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 1.93 2001/02/04 15:32:26 stevesk 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, uid_t original_real_uid,
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(original_real_uid);
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(uid_t original_real_uid, int privileged, int family)
153 * If we are running as root and want to connect to a privileged
154 * port, bind our own socket to a privileged port.
157 int p = IPPORT_RESERVED - 1;
158 sock = rresvport_af(&p, family);
160 error("rresvport: af=%d %.100s", family, strerror(errno));
162 debug("Allocated local port %d.", p);
165 * Just create an ordinary socket on arbitrary port. We use
166 * the user's uid to create the socket.
168 temporarily_use_uid(original_real_uid);
169 sock = socket(family, SOCK_STREAM, 0);
171 error("socket: %.100s", strerror(errno));
178 * Opens a TCP/IP connection to the remote server on the given host.
179 * The address of the remote host will be returned in hostaddr.
180 * If port is 0, the default port will be used. If anonymous is zero,
181 * a privileged port will be allocated to make the connection.
182 * This requires super-user privileges if anonymous is false.
183 * Connection_attempts specifies the maximum number of tries (one per
184 * second). If proxy_command is non-NULL, it specifies the command (with %h
185 * and %p substituted for host and port, respectively) to use to contact
189 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
190 u_short port, int connection_attempts,
191 int anonymous, uid_t original_real_uid,
192 const char *proxy_command)
196 int sock = -1, attempt;
197 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
198 struct addrinfo hints, *ai, *aitop;
199 struct linger linger;
202 debug("ssh_connect: getuid %u geteuid %u anon %d",
203 (u_int) getuid(), (u_int) geteuid(), anonymous);
205 /* Get default port if port has not been set. */
207 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
209 port = ntohs(sp->s_port);
211 port = SSH_DEFAULT_PORT;
213 /* If a proxy command is given, connect using it. */
214 if (proxy_command != NULL)
215 return ssh_proxy_connect(host, port, original_real_uid, proxy_command);
217 /* No proxy command. */
219 memset(&hints, 0, sizeof(hints));
220 hints.ai_family = IPv4or6;
221 hints.ai_socktype = SOCK_STREAM;
222 snprintf(strport, sizeof strport, "%d", port);
223 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
224 fatal("%s: %.100s: %s", __progname, host,
225 gai_strerror(gaierr));
228 * Try to connect several times. On some machines, the first time
229 * will sometimes fail. In general socket code appears to behave
230 * quite magically on many machines.
232 for (attempt = 0; attempt < connection_attempts; attempt++) {
234 debug("Trying again...");
236 /* Loop through addresses for this host, and try each one in
237 sequence until the connection succeeds. */
238 for (ai = aitop; ai; ai = ai->ai_next) {
239 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
241 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
242 ntop, sizeof(ntop), strport, sizeof(strport),
243 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
244 error("ssh_connect: getnameinfo failed");
247 debug("Connecting to %.200s [%.100s] port %s.",
248 host, ntop, strport);
250 /* Create a socket for connecting. */
251 sock = ssh_create_socket(original_real_uid,
255 !anonymous && geteuid() == 0,
261 /* Connect to the host. We use the user's uid in the
262 * hope that it will help with tcp_wrappers showing
263 * the remote uid as root.
265 temporarily_use_uid(original_real_uid);
266 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
267 /* Successful connection. */
268 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
272 debug("connect: %.100s", strerror(errno));
275 * Close the failed socket; there appear to
276 * be some problems when reusing a socket for
277 * which connect() has already returned an
280 shutdown(sock, SHUT_RDWR);
285 break; /* Successful connection. */
287 /* Sleep a moment before retrying. */
293 /* Return failure if we didn't get a successful connection. */
294 if (attempt >= connection_attempts)
297 debug("Connection established.");
300 * Set socket options. We would like the socket to disappear as soon
301 * as it has been closed for whatever reason.
303 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
306 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger));
308 /* Set keepalives if requested. */
309 if (options.keepalives &&
310 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
312 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
314 /* Set the connection. */
315 packet_set_connection(sock, sock);
321 * Waits for the server identification string, and sends our own
322 * identification string.
325 ssh_exchange_identification()
327 char buf[256], remote_version[256]; /* must be same size! */
328 int remote_major, remote_minor, i, mismatch;
329 int connection_in = packet_get_connection_in();
330 int connection_out = packet_get_connection_out();
331 int minor1 = PROTOCOL_MINOR_1;
333 /* Read other side\'s version identification. */
335 for (i = 0; i < sizeof(buf) - 1; i++) {
336 int len = atomicio(read, connection_in, &buf[i], 1);
338 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
340 fatal("ssh_exchange_identification: Connection closed by remote host");
341 if (buf[i] == '\r') {
344 continue; /**XXX wait for \n */
346 if (buf[i] == '\n') {
351 buf[sizeof(buf) - 1] = 0;
352 if (strncmp(buf, "SSH-", 4) == 0)
354 debug("ssh_exchange_identification: %s", buf);
356 server_version_string = xstrdup(buf);
359 * Check that the versions match. In future this might accept
360 * several versions and set appropriate flags to handle them.
362 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
363 &remote_major, &remote_minor, remote_version) != 3)
364 fatal("Bad remote protocol version identification: '%.100s'", buf);
365 debug("Remote protocol version %d.%d, remote software version %.100s",
366 remote_major, remote_minor, remote_version);
368 compat_datafellows(remote_version);
371 switch(remote_major) {
373 if (remote_minor == 99 &&
374 (options.protocol & SSH_PROTO_2) &&
375 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
379 if (!(options.protocol & SSH_PROTO_1)) {
383 if (remote_minor < 3) {
384 fatal("Remote machine has too old SSH software version.");
385 } else if (remote_minor == 3 || remote_minor == 4) {
386 /* We speak 1.3, too. */
389 if (options.forward_agent) {
390 log("Agent forwarding disabled for protocol 1.3");
391 options.forward_agent = 0;
396 if (options.protocol & SSH_PROTO_2) {
406 fatal("Protocol major versions differ: %d vs. %d",
407 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
410 packet_set_ssh2_format();
411 /* Send our own protocol version identification. */
412 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
413 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
414 compat20 ? PROTOCOL_MINOR_2 : minor1,
416 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
417 fatal("write: %.100s", strerror(errno));
418 client_version_string = xstrdup(buf);
419 chop(client_version_string);
420 chop(server_version_string);
421 debug("Local version string %.100s", client_version_string);
425 read_yes_or_no(const char *prompt, int defval)
431 if (isatty(STDIN_FILENO))
434 f = fopen("/dev/tty", "rw");
442 fprintf(stderr, "%s", prompt);
443 if (fgets(buf, sizeof(buf), f) == NULL) {
444 /* Print a newline (the prompt probably didn\'t have one). */
445 fprintf(stderr, "\n");
446 strlcpy(buf, "no", sizeof buf);
448 /* Remove newline from response. */
449 if (strchr(buf, '\n'))
450 *strchr(buf, '\n') = 0;
454 if (strcmp(buf, "yes") == 0)
456 else if (strcmp(buf, "no") == 0)
459 fprintf(stderr, "Please type 'yes' or 'no'.\n");
470 * check whether the supplied host key is valid, return only if ok.
474 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
475 const char *user_hostfile, const char *system_hostfile)
478 char *type = key_type(host_key);
480 char hostline[1000], *hostp;
481 HostStatus host_status;
482 HostStatus ip_status;
483 int local = 0, host_ip_differ = 0;
485 char ntop[NI_MAXHOST];
486 int host_line, ip_line;
487 const char *host_file = NULL, *ip_file = NULL;
490 * Force accepting of the host key for loopback/localhost. The
491 * problem is that if the home directory is NFS-mounted to multiple
492 * machines, localhost will refer to a different machine in each of
493 * them, and the user will get bogus HOST_CHANGED warnings. This
494 * essentially disables host authentication for localhost; however,
495 * this is probably not a real problem.
497 /** hostaddr == 0! */
498 switch (hostaddr->sa_family) {
500 local = (ntohl(((struct sockaddr_in *)hostaddr)->sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
501 salen = sizeof(struct sockaddr_in);
504 local = IN6_IS_ADDR_LOOPBACK(&(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
505 salen = sizeof(struct sockaddr_in6);
509 salen = sizeof(struct sockaddr_storage);
512 if (local && options.host_key_alias == NULL) {
513 debug("Forcing accepting of host key for "
514 "loopback/localhost.");
519 * We don't have the remote ip-address for connections
520 * using a proxy command
522 if (options.proxy_command == NULL) {
523 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
524 NULL, 0, NI_NUMERICHOST) != 0)
525 fatal("check_host_key: getnameinfo failed");
528 ip = xstrdup("<no hostip for proxy command>");
531 * Turn off check_host_ip if the connection is to localhost, via proxy
532 * command or if we don't have a hostname to compare with
534 if (options.check_host_ip &&
535 (local || strcmp(host, ip) == 0 || options.proxy_command != NULL))
536 options.check_host_ip = 0;
539 * Allow the user to record the key under a different name. This is
540 * useful for ssh tunneling over forwarded connections or if you run
541 * multiple sshd's on different ports on the same machine.
543 if (options.host_key_alias != NULL) {
544 host = options.host_key_alias;
545 debug("using hostkeyalias: %s", host);
549 * Store the host key from the known host file in here so that we can
550 * compare it with the key for the IP address.
552 file_key = key_new(host_key->type);
555 * Check if the host key is present in the user\'s list of known
556 * hosts or in the systemwide list.
558 host_file = user_hostfile;
559 host_status = check_host_in_hostfile(host_file, host, host_key, file_key, &host_line);
560 if (host_status == HOST_NEW) {
561 host_file = system_hostfile;
562 host_status = check_host_in_hostfile(host_file, host, host_key, file_key, &host_line);
565 * Also perform check for the ip address, skip the check if we are
566 * localhost or the hostname was an ip address to begin with
568 if (options.check_host_ip) {
569 Key *ip_key = key_new(host_key->type);
571 ip_file = user_hostfile;
572 ip_status = check_host_in_hostfile(ip_file, ip, host_key, ip_key, &ip_line);
573 if (ip_status == HOST_NEW) {
574 ip_file = system_hostfile;
575 ip_status = check_host_in_hostfile(ip_file, ip, host_key, ip_key, &ip_line);
577 if (host_status == HOST_CHANGED &&
578 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
583 ip_status = host_status;
587 switch (host_status) {
589 /* The host is known and the key matches. */
590 debug("Host '%.200s' is known and matches the %s host key.",
592 debug("Found key in %s:%d", host_file, host_line);
593 if (options.check_host_ip && ip_status == HOST_NEW) {
594 if (!add_host_to_hostfile(user_hostfile, ip, host_key))
595 log("Failed to add the %s host key for IP address '%.30s' to the list of known hosts (%.30s).",
596 type, ip, user_hostfile);
598 log("Warning: Permanently added the %s host key for IP address '%.30s' to the list of known hosts.",
603 /* The host is new. */
604 if (options.strict_host_key_checking == 1) {
605 /* User has requested strict host key checking. We will not add the host key
606 automatically. The only alternative left is to abort. */
607 fatal("No %s host key is known for %.200s and you have requested strict checking.", type, host);
608 } else if (options.strict_host_key_checking == 2) {
611 snprintf(prompt, sizeof(prompt),
612 "The authenticity of host '%.200s (%s)' can't be established.\n"
613 "%s key fingerprint is %s.\n"
614 "Are you sure you want to continue connecting (yes/no)? ",
615 host, ip, type, key_fingerprint(host_key));
616 if (!read_yes_or_no(prompt, -1))
617 fatal("Aborted by user!\n");
619 if (options.check_host_ip && ip_status == HOST_NEW) {
620 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
625 /* If not in strict mode, add the key automatically to the local known_hosts file. */
626 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
627 log("Failed to add the host to the list of known hosts (%.500s).",
630 log("Warning: Permanently added '%.200s' (%s) to the list of known hosts.",
634 if (options.check_host_ip && host_ip_differ) {
636 if (ip_status == HOST_NEW)
638 else if (ip_status == HOST_OK)
639 msg = "is unchanged";
641 msg = "has a different value";
642 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
643 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
644 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
645 error("The %s host key for %s has changed,", type, host);
646 error("and the key for the according IP address %s", ip);
647 error("%s. This could either mean that", msg);
648 error("DNS SPOOFING is happening or the IP address for the host");
649 error("and its host key have changed at the same time.");
650 if (ip_status != HOST_NEW)
651 error("Offending key for IP in %s:%d", ip_file, ip_line);
653 /* The host key has changed. */
654 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
655 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
656 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
657 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
658 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
659 error("It is also possible that the %s host key has just been changed.", type);
660 error("The fingerprint for the %s key sent by the remote host is\n%s.",
661 type, key_fingerprint(host_key));
662 error("Please contact your system administrator.");
663 error("Add correct host key in %.100s to get rid of this message.",
665 error("Offending key in %s:%d", host_file, host_line);
668 * If strict host key checking is in use, the user will have
669 * to edit the key manually and we can only abort.
671 if (options.strict_host_key_checking)
672 fatal("%s host key for %.200s has changed and you have requested strict checking.", type, host);
675 * If strict host key checking has not been requested, allow
676 * the connection but without password authentication or
679 if (options.password_authentication) {
680 error("Password authentication is disabled to avoid trojan horses.");
681 options.password_authentication = 0;
683 if (options.forward_agent) {
684 error("Agent forwarding is disabled to avoid trojan horses.");
685 options.forward_agent = 0;
687 if (options.forward_x11) {
688 error("X11 forwarding is disabled to avoid trojan horses.");
689 options.forward_x11 = 0;
691 if (options.num_local_forwards > 0 || options.num_remote_forwards > 0) {
692 error("Port forwarding is disabled to avoid trojan horses.");
693 options.num_local_forwards = options.num_remote_forwards = 0;
696 * XXX Should permit the user to change to use the new id.
697 * This could be done by converting the host key to an
698 * identifying sentence, tell that the host identifies itself
699 * by that sentence, and ask the user if he/she whishes to
700 * accept the authentication.
705 if (options.check_host_ip && host_status != HOST_CHANGED &&
706 ip_status == HOST_CHANGED) {
707 log("Warning: the %s host key for '%.200s' "
708 "differs from the key for the IP address '%.30s'",
710 if (host_status == HOST_OK)
711 log("Matching host key in %s:%d", host_file, host_line);
712 log("Offending key for IP in %s:%d", ip_file, ip_line);
713 if (options.strict_host_key_checking == 1) {
714 fatal("Exiting, you have requested strict checking.");
715 } else if (options.strict_host_key_checking == 2) {
716 if (!read_yes_or_no("Are you sure you want " \
717 "to continue connecting (yes/no)? ", -1))
718 fatal("Aborted by user!\n");
726 * Starts a dialog with the server, and authenticates the current user on the
727 * server. This does not need any extra privileges. The basic connection
728 * to the server must already have been established before this is called.
729 * If login fails, this function prints an error and never returns.
730 * This function does not require super-user privileges.
733 ssh_login(int host_key_valid, RSA *own_host_key, const char *orighost,
734 struct sockaddr *hostaddr, uid_t original_real_uid)
738 char *server_user, *local_user;
740 /* Get local user name. Use it as server user if no user name was given. */
741 pw = getpwuid(original_real_uid);
743 fatal("User id %u not found from user database.", original_real_uid);
744 local_user = xstrdup(pw->pw_name);
745 server_user = options.user ? options.user : local_user;
747 /* Convert the user-supplied hostname into all lowercase. */
748 host = xstrdup(orighost);
749 for (cp = host; *cp; cp++)
753 /* Exchange protocol version identification strings with the server. */
754 ssh_exchange_identification();
756 /* Put the connection into non-blocking mode. */
757 packet_set_nonblocking();
760 /* authenticate user */
762 ssh_kex2(host, hostaddr);
763 ssh_userauth2(server_user, host);
765 ssh_kex(host, hostaddr);
766 ssh_userauth(local_user, server_user, host, host_key_valid, own_host_key);