1 /* $OpenBSD: monitor.c,v 1.26 2019/06/28 13:32:53 deraadt Exp $ */ 2 3 /* 4 * Copyright (c) 2004 Moritz Jodeit <moritz@openbsd.org> 5 * 6 * Permission to use, copy, modify, and distribute this software for any 7 * purpose with or without fee is hereby granted, provided that the above 8 * copyright notice and this permission notice appear in all copies. 9 * 10 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 11 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 12 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 13 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 14 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 15 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 16 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 17 */ 18 19 #include <sys/types.h> 20 #include <sys/socket.h> 21 #include <sys/wait.h> 22 #include <netinet/in.h> 23 24 #include <errno.h> 25 #include <fcntl.h> 26 #include <paths.h> 27 #include <pwd.h> 28 #include <signal.h> 29 #include <stdarg.h> 30 #include <stdint.h> 31 #include <stdio.h> 32 #include <stdlib.h> 33 #include <string.h> 34 #include <syslog.h> 35 #include <unistd.h> 36 37 #include "monitor.h" 38 #include "extern.h" 39 40 enum monitor_command { 41 CMD_USER, 42 CMD_PASS, 43 CMD_SOCKET, 44 CMD_BIND 45 }; 46 47 enum monitor_state { 48 PREAUTH, 49 POSTAUTH 50 }; 51 52 extern char remotehost[]; 53 extern char ttyline[20]; 54 extern int debug; 55 56 extern void set_slave_signals(void); 57 58 int fd_monitor = -1; 59 int fd_slave = -1; 60 int nullfd; 61 pid_t slave_pid = -1; 62 enum monitor_state state = PREAUTH; 63 64 void send_data(int, void *, size_t); 65 void recv_data(int, void *, size_t); 66 void handle_cmds(void); 67 void set_monitor_signals(void); 68 void sig_pass_to_slave(int); 69 void sig_chld(int); 70 void fatalx(char *, ...); 71 void debugmsg(char *, ...); 72 73 /* 74 * Send data over a socket and exit if something fails. 75 */ 76 void 77 send_data(int sock, void *buf, size_t len) 78 { 79 ssize_t n; 80 size_t pos = 0; 81 char *ptr = buf; 82 83 while (len > pos) { 84 switch (n = write(sock, ptr + pos, len - pos)) { 85 case 0: 86 kill_slave("write failure"); 87 _exit(0); 88 /* NOTREACHED */ 89 case -1: 90 if (errno != EINTR && errno != EAGAIN) 91 fatalx("send_data: %m"); 92 break; 93 default: 94 pos += n; 95 } 96 } 97 } 98 99 /* 100 * Receive data from socket and exit if something fails. 101 */ 102 void 103 recv_data(int sock, void *buf, size_t len) 104 { 105 ssize_t n; 106 size_t pos = 0; 107 char *ptr = buf; 108 109 while (len > pos) { 110 switch (n = read(sock, ptr + pos, len - pos)) { 111 case 0: 112 kill_slave(NULL); 113 _exit(0); 114 /* NOTREACHED */ 115 case -1: 116 if (errno != EINTR && errno != EAGAIN) 117 fatalx("recv_data: %m"); 118 break; 119 default: 120 pos += n; 121 } 122 } 123 } 124 125 void 126 set_monitor_signals(void) 127 { 128 struct sigaction act; 129 int i; 130 131 sigfillset(&act.sa_mask); 132 act.sa_flags = SA_RESTART; 133 134 act.sa_handler = SIG_DFL; 135 for (i = 1; i < _NSIG; i++) 136 sigaction(i, &act, NULL); 137 138 act.sa_handler = sig_chld; 139 sigaction(SIGCHLD, &act, NULL); 140 141 act.sa_handler = sig_pass_to_slave; 142 sigaction(SIGHUP, &act, NULL); 143 sigaction(SIGINT, &act, NULL); 144 sigaction(SIGQUIT, &act, NULL); 145 sigaction(SIGTERM, &act, NULL); 146 } 147 148 /* 149 * Creates the privileged monitor process. It returns twice. 150 * It returns 1 for the unprivileged slave process and 0 for the 151 * user-privileged slave process after successful authentication. 152 */ 153 int 154 monitor_init(void) 155 { 156 struct passwd *pw; 157 int pair[2]; 158 159 if (socketpair(AF_LOCAL, SOCK_STREAM, PF_UNSPEC, pair) == -1) 160 fatalx("socketpair failed"); 161 162 fd_monitor = pair[0]; 163 fd_slave = pair[1]; 164 165 set_monitor_signals(); 166 167 slave_pid = fork(); 168 if (slave_pid == -1) 169 fatalx("fork of unprivileged slave failed"); 170 if (slave_pid == 0) { 171 /* Unprivileged slave */ 172 set_slave_signals(); 173 174 if ((pw = getpwnam(FTPD_PRIVSEP_USER)) == NULL) 175 fatalx("privilege separation user %s not found", 176 FTPD_PRIVSEP_USER); 177 178 if (chroot(pw->pw_dir) == -1) 179 fatalx("chroot %s: %m", pw->pw_dir); 180 if (chdir("/") == -1) 181 fatalx("chdir /: %m"); 182 183 if (setgroups(1, &pw->pw_gid) == -1) 184 fatalx("setgroups: %m"); 185 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) == -1) 186 fatalx("setresgid failed"); 187 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) == -1) 188 fatalx("setresuid failed"); 189 190 endpwent(); 191 close(fd_slave); 192 return (1); 193 } 194 195 setproctitle("%s: [priv pre-auth]", remotehost); 196 197 handle_cmds(); 198 199 /* User-privileged slave */ 200 return (0); 201 } 202 203 /* 204 * Creates the user-privileged slave process. It is called 205 * from the privileged monitor process and returns twice. It returns 0 206 * for the user-privileged slave process and 1 for the monitor process. 207 */ 208 int 209 monitor_post_auth() 210 { 211 slave_pid = fork(); 212 if (slave_pid == -1) 213 fatalx("fork of user-privileged slave failed"); 214 215 snprintf(ttyline, sizeof(ttyline), "ftp%ld", 216 slave_pid == 0 ? (long)getpid() : (long)slave_pid); 217 218 if (slave_pid == 0) { 219 /* User privileged slave */ 220 close(fd_slave); 221 set_slave_signals(); 222 return (0); 223 } 224 225 /* We have to keep stdout open, because reply() needs it. */ 226 if ((nullfd = open(_PATH_DEVNULL, O_RDWR, 0)) == -1) 227 fatalx("cannot open %s: %m", _PATH_DEVNULL); 228 dup2(nullfd, STDIN_FILENO); 229 dup2(nullfd, STDERR_FILENO); 230 close(nullfd); 231 close(fd_monitor); 232 233 return (1); 234 } 235 236 /* 237 * Handles commands received from the slave process. It will not return 238 * except in one situation: After successful authentication it will 239 * return as the user-privileged slave process. 240 */ 241 void 242 handle_cmds(void) 243 { 244 enum monitor_command cmd; 245 enum auth_ret auth; 246 int err, s, slavequit, serrno, domain; 247 pid_t preauth_slave_pid; 248 size_t len; 249 union sockunion sa; 250 socklen_t salen; 251 char *name, *pw; 252 253 for (;;) { 254 recv_data(fd_slave, &cmd, sizeof(cmd)); 255 256 switch (cmd) { 257 case CMD_USER: 258 debugmsg("CMD_USER received"); 259 260 recv_data(fd_slave, &len, sizeof(len)); 261 if (len == SIZE_MAX) 262 fatalx("monitor received invalid user length"); 263 if ((name = malloc(len + 1)) == NULL) 264 fatalx("malloc: %m"); 265 if (len > 0) 266 recv_data(fd_slave, name, len); 267 name[len] = '\0'; 268 269 user(name); 270 free(name); 271 break; 272 case CMD_PASS: 273 debugmsg("CMD_PASS received"); 274 275 recv_data(fd_slave, &len, sizeof(len)); 276 if (len == SIZE_MAX) 277 fatalx("monitor received invalid pass length"); 278 if ((pw = malloc(len + 1)) == NULL) 279 fatalx("malloc: %m"); 280 if (len > 0) 281 recv_data(fd_slave, pw, len); 282 pw[len] = '\0'; 283 284 preauth_slave_pid = slave_pid; 285 286 auth = pass(pw); 287 freezero(pw, len); 288 289 switch (auth) { 290 case AUTH_FAILED: 291 /* Authentication failure */ 292 debugmsg("authentication failed"); 293 slavequit = 0; 294 send_data(fd_slave, &slavequit, 295 sizeof(slavequit)); 296 break; 297 case AUTH_SLAVE: 298 /* User-privileged slave */ 299 debugmsg("user-privileged slave started"); 300 return; 301 /* NOTREACHED */ 302 case AUTH_MONITOR: 303 /* Post-auth monitor */ 304 debugmsg("monitor went into post-auth phase"); 305 state = POSTAUTH; 306 setproctitle("%s: [priv post-auth]", 307 remotehost); 308 slavequit = 1; 309 310 send_data(fd_slave, &slavequit, 311 sizeof(slavequit)); 312 313 while (waitpid(preauth_slave_pid, NULL, 0) == -1 && 314 errno == EINTR) 315 ; 316 break; 317 default: 318 fatalx("bad return value from pass()"); 319 /* NOTREACHED */ 320 } 321 break; 322 case CMD_SOCKET: 323 debugmsg("CMD_SOCKET received"); 324 325 if (state != POSTAUTH) 326 fatalx("CMD_SOCKET received in invalid state"); 327 328 recv_data(fd_slave, &domain, sizeof(domain)); 329 if (domain != AF_INET && domain != AF_INET6) 330 fatalx("monitor received invalid addr family"); 331 332 s = socket(domain, SOCK_STREAM, 0); 333 serrno = errno; 334 335 send_fd(fd_slave, s); 336 if (s == -1) 337 send_data(fd_slave, &serrno, sizeof(serrno)); 338 else 339 close(s); 340 break; 341 case CMD_BIND: 342 debugmsg("CMD_BIND received"); 343 344 if (state != POSTAUTH) 345 fatalx("CMD_BIND received in invalid state"); 346 347 s = recv_fd(fd_slave); 348 349 recv_data(fd_slave, &salen, sizeof(salen)); 350 if (salen == 0 || salen > sizeof(sa)) 351 fatalx("monitor received invalid sockaddr len"); 352 353 bzero(&sa, sizeof(sa)); 354 recv_data(fd_slave, &sa, salen); 355 356 if (sa.su_si.si_len != salen) 357 fatalx("monitor received invalid sockaddr len"); 358 359 if (sa.su_si.si_family != AF_INET && 360 sa.su_si.si_family != AF_INET6) 361 fatalx("monitor received invalid addr family"); 362 363 err = bind(s, (struct sockaddr *)&sa, salen); 364 serrno = errno; 365 366 if (s >= 0) 367 close(s); 368 369 send_data(fd_slave, &err, sizeof(err)); 370 if (err == -1) 371 send_data(fd_slave, &serrno, sizeof(serrno)); 372 break; 373 default: 374 fatalx("monitor received unknown command %d", cmd); 375 /* NOTREACHED */ 376 } 377 } 378 } 379 380 void 381 sig_pass_to_slave(int signo) 382 { 383 int olderrno = errno; 384 385 if (slave_pid > 0) 386 kill(slave_pid, signo); 387 388 errno = olderrno; 389 } 390 391 /* ARGSUSED */ 392 void 393 sig_chld(int signo) 394 { 395 pid_t pid; 396 int stat, olderrno = errno; 397 398 do { 399 pid = waitpid(slave_pid, &stat, WNOHANG); 400 if (pid > 0) 401 _exit(0); 402 } while (pid == -1 && errno == EINTR); 403 404 errno = olderrno; 405 } 406 407 void 408 kill_slave(char *reason) 409 { 410 if (slave_pid > 0) { 411 if (reason) 412 syslog(LOG_NOTICE, "kill slave %d: %s", 413 slave_pid, reason); 414 kill(slave_pid, SIGQUIT); 415 } 416 } 417 418 void 419 fatalx(char *fmt, ...) 420 { 421 va_list ap; 422 423 va_start(ap, fmt); 424 vsyslog(LOG_ERR, fmt, ap); 425 va_end(ap); 426 427 kill_slave("fatal error"); 428 429 _exit(0); 430 } 431 432 void 433 debugmsg(char *fmt, ...) 434 { 435 va_list ap; 436 437 if (debug) { 438 va_start(ap, fmt); 439 vsyslog(LOG_DEBUG, fmt, ap); 440 va_end(ap); 441 } 442 } 443 444 void 445 monitor_user(char *name) 446 { 447 enum monitor_command cmd; 448 size_t len; 449 450 cmd = CMD_USER; 451 send_data(fd_monitor, &cmd, sizeof(cmd)); 452 453 len = strlen(name); 454 send_data(fd_monitor, &len, sizeof(len)); 455 if (len > 0) 456 send_data(fd_monitor, name, len); 457 } 458 459 int 460 monitor_pass(char *pass) 461 { 462 enum monitor_command cmd; 463 int quitnow; 464 size_t len; 465 466 cmd = CMD_PASS; 467 send_data(fd_monitor, &cmd, sizeof(cmd)); 468 469 len = strlen(pass); 470 send_data(fd_monitor, &len, sizeof(len)); 471 if (len > 0) 472 send_data(fd_monitor, pass, len); 473 474 recv_data(fd_monitor, &quitnow, sizeof(quitnow)); 475 476 return (quitnow); 477 } 478 479 int 480 monitor_socket(int domain) 481 { 482 enum monitor_command cmd; 483 int s, serrno; 484 485 cmd = CMD_SOCKET; 486 send_data(fd_monitor, &cmd, sizeof(cmd)); 487 send_data(fd_monitor, &domain, sizeof(domain)); 488 489 s = recv_fd(fd_monitor); 490 if (s == -1) { 491 recv_data(fd_monitor, &serrno, sizeof(serrno)); 492 errno = serrno; 493 } 494 495 return (s); 496 } 497 498 int 499 monitor_bind(int s, struct sockaddr *name, socklen_t namelen) 500 { 501 enum monitor_command cmd; 502 int ret, serrno; 503 504 cmd = CMD_BIND; 505 send_data(fd_monitor, &cmd, sizeof(cmd)); 506 507 send_fd(fd_monitor, s); 508 send_data(fd_monitor, &namelen, sizeof(namelen)); 509 send_data(fd_monitor, name, namelen); 510 511 recv_data(fd_monitor, &ret, sizeof(ret)); 512 if (ret == -1) { 513 recv_data(fd_monitor, &serrno, sizeof(serrno)); 514 errno = serrno; 515 } 516 517 return (ret); 518 } 519