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 1.123 2002/06/09 22:17:21 itojun Exp $");
18 #include <openssl/bn.h>
28 #include "sshconnect.h"
36 char *client_version_string = NULL;
37 char *server_version_string = NULL;
39 extern Options options;
40 extern char *__progname;
42 #ifndef INET6_ADDRSTRLEN /* for non IPv6 machines */
43 #define INET6_ADDRSTRLEN 46
47 sockaddr_ntop(struct sockaddr *sa, socklen_t salen)
49 static char addrbuf[NI_MAXHOST];
51 if (getnameinfo(sa, salen, addrbuf, sizeof(addrbuf), NULL, 0,
53 fatal("sockaddr_ntop: getnameinfo NI_NUMERICHOST failed");
58 * Connect to the given ssh server using a proxy command.
61 ssh_proxy_connect(const char *host, u_short port, struct passwd *pw,
62 const char *proxy_command)
69 char strport[NI_MAXSERV];
71 /* Convert the port number into a string. */
72 snprintf(strport, sizeof strport, "%hu", port);
74 /* Build the final command string in the buffer by making the
75 appropriate substitutions to the given proxy command. */
76 buffer_init(&command);
77 for (cp = proxy_command; *cp; cp++) {
78 if (cp[0] == '%' && cp[1] == '%') {
79 buffer_append(&command, "%", 1);
83 if (cp[0] == '%' && cp[1] == 'h') {
84 buffer_append(&command, host, strlen(host));
88 if (cp[0] == '%' && cp[1] == 'p') {
89 buffer_append(&command, strport, strlen(strport));
93 buffer_append(&command, cp, 1);
95 buffer_append(&command, "\0", 1);
97 /* Get the final command string. */
98 command_string = buffer_ptr(&command);
100 /* Create pipes for communicating with the proxy. */
101 if (pipe(pin) < 0 || pipe(pout) < 0)
102 fatal("Could not create pipes to communicate with the proxy: %.100s",
105 debug("Executing proxy command: %.500s", command_string);
107 /* Fork and execute the proxy command. */
108 if ((pid = fork()) == 0) {
111 /* Child. Permanently give up superuser privileges. */
112 permanently_set_uid(pw);
114 /* Redirect stdin and stdout. */
117 if (dup2(pin[0], 0) < 0)
118 perror("dup2 stdin");
122 if (dup2(pout[1], 1) < 0)
123 perror("dup2 stdout");
124 /* Cannot be 1 because pin allocated two descriptors. */
127 /* Stderr is left as it is so that error messages get
128 printed on the user's terminal. */
129 argv[0] = _PATH_BSHELL;
131 argv[2] = command_string;
134 /* Execute the proxy command. Note that we gave up any
135 extra privileges above. */
136 execv(argv[0], argv);
142 fatal("fork failed: %.100s", strerror(errno));
144 /* Close child side of the descriptors. */
148 /* Free the command name. */
149 buffer_free(&command);
151 /* Set the connection file descriptors. */
152 packet_set_connection(pout[0], pin[1]);
154 /* Indicate OK return */
159 * Creates a (possibly privileged) socket for use as the ssh connection.
162 ssh_create_socket(struct passwd *pw, int privileged, int family)
165 struct addrinfo hints, *res;
168 * If we are running as root and want to connect to a privileged
169 * port, bind our own socket to a privileged port.
172 int p = IPPORT_RESERVED - 1;
173 sock = rresvport_af(&p, family);
175 error("rresvport: af=%d %.100s", family, strerror(errno));
177 debug("Allocated local port %d.", p);
181 * Just create an ordinary socket on arbitrary port. We use
182 * the user's uid to create the socket.
184 temporarily_use_uid(pw);
185 sock = socket(family, SOCK_STREAM, 0);
187 error("socket: %.100s", strerror(errno));
190 /* Bind the socket to an alternative local IP address */
191 if (options.bind_address == NULL)
194 memset(&hints, 0, sizeof(hints));
195 hints.ai_family = family;
196 hints.ai_socktype = SOCK_STREAM;
197 hints.ai_flags = AI_PASSIVE;
198 gaierr = getaddrinfo(options.bind_address, "0", &hints, &res);
200 error("getaddrinfo: %s: %s", options.bind_address,
201 gai_strerror(gaierr));
205 if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
206 error("bind: %s: %s", options.bind_address, strerror(errno));
216 * Opens a TCP/IP connection to the remote server on the given host.
217 * The address of the remote host will be returned in hostaddr.
218 * If port is 0, the default port will be used. If anonymous is zero,
219 * a privileged port will be allocated to make the connection.
220 * This requires super-user privileges if anonymous is false.
221 * Connection_attempts specifies the maximum number of tries (one per
222 * second). If proxy_command is non-NULL, it specifies the command (with %h
223 * and %p substituted for host and port, respectively) to use to contact
227 * ECONNREFUSED if we got a "Connection Refused" by the peer on any address
228 * ECONNABORTED if we failed without a "Connection refused"
229 * Suitable error messages for the connection failure will already have been
233 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
234 u_short port, int family, int connection_attempts,
235 int anonymous, struct passwd *pw, const char *proxy_command)
239 int sock = -1, attempt;
240 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
241 struct addrinfo hints, *ai, *aitop;
242 struct linger linger;
245 * Did we get only other errors than "Connection refused" (which
246 * should block fallback to rsh and similar), or did we get at least
247 * one "Connection refused"?
249 int full_failure = 1;
251 debug("ssh_connect: getuid %u geteuid %u anon %d",
252 (u_int) getuid(), (u_int) geteuid(), anonymous);
254 /* Get default port if port has not been set. */
256 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
258 port = ntohs(sp->s_port);
260 port = SSH_DEFAULT_PORT;
262 /* If a proxy command is given, connect using it. */
263 if (proxy_command != NULL)
264 return ssh_proxy_connect(host, port, pw, proxy_command);
266 /* No proxy command. */
268 memset(&hints, 0, sizeof(hints));
269 hints.ai_family = family;
270 hints.ai_socktype = SOCK_STREAM;
271 snprintf(strport, sizeof strport, "%d", port);
272 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
273 fatal("%s: %.100s: %s", __progname, host,
274 gai_strerror(gaierr));
277 * Try to connect several times. On some machines, the first time
278 * will sometimes fail. In general socket code appears to behave
279 * quite magically on many machines.
281 for (attempt = 0; ;) {
283 debug("Trying again...");
285 /* Loop through addresses for this host, and try each one in
286 sequence until the connection succeeds. */
287 for (ai = aitop; ai; ai = ai->ai_next) {
288 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
290 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
291 ntop, sizeof(ntop), strport, sizeof(strport),
292 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
293 error("ssh_connect: getnameinfo failed");
296 debug("Connecting to %.200s [%.100s] port %s.",
297 host, ntop, strport);
299 /* Create a socket for connecting. */
300 sock = ssh_create_socket(pw,
304 !anonymous && geteuid() == 0,
308 /* Any error is already output */
311 /* Connect to the host. We use the user's uid in the
312 * hope that it will help with tcp_wrappers showing
313 * the remote uid as root.
315 temporarily_use_uid(pw);
316 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
317 /* Successful connection. */
318 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
322 if (errno == ECONNREFUSED)
324 log("ssh: connect to address %s port %s: %s",
325 sockaddr_ntop(ai->ai_addr, ai->ai_addrlen),
326 strport, strerror(errno));
329 * Close the failed socket; there appear to
330 * be some problems when reusing a socket for
331 * which connect() has already returned an
338 break; /* Successful connection. */
341 if (attempt >= connection_attempts)
343 /* Sleep a moment before retrying. */
349 /* Return failure if we didn't get a successful connection. */
350 if (attempt >= connection_attempts)
351 return full_failure ? ECONNABORTED : ECONNREFUSED;
353 debug("Connection established.");
356 * Set socket options. We would like the socket to disappear as soon
357 * as it has been closed for whatever reason.
359 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
362 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger));
364 /* Set keepalives if requested. */
365 if (options.keepalives &&
366 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
368 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
370 /* Set the connection. */
371 packet_set_connection(sock, sock);
377 * Waits for the server identification string, and sends our own
378 * identification string.
381 ssh_exchange_identification(void)
383 char buf[256], remote_version[256]; /* must be same size! */
384 int remote_major, remote_minor, i, mismatch;
385 int connection_in = packet_get_connection_in();
386 int connection_out = packet_get_connection_out();
387 int minor1 = PROTOCOL_MINOR_1;
389 /* Read other side\'s version identification. */
391 for (i = 0; i < sizeof(buf) - 1; i++) {
392 int len = atomicio(read, connection_in, &buf[i], 1);
394 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
396 fatal("ssh_exchange_identification: Connection closed by remote host");
397 if (buf[i] == '\r') {
400 continue; /**XXX wait for \n */
402 if (buf[i] == '\n') {
407 buf[sizeof(buf) - 1] = 0;
408 if (strncmp(buf, "SSH-", 4) == 0)
410 debug("ssh_exchange_identification: %s", buf);
412 server_version_string = xstrdup(buf);
415 * Check that the versions match. In future this might accept
416 * several versions and set appropriate flags to handle them.
418 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
419 &remote_major, &remote_minor, remote_version) != 3)
420 fatal("Bad remote protocol version identification: '%.100s'", buf);
421 debug("Remote protocol version %d.%d, remote software version %.100s",
422 remote_major, remote_minor, remote_version);
424 compat_datafellows(remote_version);
427 switch (remote_major) {
429 if (remote_minor == 99 &&
430 (options.protocol & SSH_PROTO_2) &&
431 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
435 if (!(options.protocol & SSH_PROTO_1)) {
439 if (remote_minor < 3) {
440 fatal("Remote machine has too old SSH software version.");
441 } else if (remote_minor == 3 || remote_minor == 4) {
442 /* We speak 1.3, too. */
445 if (options.forward_agent) {
446 log("Agent forwarding disabled for protocol 1.3");
447 options.forward_agent = 0;
452 if (options.protocol & SSH_PROTO_2) {
462 fatal("Protocol major versions differ: %d vs. %d",
463 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
465 /* Send our own protocol version identification. */
466 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
467 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
468 compat20 ? PROTOCOL_MINOR_2 : minor1,
470 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
471 fatal("write: %.100s", strerror(errno));
472 client_version_string = xstrdup(buf);
473 chop(client_version_string);
474 chop(server_version_string);
475 debug("Local version string %.100s", client_version_string);
478 /* defaults to 'no' */
480 confirm(const char *prompt)
482 const char *msg, *again = "Please type 'yes' or 'no': ";
486 if (options.batch_mode)
488 for (msg = prompt;;msg = again) {
489 p = read_passphrase(msg, RP_ECHO);
491 (p[0] == '\0') || (p[0] == '\n') ||
492 strncasecmp(p, "no", 2) == 0)
494 if (strncasecmp(p, "yes", 3) == 0)
504 * check whether the supplied host key is valid, return -1 if the key
505 * is not valid. the user_hostfile will not be updated if 'readonly' is true.
509 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
510 int readonly, const char *user_hostfile, const char *system_hostfile)
513 char *type = key_type(host_key);
515 char hostline[1000], *hostp, *fp;
516 HostStatus host_status;
517 HostStatus ip_status;
518 int local = 0, host_ip_differ = 0;
520 char ntop[NI_MAXHOST];
522 int len, host_line, ip_line;
523 const char *host_file = NULL, *ip_file = NULL;
526 * Force accepting of the host key for loopback/localhost. The
527 * problem is that if the home directory is NFS-mounted to multiple
528 * machines, localhost will refer to a different machine in each of
529 * them, and the user will get bogus HOST_CHANGED warnings. This
530 * essentially disables host authentication for localhost; however,
531 * this is probably not a real problem.
533 /** hostaddr == 0! */
534 switch (hostaddr->sa_family) {
536 local = (ntohl(((struct sockaddr_in *)hostaddr)->
537 sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
538 salen = sizeof(struct sockaddr_in);
541 local = IN6_IS_ADDR_LOOPBACK(
542 &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
543 salen = sizeof(struct sockaddr_in6);
547 salen = sizeof(struct sockaddr_storage);
550 if (options.no_host_authentication_for_localhost == 1 && local &&
551 options.host_key_alias == NULL) {
552 debug("Forcing accepting of host key for "
553 "loopback/localhost.");
558 * We don't have the remote ip-address for connections
559 * using a proxy command
561 if (options.proxy_command == NULL) {
562 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
563 NULL, 0, NI_NUMERICHOST) != 0)
564 fatal("check_host_key: getnameinfo failed");
567 ip = xstrdup("<no hostip for proxy command>");
570 * Turn off check_host_ip if the connection is to localhost, via proxy
571 * command or if we don't have a hostname to compare with
573 if (options.check_host_ip &&
574 (local || strcmp(host, ip) == 0 || options.proxy_command != NULL))
575 options.check_host_ip = 0;
578 * Allow the user to record the key under a different name. This is
579 * useful for ssh tunneling over forwarded connections or if you run
580 * multiple sshd's on different ports on the same machine.
582 if (options.host_key_alias != NULL) {
583 host = options.host_key_alias;
584 debug("using hostkeyalias: %s", host);
588 * Store the host key from the known host file in here so that we can
589 * compare it with the key for the IP address.
591 file_key = key_new(host_key->type);
594 * Check if the host key is present in the user\'s list of known
595 * hosts or in the systemwide list.
597 host_file = user_hostfile;
598 host_status = check_host_in_hostfile(host_file, host, host_key,
599 file_key, &host_line);
600 if (host_status == HOST_NEW) {
601 host_file = system_hostfile;
602 host_status = check_host_in_hostfile(host_file, host, host_key,
603 file_key, &host_line);
606 * Also perform check for the ip address, skip the check if we are
607 * localhost or the hostname was an ip address to begin with
609 if (options.check_host_ip) {
610 Key *ip_key = key_new(host_key->type);
612 ip_file = user_hostfile;
613 ip_status = check_host_in_hostfile(ip_file, ip, host_key,
615 if (ip_status == HOST_NEW) {
616 ip_file = system_hostfile;
617 ip_status = check_host_in_hostfile(ip_file, ip,
618 host_key, ip_key, &ip_line);
620 if (host_status == HOST_CHANGED &&
621 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
626 ip_status = host_status;
630 switch (host_status) {
632 /* The host is known and the key matches. */
633 debug("Host '%.200s' is known and matches the %s host key.",
635 debug("Found key in %s:%d", host_file, host_line);
636 if (options.check_host_ip && ip_status == HOST_NEW) {
638 log("%s host key for IP address "
639 "'%.128s' not in list of known hosts.",
641 else if (!add_host_to_hostfile(user_hostfile, ip,
643 log("Failed to add the %s host key for IP "
644 "address '%.128s' to the list of known "
645 "hosts (%.30s).", type, ip, user_hostfile);
647 log("Warning: Permanently added the %s host "
648 "key for IP address '%.128s' to the list "
649 "of known hosts.", type, ip);
655 /* The host is new. */
656 if (options.strict_host_key_checking == 1) {
658 * User has requested strict host key checking. We
659 * will not add the host key automatically. The only
660 * alternative left is to abort.
662 error("No %s host key is known for %.200s and you "
663 "have requested strict checking.", type, host);
665 } else if (options.strict_host_key_checking == 2) {
667 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
668 snprintf(msg, sizeof(msg),
669 "The authenticity of host '%.200s (%s)' can't be "
671 "%s key fingerprint is %s.\n"
672 "Are you sure you want to continue connecting "
673 "(yes/no)? ", host, ip, type, fp);
678 if (options.check_host_ip && ip_status == HOST_NEW) {
679 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
685 * If not in strict mode, add the key automatically to the
686 * local known_hosts file.
688 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
689 log("Failed to add the host to the list of known "
690 "hosts (%.500s).", user_hostfile);
692 log("Warning: Permanently added '%.200s' (%s) to the "
693 "list of known hosts.", hostp, type);
696 if (options.check_host_ip && host_ip_differ) {
698 if (ip_status == HOST_NEW)
700 else if (ip_status == HOST_OK)
701 msg = "is unchanged";
703 msg = "has a different value";
704 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
705 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
706 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
707 error("The %s host key for %s has changed,", type, host);
708 error("and the key for the according IP address %s", ip);
709 error("%s. This could either mean that", msg);
710 error("DNS SPOOFING is happening or the IP address for the host");
711 error("and its host key have changed at the same time.");
712 if (ip_status != HOST_NEW)
713 error("Offending key for IP in %s:%d", ip_file, ip_line);
715 /* The host key has changed. */
716 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
717 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
718 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
719 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
720 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
721 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
722 error("It is also possible that the %s host key has just been changed.", type);
723 error("The fingerprint for the %s key sent by the remote host is\n%s.",
725 error("Please contact your system administrator.");
726 error("Add correct host key in %.100s to get rid of this message.",
728 error("Offending key in %s:%d", host_file, host_line);
732 * If strict host key checking is in use, the user will have
733 * to edit the key manually and we can only abort.
735 if (options.strict_host_key_checking) {
736 error("%s host key for %.200s has changed and you have "
737 "requested strict checking.", type, host);
742 * If strict host key checking has not been requested, allow
743 * the connection but without password authentication or
746 if (options.password_authentication) {
747 error("Password authentication is disabled to avoid "
748 "man-in-the-middle attacks.");
749 options.password_authentication = 0;
751 if (options.forward_agent) {
752 error("Agent forwarding is disabled to avoid "
753 "man-in-the-middle attacks.");
754 options.forward_agent = 0;
756 if (options.forward_x11) {
757 error("X11 forwarding is disabled to avoid "
758 "man-in-the-middle attacks.");
759 options.forward_x11 = 0;
761 if (options.num_local_forwards > 0 ||
762 options.num_remote_forwards > 0) {
763 error("Port forwarding is disabled to avoid "
764 "man-in-the-middle attacks.");
765 options.num_local_forwards =
766 options.num_remote_forwards = 0;
769 * XXX Should permit the user to change to use the new id.
770 * This could be done by converting the host key to an
771 * identifying sentence, tell that the host identifies itself
772 * by that sentence, and ask the user if he/she whishes to
773 * accept the authentication.
778 if (options.check_host_ip && host_status != HOST_CHANGED &&
779 ip_status == HOST_CHANGED) {
780 snprintf(msg, sizeof(msg),
781 "Warning: the %s host key for '%.200s' "
782 "differs from the key for the IP address '%.128s'"
783 "\nOffending key for IP in %s:%d",
784 type, host, ip, ip_file, ip_line);
785 if (host_status == HOST_OK) {
787 snprintf(msg + len, sizeof(msg) - len,
788 "\nMatching host key in %s:%d",
789 host_file, host_line);
791 if (options.strict_host_key_checking == 1) {
793 error("Exiting, you have requested strict checking.");
795 } else if (options.strict_host_key_checking == 2) {
796 strlcat(msg, "\nAre you sure you want "
797 "to continue connecting (yes/no)? ", sizeof(msg));
814 verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
818 /* return ok if the key can be found in an old keyfile */
819 if (stat(options.system_hostfile2, &st) == 0 ||
820 stat(options.user_hostfile2, &st) == 0) {
821 if (check_host_key(host, hostaddr, host_key, /*readonly*/ 1,
822 options.user_hostfile2, options.system_hostfile2) == 0)
825 return check_host_key(host, hostaddr, host_key, /*readonly*/ 0,
826 options.user_hostfile, options.system_hostfile);
830 * Starts a dialog with the server, and authenticates the current user on the
831 * server. This does not need any extra privileges. The basic connection
832 * to the server must already have been established before this is called.
833 * If login fails, this function prints an error and never returns.
834 * This function does not require super-user privileges.
837 ssh_login(Sensitive *sensitive, const char *orighost,
838 struct sockaddr *hostaddr, struct passwd *pw)
841 char *server_user, *local_user;
843 local_user = xstrdup(pw->pw_name);
844 server_user = options.user ? options.user : local_user;
846 /* Convert the user-supplied hostname into all lowercase. */
847 host = xstrdup(orighost);
848 for (cp = host; *cp; cp++)
852 /* Exchange protocol version identification strings with the server. */
853 ssh_exchange_identification();
855 /* Put the connection into non-blocking mode. */
856 packet_set_nonblocking();
859 /* authenticate user */
861 ssh_kex2(host, hostaddr);
862 ssh_userauth2(local_user, server_user, host, sensitive);
864 ssh_kex(host, hostaddr);
865 ssh_userauth1(local_user, server_user, host, sensitive);
870 ssh_put_password(char *password)
875 if (datafellows & SSH_BUG_PASSWORDPAD) {
876 packet_put_cstring(password);
879 size = roundup(strlen(password) + 1, 32);
880 padded = xmalloc(size);
881 memset(padded, 0, size);
882 strlcpy(padded, password, size);
883 packet_put_string(padded, size);
884 memset(padded, 0, size);