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 1.129 2002/07/09 12:04:02 itojun 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
51 sockaddr_ntop(struct sockaddr *sa, socklen_t salen)
53 static char addrbuf[NI_MAXHOST];
55 if (getnameinfo(sa, salen, addrbuf, sizeof(addrbuf), NULL, 0,
57 fatal("sockaddr_ntop: getnameinfo NI_NUMERICHOST failed");
63 * Connect to the given ssh server using a proxy command.
66 ssh_proxy_connect(const char *host, u_short port, const char *proxy_command)
73 char strport[NI_MAXSERV];
75 /* Convert the port number into a string. */
76 snprintf(strport, sizeof strport, "%hu", port);
78 /* Build the final command string in the buffer by making the
79 appropriate substitutions to the given proxy command. */
80 buffer_init(&command);
81 for (cp = proxy_command; *cp; cp++) {
82 if (cp[0] == '%' && cp[1] == '%') {
83 buffer_append(&command, "%", 1);
87 if (cp[0] == '%' && cp[1] == 'h') {
88 buffer_append(&command, host, strlen(host));
92 if (cp[0] == '%' && cp[1] == 'p') {
93 buffer_append(&command, strport, strlen(strport));
97 buffer_append(&command, cp, 1);
99 buffer_append(&command, "\0", 1);
101 /* Get the final command string. */
102 command_string = buffer_ptr(&command);
104 /* Create pipes for communicating with the proxy. */
105 if (pipe(pin) < 0 || pipe(pout) < 0)
106 fatal("Could not create pipes to communicate with the proxy: %.100s",
109 debug("Executing proxy command: %.500s", command_string);
111 /* Fork and execute the proxy command. */
112 if ((pid = fork()) == 0) {
115 /* Child. Permanently give up superuser privileges. */
116 seteuid(original_real_uid);
117 setuid(original_real_uid);
119 /* Redirect stdin and stdout. */
122 if (dup2(pin[0], 0) < 0)
123 perror("dup2 stdin");
127 if (dup2(pout[1], 1) < 0)
128 perror("dup2 stdout");
129 /* Cannot be 1 because pin allocated two descriptors. */
132 /* Stderr is left as it is so that error messages get
133 printed on the user's terminal. */
134 argv[0] = _PATH_BSHELL;
136 argv[2] = command_string;
139 /* Execute the proxy command. Note that we gave up any
140 extra privileges above. */
141 execv(argv[0], argv);
147 fatal("fork failed: %.100s", strerror(errno));
149 /* Close child side of the descriptors. */
153 /* Free the command name. */
154 buffer_free(&command);
156 /* Set the connection file descriptors. */
157 packet_set_connection(pout[0], pin[1]);
159 /* Indicate OK return */
164 * Creates a (possibly privileged) socket for use as the ssh connection.
167 ssh_create_socket(int privileged, int family)
170 struct addrinfo hints, *res;
173 * If we are running as root and want to connect to a privileged
174 * port, bind our own socket to a privileged port.
177 int p = IPPORT_RESERVED - 1;
179 sock = rresvport_af(&p, family);
182 error("rresvport: af=%d %.100s", family, strerror(errno));
184 debug("Allocated local port %d.", p);
187 sock = socket(family, SOCK_STREAM, 0);
189 error("socket: %.100s", strerror(errno));
191 /* Bind the socket to an alternative local IP address */
192 if (options.bind_address == NULL)
195 memset(&hints, 0, sizeof(hints));
196 hints.ai_family = family;
197 hints.ai_socktype = SOCK_STREAM;
198 hints.ai_flags = AI_PASSIVE;
199 gaierr = getaddrinfo(options.bind_address, "0", &hints, &res);
201 error("getaddrinfo: %s: %s", options.bind_address,
202 gai_strerror(gaierr));
206 if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
207 error("bind: %s: %s", options.bind_address, strerror(errno));
217 * Opens a TCP/IP connection to the remote server on the given host.
218 * The address of the remote host will be returned in hostaddr.
219 * If port is 0, the default port will be used. If needpriv is true,
220 * a privileged port will be allocated to make the connection.
221 * This requires super-user privileges if needpriv is true.
222 * Connection_attempts specifies the maximum number of tries (one per
223 * second). If proxy_command is non-NULL, it specifies the command (with %h
224 * and %p substituted for host and port, respectively) to use to contact
228 * ECONNREFUSED if we got a "Connection Refused" by the peer on any address
229 * ECONNABORTED if we failed without a "Connection refused"
230 * Suitable error messages for the connection failure will already have been
234 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
235 u_short port, int family, int connection_attempts,
236 int needpriv, const char *proxy_command)
240 int sock = -1, attempt;
241 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
242 struct addrinfo hints, *ai, *aitop;
243 struct linger linger;
246 * Did we get only other errors than "Connection refused" (which
247 * should block fallback to rsh and similar), or did we get at least
248 * one "Connection refused"?
250 int full_failure = 1;
252 debug("ssh_connect: needpriv %d", needpriv);
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, 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, "%u", 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(needpriv, ai->ai_family);
302 /* Any error is already output */
305 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
306 /* Successful connection. */
307 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
310 if (errno == ECONNREFUSED)
313 log("ssh: connect to address %s port %s: %s",
314 sockaddr_ntop(ai->ai_addr, ai->ai_addrlen),
315 strport, strerror(errno));
318 * Close the failed socket; there appear to
319 * be some problems when reusing a socket for
320 * which connect() has already returned an
327 break; /* Successful connection. */
330 if (attempt >= connection_attempts)
332 /* Sleep a moment before retrying. */
338 /* Return failure if we didn't get a successful connection. */
339 if (attempt >= connection_attempts)
340 return full_failure ? ECONNABORTED : ECONNREFUSED;
342 debug("Connection established.");
345 * Set socket options. We would like the socket to disappear as soon
346 * as it has been closed for whatever reason.
348 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
351 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger));
353 /* Set keepalives if requested. */
354 if (options.keepalives &&
355 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
357 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
359 /* Set the connection. */
360 packet_set_connection(sock, sock);
366 * Waits for the server identification string, and sends our own
367 * identification string.
370 ssh_exchange_identification(void)
372 char buf[256], remote_version[256]; /* must be same size! */
373 int remote_major, remote_minor, i, mismatch;
374 int connection_in = packet_get_connection_in();
375 int connection_out = packet_get_connection_out();
376 int minor1 = PROTOCOL_MINOR_1;
378 /* Read other side\'s version identification. */
380 for (i = 0; i < sizeof(buf) - 1; i++) {
381 int len = atomicio(read, connection_in, &buf[i], 1);
383 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
385 fatal("ssh_exchange_identification: Connection closed by remote host");
386 if (buf[i] == '\r') {
389 continue; /**XXX wait for \n */
391 if (buf[i] == '\n') {
396 buf[sizeof(buf) - 1] = 0;
397 if (strncmp(buf, "SSH-", 4) == 0)
399 debug("ssh_exchange_identification: %s", buf);
401 server_version_string = xstrdup(buf);
404 * Check that the versions match. In future this might accept
405 * several versions and set appropriate flags to handle them.
407 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
408 &remote_major, &remote_minor, remote_version) != 3)
409 fatal("Bad remote protocol version identification: '%.100s'", buf);
410 debug("Remote protocol version %d.%d, remote software version %.100s",
411 remote_major, remote_minor, remote_version);
413 compat_datafellows(remote_version);
416 switch (remote_major) {
418 if (remote_minor == 99 &&
419 (options.protocol & SSH_PROTO_2) &&
420 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
424 if (!(options.protocol & SSH_PROTO_1)) {
428 if (remote_minor < 3) {
429 fatal("Remote machine has too old SSH software version.");
430 } else if (remote_minor == 3 || remote_minor == 4) {
431 /* We speak 1.3, too. */
434 if (options.forward_agent) {
435 log("Agent forwarding disabled for protocol 1.3");
436 options.forward_agent = 0;
441 if (options.protocol & SSH_PROTO_2) {
451 fatal("Protocol major versions differ: %d vs. %d",
452 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
454 /* Send our own protocol version identification. */
455 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
456 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
457 compat20 ? PROTOCOL_MINOR_2 : minor1,
459 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
460 fatal("write: %.100s", strerror(errno));
461 client_version_string = xstrdup(buf);
462 chop(client_version_string);
463 chop(server_version_string);
464 debug("Local version string %.100s", client_version_string);
467 /* defaults to 'no' */
469 confirm(const char *prompt)
471 const char *msg, *again = "Please type 'yes' or 'no': ";
475 if (options.batch_mode)
477 for (msg = prompt;;msg = again) {
478 p = read_passphrase(msg, RP_ECHO);
480 (p[0] == '\0') || (p[0] == '\n') ||
481 strncasecmp(p, "no", 2) == 0)
483 if (p && strncasecmp(p, "yes", 3) == 0)
493 * check whether the supplied host key is valid, return -1 if the key
494 * is not valid. the user_hostfile will not be updated if 'readonly' is true.
497 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
498 int readonly, const char *user_hostfile, const char *system_hostfile)
501 char *type = key_type(host_key);
503 char hostline[1000], *hostp, *fp;
504 HostStatus host_status;
505 HostStatus ip_status;
506 int local = 0, host_ip_differ = 0;
508 char ntop[NI_MAXHOST];
510 int len, host_line, ip_line;
511 const char *host_file = NULL, *ip_file = NULL;
514 * Force accepting of the host key for loopback/localhost. The
515 * problem is that if the home directory is NFS-mounted to multiple
516 * machines, localhost will refer to a different machine in each of
517 * them, and the user will get bogus HOST_CHANGED warnings. This
518 * essentially disables host authentication for localhost; however,
519 * this is probably not a real problem.
521 /** hostaddr == 0! */
522 switch (hostaddr->sa_family) {
524 local = (ntohl(((struct sockaddr_in *)hostaddr)->
525 sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
526 salen = sizeof(struct sockaddr_in);
529 local = IN6_IS_ADDR_LOOPBACK(
530 &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
531 salen = sizeof(struct sockaddr_in6);
535 salen = sizeof(struct sockaddr_storage);
538 if (options.no_host_authentication_for_localhost == 1 && local &&
539 options.host_key_alias == NULL) {
540 debug("Forcing accepting of host key for "
541 "loopback/localhost.");
546 * We don't have the remote ip-address for connections
547 * using a proxy command
549 if (options.proxy_command == NULL) {
550 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
551 NULL, 0, NI_NUMERICHOST) != 0)
552 fatal("check_host_key: getnameinfo failed");
555 ip = xstrdup("<no hostip for proxy command>");
558 * Turn off check_host_ip if the connection is to localhost, via proxy
559 * command or if we don't have a hostname to compare with
561 if (options.check_host_ip &&
562 (local || strcmp(host, ip) == 0 || options.proxy_command != NULL))
563 options.check_host_ip = 0;
566 * Allow the user to record the key under a different name. This is
567 * useful for ssh tunneling over forwarded connections or if you run
568 * multiple sshd's on different ports on the same machine.
570 if (options.host_key_alias != NULL) {
571 host = options.host_key_alias;
572 debug("using hostkeyalias: %s", host);
576 * Store the host key from the known host file in here so that we can
577 * compare it with the key for the IP address.
579 file_key = key_new(host_key->type);
582 * Check if the host key is present in the user\'s list of known
583 * hosts or in the systemwide list.
585 host_file = user_hostfile;
586 host_status = check_host_in_hostfile(host_file, host, host_key,
587 file_key, &host_line);
588 if (host_status == HOST_NEW) {
589 host_file = system_hostfile;
590 host_status = check_host_in_hostfile(host_file, host, host_key,
591 file_key, &host_line);
594 * Also perform check for the ip address, skip the check if we are
595 * localhost or the hostname was an ip address to begin with
597 if (options.check_host_ip) {
598 Key *ip_key = key_new(host_key->type);
600 ip_file = user_hostfile;
601 ip_status = check_host_in_hostfile(ip_file, ip, host_key,
603 if (ip_status == HOST_NEW) {
604 ip_file = system_hostfile;
605 ip_status = check_host_in_hostfile(ip_file, ip,
606 host_key, ip_key, &ip_line);
608 if (host_status == HOST_CHANGED &&
609 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
614 ip_status = host_status;
618 switch (host_status) {
620 /* The host is known and the key matches. */
621 debug("Host '%.200s' is known and matches the %s host key.",
623 debug("Found key in %s:%d", host_file, host_line);
624 if (options.check_host_ip && ip_status == HOST_NEW) {
626 log("%s host key for IP address "
627 "'%.128s' not in list of known hosts.",
629 else if (!add_host_to_hostfile(user_hostfile, ip,
631 log("Failed to add the %s host key for IP "
632 "address '%.128s' to the list of known "
633 "hosts (%.30s).", type, ip, user_hostfile);
635 log("Warning: Permanently added the %s host "
636 "key for IP address '%.128s' to the list "
637 "of known hosts.", type, ip);
643 /* The host is new. */
644 if (options.strict_host_key_checking == 1) {
646 * User has requested strict host key checking. We
647 * will not add the host key automatically. The only
648 * alternative left is to abort.
650 error("No %s host key is known for %.200s and you "
651 "have requested strict checking.", type, host);
653 } else if (options.strict_host_key_checking == 2) {
655 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
656 snprintf(msg, sizeof(msg),
657 "The authenticity of host '%.200s (%s)' can't be "
659 "%s key fingerprint is %s.\n"
660 "Are you sure you want to continue connecting "
661 "(yes/no)? ", host, ip, type, fp);
666 if (options.check_host_ip && ip_status == HOST_NEW) {
667 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
673 * If not in strict mode, add the key automatically to the
674 * local known_hosts file.
676 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
677 log("Failed to add the host to the list of known "
678 "hosts (%.500s).", user_hostfile);
680 log("Warning: Permanently added '%.200s' (%s) to the "
681 "list of known hosts.", hostp, type);
684 if (options.check_host_ip && host_ip_differ) {
686 if (ip_status == HOST_NEW)
688 else if (ip_status == HOST_OK)
689 msg = "is unchanged";
691 msg = "has a different value";
692 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
693 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
694 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
695 error("The %s host key for %s has changed,", type, host);
696 error("and the key for the according IP address %s", ip);
697 error("%s. This could either mean that", msg);
698 error("DNS SPOOFING is happening or the IP address for the host");
699 error("and its host key have changed at the same time.");
700 if (ip_status != HOST_NEW)
701 error("Offending key for IP in %s:%d", ip_file, ip_line);
703 /* The host key has changed. */
704 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
705 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
706 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
707 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
708 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
709 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
710 error("It is also possible that the %s host key has just been changed.", type);
711 error("The fingerprint for the %s key sent by the remote host is\n%s.",
713 error("Please contact your system administrator.");
714 error("Add correct host key in %.100s to get rid of this message.",
716 error("Offending key in %s:%d", host_file, host_line);
720 * If strict host key checking is in use, the user will have
721 * to edit the key manually and we can only abort.
723 if (options.strict_host_key_checking) {
724 error("%s host key for %.200s has changed and you have "
725 "requested strict checking.", type, host);
730 * If strict host key checking has not been requested, allow
731 * the connection but without password authentication or
734 if (options.password_authentication) {
735 error("Password authentication is disabled to avoid "
736 "man-in-the-middle attacks.");
737 options.password_authentication = 0;
739 if (options.forward_agent) {
740 error("Agent forwarding is disabled to avoid "
741 "man-in-the-middle attacks.");
742 options.forward_agent = 0;
744 if (options.forward_x11) {
745 error("X11 forwarding is disabled to avoid "
746 "man-in-the-middle attacks.");
747 options.forward_x11 = 0;
749 if (options.num_local_forwards > 0 ||
750 options.num_remote_forwards > 0) {
751 error("Port forwarding is disabled to avoid "
752 "man-in-the-middle attacks.");
753 options.num_local_forwards =
754 options.num_remote_forwards = 0;
757 * XXX Should permit the user to change to use the new id.
758 * This could be done by converting the host key to an
759 * identifying sentence, tell that the host identifies itself
760 * by that sentence, and ask the user if he/she whishes to
761 * accept the authentication.
766 if (options.check_host_ip && host_status != HOST_CHANGED &&
767 ip_status == HOST_CHANGED) {
768 snprintf(msg, sizeof(msg),
769 "Warning: the %s host key for '%.200s' "
770 "differs from the key for the IP address '%.128s'"
771 "\nOffending key for IP in %s:%d",
772 type, host, ip, ip_file, ip_line);
773 if (host_status == HOST_OK) {
775 snprintf(msg + len, sizeof(msg) - len,
776 "\nMatching host key in %s:%d",
777 host_file, host_line);
779 if (options.strict_host_key_checking == 1) {
781 error("Exiting, you have requested strict checking.");
783 } else if (options.strict_host_key_checking == 2) {
784 strlcat(msg, "\nAre you sure you want "
785 "to continue connecting (yes/no)? ", sizeof(msg));
802 verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
806 /* return ok if the key can be found in an old keyfile */
807 if (stat(options.system_hostfile2, &st) == 0 ||
808 stat(options.user_hostfile2, &st) == 0) {
809 if (check_host_key(host, hostaddr, host_key, /*readonly*/ 1,
810 options.user_hostfile2, options.system_hostfile2) == 0)
813 return check_host_key(host, hostaddr, host_key, /*readonly*/ 0,
814 options.user_hostfile, options.system_hostfile);
818 * Starts a dialog with the server, and authenticates the current user on the
819 * server. This does not need any extra privileges. The basic connection
820 * to the server must already have been established before this is called.
821 * If login fails, this function prints an error and never returns.
822 * This function does not require super-user privileges.
825 ssh_login(Sensitive *sensitive, const char *orighost,
826 struct sockaddr *hostaddr, struct passwd *pw)
829 char *server_user, *local_user;
831 local_user = xstrdup(pw->pw_name);
832 server_user = options.user ? options.user : local_user;
834 /* Convert the user-supplied hostname into all lowercase. */
835 host = xstrdup(orighost);
836 for (cp = host; *cp; cp++)
840 /* Exchange protocol version identification strings with the server. */
841 ssh_exchange_identification();
843 /* Put the connection into non-blocking mode. */
844 packet_set_nonblocking();
847 /* authenticate user */
849 ssh_kex2(host, hostaddr);
850 ssh_userauth2(local_user, server_user, host, sensitive);
852 ssh_kex(host, hostaddr);
853 ssh_userauth1(local_user, server_user, host, sensitive);
858 ssh_put_password(char *password)
863 if (datafellows & SSH_BUG_PASSWORDPAD) {
864 packet_put_cstring(password);
867 size = roundup(strlen(password) + 1, 32);
868 padded = xmalloc(size);
869 memset(padded, 0, size);
870 strlcpy(padded, password, size);
871 packet_put_string(padded, size);
872 memset(padded, 0, size);