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1 | /* | |
2 | * Author: Tatu Ylonen <ylo@cs.hut.fi> | |
3 | * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland | |
4 | * All rights reserved | |
5 | * Created: Fri Mar 17 17:09:28 1995 ylo | |
6 | * This program is the ssh daemon. It listens for connections from clients, and | |
7 | * performs authentication, executes use commands or shell, and forwards | |
8 | * information to/from the application to the user client over an encrypted | |
9 | * connection. This can also handle forwarding of X11, TCP/IP, and authentication | |
10 | * agent connections. | |
11 | */ | |
12 | ||
13 | #include "includes.h" | |
14 | RCSID("$OpenBSD: sshd.c,v 1.97 2000/04/04 21:37:27 markus Exp $"); | |
15 | ||
16 | #include "xmalloc.h" | |
17 | #include "rsa.h" | |
18 | #include "ssh.h" | |
19 | #include "pty.h" | |
20 | #include "packet.h" | |
21 | #include "cipher.h" | |
22 | #include "mpaux.h" | |
23 | #include "servconf.h" | |
24 | #include "uidswap.h" | |
25 | #include "compat.h" | |
26 | #include "buffer.h" | |
27 | ||
28 | #ifdef HAVE_OPENSSL | |
29 | # include <openssl/dh.h> | |
30 | # include <openssl/bn.h> | |
31 | # include <openssl/hmac.h> | |
32 | # include <openssl/dsa.h> | |
33 | # include <openssl/rsa.h> | |
34 | #endif | |
35 | #ifdef HAVE_SSL | |
36 | # include <ssl/dh.h> | |
37 | # include <ssl/bn.h> | |
38 | # include <ssl/hmac.h> | |
39 | # include <ssl/dsa.h> | |
40 | # include <ssl/rsa.h> | |
41 | #endif | |
42 | #include "key.h" | |
43 | ||
44 | #include "auth.h" | |
45 | ||
46 | #ifdef LIBWRAP | |
47 | #include <tcpd.h> | |
48 | #include <syslog.h> | |
49 | int allow_severity = LOG_INFO; | |
50 | int deny_severity = LOG_WARNING; | |
51 | #endif /* LIBWRAP */ | |
52 | ||
53 | #ifndef O_NOCTTY | |
54 | #define O_NOCTTY 0 | |
55 | #endif | |
56 | ||
57 | /* Server configuration options. */ | |
58 | ServerOptions options; | |
59 | ||
60 | /* Name of the server configuration file. */ | |
61 | char *config_file_name = SERVER_CONFIG_FILE; | |
62 | ||
63 | /* | |
64 | * Flag indicating whether IPv4 or IPv6. This can be set on the command line. | |
65 | * Default value is AF_UNSPEC means both IPv4 and IPv6. | |
66 | */ | |
67 | #ifdef IPV4_DEFAULT | |
68 | int IPv4or6 = AF_INET; | |
69 | #else | |
70 | int IPv4or6 = AF_UNSPEC; | |
71 | #endif | |
72 | ||
73 | /* | |
74 | * Debug mode flag. This can be set on the command line. If debug | |
75 | * mode is enabled, extra debugging output will be sent to the system | |
76 | * log, the daemon will not go to background, and will exit after processing | |
77 | * the first connection. | |
78 | */ | |
79 | int debug_flag = 0; | |
80 | ||
81 | /* Flag indicating that the daemon is being started from inetd. */ | |
82 | int inetd_flag = 0; | |
83 | ||
84 | /* debug goes to stderr unless inetd_flag is set */ | |
85 | int log_stderr = 0; | |
86 | ||
87 | /* argv[0] without path. */ | |
88 | char *av0; | |
89 | ||
90 | /* Saved arguments to main(). */ | |
91 | char **saved_argv; | |
92 | ||
93 | /* | |
94 | * The sockets that the server is listening; this is used in the SIGHUP | |
95 | * signal handler. | |
96 | */ | |
97 | #define MAX_LISTEN_SOCKS 16 | |
98 | int listen_socks[MAX_LISTEN_SOCKS]; | |
99 | int num_listen_socks = 0; | |
100 | ||
101 | /* | |
102 | * the client's version string, passed by sshd2 in compat mode. if != NULL, | |
103 | * sshd will skip the version-number exchange | |
104 | */ | |
105 | char *client_version_string = NULL; | |
106 | char *server_version_string = NULL; | |
107 | ||
108 | /* | |
109 | * Any really sensitive data in the application is contained in this | |
110 | * structure. The idea is that this structure could be locked into memory so | |
111 | * that the pages do not get written into swap. However, there are some | |
112 | * problems. The private key contains BIGNUMs, and we do not (in principle) | |
113 | * have access to the internals of them, and locking just the structure is | |
114 | * not very useful. Currently, memory locking is not implemented. | |
115 | */ | |
116 | struct { | |
117 | RSA *private_key; /* Private part of server key. */ | |
118 | RSA *host_key; /* Private part of host key. */ | |
119 | } sensitive_data; | |
120 | ||
121 | /* | |
122 | * Flag indicating whether the current session key has been used. This flag | |
123 | * is set whenever the key is used, and cleared when the key is regenerated. | |
124 | */ | |
125 | int key_used = 0; | |
126 | ||
127 | /* This is set to true when SIGHUP is received. */ | |
128 | int received_sighup = 0; | |
129 | ||
130 | /* Public side of the server key. This value is regenerated regularly with | |
131 | the private key. */ | |
132 | RSA *public_key; | |
133 | ||
134 | /* session identifier, used by RSA-auth */ | |
135 | unsigned char session_id[16]; | |
136 | ||
137 | /* Prototypes for various functions defined later in this file. */ | |
138 | void do_ssh1_kex(); | |
139 | ||
140 | /* | |
141 | * Close all listening sockets | |
142 | */ | |
143 | void | |
144 | close_listen_socks(void) | |
145 | { | |
146 | int i; | |
147 | for (i = 0; i < num_listen_socks; i++) | |
148 | close(listen_socks[i]); | |
149 | num_listen_socks = -1; | |
150 | } | |
151 | ||
152 | /* | |
153 | * Signal handler for SIGHUP. Sshd execs itself when it receives SIGHUP; | |
154 | * the effect is to reread the configuration file (and to regenerate | |
155 | * the server key). | |
156 | */ | |
157 | void | |
158 | sighup_handler(int sig) | |
159 | { | |
160 | received_sighup = 1; | |
161 | signal(SIGHUP, sighup_handler); | |
162 | } | |
163 | ||
164 | /* | |
165 | * Called from the main program after receiving SIGHUP. | |
166 | * Restarts the server. | |
167 | */ | |
168 | void | |
169 | sighup_restart() | |
170 | { | |
171 | log("Received SIGHUP; restarting."); | |
172 | close_listen_socks(); | |
173 | execv(saved_argv[0], saved_argv); | |
174 | log("RESTART FAILED: av0='%s', error: %s.", av0, strerror(errno)); | |
175 | exit(1); | |
176 | } | |
177 | ||
178 | /* | |
179 | * Generic signal handler for terminating signals in the master daemon. | |
180 | * These close the listen socket; not closing it seems to cause "Address | |
181 | * already in use" problems on some machines, which is inconvenient. | |
182 | */ | |
183 | void | |
184 | sigterm_handler(int sig) | |
185 | { | |
186 | log("Received signal %d; terminating.", sig); | |
187 | close_listen_socks(); | |
188 | exit(255); | |
189 | } | |
190 | ||
191 | /* | |
192 | * SIGCHLD handler. This is called whenever a child dies. This will then | |
193 | * reap any zombies left by exited c. | |
194 | */ | |
195 | void | |
196 | main_sigchld_handler(int sig) | |
197 | { | |
198 | int save_errno = errno; | |
199 | int status; | |
200 | ||
201 | while (waitpid(-1, &status, WNOHANG) > 0) | |
202 | ; | |
203 | ||
204 | signal(SIGCHLD, main_sigchld_handler); | |
205 | errno = save_errno; | |
206 | } | |
207 | ||
208 | /* | |
209 | * Signal handler for the alarm after the login grace period has expired. | |
210 | */ | |
211 | void | |
212 | grace_alarm_handler(int sig) | |
213 | { | |
214 | /* Close the connection. */ | |
215 | packet_close(); | |
216 | ||
217 | /* Log error and exit. */ | |
218 | fatal("Timeout before authentication for %s.", get_remote_ipaddr()); | |
219 | } | |
220 | ||
221 | /* | |
222 | * Signal handler for the key regeneration alarm. Note that this | |
223 | * alarm only occurs in the daemon waiting for connections, and it does not | |
224 | * do anything with the private key or random state before forking. | |
225 | * Thus there should be no concurrency control/asynchronous execution | |
226 | * problems. | |
227 | */ | |
228 | void | |
229 | key_regeneration_alarm(int sig) | |
230 | { | |
231 | int save_errno = errno; | |
232 | ||
233 | /* Check if we should generate a new key. */ | |
234 | if (key_used) { | |
235 | /* This should really be done in the background. */ | |
236 | log("Generating new %d bit RSA key.", options.server_key_bits); | |
237 | ||
238 | if (sensitive_data.private_key != NULL) | |
239 | RSA_free(sensitive_data.private_key); | |
240 | sensitive_data.private_key = RSA_new(); | |
241 | ||
242 | if (public_key != NULL) | |
243 | RSA_free(public_key); | |
244 | public_key = RSA_new(); | |
245 | ||
246 | rsa_generate_key(sensitive_data.private_key, public_key, | |
247 | options.server_key_bits); | |
248 | arc4random_stir(); | |
249 | key_used = 0; | |
250 | log("RSA key generation complete."); | |
251 | } | |
252 | /* Reschedule the alarm. */ | |
253 | signal(SIGALRM, key_regeneration_alarm); | |
254 | alarm(options.key_regeneration_time); | |
255 | errno = save_errno; | |
256 | } | |
257 | ||
258 | void | |
259 | sshd_exchange_identification(int sock_in, int sock_out) | |
260 | { | |
261 | int i; | |
262 | int remote_major, remote_minor; | |
263 | char *s; | |
264 | char buf[256]; /* Must not be larger than remote_version. */ | |
265 | char remote_version[256]; /* Must be at least as big as buf. */ | |
266 | ||
267 | snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n", | |
268 | PROTOCOL_MAJOR, PROTOCOL_MINOR, SSH_VERSION); | |
269 | server_version_string = xstrdup(buf); | |
270 | ||
271 | if (client_version_string == NULL) { | |
272 | /* Send our protocol version identification. */ | |
273 | if (atomicio(write, sock_out, server_version_string, strlen(server_version_string)) | |
274 | != strlen(server_version_string)) { | |
275 | log("Could not write ident string to %s.", get_remote_ipaddr()); | |
276 | fatal_cleanup(); | |
277 | } | |
278 | ||
279 | /* Read other side\'s version identification. */ | |
280 | for (i = 0; i < sizeof(buf) - 1; i++) { | |
281 | if (read(sock_in, &buf[i], 1) != 1) { | |
282 | log("Did not receive ident string from %s.", get_remote_ipaddr()); | |
283 | fatal_cleanup(); | |
284 | } | |
285 | if (buf[i] == '\r') { | |
286 | buf[i] = '\n'; | |
287 | buf[i + 1] = 0; | |
288 | continue; | |
289 | /*break; XXX eat \r */ | |
290 | } | |
291 | if (buf[i] == '\n') { | |
292 | /* buf[i] == '\n' */ | |
293 | buf[i + 1] = 0; | |
294 | break; | |
295 | } | |
296 | } | |
297 | buf[sizeof(buf) - 1] = 0; | |
298 | client_version_string = xstrdup(buf); | |
299 | } | |
300 | ||
301 | /* | |
302 | * Check that the versions match. In future this might accept | |
303 | * several versions and set appropriate flags to handle them. | |
304 | */ | |
305 | if (sscanf(client_version_string, "SSH-%d.%d-%[^\n]\n", | |
306 | &remote_major, &remote_minor, remote_version) != 3) { | |
307 | s = "Protocol mismatch.\n"; | |
308 | (void) atomicio(write, sock_out, s, strlen(s)); | |
309 | close(sock_in); | |
310 | close(sock_out); | |
311 | log("Bad protocol version identification '%.100s' from %s", | |
312 | client_version_string, get_remote_ipaddr()); | |
313 | fatal_cleanup(); | |
314 | } | |
315 | debug("Client protocol version %d.%d; client software version %.100s", | |
316 | remote_major, remote_minor, remote_version); | |
317 | ||
318 | switch(remote_major) { | |
319 | case 1: | |
320 | if (remote_minor < 3) { | |
321 | packet_disconnect("Your ssh version is too old and" | |
322 | "is no longer supported. Please install a newer version."); | |
323 | } else if (remote_minor == 3) { | |
324 | /* note that this disables agent-forwarding */ | |
325 | enable_compat13(); | |
326 | } | |
327 | break; | |
328 | default: | |
329 | s = "Protocol major versions differ.\n"; | |
330 | (void) atomicio(write, sock_out, s, strlen(s)); | |
331 | close(sock_in); | |
332 | close(sock_out); | |
333 | log("Protocol major versions differ for %s: %d vs. %d", | |
334 | get_remote_ipaddr(), PROTOCOL_MAJOR, remote_major); | |
335 | fatal_cleanup(); | |
336 | break; | |
337 | } | |
338 | } | |
339 | ||
340 | /* | |
341 | * Main program for the daemon. | |
342 | */ | |
343 | int | |
344 | main(int ac, char **av) | |
345 | { | |
346 | extern char *optarg; | |
347 | extern int optind; | |
348 | int opt, sock_in = 0, sock_out = 0, newsock, i, fdsetsz, pid, on = 1; | |
349 | socklen_t fromlen; | |
350 | int silentrsa = 0; | |
351 | fd_set *fdset; | |
352 | struct sockaddr_storage from; | |
353 | const char *remote_ip; | |
354 | int remote_port; | |
355 | char *comment; | |
356 | FILE *f; | |
357 | struct linger linger; | |
358 | struct addrinfo *ai; | |
359 | char ntop[NI_MAXHOST], strport[NI_MAXSERV]; | |
360 | int listen_sock, maxfd; | |
361 | ||
362 | /* Save argv[0]. */ | |
363 | saved_argv = av; | |
364 | if (strchr(av[0], '/')) | |
365 | av0 = strrchr(av[0], '/') + 1; | |
366 | else | |
367 | av0 = av[0]; | |
368 | ||
369 | /* Initialize configuration options to their default values. */ | |
370 | initialize_server_options(&options); | |
371 | ||
372 | /* Parse command-line arguments. */ | |
373 | while ((opt = getopt(ac, av, "f:p:b:k:h:g:V:diqQ46")) != EOF) { | |
374 | switch (opt) { | |
375 | case '4': | |
376 | IPv4or6 = AF_INET; | |
377 | break; | |
378 | case '6': | |
379 | IPv4or6 = AF_INET6; | |
380 | break; | |
381 | case 'f': | |
382 | config_file_name = optarg; | |
383 | break; | |
384 | case 'd': | |
385 | debug_flag = 1; | |
386 | options.log_level = SYSLOG_LEVEL_DEBUG; | |
387 | break; | |
388 | case 'i': | |
389 | inetd_flag = 1; | |
390 | break; | |
391 | case 'Q': | |
392 | silentrsa = 1; | |
393 | break; | |
394 | case 'q': | |
395 | options.log_level = SYSLOG_LEVEL_QUIET; | |
396 | break; | |
397 | case 'b': | |
398 | options.server_key_bits = atoi(optarg); | |
399 | break; | |
400 | case 'p': | |
401 | options.ports_from_cmdline = 1; | |
402 | if (options.num_ports >= MAX_PORTS) | |
403 | fatal("too many ports.\n"); | |
404 | options.ports[options.num_ports++] = atoi(optarg); | |
405 | break; | |
406 | case 'g': | |
407 | options.login_grace_time = atoi(optarg); | |
408 | break; | |
409 | case 'k': | |
410 | options.key_regeneration_time = atoi(optarg); | |
411 | break; | |
412 | case 'h': | |
413 | options.host_key_file = optarg; | |
414 | break; | |
415 | case 'V': | |
416 | client_version_string = optarg; | |
417 | /* only makes sense with inetd_flag, i.e. no listen() */ | |
418 | inetd_flag = 1; | |
419 | break; | |
420 | case '?': | |
421 | default: | |
422 | fprintf(stderr, "sshd version %s\n", SSH_VERSION); | |
423 | fprintf(stderr, "Usage: %s [options]\n", av0); | |
424 | fprintf(stderr, "Options:\n"); | |
425 | fprintf(stderr, " -f file Configuration file (default %s)\n", SERVER_CONFIG_FILE); | |
426 | fprintf(stderr, " -d Debugging mode\n"); | |
427 | fprintf(stderr, " -i Started from inetd\n"); | |
428 | fprintf(stderr, " -q Quiet (no logging)\n"); | |
429 | fprintf(stderr, " -p port Listen on the specified port (default: 22)\n"); | |
430 | fprintf(stderr, " -k seconds Regenerate server key every this many seconds (default: 3600)\n"); | |
431 | fprintf(stderr, " -g seconds Grace period for authentication (default: 300)\n"); | |
432 | fprintf(stderr, " -b bits Size of server RSA key (default: 768 bits)\n"); | |
433 | fprintf(stderr, " -h file File from which to read host key (default: %s)\n", | |
434 | HOST_KEY_FILE); | |
435 | fprintf(stderr, " -4 Use IPv4 only\n"); | |
436 | fprintf(stderr, " -6 Use IPv6 only\n"); | |
437 | exit(1); | |
438 | } | |
439 | } | |
440 | ||
441 | /* | |
442 | * Force logging to stderr until we have loaded the private host | |
443 | * key (unless started from inetd) | |
444 | */ | |
445 | log_init(av0, | |
446 | options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level, | |
447 | options.log_facility == -1 ? SYSLOG_FACILITY_AUTH : options.log_facility, | |
448 | !inetd_flag); | |
449 | ||
450 | /* check if RSA support exists */ | |
451 | if (rsa_alive() == 0) { | |
452 | if (silentrsa == 0) | |
453 | printf("sshd: no RSA support in libssl and libcrypto -- exiting. See ssl(8)\n"); | |
454 | log("no RSA support in libssl and libcrypto -- exiting. See ssl(8)"); | |
455 | exit(1); | |
456 | } | |
457 | /* Read server configuration options from the configuration file. */ | |
458 | read_server_config(&options, config_file_name); | |
459 | ||
460 | /* Fill in default values for those options not explicitly set. */ | |
461 | fill_default_server_options(&options); | |
462 | ||
463 | /* Check certain values for sanity. */ | |
464 | if (options.server_key_bits < 512 || | |
465 | options.server_key_bits > 32768) { | |
466 | fprintf(stderr, "Bad server key size.\n"); | |
467 | exit(1); | |
468 | } | |
469 | /* Check that there are no remaining arguments. */ | |
470 | if (optind < ac) { | |
471 | fprintf(stderr, "Extra argument %s.\n", av[optind]); | |
472 | exit(1); | |
473 | } | |
474 | ||
475 | debug("sshd version %.100s", SSH_VERSION); | |
476 | ||
477 | sensitive_data.host_key = RSA_new(); | |
478 | errno = 0; | |
479 | /* Load the host key. It must have empty passphrase. */ | |
480 | if (!load_private_key(options.host_key_file, "", | |
481 | sensitive_data.host_key, &comment)) { | |
482 | error("Could not load host key: %.200s: %.100s", | |
483 | options.host_key_file, strerror(errno)); | |
484 | exit(1); | |
485 | } | |
486 | xfree(comment); | |
487 | ||
488 | /* Initialize the log (it is reinitialized below in case we | |
489 | forked). */ | |
490 | if (debug_flag && !inetd_flag) | |
491 | log_stderr = 1; | |
492 | log_init(av0, options.log_level, options.log_facility, log_stderr); | |
493 | ||
494 | /* If not in debugging mode, and not started from inetd, | |
495 | disconnect from the controlling terminal, and fork. The | |
496 | original process exits. */ | |
497 | if (!debug_flag && !inetd_flag) { | |
498 | #ifdef TIOCNOTTY | |
499 | int fd; | |
500 | #endif /* TIOCNOTTY */ | |
501 | if (daemon(0, 0) < 0) | |
502 | fatal("daemon() failed: %.200s", strerror(errno)); | |
503 | ||
504 | /* Disconnect from the controlling tty. */ | |
505 | #ifdef TIOCNOTTY | |
506 | fd = open("/dev/tty", O_RDWR | O_NOCTTY); | |
507 | if (fd >= 0) { | |
508 | (void) ioctl(fd, TIOCNOTTY, NULL); | |
509 | close(fd); | |
510 | } | |
511 | #endif /* TIOCNOTTY */ | |
512 | } | |
513 | /* Reinitialize the log (because of the fork above). */ | |
514 | log_init(av0, options.log_level, options.log_facility, log_stderr); | |
515 | ||
516 | /* Check that server and host key lengths differ sufficiently. | |
517 | This is necessary to make double encryption work with rsaref. | |
518 | Oh, I hate software patents. I dont know if this can go? Niels */ | |
519 | if (options.server_key_bits > | |
520 | BN_num_bits(sensitive_data.host_key->n) - SSH_KEY_BITS_RESERVED && | |
521 | options.server_key_bits < | |
522 | BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) { | |
523 | options.server_key_bits = | |
524 | BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED; | |
525 | debug("Forcing server key to %d bits to make it differ from host key.", | |
526 | options.server_key_bits); | |
527 | } | |
528 | /* Do not display messages to stdout in RSA code. */ | |
529 | rsa_set_verbose(0); | |
530 | ||
531 | /* Initialize the random number generator. */ | |
532 | arc4random_stir(); | |
533 | ||
534 | /* Chdir to the root directory so that the current disk can be | |
535 | unmounted if desired. */ | |
536 | chdir("/"); | |
537 | ||
538 | /* Start listening for a socket, unless started from inetd. */ | |
539 | if (inetd_flag) { | |
540 | int s1, s2; | |
541 | s1 = dup(0); /* Make sure descriptors 0, 1, and 2 are in use. */ | |
542 | s2 = dup(s1); | |
543 | sock_in = dup(0); | |
544 | sock_out = dup(1); | |
545 | /* We intentionally do not close the descriptors 0, 1, and 2 | |
546 | as our code for setting the descriptors won\'t work | |
547 | if ttyfd happens to be one of those. */ | |
548 | debug("inetd sockets after dupping: %d, %d", sock_in, sock_out); | |
549 | ||
550 | public_key = RSA_new(); | |
551 | sensitive_data.private_key = RSA_new(); | |
552 | ||
553 | log("Generating %d bit RSA key.", options.server_key_bits); | |
554 | rsa_generate_key(sensitive_data.private_key, public_key, | |
555 | options.server_key_bits); | |
556 | arc4random_stir(); | |
557 | log("RSA key generation complete."); | |
558 | } else { | |
559 | for (ai = options.listen_addrs; ai; ai = ai->ai_next) { | |
560 | if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6) | |
561 | continue; | |
562 | if (num_listen_socks >= MAX_LISTEN_SOCKS) | |
563 | fatal("Too many listen sockets. " | |
564 | "Enlarge MAX_LISTEN_SOCKS"); | |
565 | if (getnameinfo(ai->ai_addr, ai->ai_addrlen, | |
566 | ntop, sizeof(ntop), strport, sizeof(strport), | |
567 | NI_NUMERICHOST|NI_NUMERICSERV) != 0) { | |
568 | error("getnameinfo failed"); | |
569 | continue; | |
570 | } | |
571 | /* Create socket for listening. */ | |
572 | listen_sock = socket(ai->ai_family, SOCK_STREAM, 0); | |
573 | if (listen_sock < 0) { | |
574 | /* kernel may not support ipv6 */ | |
575 | verbose("socket: %.100s", strerror(errno)); | |
576 | continue; | |
577 | } | |
578 | if (fcntl(listen_sock, F_SETFL, O_NONBLOCK) < 0) { | |
579 | error("listen_sock O_NONBLOCK: %s", strerror(errno)); | |
580 | close(listen_sock); | |
581 | continue; | |
582 | } | |
583 | /* | |
584 | * Set socket options. We try to make the port | |
585 | * reusable and have it close as fast as possible | |
586 | * without waiting in unnecessary wait states on | |
587 | * close. | |
588 | */ | |
589 | setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR, | |
590 | (void *) &on, sizeof(on)); | |
591 | linger.l_onoff = 1; | |
592 | linger.l_linger = 5; | |
593 | setsockopt(listen_sock, SOL_SOCKET, SO_LINGER, | |
594 | (void *) &linger, sizeof(linger)); | |
595 | ||
596 | debug("Bind to port %s on %s.", strport, ntop); | |
597 | ||
598 | /* Bind the socket to the desired port. */ | |
599 | if ((bind(listen_sock, ai->ai_addr, ai->ai_addrlen) < 0) && | |
600 | (!ai->ai_next)) { | |
601 | error("Bind to port %s on %s failed: %.200s.", | |
602 | strport, ntop, strerror(errno)); | |
603 | close(listen_sock); | |
604 | continue; | |
605 | } | |
606 | listen_socks[num_listen_socks] = listen_sock; | |
607 | num_listen_socks++; | |
608 | ||
609 | /* Start listening on the port. */ | |
610 | log("Server listening on %s port %s.", ntop, strport); | |
611 | if (listen(listen_sock, 5) < 0) | |
612 | fatal("listen: %.100s", strerror(errno)); | |
613 | ||
614 | } | |
615 | freeaddrinfo(options.listen_addrs); | |
616 | ||
617 | if (!num_listen_socks) | |
618 | fatal("Cannot bind any address."); | |
619 | ||
620 | if (!debug_flag) { | |
621 | /* | |
622 | * Record our pid in /etc/sshd_pid to make it easier | |
623 | * to kill the correct sshd. We don\'t want to do | |
624 | * this before the bind above because the bind will | |
625 | * fail if there already is a daemon, and this will | |
626 | * overwrite any old pid in the file. | |
627 | */ | |
628 | f = fopen(SSH_DAEMON_PID_FILE, "w"); | |
629 | if (f) { | |
630 | fprintf(f, "%u\n", (unsigned int) getpid()); | |
631 | fclose(f); | |
632 | } | |
633 | } | |
634 | ||
635 | public_key = RSA_new(); | |
636 | sensitive_data.private_key = RSA_new(); | |
637 | ||
638 | log("Generating %d bit RSA key.", options.server_key_bits); | |
639 | rsa_generate_key(sensitive_data.private_key, public_key, | |
640 | options.server_key_bits); | |
641 | arc4random_stir(); | |
642 | log("RSA key generation complete."); | |
643 | ||
644 | /* Schedule server key regeneration alarm. */ | |
645 | signal(SIGALRM, key_regeneration_alarm); | |
646 | alarm(options.key_regeneration_time); | |
647 | ||
648 | /* Arrange to restart on SIGHUP. The handler needs listen_sock. */ | |
649 | signal(SIGHUP, sighup_handler); | |
650 | signal(SIGTERM, sigterm_handler); | |
651 | signal(SIGQUIT, sigterm_handler); | |
652 | ||
653 | /* Arrange SIGCHLD to be caught. */ | |
654 | signal(SIGCHLD, main_sigchld_handler); | |
655 | ||
656 | /* setup fd set for listen */ | |
657 | maxfd = 0; | |
658 | for (i = 0; i < num_listen_socks; i++) | |
659 | if (listen_socks[i] > maxfd) | |
660 | maxfd = listen_socks[i]; | |
661 | fdsetsz = howmany(maxfd, NFDBITS) * sizeof(fd_mask); | |
662 | fdset = (fd_set *)xmalloc(fdsetsz); | |
663 | ||
664 | /* | |
665 | * Stay listening for connections until the system crashes or | |
666 | * the daemon is killed with a signal. | |
667 | */ | |
668 | for (;;) { | |
669 | if (received_sighup) | |
670 | sighup_restart(); | |
671 | /* Wait in select until there is a connection. */ | |
672 | memset(fdset, 0, fdsetsz); | |
673 | for (i = 0; i < num_listen_socks; i++) | |
674 | FD_SET(listen_socks[i], fdset); | |
675 | if (select(maxfd + 1, fdset, NULL, NULL, NULL) < 0) { | |
676 | if (errno != EINTR) | |
677 | error("select: %.100s", strerror(errno)); | |
678 | continue; | |
679 | } | |
680 | for (i = 0; i < num_listen_socks; i++) { | |
681 | if (!FD_ISSET(listen_socks[i], fdset)) | |
682 | continue; | |
683 | fromlen = sizeof(from); | |
684 | newsock = accept(listen_socks[i], (struct sockaddr *)&from, | |
685 | &fromlen); | |
686 | if (newsock < 0) { | |
687 | if (errno != EINTR && errno != EWOULDBLOCK) | |
688 | error("accept: %.100s", strerror(errno)); | |
689 | continue; | |
690 | } | |
691 | if (fcntl(newsock, F_SETFL, 0) < 0) { | |
692 | error("newsock del O_NONBLOCK: %s", strerror(errno)); | |
693 | continue; | |
694 | } | |
695 | /* | |
696 | * Got connection. Fork a child to handle it, unless | |
697 | * we are in debugging mode. | |
698 | */ | |
699 | if (debug_flag) { | |
700 | /* | |
701 | * In debugging mode. Close the listening | |
702 | * socket, and start processing the | |
703 | * connection without forking. | |
704 | */ | |
705 | debug("Server will not fork when running in debugging mode."); | |
706 | close_listen_socks(); | |
707 | sock_in = newsock; | |
708 | sock_out = newsock; | |
709 | pid = getpid(); | |
710 | break; | |
711 | } else { | |
712 | /* | |
713 | * Normal production daemon. Fork, and have | |
714 | * the child process the connection. The | |
715 | * parent continues listening. | |
716 | */ | |
717 | if ((pid = fork()) == 0) { | |
718 | /* | |
719 | * Child. Close the listening socket, and start using the | |
720 | * accepted socket. Reinitialize logging (since our pid has | |
721 | * changed). We break out of the loop to handle the connection. | |
722 | */ | |
723 | close_listen_socks(); | |
724 | sock_in = newsock; | |
725 | sock_out = newsock; | |
726 | log_init(av0, options.log_level, options.log_facility, log_stderr); | |
727 | break; | |
728 | } | |
729 | } | |
730 | ||
731 | /* Parent. Stay in the loop. */ | |
732 | if (pid < 0) | |
733 | error("fork: %.100s", strerror(errno)); | |
734 | else | |
735 | debug("Forked child %d.", pid); | |
736 | ||
737 | /* Mark that the key has been used (it was "given" to the child). */ | |
738 | key_used = 1; | |
739 | ||
740 | arc4random_stir(); | |
741 | ||
742 | /* Close the new socket (the child is now taking care of it). */ | |
743 | close(newsock); | |
744 | } /* for (i = 0; i < num_listen_socks; i++) */ | |
745 | /* child process check (or debug mode) */ | |
746 | if (num_listen_socks < 0) | |
747 | break; | |
748 | } | |
749 | } | |
750 | ||
751 | /* This is the child processing a new connection. */ | |
752 | ||
753 | /* | |
754 | * Disable the key regeneration alarm. We will not regenerate the | |
755 | * key since we are no longer in a position to give it to anyone. We | |
756 | * will not restart on SIGHUP since it no longer makes sense. | |
757 | */ | |
758 | alarm(0); | |
759 | signal(SIGALRM, SIG_DFL); | |
760 | signal(SIGHUP, SIG_DFL); | |
761 | signal(SIGTERM, SIG_DFL); | |
762 | signal(SIGQUIT, SIG_DFL); | |
763 | signal(SIGCHLD, SIG_DFL); | |
764 | ||
765 | /* | |
766 | * Set socket options for the connection. We want the socket to | |
767 | * close as fast as possible without waiting for anything. If the | |
768 | * connection is not a socket, these will do nothing. | |
769 | */ | |
770 | /* setsockopt(sock_in, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */ | |
771 | linger.l_onoff = 1; | |
772 | linger.l_linger = 5; | |
773 | setsockopt(sock_in, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger)); | |
774 | ||
775 | /* | |
776 | * Register our connection. This turns encryption off because we do | |
777 | * not have a key. | |
778 | */ | |
779 | packet_set_connection(sock_in, sock_out); | |
780 | ||
781 | remote_port = get_remote_port(); | |
782 | remote_ip = get_remote_ipaddr(); | |
783 | ||
784 | /* Check whether logins are denied from this host. */ | |
785 | #ifdef LIBWRAP | |
786 | /* XXX LIBWRAP noes not know about IPv6 */ | |
787 | { | |
788 | struct request_info req; | |
789 | ||
790 | request_init(&req, RQ_DAEMON, av0, RQ_FILE, sock_in, NULL); | |
791 | fromhost(&req); | |
792 | ||
793 | if (!hosts_access(&req)) { | |
794 | close(sock_in); | |
795 | close(sock_out); | |
796 | refuse(&req); | |
797 | } | |
798 | /*XXX IPv6 verbose("Connection from %.500s port %d", eval_client(&req), remote_port); */ | |
799 | } | |
800 | #endif /* LIBWRAP */ | |
801 | /* Log the connection. */ | |
802 | verbose("Connection from %.500s port %d", remote_ip, remote_port); | |
803 | ||
804 | /* | |
805 | * We don\'t want to listen forever unless the other side | |
806 | * successfully authenticates itself. So we set up an alarm which is | |
807 | * cleared after successful authentication. A limit of zero | |
808 | * indicates no limit. Note that we don\'t set the alarm in debugging | |
809 | * mode; it is just annoying to have the server exit just when you | |
810 | * are about to discover the bug. | |
811 | */ | |
812 | signal(SIGALRM, grace_alarm_handler); | |
813 | if (!debug_flag) | |
814 | alarm(options.login_grace_time); | |
815 | ||
816 | sshd_exchange_identification(sock_in, sock_out); | |
817 | /* | |
818 | * Check that the connection comes from a privileged port. Rhosts- | |
819 | * and Rhosts-RSA-Authentication only make sense from priviledged | |
820 | * programs. Of course, if the intruder has root access on his local | |
821 | * machine, he can connect from any port. So do not use these | |
822 | * authentication methods from machines that you do not trust. | |
823 | */ | |
824 | if (remote_port >= IPPORT_RESERVED || | |
825 | remote_port < IPPORT_RESERVED / 2) { | |
826 | options.rhosts_authentication = 0; | |
827 | options.rhosts_rsa_authentication = 0; | |
828 | } | |
829 | #ifdef KRB4 | |
830 | if (!packet_connection_is_ipv4() && | |
831 | options.kerberos_authentication) { | |
832 | debug("Kerberos Authentication disabled, only available for IPv4."); | |
833 | options.kerberos_authentication = 0; | |
834 | } | |
835 | #endif /* KRB4 */ | |
836 | ||
837 | packet_set_nonblocking(); | |
838 | ||
839 | /* perform the key exchange */ | |
840 | do_ssh1_kex(); | |
841 | /* authenticate user and start session */ | |
842 | do_authentication(); | |
843 | ||
844 | #ifdef KRB4 | |
845 | /* Cleanup user's ticket cache file. */ | |
846 | if (options.kerberos_ticket_cleanup) | |
847 | (void) dest_tkt(); | |
848 | #endif /* KRB4 */ | |
849 | ||
850 | /* The connection has been terminated. */ | |
851 | verbose("Closing connection to %.100s", remote_ip); | |
852 | ||
853 | #ifdef USE_PAM | |
854 | finish_pam(); | |
855 | #endif /* USE_PAM */ | |
856 | ||
857 | packet_close(); | |
858 | exit(0); | |
859 | } | |
860 | ||
861 | /* | |
862 | * SSH1 key exchange | |
863 | */ | |
864 | void | |
865 | do_ssh1_kex() | |
866 | { | |
867 | int i, len; | |
868 | int plen, slen; | |
869 | BIGNUM *session_key_int; | |
870 | unsigned char session_key[SSH_SESSION_KEY_LENGTH]; | |
871 | unsigned char cookie[8]; | |
872 | unsigned int cipher_type, auth_mask, protocol_flags; | |
873 | u_int32_t rand = 0; | |
874 | ||
875 | /* | |
876 | * Generate check bytes that the client must send back in the user | |
877 | * packet in order for it to be accepted; this is used to defy ip | |
878 | * spoofing attacks. Note that this only works against somebody | |
879 | * doing IP spoofing from a remote machine; any machine on the local | |
880 | * network can still see outgoing packets and catch the random | |
881 | * cookie. This only affects rhosts authentication, and this is one | |
882 | * of the reasons why it is inherently insecure. | |
883 | */ | |
884 | for (i = 0; i < 8; i++) { | |
885 | if (i % 4 == 0) | |
886 | rand = arc4random(); | |
887 | cookie[i] = rand & 0xff; | |
888 | rand >>= 8; | |
889 | } | |
890 | ||
891 | /* | |
892 | * Send our public key. We include in the packet 64 bits of random | |
893 | * data that must be matched in the reply in order to prevent IP | |
894 | * spoofing. | |
895 | */ | |
896 | packet_start(SSH_SMSG_PUBLIC_KEY); | |
897 | for (i = 0; i < 8; i++) | |
898 | packet_put_char(cookie[i]); | |
899 | ||
900 | /* Store our public server RSA key. */ | |
901 | packet_put_int(BN_num_bits(public_key->n)); | |
902 | packet_put_bignum(public_key->e); | |
903 | packet_put_bignum(public_key->n); | |
904 | ||
905 | /* Store our public host RSA key. */ | |
906 | packet_put_int(BN_num_bits(sensitive_data.host_key->n)); | |
907 | packet_put_bignum(sensitive_data.host_key->e); | |
908 | packet_put_bignum(sensitive_data.host_key->n); | |
909 | ||
910 | /* Put protocol flags. */ | |
911 | packet_put_int(SSH_PROTOFLAG_HOST_IN_FWD_OPEN); | |
912 | ||
913 | /* Declare which ciphers we support. */ | |
914 | packet_put_int(cipher_mask1()); | |
915 | ||
916 | /* Declare supported authentication types. */ | |
917 | auth_mask = 0; | |
918 | if (options.rhosts_authentication) | |
919 | auth_mask |= 1 << SSH_AUTH_RHOSTS; | |
920 | if (options.rhosts_rsa_authentication) | |
921 | auth_mask |= 1 << SSH_AUTH_RHOSTS_RSA; | |
922 | if (options.rsa_authentication) | |
923 | auth_mask |= 1 << SSH_AUTH_RSA; | |
924 | #ifdef KRB4 | |
925 | if (options.kerberos_authentication) | |
926 | auth_mask |= 1 << SSH_AUTH_KERBEROS; | |
927 | #endif | |
928 | #ifdef AFS | |
929 | if (options.kerberos_tgt_passing) | |
930 | auth_mask |= 1 << SSH_PASS_KERBEROS_TGT; | |
931 | if (options.afs_token_passing) | |
932 | auth_mask |= 1 << SSH_PASS_AFS_TOKEN; | |
933 | #endif | |
934 | #ifdef SKEY | |
935 | if (options.skey_authentication == 1) | |
936 | auth_mask |= 1 << SSH_AUTH_TIS; | |
937 | #endif | |
938 | if (options.password_authentication) | |
939 | auth_mask |= 1 << SSH_AUTH_PASSWORD; | |
940 | packet_put_int(auth_mask); | |
941 | ||
942 | /* Send the packet and wait for it to be sent. */ | |
943 | packet_send(); | |
944 | packet_write_wait(); | |
945 | ||
946 | debug("Sent %d bit public key and %d bit host key.", | |
947 | BN_num_bits(public_key->n), BN_num_bits(sensitive_data.host_key->n)); | |
948 | ||
949 | /* Read clients reply (cipher type and session key). */ | |
950 | packet_read_expect(&plen, SSH_CMSG_SESSION_KEY); | |
951 | ||
952 | /* Get cipher type and check whether we accept this. */ | |
953 | cipher_type = packet_get_char(); | |
954 | ||
955 | if (!(cipher_mask() & (1 << cipher_type))) | |
956 | packet_disconnect("Warning: client selects unsupported cipher."); | |
957 | ||
958 | /* Get check bytes from the packet. These must match those we | |
959 | sent earlier with the public key packet. */ | |
960 | for (i = 0; i < 8; i++) | |
961 | if (cookie[i] != packet_get_char()) | |
962 | packet_disconnect("IP Spoofing check bytes do not match."); | |
963 | ||
964 | debug("Encryption type: %.200s", cipher_name(cipher_type)); | |
965 | ||
966 | /* Get the encrypted integer. */ | |
967 | session_key_int = BN_new(); | |
968 | packet_get_bignum(session_key_int, &slen); | |
969 | ||
970 | protocol_flags = packet_get_int(); | |
971 | packet_set_protocol_flags(protocol_flags); | |
972 | ||
973 | packet_integrity_check(plen, 1 + 8 + slen + 4, SSH_CMSG_SESSION_KEY); | |
974 | ||
975 | /* | |
976 | * Decrypt it using our private server key and private host key (key | |
977 | * with larger modulus first). | |
978 | */ | |
979 | if (BN_cmp(sensitive_data.private_key->n, sensitive_data.host_key->n) > 0) { | |
980 | /* Private key has bigger modulus. */ | |
981 | if (BN_num_bits(sensitive_data.private_key->n) < | |
982 | BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) { | |
983 | fatal("do_connection: %s: private_key %d < host_key %d + SSH_KEY_BITS_RESERVED %d", | |
984 | get_remote_ipaddr(), | |
985 | BN_num_bits(sensitive_data.private_key->n), | |
986 | BN_num_bits(sensitive_data.host_key->n), | |
987 | SSH_KEY_BITS_RESERVED); | |
988 | } | |
989 | rsa_private_decrypt(session_key_int, session_key_int, | |
990 | sensitive_data.private_key); | |
991 | rsa_private_decrypt(session_key_int, session_key_int, | |
992 | sensitive_data.host_key); | |
993 | } else { | |
994 | /* Host key has bigger modulus (or they are equal). */ | |
995 | if (BN_num_bits(sensitive_data.host_key->n) < | |
996 | BN_num_bits(sensitive_data.private_key->n) + SSH_KEY_BITS_RESERVED) { | |
997 | fatal("do_connection: %s: host_key %d < private_key %d + SSH_KEY_BITS_RESERVED %d", | |
998 | get_remote_ipaddr(), | |
999 | BN_num_bits(sensitive_data.host_key->n), | |
1000 | BN_num_bits(sensitive_data.private_key->n), | |
1001 | SSH_KEY_BITS_RESERVED); | |
1002 | } | |
1003 | rsa_private_decrypt(session_key_int, session_key_int, | |
1004 | sensitive_data.host_key); | |
1005 | rsa_private_decrypt(session_key_int, session_key_int, | |
1006 | sensitive_data.private_key); | |
1007 | } | |
1008 | ||
1009 | compute_session_id(session_id, cookie, | |
1010 | sensitive_data.host_key->n, | |
1011 | sensitive_data.private_key->n); | |
1012 | ||
1013 | /* Destroy the private and public keys. They will no longer be needed. */ | |
1014 | RSA_free(public_key); | |
1015 | RSA_free(sensitive_data.private_key); | |
1016 | RSA_free(sensitive_data.host_key); | |
1017 | ||
1018 | /* | |
1019 | * Extract session key from the decrypted integer. The key is in the | |
1020 | * least significant 256 bits of the integer; the first byte of the | |
1021 | * key is in the highest bits. | |
1022 | */ | |
1023 | BN_mask_bits(session_key_int, sizeof(session_key) * 8); | |
1024 | len = BN_num_bytes(session_key_int); | |
1025 | if (len < 0 || len > sizeof(session_key)) | |
1026 | fatal("do_connection: bad len from %s: session_key_int %d > sizeof(session_key) %d", | |
1027 | get_remote_ipaddr(), | |
1028 | len, sizeof(session_key)); | |
1029 | memset(session_key, 0, sizeof(session_key)); | |
1030 | BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len); | |
1031 | ||
1032 | /* Destroy the decrypted integer. It is no longer needed. */ | |
1033 | BN_clear_free(session_key_int); | |
1034 | ||
1035 | /* Xor the first 16 bytes of the session key with the session id. */ | |
1036 | for (i = 0; i < 16; i++) | |
1037 | session_key[i] ^= session_id[i]; | |
1038 | ||
1039 | /* Set the session key. From this on all communications will be encrypted. */ | |
1040 | packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, cipher_type); | |
1041 | ||
1042 | /* Destroy our copy of the session key. It is no longer needed. */ | |
1043 | memset(session_key, 0, sizeof(session_key)); | |
1044 | ||
1045 | debug("Received session key; encryption turned on."); | |
1046 | ||
1047 | /* Send an acknowledgement packet. Note that this packet is sent encrypted. */ | |
1048 | packet_start(SSH_SMSG_SUCCESS); | |
1049 | packet_send(); | |
1050 | packet_write_wait(); | |
1051 | } |