2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * Code to connect to a remote host, and to perform the client side of the
6 * login (authentication) dialog.
8 * As far as I am concerned, the code I have written for this software
9 * can be used freely for any purpose. Any derived versions of this
10 * software must be clearly marked as such, and if the derived work is
11 * incompatible with the protocol description in the RFC file, it must be
12 * called by a name other than "ssh" or "Secure Shell".
16 RCSID("$OpenBSD: sshconnect.c,v 1.109 2001/06/23 15:12:21 itojun Exp $");
18 #include <openssl/bn.h>
28 #include "sshconnect.h"
35 char *client_version_string = NULL;
36 char *server_version_string = NULL;
38 extern Options options;
39 extern char *__progname;
41 /* AF_UNSPEC or AF_INET or AF_INET6 */
45 * Connect to the given ssh server using a proxy command.
48 ssh_proxy_connect(const char *host, u_short port, struct passwd *pw,
49 const char *proxy_command)
56 char strport[NI_MAXSERV];
58 /* Convert the port number into a string. */
59 snprintf(strport, sizeof strport, "%hu", port);
61 /* Build the final command string in the buffer by making the
62 appropriate substitutions to the given proxy command. */
63 buffer_init(&command);
64 for (cp = proxy_command; *cp; cp++) {
65 if (cp[0] == '%' && cp[1] == '%') {
66 buffer_append(&command, "%", 1);
70 if (cp[0] == '%' && cp[1] == 'h') {
71 buffer_append(&command, host, strlen(host));
75 if (cp[0] == '%' && cp[1] == 'p') {
76 buffer_append(&command, strport, strlen(strport));
80 buffer_append(&command, cp, 1);
82 buffer_append(&command, "\0", 1);
84 /* Get the final command string. */
85 command_string = buffer_ptr(&command);
87 /* Create pipes for communicating with the proxy. */
88 if (pipe(pin) < 0 || pipe(pout) < 0)
89 fatal("Could not create pipes to communicate with the proxy: %.100s",
92 debug("Executing proxy command: %.500s", command_string);
94 /* Fork and execute the proxy command. */
95 if ((pid = fork()) == 0) {
98 /* Child. Permanently give up superuser privileges. */
99 permanently_set_uid(pw);
101 /* Redirect stdin and stdout. */
104 if (dup2(pin[0], 0) < 0)
105 perror("dup2 stdin");
109 if (dup2(pout[1], 1) < 0)
110 perror("dup2 stdout");
111 /* Cannot be 1 because pin allocated two descriptors. */
114 /* Stderr is left as it is so that error messages get
115 printed on the user's terminal. */
116 argv[0] = _PATH_BSHELL;
118 argv[2] = command_string;
121 /* Execute the proxy command. Note that we gave up any
122 extra privileges above. */
123 execv(argv[0], argv);
129 fatal("fork failed: %.100s", strerror(errno));
131 /* Close child side of the descriptors. */
135 /* Free the command name. */
136 buffer_free(&command);
138 /* Set the connection file descriptors. */
139 packet_set_connection(pout[0], pin[1]);
145 * Creates a (possibly privileged) socket for use as the ssh connection.
148 ssh_create_socket(struct passwd *pw, int privileged, int family)
151 struct addrinfo hints, *res;
154 * If we are running as root and want to connect to a privileged
155 * port, bind our own socket to a privileged port.
158 int p = IPPORT_RESERVED - 1;
159 sock = rresvport_af(&p, family);
161 error("rresvport: af=%d %.100s", family, strerror(errno));
163 debug("Allocated local port %d.", p);
167 * Just create an ordinary socket on arbitrary port. We use
168 * the user's uid to create the socket.
170 temporarily_use_uid(pw);
171 sock = socket(family, SOCK_STREAM, 0);
173 error("socket: %.100s", strerror(errno));
176 /* Bind the socket to an alternative local IP address */
177 if (options.bind_address == NULL)
180 memset(&hints, 0, sizeof(hints));
181 hints.ai_family = IPv4or6;
182 hints.ai_socktype = SOCK_STREAM;
183 hints.ai_flags = AI_PASSIVE;
184 gaierr = getaddrinfo(options.bind_address, "0", &hints, &res);
186 error("getaddrinfo: %s: %s", options.bind_address,
187 gai_strerror(gaierr));
191 if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
192 error("bind: %s: %s", options.bind_address, strerror(errno));
202 * Opens a TCP/IP connection to the remote server on the given host.
203 * The address of the remote host will be returned in hostaddr.
204 * If port is 0, the default port will be used. If anonymous is zero,
205 * a privileged port will be allocated to make the connection.
206 * This requires super-user privileges if anonymous is false.
207 * Connection_attempts specifies the maximum number of tries (one per
208 * second). If proxy_command is non-NULL, it specifies the command (with %h
209 * and %p substituted for host and port, respectively) to use to contact
213 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
214 u_short port, int connection_attempts,
215 int anonymous, struct passwd *pw,
216 const char *proxy_command)
220 int sock = -1, attempt;
221 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
222 struct addrinfo hints, *ai, *aitop;
223 struct linger linger;
226 debug("ssh_connect: getuid %u geteuid %u anon %d",
227 (u_int) getuid(), (u_int) geteuid(), anonymous);
229 /* Get default port if port has not been set. */
231 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
233 port = ntohs(sp->s_port);
235 port = SSH_DEFAULT_PORT;
237 /* If a proxy command is given, connect using it. */
238 if (proxy_command != NULL)
239 return ssh_proxy_connect(host, port, pw, proxy_command);
241 /* No proxy command. */
243 memset(&hints, 0, sizeof(hints));
244 hints.ai_family = IPv4or6;
245 hints.ai_socktype = SOCK_STREAM;
246 snprintf(strport, sizeof strport, "%d", port);
247 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
248 fatal("%s: %.100s: %s", __progname, host,
249 gai_strerror(gaierr));
252 * Try to connect several times. On some machines, the first time
253 * will sometimes fail. In general socket code appears to behave
254 * quite magically on many machines.
256 for (attempt = 0; attempt < connection_attempts; attempt++) {
258 debug("Trying again...");
260 /* Loop through addresses for this host, and try each one in
261 sequence until the connection succeeds. */
262 for (ai = aitop; ai; ai = ai->ai_next) {
263 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
265 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
266 ntop, sizeof(ntop), strport, sizeof(strport),
267 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
268 error("ssh_connect: getnameinfo failed");
271 debug("Connecting to %.200s [%.100s] port %s.",
272 host, ntop, strport);
274 /* Create a socket for connecting. */
275 sock = ssh_create_socket(pw,
279 !anonymous && geteuid() == 0,
285 /* Connect to the host. We use the user's uid in the
286 * hope that it will help with tcp_wrappers showing
287 * the remote uid as root.
289 temporarily_use_uid(pw);
290 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
291 /* Successful connection. */
292 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
296 debug("connect: %.100s", strerror(errno));
299 * Close the failed socket; there appear to
300 * be some problems when reusing a socket for
301 * which connect() has already returned an
304 shutdown(sock, SHUT_RDWR);
309 break; /* Successful connection. */
311 /* Sleep a moment before retrying. */
317 /* Return failure if we didn't get a successful connection. */
318 if (attempt >= connection_attempts)
321 debug("Connection established.");
324 * Set socket options. We would like the socket to disappear as soon
325 * as it has been closed for whatever reason.
327 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
330 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger));
332 /* Set keepalives if requested. */
333 if (options.keepalives &&
334 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
336 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
338 /* Set the connection. */
339 packet_set_connection(sock, sock);
345 * Waits for the server identification string, and sends our own
346 * identification string.
349 ssh_exchange_identification(void)
351 char buf[256], remote_version[256]; /* must be same size! */
352 int remote_major, remote_minor, i, mismatch;
353 int connection_in = packet_get_connection_in();
354 int connection_out = packet_get_connection_out();
355 int minor1 = PROTOCOL_MINOR_1;
357 /* Read other side\'s version identification. */
359 for (i = 0; i < sizeof(buf) - 1; i++) {
360 int len = atomicio(read, connection_in, &buf[i], 1);
362 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
364 fatal("ssh_exchange_identification: Connection closed by remote host");
365 if (buf[i] == '\r') {
368 continue; /**XXX wait for \n */
370 if (buf[i] == '\n') {
375 buf[sizeof(buf) - 1] = 0;
376 if (strncmp(buf, "SSH-", 4) == 0)
378 debug("ssh_exchange_identification: %s", buf);
380 server_version_string = xstrdup(buf);
383 * Check that the versions match. In future this might accept
384 * several versions and set appropriate flags to handle them.
386 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
387 &remote_major, &remote_minor, remote_version) != 3)
388 fatal("Bad remote protocol version identification: '%.100s'", buf);
389 debug("Remote protocol version %d.%d, remote software version %.100s",
390 remote_major, remote_minor, remote_version);
392 compat_datafellows(remote_version);
395 switch(remote_major) {
397 if (remote_minor == 99 &&
398 (options.protocol & SSH_PROTO_2) &&
399 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
403 if (!(options.protocol & SSH_PROTO_1)) {
407 if (remote_minor < 3) {
408 fatal("Remote machine has too old SSH software version.");
409 } else if (remote_minor == 3 || remote_minor == 4) {
410 /* We speak 1.3, too. */
413 if (options.forward_agent) {
414 log("Agent forwarding disabled for protocol 1.3");
415 options.forward_agent = 0;
420 if (options.protocol & SSH_PROTO_2) {
430 fatal("Protocol major versions differ: %d vs. %d",
431 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
433 /* Send our own protocol version identification. */
434 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
435 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
436 compat20 ? PROTOCOL_MINOR_2 : minor1,
438 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
439 fatal("write: %.100s", strerror(errno));
440 client_version_string = xstrdup(buf);
441 chop(client_version_string);
442 chop(server_version_string);
443 debug("Local version string %.100s", client_version_string);
446 /* defaults to 'no' */
448 read_yes_or_no(const char *prompt, int defval)
454 if (options.batch_mode)
457 if (isatty(STDIN_FILENO))
460 f = fopen(_PATH_TTY, "rw");
468 fprintf(stderr, "%s", prompt);
469 if (fgets(buf, sizeof(buf), f) == NULL) {
471 * Print a newline (the prompt probably didn\'t have
474 fprintf(stderr, "\n");
475 strlcpy(buf, "no", sizeof buf);
477 /* Remove newline from response. */
478 if (strchr(buf, '\n'))
479 *strchr(buf, '\n') = 0;
483 if (strcmp(buf, "yes") == 0)
485 else if (strcmp(buf, "no") == 0)
488 fprintf(stderr, "Please type 'yes' or 'no'.\n");
499 * check whether the supplied host key is valid, return -1 if the key
500 * is not valid. the user_hostfile will not be updated if 'readonly' is true.
504 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
505 int readonly, const char *user_hostfile, const char *system_hostfile)
508 char *type = key_type(host_key);
510 char hostline[1000], *hostp, *fp;
511 HostStatus host_status;
512 HostStatus ip_status;
513 int local = 0, host_ip_differ = 0;
515 char ntop[NI_MAXHOST];
516 int host_line, ip_line;
517 const char *host_file = NULL, *ip_file = NULL;
520 * Force accepting of the host key for loopback/localhost. The
521 * problem is that if the home directory is NFS-mounted to multiple
522 * machines, localhost will refer to a different machine in each of
523 * them, and the user will get bogus HOST_CHANGED warnings. This
524 * essentially disables host authentication for localhost; however,
525 * this is probably not a real problem.
527 /** hostaddr == 0! */
528 switch (hostaddr->sa_family) {
530 local = (ntohl(((struct sockaddr_in *)hostaddr)->
531 sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
532 salen = sizeof(struct sockaddr_in);
535 local = IN6_IS_ADDR_LOOPBACK(
536 &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
537 salen = sizeof(struct sockaddr_in6);
541 salen = sizeof(struct sockaddr_storage);
544 if (local && options.host_key_alias == NULL) {
545 debug("Forcing accepting of host key for "
546 "loopback/localhost.");
551 * We don't have the remote ip-address for connections
552 * using a proxy command
554 if (options.proxy_command == NULL) {
555 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
556 NULL, 0, NI_NUMERICHOST) != 0)
557 fatal("check_host_key: getnameinfo failed");
560 ip = xstrdup("<no hostip for proxy command>");
563 * Turn off check_host_ip if the connection is to localhost, via proxy
564 * command or if we don't have a hostname to compare with
566 if (options.check_host_ip &&
567 (local || strcmp(host, ip) == 0 || options.proxy_command != NULL))
568 options.check_host_ip = 0;
571 * Allow the user to record the key under a different name. This is
572 * useful for ssh tunneling over forwarded connections or if you run
573 * multiple sshd's on different ports on the same machine.
575 if (options.host_key_alias != NULL) {
576 host = options.host_key_alias;
577 debug("using hostkeyalias: %s", host);
581 * Store the host key from the known host file in here so that we can
582 * compare it with the key for the IP address.
584 file_key = key_new(host_key->type);
587 * Check if the host key is present in the user\'s list of known
588 * hosts or in the systemwide list.
590 host_file = user_hostfile;
591 host_status = check_host_in_hostfile(host_file, host, host_key,
592 file_key, &host_line);
593 if (host_status == HOST_NEW) {
594 host_file = system_hostfile;
595 host_status = check_host_in_hostfile(host_file, host, host_key,
596 file_key, &host_line);
599 * Also perform check for the ip address, skip the check if we are
600 * localhost or the hostname was an ip address to begin with
602 if (options.check_host_ip) {
603 Key *ip_key = key_new(host_key->type);
605 ip_file = user_hostfile;
606 ip_status = check_host_in_hostfile(ip_file, ip, host_key,
608 if (ip_status == HOST_NEW) {
609 ip_file = system_hostfile;
610 ip_status = check_host_in_hostfile(ip_file, ip,
611 host_key, ip_key, &ip_line);
613 if (host_status == HOST_CHANGED &&
614 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
619 ip_status = host_status;
623 switch (host_status) {
625 /* The host is known and the key matches. */
626 debug("Host '%.200s' is known and matches the %s host key.",
628 debug("Found key in %s:%d", host_file, host_line);
629 if (options.check_host_ip && ip_status == HOST_NEW) {
631 log("%s host key for IP address "
632 "'%.128s' not in list of known hosts.",
634 else if (!add_host_to_hostfile(user_hostfile, ip,
636 log("Failed to add the %s host key for IP "
637 "address '%.128s' to the list of known "
638 "hosts (%.30s).", type, ip, user_hostfile);
640 log("Warning: Permanently added the %s host "
641 "key for IP address '%.128s' to the list "
642 "of known hosts.", type, ip);
648 /* The host is new. */
649 if (options.strict_host_key_checking == 1) {
651 * User has requested strict host key checking. We
652 * will not add the host key automatically. The only
653 * alternative left is to abort.
655 error("No %s host key is known for %.200s and you "
656 "have requested strict checking.", type, host);
658 } else if (options.strict_host_key_checking == 2) {
661 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
662 snprintf(prompt, sizeof(prompt),
663 "The authenticity of host '%.200s (%s)' can't be "
665 "%s key fingerprint is %s.\n"
666 "Are you sure you want to continue connecting "
667 "(yes/no)? ", host, ip, type, fp);
669 if (!read_yes_or_no(prompt, -1)) {
670 log("Aborted by user!");
674 if (options.check_host_ip && ip_status == HOST_NEW) {
675 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
681 * If not in strict mode, add the key automatically to the
682 * local known_hosts file.
684 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
685 log("Failed to add the host to the list of known "
686 "hosts (%.500s).", user_hostfile);
688 log("Warning: Permanently added '%.200s' (%s) to the "
689 "list of known hosts.", hostp, type);
692 if (options.check_host_ip && host_ip_differ) {
694 if (ip_status == HOST_NEW)
696 else if (ip_status == HOST_OK)
697 msg = "is unchanged";
699 msg = "has a different value";
700 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
701 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
702 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
703 error("The %s host key for %s has changed,", type, host);
704 error("and the key for the according IP address %s", ip);
705 error("%s. This could either mean that", msg);
706 error("DNS SPOOFING is happening or the IP address for the host");
707 error("and its host key have changed at the same time.");
708 if (ip_status != HOST_NEW)
709 error("Offending key for IP in %s:%d", ip_file, ip_line);
711 /* The host key has changed. */
712 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
713 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
714 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
715 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
716 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
717 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
718 error("It is also possible that the %s host key has just been changed.", type);
719 error("The fingerprint for the %s key sent by the remote host is\n%s.",
721 error("Please contact your system administrator.");
722 error("Add correct host key in %.100s to get rid of this message.",
724 error("Offending key in %s:%d", host_file, host_line);
728 * If strict host key checking is in use, the user will have
729 * to edit the key manually and we can only abort.
731 if (options.strict_host_key_checking) {
732 error("%s host key for %.200s has changed and you have "
733 "requested strict checking.", type, host);
738 * If strict host key checking has not been requested, allow
739 * the connection but without password authentication or
742 if (options.password_authentication) {
743 error("Password authentication is disabled to avoid "
744 "man-in-the-middle attacks.");
745 options.password_authentication = 0;
747 if (options.forward_agent) {
748 error("Agent forwarding is disabled to avoid "
749 "man-in-the-middle attacks.");
750 options.forward_agent = 0;
752 if (options.forward_x11) {
753 error("X11 forwarding is disabled to avoid "
754 "man-in-the-middle attacks.");
755 options.forward_x11 = 0;
757 if (options.num_local_forwards > 0 ||
758 options.num_remote_forwards > 0) {
759 error("Port forwarding is disabled to avoid "
760 "man-in-the-middle attacks.");
761 options.num_local_forwards =
762 options.num_remote_forwards = 0;
765 * XXX Should permit the user to change to use the new id.
766 * This could be done by converting the host key to an
767 * identifying sentence, tell that the host identifies itself
768 * by that sentence, and ask the user if he/she whishes to
769 * accept the authentication.
774 if (options.check_host_ip && host_status != HOST_CHANGED &&
775 ip_status == HOST_CHANGED) {
776 log("Warning: the %s host key for '%.200s' "
777 "differs from the key for the IP address '%.128s'",
779 if (host_status == HOST_OK)
780 log("Matching host key in %s:%d", host_file, host_line);
781 log("Offending key for IP in %s:%d", ip_file, ip_line);
782 if (options.strict_host_key_checking == 1) {
783 error("Exiting, you have requested strict checking.");
785 } else if (options.strict_host_key_checking == 2) {
786 if (!read_yes_or_no("Are you sure you want "
787 "to continue connecting (yes/no)? ", -1)) {
788 log("Aborted by user!");
803 verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
807 /* return ok if the key can be found in an old keyfile */
808 if (stat(options.system_hostfile2, &st) == 0 ||
809 stat(options.user_hostfile2, &st) == 0) {
810 if (check_host_key(host, hostaddr, host_key, /*readonly*/ 1,
811 options.user_hostfile2, options.system_hostfile2) == 0)
814 return check_host_key(host, hostaddr, host_key, /*readonly*/ 0,
815 options.user_hostfile, options.system_hostfile);
819 * Starts a dialog with the server, and authenticates the current user on the
820 * server. This does not need any extra privileges. The basic connection
821 * to the server must already have been established before this is called.
822 * If login fails, this function prints an error and never returns.
823 * This function does not require super-user privileges.
826 ssh_login(Key **keys, int nkeys, const char *orighost,
827 struct sockaddr *hostaddr, struct passwd *pw)
830 char *server_user, *local_user;
832 local_user = xstrdup(pw->pw_name);
833 server_user = options.user ? options.user : local_user;
835 /* Convert the user-supplied hostname into all lowercase. */
836 host = xstrdup(orighost);
837 for (cp = host; *cp; cp++)
841 /* Exchange protocol version identification strings with the server. */
842 ssh_exchange_identification();
844 /* Put the connection into non-blocking mode. */
845 packet_set_nonblocking();
848 /* authenticate user */
850 ssh_kex2(host, hostaddr);
851 ssh_userauth2(local_user, server_user, host, keys, nkeys);
853 ssh_kex(host, hostaddr);
854 ssh_userauth1(local_user, server_user, host, keys, nkeys);
859 ssh_put_password(char *password)
864 if (datafellows & SSH_BUG_PASSWORDPAD) {
865 packet_put_cstring(password);
868 size = roundup(strlen(password) + 1, 32);
869 padded = xmalloc(size);
870 memset(padded, 0, size);
871 strlcpy(padded, password, size);
872 packet_put_string(padded, size);
873 memset(padded, 0, size);