1 /* $OpenBSD: auth1.c,v 1.80 2014/02/02 03:44:31 djm 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 #include <sys/types.h>
16
17 #include <stdarg.h>
18 #include <stdio.h>
19 #include <string.h>
20 #include <unistd.h>
21 #include <pwd.h>
22
23 #include "openbsd-compat/sys-queue.h"
24 #include "xmalloc.h"
25 #include "rsa.h"
26 #include "ssh1.h"
27 #include "packet.h"
28 #include "buffer.h"
29 #include "log.h"
30 #include "servconf.h"
31 #include "compat.h"
32 #include "key.h"
33 #include "hostfile.h"
34 #include "auth.h"
35 #include "channels.h"
36 #include "session.h"
37 #include "uidswap.h"
38 #ifdef GSSAPI
39 #include "ssh-gss.h"
40 #endif
41 #include "monitor_wrap.h"
42 #include "buffer.h"
43
44 /* import */
45 extern ServerOptions options;
46 extern Buffer loginmsg;
47
48 static int auth1_process_password(Authctxt *);
49 static int auth1_process_rsa(Authctxt *);
50 static int auth1_process_rhosts_rsa(Authctxt *);
51 static int auth1_process_tis_challenge(Authctxt *);
52 static int auth1_process_tis_response(Authctxt *);
53
54 static char *client_user = NULL; /* Used to fill in remote user for PAM */
55
56 struct AuthMethod1 {
57 int type;
58 char *name;
59 int *enabled;
60 int (*method)(Authctxt *);
61 };
62
63 const struct AuthMethod1 auth1_methods[] = {
64 {
65 SSH_CMSG_AUTH_PASSWORD, "password",
66 &options.password_authentication, auth1_process_password
67 },
68 {
69 SSH_CMSG_AUTH_RSA, "rsa",
70 &options.rsa_authentication, auth1_process_rsa
71 },
72 {
73 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
74 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
75 },
76 {
77 SSH_CMSG_AUTH_TIS, "challenge-response",
78 &options.challenge_response_authentication,
79 auth1_process_tis_challenge
80 },
81 {
82 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
83 &options.challenge_response_authentication,
84 auth1_process_tis_response
85 },
86 { -1, NULL, NULL, NULL}
87 };
88
89 static const struct AuthMethod1
lookup_authmethod1(int type)90 *lookup_authmethod1(int type)
91 {
92 int i;
93
94 for (i = 0; auth1_methods[i].name != NULL; i++)
95 if (auth1_methods[i].type == type)
96 return (&(auth1_methods[i]));
97
98 return (NULL);
99 }
100
101 static char *
get_authname(int type)102 get_authname(int type)
103 {
104 const struct AuthMethod1 *a;
105 static char buf[64];
106
107 if ((a = lookup_authmethod1(type)) != NULL)
108 return (a->name);
109 snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
110 return (buf);
111 }
112
113 /*ARGSUSED*/
114 static int
auth1_process_password(Authctxt * authctxt)115 auth1_process_password(Authctxt *authctxt)
116 {
117 int authenticated = 0;
118 char *password;
119 u_int dlen;
120
121 /*
122 * Read user password. It is in plain text, but was
123 * transmitted over the encrypted channel so it is
124 * not visible to an outside observer.
125 */
126 password = packet_get_string(&dlen);
127 packet_check_eom();
128
129 /* Try authentication with the password. */
130 authenticated = PRIVSEP(auth_password(authctxt, password));
131
132 explicit_bzero(password, dlen);
133 free(password);
134
135 return (authenticated);
136 }
137
138 /*ARGSUSED*/
139 static int
auth1_process_rsa(Authctxt * authctxt)140 auth1_process_rsa(Authctxt *authctxt)
141 {
142 int authenticated = 0;
143 BIGNUM *n;
144
145 /* RSA authentication requested. */
146 if ((n = BN_new()) == NULL)
147 fatal("do_authloop: BN_new failed");
148 packet_get_bignum(n);
149 packet_check_eom();
150 authenticated = auth_rsa(authctxt, n);
151 BN_clear_free(n);
152
153 return (authenticated);
154 }
155
156 /*ARGSUSED*/
157 static int
auth1_process_rhosts_rsa(Authctxt * authctxt)158 auth1_process_rhosts_rsa(Authctxt *authctxt)
159 {
160 int keybits, authenticated = 0;
161 u_int bits;
162 Key *client_host_key;
163 u_int ulen;
164
165 /*
166 * Get client user name. Note that we just have to
167 * trust the client; root on the client machine can
168 * claim to be any user.
169 */
170 client_user = packet_get_cstring(&ulen);
171
172 /* Get the client host key. */
173 client_host_key = key_new(KEY_RSA1);
174 bits = packet_get_int();
175 packet_get_bignum(client_host_key->rsa->e);
176 packet_get_bignum(client_host_key->rsa->n);
177
178 keybits = BN_num_bits(client_host_key->rsa->n);
179 if (keybits < 0 || bits != (u_int)keybits) {
180 verbose("Warning: keysize mismatch for client_host_key: "
181 "actual %d, announced %d",
182 BN_num_bits(client_host_key->rsa->n), bits);
183 }
184 packet_check_eom();
185
186 authenticated = auth_rhosts_rsa(authctxt, client_user,
187 client_host_key);
188 key_free(client_host_key);
189
190 auth_info(authctxt, "ruser %.100s", client_user);
191
192 return (authenticated);
193 }
194
195 /*ARGSUSED*/
196 static int
auth1_process_tis_challenge(Authctxt * authctxt)197 auth1_process_tis_challenge(Authctxt *authctxt)
198 {
199 char *challenge;
200
201 if ((challenge = get_challenge(authctxt)) == NULL)
202 return (0);
203
204 debug("sending challenge '%s'", challenge);
205 packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
206 packet_put_cstring(challenge);
207 free(challenge);
208 packet_send();
209 packet_write_wait();
210
211 return (-1);
212 }
213
214 /*ARGSUSED*/
215 static int
auth1_process_tis_response(Authctxt * authctxt)216 auth1_process_tis_response(Authctxt *authctxt)
217 {
218 int authenticated = 0;
219 char *response;
220 u_int dlen;
221
222 response = packet_get_string(&dlen);
223 packet_check_eom();
224 authenticated = verify_response(authctxt, response);
225 explicit_bzero(response, dlen);
226 free(response);
227
228 return (authenticated);
229 }
230
231 /*
232 * read packets, try to authenticate the user and
233 * return only if authentication is successful
234 */
235 static void
do_authloop(Authctxt * authctxt)236 do_authloop(Authctxt *authctxt)
237 {
238 int authenticated = 0;
239 int prev = 0, type = 0;
240 const struct AuthMethod1 *meth;
241
242 debug("Attempting authentication for %s%.100s.",
243 authctxt->valid ? "" : "invalid user ", authctxt->user);
244
245 /* If the user has no password, accept authentication immediately. */
246 if (options.permit_empty_passwd && options.password_authentication &&
247 #ifdef KRB5
248 (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
249 #endif
250 PRIVSEP(auth_password(authctxt, ""))) {
251 #ifdef USE_PAM
252 if (options.use_pam && (PRIVSEP(do_pam_account())))
253 #endif
254 {
255 auth_log(authctxt, 1, 0, "without authentication",
256 NULL);
257 return;
258 }
259 }
260
261 /* Indicate that authentication is needed. */
262 packet_start(SSH_SMSG_FAILURE);
263 packet_send();
264 packet_write_wait();
265
266 for (;;) {
267 /* default to fail */
268 authenticated = 0;
269
270
271 /* Get a packet from the client. */
272 prev = type;
273 type = packet_read();
274
275 /*
276 * If we started challenge-response authentication but the
277 * next packet is not a response to our challenge, release
278 * the resources allocated by get_challenge() (which would
279 * normally have been released by verify_response() had we
280 * received such a response)
281 */
282 if (prev == SSH_CMSG_AUTH_TIS &&
283 type != SSH_CMSG_AUTH_TIS_RESPONSE)
284 abandon_challenge_response(authctxt);
285
286 if (authctxt->failures >= options.max_authtries)
287 goto skip;
288 if ((meth = lookup_authmethod1(type)) == NULL) {
289 logit("Unknown message during authentication: "
290 "type %d", type);
291 goto skip;
292 }
293
294 if (!*(meth->enabled)) {
295 verbose("%s authentication disabled.", meth->name);
296 goto skip;
297 }
298
299 authenticated = meth->method(authctxt);
300 if (authenticated == -1)
301 continue; /* "postponed" */
302
303 #ifdef BSD_AUTH
304 if (authctxt->as) {
305 auth_close(authctxt->as);
306 authctxt->as = NULL;
307 }
308 #endif
309 if (!authctxt->valid && authenticated)
310 fatal("INTERNAL ERROR: authenticated invalid user %s",
311 authctxt->user);
312
313 #ifdef _UNICOS
314 if (authenticated && cray_access_denied(authctxt->user)) {
315 authenticated = 0;
316 fatal("Access denied for user %s.",authctxt->user);
317 }
318 #endif /* _UNICOS */
319
320 #ifndef HAVE_CYGWIN
321 /* Special handling for root */
322 if (authenticated && authctxt->pw->pw_uid == 0 &&
323 !auth_root_allowed(meth->name)) {
324 authenticated = 0;
325 # ifdef SSH_AUDIT_EVENTS
326 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
327 # endif
328 }
329 #endif
330
331 #ifdef USE_PAM
332 if (options.use_pam && authenticated &&
333 !PRIVSEP(do_pam_account())) {
334 char *msg;
335 size_t len;
336
337 error("Access denied for user %s by PAM account "
338 "configuration", authctxt->user);
339 len = buffer_len(&loginmsg);
340 buffer_append(&loginmsg, "\0", 1);
341 msg = buffer_ptr(&loginmsg);
342 /* strip trailing newlines */
343 if (len > 0)
344 while (len > 0 && msg[--len] == '\n')
345 msg[len] = '\0';
346 else
347 msg = "Access denied.";
348 packet_disconnect("%s", msg);
349 }
350 #endif
351
352 skip:
353 /* Log before sending the reply */
354 auth_log(authctxt, authenticated, 0, get_authname(type), NULL);
355
356 free(client_user);
357 client_user = NULL;
358
359 if (authenticated)
360 return;
361
362 if (++authctxt->failures >= options.max_authtries) {
363 #ifdef SSH_AUDIT_EVENTS
364 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
365 #endif
366 packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
367 }
368
369 packet_start(SSH_SMSG_FAILURE);
370 packet_send();
371 packet_write_wait();
372 }
373 }
374
375 /*
376 * Performs authentication of an incoming connection. Session key has already
377 * been exchanged and encryption is enabled.
378 */
379 void
do_authentication(Authctxt * authctxt)380 do_authentication(Authctxt *authctxt)
381 {
382 u_int ulen;
383 char *user, *style = NULL;
384
385 /* Get the name of the user that we wish to log in as. */
386 packet_read_expect(SSH_CMSG_USER);
387
388 /* Get the user name. */
389 user = packet_get_cstring(&ulen);
390 packet_check_eom();
391
392 if ((style = strchr(user, ':')) != NULL)
393 *style++ = '\0';
394
395 authctxt->user = user;
396 authctxt->style = style;
397
398 /* Verify that the user is a valid user. */
399 if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
400 authctxt->valid = 1;
401 else {
402 debug("do_authentication: invalid user %s", user);
403 authctxt->pw = fakepw();
404 }
405
406 /* Configuration may have changed as a result of Match */
407 if (options.num_auth_methods != 0)
408 fatal("AuthenticationMethods is not supported with SSH "
409 "protocol 1");
410
411 setproctitle("%s%s", authctxt->valid ? user : "unknown",
412 use_privsep ? " [net]" : "");
413
414 #ifdef USE_PAM
415 if (options.use_pam)
416 PRIVSEP(start_pam(authctxt));
417 #endif
418
419 /*
420 * If we are not running as root, the user must have the same uid as
421 * the server.
422 */
423 #ifndef HAVE_CYGWIN
424 if (!use_privsep && getuid() != 0 && authctxt->pw &&
425 authctxt->pw->pw_uid != getuid())
426 packet_disconnect("Cannot change user when server not running as root.");
427 #endif
428
429 /*
430 * Loop until the user has been authenticated or the connection is
431 * closed, do_authloop() returns only if authentication is successful
432 */
433 do_authloop(authctxt);
434
435 /* The user has been authenticated and accepted. */
436 packet_start(SSH_SMSG_SUCCESS);
437 packet_send();
438 packet_write_wait();
439 }
440