1 /* $OpenBSD: sshconnect.c,v 1.234 2011/05/24 07:15:47 djm Exp $ */
2 /*
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * All rights reserved
6 * Code to connect to a remote host, and to perform the client side of the
7 * login (authentication) dialog.
8 *
9 * As far as I am concerned, the code I have written for this software
10 * can be used freely for any purpose. Any derived versions of this
11 * software must be clearly marked as such, and if the derived work is
12 * incompatible with the protocol description in the RFC file, it must be
13 * called by a name other than "ssh" or "Secure Shell".
14 */
15
16 #include "includes.h"
17
18 #include <sys/types.h>
19 #include <sys/wait.h>
20 #include <sys/stat.h>
21 #include <sys/socket.h>
22 #ifdef HAVE_SYS_TIME_H
23 # include <sys/time.h>
24 #endif
25
26 #include <netinet/in.h>
27 #include <arpa/inet.h>
28
29 #include <ctype.h>
30 #include <errno.h>
31 #include <fcntl.h>
32 #include <netdb.h>
33 #ifdef HAVE_PATHS_H
34 #include <paths.h>
35 #endif
36 #include <pwd.h>
37 #include <signal.h>
38 #include <stdarg.h>
39 #include <stdio.h>
40 #include <stdlib.h>
41 #include <string.h>
42 #include <unistd.h>
43
44 #include "xmalloc.h"
45 #include "key.h"
46 #include "hostfile.h"
47 #include "ssh.h"
48 #include "rsa.h"
49 #include "buffer.h"
50 #include "packet.h"
51 #include "uidswap.h"
52 #include "compat.h"
53 #include "key.h"
54 #include "sshconnect.h"
55 #include "hostfile.h"
56 #include "log.h"
57 #include "readconf.h"
58 #include "atomicio.h"
59 #include "misc.h"
60 #include "dns.h"
61 #include "roaming.h"
62 #include "ssh2.h"
63 #include "version.h"
64
65 char *client_version_string = NULL;
66 char *server_version_string = NULL;
67
68 static int matching_host_key_dns = 0;
69
70 static pid_t proxy_command_pid = 0;
71
72 /* import */
73 extern Options options;
74 extern char *__progname;
75 extern uid_t original_real_uid;
76 extern uid_t original_effective_uid;
77
78 static int show_other_keys(struct hostkeys *, Key *);
79 static void warn_changed_key(Key *);
80
81 /*
82 * Connect to the given ssh server using a proxy command.
83 */
84 static int
ssh_proxy_connect(const char * host,u_short port,const char * proxy_command)85 ssh_proxy_connect(const char *host, u_short port, const char *proxy_command)
86 {
87 char *command_string, *tmp;
88 int pin[2], pout[2];
89 pid_t pid;
90 char *shell, strport[NI_MAXSERV];
91
92 if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
93 shell = _PATH_BSHELL;
94
95 /* Convert the port number into a string. */
96 snprintf(strport, sizeof strport, "%hu", port);
97
98 /*
99 * Build the final command string in the buffer by making the
100 * appropriate substitutions to the given proxy command.
101 *
102 * Use "exec" to avoid "sh -c" processes on some platforms
103 * (e.g. Solaris)
104 */
105 xasprintf(&tmp, "exec %s", proxy_command);
106 command_string = percent_expand(tmp, "h", host, "p", strport,
107 "r", options.user, (char *)NULL);
108 xfree(tmp);
109
110 /* Create pipes for communicating with the proxy. */
111 if (pipe(pin) < 0 || pipe(pout) < 0)
112 fatal("Could not create pipes to communicate with the proxy: %.100s",
113 strerror(errno));
114
115 debug("Executing proxy command: %.500s", command_string);
116
117 /* Fork and execute the proxy command. */
118 if ((pid = fork()) == 0) {
119 char *argv[10];
120
121 /* Child. Permanently give up superuser privileges. */
122 permanently_drop_suid(original_real_uid);
123
124 /* Redirect stdin and stdout. */
125 close(pin[1]);
126 if (pin[0] != 0) {
127 if (dup2(pin[0], 0) < 0)
128 perror("dup2 stdin");
129 close(pin[0]);
130 }
131 close(pout[0]);
132 if (dup2(pout[1], 1) < 0)
133 perror("dup2 stdout");
134 /* Cannot be 1 because pin allocated two descriptors. */
135 close(pout[1]);
136
137 /* Stderr is left as it is so that error messages get
138 printed on the user's terminal. */
139 argv[0] = shell;
140 argv[1] = "-c";
141 argv[2] = command_string;
142 argv[3] = NULL;
143
144 /* Execute the proxy command. Note that we gave up any
145 extra privileges above. */
146 signal(SIGPIPE, SIG_DFL);
147 execv(argv[0], argv);
148 perror(argv[0]);
149 exit(1);
150 }
151 /* Parent. */
152 if (pid < 0)
153 fatal("fork failed: %.100s", strerror(errno));
154 else
155 proxy_command_pid = pid; /* save pid to clean up later */
156
157 /* Close child side of the descriptors. */
158 close(pin[0]);
159 close(pout[1]);
160
161 /* Free the command name. */
162 xfree(command_string);
163
164 /* Set the connection file descriptors. */
165 packet_set_connection(pout[0], pin[1]);
166 packet_set_timeout(options.server_alive_interval,
167 options.server_alive_count_max);
168
169 /* Indicate OK return */
170 return 0;
171 }
172
173 void
ssh_kill_proxy_command(void)174 ssh_kill_proxy_command(void)
175 {
176 /*
177 * Send SIGHUP to proxy command if used. We don't wait() in
178 * case it hangs and instead rely on init to reap the child
179 */
180 if (proxy_command_pid > 1)
181 kill(proxy_command_pid, SIGHUP);
182 }
183
184 /*
185 * Creates a (possibly privileged) socket for use as the ssh connection.
186 */
187 static int
ssh_create_socket(int privileged,struct addrinfo * ai)188 ssh_create_socket(int privileged, struct addrinfo *ai)
189 {
190 int sock, gaierr;
191 struct addrinfo hints, *res;
192
193 /*
194 * If we are running as root and want to connect to a privileged
195 * port, bind our own socket to a privileged port.
196 */
197 if (privileged) {
198 int p = IPPORT_RESERVED - 1;
199 PRIV_START;
200 sock = rresvport_af(&p, ai->ai_family);
201 PRIV_END;
202 if (sock < 0)
203 error("rresvport: af=%d %.100s", ai->ai_family,
204 strerror(errno));
205 else
206 debug("Allocated local port %d.", p);
207 return sock;
208 }
209 sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
210 if (sock < 0) {
211 error("socket: %.100s", strerror(errno));
212 return -1;
213 }
214 fcntl(sock, F_SETFD, FD_CLOEXEC);
215
216 /* Bind the socket to an alternative local IP address */
217 if (options.bind_address == NULL)
218 return sock;
219
220 memset(&hints, 0, sizeof(hints));
221 hints.ai_family = ai->ai_family;
222 hints.ai_socktype = ai->ai_socktype;
223 hints.ai_protocol = ai->ai_protocol;
224 hints.ai_flags = AI_PASSIVE;
225 gaierr = getaddrinfo(options.bind_address, NULL, &hints, &res);
226 if (gaierr) {
227 error("getaddrinfo: %s: %s", options.bind_address,
228 ssh_gai_strerror(gaierr));
229 close(sock);
230 return -1;
231 }
232 if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
233 error("bind: %s: %s", options.bind_address, strerror(errno));
234 close(sock);
235 freeaddrinfo(res);
236 return -1;
237 }
238 freeaddrinfo(res);
239 return sock;
240 }
241
242 static int
timeout_connect(int sockfd,const struct sockaddr * serv_addr,socklen_t addrlen,int * timeoutp)243 timeout_connect(int sockfd, const struct sockaddr *serv_addr,
244 socklen_t addrlen, int *timeoutp)
245 {
246 fd_set *fdset;
247 struct timeval tv, t_start;
248 socklen_t optlen;
249 int optval, rc, result = -1;
250
251 gettimeofday(&t_start, NULL);
252
253 if (*timeoutp <= 0) {
254 result = connect(sockfd, serv_addr, addrlen);
255 goto done;
256 }
257
258 set_nonblock(sockfd);
259 rc = connect(sockfd, serv_addr, addrlen);
260 if (rc == 0) {
261 unset_nonblock(sockfd);
262 result = 0;
263 goto done;
264 }
265 if (errno != EINPROGRESS) {
266 result = -1;
267 goto done;
268 }
269
270 fdset = (fd_set *)xcalloc(howmany(sockfd + 1, NFDBITS),
271 sizeof(fd_mask));
272 FD_SET(sockfd, fdset);
273 ms_to_timeval(&tv, *timeoutp);
274
275 for (;;) {
276 rc = select(sockfd + 1, NULL, fdset, NULL, &tv);
277 if (rc != -1 || errno != EINTR)
278 break;
279 }
280
281 switch (rc) {
282 case 0:
283 /* Timed out */
284 errno = ETIMEDOUT;
285 break;
286 case -1:
287 /* Select error */
288 debug("select: %s", strerror(errno));
289 break;
290 case 1:
291 /* Completed or failed */
292 optval = 0;
293 optlen = sizeof(optval);
294 if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &optval,
295 &optlen) == -1) {
296 debug("getsockopt: %s", strerror(errno));
297 break;
298 }
299 if (optval != 0) {
300 errno = optval;
301 break;
302 }
303 result = 0;
304 unset_nonblock(sockfd);
305 break;
306 default:
307 /* Should not occur */
308 fatal("Bogus return (%d) from select()", rc);
309 }
310
311 xfree(fdset);
312
313 done:
314 if (result == 0 && *timeoutp > 0) {
315 ms_subtract_diff(&t_start, timeoutp);
316 if (*timeoutp <= 0) {
317 errno = ETIMEDOUT;
318 result = -1;
319 }
320 }
321
322 return (result);
323 }
324
325 /*
326 * Opens a TCP/IP connection to the remote server on the given host.
327 * The address of the remote host will be returned in hostaddr.
328 * If port is 0, the default port will be used. If needpriv is true,
329 * a privileged port will be allocated to make the connection.
330 * This requires super-user privileges if needpriv is true.
331 * Connection_attempts specifies the maximum number of tries (one per
332 * second). If proxy_command is non-NULL, it specifies the command (with %h
333 * and %p substituted for host and port, respectively) to use to contact
334 * the daemon.
335 */
336 int
ssh_connect(const char * host,struct sockaddr_storage * hostaddr,u_short port,int family,int connection_attempts,int * timeout_ms,int want_keepalive,int needpriv,const char * proxy_command)337 ssh_connect(const char *host, struct sockaddr_storage * hostaddr,
338 u_short port, int family, int connection_attempts, int *timeout_ms,
339 int want_keepalive, int needpriv, const char *proxy_command)
340 {
341 int gaierr;
342 int on = 1;
343 int sock = -1, attempt;
344 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
345 struct addrinfo hints, *ai, *aitop;
346
347 debug2("ssh_connect: needpriv %d", needpriv);
348
349 /* If a proxy command is given, connect using it. */
350 if (proxy_command != NULL)
351 return ssh_proxy_connect(host, port, proxy_command);
352
353 /* No proxy command. */
354
355 memset(&hints, 0, sizeof(hints));
356 hints.ai_family = family;
357 hints.ai_socktype = SOCK_STREAM;
358 snprintf(strport, sizeof strport, "%u", port);
359 if ((gaierr = getaddrinfo(host, strport, &hints, &aitop)) != 0)
360 fatal("%s: Could not resolve hostname %.100s: %s", __progname,
361 host, ssh_gai_strerror(gaierr));
362
363 for (attempt = 0; attempt < connection_attempts; attempt++) {
364 if (attempt > 0) {
365 /* Sleep a moment before retrying. */
366 sleep(1);
367 debug("Trying again...");
368 }
369 /*
370 * Loop through addresses for this host, and try each one in
371 * sequence until the connection succeeds.
372 */
373 for (ai = aitop; ai; ai = ai->ai_next) {
374 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
375 continue;
376 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
377 ntop, sizeof(ntop), strport, sizeof(strport),
378 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
379 error("ssh_connect: getnameinfo failed");
380 continue;
381 }
382 debug("Connecting to %.200s [%.100s] port %s.",
383 host, ntop, strport);
384
385 /* Create a socket for connecting. */
386 sock = ssh_create_socket(needpriv, ai);
387 if (sock < 0)
388 /* Any error is already output */
389 continue;
390
391 if (timeout_connect(sock, ai->ai_addr, ai->ai_addrlen,
392 timeout_ms) >= 0) {
393 /* Successful connection. */
394 memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
395 break;
396 } else {
397 debug("connect to address %s port %s: %s",
398 ntop, strport, strerror(errno));
399 close(sock);
400 sock = -1;
401 }
402 }
403 if (sock != -1)
404 break; /* Successful connection. */
405 }
406
407 freeaddrinfo(aitop);
408
409 /* Return failure if we didn't get a successful connection. */
410 if (sock == -1) {
411 error("ssh: connect to host %s port %s: %s",
412 host, strport, strerror(errno));
413 return (-1);
414 }
415
416 debug("Connection established.");
417
418 /* Set SO_KEEPALIVE if requested. */
419 if (want_keepalive &&
420 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
421 sizeof(on)) < 0)
422 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
423
424 /* Set the connection. */
425 packet_set_connection(sock, sock);
426 packet_set_timeout(options.server_alive_interval,
427 options.server_alive_count_max);
428
429 return 0;
430 }
431
432 /*
433 * Waits for the server identification string, and sends our own
434 * identification string.
435 */
436 void
ssh_exchange_identification(int timeout_ms)437 ssh_exchange_identification(int timeout_ms)
438 {
439 char buf[256], remote_version[256]; /* must be same size! */
440 int remote_major, remote_minor, mismatch;
441 int connection_in = packet_get_connection_in();
442 int connection_out = packet_get_connection_out();
443 int minor1 = PROTOCOL_MINOR_1;
444 u_int i, n;
445 size_t len;
446 int fdsetsz, remaining, rc;
447 struct timeval t_start, t_remaining;
448 fd_set *fdset;
449
450 fdsetsz = howmany(connection_in + 1, NFDBITS) * sizeof(fd_mask);
451 fdset = xcalloc(1, fdsetsz);
452
453 /* Read other side's version identification. */
454 remaining = timeout_ms;
455 for (n = 0;;) {
456 for (i = 0; i < sizeof(buf) - 1; i++) {
457 if (timeout_ms > 0) {
458 gettimeofday(&t_start, NULL);
459 ms_to_timeval(&t_remaining, remaining);
460 FD_SET(connection_in, fdset);
461 rc = select(connection_in + 1, fdset, NULL,
462 fdset, &t_remaining);
463 ms_subtract_diff(&t_start, &remaining);
464 if (rc == 0 || remaining <= 0)
465 fatal("Connection timed out during "
466 "banner exchange");
467 if (rc == -1) {
468 if (errno == EINTR)
469 continue;
470 fatal("ssh_exchange_identification: "
471 "select: %s", strerror(errno));
472 }
473 }
474
475 len = roaming_atomicio(read, connection_in, &buf[i], 1);
476
477 if (len != 1 && errno == EPIPE)
478 fatal("ssh_exchange_identification: "
479 "Connection closed by remote host");
480 else if (len != 1)
481 fatal("ssh_exchange_identification: "
482 "read: %.100s", strerror(errno));
483 if (buf[i] == '\r') {
484 buf[i] = '\n';
485 buf[i + 1] = 0;
486 continue; /**XXX wait for \n */
487 }
488 if (buf[i] == '\n') {
489 buf[i + 1] = 0;
490 break;
491 }
492 if (++n > 65536)
493 fatal("ssh_exchange_identification: "
494 "No banner received");
495 }
496 buf[sizeof(buf) - 1] = 0;
497 if (strncmp(buf, "SSH-", 4) == 0)
498 break;
499 debug("ssh_exchange_identification: %s", buf);
500 }
501 server_version_string = xstrdup(buf);
502 xfree(fdset);
503
504 /*
505 * Check that the versions match. In future this might accept
506 * several versions and set appropriate flags to handle them.
507 */
508 if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
509 &remote_major, &remote_minor, remote_version) != 3)
510 fatal("Bad remote protocol version identification: '%.100s'", buf);
511 debug("Remote protocol version %d.%d, remote software version %.100s",
512 remote_major, remote_minor, remote_version);
513
514 compat_datafellows(remote_version);
515 mismatch = 0;
516
517 switch (remote_major) {
518 case 1:
519 if (remote_minor == 99 &&
520 (options.protocol & SSH_PROTO_2) &&
521 !(options.protocol & SSH_PROTO_1_PREFERRED)) {
522 enable_compat20();
523 break;
524 }
525 if (!(options.protocol & SSH_PROTO_1)) {
526 mismatch = 1;
527 break;
528 }
529 if (remote_minor < 3) {
530 fatal("Remote machine has too old SSH software version.");
531 } else if (remote_minor == 3 || remote_minor == 4) {
532 /* We speak 1.3, too. */
533 enable_compat13();
534 minor1 = 3;
535 if (options.forward_agent) {
536 logit("Agent forwarding disabled for protocol 1.3");
537 options.forward_agent = 0;
538 }
539 }
540 break;
541 case 2:
542 if (options.protocol & SSH_PROTO_2) {
543 enable_compat20();
544 break;
545 }
546 /* FALLTHROUGH */
547 default:
548 mismatch = 1;
549 break;
550 }
551 if (mismatch)
552 fatal("Protocol major versions differ: %d vs. %d",
553 (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
554 remote_major);
555 /* Send our own protocol version identification. */
556 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s%s",
557 compat20 ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
558 compat20 ? PROTOCOL_MINOR_2 : minor1,
559 SSH_VERSION, compat20 ? "\r\n" : "\n");
560 if (roaming_atomicio(vwrite, connection_out, buf, strlen(buf))
561 != strlen(buf))
562 fatal("write: %.100s", strerror(errno));
563 client_version_string = xstrdup(buf);
564 chop(client_version_string);
565 chop(server_version_string);
566 debug("Local version string %.100s", client_version_string);
567 }
568
569 /* defaults to 'no' */
570 static int
confirm(const char * prompt)571 confirm(const char *prompt)
572 {
573 const char *msg, *again = "Please type 'yes' or 'no': ";
574 char *p;
575 int ret = -1;
576
577 if (options.batch_mode)
578 return 0;
579 for (msg = prompt;;msg = again) {
580 p = read_passphrase(msg, RP_ECHO);
581 if (p == NULL ||
582 (p[0] == '\0') || (p[0] == '\n') ||
583 strncasecmp(p, "no", 2) == 0)
584 ret = 0;
585 if (p && strncasecmp(p, "yes", 3) == 0)
586 ret = 1;
587 if (p)
588 xfree(p);
589 if (ret != -1)
590 return ret;
591 }
592 }
593
594 static int
check_host_cert(const char * host,const Key * host_key)595 check_host_cert(const char *host, const Key *host_key)
596 {
597 const char *reason;
598
599 if (key_cert_check_authority(host_key, 1, 0, host, &reason) != 0) {
600 error("%s", reason);
601 return 0;
602 }
603 if (buffer_len(&host_key->cert->critical) != 0) {
604 error("Certificate for %s contains unsupported "
605 "critical options(s)", host);
606 return 0;
607 }
608 return 1;
609 }
610
611 static int
sockaddr_is_local(struct sockaddr * hostaddr)612 sockaddr_is_local(struct sockaddr *hostaddr)
613 {
614 switch (hostaddr->sa_family) {
615 case AF_INET:
616 return (ntohl(((struct sockaddr_in *)hostaddr)->
617 sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
618 case AF_INET6:
619 return IN6_IS_ADDR_LOOPBACK(
620 &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
621 default:
622 return 0;
623 }
624 }
625
626 /*
627 * Prepare the hostname and ip address strings that are used to lookup
628 * host keys in known_hosts files. These may have a port number appended.
629 */
630 void
get_hostfile_hostname_ipaddr(char * hostname,struct sockaddr * hostaddr,u_short port,char ** hostfile_hostname,char ** hostfile_ipaddr)631 get_hostfile_hostname_ipaddr(char *hostname, struct sockaddr *hostaddr,
632 u_short port, char **hostfile_hostname, char **hostfile_ipaddr)
633 {
634 char ntop[NI_MAXHOST];
635 socklen_t addrlen;
636
637 switch (hostaddr == NULL ? -1 : hostaddr->sa_family) {
638 case -1:
639 addrlen = 0;
640 break;
641 case AF_INET:
642 addrlen = sizeof(struct sockaddr_in);
643 break;
644 case AF_INET6:
645 addrlen = sizeof(struct sockaddr_in6);
646 break;
647 default:
648 addrlen = sizeof(struct sockaddr);
649 break;
650 }
651
652 /*
653 * We don't have the remote ip-address for connections
654 * using a proxy command
655 */
656 if (hostfile_ipaddr != NULL) {
657 if (options.proxy_command == NULL) {
658 if (getnameinfo(hostaddr, addrlen,
659 ntop, sizeof(ntop), NULL, 0, NI_NUMERICHOST) != 0)
660 fatal("check_host_key: getnameinfo failed");
661 *hostfile_ipaddr = put_host_port(ntop, port);
662 } else {
663 *hostfile_ipaddr = xstrdup("<no hostip for proxy "
664 "command>");
665 }
666 }
667
668 /*
669 * Allow the user to record the key under a different name or
670 * differentiate a non-standard port. This is useful for ssh
671 * tunneling over forwarded connections or if you run multiple
672 * sshd's on different ports on the same machine.
673 */
674 if (hostfile_hostname != NULL) {
675 if (options.host_key_alias != NULL) {
676 *hostfile_hostname = xstrdup(options.host_key_alias);
677 debug("using hostkeyalias: %s", *hostfile_hostname);
678 } else {
679 *hostfile_hostname = put_host_port(hostname, port);
680 }
681 }
682 }
683
684 /*
685 * check whether the supplied host key is valid, return -1 if the key
686 * is not valid. user_hostfile[0] will not be updated if 'readonly' is true.
687 */
688 #define RDRW 0
689 #define RDONLY 1
690 #define ROQUIET 2
691 static int
check_host_key(char * hostname,struct sockaddr * hostaddr,u_short port,Key * host_key,int readonly,char ** user_hostfiles,u_int num_user_hostfiles,char ** system_hostfiles,u_int num_system_hostfiles)692 check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
693 Key *host_key, int readonly,
694 char **user_hostfiles, u_int num_user_hostfiles,
695 char **system_hostfiles, u_int num_system_hostfiles)
696 {
697 HostStatus host_status;
698 HostStatus ip_status;
699 Key *raw_key = NULL;
700 char *ip = NULL, *host = NULL;
701 char hostline[1000], *hostp, *fp, *ra;
702 char msg[1024];
703 const char *type;
704 const struct hostkey_entry *host_found, *ip_found;
705 int len, cancelled_forwarding = 0;
706 int local = sockaddr_is_local(hostaddr);
707 int r, want_cert = key_is_cert(host_key), host_ip_differ = 0;
708 struct hostkeys *host_hostkeys, *ip_hostkeys;
709 u_int i;
710
711 /*
712 * Force accepting of the host key for loopback/localhost. The
713 * problem is that if the home directory is NFS-mounted to multiple
714 * machines, localhost will refer to a different machine in each of
715 * them, and the user will get bogus HOST_CHANGED warnings. This
716 * essentially disables host authentication for localhost; however,
717 * this is probably not a real problem.
718 */
719 if (options.no_host_authentication_for_localhost == 1 && local &&
720 options.host_key_alias == NULL) {
721 debug("Forcing accepting of host key for "
722 "loopback/localhost.");
723 return 0;
724 }
725
726 /*
727 * Prepare the hostname and address strings used for hostkey lookup.
728 * In some cases, these will have a port number appended.
729 */
730 get_hostfile_hostname_ipaddr(hostname, hostaddr, port, &host, &ip);
731
732 /*
733 * Turn off check_host_ip if the connection is to localhost, via proxy
734 * command or if we don't have a hostname to compare with
735 */
736 if (options.check_host_ip && (local ||
737 strcmp(hostname, ip) == 0 || options.proxy_command != NULL))
738 options.check_host_ip = 0;
739
740 host_hostkeys = init_hostkeys();
741 for (i = 0; i < num_user_hostfiles; i++)
742 load_hostkeys(host_hostkeys, host, user_hostfiles[i]);
743 for (i = 0; i < num_system_hostfiles; i++)
744 load_hostkeys(host_hostkeys, host, system_hostfiles[i]);
745
746 ip_hostkeys = NULL;
747 if (!want_cert && options.check_host_ip) {
748 ip_hostkeys = init_hostkeys();
749 for (i = 0; i < num_user_hostfiles; i++)
750 load_hostkeys(ip_hostkeys, ip, user_hostfiles[i]);
751 for (i = 0; i < num_system_hostfiles; i++)
752 load_hostkeys(ip_hostkeys, ip, system_hostfiles[i]);
753 }
754
755 retry:
756 /* Reload these as they may have changed on cert->key downgrade */
757 want_cert = key_is_cert(host_key);
758 type = key_type(host_key);
759
760 /*
761 * Check if the host key is present in the user's list of known
762 * hosts or in the systemwide list.
763 */
764 host_status = check_key_in_hostkeys(host_hostkeys, host_key,
765 &host_found);
766
767 /*
768 * Also perform check for the ip address, skip the check if we are
769 * localhost, looking for a certificate, or the hostname was an ip
770 * address to begin with.
771 */
772 if (!want_cert && ip_hostkeys != NULL) {
773 ip_status = check_key_in_hostkeys(ip_hostkeys, host_key,
774 &ip_found);
775 if (host_status == HOST_CHANGED &&
776 (ip_status != HOST_CHANGED ||
777 (ip_found != NULL &&
778 !key_equal(ip_found->key, host_found->key))))
779 host_ip_differ = 1;
780 } else
781 ip_status = host_status;
782
783 switch (host_status) {
784 case HOST_OK:
785 /* The host is known and the key matches. */
786 debug("Host '%.200s' is known and matches the %s host %s.",
787 host, type, want_cert ? "certificate" : "key");
788 debug("Found %s in %s:%lu", want_cert ? "CA key" : "key",
789 host_found->file, host_found->line);
790 if (want_cert && !check_host_cert(hostname, host_key))
791 goto fail;
792 if (options.check_host_ip && ip_status == HOST_NEW) {
793 if (readonly || want_cert)
794 logit("%s host key for IP address "
795 "'%.128s' not in list of known hosts.",
796 type, ip);
797 else if (!add_host_to_hostfile(user_hostfiles[0], ip,
798 host_key, options.hash_known_hosts))
799 logit("Failed to add the %s host key for IP "
800 "address '%.128s' to the list of known "
801 "hosts (%.30s).", type, ip,
802 user_hostfiles[0]);
803 else
804 logit("Warning: Permanently added the %s host "
805 "key for IP address '%.128s' to the list "
806 "of known hosts.", type, ip);
807 } else if (options.visual_host_key) {
808 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
809 ra = key_fingerprint(host_key, SSH_FP_MD5,
810 SSH_FP_RANDOMART);
811 logit("Host key fingerprint is %s\n%s\n", fp, ra);
812 xfree(ra);
813 xfree(fp);
814 }
815 break;
816 case HOST_NEW:
817 if (options.host_key_alias == NULL && port != 0 &&
818 port != SSH_DEFAULT_PORT) {
819 debug("checking without port identifier");
820 if (check_host_key(hostname, hostaddr, 0, host_key,
821 ROQUIET, user_hostfiles, num_user_hostfiles,
822 system_hostfiles, num_system_hostfiles) == 0) {
823 debug("found matching key w/out port");
824 break;
825 }
826 }
827 if (readonly || want_cert)
828 goto fail;
829 /* The host is new. */
830 if (options.strict_host_key_checking == 1) {
831 /*
832 * User has requested strict host key checking. We
833 * will not add the host key automatically. The only
834 * alternative left is to abort.
835 */
836 error("No %s host key is known for %.200s and you "
837 "have requested strict checking.", type, host);
838 goto fail;
839 } else if (options.strict_host_key_checking == 2) {
840 char msg1[1024], msg2[1024];
841
842 if (show_other_keys(host_hostkeys, host_key))
843 snprintf(msg1, sizeof(msg1),
844 "\nbut keys of different type are already"
845 " known for this host.");
846 else
847 snprintf(msg1, sizeof(msg1), ".");
848 /* The default */
849 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
850 ra = key_fingerprint(host_key, SSH_FP_MD5,
851 SSH_FP_RANDOMART);
852 msg2[0] = '\0';
853 if (options.verify_host_key_dns) {
854 if (matching_host_key_dns)
855 snprintf(msg2, sizeof(msg2),
856 "Matching host key fingerprint"
857 " found in DNS.\n");
858 else
859 snprintf(msg2, sizeof(msg2),
860 "No matching host key fingerprint"
861 " found in DNS.\n");
862 }
863 snprintf(msg, sizeof(msg),
864 "The authenticity of host '%.200s (%s)' can't be "
865 "established%s\n"
866 "%s key fingerprint is %s.%s%s\n%s"
867 "Are you sure you want to continue connecting "
868 "(yes/no)? ",
869 host, ip, msg1, type, fp,
870 options.visual_host_key ? "\n" : "",
871 options.visual_host_key ? ra : "",
872 msg2);
873 xfree(ra);
874 xfree(fp);
875 if (!confirm(msg))
876 goto fail;
877 }
878 /*
879 * If not in strict mode, add the key automatically to the
880 * local known_hosts file.
881 */
882 if (options.check_host_ip && ip_status == HOST_NEW) {
883 snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
884 hostp = hostline;
885 if (options.hash_known_hosts) {
886 /* Add hash of host and IP separately */
887 r = add_host_to_hostfile(user_hostfiles[0],
888 host, host_key, options.hash_known_hosts) &&
889 add_host_to_hostfile(user_hostfiles[0], ip,
890 host_key, options.hash_known_hosts);
891 } else {
892 /* Add unhashed "host,ip" */
893 r = add_host_to_hostfile(user_hostfiles[0],
894 hostline, host_key,
895 options.hash_known_hosts);
896 }
897 } else {
898 r = add_host_to_hostfile(user_hostfiles[0], host,
899 host_key, options.hash_known_hosts);
900 hostp = host;
901 }
902
903 if (!r)
904 logit("Failed to add the host to the list of known "
905 "hosts (%.500s).", user_hostfiles[0]);
906 else
907 logit("Warning: Permanently added '%.200s' (%s) to the "
908 "list of known hosts.", hostp, type);
909 break;
910 case HOST_REVOKED:
911 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
912 error("@ WARNING: REVOKED HOST KEY DETECTED! @");
913 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
914 error("The %s host key for %s is marked as revoked.", type, host);
915 error("This could mean that a stolen key is being used to");
916 error("impersonate this host.");
917
918 /*
919 * If strict host key checking is in use, the user will have
920 * to edit the key manually and we can only abort.
921 */
922 if (options.strict_host_key_checking) {
923 error("%s host key for %.200s was revoked and you have "
924 "requested strict checking.", type, host);
925 goto fail;
926 }
927 goto continue_unsafe;
928
929 case HOST_CHANGED:
930 if (want_cert) {
931 /*
932 * This is only a debug() since it is valid to have
933 * CAs with wildcard DNS matches that don't match
934 * all hosts that one might visit.
935 */
936 debug("Host certificate authority does not "
937 "match %s in %s:%lu", CA_MARKER,
938 host_found->file, host_found->line);
939 goto fail;
940 }
941 if (readonly == ROQUIET)
942 goto fail;
943 if (options.check_host_ip && host_ip_differ) {
944 char *key_msg;
945 if (ip_status == HOST_NEW)
946 key_msg = "is unknown";
947 else if (ip_status == HOST_OK)
948 key_msg = "is unchanged";
949 else
950 key_msg = "has a different value";
951 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
952 error("@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @");
953 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
954 error("The %s host key for %s has changed,", type, host);
955 error("and the key for the corresponding IP address %s", ip);
956 error("%s. This could either mean that", key_msg);
957 error("DNS SPOOFING is happening or the IP address for the host");
958 error("and its host key have changed at the same time.");
959 if (ip_status != HOST_NEW)
960 error("Offending key for IP in %s:%lu",
961 ip_found->file, ip_found->line);
962 }
963 /* The host key has changed. */
964 warn_changed_key(host_key);
965 error("Add correct host key in %.100s to get rid of this message.",
966 user_hostfiles[0]);
967 error("Offending %s key in %s:%lu", key_type(host_found->key),
968 host_found->file, host_found->line);
969
970 /*
971 * If strict host key checking is in use, the user will have
972 * to edit the key manually and we can only abort.
973 */
974 if (options.strict_host_key_checking) {
975 error("%s host key for %.200s has changed and you have "
976 "requested strict checking.", type, host);
977 goto fail;
978 }
979
980 continue_unsafe:
981 /*
982 * If strict host key checking has not been requested, allow
983 * the connection but without MITM-able authentication or
984 * forwarding.
985 */
986 if (options.password_authentication) {
987 error("Password authentication is disabled to avoid "
988 "man-in-the-middle attacks.");
989 options.password_authentication = 0;
990 cancelled_forwarding = 1;
991 }
992 if (options.kbd_interactive_authentication) {
993 error("Keyboard-interactive authentication is disabled"
994 " to avoid man-in-the-middle attacks.");
995 options.kbd_interactive_authentication = 0;
996 options.challenge_response_authentication = 0;
997 cancelled_forwarding = 1;
998 }
999 if (options.challenge_response_authentication) {
1000 error("Challenge/response authentication is disabled"
1001 " to avoid man-in-the-middle attacks.");
1002 options.challenge_response_authentication = 0;
1003 cancelled_forwarding = 1;
1004 }
1005 if (options.forward_agent) {
1006 error("Agent forwarding is disabled to avoid "
1007 "man-in-the-middle attacks.");
1008 options.forward_agent = 0;
1009 cancelled_forwarding = 1;
1010 }
1011 if (options.forward_x11) {
1012 error("X11 forwarding is disabled to avoid "
1013 "man-in-the-middle attacks.");
1014 options.forward_x11 = 0;
1015 cancelled_forwarding = 1;
1016 }
1017 if (options.num_local_forwards > 0 ||
1018 options.num_remote_forwards > 0) {
1019 error("Port forwarding is disabled to avoid "
1020 "man-in-the-middle attacks.");
1021 options.num_local_forwards =
1022 options.num_remote_forwards = 0;
1023 cancelled_forwarding = 1;
1024 }
1025 if (options.tun_open != SSH_TUNMODE_NO) {
1026 error("Tunnel forwarding is disabled to avoid "
1027 "man-in-the-middle attacks.");
1028 options.tun_open = SSH_TUNMODE_NO;
1029 cancelled_forwarding = 1;
1030 }
1031 if (options.exit_on_forward_failure && cancelled_forwarding)
1032 fatal("Error: forwarding disabled due to host key "
1033 "check failure");
1034
1035 /*
1036 * XXX Should permit the user to change to use the new id.
1037 * This could be done by converting the host key to an
1038 * identifying sentence, tell that the host identifies itself
1039 * by that sentence, and ask the user if he/she wishes to
1040 * accept the authentication.
1041 */
1042 break;
1043 case HOST_FOUND:
1044 fatal("internal error");
1045 break;
1046 }
1047
1048 if (options.check_host_ip && host_status != HOST_CHANGED &&
1049 ip_status == HOST_CHANGED) {
1050 snprintf(msg, sizeof(msg),
1051 "Warning: the %s host key for '%.200s' "
1052 "differs from the key for the IP address '%.128s'"
1053 "\nOffending key for IP in %s:%lu",
1054 type, host, ip, ip_found->file, ip_found->line);
1055 if (host_status == HOST_OK) {
1056 len = strlen(msg);
1057 snprintf(msg + len, sizeof(msg) - len,
1058 "\nMatching host key in %s:%lu",
1059 host_found->file, host_found->line);
1060 }
1061 if (options.strict_host_key_checking == 1) {
1062 logit("%s", msg);
1063 error("Exiting, you have requested strict checking.");
1064 goto fail;
1065 } else if (options.strict_host_key_checking == 2) {
1066 strlcat(msg, "\nAre you sure you want "
1067 "to continue connecting (yes/no)? ", sizeof(msg));
1068 if (!confirm(msg))
1069 goto fail;
1070 } else {
1071 logit("%s", msg);
1072 }
1073 }
1074
1075 xfree(ip);
1076 xfree(host);
1077 if (host_hostkeys != NULL)
1078 free_hostkeys(host_hostkeys);
1079 if (ip_hostkeys != NULL)
1080 free_hostkeys(ip_hostkeys);
1081 return 0;
1082
1083 fail:
1084 if (want_cert && host_status != HOST_REVOKED) {
1085 /*
1086 * No matching certificate. Downgrade cert to raw key and
1087 * search normally.
1088 */
1089 debug("No matching CA found. Retry with plain key");
1090 raw_key = key_from_private(host_key);
1091 if (key_drop_cert(raw_key) != 0)
1092 fatal("Couldn't drop certificate");
1093 host_key = raw_key;
1094 goto retry;
1095 }
1096 if (raw_key != NULL)
1097 key_free(raw_key);
1098 xfree(ip);
1099 xfree(host);
1100 if (host_hostkeys != NULL)
1101 free_hostkeys(host_hostkeys);
1102 if (ip_hostkeys != NULL)
1103 free_hostkeys(ip_hostkeys);
1104 return -1;
1105 }
1106
1107 /* returns 0 if key verifies or -1 if key does NOT verify */
1108 int
verify_host_key(char * host,struct sockaddr * hostaddr,Key * host_key)1109 verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
1110 {
1111 int flags = 0;
1112 char *fp;
1113
1114 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
1115 debug("Server host key: %s %s", key_type(host_key), fp);
1116 xfree(fp);
1117
1118 /* XXX certs are not yet supported for DNS */
1119 if (!key_is_cert(host_key) && options.verify_host_key_dns &&
1120 verify_host_key_dns(host, hostaddr, host_key, &flags) == 0) {
1121 if (flags & DNS_VERIFY_FOUND) {
1122
1123 if (options.verify_host_key_dns == 1 &&
1124 flags & DNS_VERIFY_MATCH &&
1125 flags & DNS_VERIFY_SECURE)
1126 return 0;
1127
1128 if (flags & DNS_VERIFY_MATCH) {
1129 matching_host_key_dns = 1;
1130 } else {
1131 warn_changed_key(host_key);
1132 error("Update the SSHFP RR in DNS with the new "
1133 "host key to get rid of this message.");
1134 }
1135 }
1136 }
1137
1138 return check_host_key(host, hostaddr, options.port, host_key, RDRW,
1139 options.user_hostfiles, options.num_user_hostfiles,
1140 options.system_hostfiles, options.num_system_hostfiles);
1141 }
1142
1143 /*
1144 * Starts a dialog with the server, and authenticates the current user on the
1145 * server. This does not need any extra privileges. The basic connection
1146 * to the server must already have been established before this is called.
1147 * If login fails, this function prints an error and never returns.
1148 * This function does not require super-user privileges.
1149 */
1150 void
ssh_login(Sensitive * sensitive,const char * orighost,struct sockaddr * hostaddr,u_short port,struct passwd * pw,int timeout_ms)1151 ssh_login(Sensitive *sensitive, const char *orighost,
1152 struct sockaddr *hostaddr, u_short port, struct passwd *pw, int timeout_ms)
1153 {
1154 char *host, *cp;
1155 char *server_user, *local_user;
1156
1157 local_user = xstrdup(pw->pw_name);
1158 server_user = options.user ? options.user : local_user;
1159
1160 /* Convert the user-supplied hostname into all lowercase. */
1161 host = xstrdup(orighost);
1162 for (cp = host; *cp; cp++)
1163 if (isupper(*cp))
1164 *cp = (char)tolower(*cp);
1165
1166 /* Exchange protocol version identification strings with the server. */
1167 ssh_exchange_identification(timeout_ms);
1168
1169 /* Put the connection into non-blocking mode. */
1170 packet_set_nonblocking();
1171
1172 /* key exchange */
1173 /* authenticate user */
1174 if (compat20) {
1175 ssh_kex2(host, hostaddr, port);
1176 ssh_userauth2(local_user, server_user, host, sensitive);
1177 } else {
1178 ssh_kex(host, hostaddr);
1179 ssh_userauth1(local_user, server_user, host, sensitive);
1180 }
1181 xfree(local_user);
1182 }
1183
1184 void
ssh_put_password(char * password)1185 ssh_put_password(char *password)
1186 {
1187 int size;
1188 char *padded;
1189
1190 if (datafellows & SSH_BUG_PASSWORDPAD) {
1191 packet_put_cstring(password);
1192 return;
1193 }
1194 size = roundup(strlen(password) + 1, 32);
1195 padded = xcalloc(1, size);
1196 strlcpy(padded, password, size);
1197 packet_put_string(padded, size);
1198 memset(padded, 0, size);
1199 xfree(padded);
1200 }
1201
1202 /* print all known host keys for a given host, but skip keys of given type */
1203 static int
show_other_keys(struct hostkeys * hostkeys,Key * key)1204 show_other_keys(struct hostkeys *hostkeys, Key *key)
1205 {
1206 int type[] = { KEY_RSA1, KEY_RSA, KEY_DSA, KEY_ECDSA, -1};
1207 int i, ret = 0;
1208 char *fp, *ra;
1209 const struct hostkey_entry *found;
1210
1211 for (i = 0; type[i] != -1; i++) {
1212 if (type[i] == key->type)
1213 continue;
1214 if (!lookup_key_in_hostkeys_by_type(hostkeys, type[i], &found))
1215 continue;
1216 fp = key_fingerprint(found->key, SSH_FP_MD5, SSH_FP_HEX);
1217 ra = key_fingerprint(found->key, SSH_FP_MD5, SSH_FP_RANDOMART);
1218 logit("WARNING: %s key found for host %s\n"
1219 "in %s:%lu\n"
1220 "%s key fingerprint %s.",
1221 key_type(found->key),
1222 found->host, found->file, found->line,
1223 key_type(found->key), fp);
1224 if (options.visual_host_key)
1225 logit("%s", ra);
1226 xfree(ra);
1227 xfree(fp);
1228 ret = 1;
1229 }
1230 return ret;
1231 }
1232
1233 static void
warn_changed_key(Key * host_key)1234 warn_changed_key(Key *host_key)
1235 {
1236 char *fp;
1237
1238 fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
1239
1240 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
1241 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
1242 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
1243 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
1244 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
1245 error("It is also possible that a host key has just been changed.");
1246 error("The fingerprint for the %s key sent by the remote host is\n%s.",
1247 key_type(host_key), fp);
1248 error("Please contact your system administrator.");
1249
1250 xfree(fp);
1251 }
1252
1253 /*
1254 * Execute a local command
1255 */
1256 int
ssh_local_cmd(const char * args)1257 ssh_local_cmd(const char *args)
1258 {
1259 char *shell;
1260 pid_t pid;
1261 int status;
1262 void (*osighand)(int);
1263
1264 if (!options.permit_local_command ||
1265 args == NULL || !*args)
1266 return (1);
1267
1268 if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
1269 shell = _PATH_BSHELL;
1270
1271 osighand = signal(SIGCHLD, SIG_DFL);
1272 pid = fork();
1273 if (pid == 0) {
1274 signal(SIGPIPE, SIG_DFL);
1275 debug3("Executing %s -c \"%s\"", shell, args);
1276 execl(shell, shell, "-c", args, (char *)NULL);
1277 error("Couldn't execute %s -c \"%s\": %s",
1278 shell, args, strerror(errno));
1279 _exit(1);
1280 } else if (pid == -1)
1281 fatal("fork failed: %.100s", strerror(errno));
1282 while (waitpid(pid, &status, 0) == -1)
1283 if (errno != EINTR)
1284 fatal("Couldn't wait for child: %s", strerror(errno));
1285 signal(SIGCHLD, osighand);
1286
1287 if (!WIFEXITED(status))
1288 return (1);
1289
1290 return (WEXITSTATUS(status));
1291 }
1292