2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * This program is the ssh daemon. It listens for connections from clients,
6 * and performs authentication, executes use commands or shell, and forwards
7 * information to/from the application to the user client over an encrypted
8 * connection. This can also handle forwarding of X11, TCP/IP, and
9 * authentication agent connections.
11 * As far as I am concerned, the code I have written for this software
12 * can be used freely for any purpose. Any derived versions of this
13 * software must be clearly marked as such, and if the derived work is
14 * incompatible with the protocol description in the RFC file, it must be
15 * called by a name other than "ssh" or "Secure Shell".
17 * SSH2 implementation:
19 * Copyright (c) 2000 Markus Friedl. All rights reserved.
21 * Redistribution and use in source and binary forms, with or without
22 * modification, are permitted provided that the following conditions
24 * 1. Redistributions of source code must retain the above copyright
25 * notice, this list of conditions and the following disclaimer.
26 * 2. Redistributions in binary form must reproduce the above copyright
27 * notice, this list of conditions and the following disclaimer in the
28 * documentation and/or other materials provided with the distribution.
30 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
31 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
32 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
33 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
34 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
35 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
36 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
37 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
38 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
39 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
43 RCSID("$OpenBSD: sshd.c,v 1.128 2000/09/17 15:38:59 markus Exp $");
58 #include <openssl/dh.h>
59 #include <openssl/bn.h>
60 #include <openssl/hmac.h>
62 #include <openssl/dsa.h>
63 #include <openssl/rsa.h>
68 #include "myproposal.h"
74 int allow_severity = LOG_INFO;
75 int deny_severity = LOG_WARNING;
82 /* Server configuration options. */
83 ServerOptions options;
85 /* Name of the server configuration file. */
86 char *config_file_name = SERVER_CONFIG_FILE;
89 * Flag indicating whether IPv4 or IPv6. This can be set on the command line.
90 * Default value is AF_UNSPEC means both IPv4 and IPv6.
93 int IPv4or6 = AF_INET;
95 int IPv4or6 = AF_UNSPEC;
99 * Debug mode flag. This can be set on the command line. If debug
100 * mode is enabled, extra debugging output will be sent to the system
101 * log, the daemon will not go to background, and will exit after processing
102 * the first connection.
106 /* Flag indicating that the daemon is being started from inetd. */
109 /* debug goes to stderr unless inetd_flag is set */
112 /* argv[0] without path. */
115 /* Saved arguments to main(). */
120 * The sockets that the server is listening; this is used in the SIGHUP
123 #define MAX_LISTEN_SOCKS 16
124 int listen_socks[MAX_LISTEN_SOCKS];
125 int num_listen_socks = 0;
128 * the client's version string, passed by sshd2 in compat mode. if != NULL,
129 * sshd will skip the version-number exchange
131 char *client_version_string = NULL;
132 char *server_version_string = NULL;
135 * Any really sensitive data in the application is contained in this
136 * structure. The idea is that this structure could be locked into memory so
137 * that the pages do not get written into swap. However, there are some
138 * problems. The private key contains BIGNUMs, and we do not (in principle)
139 * have access to the internals of them, and locking just the structure is
140 * not very useful. Currently, memory locking is not implemented.
143 RSA *private_key; /* Private part of empheral server key. */
144 RSA *host_key; /* Private part of host key. */
145 Key *dsa_host_key; /* Private DSA host key. */
149 * Flag indicating whether the current session key has been used. This flag
150 * is set whenever the key is used, and cleared when the key is regenerated.
154 /* This is set to true when SIGHUP is received. */
155 int received_sighup = 0;
157 /* Public side of the server key. This value is regenerated regularly with
161 /* session identifier, used by RSA-auth */
162 unsigned char session_id[16];
165 unsigned char *session_id2 = NULL;
166 int session_id2_len = 0;
168 /* record remote hostname or ip */
169 unsigned int utmp_len = MAXHOSTNAMELEN;
171 /* Prototypes for various functions defined later in this file. */
176 * Close all listening sockets
179 close_listen_socks(void)
182 for (i = 0; i < num_listen_socks; i++)
183 close(listen_socks[i]);
184 num_listen_socks = -1;
188 * Signal handler for SIGHUP. Sshd execs itself when it receives SIGHUP;
189 * the effect is to reread the configuration file (and to regenerate
193 sighup_handler(int sig)
196 signal(SIGHUP, sighup_handler);
200 * Called from the main program after receiving SIGHUP.
201 * Restarts the server.
206 log("Received SIGHUP; restarting.");
207 close_listen_socks();
208 execv(saved_argv[0], saved_argv);
209 log("RESTART FAILED: av0='%s', error: %s.", av0, strerror(errno));
214 * Generic signal handler for terminating signals in the master daemon.
215 * These close the listen socket; not closing it seems to cause "Address
216 * already in use" problems on some machines, which is inconvenient.
219 sigterm_handler(int sig)
221 log("Received signal %d; terminating.", sig);
222 close_listen_socks();
223 unlink(options.pid_file);
228 * SIGCHLD handler. This is called whenever a child dies. This will then
229 * reap any zombies left by exited c.
232 main_sigchld_handler(int sig)
234 int save_errno = errno;
237 while (waitpid(-1, &status, WNOHANG) > 0)
240 signal(SIGCHLD, main_sigchld_handler);
245 * Signal handler for the alarm after the login grace period has expired.
248 grace_alarm_handler(int sig)
250 /* Close the connection. */
253 /* Log error and exit. */
254 fatal("Timeout before authentication for %s.", get_remote_ipaddr());
258 * Signal handler for the key regeneration alarm. Note that this
259 * alarm only occurs in the daemon waiting for connections, and it does not
260 * do anything with the private key or random state before forking.
261 * Thus there should be no concurrency control/asynchronous execution
264 /* XXX do we really want this work to be done in a signal handler ? -m */
266 key_regeneration_alarm(int sig)
268 int save_errno = errno;
270 /* Check if we should generate a new key. */
272 /* This should really be done in the background. */
273 log("Generating new %d bit RSA key.", options.server_key_bits);
275 if (sensitive_data.private_key != NULL)
276 RSA_free(sensitive_data.private_key);
277 sensitive_data.private_key = RSA_new();
279 if (public_key != NULL)
280 RSA_free(public_key);
281 public_key = RSA_new();
283 rsa_generate_key(sensitive_data.private_key, public_key,
284 options.server_key_bits);
287 log("RSA key generation complete.");
289 /* Reschedule the alarm. */
290 signal(SIGALRM, key_regeneration_alarm);
291 alarm(options.key_regeneration_time);
296 sshd_exchange_identification(int sock_in, int sock_out)
299 int remote_major, remote_minor;
302 char buf[256]; /* Must not be larger than remote_version. */
303 char remote_version[256]; /* Must be at least as big as buf. */
305 if ((options.protocol & SSH_PROTO_1) &&
306 (options.protocol & SSH_PROTO_2)) {
307 major = PROTOCOL_MAJOR_1;
309 } else if (options.protocol & SSH_PROTO_2) {
310 major = PROTOCOL_MAJOR_2;
311 minor = PROTOCOL_MINOR_2;
313 major = PROTOCOL_MAJOR_1;
314 minor = PROTOCOL_MINOR_1;
316 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n", major, minor, SSH_VERSION);
317 server_version_string = xstrdup(buf);
319 if (client_version_string == NULL) {
320 /* Send our protocol version identification. */
321 if (atomicio(write, sock_out, server_version_string, strlen(server_version_string))
322 != strlen(server_version_string)) {
323 log("Could not write ident string to %s.", get_remote_ipaddr());
327 /* Read other side\'s version identification. */
328 for (i = 0; i < sizeof(buf) - 1; i++) {
329 if (atomicio(read, sock_in, &buf[i], 1) != 1) {
330 log("Did not receive ident string from %s.", get_remote_ipaddr());
333 if (buf[i] == '\r') {
338 if (buf[i] == '\n') {
344 buf[sizeof(buf) - 1] = 0;
345 client_version_string = xstrdup(buf);
349 * Check that the versions match. In future this might accept
350 * several versions and set appropriate flags to handle them.
352 if (sscanf(client_version_string, "SSH-%d.%d-%[^\n]\n",
353 &remote_major, &remote_minor, remote_version) != 3) {
354 s = "Protocol mismatch.\n";
355 (void) atomicio(write, sock_out, s, strlen(s));
358 log("Bad protocol version identification '%.100s' from %s",
359 client_version_string, get_remote_ipaddr());
362 debug("Client protocol version %d.%d; client software version %.100s",
363 remote_major, remote_minor, remote_version);
365 compat_datafellows(remote_version);
368 switch(remote_major) {
370 if (remote_minor == 99) {
371 if (options.protocol & SSH_PROTO_2)
377 if (!(options.protocol & SSH_PROTO_1)) {
381 if (remote_minor < 3) {
382 packet_disconnect("Your ssh version is too old and "
383 "is no longer supported. Please install a newer version.");
384 } else if (remote_minor == 3) {
385 /* note that this disables agent-forwarding */
390 if (options.protocol & SSH_PROTO_2) {
399 chop(server_version_string);
400 chop(client_version_string);
401 debug("Local version string %.200s", server_version_string);
404 s = "Protocol major versions differ.\n";
405 (void) atomicio(write, sock_out, s, strlen(s));
408 log("Protocol major versions differ for %s: %.200s vs. %.200s",
410 server_version_string, client_version_string);
414 packet_set_ssh2_format();
419 destroy_sensitive_data(void)
421 /* Destroy the private and public keys. They will no longer be needed. */
423 RSA_free(public_key);
424 if (sensitive_data.private_key)
425 RSA_free(sensitive_data.private_key);
426 if (sensitive_data.host_key)
427 RSA_free(sensitive_data.host_key);
428 if (sensitive_data.dsa_host_key != NULL)
429 key_free(sensitive_data.dsa_host_key);
433 * returns 1 if connection should be dropped, 0 otherwise.
434 * dropping starts at connection #max_startups_begin with a probability
435 * of (max_startups_rate/100). the probability increases linearly until
436 * all connections are dropped for startups > max_startups
439 drop_connection(int startups)
443 if (startups < options.max_startups_begin)
445 if (startups >= options.max_startups)
447 if (options.max_startups_rate == 100)
450 p = 100 - options.max_startups_rate;
451 p *= startups - options.max_startups_begin;
452 p /= (double) (options.max_startups - options.max_startups_begin);
453 p += options.max_startups_rate;
455 r = arc4random() / (double) UINT_MAX;
457 debug("drop_connection: p %g, r %g", p, r);
458 return (r < p) ? 1 : 0;
461 int *startup_pipes = NULL; /* options.max_startup sized array of fd ints */
462 int startup_pipe; /* in child */
465 * Main program for the daemon.
468 main(int ac, char **av)
472 int opt, sock_in = 0, sock_out = 0, newsock, j, i, fdsetsz, on = 1;
477 struct sockaddr_storage from;
478 const char *remote_ip;
481 struct linger linger;
483 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
484 int listen_sock, maxfd;
493 if (strchr(av[0], '/'))
494 av0 = strrchr(av[0], '/') + 1;
498 /* Initialize configuration options to their default values. */
499 initialize_server_options(&options);
501 /* Parse command-line arguments. */
502 while ((opt = getopt(ac, av, "f:p:b:k:h:g:V:u:diqQ46")) != EOF) {
511 config_file_name = optarg;
514 if (0 == debug_flag) {
516 options.log_level = SYSLOG_LEVEL_DEBUG1;
517 } else if (options.log_level < SYSLOG_LEVEL_DEBUG3) {
520 fprintf(stderr, "Too high debugging level.\n");
531 options.log_level = SYSLOG_LEVEL_QUIET;
534 options.server_key_bits = atoi(optarg);
537 options.ports_from_cmdline = 1;
538 if (options.num_ports >= MAX_PORTS) {
539 fprintf(stderr, "too many ports.\n");
542 options.ports[options.num_ports++] = atoi(optarg);
545 options.login_grace_time = atoi(optarg);
548 options.key_regeneration_time = atoi(optarg);
551 options.host_key_file = optarg;
554 client_version_string = optarg;
555 /* only makes sense with inetd_flag, i.e. no listen() */
559 utmp_len = atoi(optarg);
563 fprintf(stderr, "sshd version %s\n", SSH_VERSION);
564 fprintf(stderr, "Usage: %s [options]\n", av0);
565 fprintf(stderr, "Options:\n");
566 fprintf(stderr, " -f file Configuration file (default %s)\n", SERVER_CONFIG_FILE);
567 fprintf(stderr, " -d Debugging mode (multiple -d means more debugging)\n");
568 fprintf(stderr, " -i Started from inetd\n");
569 fprintf(stderr, " -q Quiet (no logging)\n");
570 fprintf(stderr, " -p port Listen on the specified port (default: 22)\n");
571 fprintf(stderr, " -k seconds Regenerate server key every this many seconds (default: 3600)\n");
572 fprintf(stderr, " -g seconds Grace period for authentication (default: 300)\n");
573 fprintf(stderr, " -b bits Size of server RSA key (default: 768 bits)\n");
574 fprintf(stderr, " -h file File from which to read host key (default: %s)\n",
576 fprintf(stderr, " -u len Maximum hostname length for utmp recording\n");
577 fprintf(stderr, " -4 Use IPv4 only\n");
578 fprintf(stderr, " -6 Use IPv6 only\n");
584 * Force logging to stderr until we have loaded the private host
585 * key (unless started from inetd)
588 options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level,
589 options.log_facility == -1 ? SYSLOG_FACILITY_AUTH : options.log_facility,
590 !silent && !inetd_flag);
592 /* Read server configuration options from the configuration file. */
593 read_server_config(&options, config_file_name);
595 /* Fill in default values for those options not explicitly set. */
596 fill_default_server_options(&options);
598 /* Check that there are no remaining arguments. */
600 fprintf(stderr, "Extra argument %s.\n", av[optind]);
604 debug("sshd version %.100s", SSH_VERSION);
606 sensitive_data.dsa_host_key = NULL;
607 sensitive_data.host_key = NULL;
609 /* check if RSA support exists */
610 if ((options.protocol & SSH_PROTO_1) &&
612 log("no RSA support in libssl and libcrypto. See ssl(8)");
613 log("Disabling protocol version 1");
614 options.protocol &= ~SSH_PROTO_1;
616 /* Load the RSA/DSA host key. It must have empty passphrase. */
617 if (options.protocol & SSH_PROTO_1) {
619 sensitive_data.host_key = RSA_new();
621 k.rsa = sensitive_data.host_key;
623 if (!load_private_key(options.host_key_file, "", &k, NULL)) {
624 error("Could not load host key: %.200s: %.100s",
625 options.host_key_file, strerror(errno));
626 log("Disabling protocol version 1");
627 options.protocol &= ~SSH_PROTO_1;
631 if (options.protocol & SSH_PROTO_2) {
632 sensitive_data.dsa_host_key = key_new(KEY_DSA);
633 if (!load_private_key(options.host_dsa_key_file, "", sensitive_data.dsa_host_key, NULL)) {
635 error("Could not load DSA host key: %.200s", options.host_dsa_key_file);
636 log("Disabling protocol version 2");
637 options.protocol &= ~SSH_PROTO_2;
640 if (! options.protocol & (SSH_PROTO_1|SSH_PROTO_2)) {
642 fprintf(stderr, "sshd: no hostkeys available -- exiting.\n");
643 log("sshd: no hostkeys available -- exiting.\n");
647 /* Check certain values for sanity. */
648 if (options.protocol & SSH_PROTO_1) {
649 if (options.server_key_bits < 512 ||
650 options.server_key_bits > 32768) {
651 fprintf(stderr, "Bad server key size.\n");
655 * Check that server and host key lengths differ sufficiently. This
656 * is necessary to make double encryption work with rsaref. Oh, I
657 * hate software patents. I dont know if this can go? Niels
659 if (options.server_key_bits >
660 BN_num_bits(sensitive_data.host_key->n) - SSH_KEY_BITS_RESERVED &&
661 options.server_key_bits <
662 BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
663 options.server_key_bits =
664 BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED;
665 debug("Forcing server key to %d bits to make it differ from host key.",
666 options.server_key_bits);
670 #ifdef HAVE_SCO_PROTECTED_PW
671 (void) set_auth_parameters(ac, av);
674 /* Initialize the log (it is reinitialized below in case we forked). */
675 if (debug_flag && !inetd_flag)
677 log_init(av0, options.log_level, options.log_facility, log_stderr);
680 * If not in debugging mode, and not started from inetd, disconnect
681 * from the controlling terminal, and fork. The original process
684 if (!debug_flag && !inetd_flag) {
687 #endif /* TIOCNOTTY */
688 if (daemon(0, 0) < 0)
689 fatal("daemon() failed: %.200s", strerror(errno));
691 /* Disconnect from the controlling tty. */
693 fd = open("/dev/tty", O_RDWR | O_NOCTTY);
695 (void) ioctl(fd, TIOCNOTTY, NULL);
698 #endif /* TIOCNOTTY */
700 /* Reinitialize the log (because of the fork above). */
701 log_init(av0, options.log_level, options.log_facility, log_stderr);
703 /* Do not display messages to stdout in RSA code. */
706 /* Initialize the random number generator. */
709 /* Chdir to the root directory so that the current disk can be
710 unmounted if desired. */
713 /* Start listening for a socket, unless started from inetd. */
716 s1 = dup(0); /* Make sure descriptors 0, 1, and 2 are in use. */
722 * We intentionally do not close the descriptors 0, 1, and 2
723 * as our code for setting the descriptors won\'t work if
724 * ttyfd happens to be one of those.
726 debug("inetd sockets after dupping: %d, %d", sock_in, sock_out);
728 if (options.protocol & SSH_PROTO_1) {
729 public_key = RSA_new();
730 sensitive_data.private_key = RSA_new();
731 log("Generating %d bit RSA key.", options.server_key_bits);
732 rsa_generate_key(sensitive_data.private_key, public_key,
733 options.server_key_bits);
735 log("RSA key generation complete.");
738 for (ai = options.listen_addrs; ai; ai = ai->ai_next) {
739 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
741 if (num_listen_socks >= MAX_LISTEN_SOCKS)
742 fatal("Too many listen sockets. "
743 "Enlarge MAX_LISTEN_SOCKS");
744 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
745 ntop, sizeof(ntop), strport, sizeof(strport),
746 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
747 error("getnameinfo failed");
750 /* Create socket for listening. */
751 listen_sock = socket(ai->ai_family, SOCK_STREAM, 0);
752 if (listen_sock < 0) {
753 /* kernel may not support ipv6 */
754 verbose("socket: %.100s", strerror(errno));
757 if (fcntl(listen_sock, F_SETFL, O_NONBLOCK) < 0) {
758 error("listen_sock O_NONBLOCK: %s", strerror(errno));
763 * Set socket options. We try to make the port
764 * reusable and have it close as fast as possible
765 * without waiting in unnecessary wait states on
768 setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR,
769 (void *) &on, sizeof(on));
772 setsockopt(listen_sock, SOL_SOCKET, SO_LINGER,
773 (void *) &linger, sizeof(linger));
775 debug("Bind to port %s on %s.", strport, ntop);
777 /* Bind the socket to the desired port. */
778 if ((bind(listen_sock, ai->ai_addr, ai->ai_addrlen) < 0) &&
780 error("Bind to port %s on %s failed: %.200s.",
781 strport, ntop, strerror(errno));
785 listen_socks[num_listen_socks] = listen_sock;
788 /* Start listening on the port. */
789 log("Server listening on %s port %s.", ntop, strport);
790 if (listen(listen_sock, 5) < 0)
791 fatal("listen: %.100s", strerror(errno));
794 freeaddrinfo(options.listen_addrs);
796 if (!num_listen_socks)
797 fatal("Cannot bind any address.");
801 * Record our pid in /etc/sshd_pid to make it easier
802 * to kill the correct sshd. We don\'t want to do
803 * this before the bind above because the bind will
804 * fail if there already is a daemon, and this will
805 * overwrite any old pid in the file.
807 f = fopen(options.pid_file, "wb");
809 fprintf(f, "%u\n", (unsigned int) getpid());
813 if (options.protocol & SSH_PROTO_1) {
814 public_key = RSA_new();
815 sensitive_data.private_key = RSA_new();
817 log("Generating %d bit RSA key.", options.server_key_bits);
818 rsa_generate_key(sensitive_data.private_key, public_key,
819 options.server_key_bits);
821 log("RSA key generation complete.");
823 /* Schedule server key regeneration alarm. */
824 signal(SIGALRM, key_regeneration_alarm);
825 alarm(options.key_regeneration_time);
828 /* Arrange to restart on SIGHUP. The handler needs listen_sock. */
829 signal(SIGHUP, sighup_handler);
831 signal(SIGTERM, sigterm_handler);
832 signal(SIGQUIT, sigterm_handler);
834 /* Arrange SIGCHLD to be caught. */
835 signal(SIGCHLD, main_sigchld_handler);
837 /* setup fd set for listen */
840 for (i = 0; i < num_listen_socks; i++)
841 if (listen_socks[i] > maxfd)
842 maxfd = listen_socks[i];
843 /* pipes connected to unauthenticated childs */
844 startup_pipes = xmalloc(options.max_startups * sizeof(int));
845 for (i = 0; i < options.max_startups; i++)
846 startup_pipes[i] = -1;
849 * Stay listening for connections until the system crashes or
850 * the daemon is killed with a signal.
857 fdsetsz = howmany(maxfd, NFDBITS) * sizeof(fd_mask);
858 fdset = (fd_set *)xmalloc(fdsetsz);
859 memset(fdset, 0, fdsetsz);
861 for (i = 0; i < num_listen_socks; i++)
862 FD_SET(listen_socks[i], fdset);
863 for (i = 0; i < options.max_startups; i++)
864 if (startup_pipes[i] != -1)
865 FD_SET(startup_pipes[i], fdset);
867 /* Wait in select until there is a connection. */
868 if (select(maxfd + 1, fdset, NULL, NULL, NULL) < 0) {
870 error("select: %.100s", strerror(errno));
873 for (i = 0; i < options.max_startups; i++)
874 if (startup_pipes[i] != -1 &&
875 FD_ISSET(startup_pipes[i], fdset)) {
877 * the read end of the pipe is ready
878 * if the child has closed the pipe
879 * after successfull authentication
880 * or if the child has died
882 close(startup_pipes[i]);
883 startup_pipes[i] = -1;
886 for (i = 0; i < num_listen_socks; i++) {
887 if (!FD_ISSET(listen_socks[i], fdset))
889 fromlen = sizeof(from);
890 newsock = accept(listen_socks[i], (struct sockaddr *)&from,
893 if (errno != EINTR && errno != EWOULDBLOCK)
894 error("accept: %.100s", strerror(errno));
897 if (fcntl(newsock, F_SETFL, 0) < 0) {
898 error("newsock del O_NONBLOCK: %s", strerror(errno));
901 if (drop_connection(startups) == 1) {
902 debug("drop connection #%d", startups);
906 if (pipe(startup_p) == -1) {
911 for (j = 0; j < options.max_startups; j++)
912 if (startup_pipes[j] == -1) {
913 startup_pipes[j] = startup_p[0];
914 if (maxfd < startup_p[0])
915 maxfd = startup_p[0];
921 * Got connection. Fork a child to handle it, unless
922 * we are in debugging mode.
926 * In debugging mode. Close the listening
927 * socket, and start processing the
928 * connection without forking.
930 debug("Server will not fork when running in debugging mode.");
931 close_listen_socks();
939 * Normal production daemon. Fork, and have
940 * the child process the connection. The
941 * parent continues listening.
943 if ((pid = fork()) == 0) {
945 * Child. Close the listening and max_startup
946 * sockets. Start using the accepted socket.
947 * Reinitialize logging (since our pid has
948 * changed). We break out of the loop to handle
951 startup_pipe = startup_p[1];
952 for (j = 0; j < options.max_startups; j++)
953 if (startup_pipes[j] != -1)
954 close(startup_pipes[j]);
955 close_listen_socks();
958 log_init(av0, options.log_level, options.log_facility, log_stderr);
963 /* Parent. Stay in the loop. */
965 error("fork: %.100s", strerror(errno));
967 debug("Forked child %d.", pid);
971 /* Mark that the key has been used (it was "given" to the child). */
976 /* Close the new socket (the child is now taking care of it). */
979 /* child process check (or debug mode) */
980 if (num_listen_socks < 0)
985 /* This is the child processing a new connection. */
988 * Disable the key regeneration alarm. We will not regenerate the
989 * key since we are no longer in a position to give it to anyone. We
990 * will not restart on SIGHUP since it no longer makes sense.
993 signal(SIGALRM, SIG_DFL);
994 signal(SIGHUP, SIG_DFL);
995 signal(SIGTERM, SIG_DFL);
996 signal(SIGQUIT, SIG_DFL);
997 signal(SIGCHLD, SIG_DFL);
998 signal(SIGINT, SIG_DFL);
1001 * Set socket options for the connection. We want the socket to
1002 * close as fast as possible without waiting for anything. If the
1003 * connection is not a socket, these will do nothing.
1005 /* setsockopt(sock_in, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
1007 linger.l_linger = 5;
1008 setsockopt(sock_in, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));
1011 * Register our connection. This turns encryption off because we do
1014 packet_set_connection(sock_in, sock_out);
1016 remote_port = get_remote_port();
1017 remote_ip = get_remote_ipaddr();
1019 /* Check whether logins are denied from this host. */
1021 /* XXX LIBWRAP noes not know about IPv6 */
1023 struct request_info req;
1025 request_init(&req, RQ_DAEMON, av0, RQ_FILE, sock_in, NULL);
1028 if (!hosts_access(&req)) {
1033 /*XXX IPv6 verbose("Connection from %.500s port %d", eval_client(&req), remote_port); */
1035 #endif /* LIBWRAP */
1036 /* Log the connection. */
1037 verbose("Connection from %.500s port %d", remote_ip, remote_port);
1040 * We don\'t want to listen forever unless the other side
1041 * successfully authenticates itself. So we set up an alarm which is
1042 * cleared after successful authentication. A limit of zero
1043 * indicates no limit. Note that we don\'t set the alarm in debugging
1044 * mode; it is just annoying to have the server exit just when you
1045 * are about to discover the bug.
1047 signal(SIGALRM, grace_alarm_handler);
1049 alarm(options.login_grace_time);
1051 sshd_exchange_identification(sock_in, sock_out);
1053 * Check that the connection comes from a privileged port. Rhosts-
1054 * and Rhosts-RSA-Authentication only make sense from priviledged
1055 * programs. Of course, if the intruder has root access on his local
1056 * machine, he can connect from any port. So do not use these
1057 * authentication methods from machines that you do not trust.
1059 if (remote_port >= IPPORT_RESERVED ||
1060 remote_port < IPPORT_RESERVED / 2) {
1061 options.rhosts_authentication = 0;
1062 options.rhosts_rsa_authentication = 0;
1065 if (!packet_connection_is_ipv4() &&
1066 options.kerberos_authentication) {
1067 debug("Kerberos Authentication disabled, only available for IPv4.");
1068 options.kerberos_authentication = 0;
1072 packet_set_nonblocking();
1074 /* perform the key exchange */
1075 /* authenticate user and start session */
1078 do_authentication2();
1081 do_authentication();
1085 /* Cleanup user's ticket cache file. */
1086 if (options.kerberos_ticket_cleanup)
1090 /* The connection has been terminated. */
1091 verbose("Closing connection to %.100s", remote_ip);
1095 #endif /* USE_PAM */
1109 BIGNUM *session_key_int;
1110 unsigned char session_key[SSH_SESSION_KEY_LENGTH];
1111 unsigned char cookie[8];
1112 unsigned int cipher_type, auth_mask, protocol_flags;
1116 * Generate check bytes that the client must send back in the user
1117 * packet in order for it to be accepted; this is used to defy ip
1118 * spoofing attacks. Note that this only works against somebody
1119 * doing IP spoofing from a remote machine; any machine on the local
1120 * network can still see outgoing packets and catch the random
1121 * cookie. This only affects rhosts authentication, and this is one
1122 * of the reasons why it is inherently insecure.
1124 for (i = 0; i < 8; i++) {
1126 rand = arc4random();
1127 cookie[i] = rand & 0xff;
1132 * Send our public key. We include in the packet 64 bits of random
1133 * data that must be matched in the reply in order to prevent IP
1136 packet_start(SSH_SMSG_PUBLIC_KEY);
1137 for (i = 0; i < 8; i++)
1138 packet_put_char(cookie[i]);
1140 /* Store our public server RSA key. */
1141 packet_put_int(BN_num_bits(public_key->n));
1142 packet_put_bignum(public_key->e);
1143 packet_put_bignum(public_key->n);
1145 /* Store our public host RSA key. */
1146 packet_put_int(BN_num_bits(sensitive_data.host_key->n));
1147 packet_put_bignum(sensitive_data.host_key->e);
1148 packet_put_bignum(sensitive_data.host_key->n);
1150 /* Put protocol flags. */
1151 packet_put_int(SSH_PROTOFLAG_HOST_IN_FWD_OPEN);
1153 /* Declare which ciphers we support. */
1154 packet_put_int(cipher_mask1());
1156 /* Declare supported authentication types. */
1158 if (options.rhosts_authentication)
1159 auth_mask |= 1 << SSH_AUTH_RHOSTS;
1160 if (options.rhosts_rsa_authentication)
1161 auth_mask |= 1 << SSH_AUTH_RHOSTS_RSA;
1162 if (options.rsa_authentication)
1163 auth_mask |= 1 << SSH_AUTH_RSA;
1165 if (options.kerberos_authentication)
1166 auth_mask |= 1 << SSH_AUTH_KERBEROS;
1169 if (options.kerberos_tgt_passing)
1170 auth_mask |= 1 << SSH_PASS_KERBEROS_TGT;
1171 if (options.afs_token_passing)
1172 auth_mask |= 1 << SSH_PASS_AFS_TOKEN;
1175 if (options.skey_authentication == 1)
1176 auth_mask |= 1 << SSH_AUTH_TIS;
1178 if (options.password_authentication)
1179 auth_mask |= 1 << SSH_AUTH_PASSWORD;
1180 packet_put_int(auth_mask);
1182 /* Send the packet and wait for it to be sent. */
1184 packet_write_wait();
1186 debug("Sent %d bit public key and %d bit host key.",
1187 BN_num_bits(public_key->n), BN_num_bits(sensitive_data.host_key->n));
1189 /* Read clients reply (cipher type and session key). */
1190 packet_read_expect(&plen, SSH_CMSG_SESSION_KEY);
1192 /* Get cipher type and check whether we accept this. */
1193 cipher_type = packet_get_char();
1195 if (!(cipher_mask() & (1 << cipher_type)))
1196 packet_disconnect("Warning: client selects unsupported cipher.");
1198 /* Get check bytes from the packet. These must match those we
1199 sent earlier with the public key packet. */
1200 for (i = 0; i < 8; i++)
1201 if (cookie[i] != packet_get_char())
1202 packet_disconnect("IP Spoofing check bytes do not match.");
1204 debug("Encryption type: %.200s", cipher_name(cipher_type));
1206 /* Get the encrypted integer. */
1207 session_key_int = BN_new();
1208 packet_get_bignum(session_key_int, &slen);
1210 protocol_flags = packet_get_int();
1211 packet_set_protocol_flags(protocol_flags);
1213 packet_integrity_check(plen, 1 + 8 + slen + 4, SSH_CMSG_SESSION_KEY);
1216 * Decrypt it using our private server key and private host key (key
1217 * with larger modulus first).
1219 if (BN_cmp(sensitive_data.private_key->n, sensitive_data.host_key->n) > 0) {
1220 /* Private key has bigger modulus. */
1221 if (BN_num_bits(sensitive_data.private_key->n) <
1222 BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
1223 fatal("do_connection: %s: private_key %d < host_key %d + SSH_KEY_BITS_RESERVED %d",
1224 get_remote_ipaddr(),
1225 BN_num_bits(sensitive_data.private_key->n),
1226 BN_num_bits(sensitive_data.host_key->n),
1227 SSH_KEY_BITS_RESERVED);
1229 rsa_private_decrypt(session_key_int, session_key_int,
1230 sensitive_data.private_key);
1231 rsa_private_decrypt(session_key_int, session_key_int,
1232 sensitive_data.host_key);
1234 /* Host key has bigger modulus (or they are equal). */
1235 if (BN_num_bits(sensitive_data.host_key->n) <
1236 BN_num_bits(sensitive_data.private_key->n) + SSH_KEY_BITS_RESERVED) {
1237 fatal("do_connection: %s: host_key %d < private_key %d + SSH_KEY_BITS_RESERVED %d",
1238 get_remote_ipaddr(),
1239 BN_num_bits(sensitive_data.host_key->n),
1240 BN_num_bits(sensitive_data.private_key->n),
1241 SSH_KEY_BITS_RESERVED);
1243 rsa_private_decrypt(session_key_int, session_key_int,
1244 sensitive_data.host_key);
1245 rsa_private_decrypt(session_key_int, session_key_int,
1246 sensitive_data.private_key);
1249 compute_session_id(session_id, cookie,
1250 sensitive_data.host_key->n,
1251 sensitive_data.private_key->n);
1253 /* Destroy the private and public keys. They will no longer be needed. */
1254 destroy_sensitive_data();
1257 * Extract session key from the decrypted integer. The key is in the
1258 * least significant 256 bits of the integer; the first byte of the
1259 * key is in the highest bits.
1261 BN_mask_bits(session_key_int, sizeof(session_key) * 8);
1262 len = BN_num_bytes(session_key_int);
1263 if (len < 0 || len > sizeof(session_key))
1264 fatal("do_connection: bad len from %s: session_key_int %d > sizeof(session_key) %d",
1265 get_remote_ipaddr(),
1266 len, (int) sizeof(session_key));
1267 memset(session_key, 0, sizeof(session_key));
1268 BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len);
1270 /* Destroy the decrypted integer. It is no longer needed. */
1271 BN_clear_free(session_key_int);
1273 /* Xor the first 16 bytes of the session key with the session id. */
1274 for (i = 0; i < 16; i++)
1275 session_key[i] ^= session_id[i];
1277 /* Set the session key. From this on all communications will be encrypted. */
1278 packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, cipher_type);
1280 /* Destroy our copy of the session key. It is no longer needed. */
1281 memset(session_key, 0, sizeof(session_key));
1283 debug("Received session key; encryption turned on.");
1285 /* Send an acknowledgement packet. Note that this packet is sent encrypted. */
1286 packet_start(SSH_SMSG_SUCCESS);
1288 packet_write_wait();
1292 * SSH2 key exchange: diffie-hellman-group1-sha1
1297 Buffer *server_kexinit;
1298 Buffer *client_kexinit;
1299 int payload_len, dlen;
1301 unsigned int klen, kout;
1302 unsigned char *signature = NULL;
1303 unsigned char *server_host_key_blob = NULL;
1304 unsigned int sbloblen;
1306 BIGNUM *dh_client_pub = 0;
1307 BIGNUM *shared_secret = 0;
1309 unsigned char *kbuf;
1310 unsigned char *hash;
1312 char *cprop[PROPOSAL_MAX];
1316 if (options.ciphers != NULL) {
1317 myproposal[PROPOSAL_ENC_ALGS_CTOS] =
1318 myproposal[PROPOSAL_ENC_ALGS_STOC] = options.ciphers;
1320 server_kexinit = kex_init(myproposal);
1321 client_kexinit = xmalloc(sizeof(*client_kexinit));
1322 buffer_init(client_kexinit);
1324 /* algorithm negotiation */
1325 kex_exchange_kexinit(server_kexinit, client_kexinit, cprop);
1326 kex = kex_choose_conf(cprop, myproposal, 1);
1327 for (i = 0; i < PROPOSAL_MAX; i++)
1332 debug("Wait SSH2_MSG_KEXDH_INIT.");
1333 packet_read_expect(&payload_len, SSH2_MSG_KEXDH_INIT);
1336 dh_client_pub = BN_new();
1337 if (dh_client_pub == NULL)
1338 fatal("dh_client_pub == NULL");
1339 packet_get_bignum2(dh_client_pub, &dlen);
1342 fprintf(stderr, "\ndh_client_pub= ");
1343 BN_print_fp(stderr, dh_client_pub);
1344 fprintf(stderr, "\n");
1345 debug("bits %d", BN_num_bits(dh_client_pub));
1348 /* generate DH key */
1349 dh = dh_new_group1(); /* XXX depends on 'kex' */
1352 fprintf(stderr, "\np= ");
1353 BN_print_fp(stderr, dh->p);
1354 fprintf(stderr, "\ng= ");
1356 fprintf(stderr, "\npub= ");
1357 BN_print_fp(stderr, dh->pub_key);
1358 fprintf(stderr, "\n");
1359 DHparams_print_fp(stderr, dh);
1361 if (!dh_pub_is_valid(dh, dh_client_pub))
1362 packet_disconnect("bad client public DH value");
1365 kbuf = xmalloc(klen);
1366 kout = DH_compute_key(kbuf, dh_client_pub, dh);
1369 debug("shared secret: len %d/%d", klen, kout);
1370 fprintf(stderr, "shared secret == ");
1371 for (i = 0; i< kout; i++)
1372 fprintf(stderr, "%02x", (kbuf[i])&0xff);
1373 fprintf(stderr, "\n");
1375 shared_secret = BN_new();
1377 BN_bin2bn(kbuf, kout, shared_secret);
1378 memset(kbuf, 0, klen);
1381 /* XXX precompute? */
1382 dsa_make_key_blob(sensitive_data.dsa_host_key, &server_host_key_blob, &sbloblen);
1384 /* calc H */ /* XXX depends on 'kex' */
1386 client_version_string,
1387 server_version_string,
1388 buffer_ptr(client_kexinit), buffer_len(client_kexinit),
1389 buffer_ptr(server_kexinit), buffer_len(server_kexinit),
1390 (char *)server_host_key_blob, sbloblen,
1395 buffer_free(client_kexinit);
1396 buffer_free(server_kexinit);
1397 xfree(client_kexinit);
1398 xfree(server_kexinit);
1400 fprintf(stderr, "hash == ");
1401 for (i = 0; i< 20; i++)
1402 fprintf(stderr, "%02x", (hash[i])&0xff);
1403 fprintf(stderr, "\n");
1405 /* save session id := H */
1406 /* XXX hashlen depends on KEX */
1407 session_id2_len = 20;
1408 session_id2 = xmalloc(session_id2_len);
1409 memcpy(session_id2, hash, session_id2_len);
1412 /* XXX hashlen depends on KEX */
1413 dsa_sign(sensitive_data.dsa_host_key, &signature, &slen, hash, 20);
1415 destroy_sensitive_data();
1417 /* send server hostkey, DH pubkey 'f' and singed H */
1418 packet_start(SSH2_MSG_KEXDH_REPLY);
1419 packet_put_string((char *)server_host_key_blob, sbloblen);
1420 packet_put_bignum2(dh->pub_key); /* f */
1421 packet_put_string((char *)signature, slen);
1424 xfree(server_host_key_blob);
1425 packet_write_wait();
1427 kex_derive_keys(kex, hash, shared_secret);
1428 packet_set_kex(kex);
1430 /* have keys, free DH */
1433 debug("send SSH2_MSG_NEWKEYS.");
1434 packet_start(SSH2_MSG_NEWKEYS);
1436 packet_write_wait();
1437 debug("done: send SSH2_MSG_NEWKEYS.");
1439 debug("Wait SSH2_MSG_NEWKEYS.");
1440 packet_read_expect(&payload_len, SSH2_MSG_NEWKEYS);
1441 debug("GOT SSH2_MSG_NEWKEYS.");
1444 /* send 1st encrypted/maced/compressed message */
1445 packet_start(SSH2_MSG_IGNORE);
1446 packet_put_cstring("markus");
1448 packet_write_wait();
1450 debug("done: KEX2.");