h>
  75 #include <libutil.h>
  76 #include <paths.h>
  77 #include <pwd.h>
  78 #include <signal.h>
  79 #include <stdarg.h>
  80 #include <stdio.h>
  81 #include <stdlib.h>
  82 #include <string.h>
  83 #include <syslog.h>
  84 #include <unistd.h>
  85 #include <login_cap.h>
  86
  87 #include <security/pam_appl.h>
  88 #include <security/openpam.h>
  89 #include <sys/wait.h>
  90
  91 #ifdef USE_BLACKLIST
  92 #include <blacklist.h>
  93 #endif
  94
  95 static struct pam_conv pamc = { openpam_nullconv, NULL };
  96 static pam_handle_t *pamh;
  97 static int pam_err;
  98
  99 #define PAM_END { \
 100         if ((pam_err = pam_setcred(pamh, PAM_DELETE_CRED)) != PAM_SUCCESS) \
 101                 syslog(LOG_ERR|LOG_AUTH, "pam_setcred(): %s", pam_strerror(pamh, pam_err)); \
 102         if ((pam_err = pam_close_session(pamh,0)) != PAM_SUCCESS) \
 103                 syslog(LOG_ERR|LOG_AUTH, "pam_close_session(): %s", pam_strerror(pamh, pam_err)); \
 104         if ((pam_err = pam_end(pamh, pam_err)) != PAM_SUCCESS) \
 105                 syslog(LOG_ERR|LOG_AUTH, "pam_end(): %s", pam_strerror(pamh, pam_err)); \
 106 }
 107
 108 int     keepalive = 1;
 109 int     log_success;            /* If TRUE, log all successful accesses */
 110 int     sent_null;
 111 int     no_delay;
 112
 113 void     doit(struct sockaddr *);
 114 static void      rshd_errx(int, const char *, ...) __printf0like(2, 3);
 115 void     getstr(char *, int, const char *);
 116 int      local_domain(char *);
 117 char    *topdomain(char *);
 118 void     usage(void);
 119
 120 char     slash[] = "/";
 121 char     bshell[] = _PATH_BSHELL;
 122
 123 #define OPTIONS "aDLln"
 124
 125 int
 126 main(int argc, char *argv[])
 127 {
 128         extern int __check_rhosts_file;
 129         struct linger linger;
 130         socklen_t fromlen;
 131         int ch, on = 1;
 132         struct sockaddr_storage from;
 133
 134         openlog("rshd", LOG_PID, LOG_DAEMON);
 135
 136         opterr = 0;
 137         while ((ch = getopt(argc, argv, OPTIONS)) != -1)
 138                 switch (ch) {
 139                 case 'a':
 140                         /* ignored for compatibility */
 141                         break;
 142                 case 'l':
 143                         __check_rhosts_file = 0;
 144                         break;
 145                 case 'n':
 146                         keepalive = 0;
 147                         break;
 148                 case 'D':
 149                         no_delay = 1;
 150                         break;
 151                 case 'L':
 152                         log_success = 1;
 153                         break;
 154                 case '?':
 155                 default:
 156                         usage();
 157                         break;
 158                 }
 159
 160         argc -= optind;
 161         argv += optind;
 162
 163         fromlen = sizeof (from);
 164         if (getpeername(0, (struct sockaddr *)&from, &fromlen) < 0) {
 165                 syslog(LOG_ERR, "getpeername: %m");
 166                 exit(1);
 167         }
 168         if (keepalive &&
 169             setsockopt(0, SOL_SOCKET, SO_KEEPALIVE, (char *)&on,
 170             sizeof(on)) < 0)
 171                 syslog(LOG_WARNING, "setsockopt (SO_KEEPALIVE): %m");
 172         linger.l_onoff = 1;
 173         linger.l_linger = 60;                   /* XXX */
 174         if (setsockopt(0, SOL_SOCKET, SO_LINGER, (char *)&linger,
 175             sizeof (linger)) < 0)
 176                 syslog(LOG_WARNING, "setsockopt (SO_LINGER): %m");
 177         if (no_delay &&
 178             setsockopt(0, IPPROTO_TCP, TCP_NODELAY, &on, sizeof(on)) < 0)
 179                 syslog(LOG_WARNING, "setsockopt (TCP_NODELAY): %m");
 180         doit((struct sockaddr *)&from);
 181         /* NOTREACHED */
 182         return(0);
 183 }
 184
 185 extern char **environ;
 186
 187 void
 188 doit(struct sockaddr *fromp)
 189 {
 190         extern char *__rcmd_errstr;     /* syslog hook from libc/net/rcmd.c. */
 191         struct passwd *pwd;
 192         u_short port;
 193         fd_set ready, readfrom;
 194         int cc, nfd, pv[2], pid, s;
 195         int one = 1;
 196         const char *cp, *errorstr;
 197         char sig, buf[BUFSIZ];
 198         char *cmdbuf, luser[16], ruser[16];
 199         char rhost[2 * MAXHOSTNAMELEN + 1];
 200         char numericname[INET6_ADDRSTRLEN];
 201         int af, srcport;
 202         int maxcmdlen;
 203         login_cap_t *lc;
 204
 205         maxcmdlen = (int)sysconf(_SC_ARG_MAX);
 206         if (maxcmdlen <= 0 || (cmdbuf = malloc(maxcmdlen)) == NULL)
 207                 exit(1);
 208
 209         (void) signal(SIGINT, SIG_DFL);
 210         (void) signal(SIGQUIT, SIG_DFL);
 211         (void) signal(SIGTERM, SIG_DFL);
 212         af = fromp->sa_family;
 213         srcport = ntohs(*((in_port_t *)&fromp->sa_data));
 214         if (af == AF_INET) {
 215                 inet_ntop(af, &((struct sockaddr_in *)fromp)->sin_addr,
 216                     numericname, sizeof numericname);
 217         } else if (af == AF_INET6) {
 218                 inet_ntop(af, &((struct sockaddr_in6 *)fromp)->sin6_addr,
 219                     numericname, sizeof numericname);
 220         } else {
 221                 syslog(LOG_ERR, "malformed \"from\" address (af %d)", af);
 222                 exit(1);
 223         }
 224 #ifdef IP_OPTIONS
 225         if (af == AF_INET) {
 226                 u_char optbuf[BUFSIZ/3];
 227                 socklen_t optsize = sizeof(optbuf), ipproto, i;
 228                 struct protoent *ip;
 229
 230                 if ((ip = getprotobyname("ip")) != NULL)
 231                         ipproto = ip->p_proto;
 232                 else
 233                         ipproto = IPPROTO_IP;
 234                 if (!getsockopt(0, ipproto, IP_OPTIONS, optbuf, &optsize) &&
 235                     optsize != 0) {
 236                         for (i = 0; i < optsize; ) {
 237                                 u_char c = optbuf[i];
 238                                 if (c == IPOPT_LSRR || c == IPOPT_SSRR) {
 239                                         syslog(LOG_NOTICE,
 240                                             "connection refused from %s with IP option %s",
 241                                             numericname,
 242                                             c == IPOPT_LSRR ? "LSRR" : "SSRR");
 243                                         exit(1);
 244                                 }
 245                                 if (c == IPOPT_EOL)
 246                                         break;
 247                                 i += (c == IPOPT_NOP) ? 1 : optbuf[i+1];
 248                         }
 249                 }
 250         }
 251 #endif
 252
 253         if (srcport >= IPPORT_RESERVED ||
 254             srcport < IPPORT_RESERVED/2) {
 255                 syslog(LOG_NOTICE|LOG_AUTH,
 256                     "connection from %s on illegal port %u",
 257                     numericname,
 258                     srcport);
 259 #ifdef USE_BLACKLIST
 260                 blacklist(1, STDIN_FILENO, "illegal port");
 261 #endif
 262                 exit(1);
 263         }
 264
 265         (void) alarm(60);
 266         port = 0;
 267         s = 0;          /* not set or used if port == 0 */
 268         for (;;) {
 269                 char c;
 270                 if ((cc = read(STDIN_FILENO, &c, 1)) != 1) {
 271                         if (cc < 0)
 272                                 syslog(LOG_NOTICE, "read: %m");
 273                         shutdown(0, SHUT_RDWR);
 274                         exit(1);
 275                 }
 276                 if (c == 0)
 277                         break;
 278                 port = port * 10 + c - '0';
 279         }
 280
 281         (void) alarm(0);
 282         if (port != 0) {
 283                 int lport = IPPORT_RESERVED - 1;
 284                 s = rresvport_af(&lport, af);
 285                 if (s < 0) {
 286                         syslog(LOG_ERR, "can't get stderr port: %m");
 287                         exit(1);
 288                 }
 289                 if (port >= IPPORT_RESERVED ||
 290                     port < IPPORT_RESERVED/2) {
 291                         syslog(LOG_NOTICE|LOG_AUTH,
 292                             "2nd socket from %s on unreserved port %u",
 293                             numericname,
 294                             port);
 295 #ifdef USE_BLACKLIST
 296                         blacklist(1, STDIN_FILENO, "unreserved port");
 297 #endif
 298                         exit(1);
 299                 }
 300                 *((in_port_t *)&fromp->sa_data) = htons(port);
 301                 if (connect(s, fromp, fromp->sa_len) < 0) {
 302                         syslog(LOG_INFO, "connect second port %d: %m", port);
 303                         exit(1);
 304                 }
 305         }
 306
 307         errorstr = NULL;
 308         realhostname_sa(rhost, sizeof(rhost) - 1, fromp, fromp->sa_len);
 309         rhost[sizeof(rhost) - 1] = '\0';
 310         /* XXX truncation! */
 311
 312         (void) alarm(60);
 313         getstr(ruser, sizeof(ruser), "ruser");
 314         getstr(luser, sizeof(luser), "luser");
 315         getstr(cmdbuf, maxcmdlen, "command");
 316         (void) alarm(0);
 317
 318         pam_err = pam_start("rsh", luser, &pamc, &pamh);
 319         if (pam_err != PAM_SUCCESS) {
 320                 syslog(LOG_ERR|LOG_AUTH, "pam_start(): %s",
 321                     pam_strerror(pamh, pam_err));
 322 #ifdef USE_BLACKLIST
 323                 blacklist(1, STDIN_FILENO, "login incorrect");
 324 #endif
 325                 rshd_errx(1, "Login incorrect.");
 326         }
 327
 328         if ((pam_err = pam_set_item(pamh, PAM_RUSER, ruser)) != PAM_SUCCESS ||
 329             (pam_err = pam_set_item(pamh, PAM_RHOST, rhost)) != PAM_SUCCESS) {
 330                 syslog(LOG_ERR|LOG_AUTH, "pam_set_item(): %s",
 331                     pam_strerror(pamh, pam_err));
 332 #ifdef USE_BLACKLIST
 333                 blacklist(1, STDIN_FILENO, "login incorrect");
 334 #endif
 335                 rshd_errx(1, "Login incorrect.");
 336         }
 337
 338         pam_err = pam_authenticate(pamh, 0);
 339         if (pam_err == PAM_SUCCESS) {
 340                 if ((pam_err = pam_get_user(pamh, &cp, NULL)) == PAM_SUCCESS) {
 341                         strlcpy(luser, cp, sizeof(luser));
 342                         /* XXX truncation! */
 343                 }
 344                 pam_err = pam_acct_mgmt(pamh, 0);
 345         }
 346         if (pam_err != PAM_SUCCESS) {
 347                 syslog(LOG_INFO|LOG_AUTH,
 348                     "%s@%s as %s: permission denied (%s). cmd='%.80s'",
 349                     ruser, rhost, luser, pam_strerror(pamh, pam_err), cmdbuf);
 350 #ifdef USE_BLACKLIST
 351                 blacklist(1, STDIN_FILENO, "permission denied");
 352 #endif
 353                 rshd_errx(1, "Login incorrect.");
 354         }
 355
 356         setpwent();
 357         pwd = getpwnam(luser);
 358         if (pwd == NULL) {
 359                 syslog(LOG_INFO|LOG_AUTH,
 360                     "%s@%s as %s: unknown login. cmd='%.80s'",
 361                     ruser, rhost, luser, cmdbuf);
 362 #ifdef USE_BLACKLIST
 363                 blacklist(1, STDIN_FILENO, "unknown login");
 364 #endif
 365                 if (errorstr == NULL)
 366                         errorstr = "Login incorrect.";
 367                 rshd_errx(1, errorstr, rhost);
 368         }
 369
 370         lc = login_getpwclass(pwd);
 371         if (pwd->pw_uid)
 372                 auth_checknologin(lc);
 373
 374         if (chdir(pwd->pw_dir) < 0) {
 375                 if (chdir("/") < 0 ||
 376                     login_getcapbool(lc, "requirehome", !!pwd->pw_uid)) {
 377                         syslog(LOG_INFO|LOG_AUTH,
 378                         "%s@%s as %s: no home directory. cmd='%.80s'",
 379                         ruser, rhost, luser, cmdbuf);
 380                         rshd_errx(0, "No remote home directory.");
 381                 }
 382                 pwd->pw_dir = slash;
 383         }
 384
 385         if (lc != NULL && fromp->sa_family == AF_INET) {        /*XXX*/
 386                 char    remote_ip[MAXHOSTNAMELEN];
 387
 388                 strlcpy(remote_ip, numericname, sizeof(remote_ip));
 389                 /* XXX truncation! */
 390                 if (!auth_hostok(lc, rhost, remote_ip)) {
 391                         syslog(LOG_INFO|LOG_AUTH,
 392                             "%s@%s as %s: permission denied (%s). cmd='%.80s'",
 393                             ruser, rhost, luser, __rcmd_errstr,
 394                             cmdbuf);
 395 #ifdef USE_BLACKLIST
 396                         blacklist(1, STDIN_FILENO, "permission denied");
 397 #endif
 398                         rshd_errx(1, "Login incorrect.");
 399                 }
 400                 if (!auth_timeok(lc, time(NULL)))
 401                         rshd_errx(1, "Logins not available right now");
 402         }
 403
 404         /*
 405          * PAM modules might add supplementary groups in
 406          * pam_setcred(), so initialize them first.
 407          * But we need to open the session as root.
 408          */
 409         if (setusercontext(lc, pwd, pwd->pw_uid, LOGIN_SETGROUP) != 0) {
 410                 syslog(LOG_ERR, "setusercontext: %m");
 411                 exit(1);
 412         }
 413
 414         if ((pam_err = pam_open_session(pamh, 0)) != PAM_SUCCESS) {
 415                 syslog(LOG_ERR, "pam_open_session: %s", pam_strerror(pamh, pam_err));
 416         } else if ((pam_err = pam_setcred(pamh, PAM_ESTABLISH_CRED)) != PAM_SUCCESS) {
 417                 syslog(LOG_ERR, "pam_setcred: %s", pam_strerror(pamh, pam_err));
 418         }
 419
 420         (void) write(STDERR_FILENO, "\0", 1);
 421         sent_null = 1;
 422
 423         if (port) {
 424                 if (pipe(pv) < 0)
 425                         rshd_errx(1, "Can't make pipe.");
 426                 pid = fork();
 427                 if (pid == -1)
 428                         rshd_errx(1, "Can't fork; try again.");
 429                 if (pid) {
 430                         (void) close(0);
 431                         (void) close(1);
 432                         (void) close(2);
 433                         (void) close(pv[1]);
 434
 435                         FD_ZERO(&readfrom);
 436                         FD_SET(s, &readfrom);
 437                         FD_SET(pv[0], &readfrom);
 438                         if (pv[0] > s)
 439                                 nfd = pv[0];
 440                         else
 441                                 nfd = s;
 442                                 ioctl(pv[0], FIONBIO, (char *)&one);
 443
 444                         /* should set s nbio! */
 445                         nfd++;
 446                         do {
 447                                 ready = readfrom;
 448                                 if (select(nfd, &ready, (fd_set *)0,
 449                                   (fd_set *)0, (struct timeval *)0) < 0)
 450                                         break;
 451                                 if (FD_ISSET(s, &ready)) {
 452                                         int     ret;
 453                                                 ret = read(s, &sig, 1);
 454                                 if (ret <= 0)
 455                                         FD_CLR(s, &readfrom);
 456                                 else
 457                                         killpg(pid, sig);
 458                                 }
 459                                 if (FD_ISSET(pv[0], &ready)) {
 460                                         errno = 0;
 461                                         cc = read(pv[0], buf, sizeof(buf));
 462                                         if (cc <= 0) {
 463                                                 shutdown(s, SHUT_RDWR);
 464                                                 FD_CLR(pv[0], &readfrom);
 465                                         } else {
 466                                                 (void)write(s, buf, cc);
 467                                         }
 468                                 }
 469
 470                         } while (FD_ISSET(s, &readfrom) ||
 471                             FD_ISSET(pv[0], &readfrom));
 472                         PAM_END;
 473                         exit(0);
 474                 }
 475                 (void) close(s);
 476                 (void) close(pv[0]);
 477                 dup2(pv[1], 2);
 478                 close(pv[1]);
 479         }
 480         else {
 481                 pid = fork();
 482                 if (pid == -1)
 483                         rshd_errx(1, "Can't fork; try again.");
 484                 if (pid) {
 485                         /* Parent. */
 486                         while (wait(NULL) > 0 || errno == EINTR)
 487                                 /* nothing */ ;
 488                         PAM_END;
 489                         exit(0);
 490                 }
 491         }
 492
 493 #ifdef USE_BLACKLIST
 494         blacklist(0, STDIN_FILENO, "success");
 495 #endif
 496         closefrom(3);
 497         if (setsid() == -1)
 498                 syslog(LOG_ERR, "setsid() failed: %m");
 499         if (setlogin(pwd->pw_name) < 0)
 500                 syslog(LOG_ERR, "setlogin() failed: %m");
 501
 502         if (*pwd->pw_shell == '\0')
 503                 pwd->pw_shell = bshell;
 504         (void) pam_setenv(pamh, "HOME", pwd->pw_dir, 1);
 505         (void) pam_setenv(pamh, "SHELL", pwd->pw_shell, 1);
 506         (void) pam_setenv(pamh, "USER", pwd->pw_name, 1);
 507         (void) pam_setenv(pamh, "PATH", _PATH_DEFPATH, 1);
 508         environ = pam_getenvlist(pamh);
 509         (void) pam_end(pamh, pam_err);
 510         cp = strrchr(pwd->pw_shell, '/');
 511         if (cp)
 512                 cp++;
 513         else
 514                 cp = pwd->pw_shell;
 515
 516         if (setusercontext(lc, pwd, pwd->pw_uid,
 517                 LOGIN_SETALL & ~LOGIN_SETGROUP) < 0) {
 518                 syslog(LOG_ERR, "setusercontext(): %m");
 519                 exit(1);
 520         }
 521         login_close(lc);
 522         endpwent();
 523         if (log_success || pwd->pw_uid == 0) {
 524                     syslog(LOG_INFO|LOG_AUTH, "%s@%s as %s: cmd='%.80s'",
 525                         ruser, rhost, luser, cmdbuf);
 526         }
 527         execl(pwd->pw_shell, cp, "-c", cmdbuf, (char *)NULL);
 528         err(1, "%s", pwd->pw_shell);
 529         exit(1);
 530 }
 531
 532 /*
 533  * Report error to client.  Note: can't be used until second socket has
 534  * connected to client, or older clients will hang waiting for that
 535  * connection first.
 536  */
 537
 538 static void
 539 rshd_errx(int errcode, const char *fmt, ...)
 540 {
 541         va_list ap;
 542
 543         va_start(ap, fmt);
 544
 545         if (sent_null == 0)
 546                 write(STDERR_FILENO, "\1", 1);
 547
 548         verrx(errcode, fmt, ap);
 549         /* NOTREACHED */
 550 }
 551
 552 void
 553 getstr(char *buf, int cnt, const char *error)
 554 {
 555         char c;
 556
 557         do {
 558                 if (read(STDIN_FILENO, &c, 1) != 1)
 559                         exit(1);
 560                 *buf++ = c;
 561                 if (--cnt == 0) {
 562 #ifdef USE_BLACKLIST
 563                         blacklist(1, STDIN_FILENO, "buffer overflow");
 564 #endif
 565                         rshd_errx(1, "%s too long", error);
 566                 }
 567         } while (c != 0);
 568 }
 569
 570 /*
 571  * Check whether host h is in our local domain,
 572  * defined as sharing the last two components of the domain part,
 573  * or the entire domain part if the local domain has only one component.
 574  * If either name is unqualified (contains no '.'),
 575  * assume that the host is local, as it will be
 576  * interpreted as such.
 577  */
 578 int
 579 local_domain(char *h)
 580 {
 581         char localhost[MAXHOSTNAMELEN];
 582         char *p1, *p2;
 583
 584         localhost[0] = 0;
 585         (void) gethostname(localhost, sizeof(localhost) - 1);
 586         localhost[sizeof(localhost) - 1] = '\0';
 587         /* XXX truncation! */
 588         p1 = topdomain(localhost);
 589         p2 = topdomain(h);
 590         if (p1 == NULL || p2 == NULL || !strcasecmp(p1, p2))
 591                 return (1);
 592         return (0);
 593 }
 594
 595 char *
 596 topdomain(char *h)
 597 {
 598         char *p, *maybe = NULL;
 599         int dots = 0;
 600
 601         for (p = h + strlen(h); p >= h; p--) {
 602                 if (*p == '.') {
 603                         if (++dots == 2)
 604                                 return (p);
 605                         maybe = p;
 606                 }
 607         }
 608         return (maybe);
 609 }
 610
 611 void
 612 usage(void)
 613 {
 614
 615         syslog(LOG_ERR, "usage: rshd [-%s]", OPTIONS);
 616         exit(2);
 617 }