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 1.79 2000/09/17 15:52:51 markus Exp $");
19 #include <openssl/bn.h>
20 #include <openssl/dsa.h>
21 #include <openssl/rsa.h>
32 #include "sshconnect.h"
35 char *client_version_string = NULL;
36 char *server_version_string = NULL;
38 extern Options options;
39 extern char *__progname;
42 * Connect to the given ssh server using a proxy command.
45 ssh_proxy_connect(const char *host, u_short port, uid_t original_real_uid,
46 const char *proxy_command)
53 char strport[NI_MAXSERV];
55 /* Convert the port number into a string. */
56 snprintf(strport, sizeof strport, "%hu", port);
58 /* Build the final command string in the buffer by making the
59 appropriate substitutions to the given proxy command. */
60 buffer_init(&command);
61 for (cp = proxy_command; *cp; cp++) {
62 if (cp[0] == '%' && cp[1] == '%') {
63 buffer_append(&command, "%", 1);
67 if (cp[0] == '%' && cp[1] == 'h') {
68 buffer_append(&command, host, strlen(host));
72 if (cp[0] == '%' && cp[1] == 'p') {
73 buffer_append(&command, strport, strlen(strport));
77 buffer_append(&command, cp, 1);
79 buffer_append(&command, "\0", 1);
81 /* Get the final command string. */
82 command_string = buffer_ptr(&command);
84 /* Create pipes for communicating with the proxy. */
85 if (pipe(pin) < 0 || pipe(pout) < 0)
86 fatal("Could not create pipes to communicate with the proxy: %.100s",
89 debug("Executing proxy command: %.500s", command_string);
91 /* Fork and execute the proxy command. */
92 if ((pid = fork()) == 0) {
95 /* Child. Permanently give up superuser privileges. */
96 permanently_set_uid(original_real_uid);
98 /* Redirect stdin and stdout. */
101 if (dup2(pin[0], 0) < 0)
102 perror("dup2 stdin");
106 if (dup2(pout[1], 1) < 0)
107 perror("dup2 stdout");
108 /* Cannot be 1 because pin allocated two descriptors. */
111 /* Stderr is left as it is so that error messages get
112 printed on the user's terminal. */
115 argv[2] = command_string;
118 /* Execute the proxy command. Note that we gave up any
119 extra privileges above. */
120 execv("/bin/sh", argv);
126 fatal("fork failed: %.100s", strerror(errno));
128 /* Close child side of the descriptors. */
132 /* Free the command name. */
133 buffer_free(&command);
135 /* Set the connection file descriptors. */
136 packet_set_connection(pout[0], pin[1]);
142 * Creates a (possibly privileged) socket for use as the ssh connection.
145 ssh_create_socket(uid_t original_real_uid, int privileged, int family)
150 * If we are running as root and want to connect to a privileged
151 * port, bind our own socket to a privileged port.
154 int p = IPPORT_RESERVED - 1;
155 sock = rresvport_af(&p, family);
157 error("rresvport: af=%d %.100s", family, strerror(errno));
159 debug("Allocated local port %d.", p);
162 * Just create an ordinary socket on arbitrary port. We use
163 * the user's uid to create the socket.
165 temporarily_use_uid(original_real_uid);
166 sock = socket(family, SOCK_STREAM, 0);
168 error("socket: %.100s", strerror(errno));
175 * Opens a TCP/IP connection to the remote server on the given host.
176 * The address of the remote host will be returned in hostaddr.
177 * If port is 0, the default port will be used. If anonymous is zero,
178 * a privileged port will be allocated to make the connection.
179 * This requires super-user privileges if anonymous is false.
180 * Connection_attempts specifies the maximum number of tries (one per
181 * second). If proxy_command is non-NULL, it specifies the command (with %h
182 * and %p substituted for host and port, respectively) to use to contact
186 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
187 u_short port, int connection_attempts,
188 int anonymous, uid_t original_real_uid,
189 const char *proxy_command)
191 int sock = -1, attempt;
193 struct addrinfo hints, *ai, *aitop;
194 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
196 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,
248 !anonymous && geteuid() == 0 && port < IPPORT_RESERVED,
253 /* Connect to the host. We use the user's uid in the
254 * hope that it will help with tcp_wrappers showing
255 * the remote uid as root.
257 temporarily_use_uid(original_real_uid);
258 if (connect(sock, ai->ai_addr, ai->ai_addrlen) >= 0) {
259 /* Successful connection. */
260 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
264 debug("connect: %.100s", strerror(errno));
267 * Close the failed socket; there appear to
268 * be some problems when reusing a socket for
269 * which connect() has already returned an
272 shutdown(sock, SHUT_RDWR);
277 break; /* Successful connection. */
279 /* Sleep a moment before retrying. */
285 /* Return failure if we didn't get a successful connection. */
286 if (attempt >= connection_attempts)
289 debug("Connection established.");
292 * Set socket options. We would like the socket to disappear as soon
293 * as it has been closed for whatever reason.
295 /* setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
298 setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));
300 /* Set the connection. */
301 packet_set_connection(sock, sock);
307 * Waits for the server identification string, and sends our own
308 * identification string.
311 ssh_exchange_identification()
313 char buf[256], remote_version[256]; /* must be same size! */
314 int remote_major, remote_minor, i, mismatch;
315 int connection_in = packet_get_connection_in();
316 int connection_out = packet_get_connection_out();
318 /* Read other side\'s version identification. */
320 for (i = 0; i < sizeof(buf) - 1; i++) {
321 int len = atomicio(read, connection_in, &buf[i], 1);
323 fatal("ssh_exchange_identification: read: %.100s", strerror(errno));
325 fatal("ssh_exchange_identification: Connection closed by remote host");
326 if (buf[i] == '\r') {
329 continue; /**XXX wait for \n */
331 if (buf[i] == '\n') {
336 buf[sizeof(buf) - 1] = 0;
337 if (strncmp(buf, "SSH-", 4) == 0)
339 debug("ssh_exchange_identification: %s", buf);
341 server_version_string = xstrdup(buf);
344 * Check that the versions match. In future this might accept
345 * several versions and set appropriate flags to handle them.
347 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
348 &remote_major, &remote_minor, remote_version) != 3)
349 fatal("Bad remote protocol version identification: '%.100s'", buf);
350 debug("Remote protocol version %d.%d, remote software version %.100s",
351 remote_major, remote_minor, remote_version);
353 compat_datafellows(remote_version);
356 switch(remote_major) {
358 if (remote_minor == 99 &&
359 (options.protocol & SSH_PROTO_2) &&
360 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
364 if (!(options.protocol & SSH_PROTO_1)) {
368 if (remote_minor < 3) {
369 fatal("Remote machine has too old SSH software version.");
370 } else if (remote_minor == 3) {
371 /* We speak 1.3, too. */
373 if (options.forward_agent) {
374 log("Agent forwarding disabled for protocol 1.3");
375 options.forward_agent = 0;
380 if (options.protocol & SSH_PROTO_2) {
390 fatal("Protocol major versions differ: %d vs. %d",
391 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
394 packet_set_ssh2_format();
395 /* Send our own protocol version identification. */
396 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
397 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
398 compat20 ? PROTOCOL_MINOR_2 : PROTOCOL_MINOR_1,
400 if (atomicio(write, connection_out, buf, strlen(buf)) != strlen(buf))
401 fatal("write: %.100s", strerror(errno));
402 client_version_string = xstrdup(buf);
403 chop(client_version_string);
404 chop(server_version_string);
405 debug("Local version string %.100s", client_version_string);
409 read_yes_or_no(const char *prompt, int defval)
418 f = fopen("/dev/tty", "rw");
426 fprintf(stderr, "%s", prompt);
427 if (fgets(buf, sizeof(buf), f) == NULL) {
428 /* Print a newline (the prompt probably didn\'t have one). */
429 fprintf(stderr, "\n");
430 strlcpy(buf, "no", sizeof buf);
432 /* Remove newline from response. */
433 if (strchr(buf, '\n'))
434 *strchr(buf, '\n') = 0;
438 if (strcmp(buf, "yes") == 0)
440 else if (strcmp(buf, "no") == 0)
443 fprintf(stderr, "Please type 'yes' or 'no'.\n");
454 * check whether the supplied host key is valid, return only if ok.
458 check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
459 const char *user_hostfile, const char *system_hostfile)
462 char *type = key_type(host_key);
464 char hostline[1000], *hostp;
465 HostStatus host_status;
466 HostStatus ip_status;
467 int local = 0, host_ip_differ = 0;
468 char ntop[NI_MAXHOST];
471 * Force accepting of the host key for loopback/localhost. The
472 * problem is that if the home directory is NFS-mounted to multiple
473 * machines, localhost will refer to a different machine in each of
474 * them, and the user will get bogus HOST_CHANGED warnings. This
475 * essentially disables host authentication for localhost; however,
476 * this is probably not a real problem.
478 /** hostaddr == 0! */
479 switch (hostaddr->sa_family) {
481 local = (ntohl(((struct sockaddr_in *)hostaddr)->sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
484 local = IN6_IS_ADDR_LOOPBACK(&(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
491 debug("Forcing accepting of host key for loopback/localhost.");
496 * Turn off check_host_ip for proxy connects, since
497 * we don't have the remote ip-address
499 if (options.proxy_command != NULL && options.check_host_ip)
500 options.check_host_ip = 0;
502 if (options.check_host_ip) {
503 if (getnameinfo(hostaddr, hostaddr->sa_len, ntop, sizeof(ntop),
504 NULL, 0, NI_NUMERICHOST) != 0)
505 fatal("check_host_key: getnameinfo failed");
510 * Store the host key from the known host file in here so that we can
511 * compare it with the key for the IP address.
513 file_key = key_new(host_key->type);
516 * Check if the host key is present in the user\'s list of known
517 * hosts or in the systemwide list.
519 host_status = check_host_in_hostfile(user_hostfile, host, host_key, file_key);
520 if (host_status == HOST_NEW)
521 host_status = check_host_in_hostfile(system_hostfile, host, host_key, file_key);
523 * Also perform check for the ip address, skip the check if we are
524 * localhost or the hostname was an ip address to begin with
526 if (options.check_host_ip && !local && strcmp(host, ip)) {
527 Key *ip_key = key_new(host_key->type);
528 ip_status = check_host_in_hostfile(user_hostfile, ip, host_key, ip_key);
530 if (ip_status == HOST_NEW)
531 ip_status = check_host_in_hostfile(system_hostfile, ip, host_key, ip_key);
532 if (host_status == HOST_CHANGED &&
533 (ip_status != HOST_CHANGED || !key_equal(ip_key, file_key)))
538 ip_status = host_status;
542 switch (host_status) {
544 /* The host is known and the key matches. */
545 debug("Host '%.200s' is known and matches the %s host key.",
547 if (options.check_host_ip) {
548 if (ip_status == HOST_NEW) {
549 if (!add_host_to_hostfile(user_hostfile, ip, host_key))
550 log("Failed to add the %s host key for IP address '%.30s' to the list of known hosts (%.30s).",
551 type, ip, user_hostfile);
553 log("Warning: Permanently added the %s host key for IP address '%.30s' to the list of known hosts.",
555 } else if (ip_status != HOST_OK)
556 log("Warning: the %s host key for '%.200s' differs from the key for the IP address '%.30s'",
561 /* The host is new. */
562 if (options.strict_host_key_checking == 1) {
563 /* User has requested strict host key checking. We will not add the host key
564 automatically. The only alternative left is to abort. */
565 fatal("No %s host key is known for %.200s and you have requested strict checking.", type, host);
566 } else if (options.strict_host_key_checking == 2) {
569 char *fp = key_fingerprint(host_key);
570 snprintf(prompt, sizeof(prompt),
571 "The authenticity of host '%.200s' can't be established.\n"
572 "%s key fingerprint is %s.\n"
573 "Are you sure you want to continue connecting (yes/no)? ",
575 if (!read_yes_or_no(prompt, -1))
576 fatal("Aborted by user!\n");
578 if (options.check_host_ip && ip_status == HOST_NEW && strcmp(host, ip)) {
579 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
584 /* If not in strict mode, add the key automatically to the local known_hosts file. */
585 if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
586 log("Failed to add the host to the list of known hosts (%.500s).",
589 log("Warning: Permanently added '%.200s' (%s) to the list of known hosts.",
593 if (options.check_host_ip && host_ip_differ) {
595 if (ip_status == HOST_NEW)
597 else if (ip_status == HOST_OK)
598 msg = "is unchanged";
600 msg = "has a different value";
601 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
602 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
603 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
604 error("The %s host key for %s has changed,", type, host);
605 error("and the key for the according IP address %s", ip);
606 error("%s. This could either mean that", msg);
607 error("DNS SPOOFING is happening or the IP address for the host");
608 error("and its host key have changed at the same time");
610 /* The host key has changed. */
611 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
612 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
613 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
614 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
615 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
616 error("It is also possible that the %s host key has just been changed.", type);
617 error("Please contact your system administrator.");
618 error("Add correct host key in %.100s to get rid of this message.",
622 * If strict host key checking is in use, the user will have
623 * to edit the key manually and we can only abort.
625 if (options.strict_host_key_checking)
626 fatal("%s host key for %.200s has changed and you have requested strict checking.", type, host);
629 * If strict host key checking has not been requested, allow
630 * the connection but without password authentication or
633 if (options.password_authentication) {
634 error("Password authentication is disabled to avoid trojan horses.");
635 options.password_authentication = 0;
637 if (options.forward_agent) {
638 error("Agent forwarding is disabled to avoid trojan horses.");
639 options.forward_agent = 0;
642 * XXX Should permit the user to change to use the new id.
643 * This could be done by converting the host key to an
644 * identifying sentence, tell that the host identifies itself
645 * by that sentence, and ask the user if he/she whishes to
646 * accept the authentication.
650 if (options.check_host_ip)
656 try_krb5_authentication(krb5_context *context, krb5_auth_context *auth_context)
658 krb5_error_code problem;
661 krb5_ccache ccache = NULL;
662 const char *remotehost;
664 int type, payload_len;
665 krb5_ap_rep_enc_part *reply = NULL;
668 memset(&ap, 0, sizeof(ap));
670 problem = krb5_init_context(context);
676 tkfile = krb5_cc_default_name(*context);
677 if (strncmp(tkfile, "FILE:", 5) == 0)
680 if (stat(tkfile, &buf) == 0 && getuid() != buf.st_uid) {
681 debug("Kerberos V5: could not get default ccache (permission denied).");
686 problem = krb5_cc_default(*context, &ccache);
692 remotehost = get_canonical_hostname();
694 problem = krb5_mk_req(*context, auth_context, AP_OPTS_MUTUAL_REQUIRED,
695 "host", remotehost, NULL, ccache, &ap);
701 packet_start(SSH_CMSG_AUTH_KERBEROS);
702 packet_put_string((char *) ap.data, ap.length);
709 type = packet_read(&payload_len);
711 case SSH_SMSG_FAILURE:
712 /* Should really be SSH_SMSG_AUTH_KERBEROS_FAILURE */
713 debug("Kerberos V5 authentication failed.");
717 case SSH_SMSG_AUTH_KERBEROS_RESPONSE:
718 /* SSH_SMSG_AUTH_KERBEROS_SUCCESS */
719 debug("Kerberos V5 authentication accepted.");
721 /* Get server's response. */
722 ap.data = packet_get_string((unsigned int *) &ap.length);
724 packet_integrity_check(payload_len, 4 + ap.length, type);
725 /* XXX je to dobre? */
727 problem = krb5_rd_rep(*context, *auth_context, &ap, &reply);
735 packet_disconnect("Protocol error on Kerberos V5 response: %d", type);
743 krb5_cc_close(*context, ccache);
745 krb5_free_ap_rep_enc_part(*context, reply);
754 send_krb5_tgt(krb5_context context, krb5_auth_context auth_context)
757 int type, payload_len;
758 krb5_error_code problem;
760 krb5_ccache ccache = NULL;
762 krb5_kdc_flags flags;
763 const char* remotehost = get_canonical_hostname();
765 memset(&creds, 0, sizeof(creds));
766 memset(&outbuf, 0, sizeof(outbuf));
768 fd = packet_get_connection_in();
769 problem = krb5_auth_con_setaddrs_from_fd(context, auth_context, &fd);
775 tkfile = krb5_cc_default_name(context);
776 if (strncmp(tkfile, "FILE:", 5) == 0)
779 if (stat(tkfile, &buf) == 0 && getuid() != buf.st_uid) {
780 debug("Kerberos V5: could not get default ccache (permission denied).");
785 problem = krb5_cc_default(context, &ccache);
790 problem = krb5_cc_get_principal(context, ccache, &creds.client);
795 problem = krb5_build_principal(context, &creds.server,
796 strlen(creds.client->realm),
805 creds.times.endtime = 0;
808 flags.b.forwarded = 1;
809 flags.b.forwardable = krb5_config_get_bool(context, NULL,
810 "libdefaults", "forwardable", NULL);
812 problem = krb5_get_forwarded_creds (context,
823 packet_start(SSH_CMSG_HAVE_KERBEROS_TGT);
824 packet_put_string((char *)outbuf.data, outbuf.length);
828 type = packet_read(&payload_len);
830 case SSH_SMSG_SUCCESS:
832 case SSH_SMSG_FAILURE:
840 krb5_free_principal(context, creds.client);
842 krb5_free_principal(context, creds.server);
844 krb5_cc_close(context, ccache);
853 * Starts a dialog with the server, and authenticates the current user on the
854 * server. This does not need any extra privileges. The basic connection
855 * to the server must already have been established before this is called.
856 * If login fails, this function prints an error and never returns.
857 * This function does not require super-user privileges.
860 ssh_login(int host_key_valid, RSA *own_host_key, const char *orighost,
861 struct sockaddr *hostaddr, uid_t original_real_uid)
865 char *server_user, *local_user;
867 /* Get local user name. Use it as server user if no user name was given. */
868 pw = getpwuid(original_real_uid);
870 fatal("User id %u not found from user database.", original_real_uid);
871 local_user = xstrdup(pw->pw_name);
872 server_user = options.user ? options.user : local_user;
874 /* Convert the user-supplied hostname into all lowercase. */
875 host = xstrdup(orighost);
876 for (cp = host; *cp; cp++)
880 /* Exchange protocol version identification strings with the server. */
881 ssh_exchange_identification();
883 /* Put the connection into non-blocking mode. */
884 packet_set_nonblocking();
887 /* authenticate user */
889 ssh_kex2(host, hostaddr);
890 ssh_userauth2(server_user, host);
892 ssh_kex(host, hostaddr);
893 ssh_userauth(local_user, server_user, host, host_key_valid, own_host_key);
898 ssh_put_password(char *password)
903 size = roundup(strlen(password) + 1, 32);
904 padded = xmalloc(size);
905 memset(padded, 0, size);
906 strlcpy(padded, password, size);
907 packet_put_string(padded, size);
908 memset(padded, 0, size);