1/*
2 * Dropbear - a SSH2 server
3 *
4 * Copyright (c) 2002,2003 Matt Johnston
5 * All rights reserved.
6 *
7 * Permission is hereby granted, free of charge, to any person obtaining a copy
8 * of this software and associated documentation files (the "Software"), to deal
9 * in the Software without restriction, including without limitation the rights
10 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
11 * copies of the Software, and to permit persons to whom the Software is
12 * furnished to do so, subject to the following conditions:
13 *
14 * The above copyright notice and this permission notice shall be included in
15 * all copies or substantial portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
20 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
21 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
22 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
23 * SOFTWARE. */
24
25/* This file (auth.c) handles authentication requests, passing it to the
26 * particular type (auth-passwd, auth-pubkey). */
27
28#include "includes.h"
29#include "dbutil.h"
30#include "session.h"
31#include "buffer.h"
32#include "ssh.h"
33#include "packet.h"
34#include "auth.h"
35#include "runopts.h"
36
37static void authclear();
38static int checkusername(unsigned char *username, unsigned int userlen);
39static void send_msg_userauth_banner();
40
41/* initialise the first time for a session, resetting all parameters */
42void svr_authinitialise() {
43
44	ses.authstate.failcount = 0;
45	authclear();
46
47}
48
49/* Reset the auth state, but don't reset the failcount. This is for if the
50 * user decides to try with a different username etc, and is also invoked
51 * on initialisation */
52static void authclear() {
53
54	memset(&ses.authstate, 0, sizeof(ses.authstate));
55#ifdef ENABLE_SVR_PUBKEY_AUTH
56	ses.authstate.authtypes |= AUTH_TYPE_PUBKEY;
57#endif
58#if defined(ENABLE_SVR_PASSWORD_AUTH) || defined(ENABLE_SVR_PAM_AUTH)
59	if (!svr_opts.noauthpass) {
60		ses.authstate.authtypes |= AUTH_TYPE_PASSWORD;
61	}
62#endif
63
64}
65
66/* Send a banner message if specified to the client. The client might
67 * ignore this, but possibly serves as a legal "no trespassing" sign */
68static void send_msg_userauth_banner() {
69
70	TRACE(("enter send_msg_userauth_banner"))
71	if (svr_opts.banner == NULL) {
72		TRACE(("leave send_msg_userauth_banner: banner is NULL"))
73		return;
74	}
75
76	CHECKCLEARTOWRITE();
77
78	buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_BANNER);
79	buf_putstring(ses.writepayload, buf_getptr(svr_opts.banner,
80				svr_opts.banner->len), svr_opts.banner->len);
81	buf_putstring(ses.writepayload, "en", 2);
82
83	encrypt_packet();
84	buf_free(svr_opts.banner);
85	svr_opts.banner = NULL;
86
87	TRACE(("leave send_msg_userauth_banner"))
88}
89
90/* handle a userauth request, check validity, pass to password or pubkey
91 * checking, and handle success or failure */
92void recv_msg_userauth_request() {
93
94	unsigned char *username = NULL, *servicename = NULL, *methodname = NULL;
95	unsigned int userlen, servicelen, methodlen;
96
97	TRACE(("enter recv_msg_userauth_request"))
98
99	/* ignore packets if auth is already done */
100	if (ses.authstate.authdone == 1) {
101		TRACE(("leave recv_msg_userauth_request: authdone already"))
102		return;
103	}
104
105	/* send the banner if it exists, it will only exist once */
106	if (svr_opts.banner) {
107		send_msg_userauth_banner();
108	}
109
110
111	username = buf_getstring(ses.payload, &userlen);
112	servicename = buf_getstring(ses.payload, &servicelen);
113	methodname = buf_getstring(ses.payload, &methodlen);
114
115	/* only handle 'ssh-connection' currently */
116	if (servicelen != SSH_SERVICE_CONNECTION_LEN
117			&& (strncmp(servicename, SSH_SERVICE_CONNECTION,
118					SSH_SERVICE_CONNECTION_LEN) != 0)) {
119
120		/* TODO - disconnect here */
121		m_free(username);
122		m_free(servicename);
123		m_free(methodname);
124		dropbear_exit("unknown service in auth");
125	}
126
127	/* user wants to know what methods are supported */
128	if (methodlen == AUTH_METHOD_NONE_LEN &&
129			strncmp(methodname, AUTH_METHOD_NONE,
130				AUTH_METHOD_NONE_LEN) == 0) {
131		TRACE(("recv_msg_userauth_request: 'none' request"))
132		send_msg_userauth_failure(0, 0);
133		goto out;
134	}
135
136	/* check username is good before continuing */
137	if (checkusername(username, userlen) == DROPBEAR_FAILURE) {
138		/* username is invalid/no shell/etc - send failure */
139		TRACE(("sending checkusername failure"))
140		send_msg_userauth_failure(0, 1);
141		goto out;
142	}
143
144#ifdef ENABLE_SVR_PASSWORD_AUTH
145	if (!svr_opts.noauthpass &&
146			!(svr_opts.norootpass && ses.authstate.pw->pw_uid == 0) ) {
147		/* user wants to try password auth */
148		if (methodlen == AUTH_METHOD_PASSWORD_LEN &&
149				strncmp(methodname, AUTH_METHOD_PASSWORD,
150					AUTH_METHOD_PASSWORD_LEN) == 0) {
151			svr_auth_password();
152			goto out;
153		}
154	}
155#endif
156
157#ifdef ENABLE_SVR_PAM_AUTH
158	if (!svr_opts.noauthpass &&
159			!(svr_opts.norootpass && ses.authstate.pw->pw_uid == 0) ) {
160		/* user wants to try password auth */
161		if (methodlen == AUTH_METHOD_PASSWORD_LEN &&
162				strncmp(methodname, AUTH_METHOD_PASSWORD,
163					AUTH_METHOD_PASSWORD_LEN) == 0) {
164			svr_auth_pam();
165			goto out;
166		}
167	}
168#endif
169
170#ifdef ENABLE_SVR_PUBKEY_AUTH
171	/* user wants to try pubkey auth */
172	if (methodlen == AUTH_METHOD_PUBKEY_LEN &&
173			strncmp(methodname, AUTH_METHOD_PUBKEY,
174				AUTH_METHOD_PUBKEY_LEN) == 0) {
175		svr_auth_pubkey();
176		goto out;
177	}
178#endif
179
180	/* nothing matched, we just fail */
181	send_msg_userauth_failure(0, 1);
182
183out:
184
185	m_free(username);
186	m_free(servicename);
187	m_free(methodname);
188}
189
190/* Check that the username exists, has a non-empty password, and has a valid
191 * shell.
192 * returns DROPBEAR_SUCCESS on valid username, DROPBEAR_FAILURE on failure */
193static int checkusername(unsigned char *username, unsigned int userlen) {
194
195	char* listshell = NULL;
196	char* usershell = NULL;
197
198	TRACE(("enter checkusername"))
199	if (userlen > MAX_USERNAME_LEN) {
200		return DROPBEAR_FAILURE;
201	}
202
203	/* new user or username has changed */
204	if (ses.authstate.username == NULL ||
205		strcmp(username, ses.authstate.username) != 0) {
206			/* the username needs resetting */
207			if (ses.authstate.username != NULL) {
208				dropbear_log(LOG_WARNING, "client trying multiple usernames from %s",
209							svr_ses.addrstring);
210				m_free(ses.authstate.username);
211			}
212			authclear();
213			ses.authstate.pw = getpwnam((char*)username);
214			ses.authstate.username = m_strdup(username);
215			m_free(ses.authstate.printableuser);
216	}
217
218	/* check that user exists */
219	if (ses.authstate.pw == NULL) {
220		TRACE(("leave checkusername: user '%s' doesn't exist", username))
221		dropbear_log(LOG_WARNING,
222				"login attempt for nonexistent user from %s",
223				svr_ses.addrstring);
224		send_msg_userauth_failure(0, 1);
225		return DROPBEAR_FAILURE;
226	}
227
228	/* We can set it once we know its a real user */
229	ses.authstate.printableuser = m_strdup(ses.authstate.pw->pw_name);
230
231	/* check for non-root if desired */
232	if (svr_opts.norootlogin && ses.authstate.pw->pw_uid == 0) {
233		TRACE(("leave checkusername: root login disabled"))
234		dropbear_log(LOG_WARNING, "root login rejected");
235		send_msg_userauth_failure(0, 1);
236		return DROPBEAR_FAILURE;
237	}
238
239	/* check for an empty password */
240	if (ses.authstate.pw->pw_passwd[0] == '\0') {
241		TRACE(("leave checkusername: empty pword"))
242		dropbear_log(LOG_WARNING, "user '%s' has blank password, rejected",
243				ses.authstate.printableuser);
244		send_msg_userauth_failure(0, 1);
245		return DROPBEAR_FAILURE;
246	}
247
248	TRACE(("shell is %s", ses.authstate.pw->pw_shell))
249
250	/* check that the shell is set */
251	usershell = ses.authstate.pw->pw_shell;
252	if (usershell[0] == '\0') {
253		/* empty shell in /etc/passwd means /bin/sh according to passwd(5) */
254		usershell = "/bin/sh";
255	}
256
257	/* check the shell is valid. If /etc/shells doesn't exist, getusershell()
258	 * should return some standard shells like "/bin/sh" and "/bin/csh" (this
259	 * is platform-specific) */
260	setusershell();
261	while ((listshell = getusershell()) != NULL) {
262		TRACE(("test shell is '%s'", listshell))
263		if (strcmp(listshell, usershell) == 0) {
264			/* have a match */
265			goto goodshell;
266		}
267	}
268	/* no matching shell */
269	endusershell();
270	TRACE(("no matching shell"))
271	dropbear_log(LOG_WARNING, "user '%s' has invalid shell, rejected",
272				ses.authstate.printableuser);
273	send_msg_userauth_failure(0, 1);
274	return DROPBEAR_FAILURE;
275
276goodshell:
277	endusershell();
278	TRACE(("matching shell"))
279
280	TRACE(("uid = %d", ses.authstate.pw->pw_uid))
281	TRACE(("leave checkusername"))
282	return DROPBEAR_SUCCESS;
283
284}
285
286/* Send a failure message to the client, in responds to a userauth_request.
287 * Partial indicates whether to set the "partial success" flag,
288 * incrfail is whether to count this failure in the failure count (which
289 * is limited. This function also handles disconnection after too many
290 * failures */
291void send_msg_userauth_failure(int partial, int incrfail) {
292
293	buffer *typebuf = NULL;
294
295	TRACE(("enter send_msg_userauth_failure"))
296
297	CHECKCLEARTOWRITE();
298
299	buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_FAILURE);
300
301	/* put a list of allowed types */
302	typebuf = buf_new(30); /* long enough for PUBKEY and PASSWORD */
303
304	if (ses.authstate.authtypes & AUTH_TYPE_PUBKEY) {
305		buf_putbytes(typebuf, AUTH_METHOD_PUBKEY, AUTH_METHOD_PUBKEY_LEN);
306		if (ses.authstate.authtypes & AUTH_TYPE_PASSWORD) {
307			buf_putbyte(typebuf, ',');
308		}
309	}
310
311	if (ses.authstate.authtypes & AUTH_TYPE_PASSWORD) {
312		buf_putbytes(typebuf, AUTH_METHOD_PASSWORD, AUTH_METHOD_PASSWORD_LEN);
313	}
314
315	buf_setpos(typebuf, 0);
316	buf_putstring(ses.writepayload, buf_getptr(typebuf, typebuf->len),
317			typebuf->len);
318
319	TRACE(("auth fail: methods %d, '%s'", ses.authstate.authtypes,
320				buf_getptr(typebuf, typebuf->len)));
321
322	buf_free(typebuf);
323
324	buf_putbyte(ses.writepayload, partial ? 1 : 0);
325	encrypt_packet();
326
327	if (incrfail) {
328		usleep(300000); /* XXX improve this */
329		ses.authstate.failcount++;
330	}
331
332	if (ses.authstate.failcount >= MAX_AUTH_TRIES) {
333		char * userstr;
334		/* XXX - send disconnect ? */
335		TRACE(("Max auth tries reached, exiting"))
336
337		if (ses.authstate.printableuser == NULL) {
338			userstr = "is invalid";
339		} else {
340			userstr = ses.authstate.printableuser;
341		}
342		dropbear_exit("Max auth tries reached - user '%s' from %s",
343				userstr, svr_ses.addrstring);
344	}
345
346	TRACE(("leave send_msg_userauth_failure"))
347}
348
349/* Send a success message to the user, and set the "authdone" flag */
350void send_msg_userauth_success() {
351
352	TRACE(("enter send_msg_userauth_success"))
353
354	CHECKCLEARTOWRITE();
355
356	buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_SUCCESS);
357	encrypt_packet();
358
359	ses.authstate.authdone = 1;
360	ses.connecttimeout = 0;
361
362
363	if (ses.authstate.pw->pw_uid == 0) {
364		ses.allowprivport = 1;
365	}
366
367	/* Remove from the list of pre-auth sockets. Should be m_close(), since if
368	 * we fail, we might end up leaking connection slots, and disallow new
369	 * logins - a nasty situation. */
370	m_close(svr_ses.childpipe);
371
372	TRACE(("leave send_msg_userauth_success"))
373
374}
375