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1 | /* $OpenBSD: auth1.c,v 1.70 2006/08/03 03:34:41 deraadt 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 "xmalloc.h" | |
24 | #include "rsa.h" | |
25 | #include "ssh1.h" | |
26 | #include "packet.h" | |
27 | #include "buffer.h" | |
28 | #include "log.h" | |
29 | #include "servconf.h" | |
30 | #include "compat.h" | |
31 | #include "key.h" | |
32 | #include "hostfile.h" | |
33 | #include "auth.h" | |
34 | #include "channels.h" | |
35 | #include "session.h" | |
36 | #include "uidswap.h" | |
37 | #ifdef GSSAPI | |
38 | #include "ssh-gss.h" | |
39 | #endif | |
40 | #include "monitor_wrap.h" | |
41 | #include "buffer.h" | |
42 | ||
43 | /* import */ | |
44 | extern ServerOptions options; | |
45 | extern Buffer loginmsg; | |
46 | ||
47 | static int auth1_process_password(Authctxt *, char *, size_t); | |
48 | static int auth1_process_rsa(Authctxt *, char *, size_t); | |
49 | static int auth1_process_rhosts_rsa(Authctxt *, char *, size_t); | |
50 | static int auth1_process_tis_challenge(Authctxt *, char *, size_t); | |
51 | static int auth1_process_tis_response(Authctxt *, char *, size_t); | |
52 | ||
53 | static char *client_user = NULL; /* Used to fill in remote user for PAM */ | |
54 | ||
55 | struct AuthMethod1 { | |
56 | int type; | |
57 | char *name; | |
58 | int *enabled; | |
59 | int (*method)(Authctxt *, char *, size_t); | |
60 | }; | |
61 | ||
62 | const struct AuthMethod1 auth1_methods[] = { | |
63 | { | |
64 | SSH_CMSG_AUTH_PASSWORD, "password", | |
65 | &options.password_authentication, auth1_process_password | |
66 | }, | |
67 | { | |
68 | SSH_CMSG_AUTH_RSA, "rsa", | |
69 | &options.rsa_authentication, auth1_process_rsa | |
70 | }, | |
71 | { | |
72 | SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa", | |
73 | &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa | |
74 | }, | |
75 | { | |
76 | SSH_CMSG_AUTH_TIS, "challenge-response", | |
77 | &options.challenge_response_authentication, | |
78 | auth1_process_tis_challenge | |
79 | }, | |
80 | { | |
81 | SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response", | |
82 | &options.challenge_response_authentication, | |
83 | auth1_process_tis_response | |
84 | }, | |
85 | { -1, NULL, NULL, NULL} | |
86 | }; | |
87 | ||
88 | static const struct AuthMethod1 | |
89 | *lookup_authmethod1(int type) | |
90 | { | |
91 | int i; | |
92 | ||
93 | for (i = 0; auth1_methods[i].name != NULL; i++) | |
94 | if (auth1_methods[i].type == type) | |
95 | return (&(auth1_methods[i])); | |
96 | ||
97 | return (NULL); | |
98 | } | |
99 | ||
100 | static char * | |
101 | get_authname(int type) | |
102 | { | |
103 | const struct AuthMethod1 *a; | |
104 | static char buf[64]; | |
105 | ||
106 | if ((a = lookup_authmethod1(type)) != NULL) | |
107 | return (a->name); | |
108 | snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type); | |
109 | return (buf); | |
110 | } | |
111 | ||
112 | /*ARGSUSED*/ | |
113 | static int | |
114 | auth1_process_password(Authctxt *authctxt, char *info, size_t infolen) | |
115 | { | |
116 | int authenticated = 0; | |
117 | char *password; | |
118 | u_int dlen; | |
119 | ||
120 | /* | |
121 | * Read user password. It is in plain text, but was | |
122 | * transmitted over the encrypted channel so it is | |
123 | * not visible to an outside observer. | |
124 | */ | |
125 | password = packet_get_string(&dlen); | |
126 | packet_check_eom(); | |
127 | ||
128 | /* Try authentication with the password. */ | |
129 | authenticated = PRIVSEP(auth_password(authctxt, password)); | |
130 | ||
131 | memset(password, 0, dlen); | |
132 | xfree(password); | |
133 | ||
134 | return (authenticated); | |
135 | } | |
136 | ||
137 | /*ARGSUSED*/ | |
138 | static int | |
139 | auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen) | |
140 | { | |
141 | int authenticated = 0; | |
142 | BIGNUM *n; | |
143 | ||
144 | /* RSA authentication requested. */ | |
145 | if ((n = BN_new()) == NULL) | |
146 | fatal("do_authloop: BN_new failed"); | |
147 | packet_get_bignum(n); | |
148 | packet_check_eom(); | |
149 | authenticated = auth_rsa(authctxt, n); | |
150 | BN_clear_free(n); | |
151 | ||
152 | return (authenticated); | |
153 | } | |
154 | ||
155 | /*ARGSUSED*/ | |
156 | static int | |
157 | auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen) | |
158 | { | |
159 | int keybits, authenticated = 0; | |
160 | u_int bits; | |
161 | Key *client_host_key; | |
162 | u_int ulen; | |
163 | ||
164 | /* | |
165 | * Get client user name. Note that we just have to | |
166 | * trust the client; root on the client machine can | |
167 | * claim to be any user. | |
168 | */ | |
169 | client_user = packet_get_string(&ulen); | |
170 | ||
171 | /* Get the client host key. */ | |
172 | client_host_key = key_new(KEY_RSA1); | |
173 | bits = packet_get_int(); | |
174 | packet_get_bignum(client_host_key->rsa->e); | |
175 | packet_get_bignum(client_host_key->rsa->n); | |
176 | ||
177 | keybits = BN_num_bits(client_host_key->rsa->n); | |
178 | if (keybits < 0 || bits != (u_int)keybits) { | |
179 | verbose("Warning: keysize mismatch for client_host_key: " | |
180 | "actual %d, announced %d", | |
181 | BN_num_bits(client_host_key->rsa->n), bits); | |
182 | } | |
183 | packet_check_eom(); | |
184 | ||
185 | authenticated = auth_rhosts_rsa(authctxt, client_user, | |
186 | client_host_key); | |
187 | key_free(client_host_key); | |
188 | ||
189 | snprintf(info, infolen, " ruser %.100s", client_user); | |
190 | ||
191 | return (authenticated); | |
192 | } | |
193 | ||
194 | /*ARGSUSED*/ | |
195 | static int | |
196 | auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen) | |
197 | { | |
198 | char *challenge; | |
199 | ||
200 | if ((challenge = get_challenge(authctxt)) == NULL) | |
201 | return (0); | |
202 | ||
203 | debug("sending challenge '%s'", challenge); | |
204 | packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE); | |
205 | packet_put_cstring(challenge); | |
206 | xfree(challenge); | |
207 | packet_send(); | |
208 | packet_write_wait(); | |
209 | ||
210 | return (-1); | |
211 | } | |
212 | ||
213 | /*ARGSUSED*/ | |
214 | static int | |
215 | auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen) | |
216 | { | |
217 | int authenticated = 0; | |
218 | char *response; | |
219 | u_int dlen; | |
220 | ||
221 | response = packet_get_string(&dlen); | |
222 | packet_check_eom(); | |
223 | authenticated = verify_response(authctxt, response); | |
224 | memset(response, 'r', dlen); | |
225 | xfree(response); | |
226 | ||
227 | return (authenticated); | |
228 | } | |
229 | ||
230 | /* | |
231 | * read packets, try to authenticate the user and | |
232 | * return only if authentication is successful | |
233 | */ | |
234 | static void | |
235 | do_authloop(Authctxt *authctxt) | |
236 | { | |
237 | int authenticated = 0; | |
238 | char info[1024]; | |
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.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, "without authentication", ""); | |
256 | return; | |
257 | } | |
258 | } | |
259 | ||
260 | /* Indicate that authentication is needed. */ | |
261 | packet_start(SSH_SMSG_FAILURE); | |
262 | packet_send(); | |
263 | packet_write_wait(); | |
264 | ||
265 | for (;;) { | |
266 | /* default to fail */ | |
267 | authenticated = 0; | |
268 | ||
269 | info[0] = '\0'; | |
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 ((meth = lookup_authmethod1(type)) == NULL) { | |
287 | logit("Unknown message during authentication: " | |
288 | "type %d", type); | |
289 | goto skip; | |
290 | } | |
291 | ||
292 | if (!*(meth->enabled)) { | |
293 | verbose("%s authentication disabled.", meth->name); | |
294 | goto skip; | |
295 | } | |
296 | ||
297 | authenticated = meth->method(authctxt, info, sizeof(info)); | |
298 | if (authenticated == -1) | |
299 | continue; /* "postponed" */ | |
300 | ||
301 | #ifdef BSD_AUTH | |
302 | if (authctxt->as) { | |
303 | auth_close(authctxt->as); | |
304 | authctxt->as = NULL; | |
305 | } | |
306 | #endif | |
307 | if (!authctxt->valid && authenticated) | |
308 | fatal("INTERNAL ERROR: authenticated invalid user %s", | |
309 | authctxt->user); | |
310 | ||
311 | #ifdef _UNICOS | |
312 | if (authenticated && cray_access_denied(authctxt->user)) { | |
313 | authenticated = 0; | |
314 | fatal("Access denied for user %s.",authctxt->user); | |
315 | } | |
316 | #endif /* _UNICOS */ | |
317 | ||
318 | #ifdef HAVE_CYGWIN | |
319 | if (authenticated && | |
320 | !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, | |
321 | authctxt->pw)) { | |
322 | packet_disconnect("Authentication rejected for uid %d.", | |
323 | authctxt->pw == NULL ? -1 : authctxt->pw->pw_uid); | |
324 | authenticated = 0; | |
325 | } | |
326 | #else | |
327 | /* Special handling for root */ | |
328 | if (authenticated && authctxt->pw->pw_uid == 0 && | |
329 | !auth_root_allowed(meth->name)) { | |
330 | authenticated = 0; | |
331 | # ifdef SSH_AUDIT_EVENTS | |
332 | PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); | |
333 | # endif | |
334 | } | |
335 | #endif | |
336 | ||
337 | #ifdef USE_PAM | |
338 | if (options.use_pam && authenticated && | |
339 | !PRIVSEP(do_pam_account())) { | |
340 | char *msg; | |
341 | size_t len; | |
342 | ||
343 | error("Access denied for user %s by PAM account " | |
344 | "configuration", authctxt->user); | |
345 | len = buffer_len(&loginmsg); | |
346 | buffer_append(&loginmsg, "\0", 1); | |
347 | msg = buffer_ptr(&loginmsg); | |
348 | /* strip trailing newlines */ | |
349 | if (len > 0) | |
350 | while (len > 0 && msg[--len] == '\n') | |
351 | msg[len] = '\0'; | |
352 | else | |
353 | msg = "Access denied."; | |
354 | packet_disconnect(msg); | |
355 | } | |
356 | #endif | |
357 | ||
358 | skip: | |
359 | /* Log before sending the reply */ | |
360 | auth_log(authctxt, authenticated, get_authname(type), info); | |
361 | ||
362 | if (client_user != NULL) { | |
363 | xfree(client_user); | |
364 | client_user = NULL; | |
365 | } | |
366 | ||
367 | if (authenticated) | |
368 | return; | |
369 | ||
370 | if (authctxt->failures++ > options.max_authtries) { | |
371 | #ifdef SSH_AUDIT_EVENTS | |
372 | PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); | |
373 | #endif | |
374 | packet_disconnect(AUTH_FAIL_MSG, authctxt->user); | |
375 | } | |
376 | ||
377 | packet_start(SSH_SMSG_FAILURE); | |
378 | packet_send(); | |
379 | packet_write_wait(); | |
380 | } | |
381 | } | |
382 | ||
383 | /* | |
384 | * Performs authentication of an incoming connection. Session key has already | |
385 | * been exchanged and encryption is enabled. | |
386 | */ | |
387 | void | |
388 | do_authentication(Authctxt *authctxt) | |
389 | { | |
390 | u_int ulen; | |
391 | char *user, *style = NULL; | |
392 | ||
393 | /* Get the name of the user that we wish to log in as. */ | |
394 | packet_read_expect(SSH_CMSG_USER); | |
395 | ||
396 | /* Get the user name. */ | |
397 | user = packet_get_string(&ulen); | |
398 | packet_check_eom(); | |
399 | ||
400 | if ((style = strchr(user, ':')) != NULL) | |
401 | *style++ = '\0'; | |
402 | ||
403 | authctxt->user = user; | |
404 | authctxt->style = style; | |
405 | ||
406 | /* Verify that the user is a valid user. */ | |
407 | if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL) | |
408 | authctxt->valid = 1; | |
409 | else { | |
410 | debug("do_authentication: invalid user %s", user); | |
411 | authctxt->pw = fakepw(); | |
412 | } | |
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 | } |