File: ccreds_chkpwd.c

package info (click to toggle)
libpam-ccreds 10-7
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, buster, sid
  • size: 644 kB
  • sloc: sh: 2,981; ansic: 2,066; makefile: 60
file content (255 lines) | stat: -rw-r--r-- 7,437 bytes parent folder | download | duplicates (4)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
/*
 * This program is designed to run setuid(root) or with sufficient
 * privilege to read the cached password database. It is designed
 * to provide a mechanism for the current user (defined by this
 * process' uid) to verify their own password.
 *
 * The password is read from the standard input. The exit status of
 * this program indicates whether the user is authenticated or not.
 *
 * Copyright information is located at the end of the file.
 *
 */

#ifdef MEMORY_DEBUG
# undef exit
# undef strdup
# undef free
#endif /* MEMORY_DEBUG */

#include <stdarg.h>
#include <signal.h>
#include <sys/types.h>
#include <pwd.h>
#include <syslog.h>

#include "cc_private.h"

#define MAXPASS		200	/* the maximum length of a password */

#define CCREDS_PASSED	0
#define CCREDS_FAILED	1

/* syslogging function for errors and other information */

static void _log_err(int err, const char *format,...)
{
	va_list args;

	va_start(args, format);
	openlog("ccreds_chkpwd", LOG_CONS | LOG_PID, LOG_AUTH);
	vsyslog(err, format, args);
	va_end(args);
	closelog();
}

static void su_sighandler(int sig)
{
#ifndef SA_RESETHAND
	/* emulate the behaviour of the SA_RESETHAND flag */
	if ( sig == SIGILL || sig == SIGTRAP || sig == SIGBUS || sig = SIGSERV )
		signal(sig, SIG_DFL);
#endif
	if (sig > 0) {
		_log_err(LOG_NOTICE, "caught signal %d.", sig);
		exit(sig);
	}
}

static void setup_signals(void)
{
	struct sigaction action;	/* posix signal structure */

	/*
	 * Setup signal handlers
	 */
	(void) memset((void *) &action, 0, sizeof(action));
	action.sa_handler = su_sighandler;
#ifdef SA_RESETHAND
	action.sa_flags = SA_RESETHAND;
#endif
	(void) sigaction(SIGILL, &action, NULL);
	(void) sigaction(SIGTRAP, &action, NULL);
	(void) sigaction(SIGBUS, &action, NULL);
	(void) sigaction(SIGSEGV, &action, NULL);
	action.sa_handler = SIG_IGN;
	action.sa_flags = 0;
	(void) sigaction(SIGTERM, &action, NULL);
	(void) sigaction(SIGHUP, &action, NULL);
	(void) sigaction(SIGINT, &action, NULL);
	(void) sigaction(SIGQUIT, &action, NULL);
}

static int _ccreds_verify_password(const char *service, const char *name,
                                   const char *ccredsfile, const char *p)
{
	int rc, retval = CCREDS_FAILED;
	pam_cc_handle_t *pamcch;

	rc = pam_cc_start(service, name, ccredsfile, CC_FLAGS_READ_ONLY,
	                  &pamcch);
	if (rc != PAM_SUCCESS) {
		_log_err(LOG_DEBUG, "error initializing");
		retval = CCREDS_FAILED;
		goto _return;
	}

	rc = pam_cc_validate_credentials(pamcch, PAM_CC_TYPE_DEFAULT, p,
	                                 strlen(p));
	if (rc != PAM_SUCCESS) {
		_log_err(LOG_DEBUG, "error reading cached credentials");
		retval = CCREDS_FAILED;
		goto _return;
	}

	retval = CCREDS_PASSED;

	pam_cc_end(&pamcch);

_return:
	return retval;
}

static char *getuidname(uid_t uid)
{
	struct passwd *pw;
	static char username[32];

	pw = getpwuid(uid);
	if (pw == NULL)
		return NULL;

	strncpy(username, pw->pw_name, sizeof(username));
	username[sizeof(username) - 1] = '\0';

	return username;
}

int main(int argc, char *argv[])
{
	char pass[MAXPASS + 1];
	int npass;
	int force_failure = 0;
	int retval = CCREDS_FAILED;
	char *user;
	char *user_arg;
	char *service;

	/*
	 * Catch or ignore as many signal as possible.
	 */
	setup_signals();

	/*
	 * we establish that this program is running with non-tty stdin.
	 * this is to discourage casual use. It does *NOT* prevent an
	 * intruder from repeatadly running this program to determine the
	 * password of the current user (brute force attack, but one for
	 * which the attacker must already have gained access to the user's
	 * account).
	 */

	if (isatty(STDIN_FILENO)) {

		_log_err(LOG_NOTICE
		      ,"inappropriate use of ccreds helper binary [UID=%d,tty]"
			 ,getuid());
		fprintf(stderr
		 ,"This binary is not designed for running in this way\n"
		      "-- the system administrator has been informed\n");
		sleep(10);	/* this should discourage/annoy the user */
		return CCREDS_FAILED;
	}

	/*
	 * determine the current user's name is
	 */
	user = getuidname(getuid());

	if (argc < 2 || argc > 3) {
		_log_err(LOG_NOTICE
		      ,"inappropriate use of ccreds helper binary [UID=%d,bad argv]"
			 ,getuid());
		fprintf(stderr
		 ,"This binary is not designed for running in this way\n"
		      "-- the system administrator has been informed\n");
		sleep(10);	/* this should discourage/annoy the user */
		return CCREDS_FAILED;
	}

	user_arg = argv[1];
	service = (argc > 2) ? argv[2] : NULL;

	/* Verify that user matches */
        if (strcmp(user, user_arg)) {
	    force_failure = 1;
	}

	/* read the password from stdin (a pipe from the pam_ccreds module) */
	npass = read(STDIN_FILENO, pass, MAXPASS);

	if (npass < 0) {	/* is it a valid password? */
		_log_err(LOG_DEBUG, "no password supplied");
	} else if (npass >= MAXPASS) {
		_log_err(LOG_DEBUG, "password too long");
	} else {
		if (npass == 0) {
			/* the password is blank */
			retval = _ccreds_verify_password(service, user, NULL, "");
		} else {
			/* does pass agree with the official one? */
			pass[npass] = '\0';	/* NUL terminate */
			retval = _ccreds_verify_password(service, user, NULL, pass);
		}
	}
	memset(pass, '\0', MAXPASS);	/* clear memory of the password */

	/* return pass or fail */
	if ((retval != CCREDS_PASSED) || force_failure) {
	    return CCREDS_FAILED;
	} else {
	    return CCREDS_PASSED;
	}
}

/*
 * This program is based on unix_chkpwd by Andrew G. Morgan.
 *
 * The modifications are Copyright (c) W. Michael Petullo, 2005.
 * All rights reserved.
 *
 * See below for the original unix_chkpwd copyright notice.
 *
 * Copyright (c) Andrew G. Morgan, 1996. All rights reserved
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, and the entire permission notice in its entirety,
 *    including the disclaimer of warranties.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.
 *
 * ALTERNATIVELY, this product may be distributed under the terms of
 * the GNU Public License, in which case the provisions of the GPL are
 * required INSTEAD OF the above restrictions.  (This clause is
 * necessary due to a potential bad interaction between the GPL and
 * the restrictions contained in a BSD-style copyright.)
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */