auth1.c revision 126277 
1/*
2 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
3 *                    All rights reserved
4 *
5 * As far as I am concerned, the code I have written for this software
6 * can be used freely for any purpose.  Any derived versions of this
7 * software must be clearly marked as such, and if the derived work is
8 * incompatible with the protocol description in the RFC file, it must be
9 * called by a name other than "ssh" or "Secure Shell".
10 */
11
12#include "includes.h"
13RCSID("$OpenBSD: auth1.c,v 1.55 2003/11/08 16:02:40 jakob Exp $");
14RCSID("$FreeBSD: head/crypto/openssh/auth1.c 126277 2004-02-26 10:52:33Z des $");
15
16#include "xmalloc.h"
17#include "rsa.h"
18#include "ssh1.h"
19#include "packet.h"
20#include "buffer.h"
21#include "mpaux.h"
22#include "log.h"
23#include "servconf.h"
24#include "compat.h"
25#include "auth.h"
26#include "channels.h"
27#include "session.h"
28#include "uidswap.h"
29#include "monitor_wrap.h"
30
31/* import */
32extern ServerOptions options;
33
34/*
35 * convert ssh auth msg type into description
36 */
37static char *
38get_authname(int type)
39{
40	static char buf[1024];
41	switch (type) {
42	case SSH_CMSG_AUTH_PASSWORD:
43		return "password";
44	case SSH_CMSG_AUTH_RSA:
45		return "rsa";
46	case SSH_CMSG_AUTH_RHOSTS_RSA:
47		return "rhosts-rsa";
48	case SSH_CMSG_AUTH_RHOSTS:
49		return "rhosts";
50	case SSH_CMSG_AUTH_TIS:
51	case SSH_CMSG_AUTH_TIS_RESPONSE:
52		return "challenge-response";
53	}
54	snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
55	return buf;
56}
57
58/*
59 * read packets, try to authenticate the user and
60 * return only if authentication is successful
61 */
62static void
63do_authloop(Authctxt *authctxt)
64{
65	int authenticated = 0;
66	u_int bits;
67	Key *client_host_key;
68	BIGNUM *n;
69	char *client_user, *password;
70	char info[1024];
71	u_int dlen;
72	u_int ulen;
73	int prev, type = 0;
74	struct passwd *pw = authctxt->pw;
75
76	debug("Attempting authentication for %s%.100s.",
77	    authctxt->valid ? "" : "illegal user ", authctxt->user);
78
79	/* If the user has no password, accept authentication immediately. */
80	if (options.password_authentication &&
81#ifdef KRB5
82	    (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
83#endif
84	    PRIVSEP(auth_password(authctxt, ""))) {
85		auth_log(authctxt, 1, "without authentication", "");
86		return;
87	}
88
89	/* Indicate that authentication is needed. */
90	packet_start(SSH_SMSG_FAILURE);
91	packet_send();
92	packet_write_wait();
93
94	client_user = NULL;
95
96	for (;;) {
97		/* default to fail */
98		authenticated = 0;
99
100		info[0] = '\0';
101
102		/* Get a packet from the client. */
103		prev = type;
104		type = packet_read();
105
106		/*
107		 * If we started challenge-response authentication but the
108		 * next packet is not a response to our challenge, release
109		 * the resources allocated by get_challenge() (which would
110		 * normally have been released by verify_response() had we
111		 * received such a response)
112		 */
113		if (prev == SSH_CMSG_AUTH_TIS &&
114		    type != SSH_CMSG_AUTH_TIS_RESPONSE)
115			abandon_challenge_response(authctxt);
116
117		/* Process the packet. */
118		switch (type) {
119		case SSH_CMSG_AUTH_RHOSTS_RSA:
120			if (!options.rhosts_rsa_authentication) {
121				verbose("Rhosts with RSA authentication disabled.");
122				break;
123			}
124			/*
125			 * Get client user name.  Note that we just have to
126			 * trust the client; root on the client machine can
127			 * claim to be any user.
128			 */
129			client_user = packet_get_string(&ulen);
130
131			/* Get the client host key. */
132			client_host_key = key_new(KEY_RSA1);
133			bits = packet_get_int();
134			packet_get_bignum(client_host_key->rsa->e);
135			packet_get_bignum(client_host_key->rsa->n);
136
137			if (bits != BN_num_bits(client_host_key->rsa->n))
138				verbose("Warning: keysize mismatch for client_host_key: "
139				    "actual %d, announced %d",
140				    BN_num_bits(client_host_key->rsa->n), bits);
141			packet_check_eom();
142
143			authenticated = auth_rhosts_rsa(authctxt, client_user,
144			    client_host_key);
145			key_free(client_host_key);
146
147			snprintf(info, sizeof info, " ruser %.100s", client_user);
148			break;
149
150		case SSH_CMSG_AUTH_RSA:
151			if (!options.rsa_authentication) {
152				verbose("RSA authentication disabled.");
153				break;
154			}
155			/* RSA authentication requested. */
156			if ((n = BN_new()) == NULL)
157				fatal("do_authloop: BN_new failed");
158			packet_get_bignum(n);
159			packet_check_eom();
160			authenticated = auth_rsa(authctxt, n);
161			BN_clear_free(n);
162			break;
163
164		case SSH_CMSG_AUTH_PASSWORD:
165			if (!options.password_authentication) {
166				verbose("Password authentication disabled.");
167				break;
168			}
169			/*
170			 * Read user password.  It is in plain text, but was
171			 * transmitted over the encrypted channel so it is
172			 * not visible to an outside observer.
173			 */
174			password = packet_get_string(&dlen);
175			packet_check_eom();
176
177			/* Try authentication with the password. */
178			authenticated = PRIVSEP(auth_password(authctxt, password));
179
180			memset(password, 0, strlen(password));
181			xfree(password);
182			break;
183
184		case SSH_CMSG_AUTH_TIS:
185			debug("rcvd SSH_CMSG_AUTH_TIS");
186			if (options.challenge_response_authentication == 1) {
187				char *challenge = get_challenge(authctxt);
188				if (challenge != NULL) {
189					debug("sending challenge '%s'", challenge);
190					packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
191					packet_put_cstring(challenge);
192					xfree(challenge);
193					packet_send();
194					packet_write_wait();
195					continue;
196				}
197			}
198			break;
199		case SSH_CMSG_AUTH_TIS_RESPONSE:
200			debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
201			if (options.challenge_response_authentication == 1) {
202				char *response = packet_get_string(&dlen);
203				packet_check_eom();
204				authenticated = verify_response(authctxt, response);
205				memset(response, 'r', dlen);
206				xfree(response);
207			}
208			break;
209
210		default:
211			/*
212			 * Any unknown messages will be ignored (and failure
213			 * returned) during authentication.
214			 */
215			logit("Unknown message during authentication: type %d", type);
216			break;
217		}
218#ifdef BSD_AUTH
219		if (authctxt->as) {
220			auth_close(authctxt->as);
221			authctxt->as = NULL;
222		}
223#endif
224		if (!authctxt->valid && authenticated)
225			fatal("INTERNAL ERROR: authenticated invalid user %s",
226			    authctxt->user);
227
228#ifdef _UNICOS
229		if (authenticated && cray_access_denied(authctxt->user)) {
230			authenticated = 0;
231			fatal("Access denied for user %s.",authctxt->user);
232		}
233#endif /* _UNICOS */
234
235#ifdef HAVE_CYGWIN
236		if (authenticated &&
237		    !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
238			packet_disconnect("Authentication rejected for uid %d.",
239			    pw == NULL ? -1 : pw->pw_uid);
240			authenticated = 0;
241		}
242#else
243		/* Special handling for root */
244		if (authenticated && authctxt->pw->pw_uid == 0 &&
245		    !auth_root_allowed(get_authname(type)))
246			authenticated = 0;
247#endif
248
249#ifdef USE_PAM
250		if (options.use_pam && authenticated &&
251		    !PRIVSEP(do_pam_account()))
252			authenticated = 0;
253#endif
254
255		/* Log before sending the reply */
256		auth_log(authctxt, authenticated, get_authname(type), info);
257
258		if (client_user != NULL) {
259			xfree(client_user);
260			client_user = NULL;
261		}
262
263		if (authenticated)
264			return;
265
266		if (authctxt->failures++ > AUTH_FAIL_MAX)
267			packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
268
269		packet_start(SSH_SMSG_FAILURE);
270		packet_send();
271		packet_write_wait();
272	}
273}
274
275/*
276 * Performs authentication of an incoming connection.  Session key has already
277 * been exchanged and encryption is enabled.
278 */
279void
280do_authentication(Authctxt *authctxt)
281{
282	u_int ulen;
283	char *user, *style = NULL;
284
285	/* Get the name of the user that we wish to log in as. */
286	packet_read_expect(SSH_CMSG_USER);
287
288	/* Get the user name. */
289	user = packet_get_string(&ulen);
290	packet_check_eom();
291
292	if ((style = strchr(user, ':')) != NULL)
293		*style++ = '\0';
294
295	authctxt->user = user;
296	authctxt->style = style;
297
298	/* Verify that the user is a valid user. */
299	if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
300		authctxt->valid = 1;
301	else {
302		debug("do_authentication: illegal user %s", user);
303		authctxt->pw = fakepw();
304	}
305
306	setproctitle("%s%s", authctxt->pw ? user : "unknown",
307	    use_privsep ? " [net]" : "");
308
309#ifdef USE_PAM
310	if (options.use_pam)
311		PRIVSEP(start_pam(user));
312#endif
313
314	/*
315	 * If we are not running as root, the user must have the same uid as
316	 * the server. (Unless you are running Windows)
317	 */
318#ifndef HAVE_CYGWIN
319	if (!use_privsep && getuid() != 0 && authctxt->pw &&
320	    authctxt->pw->pw_uid != getuid())
321		packet_disconnect("Cannot change user when server not running as root.");
322#endif
323
324	/*
325	 * Loop until the user has been authenticated or the connection is
326	 * closed, do_authloop() returns only if authentication is successful
327	 */
328	do_authloop(authctxt);
329
330	/* The user has been authenticated and accepted. */
331	packet_start(SSH_SMSG_SUCCESS);
332	packet_send();
333	packet_write_wait();
334}
335