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 1.71 2000/04/26 21:28:33 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 extern char *__progname;
36 * Connect to the given ssh server using a proxy command.
39 ssh_proxy_connect(const char *host, u_short port, uid_t original_real_uid,
40 const char *proxy_command)
47 char strport[NI_MAXSERV];
49 /* Convert the port number into a string. */
50 snprintf(strport, sizeof strport, "%hu", port);
52 /* Build the final command string in the buffer by making the
53 appropriate substitutions to the given proxy command. */
54 buffer_init(&command);
55 for (cp = proxy_command; *cp; cp++) {
56 if (cp[0] == '%' && cp[1] == '%') {
57 buffer_append(&command, "%", 1);
61 if (cp[0] == '%' && cp[1] == 'h') {
62 buffer_append(&command, host, strlen(host));
66 if (cp[0] == '%' && cp[1] == 'p') {
67 buffer_append(&command, strport, strlen(strport));
71 buffer_append(&command, cp, 1);
73 buffer_append(&command, "\0", 1);
75 /* Get the final command string. */
76 command_string = buffer_ptr(&command);
78 /* Create pipes for communicating with the proxy. */
79 if (pipe(pin) < 0 || pipe(pout) < 0)
80 fatal("Could not create pipes to communicate with the proxy: %.100s",
83 debug("Executing proxy command: %.500s", command_string);
85 /* Fork and execute the proxy command. */
86 if ((pid = fork()) == 0) {
89 /* Child. Permanently give up superuser privileges. */
90 permanently_set_uid(original_real_uid);
92 /* Redirect stdin and stdout. */
95 if (dup2(pin[0], 0) < 0)
100 if (dup2(pout[1], 1) < 0)
101 perror("dup2 stdout");
102 /* Cannot be 1 because pin allocated two descriptors. */
105 /* Stderr is left as it is so that error messages get
106 printed on the user's terminal. */
109 argv[2] = command_string;
112 /* Execute the proxy command. Note that we gave up any
113 extra privileges above. */
114 execv("/bin/sh", argv);
120 fatal("fork failed: %.100s", strerror(errno));
122 /* Close child side of the descriptors. */
126 /* Free the command name. */
127 buffer_free(&command);
129 /* Set the connection file descriptors. */
130 packet_set_connection(pout[0], pin[1]);
136 * Creates a (possibly privileged) socket for use as the ssh connection.
139 ssh_create_socket(uid_t original_real_uid, int privileged, int family)
144 * If we are running as root and want to connect to a privileged
145 * port, bind our own socket to a privileged port.
148 int p = IPPORT_RESERVED - 1;
149 sock = rresvport_af(&p, family);
151 error("rresvport: af=%d %.100s", family, strerror(errno));
153 debug("Allocated local port %d.", p);
156 * Just create an ordinary socket on arbitrary port. We use
157 * the user's uid to create the socket.
159 temporarily_use_uid(original_real_uid);
160 sock = socket(family, SOCK_STREAM, 0);
162 error("socket: %.100s", strerror(errno));
169 * Opens a TCP/IP connection to the remote server on the given host.
170 * The address of the remote host will be returned in hostaddr.
171 * If port is 0, the default port will be used. If anonymous is zero,
172 * a privileged port will be allocated to make the connection.
173 * This requires super-user privileges if anonymous is false.
174 * Connection_attempts specifies the maximum number of tries (one per
175 * second). If proxy_command is non-NULL, it specifies the command (with %h
176 * and %p substituted for host and port, respectively) to use to contact
180 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
181 u_short port, int connection_attempts,
182 int anonymous, uid_t original_real_uid,
183 const char *proxy_command)
185 int sock = -1, attempt;
187 struct addrinfo hints, *ai, *aitop;
188 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
190 struct linger linger;
192 debug("ssh_connect: getuid %d geteuid %d anon %d",
193 (int) getuid(), (int) geteuid(), anonymous);
195 /* Get default port if port has not been set. */
197 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
199 port = ntohs(sp->s_port);
201 port = SSH_DEFAULT_PORT;
203 /* If a proxy command is given, connect using it. */
204 if (proxy_command != NULL)
205 return ssh_proxy_connect(host, port, original_real_uid, proxy_command);
207 /* No proxy command. */
209 memset(&hints, 0, sizeof(hints));
210 hints.ai_family = IPv4or6;
211 hints.ai_socktype = SOCK_STREAM;
212 snprintf(strport, sizeof strport, "%d", port);
213 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
214 fatal("%s: %.100s: %s", __progname, host,
215 gai_strerror(gaierr));
218 * Try to connect several times. On some machines, the first time
219 * will sometimes fail. In general socket code appears to behave
220 * quite magically on many machines.
222 for (attempt = 0; attempt < connection_attempts; attempt++) {
224 debug("Trying again...");
226 /* Loop through addresses for this host, and try each one in
227 sequence until the connection succeeds. */
228 for (ai = aitop; ai; ai = ai->ai_next) {
229 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
231 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
232 ntop, sizeof(ntop), strport, sizeof(strport),
233 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
234 error("ssh_connect: getnameinfo failed");
237 debug("Connecting to %.200s [%.100s] port %s.",
238 host, ntop, strport);
240 /* Create a socket for connecting. */
241 sock = ssh_create_socket(original_real_uid,
242 !anonymous && geteuid() == 0 && port < IPPORT_RESERVED,
247 /* Connect to the host. We use the user's uid in the
248 * hope that it will help with tcp_wrappers showing
249 * the remote uid as root.
251 temporarily_use_uid(original_real_uid);
252 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
253 /* Successful connection. */
254 memcpy(hostaddr, ai->ai_addr, sizeof(*(ai->ai_addr)));
258 debug("connect: %.100s", strerror(errno));
261 * Close the failed socket; there appear to
262 * be some problems when reusing a socket for
263 * which connect() has already returned an
266 shutdown(sock, SHUT_RDWR);
271 break; /* Successful connection. */
273 /* Sleep a moment before retrying. */
279 /* Return failure if we didn't get a successful connection. */
280 if (attempt >= connection_attempts)
283 debug("Connection established.");
286 * Set socket options. We would like the socket to disappear as soon
287 * as it has been closed for whatever reason.
289 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
292 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));
294 /* Set the connection. */
295 packet_set_connection(sock, sock);
305 if(*t == '\n' || *t == '\r') {
316 * Waits for the server identification string, and sends our own
317 * identification string.
320 ssh_exchange_identification()
322 char buf[256], remote_version[256]; /* must be same size! */
323 int remote_major, remote_minor, i, mismatch;
324 int connection_in = packet_get_connection_in();
325 int connection_out = packet_get_connection_out();
327 /* Read other side\'s version identification. */
328 for (i = 0; i < sizeof(buf) - 1; i++) {
329 int len = read(connection_in, &buf[i], 1);
331 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
333 fatal("ssh_exchange_identification: Connection closed by remote host");
334 if (buf[i] == '\r') {
337 continue; /**XXX wait for \n */
339 if (buf[i] == '\n') {
344 buf[sizeof(buf) - 1] = 0;
345 server_version_string = xstrdup(buf);
348 * Check that the versions match. In future this might accept
349 * several versions and set appropriate flags to handle them.
351 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
352 &remote_major, &remote_minor, remote_version) != 3)
353 fatal("Bad remote protocol version identification: '%.100s'", buf);
354 debug("Remote protocol version %d.%d, remote software version %.100s",
355 remote_major, remote_minor, remote_version);
357 compat_datafellows(remote_version);
360 switch(remote_major) {
362 if (remote_minor == 99 &&
363 (options.protocol & SSH_PROTO_2) &&
364 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
368 if (!(options.protocol & SSH_PROTO_1)) {
372 if (remote_minor < 3) {
373 fatal("Remote machine has too old SSH software version.");
374 } else if (remote_minor == 3) {
375 /* We speak 1.3, too. */
377 if (options.forward_agent) {
378 log("Agent forwarding disabled for protocol 1.3");
379 options.forward_agent = 0;
384 if (options.protocol & SSH_PROTO_2) {
394 fatal("Protocol major versions differ: %d vs. %d",
395 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
398 packet_set_ssh2_format();
399 /* Send our own protocol version identification. */
400 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
401 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
402 compat20 ? PROTOCOL_MINOR_2 : PROTOCOL_MINOR_1,
404 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
405 fatal("write: %.100s", strerror(errno));
406 client_version_string = xstrdup(buf);
407 chop(client_version_string);
408 chop(server_version_string);
409 debug("Local version string %.100s", client_version_string);
413 read_yes_or_no(const char *prompt, int defval)
422 f = fopen("/dev/tty", "rw");
430 fprintf(stderr, "%s", prompt);
431 if (fgets(buf, sizeof(buf), f) == NULL) {
432 /* Print a newline (the prompt probably didn\'t have one). */
433 fprintf(stderr, "\n");
434 strlcpy(buf, "no", sizeof buf);
436 /* Remove newline from response. */
437 if (strchr(buf, '\n'))
438 *strchr(buf, '\n') = 0;
442 if (strcmp(buf, "yes") == 0)
444 if (strcmp(buf, "no") == 0)
456 * check whether the supplied host key is valid, return only if ok.
460 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
461 const char *user_hostfile, const char *system_hostfile)
465 char hostline[1000], *hostp;
466 HostStatus host_status;
467 HostStatus ip_status;
468 int local = 0, host_ip_differ = 0;
470 char ntop[NI_MAXHOST];
473 * Force accepting of the host key for loopback/localhost. The
474 * problem is that if the home directory is NFS-mounted to multiple
475 * machines, localhost will refer to a different machine in each of
476 * them, and the user will get bogus HOST_CHANGED warnings. This
477 * essentially disables host authentication for localhost; however,
478 * this is probably not a real problem.
480 /** hostaddr == 0! */
481 switch (hostaddr->sa_family) {
483 local = (ntohl(((struct sockaddr_in *)hostaddr)->sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
484 salen = sizeof(struct sockaddr_in);
487 local = IN6_IS_ADDR_LOOPBACK(&(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
488 salen = sizeof(struct sockaddr_in6);
492 salen = sizeof(struct sockaddr_storage);
496 debug("Forcing accepting of host key for loopback/localhost.");
501 * Turn off check_host_ip for proxy connects, since
502 * we don't have the remote ip-address
504 if (options.proxy_command != NULL && options.check_host_ip)
505 options.check_host_ip = 0;
507 if (options.check_host_ip) {
508 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
509 NULL, 0, NI_NUMERICHOST) != 0)
510 fatal("check_host_key: getnameinfo failed");
515 * Store the host key from the known host file in here so that we can
516 * compare it with the key for the IP address.
518 file_key = key_new(host_key->type);
521 * Check if the host key is present in the user\'s list of known
522 * hosts or in the systemwide list.
524 host_status = check_host_in_hostfile(user_hostfile, host, host_key, file_key);
525 if (host_status == HOST_NEW)
526 host_status = check_host_in_hostfile(system_hostfile, host, host_key, file_key);
528 * Also perform check for the ip address, skip the check if we are
529 * localhost or the hostname was an ip address to begin with
531 if (options.check_host_ip && !local && strcmp(host, ip)) {
532 Key *ip_key = key_new(host_key->type);
533 ip_status = check_host_in_hostfile(user_hostfile, ip, host_key, ip_key);
535 if (ip_status == HOST_NEW)
536 ip_status = check_host_in_hostfile(system_hostfile, ip, host_key, ip_key);
537 if (host_status == HOST_CHANGED &&
538 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
543 ip_status = host_status;
547 switch (host_status) {
549 /* The host is known and the key matches. */
550 debug("Host '%.200s' is known and matches the host key.", host);
551 if (options.check_host_ip) {
552 if (ip_status == HOST_NEW) {
553 if (!add_host_to_hostfile(user_hostfile, ip, host_key))
554 log("Failed to add the host key for IP address '%.30s' to the list of known hosts (%.30s).",
557 log("Warning: Permanently added host key for IP address '%.30s' to the list of known hosts.",
559 } else if (ip_status != HOST_OK)
560 log("Warning: the host key for '%.200s' differs from the key for the IP address '%.30s'",
565 /* The host is new. */
566 if (options.strict_host_key_checking == 1) {
567 /* User has requested strict host key checking. We will not add the host key
568 automatically. The only alternative left is to abort. */
569 fatal("No host key is known for %.200s and you have requested strict checking.", host);
570 } else if (options.strict_host_key_checking == 2) {
573 char *fp = key_fingerprint(host_key);
574 snprintf(prompt, sizeof(prompt),
575 "The authenticity of host '%.200s' can't be established.\n"
576 "Key fingerprint is %s.\n"
577 "Are you sure you want to continue connecting (yes/no)? ",
579 if (!read_yes_or_no(prompt, -1))
580 fatal("Aborted by user!\n");
582 if (options.check_host_ip && ip_status == HOST_NEW && strcmp(host, ip)) {
583 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
588 /* If not in strict mode, add the key automatically to the local known_hosts file. */
589 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
590 log("Failed to add the host to the list of known hosts (%.500s).",
593 log("Warning: Permanently added '%.200s' to the list of known hosts.",
597 if (options.check_host_ip && host_ip_differ) {
599 if (ip_status == HOST_NEW)
601 else if (ip_status == HOST_OK)
602 msg = "is unchanged";
604 msg = "has a different value";
605 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
606 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
607 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
608 error("The host key for %s has changed,", host);
609 error("and the key for the according IP address %s", ip);
610 error("%s. This could either mean that", msg);
611 error("DNS SPOOFING is happening or the IP address for the host");
612 error("and its host key have changed at the same time");
614 /* The host key has changed. */
615 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
616 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
617 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
618 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
619 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
620 error("It is also possible that the host key has just been changed.");
621 error("Please contact your system administrator.");
622 error("Add correct host key in %.100s to get rid of this message.",
626 * If strict host key checking is in use, the user will have
627 * to edit the key manually and we can only abort.
629 if (options.strict_host_key_checking)
630 fatal("Host key for %.200s has changed and you have requested strict checking.", host);
633 * If strict host key checking has not been requested, allow
634 * the connection but without password authentication or
637 if (options.password_authentication) {
638 error("Password authentication is disabled to avoid trojan horses.");
639 options.password_authentication = 0;
641 if (options.forward_agent) {
642 error("Agent forwarding is disabled to avoid trojan horses.");
643 options.forward_agent = 0;
646 * XXX Should permit the user to change to use the new id.
647 * This could be done by converting the host key to an
648 * identifying sentence, tell that the host identifies itself
649 * by that sentence, and ask the user if he/she whishes to
650 * accept the authentication.
654 if (options.check_host_ip)
659 * Starts a dialog with the server, and authenticates the current user on the
660 * server. This does not need any extra privileges. The basic connection
661 * to the server must already have been established before this is called.
662 * If login fails, this function prints an error and never returns.
663 * This function does not require super-user privileges.
666 ssh_login(int host_key_valid, RSA *own_host_key, const char *orighost,
667 struct sockaddr *hostaddr, uid_t original_real_uid)
671 char *server_user, *local_user;
673 /* Get local user name. Use it as server user if no user name was given. */
674 pw = getpwuid(original_real_uid);
676 fatal("User id %d not found from user database.", original_real_uid);
677 local_user = xstrdup(pw->pw_name);
678 server_user = options.user ? options.user : local_user;
680 /* Convert the user-supplied hostname into all lowercase. */
681 host = xstrdup(orighost);
682 for (cp = host; *cp; cp++)
686 /* Exchange protocol version identification strings with the server. */
687 ssh_exchange_identification();
689 /* Put the connection into non-blocking mode. */
690 packet_set_nonblocking();
693 /* authenticate user */
695 ssh_kex2(host, hostaddr);
696 ssh_userauth2(server_user, host);
698 ssh_kex(host, hostaddr);
699 ssh_userauth(local_user, server_user, host, host_key_valid, own_host_key);