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 1.131 2002/07/12 13:29:09 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
50 * Connect to the given ssh server using a proxy command.
53 ssh_proxy_connect(const char *host, u_short port, const char *proxy_command)
60 char strport[NI_MAXSERV];
62 /* Convert the port number into a string. */
63 snprintf(strport, sizeof strport, "%hu", port);
65 /* Build the final command string in the buffer by making the
66 appropriate substitutions to the given proxy command. */
67 buffer_init(&command);
68 for (cp = proxy_command; *cp; cp++) {
69 if (cp[0] == '%' && cp[1] == '%') {
70 buffer_append(&command, "%", 1);
74 if (cp[0] == '%' && cp[1] == 'h') {
75 buffer_append(&command, host, strlen(host));
79 if (cp[0] == '%' && cp[1] == 'p') {
80 buffer_append(&command, strport, strlen(strport));
84 buffer_append(&command, cp, 1);
86 buffer_append(&command, "\0", 1);
88 /* Get the final command string. */
89 command_string = buffer_ptr(&command);
91 /* Create pipes for communicating with the proxy. */
92 if (pipe(pin) < 0 || pipe(pout) < 0)
93 fatal("Could not create pipes to communicate with the proxy: %.100s",
96 debug("Executing proxy command: %.500s", command_string);
98 /* Fork and execute the proxy command. */
99 if ((pid = fork()) == 0) {
102 /* Child. Permanently give up superuser privileges. */
103 seteuid(original_real_uid);
104 setuid(original_real_uid);
106 /* Redirect stdin and stdout. */
109 if (dup2(pin[0], 0) < 0)
110 perror("dup2 stdin");
114 if (dup2(pout[1], 1) < 0)
115 perror("dup2 stdout");
116 /* Cannot be 1 because pin allocated two descriptors. */
119 /* Stderr is left as it is so that error messages get
120 printed on the user's terminal. */
121 argv[0] = _PATH_BSHELL;
123 argv[2] = command_string;
126 /* Execute the proxy command. Note that we gave up any
127 extra privileges above. */
128 execv(argv[0], argv);
134 fatal("fork failed: %.100s", strerror(errno));
136 /* Close child side of the descriptors. */
140 /* Free the command name. */
141 buffer_free(&command);
143 /* Set the connection file descriptors. */
144 packet_set_connection(pout[0], pin[1]);
146 /* Indicate OK return */
151 * Creates a (possibly privileged) socket for use as the ssh connection.
154 ssh_create_socket(int privileged, int family)
157 struct addrinfo hints, *res;
160 * If we are running as root and want to connect to a privileged
161 * port, bind our own socket to a privileged port.
164 int p = IPPORT_RESERVED - 1;
166 sock = rresvport_af(&p, family);
169 error("rresvport: af=%d %.100s", family, strerror(errno));
171 debug("Allocated local port %d.", p);
174 sock = socket(family, SOCK_STREAM, 0);
176 error("socket: %.100s", strerror(errno));
178 /* Bind the socket to an alternative local IP address */
179 if (options.bind_address == NULL)
182 memset(&hints, 0, sizeof(hints));
183 hints.ai_family = family;
184 hints.ai_socktype = SOCK_STREAM;
185 hints.ai_flags = AI_PASSIVE;
186 gaierr = getaddrinfo(options.bind_address, "0", &hints, &res);
188 error("getaddrinfo: %s: %s", options.bind_address,
189 gai_strerror(gaierr));
193 if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
194 error("bind: %s: %s", options.bind_address, strerror(errno));
204 * Opens a TCP/IP connection to the remote server on the given host.
205 * The address of the remote host will be returned in hostaddr.
206 * If port is 0, the default port will be used. If needpriv is true,
207 * a privileged port will be allocated to make the connection.
208 * This requires super-user privileges if needpriv is true.
209 * Connection_attempts specifies the maximum number of tries (one per
210 * second). If proxy_command is non-NULL, it specifies the command (with %h
211 * and %p substituted for host and port, respectively) to use to contact
215 * ECONNREFUSED if we got a "Connection Refused" by the peer on any address
216 * ECONNABORTED if we failed without a "Connection refused"
217 * Suitable error messages for the connection failure will already have been
221 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
222 u_short port, int family, int connection_attempts,
223 int needpriv, const char *proxy_command)
227 int sock = -1, attempt;
228 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
229 struct addrinfo hints, *ai, *aitop;
230 struct linger linger;
233 * Did we get only other errors than "Connection refused" (which
234 * should block fallback to rsh and similar), or did we get at least
235 * one "Connection refused"?
237 int full_failure = 1;
239 debug("ssh_connect: needpriv %d", needpriv);
241 /* Get default port if port has not been set. */
243 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
245 port = ntohs(sp->s_port);
247 port = SSH_DEFAULT_PORT;
249 /* If a proxy command is given, connect using it. */
250 if (proxy_command != NULL)
251 return ssh_proxy_connect(host, port, proxy_command);
253 /* No proxy command. */
255 memset(&hints, 0, sizeof(hints));
256 hints.ai_family = family;
257 hints.ai_socktype = SOCK_STREAM;
258 snprintf(strport, sizeof strport, "%u", port);
259 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
260 fatal("%s: %.100s: %s", __progname, host,
261 gai_strerror(gaierr));
264 * Try to connect several times. On some machines, the first time
265 * will sometimes fail. In general socket code appears to behave
266 * quite magically on many machines.
268 for (attempt = 0; ;) {
270 debug("Trying again...");
272 /* Loop through addresses for this host, and try each one in
273 sequence until the connection succeeds. */
274 for (ai = aitop; ai; ai = ai->ai_next) {
275 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
277 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
278 ntop, sizeof(ntop), strport, sizeof(strport),
279 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
280 error("ssh_connect: getnameinfo failed");
283 debug("Connecting to %.200s [%.100s] port %s.",
284 host, ntop, strport);
286 /* Create a socket for connecting. */
287 sock = ssh_create_socket(needpriv, ai->ai_family);
289 /* Any error is already output */
292 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
293 /* Successful connection. */
294 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
297 if (errno == ECONNREFUSED)
299 debug("connect to address %s port %s: %s",
300 ntop, strport, strerror(errno));
302 * Close the failed socket; there appear to
303 * be some problems when reusing a socket for
304 * which connect() has already returned an
311 break; /* Successful connection. */
314 if (attempt >= connection_attempts)
316 /* Sleep a moment before retrying. */
322 /* Return failure if we didn't get a successful connection. */
323 if (attempt >= connection_attempts) {
324 log("ssh: connect to host %s port %s: %s",
325 host, strport, strerror(errno));
326 return full_failure ? ECONNABORTED : ECONNREFUSED;
329 debug("Connection established.");
332 * Set socket options. We would like the socket to disappear as soon
333 * as it has been closed for whatever reason.
335 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
338 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger));
340 /* Set keepalives if requested. */
341 if (options.keepalives &&
342 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
344 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
346 /* Set the connection. */
347 packet_set_connection(sock, sock);
353 * Waits for the server identification string, and sends our own
354 * identification string.
357 ssh_exchange_identification(void)
359 char buf[256], remote_version[256]; /* must be same size! */
360 int remote_major, remote_minor, i, mismatch;
361 int connection_in = packet_get_connection_in();
362 int connection_out = packet_get_connection_out();
363 int minor1 = PROTOCOL_MINOR_1;
365 /* Read other side\'s version identification. */
367 for (i = 0; i < sizeof(buf) - 1; i++) {
368 int len = atomicio(read, connection_in, &buf[i], 1);
370 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
372 fatal("ssh_exchange_identification: Connection closed by remote host");
373 if (buf[i] == '\r') {
376 continue; /**XXX wait for \n */
378 if (buf[i] == '\n') {
383 buf[sizeof(buf) - 1] = 0;
384 if (strncmp(buf, "SSH-", 4) == 0)
386 debug("ssh_exchange_identification: %s", buf);
388 server_version_string = xstrdup(buf);
391 * Check that the versions match. In future this might accept
392 * several versions and set appropriate flags to handle them.
394 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
395 &remote_major, &remote_minor, remote_version) != 3)
396 fatal("Bad remote protocol version identification: '%.100s'", buf);
397 debug("Remote protocol version %d.%d, remote software version %.100s",
398 remote_major, remote_minor, remote_version);
400 compat_datafellows(remote_version);
403 switch (remote_major) {
405 if (remote_minor == 99 &&
406 (options.protocol & SSH_PROTO_2) &&
407 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
411 if (!(options.protocol & SSH_PROTO_1)) {
415 if (remote_minor < 3) {
416 fatal("Remote machine has too old SSH software version.");
417 } else if (remote_minor == 3 || remote_minor == 4) {
418 /* We speak 1.3, too. */
421 if (options.forward_agent) {
422 log("Agent forwarding disabled for protocol 1.3");
423 options.forward_agent = 0;
428 if (options.protocol & SSH_PROTO_2) {
438 fatal("Protocol major versions differ: %d vs. %d",
439 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
441 /* Send our own protocol version identification. */
442 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
443 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
444 compat20 ? PROTOCOL_MINOR_2 : minor1,
446 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
447 fatal("write: %.100s", strerror(errno));
448 client_version_string = xstrdup(buf);
449 chop(client_version_string);
450 chop(server_version_string);
451 debug("Local version string %.100s", client_version_string);
454 /* defaults to 'no' */
456 confirm(const char *prompt)
458 const char *msg, *again = "Please type 'yes' or 'no': ";
462 if (options.batch_mode)
464 for (msg = prompt;;msg = again) {
465 p = read_passphrase(msg, RP_ECHO);
467 (p[0] == '\0') || (p[0] == '\n') ||
468 strncasecmp(p, "no", 2) == 0)
470 if (p && strncasecmp(p, "yes", 3) == 0)
480 * check whether the supplied host key is valid, return -1 if the key
481 * is not valid. the user_hostfile will not be updated if 'readonly' is true.
484 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
485 int readonly, const char *user_hostfile, const char *system_hostfile)
488 char *type = key_type(host_key);
490 char hostline[1000], *hostp, *fp;
491 HostStatus host_status;
492 HostStatus ip_status;
493 int local = 0, host_ip_differ = 0;
495 char ntop[NI_MAXHOST];
497 int len, host_line, ip_line;
498 const char *host_file = NULL, *ip_file = NULL;
501 * Force accepting of the host key for loopback/localhost. The
502 * problem is that if the home directory is NFS-mounted to multiple
503 * machines, localhost will refer to a different machine in each of
504 * them, and the user will get bogus HOST_CHANGED warnings. This
505 * essentially disables host authentication for localhost; however,
506 * this is probably not a real problem.
508 /** hostaddr == 0! */
509 switch (hostaddr->sa_family) {
511 local = (ntohl(((struct sockaddr_in *)hostaddr)->
512 sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
513 salen = sizeof(struct sockaddr_in);
516 local = IN6_IS_ADDR_LOOPBACK(
517 &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
518 salen = sizeof(struct sockaddr_in6);
522 salen = sizeof(struct sockaddr_storage);
525 if (options.no_host_authentication_for_localhost == 1 && local &&
526 options.host_key_alias == NULL) {
527 debug("Forcing accepting of host key for "
528 "loopback/localhost.");
533 * We don't have the remote ip-address for connections
534 * using a proxy command
536 if (options.proxy_command == NULL) {
537 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
538 NULL, 0, NI_NUMERICHOST) != 0)
539 fatal("check_host_key: getnameinfo failed");
542 ip = xstrdup("<no hostip for proxy command>");
545 * Turn off check_host_ip if the connection is to localhost, via proxy
546 * command or if we don't have a hostname to compare with
548 if (options.check_host_ip &&
549 (local || strcmp(host, ip) == 0 || options.proxy_command != NULL))
550 options.check_host_ip = 0;
553 * Allow the user to record the key under a different name. This is
554 * useful for ssh tunneling over forwarded connections or if you run
555 * multiple sshd's on different ports on the same machine.
557 if (options.host_key_alias != NULL) {
558 host = options.host_key_alias;
559 debug("using hostkeyalias: %s", host);
563 * Store the host key from the known host file in here so that we can
564 * compare it with the key for the IP address.
566 file_key = key_new(host_key->type);
569 * Check if the host key is present in the user\'s list of known
570 * hosts or in the systemwide list.
572 host_file = user_hostfile;
573 host_status = check_host_in_hostfile(host_file, host, host_key,
574 file_key, &host_line);
575 if (host_status == HOST_NEW) {
576 host_file = system_hostfile;
577 host_status = check_host_in_hostfile(host_file, host, host_key,
578 file_key, &host_line);
581 * Also perform check for the ip address, skip the check if we are
582 * localhost or the hostname was an ip address to begin with
584 if (options.check_host_ip) {
585 Key *ip_key = key_new(host_key->type);
587 ip_file = user_hostfile;
588 ip_status = check_host_in_hostfile(ip_file, ip, host_key,
590 if (ip_status == HOST_NEW) {
591 ip_file = system_hostfile;
592 ip_status = check_host_in_hostfile(ip_file, ip,
593 host_key, ip_key, &ip_line);
595 if (host_status == HOST_CHANGED &&
596 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
601 ip_status = host_status;
605 switch (host_status) {
607 /* The host is known and the key matches. */
608 debug("Host '%.200s' is known and matches the %s host key.",
610 debug("Found key in %s:%d", host_file, host_line);
611 if (options.check_host_ip && ip_status == HOST_NEW) {
613 log("%s host key for IP address "
614 "'%.128s' not in list of known hosts.",
616 else if (!add_host_to_hostfile(user_hostfile, ip,
618 log("Failed to add the %s host key for IP "
619 "address '%.128s' to the list of known "
620 "hosts (%.30s).", type, ip, user_hostfile);
622 log("Warning: Permanently added the %s host "
623 "key for IP address '%.128s' to the list "
624 "of known hosts.", type, ip);
630 /* The host is new. */
631 if (options.strict_host_key_checking == 1) {
633 * User has requested strict host key checking. We
634 * will not add the host key automatically. The only
635 * alternative left is to abort.
637 error("No %s host key is known for %.200s and you "
638 "have requested strict checking.", type, host);
640 } else if (options.strict_host_key_checking == 2) {
642 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
643 snprintf(msg, sizeof(msg),
644 "The authenticity of host '%.200s (%s)' can't be "
646 "%s key fingerprint is %s.\n"
647 "Are you sure you want to continue connecting "
648 "(yes/no)? ", host, ip, type, fp);
653 if (options.check_host_ip && ip_status == HOST_NEW) {
654 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
660 * If not in strict mode, add the key automatically to the
661 * local known_hosts file.
663 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
664 log("Failed to add the host to the list of known "
665 "hosts (%.500s).", user_hostfile);
667 log("Warning: Permanently added '%.200s' (%s) to the "
668 "list of known hosts.", hostp, type);
671 if (options.check_host_ip && host_ip_differ) {
673 if (ip_status == HOST_NEW)
675 else if (ip_status == HOST_OK)
676 msg = "is unchanged";
678 msg = "has a different value";
679 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
680 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
681 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
682 error("The %s host key for %s has changed,", type, host);
683 error("and the key for the according IP address %s", ip);
684 error("%s. This could either mean that", msg);
685 error("DNS SPOOFING is happening or the IP address for the host");
686 error("and its host key have changed at the same time.");
687 if (ip_status != HOST_NEW)
688 error("Offending key for IP in %s:%d", ip_file, ip_line);
690 /* The host key has changed. */
691 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
692 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
693 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
694 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
695 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
696 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
697 error("It is also possible that the %s host key has just been changed.", type);
698 error("The fingerprint for the %s key sent by the remote host is\n%s.",
700 error("Please contact your system administrator.");
701 error("Add correct host key in %.100s to get rid of this message.",
703 error("Offending key in %s:%d", host_file, host_line);
707 * If strict host key checking is in use, the user will have
708 * to edit the key manually and we can only abort.
710 if (options.strict_host_key_checking) {
711 error("%s host key for %.200s has changed and you have "
712 "requested strict checking.", type, host);
717 * If strict host key checking has not been requested, allow
718 * the connection but without password authentication or
721 if (options.password_authentication) {
722 error("Password authentication is disabled to avoid "
723 "man-in-the-middle attacks.");
724 options.password_authentication = 0;
726 if (options.forward_agent) {
727 error("Agent forwarding is disabled to avoid "
728 "man-in-the-middle attacks.");
729 options.forward_agent = 0;
731 if (options.forward_x11) {
732 error("X11 forwarding is disabled to avoid "
733 "man-in-the-middle attacks.");
734 options.forward_x11 = 0;
736 if (options.num_local_forwards > 0 ||
737 options.num_remote_forwards > 0) {
738 error("Port forwarding is disabled to avoid "
739 "man-in-the-middle attacks.");
740 options.num_local_forwards =
741 options.num_remote_forwards = 0;
744 * XXX Should permit the user to change to use the new id.
745 * This could be done by converting the host key to an
746 * identifying sentence, tell that the host identifies itself
747 * by that sentence, and ask the user if he/she whishes to
748 * accept the authentication.
753 if (options.check_host_ip && host_status != HOST_CHANGED &&
754 ip_status == HOST_CHANGED) {
755 snprintf(msg, sizeof(msg),
756 "Warning: the %s host key for '%.200s' "
757 "differs from the key for the IP address '%.128s'"
758 "\nOffending key for IP in %s:%d",
759 type, host, ip, ip_file, ip_line);
760 if (host_status == HOST_OK) {
762 snprintf(msg + len, sizeof(msg) - len,
763 "\nMatching host key in %s:%d",
764 host_file, host_line);
766 if (options.strict_host_key_checking == 1) {
768 error("Exiting, you have requested strict checking.");
770 } else if (options.strict_host_key_checking == 2) {
771 strlcat(msg, "\nAre you sure you want "
772 "to continue connecting (yes/no)? ", sizeof(msg));
789 verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
793 /* return ok if the key can be found in an old keyfile */
794 if (stat(options.system_hostfile2, &st) == 0 ||
795 stat(options.user_hostfile2, &st) == 0) {
796 if (check_host_key(host, hostaddr, host_key, /*readonly*/ 1,
797 options.user_hostfile2, options.system_hostfile2) == 0)
800 return check_host_key(host, hostaddr, host_key, /*readonly*/ 0,
801 options.user_hostfile, options.system_hostfile);
805 * Starts a dialog with the server, and authenticates the current user on the
806 * server. This does not need any extra privileges. The basic connection
807 * to the server must already have been established before this is called.
808 * If login fails, this function prints an error and never returns.
809 * This function does not require super-user privileges.
812 ssh_login(Sensitive *sensitive, const char *orighost,
813 struct sockaddr *hostaddr, struct passwd *pw)
816 char *server_user, *local_user;
818 local_user = xstrdup(pw->pw_name);
819 server_user = options.user ? options.user : local_user;
821 /* Convert the user-supplied hostname into all lowercase. */
822 host = xstrdup(orighost);
823 for (cp = host; *cp; cp++)
827 /* Exchange protocol version identification strings with the server. */
828 ssh_exchange_identification();
830 /* Put the connection into non-blocking mode. */
831 packet_set_nonblocking();
834 /* authenticate user */
836 ssh_kex2(host, hostaddr);
837 ssh_userauth2(local_user, server_user, host, sensitive);
839 ssh_kex(host, hostaddr);
840 ssh_userauth1(local_user, server_user, host, sensitive);
845 ssh_put_password(char *password)
850 if (datafellows & SSH_BUG_PASSWORDPAD) {
851 packet_put_cstring(password);
854 size = roundup(strlen(password) + 1, 32);
855 padded = xmalloc(size);
856 memset(padded, 0, size);
857 strlcpy(padded, password, size);
858 packet_put_string(padded, size);
859 memset(padded, 0, size);