xref: /freebsd/crypto/openssh/auth2.c (revision 39beb93c3f8bdbf72a61fda42300b5ebed7390c8)
1 /* $OpenBSD: auth2.c,v 1.119 2008/07/04 23:30:16 djm Exp $ */
2 /*
3  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24  */
25 
26 #include "includes.h"
27 __RCSID("$FreeBSD$");
28 
29 #include <sys/types.h>
30 #include <sys/stat.h>
31 #include <sys/uio.h>
32 
33 #include <fcntl.h>
34 #include <pwd.h>
35 #include <stdarg.h>
36 #include <string.h>
37 #include <unistd.h>
38 
39 #include "xmalloc.h"
40 #include "atomicio.h"
41 #include "ssh2.h"
42 #include "packet.h"
43 #include "log.h"
44 #include "buffer.h"
45 #include "servconf.h"
46 #include "compat.h"
47 #include "key.h"
48 #include "hostfile.h"
49 #include "auth.h"
50 #include "dispatch.h"
51 #include "pathnames.h"
52 #include "buffer.h"
53 #include "canohost.h"
54 
55 #ifdef GSSAPI
56 #include "ssh-gss.h"
57 #endif
58 #include "monitor_wrap.h"
59 
60 /* import */
61 extern ServerOptions options;
62 extern u_char *session_id2;
63 extern u_int session_id2_len;
64 extern Buffer loginmsg;
65 
66 /* methods */
67 
68 extern Authmethod method_none;
69 extern Authmethod method_pubkey;
70 extern Authmethod method_passwd;
71 extern Authmethod method_kbdint;
72 extern Authmethod method_hostbased;
73 #ifdef GSSAPI
74 extern Authmethod method_gssapi;
75 #endif
76 
77 Authmethod *authmethods[] = {
78 	&method_none,
79 	&method_pubkey,
80 #ifdef GSSAPI
81 	&method_gssapi,
82 #endif
83 	&method_passwd,
84 	&method_kbdint,
85 	&method_hostbased,
86 	NULL
87 };
88 
89 /* protocol */
90 
91 static void input_service_request(int, u_int32_t, void *);
92 static void input_userauth_request(int, u_int32_t, void *);
93 
94 /* helper */
95 static Authmethod *authmethod_lookup(const char *);
96 static char *authmethods_get(void);
97 
98 char *
99 auth2_read_banner(void)
100 {
101 	struct stat st;
102 	char *banner = NULL;
103 	size_t len, n;
104 	int fd;
105 
106 	if ((fd = open(options.banner, O_RDONLY)) == -1)
107 		return (NULL);
108 	if (fstat(fd, &st) == -1) {
109 		close(fd);
110 		return (NULL);
111 	}
112 	if (st.st_size > 1*1024*1024) {
113 		close(fd);
114 		return (NULL);
115 	}
116 
117 	len = (size_t)st.st_size;		/* truncate */
118 	banner = xmalloc(len + 1);
119 	n = atomicio(read, fd, banner, len);
120 	close(fd);
121 
122 	if (n != len) {
123 		xfree(banner);
124 		return (NULL);
125 	}
126 	banner[n] = '\0';
127 
128 	return (banner);
129 }
130 
131 void
132 userauth_send_banner(const char *msg)
133 {
134 	if (datafellows & SSH_BUG_BANNER)
135 		return;
136 
137 	packet_start(SSH2_MSG_USERAUTH_BANNER);
138 	packet_put_cstring(msg);
139 	packet_put_cstring("");		/* language, unused */
140 	packet_send();
141 	debug("%s: sent", __func__);
142 }
143 
144 static void
145 userauth_banner(void)
146 {
147 	char *banner = NULL;
148 
149 	if (options.banner == NULL ||
150 	    strcasecmp(options.banner, "none") == 0 ||
151 	    (datafellows & SSH_BUG_BANNER) != 0)
152 		return;
153 
154 	if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
155 		goto done;
156 	userauth_send_banner(banner);
157 
158 done:
159 	if (banner)
160 		xfree(banner);
161 }
162 
163 /*
164  * loop until authctxt->success == TRUE
165  */
166 void
167 do_authentication2(Authctxt *authctxt)
168 {
169 	dispatch_init(&dispatch_protocol_error);
170 	dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
171 	dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
172 }
173 
174 /*ARGSUSED*/
175 static void
176 input_service_request(int type, u_int32_t seq, void *ctxt)
177 {
178 	Authctxt *authctxt = ctxt;
179 	u_int len;
180 	int acceptit = 0;
181 	char *service = packet_get_string(&len);
182 	packet_check_eom();
183 
184 	if (authctxt == NULL)
185 		fatal("input_service_request: no authctxt");
186 
187 	if (strcmp(service, "ssh-userauth") == 0) {
188 		if (!authctxt->success) {
189 			acceptit = 1;
190 			/* now we can handle user-auth requests */
191 			dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
192 		}
193 	}
194 	/* XXX all other service requests are denied */
195 
196 	if (acceptit) {
197 		packet_start(SSH2_MSG_SERVICE_ACCEPT);
198 		packet_put_cstring(service);
199 		packet_send();
200 		packet_write_wait();
201 	} else {
202 		debug("bad service request %s", service);
203 		packet_disconnect("bad service request %s", service);
204 	}
205 	xfree(service);
206 }
207 
208 /*ARGSUSED*/
209 static void
210 input_userauth_request(int type, u_int32_t seq, void *ctxt)
211 {
212 	Authctxt *authctxt = ctxt;
213 	Authmethod *m = NULL;
214 	char *user, *service, *method, *style = NULL;
215 	int authenticated = 0;
216 #ifdef HAVE_LOGIN_CAP
217 	login_cap_t *lc;
218 	const char *from_host, *from_ip;
219 
220         from_host = get_canonical_hostname(options.use_dns);
221         from_ip = get_remote_ipaddr();
222 #endif
223 
224 	if (authctxt == NULL)
225 		fatal("input_userauth_request: no authctxt");
226 
227 	user = packet_get_string(NULL);
228 	service = packet_get_string(NULL);
229 	method = packet_get_string(NULL);
230 	debug("userauth-request for user %s service %s method %s", user, service, method);
231 	debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
232 
233 	if ((style = strchr(user, ':')) != NULL)
234 		*style++ = 0;
235 
236 	if (authctxt->attempt++ == 0) {
237 		/* setup auth context */
238 		authctxt->pw = PRIVSEP(getpwnamallow(user));
239 		authctxt->user = xstrdup(user);
240 		if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
241 			authctxt->valid = 1;
242 			debug2("input_userauth_request: setting up authctxt for %s", user);
243 		} else {
244 			logit("input_userauth_request: invalid user %s", user);
245 			authctxt->pw = fakepw();
246 #ifdef SSH_AUDIT_EVENTS
247 			PRIVSEP(audit_event(SSH_INVALID_USER));
248 #endif
249 		}
250 #ifdef USE_PAM
251 		if (options.use_pam)
252 			PRIVSEP(start_pam(authctxt));
253 #endif
254 		setproctitle("%s%s", authctxt->valid ? user : "unknown",
255 		    use_privsep ? " [net]" : "");
256 		authctxt->service = xstrdup(service);
257 		authctxt->style = style ? xstrdup(style) : NULL;
258 		if (use_privsep)
259 			mm_inform_authserv(service, style);
260 		userauth_banner();
261 	} else if (strcmp(user, authctxt->user) != 0 ||
262 	    strcmp(service, authctxt->service) != 0) {
263 		packet_disconnect("Change of username or service not allowed: "
264 		    "(%s,%s) -> (%s,%s)",
265 		    authctxt->user, authctxt->service, user, service);
266 	}
267 
268 #ifdef HAVE_LOGIN_CAP
269         if (authctxt->pw != NULL) {
270                 lc = login_getpwclass(authctxt->pw);
271                 if (lc == NULL)
272                         lc = login_getclassbyname(NULL, authctxt->pw);
273                 if (!auth_hostok(lc, from_host, from_ip)) {
274                         logit("Denied connection for %.200s from %.200s [%.200s].",
275                             authctxt->pw->pw_name, from_host, from_ip);
276                         packet_disconnect("Sorry, you are not allowed to connect.");
277                 }
278                 if (!auth_timeok(lc, time(NULL))) {
279                         logit("LOGIN %.200s REFUSED (TIME) FROM %.200s",
280                             authctxt->pw->pw_name, from_host);
281                         packet_disconnect("Logins not available right now.");
282                 }
283                 login_close(lc);
284                 lc = NULL;
285         }
286 #endif  /* HAVE_LOGIN_CAP */
287 
288 	/* reset state */
289 	auth2_challenge_stop(authctxt);
290 
291 #ifdef GSSAPI
292 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
293 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
294 #endif
295 
296 	authctxt->postponed = 0;
297 
298 	/* try to authenticate user */
299 	m = authmethod_lookup(method);
300 	if (m != NULL && authctxt->failures < options.max_authtries) {
301 		debug2("input_userauth_request: try method %s", method);
302 		authenticated =	m->userauth(authctxt);
303 	}
304 	userauth_finish(authctxt, authenticated, method);
305 
306 	xfree(service);
307 	xfree(user);
308 	xfree(method);
309 }
310 
311 void
312 userauth_finish(Authctxt *authctxt, int authenticated, char *method)
313 {
314 	char *methods;
315 
316 	if (!authctxt->valid && authenticated)
317 		fatal("INTERNAL ERROR: authenticated invalid user %s",
318 		    authctxt->user);
319 
320 	/* Special handling for root */
321 	if (authenticated && authctxt->pw->pw_uid == 0 &&
322 	    !auth_root_allowed(method)) {
323 		authenticated = 0;
324 #ifdef SSH_AUDIT_EVENTS
325 		PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
326 #endif
327 	}
328 
329 #ifdef USE_PAM
330 	if (options.use_pam && authenticated) {
331 		if (!PRIVSEP(do_pam_account())) {
332 			/* if PAM returned a message, send it to the user */
333 			if (buffer_len(&loginmsg) > 0) {
334 				buffer_append(&loginmsg, "\0", 1);
335 				userauth_send_banner(buffer_ptr(&loginmsg));
336 				packet_write_wait();
337 			}
338 			fatal("Access denied for user %s by PAM account "
339 			    "configuration", authctxt->user);
340 		}
341 	}
342 #endif
343 
344 #ifdef _UNICOS
345 	if (authenticated && cray_access_denied(authctxt->user)) {
346 		authenticated = 0;
347 		fatal("Access denied for user %s.",authctxt->user);
348 	}
349 #endif /* _UNICOS */
350 
351 	/* Log before sending the reply */
352 	auth_log(authctxt, authenticated, method, " ssh2");
353 
354 	if (authctxt->postponed)
355 		return;
356 
357 	/* XXX todo: check if multiple auth methods are needed */
358 	if (authenticated == 1) {
359 		/* turn off userauth */
360 		dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
361 		packet_start(SSH2_MSG_USERAUTH_SUCCESS);
362 		packet_send();
363 		packet_write_wait();
364 		/* now we can break out */
365 		authctxt->success = 1;
366 	} else {
367 
368 		/* Allow initial try of "none" auth without failure penalty */
369 		if (authctxt->attempt > 1 || strcmp(method, "none") != 0)
370 			authctxt->failures++;
371 		if (authctxt->failures >= options.max_authtries) {
372 #ifdef SSH_AUDIT_EVENTS
373 			PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
374 #endif
375 			packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
376 		}
377 		methods = authmethods_get();
378 		packet_start(SSH2_MSG_USERAUTH_FAILURE);
379 		packet_put_cstring(methods);
380 		packet_put_char(0);	/* XXX partial success, unused */
381 		packet_send();
382 		packet_write_wait();
383 		xfree(methods);
384 	}
385 }
386 
387 static char *
388 authmethods_get(void)
389 {
390 	Buffer b;
391 	char *list;
392 	int i;
393 
394 	buffer_init(&b);
395 	for (i = 0; authmethods[i] != NULL; i++) {
396 		if (strcmp(authmethods[i]->name, "none") == 0)
397 			continue;
398 		if (authmethods[i]->enabled != NULL &&
399 		    *(authmethods[i]->enabled) != 0) {
400 			if (buffer_len(&b) > 0)
401 				buffer_append(&b, ",", 1);
402 			buffer_append(&b, authmethods[i]->name,
403 			    strlen(authmethods[i]->name));
404 		}
405 	}
406 	buffer_append(&b, "\0", 1);
407 	list = xstrdup(buffer_ptr(&b));
408 	buffer_free(&b);
409 	return list;
410 }
411 
412 static Authmethod *
413 authmethod_lookup(const char *name)
414 {
415 	int i;
416 
417 	if (name != NULL)
418 		for (i = 0; authmethods[i] != NULL; i++)
419 			if (authmethods[i]->enabled != NULL &&
420 			    *(authmethods[i]->enabled) != 0 &&
421 			    strcmp(name, authmethods[i]->name) == 0)
422 				return authmethods[i];
423 	debug2("Unrecognized authentication method name: %s",
424 	    name ? name : "NULL");
425 	return NULL;
426 }
427 
428