2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * Created: Sat Mar 18 22:15:47 1995 ylo
6 * Code to connect to a remote host, and to perform the client side of the
7 * login (authentication) dialog.
11 RCSID("$OpenBSD: sshconnect.c,v 1.74 2000/05/17 16:57:02 markus Exp $");
13 #include <openssl/bn.h>
14 #include <openssl/dsa.h>
15 #include <openssl/rsa.h>
26 #include "sshconnect.h"
29 char *client_version_string = NULL;
30 char *server_version_string = NULL;
32 extern Options options;
33 #ifdef HAVE___PROGNAME
34 extern char *__progname;
35 #else /* HAVE___PROGNAME */
36 static const char *__progname = "ssh";
37 #endif /* HAVE___PROGNAME */
40 * Connect to the given ssh server using a proxy command.
43 ssh_proxy_connect(const char *host, u_short port, uid_t original_real_uid,
44 const char *proxy_command)
51 char strport[NI_MAXSERV];
53 /* Convert the port number into a string. */
54 snprintf(strport, sizeof strport, "%hu", port);
56 /* Build the final command string in the buffer by making the
57 appropriate substitutions to the given proxy command. */
58 buffer_init(&command);
59 for (cp = proxy_command; *cp; cp++) {
60 if (cp[0] == '%' && cp[1] == '%') {
61 buffer_append(&command, "%", 1);
65 if (cp[0] == '%' && cp[1] == 'h') {
66 buffer_append(&command, host, strlen(host));
70 if (cp[0] == '%' && cp[1] == 'p') {
71 buffer_append(&command, strport, strlen(strport));
75 buffer_append(&command, cp, 1);
77 buffer_append(&command, "\0", 1);
79 /* Get the final command string. */
80 command_string = buffer_ptr(&command);
82 /* Create pipes for communicating with the proxy. */
83 if (pipe(pin) < 0 || pipe(pout) < 0)
84 fatal("Could not create pipes to communicate with the proxy: %.100s",
87 debug("Executing proxy command: %.500s", command_string);
89 /* Fork and execute the proxy command. */
90 if ((pid = fork()) == 0) {
93 /* Child. Permanently give up superuser privileges. */
94 permanently_set_uid(original_real_uid);
96 /* Redirect stdin and stdout. */
99 if (dup2(pin[0], 0) < 0)
100 perror("dup2 stdin");
104 if (dup2(pout[1], 1) < 0)
105 perror("dup2 stdout");
106 /* Cannot be 1 because pin allocated two descriptors. */
109 /* Stderr is left as it is so that error messages get
110 printed on the user's terminal. */
113 argv[2] = command_string;
116 /* Execute the proxy command. Note that we gave up any
117 extra privileges above. */
118 execv("/bin/sh", argv);
124 fatal("fork failed: %.100s", strerror(errno));
126 /* Close child side of the descriptors. */
130 /* Free the command name. */
131 buffer_free(&command);
133 /* Set the connection file descriptors. */
134 packet_set_connection(pout[0], pin[1]);
140 * Creates a (possibly privileged) socket for use as the ssh connection.
143 ssh_create_socket(uid_t original_real_uid, int privileged, int family)
148 * If we are running as root and want to connect to a privileged
149 * port, bind our own socket to a privileged port.
152 int p = IPPORT_RESERVED - 1;
153 sock = rresvport_af(&p, family);
155 error("rresvport: af=%d %.100s", family, strerror(errno));
157 debug("Allocated local port %d.", p);
160 * Just create an ordinary socket on arbitrary port. We use
161 * the user's uid to create the socket.
163 temporarily_use_uid(original_real_uid);
164 sock = socket(family, SOCK_STREAM, 0);
166 error("socket: %.100s", strerror(errno));
173 * Opens a TCP/IP connection to the remote server on the given host.
174 * The address of the remote host will be returned in hostaddr.
175 * If port is 0, the default port will be used. If anonymous is zero,
176 * a privileged port will be allocated to make the connection.
177 * This requires super-user privileges if anonymous is false.
178 * Connection_attempts specifies the maximum number of tries (one per
179 * second). If proxy_command is non-NULL, it specifies the command (with %h
180 * and %p substituted for host and port, respectively) to use to contact
184 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
185 u_short port, int connection_attempts,
186 int anonymous, uid_t original_real_uid,
187 const char *proxy_command)
189 int sock = -1, attempt;
191 struct addrinfo hints, *ai, *aitop;
192 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
194 struct linger linger;
196 debug("ssh_connect: getuid %d geteuid %d anon %d",
197 (int) getuid(), (int) geteuid(), anonymous);
199 /* Get default port if port has not been set. */
201 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
203 port = ntohs(sp->s_port);
205 port = SSH_DEFAULT_PORT;
207 /* If a proxy command is given, connect using it. */
208 if (proxy_command != NULL)
209 return ssh_proxy_connect(host, port, original_real_uid, proxy_command);
211 /* No proxy command. */
213 memset(&hints, 0, sizeof(hints));
214 hints.ai_family = IPv4or6;
215 hints.ai_socktype = SOCK_STREAM;
216 snprintf(strport, sizeof strport, "%d", port);
217 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
218 fatal("%s: %.100s: %s", __progname, host,
219 gai_strerror(gaierr));
222 * Try to connect several times. On some machines, the first time
223 * will sometimes fail. In general socket code appears to behave
224 * quite magically on many machines.
226 for (attempt = 0; attempt < connection_attempts; attempt++) {
228 debug("Trying again...");
230 /* Loop through addresses for this host, and try each one in
231 sequence until the connection succeeds. */
232 for (ai = aitop; ai; ai = ai->ai_next) {
233 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
235 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
236 ntop, sizeof(ntop), strport, sizeof(strport),
237 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
238 error("ssh_connect: getnameinfo failed");
241 debug("Connecting to %.200s [%.100s] port %s.",
242 host, ntop, strport);
244 /* Create a socket for connecting. */
245 sock = ssh_create_socket(original_real_uid,
246 !anonymous && geteuid() == 0 && port < IPPORT_RESERVED,
251 /* Connect to the host. We use the user's uid in the
252 * hope that it will help with tcp_wrappers showing
253 * the remote uid as root.
255 temporarily_use_uid(original_real_uid);
256 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
257 /* Successful connection. */
258 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
262 debug("connect: %.100s", strerror(errno));
265 * Close the failed socket; there appear to
266 * be some problems when reusing a socket for
267 * which connect() has already returned an
270 shutdown(sock, SHUT_RDWR);
275 break; /* Successful connection. */
277 /* Sleep a moment before retrying. */
283 /* Return failure if we didn't get a successful connection. */
284 if (attempt >= connection_attempts)
287 debug("Connection established.");
290 * Set socket options. We would like the socket to disappear as soon
291 * as it has been closed for whatever reason.
293 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
296 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));
298 /* Set the connection. */
299 packet_set_connection(sock, sock);
305 * Waits for the server identification string, and sends our own
306 * identification string.
309 ssh_exchange_identification()
311 char buf[256], remote_version[256]; /* must be same size! */
312 int remote_major, remote_minor, i, mismatch;
313 int connection_in = packet_get_connection_in();
314 int connection_out = packet_get_connection_out();
316 /* Read other side\'s version identification. */
317 for (i = 0; i < sizeof(buf) - 1; i++) {
318 int len = read(connection_in, &buf[i], 1);
320 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
322 fatal("ssh_exchange_identification: Connection closed by remote host");
323 if (buf[i] == '\r') {
326 continue; /**XXX wait for \n */
328 if (buf[i] == '\n') {
333 buf[sizeof(buf) - 1] = 0;
334 server_version_string = xstrdup(buf);
337 * Check that the versions match. In future this might accept
338 * several versions and set appropriate flags to handle them.
340 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
341 &remote_major, &remote_minor, remote_version) != 3)
342 fatal("Bad remote protocol version identification: '%.100s'", buf);
343 debug("Remote protocol version %d.%d, remote software version %.100s",
344 remote_major, remote_minor, remote_version);
346 compat_datafellows(remote_version);
349 switch(remote_major) {
351 if (remote_minor == 99 &&
352 (options.protocol & SSH_PROTO_2) &&
353 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
357 if (!(options.protocol & SSH_PROTO_1)) {
361 if (remote_minor < 3) {
362 fatal("Remote machine has too old SSH software version.");
363 } else if (remote_minor == 3) {
364 /* We speak 1.3, too. */
366 if (options.forward_agent) {
367 log("Agent forwarding disabled for protocol 1.3");
368 options.forward_agent = 0;
373 if (options.protocol & SSH_PROTO_2) {
383 fatal("Protocol major versions differ: %d vs. %d",
384 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
387 packet_set_ssh2_format();
388 /* Send our own protocol version identification. */
389 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
390 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
391 compat20 ? PROTOCOL_MINOR_2 : PROTOCOL_MINOR_1,
393 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
394 fatal("write: %.100s", strerror(errno));
395 client_version_string = xstrdup(buf);
396 chop(client_version_string);
397 chop(server_version_string);
398 debug("Local version string %.100s", client_version_string);
402 read_yes_or_no(const char *prompt, int defval)
411 f = fopen("/dev/tty", "rw");
419 fprintf(stderr, "%s", prompt);
420 if (fgets(buf, sizeof(buf), f) == NULL) {
421 /* Print a newline (the prompt probably didn\'t have one). */
422 fprintf(stderr, "\n");
423 strlcpy(buf, "no", sizeof buf);
425 /* Remove newline from response. */
426 if (strchr(buf, '\n'))
427 *strchr(buf, '\n') = 0;
431 if (strcmp(buf, "yes") == 0)
433 if (strcmp(buf, "no") == 0)
445 * check whether the supplied host key is valid, return only if ok.
449 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
450 const char *user_hostfile, const char *system_hostfile)
453 char *type = key_type(host_key);
455 char hostline[1000], *hostp;
456 HostStatus host_status;
457 HostStatus ip_status;
458 int local = 0, host_ip_differ = 0;
460 char ntop[NI_MAXHOST];
463 * Force accepting of the host key for loopback/localhost. The
464 * problem is that if the home directory is NFS-mounted to multiple
465 * machines, localhost will refer to a different machine in each of
466 * them, and the user will get bogus HOST_CHANGED warnings. This
467 * essentially disables host authentication for localhost; however,
468 * this is probably not a real problem.
470 /** hostaddr == 0! */
471 switch (hostaddr->sa_family) {
473 local = (ntohl(((struct sockaddr_in *)hostaddr)->sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
474 salen = sizeof(struct sockaddr_in);
477 local = IN6_IS_ADDR_LOOPBACK(&(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
478 salen = sizeof(struct sockaddr_in6);
482 salen = sizeof(struct sockaddr_storage);
486 debug("Forcing accepting of host key for loopback/localhost.");
491 * Turn off check_host_ip for proxy connects, since
492 * we don't have the remote ip-address
494 if (options.proxy_command != NULL && options.check_host_ip)
495 options.check_host_ip = 0;
497 if (options.check_host_ip) {
498 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
499 NULL, 0, NI_NUMERICHOST) != 0)
500 fatal("check_host_key: getnameinfo failed");
505 * Store the host key from the known host file in here so that we can
506 * compare it with the key for the IP address.
508 file_key = key_new(host_key->type);
511 * Check if the host key is present in the user\'s list of known
512 * hosts or in the systemwide list.
514 host_status = check_host_in_hostfile(user_hostfile, host, host_key, file_key);
515 if (host_status == HOST_NEW)
516 host_status = check_host_in_hostfile(system_hostfile, host, host_key, file_key);
518 * Also perform check for the ip address, skip the check if we are
519 * localhost or the hostname was an ip address to begin with
521 if (options.check_host_ip && !local && strcmp(host, ip)) {
522 Key *ip_key = key_new(host_key->type);
523 ip_status = check_host_in_hostfile(user_hostfile, ip, host_key, ip_key);
525 if (ip_status == HOST_NEW)
526 ip_status = check_host_in_hostfile(system_hostfile, ip, host_key, ip_key);
527 if (host_status == HOST_CHANGED &&
528 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
533 ip_status = host_status;
537 switch (host_status) {
539 /* The host is known and the key matches. */
540 debug("Host '%.200s' is known and matches the %s host key.",
542 if (options.check_host_ip) {
543 if (ip_status == HOST_NEW) {
544 if (!add_host_to_hostfile(user_hostfile, ip, host_key))
545 log("Failed to add the %s host key for IP address '%.30s' to the list of known hosts (%.30s).",
546 type, ip, user_hostfile);
548 log("Warning: Permanently added the %s host key for IP address '%.30s' to the list of known hosts.",
550 } else if (ip_status != HOST_OK)
551 log("Warning: the %s host key for '%.200s' differs from the key for the IP address '%.30s'",
556 /* The host is new. */
557 if (options.strict_host_key_checking == 1) {
558 /* User has requested strict host key checking. We will not add the host key
559 automatically. The only alternative left is to abort. */
560 fatal("No %s host key is known for %.200s and you have requested strict checking.", type, host);
561 } else if (options.strict_host_key_checking == 2) {
564 char *fp = key_fingerprint(host_key);
565 snprintf(prompt, sizeof(prompt),
566 "The authenticity of host '%.200s' can't be established.\n"
567 "%s key fingerprint is %s.\n"
568 "Are you sure you want to continue connecting (yes/no)? ",
570 if (!read_yes_or_no(prompt, -1))
571 fatal("Aborted by user!\n");
573 if (options.check_host_ip && ip_status == HOST_NEW && strcmp(host, ip)) {
574 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
579 /* If not in strict mode, add the key automatically to the local known_hosts file. */
580 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
581 log("Failed to add the host to the list of known hosts (%.500s).",
584 log("Warning: Permanently added '%.200s' (%s) to the list of known hosts.",
588 if (options.check_host_ip && host_ip_differ) {
590 if (ip_status == HOST_NEW)
592 else if (ip_status == HOST_OK)
593 msg = "is unchanged";
595 msg = "has a different value";
596 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
597 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
598 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
599 error("The %s host key for %s has changed,", type, host);
600 error("and the key for the according IP address %s", ip);
601 error("%s. This could either mean that", msg);
602 error("DNS SPOOFING is happening or the IP address for the host");
603 error("and its host key have changed at the same time");
605 /* The host key has changed. */
606 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
607 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
608 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
609 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
610 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
611 error("It is also possible that the %s host key has just been changed.", type);
612 error("Please contact your system administrator.");
613 error("Add correct host key in %.100s to get rid of this message.",
617 * If strict host key checking is in use, the user will have
618 * to edit the key manually and we can only abort.
620 if (options.strict_host_key_checking)
621 fatal("%s host key for %.200s has changed and you have requested strict checking.", type, host);
624 * If strict host key checking has not been requested, allow
625 * the connection but without password authentication or
628 if (options.password_authentication) {
629 error("Password authentication is disabled to avoid trojan horses.");
630 options.password_authentication = 0;
632 if (options.forward_agent) {
633 error("Agent forwarding is disabled to avoid trojan horses.");
634 options.forward_agent = 0;
637 * XXX Should permit the user to change to use the new id.
638 * This could be done by converting the host key to an
639 * identifying sentence, tell that the host identifies itself
640 * by that sentence, and ask the user if he/she whishes to
641 * accept the authentication.
645 if (options.check_host_ip)
650 * Starts a dialog with the server, and authenticates the current user on the
651 * server. This does not need any extra privileges. The basic connection
652 * to the server must already have been established before this is called.
653 * If login fails, this function prints an error and never returns.
654 * This function does not require super-user privileges.
657 ssh_login(int host_key_valid, RSA *own_host_key, const char *orighost,
658 struct sockaddr *hostaddr, uid_t original_real_uid)
662 char *server_user, *local_user;
664 /* Get local user name. Use it as server user if no user name was given. */
665 pw = getpwuid(original_real_uid);
667 fatal("User id %d not found from user database.", original_real_uid);
668 local_user = xstrdup(pw->pw_name);
669 server_user = options.user ? options.user : local_user;
671 /* Convert the user-supplied hostname into all lowercase. */
672 host = xstrdup(orighost);
673 for (cp = host; *cp; cp++)
677 /* Exchange protocol version identification strings with the server. */
678 ssh_exchange_identification();
680 /* Put the connection into non-blocking mode. */
681 packet_set_nonblocking();
684 /* authenticate user */
686 ssh_kex2(host, hostaddr);
687 ssh_userauth2(server_user, host);
689 ssh_kex(host, hostaddr);
690 ssh_userauth(local_user, server_user, host, host_key_valid, own_host_key);