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 1.124 2002/06/11 04:14:26 markus Exp $");
18 #include <openssl/bn.h>
28 #include "sshconnect.h"
36 char *client_version_string = NULL;
37 char *server_version_string = NULL;
40 extern Options options;
41 extern char *__progname;
42 extern uid_t original_real_uid;
43 extern uid_t original_effective_uid;
45 #ifndef INET6_ADDRSTRLEN /* for non IPv6 machines */
46 #define INET6_ADDRSTRLEN 46
50 sockaddr_ntop(struct sockaddr *sa, socklen_t salen)
52 static char addrbuf[NI_MAXHOST];
54 if (getnameinfo(sa, salen, addrbuf, sizeof(addrbuf), NULL, 0,
56 fatal("sockaddr_ntop: getnameinfo NI_NUMERICHOST failed");
61 * Connect to the given ssh server using a proxy command.
64 ssh_proxy_connect(const char *host, u_short port, const char *proxy_command)
71 char strport[NI_MAXSERV];
73 /* Convert the port number into a string. */
74 snprintf(strport, sizeof strport, "%hu", port);
76 /* Build the final command string in the buffer by making the
77 appropriate substitutions to the given proxy command. */
78 buffer_init(&command);
79 for (cp = proxy_command; *cp; cp++) {
80 if (cp[0] == '%' && cp[1] == '%') {
81 buffer_append(&command, "%", 1);
85 if (cp[0] == '%' && cp[1] == 'h') {
86 buffer_append(&command, host, strlen(host));
90 if (cp[0] == '%' && cp[1] == 'p') {
91 buffer_append(&command, strport, strlen(strport));
95 buffer_append(&command, cp, 1);
97 buffer_append(&command, "\0", 1);
99 /* Get the final command string. */
100 command_string = buffer_ptr(&command);
102 /* Create pipes for communicating with the proxy. */
103 if (pipe(pin) < 0 || pipe(pout) < 0)
104 fatal("Could not create pipes to communicate with the proxy: %.100s",
107 debug("Executing proxy command: %.500s", command_string);
109 /* Fork and execute the proxy command. */
110 if ((pid = fork()) == 0) {
113 /* Child. Permanently give up superuser privileges. */
114 seteuid(original_real_uid);
115 setuid(original_real_uid);
117 /* Redirect stdin and stdout. */
120 if (dup2(pin[0], 0) < 0)
121 perror("dup2 stdin");
125 if (dup2(pout[1], 1) < 0)
126 perror("dup2 stdout");
127 /* Cannot be 1 because pin allocated two descriptors. */
130 /* Stderr is left as it is so that error messages get
131 printed on the user's terminal. */
132 argv[0] = _PATH_BSHELL;
134 argv[2] = command_string;
137 /* Execute the proxy command. Note that we gave up any
138 extra privileges above. */
139 execv(argv[0], argv);
145 fatal("fork failed: %.100s", strerror(errno));
147 /* Close child side of the descriptors. */
151 /* Free the command name. */
152 buffer_free(&command);
154 /* Set the connection file descriptors. */
155 packet_set_connection(pout[0], pin[1]);
157 /* Indicate OK return */
162 * Creates a (possibly privileged) socket for use as the ssh connection.
165 ssh_create_socket(int privileged, int family)
168 struct addrinfo hints, *res;
171 * If we are running as root and want to connect to a privileged
172 * port, bind our own socket to a privileged port.
175 int p = IPPORT_RESERVED - 1;
177 sock = rresvport_af(&p, family);
180 error("rresvport: af=%d %.100s", family, strerror(errno));
182 debug("Allocated local port %d.", p);
185 sock = socket(family, SOCK_STREAM, 0);
187 error("socket: %.100s", strerror(errno));
189 /* Bind the socket to an alternative local IP address */
190 if (options.bind_address == NULL)
193 memset(&hints, 0, sizeof(hints));
194 hints.ai_family = family;
195 hints.ai_socktype = SOCK_STREAM;
196 hints.ai_flags = AI_PASSIVE;
197 gaierr = getaddrinfo(options.bind_address, "0", &hints, &res);
199 error("getaddrinfo: %s: %s", options.bind_address,
200 gai_strerror(gaierr));
204 if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
205 error("bind: %s: %s", options.bind_address, strerror(errno));
215 * Opens a TCP/IP connection to the remote server on the given host.
216 * The address of the remote host will be returned in hostaddr.
217 * If port is 0, the default port will be used. If needpriv is true,
218 * a privileged port will be allocated to make the connection.
219 * This requires super-user privileges if needpriv is true.
220 * Connection_attempts specifies the maximum number of tries (one per
221 * second). If proxy_command is non-NULL, it specifies the command (with %h
222 * and %p substituted for host and port, respectively) to use to contact
226 * ECONNREFUSED if we got a "Connection Refused" by the peer on any address
227 * ECONNABORTED if we failed without a "Connection refused"
228 * Suitable error messages for the connection failure will already have been
232 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
233 u_short port, int family, int connection_attempts,
234 int needpriv, const char *proxy_command)
238 int sock = -1, attempt;
239 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
240 struct addrinfo hints, *ai, *aitop;
241 struct linger linger;
244 * Did we get only other errors than "Connection refused" (which
245 * should block fallback to rsh and similar), or did we get at least
246 * one "Connection refused"?
248 int full_failure = 1;
250 debug("ssh_connect: needpriv %d", needpriv);
252 /* Get default port if port has not been set. */
254 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
256 port = ntohs(sp->s_port);
258 port = SSH_DEFAULT_PORT;
260 /* If a proxy command is given, connect using it. */
261 if (proxy_command != NULL)
262 return ssh_proxy_connect(host, port, proxy_command);
264 /* No proxy command. */
266 memset(&hints, 0, sizeof(hints));
267 hints.ai_family = family;
268 hints.ai_socktype = SOCK_STREAM;
269 snprintf(strport, sizeof strport, "%d", port);
270 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
271 fatal("%s: %.100s: %s", __progname, host,
272 gai_strerror(gaierr));
275 * Try to connect several times. On some machines, the first time
276 * will sometimes fail. In general socket code appears to behave
277 * quite magically on many machines.
279 for (attempt = 0; ;) {
281 debug("Trying again...");
283 /* Loop through addresses for this host, and try each one in
284 sequence until the connection succeeds. */
285 for (ai = aitop; ai; ai = ai->ai_next) {
286 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
288 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
289 ntop, sizeof(ntop), strport, sizeof(strport),
290 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
291 error("ssh_connect: getnameinfo failed");
294 debug("Connecting to %.200s [%.100s] port %s.",
295 host, ntop, strport);
297 /* Create a socket for connecting. */
298 sock = ssh_create_socket(needpriv, ai->ai_family);
300 /* Any error is already output */
303 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
304 /* Successful connection. */
305 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
308 if (errno == ECONNREFUSED)
310 log("ssh: connect to address %s port %s: %s",
311 sockaddr_ntop(ai->ai_addr, ai->ai_addrlen),
312 strport, strerror(errno));
314 * Close the failed socket; there appear to
315 * be some problems when reusing a socket for
316 * which connect() has already returned an
323 break; /* Successful connection. */
326 if (attempt >= connection_attempts)
328 /* Sleep a moment before retrying. */
334 /* Return failure if we didn't get a successful connection. */
335 if (attempt >= connection_attempts)
336 return full_failure ? ECONNABORTED : ECONNREFUSED;
338 debug("Connection established.");
341 * Set socket options. We would like the socket to disappear as soon
342 * as it has been closed for whatever reason.
344 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
347 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger));
349 /* Set keepalives if requested. */
350 if (options.keepalives &&
351 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
353 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
355 /* Set the connection. */
356 packet_set_connection(sock, sock);
362 * Waits for the server identification string, and sends our own
363 * identification string.
366 ssh_exchange_identification(void)
368 char buf[256], remote_version[256]; /* must be same size! */
369 int remote_major, remote_minor, i, mismatch;
370 int connection_in = packet_get_connection_in();
371 int connection_out = packet_get_connection_out();
372 int minor1 = PROTOCOL_MINOR_1;
374 /* Read other side\'s version identification. */
376 for (i = 0; i < sizeof(buf) - 1; i++) {
377 int len = atomicio(read, connection_in, &buf[i], 1);
379 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
381 fatal("ssh_exchange_identification: Connection closed by remote host");
382 if (buf[i] == '\r') {
385 continue; /**XXX wait for \n */
387 if (buf[i] == '\n') {
392 buf[sizeof(buf) - 1] = 0;
393 if (strncmp(buf, "SSH-", 4) == 0)
395 debug("ssh_exchange_identification: %s", buf);
397 server_version_string = xstrdup(buf);
400 * Check that the versions match. In future this might accept
401 * several versions and set appropriate flags to handle them.
403 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
404 &remote_major, &remote_minor, remote_version) != 3)
405 fatal("Bad remote protocol version identification: '%.100s'", buf);
406 debug("Remote protocol version %d.%d, remote software version %.100s",
407 remote_major, remote_minor, remote_version);
409 compat_datafellows(remote_version);
412 switch (remote_major) {
414 if (remote_minor == 99 &&
415 (options.protocol & SSH_PROTO_2) &&
416 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
420 if (!(options.protocol & SSH_PROTO_1)) {
424 if (remote_minor < 3) {
425 fatal("Remote machine has too old SSH software version.");
426 } else if (remote_minor == 3 || remote_minor == 4) {
427 /* We speak 1.3, too. */
430 if (options.forward_agent) {
431 log("Agent forwarding disabled for protocol 1.3");
432 options.forward_agent = 0;
437 if (options.protocol & SSH_PROTO_2) {
447 fatal("Protocol major versions differ: %d vs. %d",
448 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
450 /* Send our own protocol version identification. */
451 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
452 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
453 compat20 ? PROTOCOL_MINOR_2 : minor1,
455 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
456 fatal("write: %.100s", strerror(errno));
457 client_version_string = xstrdup(buf);
458 chop(client_version_string);
459 chop(server_version_string);
460 debug("Local version string %.100s", client_version_string);
463 /* defaults to 'no' */
465 confirm(const char *prompt)
467 const char *msg, *again = "Please type 'yes' or 'no': ";
471 if (options.batch_mode)
473 for (msg = prompt;;msg = again) {
474 p = read_passphrase(msg, RP_ECHO);
476 (p[0] == '\0') || (p[0] == '\n') ||
477 strncasecmp(p, "no", 2) == 0)
479 if (strncasecmp(p, "yes", 3) == 0)
489 * check whether the supplied host key is valid, return -1 if the key
490 * is not valid. the user_hostfile will not be updated if 'readonly' is true.
494 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
495 int readonly, const char *user_hostfile, const char *system_hostfile)
498 char *type = key_type(host_key);
500 char hostline[1000], *hostp, *fp;
501 HostStatus host_status;
502 HostStatus ip_status;
503 int local = 0, host_ip_differ = 0;
505 char ntop[NI_MAXHOST];
507 int len, host_line, ip_line;
508 const char *host_file = NULL, *ip_file = NULL;
511 * Force accepting of the host key for loopback/localhost. The
512 * problem is that if the home directory is NFS-mounted to multiple
513 * machines, localhost will refer to a different machine in each of
514 * them, and the user will get bogus HOST_CHANGED warnings. This
515 * essentially disables host authentication for localhost; however,
516 * this is probably not a real problem.
518 /** hostaddr == 0! */
519 switch (hostaddr->sa_family) {
521 local = (ntohl(((struct sockaddr_in *)hostaddr)->
522 sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
523 salen = sizeof(struct sockaddr_in);
526 local = IN6_IS_ADDR_LOOPBACK(
527 &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
528 salen = sizeof(struct sockaddr_in6);
532 salen = sizeof(struct sockaddr_storage);
535 if (options.no_host_authentication_for_localhost == 1 && local &&
536 options.host_key_alias == NULL) {
537 debug("Forcing accepting of host key for "
538 "loopback/localhost.");
543 * We don't have the remote ip-address for connections
544 * using a proxy command
546 if (options.proxy_command == NULL) {
547 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
548 NULL, 0, NI_NUMERICHOST) != 0)
549 fatal("check_host_key: getnameinfo failed");
552 ip = xstrdup("<no hostip for proxy command>");
555 * Turn off check_host_ip if the connection is to localhost, via proxy
556 * command or if we don't have a hostname to compare with
558 if (options.check_host_ip &&
559 (local || strcmp(host, ip) == 0 || options.proxy_command != NULL))
560 options.check_host_ip = 0;
563 * Allow the user to record the key under a different name. This is
564 * useful for ssh tunneling over forwarded connections or if you run
565 * multiple sshd's on different ports on the same machine.
567 if (options.host_key_alias != NULL) {
568 host = options.host_key_alias;
569 debug("using hostkeyalias: %s", host);
573 * Store the host key from the known host file in here so that we can
574 * compare it with the key for the IP address.
576 file_key = key_new(host_key->type);
579 * Check if the host key is present in the user\'s list of known
580 * hosts or in the systemwide list.
582 host_file = user_hostfile;
583 host_status = check_host_in_hostfile(host_file, host, host_key,
584 file_key, &host_line);
585 if (host_status == HOST_NEW) {
586 host_file = system_hostfile;
587 host_status = check_host_in_hostfile(host_file, host, host_key,
588 file_key, &host_line);
591 * Also perform check for the ip address, skip the check if we are
592 * localhost or the hostname was an ip address to begin with
594 if (options.check_host_ip) {
595 Key *ip_key = key_new(host_key->type);
597 ip_file = user_hostfile;
598 ip_status = check_host_in_hostfile(ip_file, ip, host_key,
600 if (ip_status == HOST_NEW) {
601 ip_file = system_hostfile;
602 ip_status = check_host_in_hostfile(ip_file, ip,
603 host_key, ip_key, &ip_line);
605 if (host_status == HOST_CHANGED &&
606 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
611 ip_status = host_status;
615 switch (host_status) {
617 /* The host is known and the key matches. */
618 debug("Host '%.200s' is known and matches the %s host key.",
620 debug("Found key in %s:%d", host_file, host_line);
621 if (options.check_host_ip && ip_status == HOST_NEW) {
623 log("%s host key for IP address "
624 "'%.128s' not in list of known hosts.",
626 else if (!add_host_to_hostfile(user_hostfile, ip,
628 log("Failed to add the %s host key for IP "
629 "address '%.128s' to the list of known "
630 "hosts (%.30s).", type, ip, user_hostfile);
632 log("Warning: Permanently added the %s host "
633 "key for IP address '%.128s' to the list "
634 "of known hosts.", type, ip);
640 /* The host is new. */
641 if (options.strict_host_key_checking == 1) {
643 * User has requested strict host key checking. We
644 * will not add the host key automatically. The only
645 * alternative left is to abort.
647 error("No %s host key is known for %.200s and you "
648 "have requested strict checking.", type, host);
650 } else if (options.strict_host_key_checking == 2) {
652 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
653 snprintf(msg, sizeof(msg),
654 "The authenticity of host '%.200s (%s)' can't be "
656 "%s key fingerprint is %s.\n"
657 "Are you sure you want to continue connecting "
658 "(yes/no)? ", host, ip, type, fp);
663 if (options.check_host_ip && ip_status == HOST_NEW) {
664 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
670 * If not in strict mode, add the key automatically to the
671 * local known_hosts file.
673 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
674 log("Failed to add the host to the list of known "
675 "hosts (%.500s).", user_hostfile);
677 log("Warning: Permanently added '%.200s' (%s) to the "
678 "list of known hosts.", hostp, type);
681 if (options.check_host_ip && host_ip_differ) {
683 if (ip_status == HOST_NEW)
685 else if (ip_status == HOST_OK)
686 msg = "is unchanged";
688 msg = "has a different value";
689 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
690 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
691 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
692 error("The %s host key for %s has changed,", type, host);
693 error("and the key for the according IP address %s", ip);
694 error("%s. This could either mean that", msg);
695 error("DNS SPOOFING is happening or the IP address for the host");
696 error("and its host key have changed at the same time.");
697 if (ip_status != HOST_NEW)
698 error("Offending key for IP in %s:%d", ip_file, ip_line);
700 /* The host key has changed. */
701 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
702 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
703 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
704 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
705 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
706 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
707 error("It is also possible that the %s host key has just been changed.", type);
708 error("The fingerprint for the %s key sent by the remote host is\n%s.",
710 error("Please contact your system administrator.");
711 error("Add correct host key in %.100s to get rid of this message.",
713 error("Offending key in %s:%d", host_file, host_line);
717 * If strict host key checking is in use, the user will have
718 * to edit the key manually and we can only abort.
720 if (options.strict_host_key_checking) {
721 error("%s host key for %.200s has changed and you have "
722 "requested strict checking.", type, host);
727 * If strict host key checking has not been requested, allow
728 * the connection but without password authentication or
731 if (options.password_authentication) {
732 error("Password authentication is disabled to avoid "
733 "man-in-the-middle attacks.");
734 options.password_authentication = 0;
736 if (options.forward_agent) {
737 error("Agent forwarding is disabled to avoid "
738 "man-in-the-middle attacks.");
739 options.forward_agent = 0;
741 if (options.forward_x11) {
742 error("X11 forwarding is disabled to avoid "
743 "man-in-the-middle attacks.");
744 options.forward_x11 = 0;
746 if (options.num_local_forwards > 0 ||
747 options.num_remote_forwards > 0) {
748 error("Port forwarding is disabled to avoid "
749 "man-in-the-middle attacks.");
750 options.num_local_forwards =
751 options.num_remote_forwards = 0;
754 * XXX Should permit the user to change to use the new id.
755 * This could be done by converting the host key to an
756 * identifying sentence, tell that the host identifies itself
757 * by that sentence, and ask the user if he/she whishes to
758 * accept the authentication.
763 if (options.check_host_ip && host_status != HOST_CHANGED &&
764 ip_status == HOST_CHANGED) {
765 snprintf(msg, sizeof(msg),
766 "Warning: the %s host key for '%.200s' "
767 "differs from the key for the IP address '%.128s'"
768 "\nOffending key for IP in %s:%d",
769 type, host, ip, ip_file, ip_line);
770 if (host_status == HOST_OK) {
772 snprintf(msg + len, sizeof(msg) - len,
773 "\nMatching host key in %s:%d",
774 host_file, host_line);
776 if (options.strict_host_key_checking == 1) {
778 error("Exiting, you have requested strict checking.");
780 } else if (options.strict_host_key_checking == 2) {
781 strlcat(msg, "\nAre you sure you want "
782 "to continue connecting (yes/no)? ", sizeof(msg));
799 verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
803 /* return ok if the key can be found in an old keyfile */
804 if (stat(options.system_hostfile2, &st) == 0 ||
805 stat(options.user_hostfile2, &st) == 0) {
806 if (check_host_key(host, hostaddr, host_key, /*readonly*/ 1,
807 options.user_hostfile2, options.system_hostfile2) == 0)
810 return check_host_key(host, hostaddr, host_key, /*readonly*/ 0,
811 options.user_hostfile, options.system_hostfile);
815 * Starts a dialog with the server, and authenticates the current user on the
816 * server. This does not need any extra privileges. The basic connection
817 * to the server must already have been established before this is called.
818 * If login fails, this function prints an error and never returns.
819 * This function does not require super-user privileges.
822 ssh_login(Sensitive *sensitive, const char *orighost,
823 struct sockaddr *hostaddr, struct passwd *pw)
826 char *server_user, *local_user;
828 local_user = xstrdup(pw->pw_name);
829 server_user = options.user ? options.user : local_user;
831 /* Convert the user-supplied hostname into all lowercase. */
832 host = xstrdup(orighost);
833 for (cp = host; *cp; cp++)
837 /* Exchange protocol version identification strings with the server. */
838 ssh_exchange_identification();
840 /* Put the connection into non-blocking mode. */
841 packet_set_nonblocking();
844 /* authenticate user */
846 ssh_kex2(host, hostaddr);
847 ssh_userauth2(local_user, server_user, host, sensitive);
849 ssh_kex(host, hostaddr);
850 ssh_userauth1(local_user, server_user, host, sensitive);
855 ssh_put_password(char *password)
860 if (datafellows & SSH_BUG_PASSWORDPAD) {
861 packet_put_cstring(password);
864 size = roundup(strlen(password) + 1, 32);
865 padded = xmalloc(size);
866 memset(padded, 0, size);
867 strlcpy(padded, password, size);
868 packet_put_string(padded, size);
869 memset(padded, 0, size);