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 1.83 2000/11/30 22:53:35 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(_PATH_BSHELL, argv);
120 perror(_PATH_BSHELL);
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)
190 int sock = -1, attempt;
192 struct addrinfo hints, *ai, *aitop;
193 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
195 struct linger linger;
197 debug("ssh_connect: getuid %u geteuid %u anon %d",
198 (u_int) getuid(), (u_int) geteuid(), anonymous);
200 /* Get default port if port has not been set. */
202 sp = getservbyname(SSH_SERVICE_NAME, "tcp");
204 port = ntohs(sp->s_port);
206 port = SSH_DEFAULT_PORT;
208 /* If a proxy command is given, connect using it. */
209 if (proxy_command != NULL)
210 return ssh_proxy_connect(host, port, original_real_uid, proxy_command);
212 /* No proxy command. */
214 memset(&hints, 0, sizeof(hints));
215 hints.ai_family = IPv4or6;
216 hints.ai_socktype = SOCK_STREAM;
217 snprintf(strport, sizeof strport, "%d", port);
218 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
219 fatal("%s: %.100s: %s", __progname, host,
220 gai_strerror(gaierr));
223 * Try to connect several times. On some machines, the first time
224 * will sometimes fail. In general socket code appears to behave
225 * quite magically on many machines.
227 for (attempt = 0; attempt < connection_attempts; attempt++) {
229 debug("Trying again...");
231 /* Loop through addresses for this host, and try each one in
232 sequence until the connection succeeds. */
233 for (ai = aitop; ai; ai = ai->ai_next) {
234 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
236 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
237 ntop, sizeof(ntop), strport, sizeof(strport),
238 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
239 error("ssh_connect: getnameinfo failed");
242 debug("Connecting to %.200s [%.100s] port %s.",
243 host, ntop, strport);
245 /* Create a socket for connecting. */
246 sock = ssh_create_socket(original_real_uid,
250 !anonymous && geteuid() == 0,
256 /* Connect to the host. We use the user's uid in the
257 * hope that it will help with tcp_wrappers showing
258 * the remote uid as root.
260 temporarily_use_uid(original_real_uid);
261 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
262 /* Successful connection. */
263 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
267 debug("connect: %.100s", strerror(errno));
270 * Close the failed socket; there appear to
271 * be some problems when reusing a socket for
272 * which connect() has already returned an
275 shutdown(sock, SHUT_RDWR);
280 break; /* Successful connection. */
282 /* Sleep a moment before retrying. */
288 /* Return failure if we didn't get a successful connection. */
289 if (attempt >= connection_attempts)
292 debug("Connection established.");
295 * Set socket options. We would like the socket to disappear as soon
296 * as it has been closed for whatever reason.
298 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
301 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));
303 /* Set the connection. */
304 packet_set_connection(sock, sock);
310 * Waits for the server identification string, and sends our own
311 * identification string.
314 ssh_exchange_identification()
316 char buf[256], remote_version[256]; /* must be same size! */
317 int remote_major, remote_minor, i, mismatch;
318 int connection_in = packet_get_connection_in();
319 int connection_out = packet_get_connection_out();
320 int minor1 = PROTOCOL_MINOR_1;
322 /* Read other side\'s version identification. */
324 for (i = 0; i < sizeof(buf) - 1; i++) {
325 int len = atomicio(read, connection_in, &buf[i], 1);
327 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
329 fatal("ssh_exchange_identification: Connection closed by remote host");
330 if (buf[i] == '\r') {
333 continue; /**XXX wait for \n */
335 if (buf[i] == '\n') {
340 buf[sizeof(buf) - 1] = 0;
341 if (strncmp(buf, "SSH-", 4) == 0)
343 debug("ssh_exchange_identification: %s", buf);
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 || remote_minor == 4) {
375 /* We speak 1.3, too. */
378 if (options.forward_agent) {
379 log("Agent forwarding disabled for protocol 1.3");
380 options.forward_agent = 0;
385 if (options.protocol & SSH_PROTO_2) {
395 fatal("Protocol major versions differ: %d vs. %d",
396 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
399 packet_set_ssh2_format();
400 /* Send our own protocol version identification. */
401 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
402 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
403 compat20 ? PROTOCOL_MINOR_2 : minor1,
405 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
406 fatal("write: %.100s", strerror(errno));
407 client_version_string = xstrdup(buf);
408 chop(client_version_string);
409 chop(server_version_string);
410 debug("Local version string %.100s", client_version_string);
414 read_yes_or_no(const char *prompt, int defval)
423 f = fopen("/dev/tty", "rw");
431 fprintf(stderr, "%s", prompt);
432 if (fgets(buf, sizeof(buf), f) == NULL) {
433 /* Print a newline (the prompt probably didn\'t have one). */
434 fprintf(stderr, "\n");
435 strlcpy(buf, "no", sizeof buf);
437 /* Remove newline from response. */
438 if (strchr(buf, '\n'))
439 *strchr(buf, '\n') = 0;
443 if (strcmp(buf, "yes") == 0)
445 else if (strcmp(buf, "no") == 0)
448 fprintf(stderr, "Please type 'yes' or 'no'.\n");
459 * check whether the supplied host key is valid, return only if ok.
463 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
464 const char *user_hostfile, const char *system_hostfile)
467 char *type = key_type(host_key);
469 char hostline[1000], *hostp;
470 HostStatus host_status;
471 HostStatus ip_status;
472 int local = 0, host_ip_differ = 0;
474 char ntop[NI_MAXHOST];
477 * Force accepting of the host key for loopback/localhost. The
478 * problem is that if the home directory is NFS-mounted to multiple
479 * machines, localhost will refer to a different machine in each of
480 * them, and the user will get bogus HOST_CHANGED warnings. This
481 * essentially disables host authentication for localhost; however,
482 * this is probably not a real problem.
484 /** hostaddr == 0! */
485 switch (hostaddr->sa_family) {
487 local = (ntohl(((struct sockaddr_in *)hostaddr)->sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
488 salen = sizeof(struct sockaddr_in);
491 local = IN6_IS_ADDR_LOOPBACK(&(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
492 salen = sizeof(struct sockaddr_in6);
496 salen = sizeof(struct sockaddr_storage);
500 debug("Forcing accepting of host key for loopback/localhost.");
505 * Turn off check_host_ip for proxy connects, since
506 * we don't have the remote ip-address
508 if (options.proxy_command != NULL && options.check_host_ip)
509 options.check_host_ip = 0;
511 if (getnameinfo(hostaddr, salen, ntop, sizeof(ntop),
512 NULL, 0, NI_NUMERICHOST) != 0)
513 fatal("check_host_key: getnameinfo failed");
517 * Store the host key from the known host file in here so that we can
518 * compare it with the key for the IP address.
520 file_key = key_new(host_key->type);
523 * Check if the host key is present in the user\'s list of known
524 * hosts or in the systemwide list.
526 host_status = check_host_in_hostfile(user_hostfile, host, host_key, file_key);
527 if (host_status == HOST_NEW)
528 host_status = check_host_in_hostfile(system_hostfile, host, host_key, file_key);
530 * Also perform check for the ip address, skip the check if we are
531 * localhost or the hostname was an ip address to begin with
533 if (options.check_host_ip && !local && strcmp(host, ip)) {
534 Key *ip_key = key_new(host_key->type);
535 ip_status = check_host_in_hostfile(user_hostfile, ip, host_key, ip_key);
537 if (ip_status == HOST_NEW)
538 ip_status = check_host_in_hostfile(system_hostfile, ip, host_key, ip_key);
539 if (host_status == HOST_CHANGED &&
540 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
545 ip_status = host_status;
549 switch (host_status) {
551 /* The host is known and the key matches. */
552 debug("Host '%.200s' is known and matches the %s host key.",
554 if (options.check_host_ip) {
555 if (ip_status == HOST_NEW) {
556 if (!add_host_to_hostfile(user_hostfile, ip, host_key))
557 log("Failed to add the %s host key for IP address '%.30s' to the list of known hosts (%.30s).",
558 type, ip, user_hostfile);
560 log("Warning: Permanently added the %s host key for IP address '%.30s' to the list of known hosts.",
562 } else if (ip_status != HOST_OK)
563 log("Warning: the %s host key for '%.200s' differs from the key for the IP address '%.30s'",
568 /* The host is new. */
569 if (options.strict_host_key_checking == 1) {
570 /* User has requested strict host key checking. We will not add the host key
571 automatically. The only alternative left is to abort. */
572 fatal("No %s host key is known for %.200s and you have requested strict checking.", type, host);
573 } else if (options.strict_host_key_checking == 2) {
576 char *fp = key_fingerprint(host_key);
577 snprintf(prompt, sizeof(prompt),
578 "The authenticity of host '%.200s (%s)' can't be established.\n"
579 "%s key fingerprint is %s.\n"
580 "Are you sure you want to continue connecting (yes/no)? ",
582 if (!read_yes_or_no(prompt, -1))
583 fatal("Aborted by user!\n");
585 if (options.check_host_ip && ip_status == HOST_NEW && strcmp(host, ip)) {
586 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
591 /* If not in strict mode, add the key automatically to the local known_hosts file. */
592 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
593 log("Failed to add the host to the list of known hosts (%.500s).",
596 log("Warning: Permanently added '%.200s' (%s) to the list of known hosts.",
600 if (options.check_host_ip && host_ip_differ) {
602 if (ip_status == HOST_NEW)
604 else if (ip_status == HOST_OK)
605 msg = "is unchanged";
607 msg = "has a different value";
608 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
609 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
610 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
611 error("The %s host key for %s has changed,", type, host);
612 error("and the key for the according IP address %s", ip);
613 error("%s. This could either mean that", msg);
614 error("DNS SPOOFING is happening or the IP address for the host");
615 error("and its host key have changed at the same time");
617 /* The host key has changed. */
618 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
619 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
620 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
621 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
622 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
623 error("It is also possible that the %s host key has just been changed.", type);
624 error("Please contact your system administrator.");
625 error("Add correct host key in %.100s to get rid of this message.",
629 * If strict host key checking is in use, the user will have
630 * to edit the key manually and we can only abort.
632 if (options.strict_host_key_checking)
633 fatal("%s host key for %.200s has changed and you have requested strict checking.", type, host);
636 * If strict host key checking has not been requested, allow
637 * the connection but without password authentication or
640 if (options.password_authentication) {
641 error("Password authentication is disabled to avoid trojan horses.");
642 options.password_authentication = 0;
644 if (options.forward_agent) {
645 error("Agent forwarding is disabled to avoid trojan horses.");
646 options.forward_agent = 0;
648 if (options.forward_x11) {
649 error("X11 forwarding is disabled to avoid trojan horses.");
650 options.forward_x11 = 0;
652 if (options.num_local_forwards > 0 || options.num_remote_forwards > 0) {
653 error("Port forwarding is disabled to avoid trojan horses.");
654 options.num_local_forwards = options.num_remote_forwards = 0;
657 * XXX Should permit the user to change to use the new id.
658 * This could be done by converting the host key to an
659 * identifying sentence, tell that the host identifies itself
660 * by that sentence, and ask the user if he/she whishes to
661 * accept the authentication.
670 * Starts a dialog with the server, and authenticates the current user on the
671 * server. This does not need any extra privileges. The basic connection
672 * to the server must already have been established before this is called.
673 * If login fails, this function prints an error and never returns.
674 * This function does not require super-user privileges.
677 ssh_login(int host_key_valid, RSA *own_host_key, const char *orighost,
678 struct sockaddr *hostaddr, uid_t original_real_uid)
682 char *server_user, *local_user;
684 /* Get local user name. Use it as server user if no user name was given. */
685 pw = getpwuid(original_real_uid);
687 fatal("User id %u not found from user database.", original_real_uid);
688 local_user = xstrdup(pw->pw_name);
689 server_user = options.user ? options.user : local_user;
691 /* Convert the user-supplied hostname into all lowercase. */
692 host = xstrdup(orighost);
693 for (cp = host; *cp; cp++)
697 /* Exchange protocol version identification strings with the server. */
698 ssh_exchange_identification();
700 /* Put the connection into non-blocking mode. */
701 packet_set_nonblocking();
704 /* authenticate user */
706 ssh_kex2(host, hostaddr);
707 ssh_userauth2(server_user, host);
709 ssh_kex(host, hostaddr);
710 ssh_userauth(local_user, server_user, host, host_key_valid, own_host_key);