1 /* $OpenBSD: auth1.c,v 1.82 2014/07/15 15:54:14 millert Exp $ */
2 /*
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4 * All rights reserved
5 *
6 * As far as I am concerned, the code I have written for this software
7 * can be used freely for any purpose. Any derived versions of this
8 * software must be clearly marked as such, and if the derived work is
9 * incompatible with the protocol description in the RFC file, it must be
10 * called by a name other than "ssh" or "Secure Shell".
11 */
12
13 #include "includes.h"
14
15 #ifdef WITH_SSH1
16
17 #include <sys/types.h>
18
19 #include <stdarg.h>
20 #include <stdio.h>
21 #include <string.h>
22 #include <unistd.h>
23 #include <pwd.h>
24
25 #include "openbsd-compat/sys-queue.h"
26 #include "xmalloc.h"
27 #include "rsa.h"
28 #include "ssh1.h"
29 #include "packet.h"
30 #include "buffer.h"
31 #include "log.h"
32 #include "misc.h"
33 #include "servconf.h"
34 #include "compat.h"
35 #include "key.h"
36 #include "hostfile.h"
37 #include "auth.h"
38 #include "channels.h"
39 #include "session.h"
40 #include "uidswap.h"
41 #ifdef GSSAPI
42 #include "ssh-gss.h"
43 #endif
44 #include "monitor_wrap.h"
45 #include "buffer.h"
46
47 /* import */
48 extern ServerOptions options;
49 extern Buffer loginmsg;
50
51 static int auth1_process_password(Authctxt *);
52 static int auth1_process_rsa(Authctxt *);
53 static int auth1_process_rhosts_rsa(Authctxt *);
54 static int auth1_process_tis_challenge(Authctxt *);
55 static int auth1_process_tis_response(Authctxt *);
56
57 static char *client_user = NULL; /* Used to fill in remote user for PAM */
58
59 struct AuthMethod1 {
60 int type;
61 char *name;
62 int *enabled;
63 int (*method)(Authctxt *);
64 };
65
66 const struct AuthMethod1 auth1_methods[] = {
67 {
68 SSH_CMSG_AUTH_PASSWORD, "password",
69 &options.password_authentication, auth1_process_password
70 },
71 {
72 SSH_CMSG_AUTH_RSA, "rsa",
73 &options.rsa_authentication, auth1_process_rsa
74 },
75 {
76 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
77 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
78 },
79 {
80 SSH_CMSG_AUTH_TIS, "challenge-response",
81 &options.challenge_response_authentication,
82 auth1_process_tis_challenge
83 },
84 {
85 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
86 &options.challenge_response_authentication,
87 auth1_process_tis_response
88 },
89 { -1, NULL, NULL, NULL}
90 };
91
92 static const struct AuthMethod1
lookup_authmethod1(int type)93 *lookup_authmethod1(int type)
94 {
95 int i;
96
97 for (i = 0; auth1_methods[i].name != NULL; i++)
98 if (auth1_methods[i].type == type)
99 return (&(auth1_methods[i]));
100
101 return (NULL);
102 }
103
104 static char *
get_authname(int type)105 get_authname(int type)
106 {
107 const struct AuthMethod1 *a;
108 static char buf[64];
109
110 if ((a = lookup_authmethod1(type)) != NULL)
111 return (a->name);
112 snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
113 return (buf);
114 }
115
116 /*ARGSUSED*/
117 static int
auth1_process_password(Authctxt * authctxt)118 auth1_process_password(Authctxt *authctxt)
119 {
120 int authenticated = 0;
121 char *password;
122 u_int dlen;
123
124 /*
125 * Read user password. It is in plain text, but was
126 * transmitted over the encrypted channel so it is
127 * not visible to an outside observer.
128 */
129 password = packet_get_string(&dlen);
130 packet_check_eom();
131
132 /* Try authentication with the password. */
133 authenticated = PRIVSEP(auth_password(authctxt, password));
134
135 explicit_bzero(password, dlen);
136 free(password);
137
138 return (authenticated);
139 }
140
141 /*ARGSUSED*/
142 static int
auth1_process_rsa(Authctxt * authctxt)143 auth1_process_rsa(Authctxt *authctxt)
144 {
145 int authenticated = 0;
146 BIGNUM *n;
147
148 /* RSA authentication requested. */
149 if ((n = BN_new()) == NULL)
150 fatal("do_authloop: BN_new failed");
151 packet_get_bignum(n);
152 packet_check_eom();
153 authenticated = auth_rsa(authctxt, n);
154 BN_clear_free(n);
155
156 return (authenticated);
157 }
158
159 /*ARGSUSED*/
160 static int
auth1_process_rhosts_rsa(Authctxt * authctxt)161 auth1_process_rhosts_rsa(Authctxt *authctxt)
162 {
163 int keybits, authenticated = 0;
164 u_int bits;
165 Key *client_host_key;
166 u_int ulen;
167
168 /*
169 * Get client user name. Note that we just have to
170 * trust the client; root on the client machine can
171 * claim to be any user.
172 */
173 client_user = packet_get_cstring(&ulen);
174
175 /* Get the client host key. */
176 client_host_key = key_new(KEY_RSA1);
177 bits = packet_get_int();
178 packet_get_bignum(client_host_key->rsa->e);
179 packet_get_bignum(client_host_key->rsa->n);
180
181 keybits = BN_num_bits(client_host_key->rsa->n);
182 if (keybits < 0 || bits != (u_int)keybits) {
183 verbose("Warning: keysize mismatch for client_host_key: "
184 "actual %d, announced %d",
185 BN_num_bits(client_host_key->rsa->n), bits);
186 }
187 packet_check_eom();
188
189 authenticated = auth_rhosts_rsa(authctxt, client_user,
190 client_host_key);
191 key_free(client_host_key);
192
193 auth_info(authctxt, "ruser %.100s", client_user);
194
195 return (authenticated);
196 }
197
198 /*ARGSUSED*/
199 static int
auth1_process_tis_challenge(Authctxt * authctxt)200 auth1_process_tis_challenge(Authctxt *authctxt)
201 {
202 char *challenge;
203
204 if ((challenge = get_challenge(authctxt)) == NULL)
205 return (0);
206
207 debug("sending challenge '%s'", challenge);
208 packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
209 packet_put_cstring(challenge);
210 free(challenge);
211 packet_send();
212 packet_write_wait();
213
214 return (-1);
215 }
216
217 /*ARGSUSED*/
218 static int
auth1_process_tis_response(Authctxt * authctxt)219 auth1_process_tis_response(Authctxt *authctxt)
220 {
221 int authenticated = 0;
222 char *response;
223 u_int dlen;
224
225 response = packet_get_string(&dlen);
226 packet_check_eom();
227 authenticated = verify_response(authctxt, response);
228 explicit_bzero(response, dlen);
229 free(response);
230
231 return (authenticated);
232 }
233
234 /*
235 * read packets, try to authenticate the user and
236 * return only if authentication is successful
237 */
238 static void
do_authloop(Authctxt * authctxt)239 do_authloop(Authctxt *authctxt)
240 {
241 int authenticated = 0;
242 int prev = 0, type = 0;
243 const struct AuthMethod1 *meth;
244
245 debug("Attempting authentication for %s%.100s.",
246 authctxt->valid ? "" : "invalid user ", authctxt->user);
247
248 /* If the user has no password, accept authentication immediately. */
249 if (options.permit_empty_passwd && options.password_authentication &&
250 #ifdef KRB5
251 (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
252 #endif
253 PRIVSEP(auth_password(authctxt, ""))) {
254 #ifdef USE_PAM
255 if (options.use_pam && (PRIVSEP(do_pam_account())))
256 #endif
257 {
258 auth_log(authctxt, 1, 0, "without authentication",
259 NULL);
260 return;
261 }
262 }
263
264 /* Indicate that authentication is needed. */
265 packet_start(SSH_SMSG_FAILURE);
266 packet_send();
267 packet_write_wait();
268
269 for (;;) {
270 /* default to fail */
271 authenticated = 0;
272
273
274 /* Get a packet from the client. */
275 prev = type;
276 type = packet_read();
277
278 /*
279 * If we started challenge-response authentication but the
280 * next packet is not a response to our challenge, release
281 * the resources allocated by get_challenge() (which would
282 * normally have been released by verify_response() had we
283 * received such a response)
284 */
285 if (prev == SSH_CMSG_AUTH_TIS &&
286 type != SSH_CMSG_AUTH_TIS_RESPONSE)
287 abandon_challenge_response(authctxt);
288
289 if (authctxt->failures >= options.max_authtries)
290 goto skip;
291 if ((meth = lookup_authmethod1(type)) == NULL) {
292 logit("Unknown message during authentication: "
293 "type %d", type);
294 goto skip;
295 }
296
297 if (!*(meth->enabled)) {
298 verbose("%s authentication disabled.", meth->name);
299 goto skip;
300 }
301
302 authenticated = meth->method(authctxt);
303 if (authenticated == -1)
304 continue; /* "postponed" */
305
306 #ifdef BSD_AUTH
307 if (authctxt->as) {
308 auth_close(authctxt->as);
309 authctxt->as = NULL;
310 }
311 #endif
312 if (!authctxt->valid && authenticated)
313 fatal("INTERNAL ERROR: authenticated invalid user %s",
314 authctxt->user);
315
316 #ifdef _UNICOS
317 if (authenticated && cray_access_denied(authctxt->user)) {
318 authenticated = 0;
319 fatal("Access denied for user %s.",authctxt->user);
320 }
321 #endif /* _UNICOS */
322
323 #ifndef HAVE_CYGWIN
324 /* Special handling for root */
325 if (authenticated && authctxt->pw->pw_uid == 0 &&
326 !auth_root_allowed(meth->name)) {
327 authenticated = 0;
328 # ifdef SSH_AUDIT_EVENTS
329 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
330 # endif
331 }
332 #endif
333
334 #ifdef USE_PAM
335 if (options.use_pam && authenticated &&
336 !PRIVSEP(do_pam_account())) {
337 char *msg;
338 size_t len;
339
340 error("Access denied for user %s by PAM account "
341 "configuration", authctxt->user);
342 len = buffer_len(&loginmsg);
343 buffer_append(&loginmsg, "\0", 1);
344 msg = buffer_ptr(&loginmsg);
345 /* strip trailing newlines */
346 if (len > 0)
347 while (len > 0 && msg[--len] == '\n')
348 msg[len] = '\0';
349 else
350 msg = "Access denied.";
351 packet_disconnect("%s", msg);
352 }
353 #endif
354
355 skip:
356 /* Log before sending the reply */
357 auth_log(authctxt, authenticated, 0, get_authname(type), NULL);
358
359 free(client_user);
360 client_user = NULL;
361
362 if (authenticated)
363 return;
364
365 if (++authctxt->failures >= options.max_authtries) {
366 #ifdef SSH_AUDIT_EVENTS
367 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
368 #endif
369 auth_maxtries_exceeded(authctxt);
370 }
371
372 packet_start(SSH_SMSG_FAILURE);
373 packet_send();
374 packet_write_wait();
375 }
376 }
377
378 /*
379 * Performs authentication of an incoming connection. Session key has already
380 * been exchanged and encryption is enabled.
381 */
382 void
do_authentication(Authctxt * authctxt)383 do_authentication(Authctxt *authctxt)
384 {
385 u_int ulen;
386 char *user, *style = NULL;
387
388 /* Get the name of the user that we wish to log in as. */
389 packet_read_expect(SSH_CMSG_USER);
390
391 /* Get the user name. */
392 user = packet_get_cstring(&ulen);
393 packet_check_eom();
394
395 if ((style = strchr(user, ':')) != NULL)
396 *style++ = '\0';
397
398 authctxt->user = user;
399 authctxt->style = style;
400
401 /* Verify that the user is a valid user. */
402 if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
403 authctxt->valid = 1;
404 else {
405 debug("do_authentication: invalid user %s", user);
406 authctxt->pw = fakepw();
407 }
408
409 /* Configuration may have changed as a result of Match */
410 if (options.num_auth_methods != 0)
411 fatal("AuthenticationMethods is not supported with SSH "
412 "protocol 1");
413
414 setproctitle("%s%s", authctxt->valid ? user : "unknown",
415 use_privsep ? " [net]" : "");
416
417 #ifdef USE_PAM
418 if (options.use_pam)
419 PRIVSEP(start_pam(authctxt));
420 #endif
421
422 /*
423 * If we are not running as root, the user must have the same uid as
424 * the server.
425 */
426 #ifndef HAVE_CYGWIN
427 if (!use_privsep && getuid() != 0 && authctxt->pw &&
428 authctxt->pw->pw_uid != getuid())
429 packet_disconnect("Cannot change user when server not running as root.");
430 #endif
431
432 /*
433 * Loop until the user has been authenticated or the connection is
434 * closed, do_authloop() returns only if authentication is successful
435 */
436 do_authloop(authctxt);
437
438 /* The user has been authenticated and accepted. */
439 packet_start(SSH_SMSG_SUCCESS);
440 packet_send();
441 packet_write_wait();
442 }
443
444 #endif /* WITH_SSH1 */
445