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 1.90 2001/01/13 18:32:50 markus Exp $");
18 #include <openssl/bn.h>
19 #include <openssl/dsa.h>
20 #include <openssl/rsa.h>
31 #include "sshconnect.h"
34 char *client_version_string = NULL;
35 char *server_version_string = NULL;
37 extern Options options;
38 extern char *__progname;
41 * Connect to the given ssh server using a proxy command.
44 ssh_proxy_connect(const char *host, u_short port, uid_t original_real_uid,
45 const char *proxy_command)
52 char strport[NI_MAXSERV];
54 /* Convert the port number into a string. */
55 snprintf(strport, sizeof strport, "%hu", port);
57 /* Build the final command string in the buffer by making the
58 appropriate substitutions to the given proxy command. */
59 buffer_init(&command);
60 for (cp = proxy_command; *cp; cp++) {
61 if (cp[0] == '%' && cp[1] == '%') {
62 buffer_append(&command, "%", 1);
66 if (cp[0] == '%' && cp[1] == 'h') {
67 buffer_append(&command, host, strlen(host));
71 if (cp[0] == '%' && cp[1] == 'p') {
72 buffer_append(&command, strport, strlen(strport));
76 buffer_append(&command, cp, 1);
78 buffer_append(&command, "\0", 1);
80 /* Get the final command string. */
81 command_string = buffer_ptr(&command);
83 /* Create pipes for communicating with the proxy. */
84 if (pipe(pin) < 0 || pipe(pout) < 0)
85 fatal("Could not create pipes to communicate with the proxy: %.100s",
88 debug("Executing proxy command: %.500s", command_string);
90 /* Fork and execute the proxy command. */
91 if ((pid = fork()) == 0) {
94 /* Child. Permanently give up superuser privileges. */
95 permanently_set_uid(original_real_uid);
97 /* Redirect stdin and stdout. */
100 if (dup2(pin[0], 0) < 0)
101 perror("dup2 stdin");
105 if (dup2(pout[1], 1) < 0)
106 perror("dup2 stdout");
107 /* Cannot be 1 because pin allocated two descriptors. */
110 /* Stderr is left as it is so that error messages get
111 printed on the user's terminal. */
112 argv[0] = _PATH_BSHELL;
114 argv[2] = command_string;
117 /* Execute the proxy command. Note that we gave up any
118 extra privileges above. */
119 execv(argv[0], argv);
125 fatal("fork failed: %.100s", strerror(errno));
127 /* Close child side of the descriptors. */
131 /* Free the command name. */
132 buffer_free(&command);
134 /* Set the connection file descriptors. */
135 packet_set_connection(pout[0], pin[1]);
141 * Creates a (possibly privileged) socket for use as the ssh connection.
144 ssh_create_socket(uid_t original_real_uid, int privileged, int family)
149 * If we are running as root and want to connect to a privileged
150 * port, bind our own socket to a privileged port.
153 int p = IPPORT_RESERVED - 1;
154 sock = rresvport_af(&p, family);
156 error("rresvport: af=%d %.100s", family, strerror(errno));
158 debug("Allocated local port %d.", p);
161 * Just create an ordinary socket on arbitrary port. We use
162 * the user's uid to create the socket.
164 temporarily_use_uid(original_real_uid);
165 sock = socket(family, SOCK_STREAM, 0);
167 error("socket: %.100s", strerror(errno));
174 * Opens a TCP/IP connection to the remote server on the given host.
175 * The address of the remote host will be returned in hostaddr.
176 * If port is 0, the default port will be used. If anonymous is zero,
177 * a privileged port will be allocated to make the connection.
178 * This requires super-user privileges if anonymous is false.
179 * Connection_attempts specifies the maximum number of tries (one per
180 * second). If proxy_command is non-NULL, it specifies the command (with %h
181 * and %p substituted for host and port, respectively) to use to contact
185 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
186 u_short port, int connection_attempts,
187 int anonymous, uid_t original_real_uid,
188 const char *proxy_command)
192 int sock = -1, attempt;
193 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
194 struct addrinfo hints, *ai, *aitop;
195 struct linger linger;
198 debug("ssh_connect: getuid %u geteuid %u anon %d",
199 (u_int) getuid(), (u_int) geteuid(), anonymous);
201 /* Get default port if port has not been set. */
203 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
205 port = ntohs(sp->s_port);
207 port = SSH_DEFAULT_PORT;
209 /* If a proxy command is given, connect using it. */
210 if (proxy_command != NULL)
211 return ssh_proxy_connect(host, port, original_real_uid, proxy_command);
213 /* No proxy command. */
215 memset(&hints, 0, sizeof(hints));
216 hints.ai_family = IPv4or6;
217 hints.ai_socktype = SOCK_STREAM;
218 snprintf(strport, sizeof strport, "%d", port);
219 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
220 fatal("%s: %.100s: %s", __progname, host,
221 gai_strerror(gaierr));
224 * Try to connect several times. On some machines, the first time
225 * will sometimes fail. In general socket code appears to behave
226 * quite magically on many machines.
228 for (attempt = 0; attempt < connection_attempts; attempt++) {
230 debug("Trying again...");
232 /* Loop through addresses for this host, and try each one in
233 sequence until the connection succeeds. */
234 for (ai = aitop; ai; ai = ai->ai_next) {
235 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
237 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
238 ntop, sizeof(ntop), strport, sizeof(strport),
239 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
240 error("ssh_connect: getnameinfo failed");
243 debug("Connecting to %.200s [%.100s] port %s.",
244 host, ntop, strport);
246 /* Create a socket for connecting. */
247 sock = ssh_create_socket(original_real_uid,
251 !anonymous && geteuid() == 0,
257 /* Connect to the host. We use the user's uid in the
258 * hope that it will help with tcp_wrappers showing
259 * the remote uid as root.
261 temporarily_use_uid(original_real_uid);
262 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
263 /* Successful connection. */
264 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
268 debug("connect: %.100s", strerror(errno));
271 * Close the failed socket; there appear to
272 * be some problems when reusing a socket for
273 * which connect() has already returned an
276 shutdown(sock, SHUT_RDWR);
281 break; /* Successful connection. */
283 /* Sleep a moment before retrying. */
289 /* Return failure if we didn't get a successful connection. */
290 if (attempt >= connection_attempts)
293 debug("Connection established.");
296 * Set socket options. We would like the socket to disappear as soon
297 * as it has been closed for whatever reason.
299 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
302 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger));
304 /* Set keepalives if requested. */
305 if (options.keepalives &&
306 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
308 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
310 /* Set the connection. */
311 packet_set_connection(sock, sock);
317 * Waits for the server identification string, and sends our own
318 * identification string.
321 ssh_exchange_identification()
323 char buf[256], remote_version[256]; /* must be same size! */
324 int remote_major, remote_minor, i, mismatch;
325 int connection_in = packet_get_connection_in();
326 int connection_out = packet_get_connection_out();
327 int minor1 = PROTOCOL_MINOR_1;
329 /* Read other side\'s version identification. */
331 for (i = 0; i < sizeof(buf) - 1; i++) {
332 int len = atomicio(read, connection_in, &buf[i], 1);
334 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
336 fatal("ssh_exchange_identification: Connection closed by remote host");
337 if (buf[i] == '\r') {
340 continue; /**XXX wait for \n */
342 if (buf[i] == '\n') {
347 buf[sizeof(buf) - 1] = 0;
348 if (strncmp(buf, "SSH-", 4) == 0)
350 debug("ssh_exchange_identification: %s", buf);
352 server_version_string = xstrdup(buf);
355 * Check that the versions match. In future this might accept
356 * several versions and set appropriate flags to handle them.
358 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
359 &remote_major, &remote_minor, remote_version) != 3)
360 fatal("Bad remote protocol version identification: '%.100s'", buf);
361 debug("Remote protocol version %d.%d, remote software version %.100s",
362 remote_major, remote_minor, remote_version);
364 compat_datafellows(remote_version);
367 switch(remote_major) {
369 if (remote_minor == 99 &&
370 (options.protocol & SSH_PROTO_2) &&
371 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
375 if (!(options.protocol & SSH_PROTO_1)) {
379 if (remote_minor < 3) {
380 fatal("Remote machine has too old SSH software version.");
381 } else if (remote_minor == 3 || remote_minor == 4) {
382 /* We speak 1.3, too. */
385 if (options.forward_agent) {
386 log("Agent forwarding disabled for protocol 1.3");
387 options.forward_agent = 0;
392 if (options.protocol & SSH_PROTO_2) {
402 fatal("Protocol major versions differ: %d vs. %d",
403 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
406 packet_set_ssh2_format();
407 /* Send our own protocol version identification. */
408 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
409 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
410 compat20 ? PROTOCOL_MINOR_2 : minor1,
412 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
413 fatal("write: %.100s", strerror(errno));
414 client_version_string = xstrdup(buf);
415 chop(client_version_string);
416 chop(server_version_string);
417 debug("Local version string %.100s", client_version_string);
421 read_yes_or_no(const char *prompt, int defval)
427 if (isatty(STDIN_FILENO))
430 f = fopen("/dev/tty", "rw");
438 fprintf(stderr, "%s", prompt);
439 if (fgets(buf, sizeof(buf), f) == NULL) {
440 /* Print a newline (the prompt probably didn\'t have one). */
441 fprintf(stderr, "\n");
442 strlcpy(buf, "no", sizeof buf);
444 /* Remove newline from response. */
445 if (strchr(buf, '\n'))
446 *strchr(buf, '\n') = 0;
450 if (strcmp(buf, "yes") == 0)
452 else if (strcmp(buf, "no") == 0)
455 fprintf(stderr, "Please type 'yes' or 'no'.\n");
466 * check whether the supplied host key is valid, return only if ok.
470 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
471 const char *user_hostfile, const char *system_hostfile)
474 char *type = key_type(host_key);
476 char hostline[1000], *hostp;
477 HostStatus host_status;
478 HostStatus ip_status;
479 int local = 0, host_ip_differ = 0;
481 char ntop[NI_MAXHOST];
482 int host_line, ip_line;
483 const char *host_file = NULL, *ip_file = NULL;
486 * Force accepting of the host key for loopback/localhost. The
487 * problem is that if the home directory is NFS-mounted to multiple
488 * machines, localhost will refer to a different machine in each of
489 * them, and the user will get bogus HOST_CHANGED warnings. This
490 * essentially disables host authentication for localhost; however,
491 * this is probably not a real problem.
493 /** hostaddr == 0! */
494 switch (hostaddr->sa_family) {
496 local = (ntohl(((struct sockaddr_in *)hostaddr)->sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
497 salen = sizeof(struct sockaddr_in);
500 local = IN6_IS_ADDR_LOOPBACK(&(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
501 salen = sizeof(struct sockaddr_in6);
505 salen = sizeof(struct sockaddr_storage);
508 if (local && options.host_key_alias == NULL) {
509 debug("Forcing accepting of host key for "
510 "loopback/localhost.");
515 * We don't have the remote ip-address for connections
516 * using a proxy command
518 if (options.proxy_command == NULL) {
519 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
520 NULL, 0, NI_NUMERICHOST) != 0)
521 fatal("check_host_key: getnameinfo failed");
524 ip = xstrdup("<no hostip for proxy command>");
527 * Turn off check_host_ip if the connection is to localhost, via proxy
528 * command or if we don't have a hostname to compare with
530 if (options.check_host_ip &&
531 (local || strcmp(host, ip) == 0 || options.proxy_command != NULL))
532 options.check_host_ip = 0;
535 * Allow the user to record the key under a different name. This is
536 * useful for ssh tunneling over forwarded connections or if you run
537 * multiple sshd's on different ports on the same machine.
539 if (options.host_key_alias != NULL) {
540 host = options.host_key_alias;
541 debug("using hostkeyalias: %s", host);
545 * Store the host key from the known host file in here so that we can
546 * compare it with the key for the IP address.
548 file_key = key_new(host_key->type);
551 * Check if the host key is present in the user\'s list of known
552 * hosts or in the systemwide list.
554 host_file = user_hostfile;
555 host_status = check_host_in_hostfile(host_file, host, host_key, file_key, &host_line);
556 if (host_status == HOST_NEW) {
557 host_file = system_hostfile;
558 host_status = check_host_in_hostfile(host_file, host, host_key, file_key, &host_line);
561 * Also perform check for the ip address, skip the check if we are
562 * localhost or the hostname was an ip address to begin with
564 if (options.check_host_ip) {
565 Key *ip_key = key_new(host_key->type);
567 ip_file = user_hostfile;
568 ip_status = check_host_in_hostfile(ip_file, ip, host_key, ip_key, &ip_line);
569 if (ip_status == HOST_NEW) {
570 ip_file = system_hostfile;
571 ip_status = check_host_in_hostfile(ip_file, ip, host_key, ip_key, &ip_line);
573 if (host_status == HOST_CHANGED &&
574 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
579 ip_status = host_status;
583 switch (host_status) {
585 /* The host is known and the key matches. */
586 debug("Host '%.200s' is known and matches the %s host key.",
588 debug("Found key in %s:%d", host_file, host_line);
589 if (options.check_host_ip && ip_status == HOST_NEW) {
590 if (!add_host_to_hostfile(user_hostfile, ip, host_key))
591 log("Failed to add the %s host key for IP address '%.30s' to the list of known hosts (%.30s).",
592 type, ip, user_hostfile);
594 log("Warning: Permanently added the %s host key for IP address '%.30s' to the list of known hosts.",
599 /* The host is new. */
600 if (options.strict_host_key_checking == 1) {
601 /* User has requested strict host key checking. We will not add the host key
602 automatically. The only alternative left is to abort. */
603 fatal("No %s host key is known for %.200s and you have requested strict checking.", type, host);
604 } else if (options.strict_host_key_checking == 2) {
607 snprintf(prompt, sizeof(prompt),
608 "The authenticity of host '%.200s (%s)' can't be established.\n"
609 "%s key fingerprint is %s.\n"
610 "Are you sure you want to continue connecting (yes/no)? ",
611 host, ip, type, key_fingerprint(host_key));
612 if (!read_yes_or_no(prompt, -1))
613 fatal("Aborted by user!\n");
615 if (options.check_host_ip && ip_status == HOST_NEW) {
616 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
621 /* If not in strict mode, add the key automatically to the local known_hosts file. */
622 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
623 log("Failed to add the host to the list of known hosts (%.500s).",
626 log("Warning: Permanently added '%.200s' (%s) to the list of known hosts.",
630 if (options.check_host_ip && host_ip_differ) {
632 if (ip_status == HOST_NEW)
634 else if (ip_status == HOST_OK)
635 msg = "is unchanged";
637 msg = "has a different value";
638 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
639 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
640 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
641 error("The %s host key for %s has changed,", type, host);
642 error("and the key for the according IP address %s", ip);
643 error("%s. This could either mean that", msg);
644 error("DNS SPOOFING is happening or the IP address for the host");
645 error("and its host key have changed at the same time.");
646 if (ip_status != HOST_NEW)
647 error("Offending key for IP in %s:%d", ip_file, ip_line);
649 /* The host key has changed. */
650 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
651 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
652 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
653 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
654 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
655 error("It is also possible that the %s host key has just been changed.", type);
656 error("The fingerprint for the %s key sent by the remote host is\n%s.",
657 type, key_fingerprint(host_key));
658 error("Please contact your system administrator.");
659 error("Add correct host key in %.100s to get rid of this message.",
661 error("Offending key in %s:%d", host_file, host_line);
664 * If strict host key checking is in use, the user will have
665 * to edit the key manually and we can only abort.
667 if (options.strict_host_key_checking)
668 fatal("%s host key for %.200s has changed and you have requested strict checking.", type, host);
671 * If strict host key checking has not been requested, allow
672 * the connection but without password authentication or
675 if (options.password_authentication) {
676 error("Password authentication is disabled to avoid trojan horses.");
677 options.password_authentication = 0;
679 if (options.forward_agent) {
680 error("Agent forwarding is disabled to avoid trojan horses.");
681 options.forward_agent = 0;
683 if (options.forward_x11) {
684 error("X11 forwarding is disabled to avoid trojan horses.");
685 options.forward_x11 = 0;
687 if (options.num_local_forwards > 0 || options.num_remote_forwards > 0) {
688 error("Port forwarding is disabled to avoid trojan horses.");
689 options.num_local_forwards = options.num_remote_forwards = 0;
692 * XXX Should permit the user to change to use the new id.
693 * This could be done by converting the host key to an
694 * identifying sentence, tell that the host identifies itself
695 * by that sentence, and ask the user if he/she whishes to
696 * accept the authentication.
701 if (options.check_host_ip && host_status != HOST_CHANGED &&
702 ip_status == HOST_CHANGED) {
703 log("Warning: the %s host key for '%.200s' "
704 "differs from the key for the IP address '%.30s'",
706 if (host_status == HOST_OK)
707 log("Matching host key in %s:%d", host_file, host_line);
708 log("Offending key for IP in %s:%d", ip_file, ip_line);
709 if (options.strict_host_key_checking == 1) {
710 fatal("Exiting, you have requested strict checking.");
711 } else if (options.strict_host_key_checking == 2) {
712 if (!read_yes_or_no("Continue?", -1))
713 fatal("Aborted by user!\n");
721 * Starts a dialog with the server, and authenticates the current user on the
722 * server. This does not need any extra privileges. The basic connection
723 * to the server must already have been established before this is called.
724 * If login fails, this function prints an error and never returns.
725 * This function does not require super-user privileges.
728 ssh_login(int host_key_valid, RSA *own_host_key, const char *orighost,
729 struct sockaddr *hostaddr, uid_t original_real_uid)
733 char *server_user, *local_user;
735 /* Get local user name. Use it as server user if no user name was given. */
736 pw = getpwuid(original_real_uid);
738 fatal("User id %u not found from user database.", original_real_uid);
739 local_user = xstrdup(pw->pw_name);
740 server_user = options.user ? options.user : local_user;
742 /* Convert the user-supplied hostname into all lowercase. */
743 host = xstrdup(orighost);
744 for (cp = host; *cp; cp++)
748 /* Exchange protocol version identification strings with the server. */
749 ssh_exchange_identification();
751 /* Put the connection into non-blocking mode. */
752 packet_set_nonblocking();
755 /* authenticate user */
757 ssh_kex2(host, hostaddr);
758 ssh_userauth2(server_user, host);
760 ssh_kex(host, hostaddr);
761 ssh_userauth(local_user, server_user, host, host_key_valid, own_host_key);