auth1.c revision 264377 
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 */
45extern ServerOptions options;
46extern Buffer loginmsg;
47
48static int auth1_process_password(Authctxt *);
49static int auth1_process_rsa(Authctxt *);
50static int auth1_process_rhosts_rsa(Authctxt *);
51static int auth1_process_tis_challenge(Authctxt *);
52static int auth1_process_tis_response(Authctxt *);
53
54static char *client_user = NULL;    /* Used to fill in remote user for PAM */
55
56struct AuthMethod1 {
57	int type;
58	char *name;
59	int *enabled;
60	int (*method)(Authctxt *);
61};
62
63const 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
89static 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
101static char *
102get_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*/
114static int
115auth1_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*/
139static int
140auth1_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*/
157static int
158auth1_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*/
196static int
197auth1_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*/
215static int
216auth1_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 */
235static void
236do_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 */
379void
380do_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