2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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
12 * SSH2 implementation,
13 * Copyright (c) 2000 Markus Friedl. All rights reserved.
17 RCSID("$OpenBSD: sshd.c,v 1.121 2000/07/05 21:35:56 provos Exp $");
32 #include <openssl/dh.h>
33 #include <openssl/bn.h>
34 #include <openssl/hmac.h>
36 #include <openssl/dsa.h>
37 #include <openssl/rsa.h>
42 #include "myproposal.h"
48 int allow_severity = LOG_INFO;
49 int deny_severity = LOG_WARNING;
56 /* Server configuration options. */
57 ServerOptions options;
59 /* Name of the server configuration file. */
60 char *config_file_name = SERVER_CONFIG_FILE;
63 * Flag indicating whether IPv4 or IPv6. This can be set on the command line.
64 * Default value is AF_UNSPEC means both IPv4 and IPv6.
67 int IPv4or6 = AF_INET;
69 int IPv4or6 = AF_UNSPEC;
73 * Debug mode flag. This can be set on the command line. If debug
74 * mode is enabled, extra debugging output will be sent to the system
75 * log, the daemon will not go to background, and will exit after processing
76 * the first connection.
80 /* Flag indicating that the daemon is being started from inetd. */
83 /* debug goes to stderr unless inetd_flag is set */
86 /* argv[0] without path. */
89 /* Saved arguments to main(). */
94 * The sockets that the server is listening; this is used in the SIGHUP
97 #define MAX_LISTEN_SOCKS 16
98 int listen_socks[MAX_LISTEN_SOCKS];
99 int num_listen_socks = 0;
102 * the client's version string, passed by sshd2 in compat mode. if != NULL,
103 * sshd will skip the version-number exchange
105 char *client_version_string = NULL;
106 char *server_version_string = NULL;
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.
117 RSA *private_key; /* Private part of empheral server key. */
118 RSA *host_key; /* Private part of host key. */
119 Key *dsa_host_key; /* Private DSA host key. */
123 * Flag indicating whether the current session key has been used. This flag
124 * is set whenever the key is used, and cleared when the key is regenerated.
128 /* This is set to true when SIGHUP is received. */
129 int received_sighup = 0;
131 /* Public side of the server key. This value is regenerated regularly with
135 /* session identifier, used by RSA-auth */
136 unsigned char session_id[16];
139 unsigned char *session_id2 = NULL;
140 int session_id2_len = 0;
142 /* Prototypes for various functions defined later in this file. */
147 * Close all listening sockets
150 close_listen_socks(void)
153 for (i = 0; i < num_listen_socks; i++)
154 close(listen_socks[i]);
155 num_listen_socks = -1;
159 * Signal handler for SIGHUP. Sshd execs itself when it receives SIGHUP;
160 * the effect is to reread the configuration file (and to regenerate
164 sighup_handler(int sig)
167 signal(SIGHUP, sighup_handler);
171 * Called from the main program after receiving SIGHUP.
172 * Restarts the server.
177 log("Received SIGHUP; restarting.");
178 close_listen_socks();
179 execv(saved_argv[0], saved_argv);
180 log("RESTART FAILED: av0='%s', error: %s.", av0, strerror(errno));
185 * Generic signal handler for terminating signals in the master daemon.
186 * These close the listen socket; not closing it seems to cause "Address
187 * already in use" problems on some machines, which is inconvenient.
190 sigterm_handler(int sig)
192 log("Received signal %d; terminating.", sig);
193 close_listen_socks();
194 unlink(options.pid_file);
199 * SIGCHLD handler. This is called whenever a child dies. This will then
200 * reap any zombies left by exited c.
203 main_sigchld_handler(int sig)
205 int save_errno = errno;
208 while (waitpid(-1, &status, WNOHANG) > 0)
211 signal(SIGCHLD, main_sigchld_handler);
216 * Signal handler for the alarm after the login grace period has expired.
219 grace_alarm_handler(int sig)
221 /* Close the connection. */
224 /* Log error and exit. */
225 fatal("Timeout before authentication for %s.", get_remote_ipaddr());
229 * Signal handler for the key regeneration alarm. Note that this
230 * alarm only occurs in the daemon waiting for connections, and it does not
231 * do anything with the private key or random state before forking.
232 * Thus there should be no concurrency control/asynchronous execution
235 /* XXX do we really want this work to be done in a signal handler ? -m */
237 key_regeneration_alarm(int sig)
239 int save_errno = errno;
241 /* Check if we should generate a new key. */
243 /* This should really be done in the background. */
244 log("Generating new %d bit RSA key.", options.server_key_bits);
246 if (sensitive_data.private_key != NULL)
247 RSA_free(sensitive_data.private_key);
248 sensitive_data.private_key = RSA_new();
250 if (public_key != NULL)
251 RSA_free(public_key);
252 public_key = RSA_new();
254 rsa_generate_key(sensitive_data.private_key, public_key,
255 options.server_key_bits);
258 log("RSA key generation complete.");
260 /* Reschedule the alarm. */
261 signal(SIGALRM, key_regeneration_alarm);
262 alarm(options.key_regeneration_time);
267 sshd_exchange_identification(int sock_in, int sock_out)
270 int remote_major, remote_minor;
273 char buf[256]; /* Must not be larger than remote_version. */
274 char remote_version[256]; /* Must be at least as big as buf. */
276 if ((options.protocol & SSH_PROTO_1) &&
277 (options.protocol & SSH_PROTO_2)) {
278 major = PROTOCOL_MAJOR_1;
280 } else if (options.protocol & SSH_PROTO_2) {
281 major = PROTOCOL_MAJOR_2;
282 minor = PROTOCOL_MINOR_2;
284 major = PROTOCOL_MAJOR_1;
285 minor = PROTOCOL_MINOR_1;
287 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n", major, minor, SSH_VERSION);
288 server_version_string = xstrdup(buf);
290 if (client_version_string == NULL) {
291 /* Send our protocol version identification. */
292 if (atomicio(write, sock_out, server_version_string, strlen(server_version_string))
293 != strlen(server_version_string)) {
294 log("Could not write ident string to %s.", get_remote_ipaddr());
298 /* Read other side\'s version identification. */
299 for (i = 0; i < sizeof(buf) - 1; i++) {
300 if (atomicio(read, sock_in, &buf[i], 1) != 1) {
301 log("Did not receive ident string from %s.", get_remote_ipaddr());
304 if (buf[i] == '\r') {
309 if (buf[i] == '\n') {
315 buf[sizeof(buf) - 1] = 0;
316 client_version_string = xstrdup(buf);
320 * Check that the versions match. In future this might accept
321 * several versions and set appropriate flags to handle them.
323 if (sscanf(client_version_string, "SSH-%d.%d-%[^\n]\n",
324 &remote_major, &remote_minor, remote_version) != 3) {
325 s = "Protocol mismatch.\n";
326 (void) atomicio(write, sock_out, s, strlen(s));
329 log("Bad protocol version identification '%.100s' from %s",
330 client_version_string, get_remote_ipaddr());
333 debug("Client protocol version %d.%d; client software version %.100s",
334 remote_major, remote_minor, remote_version);
336 compat_datafellows(remote_version);
339 switch(remote_major) {
341 if (remote_minor == 99) {
342 if (options.protocol & SSH_PROTO_2)
348 if (!(options.protocol & SSH_PROTO_1)) {
352 if (remote_minor < 3) {
353 packet_disconnect("Your ssh version is too old and "
354 "is no longer supported. Please install a newer version.");
355 } else if (remote_minor == 3) {
356 /* note that this disables agent-forwarding */
361 if (options.protocol & SSH_PROTO_2) {
370 chop(server_version_string);
371 chop(client_version_string);
372 debug("Local version string %.200s", server_version_string);
375 s = "Protocol major versions differ.\n";
376 (void) atomicio(write, sock_out, s, strlen(s));
379 log("Protocol major versions differ for %s: %.200s vs. %.200s",
381 server_version_string, client_version_string);
385 packet_set_ssh2_format();
390 destroy_sensitive_data(void)
392 /* Destroy the private and public keys. They will no longer be needed. */
394 RSA_free(public_key);
395 if (sensitive_data.private_key)
396 RSA_free(sensitive_data.private_key);
397 if (sensitive_data.host_key)
398 RSA_free(sensitive_data.host_key);
399 if (sensitive_data.dsa_host_key != NULL)
400 key_free(sensitive_data.dsa_host_key);
403 int *startup_pipes = NULL; /* options.max_startup sized array of fd ints */
404 int startup_pipe; /* in child */
407 * Main program for the daemon.
410 main(int ac, char **av)
414 int opt, sock_in = 0, sock_out = 0, newsock, j, i, fdsetsz, on = 1;
419 struct sockaddr_storage from;
420 const char *remote_ip;
423 struct linger linger;
425 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
426 int listen_sock, maxfd;
435 if (strchr(av[0], '/'))
436 av0 = strrchr(av[0], '/') + 1;
440 /* Initialize configuration options to their default values. */
441 initialize_server_options(&options);
443 /* Parse command-line arguments. */
444 while ((opt = getopt(ac, av, "f:p:b:k:h:g:V:diqQ46")) != EOF) {
453 config_file_name = optarg;
457 options.log_level = SYSLOG_LEVEL_DEBUG;
466 options.log_level = SYSLOG_LEVEL_QUIET;
469 options.server_key_bits = atoi(optarg);
472 options.ports_from_cmdline = 1;
473 if (options.num_ports >= MAX_PORTS)
474 fatal("too many ports.\n");
475 options.ports[options.num_ports++] = atoi(optarg);
478 options.login_grace_time = atoi(optarg);
481 options.key_regeneration_time = atoi(optarg);
484 options.host_key_file = optarg;
487 client_version_string = optarg;
488 /* only makes sense with inetd_flag, i.e. no listen() */
493 fprintf(stderr, "sshd version %s\n", SSH_VERSION);
494 fprintf(stderr, "Usage: %s [options]\n", av0);
495 fprintf(stderr, "Options:\n");
496 fprintf(stderr, " -f file Configuration file (default %s)\n", SERVER_CONFIG_FILE);
497 fprintf(stderr, " -d Debugging mode\n");
498 fprintf(stderr, " -i Started from inetd\n");
499 fprintf(stderr, " -q Quiet (no logging)\n");
500 fprintf(stderr, " -p port Listen on the specified port (default: 22)\n");
501 fprintf(stderr, " -k seconds Regenerate server key every this many seconds (default: 3600)\n");
502 fprintf(stderr, " -g seconds Grace period for authentication (default: 300)\n");
503 fprintf(stderr, " -b bits Size of server RSA key (default: 768 bits)\n");
504 fprintf(stderr, " -h file File from which to read host key (default: %s)\n",
506 fprintf(stderr, " -4 Use IPv4 only\n");
507 fprintf(stderr, " -6 Use IPv6 only\n");
513 * Force logging to stderr until we have loaded the private host
514 * key (unless started from inetd)
517 options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level,
518 options.log_facility == -1 ? SYSLOG_FACILITY_AUTH : options.log_facility,
519 !silent && !inetd_flag);
521 /* Read server configuration options from the configuration file. */
522 read_server_config(&options, config_file_name);
524 /* Fill in default values for those options not explicitly set. */
525 fill_default_server_options(&options);
527 /* Check that there are no remaining arguments. */
529 fprintf(stderr, "Extra argument %s.\n", av[optind]);
533 debug("sshd version %.100s", SSH_VERSION);
535 sensitive_data.dsa_host_key = NULL;
536 sensitive_data.host_key = NULL;
538 /* check if RSA support exists */
539 if ((options.protocol & SSH_PROTO_1) &&
541 log("no RSA support in libssl and libcrypto. See ssl(8)");
542 log("Disabling protocol version 1");
543 options.protocol &= ~SSH_PROTO_1;
545 /* Load the RSA/DSA host key. It must have empty passphrase. */
546 if (options.protocol & SSH_PROTO_1) {
548 sensitive_data.host_key = RSA_new();
550 k.rsa = sensitive_data.host_key;
552 if (!load_private_key(options.host_key_file, "", &k, NULL)) {
553 error("Could not load host key: %.200s: %.100s",
554 options.host_key_file, strerror(errno));
555 log("Disabling protocol version 1");
556 options.protocol &= ~SSH_PROTO_1;
560 if (options.protocol & SSH_PROTO_2) {
561 sensitive_data.dsa_host_key = key_new(KEY_DSA);
562 if (!load_private_key(options.host_dsa_key_file, "", sensitive_data.dsa_host_key, NULL)) {
564 error("Could not load DSA host key: %.200s", options.host_dsa_key_file);
565 log("Disabling protocol version 2");
566 options.protocol &= ~SSH_PROTO_2;
569 if (! options.protocol & (SSH_PROTO_1|SSH_PROTO_2)) {
571 fprintf(stderr, "sshd: no hostkeys available -- exiting.\n");
572 log("sshd: no hostkeys available -- exiting.\n");
576 /* Check certain values for sanity. */
577 if (options.protocol & SSH_PROTO_1) {
578 if (options.server_key_bits < 512 ||
579 options.server_key_bits > 32768) {
580 fprintf(stderr, "Bad server key size.\n");
584 * Check that server and host key lengths differ sufficiently. This
585 * is necessary to make double encryption work with rsaref. Oh, I
586 * hate software patents. I dont know if this can go? Niels
588 if (options.server_key_bits >
589 BN_num_bits(sensitive_data.host_key->n) - SSH_KEY_BITS_RESERVED &&
590 options.server_key_bits <
591 BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
592 options.server_key_bits =
593 BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED;
594 debug("Forcing server key to %d bits to make it differ from host key.",
595 options.server_key_bits);
599 /* Initialize the log (it is reinitialized below in case we forked). */
600 if (debug_flag && !inetd_flag)
602 log_init(av0, options.log_level, options.log_facility, log_stderr);
605 * If not in debugging mode, and not started from inetd, disconnect
606 * from the controlling terminal, and fork. The original process
609 if (!debug_flag && !inetd_flag) {
612 #endif /* TIOCNOTTY */
613 if (daemon(0, 0) < 0)
614 fatal("daemon() failed: %.200s", strerror(errno));
616 /* Disconnect from the controlling tty. */
618 fd = open("/dev/tty", O_RDWR | O_NOCTTY);
620 (void) ioctl(fd, TIOCNOTTY, NULL);
623 #endif /* TIOCNOTTY */
625 /* Reinitialize the log (because of the fork above). */
626 log_init(av0, options.log_level, options.log_facility, log_stderr);
628 /* Do not display messages to stdout in RSA code. */
631 /* Initialize the random number generator. */
634 /* Chdir to the root directory so that the current disk can be
635 unmounted if desired. */
638 /* Start listening for a socket, unless started from inetd. */
641 s1 = dup(0); /* Make sure descriptors 0, 1, and 2 are in use. */
646 * We intentionally do not close the descriptors 0, 1, and 2
647 * as our code for setting the descriptors won\'t work if
648 * ttyfd happens to be one of those.
650 debug("inetd sockets after dupping: %d, %d", sock_in, sock_out);
652 if (options.protocol & SSH_PROTO_1) {
653 public_key = RSA_new();
654 sensitive_data.private_key = RSA_new();
655 log("Generating %d bit RSA key.", options.server_key_bits);
656 rsa_generate_key(sensitive_data.private_key, public_key,
657 options.server_key_bits);
659 log("RSA key generation complete.");
662 for (ai = options.listen_addrs; ai; ai = ai->ai_next) {
663 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
665 if (num_listen_socks >= MAX_LISTEN_SOCKS)
666 fatal("Too many listen sockets. "
667 "Enlarge MAX_LISTEN_SOCKS");
668 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
669 ntop, sizeof(ntop), strport, sizeof(strport),
670 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
671 error("getnameinfo failed");
674 /* Create socket for listening. */
675 listen_sock = socket(ai->ai_family, SOCK_STREAM, 0);
676 if (listen_sock < 0) {
677 /* kernel may not support ipv6 */
678 verbose("socket: %.100s", strerror(errno));
681 if (fcntl(listen_sock, F_SETFL, O_NONBLOCK) < 0) {
682 error("listen_sock O_NONBLOCK: %s", strerror(errno));
687 * Set socket options. We try to make the port
688 * reusable and have it close as fast as possible
689 * without waiting in unnecessary wait states on
692 setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR,
693 (void *) &on, sizeof(on));
696 setsockopt(listen_sock, SOL_SOCKET, SO_LINGER,
697 (void *) &linger, sizeof(linger));
699 debug("Bind to port %s on %s.", strport, ntop);
701 /* Bind the socket to the desired port. */
702 if ((bind(listen_sock, ai->ai_addr, ai->ai_addrlen) < 0) &&
704 error("Bind to port %s on %s failed: %.200s.",
705 strport, ntop, strerror(errno));
709 listen_socks[num_listen_socks] = listen_sock;
712 /* Start listening on the port. */
713 log("Server listening on %s port %s.", ntop, strport);
714 if (listen(listen_sock, 5) < 0)
715 fatal("listen: %.100s", strerror(errno));
718 freeaddrinfo(options.listen_addrs);
720 if (!num_listen_socks)
721 fatal("Cannot bind any address.");
725 * Record our pid in /etc/sshd_pid to make it easier
726 * to kill the correct sshd. We don\'t want to do
727 * this before the bind above because the bind will
728 * fail if there already is a daemon, and this will
729 * overwrite any old pid in the file.
731 f = fopen(options.pid_file, "w");
733 fprintf(f, "%u\n", (unsigned int) getpid());
737 if (options.protocol & SSH_PROTO_1) {
738 public_key = RSA_new();
739 sensitive_data.private_key = RSA_new();
741 log("Generating %d bit RSA key.", options.server_key_bits);
742 rsa_generate_key(sensitive_data.private_key, public_key,
743 options.server_key_bits);
745 log("RSA key generation complete.");
747 /* Schedule server key regeneration alarm. */
748 signal(SIGALRM, key_regeneration_alarm);
749 alarm(options.key_regeneration_time);
752 /* Arrange to restart on SIGHUP. The handler needs listen_sock. */
753 signal(SIGHUP, sighup_handler);
755 signal(SIGTERM, sigterm_handler);
756 signal(SIGQUIT, sigterm_handler);
758 /* Arrange SIGCHLD to be caught. */
759 signal(SIGCHLD, main_sigchld_handler);
761 /* setup fd set for listen */
764 for (i = 0; i < num_listen_socks; i++)
765 if (listen_socks[i] > maxfd)
766 maxfd = listen_socks[i];
767 /* pipes connected to unauthenticated childs */
768 startup_pipes = xmalloc(options.max_startups * sizeof(int));
769 for (i = 0; i < options.max_startups; i++)
770 startup_pipes[i] = -1;
773 * Stay listening for connections until the system crashes or
774 * the daemon is killed with a signal.
781 fdsetsz = howmany(maxfd, NFDBITS) * sizeof(fd_mask);
782 fdset = (fd_set *)xmalloc(fdsetsz);
783 memset(fdset, 0, fdsetsz);
785 for (i = 0; i < num_listen_socks; i++)
786 FD_SET(listen_socks[i], fdset);
787 for (i = 0; i < options.max_startups; i++)
788 if (startup_pipes[i] != -1)
789 FD_SET(startup_pipes[i], fdset);
791 /* Wait in select until there is a connection. */
792 if (select(maxfd + 1, fdset, NULL, NULL, NULL) < 0) {
794 error("select: %.100s", strerror(errno));
797 for (i = 0; i < options.max_startups; i++)
798 if (startup_pipes[i] != -1 &&
799 FD_ISSET(startup_pipes[i], fdset)) {
801 * the read end of the pipe is ready
802 * if the child has closed the pipe
803 * after successfull authentication
804 * or if the child has died
806 close(startup_pipes[i]);
807 startup_pipes[i] = -1;
810 for (i = 0; i < num_listen_socks; i++) {
811 if (!FD_ISSET(listen_socks[i], fdset))
813 fromlen = sizeof(from);
814 newsock = accept(listen_socks[i], (struct sockaddr *)&from,
817 if (errno != EINTR && errno != EWOULDBLOCK)
818 error("accept: %.100s", strerror(errno));
821 if (fcntl(newsock, F_SETFL, 0) < 0) {
822 error("newsock del O_NONBLOCK: %s", strerror(errno));
825 if (startups >= options.max_startups) {
829 if (pipe(startup_p) == -1) {
834 for (j = 0; j < options.max_startups; j++)
835 if (startup_pipes[j] == -1) {
836 startup_pipes[j] = startup_p[0];
837 if (maxfd < startup_p[0])
838 maxfd = startup_p[0];
844 * Got connection. Fork a child to handle it, unless
845 * we are in debugging mode.
849 * In debugging mode. Close the listening
850 * socket, and start processing the
851 * connection without forking.
853 debug("Server will not fork when running in debugging mode.");
854 close_listen_socks();
861 * Normal production daemon. Fork, and have
862 * the child process the connection. The
863 * parent continues listening.
865 if ((pid = fork()) == 0) {
867 * Child. Close the listening and max_startup
868 * sockets. Start using the accepted socket.
869 * Reinitialize logging (since our pid has
870 * changed). We break out of the loop to handle
873 startup_pipe = startup_p[1];
874 for (j = 0; j < options.max_startups; j++)
875 if (startup_pipes[j] != -1)
876 close(startup_pipes[j]);
877 close_listen_socks();
880 log_init(av0, options.log_level, options.log_facility, log_stderr);
885 /* Parent. Stay in the loop. */
887 error("fork: %.100s", strerror(errno));
889 debug("Forked child %d.", pid);
893 /* Mark that the key has been used (it was "given" to the child). */
898 /* Close the new socket (the child is now taking care of it). */
901 /* child process check (or debug mode) */
902 if (num_listen_socks < 0)
907 /* This is the child processing a new connection. */
910 * Disable the key regeneration alarm. We will not regenerate the
911 * key since we are no longer in a position to give it to anyone. We
912 * will not restart on SIGHUP since it no longer makes sense.
915 signal(SIGALRM, SIG_DFL);
916 signal(SIGHUP, SIG_DFL);
917 signal(SIGTERM, SIG_DFL);
918 signal(SIGQUIT, SIG_DFL);
919 signal(SIGCHLD, SIG_DFL);
922 * Set socket options for the connection. We want the socket to
923 * close as fast as possible without waiting for anything. If the
924 * connection is not a socket, these will do nothing.
926 /* setsockopt(sock_in, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
929 setsockopt(sock_in, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));
932 * Register our connection. This turns encryption off because we do
935 packet_set_connection(sock_in, sock_out);
937 remote_port = get_remote_port();
938 remote_ip = get_remote_ipaddr();
940 /* Check whether logins are denied from this host. */
942 /* XXX LIBWRAP noes not know about IPv6 */
944 struct request_info req;
946 request_init(&req, RQ_DAEMON, av0, RQ_FILE, sock_in, NULL);
949 if (!hosts_access(&req)) {
954 /*XXX IPv6 verbose("Connection from %.500s port %d", eval_client(&req), remote_port); */
957 /* Log the connection. */
958 verbose("Connection from %.500s port %d", remote_ip, remote_port);
961 * We don\'t want to listen forever unless the other side
962 * successfully authenticates itself. So we set up an alarm which is
963 * cleared after successful authentication. A limit of zero
964 * indicates no limit. Note that we don\'t set the alarm in debugging
965 * mode; it is just annoying to have the server exit just when you
966 * are about to discover the bug.
968 signal(SIGALRM, grace_alarm_handler);
970 alarm(options.login_grace_time);
972 sshd_exchange_identification(sock_in, sock_out);
974 * Check that the connection comes from a privileged port. Rhosts-
975 * and Rhosts-RSA-Authentication only make sense from priviledged
976 * programs. Of course, if the intruder has root access on his local
977 * machine, he can connect from any port. So do not use these
978 * authentication methods from machines that you do not trust.
980 if (remote_port >= IPPORT_RESERVED ||
981 remote_port < IPPORT_RESERVED / 2) {
982 options.rhosts_authentication = 0;
983 options.rhosts_rsa_authentication = 0;
986 if (!packet_connection_is_ipv4() &&
987 options.kerberos_authentication) {
988 debug("Kerberos Authentication disabled, only available for IPv4.");
989 options.kerberos_authentication = 0;
993 packet_set_nonblocking();
995 /* perform the key exchange */
996 /* authenticate user and start session */
999 do_authentication2();
1002 do_authentication();
1006 /* Cleanup user's ticket cache file. */
1007 if (options.kerberos_ticket_cleanup)
1011 /* The connection has been terminated. */
1012 verbose("Closing connection to %.100s", remote_ip);
1016 #endif /* USE_PAM */
1030 BIGNUM *session_key_int;
1031 unsigned char session_key[SSH_SESSION_KEY_LENGTH];
1032 unsigned char cookie[8];
1033 unsigned int cipher_type, auth_mask, protocol_flags;
1037 * Generate check bytes that the client must send back in the user
1038 * packet in order for it to be accepted; this is used to defy ip
1039 * spoofing attacks. Note that this only works against somebody
1040 * doing IP spoofing from a remote machine; any machine on the local
1041 * network can still see outgoing packets and catch the random
1042 * cookie. This only affects rhosts authentication, and this is one
1043 * of the reasons why it is inherently insecure.
1045 for (i = 0; i < 8; i++) {
1047 rand = arc4random();
1048 cookie[i] = rand & 0xff;
1053 * Send our public key. We include in the packet 64 bits of random
1054 * data that must be matched in the reply in order to prevent IP
1057 packet_start(SSH_SMSG_PUBLIC_KEY);
1058 for (i = 0; i < 8; i++)
1059 packet_put_char(cookie[i]);
1061 /* Store our public server RSA key. */
1062 packet_put_int(BN_num_bits(public_key->n));
1063 packet_put_bignum(public_key->e);
1064 packet_put_bignum(public_key->n);
1066 /* Store our public host RSA key. */
1067 packet_put_int(BN_num_bits(sensitive_data.host_key->n));
1068 packet_put_bignum(sensitive_data.host_key->e);
1069 packet_put_bignum(sensitive_data.host_key->n);
1071 /* Put protocol flags. */
1072 packet_put_int(SSH_PROTOFLAG_HOST_IN_FWD_OPEN);
1074 /* Declare which ciphers we support. */
1075 packet_put_int(cipher_mask1());
1077 /* Declare supported authentication types. */
1079 if (options.rhosts_authentication)
1080 auth_mask |= 1 << SSH_AUTH_RHOSTS;
1081 if (options.rhosts_rsa_authentication)
1082 auth_mask |= 1 << SSH_AUTH_RHOSTS_RSA;
1083 if (options.rsa_authentication)
1084 auth_mask |= 1 << SSH_AUTH_RSA;
1086 if (options.kerberos_authentication)
1087 auth_mask |= 1 << SSH_AUTH_KERBEROS;
1090 if (options.kerberos_tgt_passing)
1091 auth_mask |= 1 << SSH_PASS_KERBEROS_TGT;
1092 if (options.afs_token_passing)
1093 auth_mask |= 1 << SSH_PASS_AFS_TOKEN;
1096 if (options.skey_authentication == 1)
1097 auth_mask |= 1 << SSH_AUTH_TIS;
1099 if (options.password_authentication)
1100 auth_mask |= 1 << SSH_AUTH_PASSWORD;
1101 packet_put_int(auth_mask);
1103 /* Send the packet and wait for it to be sent. */
1105 packet_write_wait();
1107 debug("Sent %d bit public key and %d bit host key.",
1108 BN_num_bits(public_key->n), BN_num_bits(sensitive_data.host_key->n));
1110 /* Read clients reply (cipher type and session key). */
1111 packet_read_expect(&plen, SSH_CMSG_SESSION_KEY);
1113 /* Get cipher type and check whether we accept this. */
1114 cipher_type = packet_get_char();
1116 if (!(cipher_mask() & (1 << cipher_type)))
1117 packet_disconnect("Warning: client selects unsupported cipher.");
1119 /* Get check bytes from the packet. These must match those we
1120 sent earlier with the public key packet. */
1121 for (i = 0; i < 8; i++)
1122 if (cookie[i] != packet_get_char())
1123 packet_disconnect("IP Spoofing check bytes do not match.");
1125 debug("Encryption type: %.200s", cipher_name(cipher_type));
1127 /* Get the encrypted integer. */
1128 session_key_int = BN_new();
1129 packet_get_bignum(session_key_int, &slen);
1131 protocol_flags = packet_get_int();
1132 packet_set_protocol_flags(protocol_flags);
1134 packet_integrity_check(plen, 1 + 8 + slen + 4, SSH_CMSG_SESSION_KEY);
1137 * Decrypt it using our private server key and private host key (key
1138 * with larger modulus first).
1140 if (BN_cmp(sensitive_data.private_key->n, sensitive_data.host_key->n) > 0) {
1141 /* Private key has bigger modulus. */
1142 if (BN_num_bits(sensitive_data.private_key->n) <
1143 BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
1144 fatal("do_connection: %s: private_key %d < host_key %d + SSH_KEY_BITS_RESERVED %d",
1145 get_remote_ipaddr(),
1146 BN_num_bits(sensitive_data.private_key->n),
1147 BN_num_bits(sensitive_data.host_key->n),
1148 SSH_KEY_BITS_RESERVED);
1150 rsa_private_decrypt(session_key_int, session_key_int,
1151 sensitive_data.private_key);
1152 rsa_private_decrypt(session_key_int, session_key_int,
1153 sensitive_data.host_key);
1155 /* Host key has bigger modulus (or they are equal). */
1156 if (BN_num_bits(sensitive_data.host_key->n) <
1157 BN_num_bits(sensitive_data.private_key->n) + SSH_KEY_BITS_RESERVED) {
1158 fatal("do_connection: %s: host_key %d < private_key %d + SSH_KEY_BITS_RESERVED %d",
1159 get_remote_ipaddr(),
1160 BN_num_bits(sensitive_data.host_key->n),
1161 BN_num_bits(sensitive_data.private_key->n),
1162 SSH_KEY_BITS_RESERVED);
1164 rsa_private_decrypt(session_key_int, session_key_int,
1165 sensitive_data.host_key);
1166 rsa_private_decrypt(session_key_int, session_key_int,
1167 sensitive_data.private_key);
1170 compute_session_id(session_id, cookie,
1171 sensitive_data.host_key->n,
1172 sensitive_data.private_key->n);
1174 /* Destroy the private and public keys. They will no longer be needed. */
1175 destroy_sensitive_data();
1178 * Extract session key from the decrypted integer. The key is in the
1179 * least significant 256 bits of the integer; the first byte of the
1180 * key is in the highest bits.
1182 BN_mask_bits(session_key_int, sizeof(session_key) * 8);
1183 len = BN_num_bytes(session_key_int);
1184 if (len < 0 || len > sizeof(session_key))
1185 fatal("do_connection: bad len from %s: session_key_int %d > sizeof(session_key) %d",
1186 get_remote_ipaddr(),
1187 len, sizeof(session_key));
1188 memset(session_key, 0, sizeof(session_key));
1189 BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len);
1191 /* Destroy the decrypted integer. It is no longer needed. */
1192 BN_clear_free(session_key_int);
1194 /* Xor the first 16 bytes of the session key with the session id. */
1195 for (i = 0; i < 16; i++)
1196 session_key[i] ^= session_id[i];
1198 /* Set the session key. From this on all communications will be encrypted. */
1199 packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, cipher_type);
1201 /* Destroy our copy of the session key. It is no longer needed. */
1202 memset(session_key, 0, sizeof(session_key));
1204 debug("Received session key; encryption turned on.");
1206 /* Send an acknowledgement packet. Note that this packet is sent encrypted. */
1207 packet_start(SSH_SMSG_SUCCESS);
1209 packet_write_wait();
1213 * SSH2 key exchange: diffie-hellman-group1-sha1
1218 Buffer *server_kexinit;
1219 Buffer *client_kexinit;
1220 int payload_len, dlen;
1222 unsigned int klen, kout;
1223 unsigned char *signature = NULL;
1224 unsigned char *server_host_key_blob = NULL;
1225 unsigned int sbloblen;
1227 BIGNUM *dh_client_pub = 0;
1228 BIGNUM *shared_secret = 0;
1230 unsigned char *kbuf;
1231 unsigned char *hash;
1233 char *cprop[PROPOSAL_MAX];
1237 if (options.ciphers != NULL) {
1238 myproposal[PROPOSAL_ENC_ALGS_CTOS] =
1239 myproposal[PROPOSAL_ENC_ALGS_STOC] = options.ciphers;
1241 server_kexinit = kex_init(myproposal);
1242 client_kexinit = xmalloc(sizeof(*client_kexinit));
1243 buffer_init(client_kexinit);
1245 /* algorithm negotiation */
1246 kex_exchange_kexinit(server_kexinit, client_kexinit, cprop);
1247 kex = kex_choose_conf(cprop, myproposal, 1);
1248 for (i = 0; i < PROPOSAL_MAX; i++)
1253 debug("Wait SSH2_MSG_KEXDH_INIT.");
1254 packet_read_expect(&payload_len, SSH2_MSG_KEXDH_INIT);
1257 dh_client_pub = BN_new();
1258 if (dh_client_pub == NULL)
1259 fatal("dh_client_pub == NULL");
1260 packet_get_bignum2(dh_client_pub, &dlen);
1263 fprintf(stderr, "\ndh_client_pub= ");
1264 bignum_print(dh_client_pub);
1265 fprintf(stderr, "\n");
1266 debug("bits %d", BN_num_bits(dh_client_pub));
1269 /* generate DH key */
1270 dh = dh_new_group1(); /* XXX depends on 'kex' */
1273 fprintf(stderr, "\np= ");
1274 bignum_print(dh->p);
1275 fprintf(stderr, "\ng= ");
1276 bignum_print(dh->g);
1277 fprintf(stderr, "\npub= ");
1278 bignum_print(dh->pub_key);
1279 fprintf(stderr, "\n");
1281 if (!dh_pub_is_valid(dh, dh_client_pub))
1282 packet_disconnect("bad client public DH value");
1285 kbuf = xmalloc(klen);
1286 kout = DH_compute_key(kbuf, dh_client_pub, dh);
1289 debug("shared secret: len %d/%d", klen, kout);
1290 fprintf(stderr, "shared secret == ");
1291 for (i = 0; i< kout; i++)
1292 fprintf(stderr, "%02x", (kbuf[i])&0xff);
1293 fprintf(stderr, "\n");
1295 shared_secret = BN_new();
1297 BN_bin2bn(kbuf, kout, shared_secret);
1298 memset(kbuf, 0, klen);
1301 /* XXX precompute? */
1302 dsa_make_key_blob(sensitive_data.dsa_host_key, &server_host_key_blob, &sbloblen);
1304 /* calc H */ /* XXX depends on 'kex' */
1306 client_version_string,
1307 server_version_string,
1308 buffer_ptr(client_kexinit), buffer_len(client_kexinit),
1309 buffer_ptr(server_kexinit), buffer_len(server_kexinit),
1310 (char *)server_host_key_blob, sbloblen,
1315 buffer_free(client_kexinit);
1316 buffer_free(server_kexinit);
1317 xfree(client_kexinit);
1318 xfree(server_kexinit);
1320 fprintf(stderr, "hash == ");
1321 for (i = 0; i< 20; i++)
1322 fprintf(stderr, "%02x", (hash[i])&0xff);
1323 fprintf(stderr, "\n");
1325 /* save session id := H */
1326 /* XXX hashlen depends on KEX */
1327 session_id2_len = 20;
1328 session_id2 = xmalloc(session_id2_len);
1329 memcpy(session_id2, hash, session_id2_len);
1332 /* XXX hashlen depends on KEX */
1333 dsa_sign(sensitive_data.dsa_host_key, &signature, &slen, hash, 20);
1335 destroy_sensitive_data();
1337 /* send server hostkey, DH pubkey 'f' and singed H */
1338 packet_start(SSH2_MSG_KEXDH_REPLY);
1339 packet_put_string((char *)server_host_key_blob, sbloblen);
1340 packet_put_bignum2(dh->pub_key); /* f */
1341 packet_put_string((char *)signature, slen);
1344 xfree(server_host_key_blob);
1345 packet_write_wait();
1347 kex_derive_keys(kex, hash, shared_secret);
1348 packet_set_kex(kex);
1350 /* have keys, free DH */
1353 debug("send SSH2_MSG_NEWKEYS.");
1354 packet_start(SSH2_MSG_NEWKEYS);
1356 packet_write_wait();
1357 debug("done: send SSH2_MSG_NEWKEYS.");
1359 debug("Wait SSH2_MSG_NEWKEYS.");
1360 packet_read_expect(&payload_len, SSH2_MSG_NEWKEYS);
1361 debug("GOT SSH2_MSG_NEWKEYS.");
1364 /* send 1st encrypted/maced/compressed message */
1365 packet_start(SSH2_MSG_IGNORE);
1366 packet_put_cstring("markus");
1368 packet_write_wait();
1370 debug("done: KEX2.");