1 /* $OpenBSD: auth1.c,v 1.75 2010/08/31 09:58:37 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 *, char *, size_t);
49 static int auth1_process_rsa(Authctxt *, char *, size_t);
50 static int auth1_process_rhosts_rsa(Authctxt *, char *, size_t);
51 static int auth1_process_tis_challenge(Authctxt *, char *, size_t);
52 static int auth1_process_tis_response(Authctxt *, char *, size_t);
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 *, char *, size_t);
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,char * info,size_t infolen)115 auth1_process_password(Authctxt *authctxt, char *info, size_t infolen)
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 #ifndef ANDROID
131 authenticated = PRIVSEP(auth_password(authctxt, password));
132
133 #else
134 /* no password authentication in android */
135 authenticated = 0;
136 #endif
137
138 memset(password, 0, dlen);
139 xfree(password);
140
141 return (authenticated);
142 }
143
144 /*ARGSUSED*/
145 static int
auth1_process_rsa(Authctxt * authctxt,char * info,size_t infolen)146 auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen)
147 {
148 int authenticated = 0;
149 BIGNUM *n;
150
151 /* RSA authentication requested. */
152 if ((n = BN_new()) == NULL)
153 fatal("do_authloop: BN_new failed");
154 packet_get_bignum(n);
155 packet_check_eom();
156 authenticated = auth_rsa(authctxt, n);
157 BN_clear_free(n);
158
159 return (authenticated);
160 }
161
162 /*ARGSUSED*/
163 static int
auth1_process_rhosts_rsa(Authctxt * authctxt,char * info,size_t infolen)164 auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen)
165 {
166 int keybits, authenticated = 0;
167 u_int bits;
168 Key *client_host_key;
169 u_int ulen;
170
171 /*
172 * Get client user name. Note that we just have to
173 * trust the client; root on the client machine can
174 * claim to be any user.
175 */
176 client_user = packet_get_cstring(&ulen);
177
178 /* Get the client host key. */
179 client_host_key = key_new(KEY_RSA1);
180 bits = packet_get_int();
181 packet_get_bignum(client_host_key->rsa->e);
182 packet_get_bignum(client_host_key->rsa->n);
183
184 keybits = BN_num_bits(client_host_key->rsa->n);
185 if (keybits < 0 || bits != (u_int)keybits) {
186 verbose("Warning: keysize mismatch for client_host_key: "
187 "actual %d, announced %d",
188 BN_num_bits(client_host_key->rsa->n), bits);
189 }
190 packet_check_eom();
191
192 authenticated = auth_rhosts_rsa(authctxt, client_user,
193 client_host_key);
194 key_free(client_host_key);
195
196 snprintf(info, infolen, " ruser %.100s", client_user);
197
198 return (authenticated);
199 }
200
201 /*ARGSUSED*/
202 static int
auth1_process_tis_challenge(Authctxt * authctxt,char * info,size_t infolen)203 auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen)
204 {
205 char *challenge;
206
207 if ((challenge = get_challenge(authctxt)) == NULL)
208 return (0);
209
210 debug("sending challenge '%s'", challenge);
211 packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
212 packet_put_cstring(challenge);
213 xfree(challenge);
214 packet_send();
215 packet_write_wait();
216
217 return (-1);
218 }
219
220 /*ARGSUSED*/
221 static int
auth1_process_tis_response(Authctxt * authctxt,char * info,size_t infolen)222 auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen)
223 {
224 int authenticated = 0;
225 char *response;
226 u_int dlen;
227
228 response = packet_get_string(&dlen);
229 packet_check_eom();
230 authenticated = verify_response(authctxt, response);
231 memset(response, 'r', dlen);
232 xfree(response);
233
234 return (authenticated);
235 }
236
237 /*
238 * read packets, try to authenticate the user and
239 * return only if authentication is successful
240 */
241 static void
do_authloop(Authctxt * authctxt)242 do_authloop(Authctxt *authctxt)
243 {
244 int authenticated = 0;
245 char info[1024];
246 int prev = 0, type = 0;
247 const struct AuthMethod1 *meth;
248
249 debug("Attempting authentication for %s%.100s.",
250 authctxt->valid ? "" : "invalid user ", authctxt->user);
251
252 /* no password authentication in android */
253 #ifndef ANDROID
254 /* If the user has no password, accept authentication immediately. */
255 if (options.permit_empty_passwd && options.password_authentication &&
256 #ifdef KRB5
257 (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
258 #endif
259 PRIVSEP(auth_password(authctxt, "")))
260 #endif
261 {
262 #ifdef USE_PAM
263 if (options.use_pam && (PRIVSEP(do_pam_account())))
264 #endif
265 {
266 auth_log(authctxt, 1, "without authentication", "");
267 return;
268 }
269 }
270
271 /* Indicate that authentication is needed. */
272 packet_start(SSH_SMSG_FAILURE);
273 packet_send();
274 packet_write_wait();
275
276 for (;;) {
277 /* default to fail */
278 authenticated = 0;
279
280 info[0] = '\0';
281
282 /* Get a packet from the client. */
283 prev = type;
284 type = packet_read();
285
286 /*
287 * If we started challenge-response authentication but the
288 * next packet is not a response to our challenge, release
289 * the resources allocated by get_challenge() (which would
290 * normally have been released by verify_response() had we
291 * received such a response)
292 */
293 if (prev == SSH_CMSG_AUTH_TIS &&
294 type != SSH_CMSG_AUTH_TIS_RESPONSE)
295 abandon_challenge_response(authctxt);
296
297 if (authctxt->failures >= options.max_authtries)
298 goto skip;
299 if ((meth = lookup_authmethod1(type)) == NULL) {
300 logit("Unknown message during authentication: "
301 "type %d", type);
302 goto skip;
303 }
304
305 if (!*(meth->enabled)) {
306 verbose("%s authentication disabled.", meth->name);
307 goto skip;
308 }
309
310 authenticated = meth->method(authctxt, info, sizeof(info));
311 if (authenticated == -1)
312 continue; /* "postponed" */
313
314 #ifdef BSD_AUTH
315 if (authctxt->as) {
316 auth_close(authctxt->as);
317 authctxt->as = NULL;
318 }
319 #endif
320 if (!authctxt->valid && authenticated)
321 fatal("INTERNAL ERROR: authenticated invalid user %s",
322 authctxt->user);
323
324 #ifdef _UNICOS
325 if (authenticated && cray_access_denied(authctxt->user)) {
326 authenticated = 0;
327 fatal("Access denied for user %s.",authctxt->user);
328 }
329 #endif /* _UNICOS */
330
331 #ifndef HAVE_CYGWIN
332 /* Special handling for root */
333 if (authenticated && authctxt->pw->pw_uid == 0 &&
334 !auth_root_allowed(meth->name)) {
335 authenticated = 0;
336 # ifdef SSH_AUDIT_EVENTS
337 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
338 # endif
339 }
340 #endif
341
342 #ifdef USE_PAM
343 if (options.use_pam && authenticated &&
344 !PRIVSEP(do_pam_account())) {
345 char *msg;
346 size_t len;
347
348 error("Access denied for user %s by PAM account "
349 "configuration", authctxt->user);
350 len = buffer_len(&loginmsg);
351 buffer_append(&loginmsg, "\0", 1);
352 msg = buffer_ptr(&loginmsg);
353 /* strip trailing newlines */
354 if (len > 0)
355 while (len > 0 && msg[--len] == '\n')
356 msg[len] = '\0';
357 else
358 msg = "Access denied.";
359 packet_disconnect("%s", msg);
360 }
361 #endif
362
363 skip:
364 /* Log before sending the reply */
365 auth_log(authctxt, authenticated, get_authname(type), info);
366
367 if (client_user != NULL) {
368 xfree(client_user);
369 client_user = NULL;
370 }
371
372 if (authenticated)
373 return;
374
375 if (++authctxt->failures >= options.max_authtries) {
376 #ifdef SSH_AUDIT_EVENTS
377 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
378 #endif
379 packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
380 }
381
382 packet_start(SSH_SMSG_FAILURE);
383 packet_send();
384 packet_write_wait();
385 }
386 }
387
388 /*
389 * Performs authentication of an incoming connection. Session key has already
390 * been exchanged and encryption is enabled.
391 */
392 void
do_authentication(Authctxt * authctxt)393 do_authentication(Authctxt *authctxt)
394 {
395 u_int ulen;
396 char *user, *style = NULL;
397
398 /* Get the name of the user that we wish to log in as. */
399 packet_read_expect(SSH_CMSG_USER);
400
401 /* Get the user name. */
402 user = packet_get_cstring(&ulen);
403 packet_check_eom();
404
405 if ((style = strchr(user, ':')) != NULL)
406 *style++ = '\0';
407
408 authctxt->user = user;
409 authctxt->style = style;
410
411 /* Verify that the user is a valid user. */
412 if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
413 authctxt->valid = 1;
414 else {
415 debug("do_authentication: invalid user %s", user);
416 authctxt->pw = fakepw();
417 }
418
419 setproctitle("%s%s", authctxt->valid ? user : "unknown",
420 use_privsep ? " [net]" : "");
421
422 #ifdef USE_PAM
423 if (options.use_pam)
424 PRIVSEP(start_pam(authctxt));
425 #endif
426
427 /*
428 * If we are not running as root, the user must have the same uid as
429 * the server.
430 */
431 #ifndef HAVE_CYGWIN
432 if (!use_privsep && getuid() != 0 && authctxt->pw &&
433 authctxt->pw->pw_uid != getuid())
434 packet_disconnect("Cannot change user when server not running as root.");
435 #endif
436
437 /*
438 * Loop until the user has been authenticated or the connection is
439 * closed, do_authloop() returns only if authentication is successful
440 */
441 do_authloop(authctxt);
442
443 /* The user has been authenticated and accepted. */
444 packet_start(SSH_SMSG_SUCCESS);
445 packet_send();
446 packet_write_wait();
447 }
448