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1 | /* $OpenBSD: auth1.c,v 1.73 2008/07/04 23:30:16 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 | |
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 * | |
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 | |
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 | authenticated = PRIVSEP(auth_password(authctxt, password)); | |
131 | ||
132 | memset(password, 0, dlen); | |
133 | xfree(password); | |
134 | ||
135 | return (authenticated); | |
136 | } | |
137 | ||
138 | /*ARGSUSED*/ | |
139 | static int | |
140 | auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen) | |
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 | |
158 | auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen) | |
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_string(&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 | snprintf(info, infolen, " ruser %.100s", client_user); | |
191 | ||
192 | return (authenticated); | |
193 | } | |
194 | ||
195 | /*ARGSUSED*/ | |
196 | static int | |
197 | auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen) | |
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 | xfree(challenge); | |
208 | packet_send(); | |
209 | packet_write_wait(); | |
210 | ||
211 | return (-1); | |
212 | } | |
213 | ||
214 | /*ARGSUSED*/ | |
215 | static int | |
216 | auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen) | |
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 | memset(response, 'r', dlen); | |
226 | xfree(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 | |
236 | do_authloop(Authctxt *authctxt) | |
237 | { | |
238 | int authenticated = 0; | |
239 | char info[1024]; | |
240 | int prev = 0, type = 0; | |
241 | const struct AuthMethod1 *meth; | |
242 | ||
243 | debug("Attempting authentication for %s%.100s.", | |
244 | authctxt->valid ? "" : "invalid user ", authctxt->user); | |
245 | ||
246 | /* If the user has no password, accept authentication immediately. */ | |
247 | if (options.password_authentication && | |
248 | #ifdef KRB5 | |
249 | (!options.kerberos_authentication || options.kerberos_or_local_passwd) && | |
250 | #endif | |
251 | PRIVSEP(auth_password(authctxt, ""))) { | |
252 | #ifdef USE_PAM | |
253 | if (options.use_pam && (PRIVSEP(do_pam_account()))) | |
254 | #endif | |
255 | { | |
256 | auth_log(authctxt, 1, "without authentication", ""); | |
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 | info[0] = '\0'; | |
271 | ||
272 | /* Get a packet from the client. */ | |
273 | prev = type; | |
274 | type = packet_read(); | |
275 | ||
276 | /* | |
277 | * If we started challenge-response authentication but the | |
278 | * next packet is not a response to our challenge, release | |
279 | * the resources allocated by get_challenge() (which would | |
280 | * normally have been released by verify_response() had we | |
281 | * received such a response) | |
282 | */ | |
283 | if (prev == SSH_CMSG_AUTH_TIS && | |
284 | type != SSH_CMSG_AUTH_TIS_RESPONSE) | |
285 | abandon_challenge_response(authctxt); | |
286 | ||
287 | if (authctxt->failures >= options.max_authtries) | |
288 | goto skip; | |
289 | if ((meth = lookup_authmethod1(type)) == NULL) { | |
290 | logit("Unknown message during authentication: " | |
291 | "type %d", type); | |
292 | goto skip; | |
293 | } | |
294 | ||
295 | if (!*(meth->enabled)) { | |
296 | verbose("%s authentication disabled.", meth->name); | |
297 | goto skip; | |
298 | } | |
299 | ||
300 | authenticated = meth->method(authctxt, info, sizeof(info)); | |
301 | if (authenticated == -1) | |
302 | continue; /* "postponed" */ | |
303 | ||
304 | #ifdef BSD_AUTH | |
305 | if (authctxt->as) { | |
306 | auth_close(authctxt->as); | |
307 | authctxt->as = NULL; | |
308 | } | |
309 | #endif | |
310 | if (!authctxt->valid && authenticated) | |
311 | fatal("INTERNAL ERROR: authenticated invalid user %s", | |
312 | authctxt->user); | |
313 | ||
314 | #ifdef _UNICOS | |
315 | if (authenticated && cray_access_denied(authctxt->user)) { | |
316 | authenticated = 0; | |
317 | fatal("Access denied for user %s.",authctxt->user); | |
318 | } | |
319 | #endif /* _UNICOS */ | |
320 | ||
321 | #ifndef HAVE_CYGWIN | |
322 | /* Special handling for root */ | |
323 | if (authenticated && authctxt->pw->pw_uid == 0 && | |
324 | !auth_root_allowed(meth->name)) { | |
325 | authenticated = 0; | |
326 | # ifdef SSH_AUDIT_EVENTS | |
327 | PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); | |
328 | # endif | |
329 | } | |
330 | #endif | |
331 | ||
332 | #ifdef USE_PAM | |
333 | if (options.use_pam && authenticated && | |
334 | !PRIVSEP(do_pam_account())) { | |
335 | char *msg; | |
336 | size_t len; | |
337 | ||
338 | error("Access denied for user %s by PAM account " | |
339 | "configuration", authctxt->user); | |
340 | len = buffer_len(&loginmsg); | |
341 | buffer_append(&loginmsg, "\0", 1); | |
342 | msg = buffer_ptr(&loginmsg); | |
343 | /* strip trailing newlines */ | |
344 | if (len > 0) | |
345 | while (len > 0 && msg[--len] == '\n') | |
346 | msg[len] = '\0'; | |
347 | else | |
348 | msg = "Access denied."; | |
349 | packet_disconnect("%s", msg); | |
350 | } | |
351 | #endif | |
352 | ||
353 | skip: | |
354 | /* Log before sending the reply */ | |
355 | auth_log(authctxt, authenticated, get_authname(type), info); | |
356 | ||
357 | if (client_user != NULL) { | |
358 | xfree(client_user); | |
359 | client_user = NULL; | |
360 | } | |
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 | packet_disconnect(AUTH_FAIL_MSG, authctxt->user); | |
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 | |
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_string(&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 | setproctitle("%s%s", authctxt->valid ? user : "unknown", | |
410 | use_privsep ? " [net]" : ""); | |
411 | ||
412 | #ifdef USE_PAM | |
413 | if (options.use_pam) | |
414 | PRIVSEP(start_pam(authctxt)); | |
415 | #endif | |
416 | ||
417 | /* | |
418 | * If we are not running as root, the user must have the same uid as | |
419 | * the server. | |
420 | */ | |
421 | #ifndef HAVE_CYGWIN | |
422 | if (!use_privsep && getuid() != 0 && authctxt->pw && | |
423 | authctxt->pw->pw_uid != getuid()) | |
424 | packet_disconnect("Cannot change user when server not running as root."); | |
425 | #endif | |
426 | ||
427 | /* | |
428 | * Loop until the user has been authenticated or the connection is | |
429 | * closed, do_authloop() returns only if authentication is successful | |
430 | */ | |
431 | do_authloop(authctxt); | |
432 | ||
433 | /* The user has been authenticated and accepted. */ | |
434 | packet_start(SSH_SMSG_SUCCESS); | |
435 | packet_send(); | |
436 | packet_write_wait(); | |
437 | } |