login_skey.c revision 1.24 
1/*	$OpenBSD: login_skey.c,v 1.24 2015/01/16 06:39:50 deraadt Exp $	*/
2
3/*
4 * Copyright (c) 2000, 2001, 2004 Todd C. Miller <Todd.Miller@courtesan.com>
5 *
6 * Permission to use, copy, modify, and distribute this software for any
7 * purpose with or without fee is hereby granted, provided that the above
8 * copyright notice and this permission notice appear in all copies.
9 *
10 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
11 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
12 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
13 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
14 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
15 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
16 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
17 */
18
19#include <sys/socket.h>
20#include <sys/stat.h>
21#include <sys/time.h>
22#include <sys/resource.h>
23
24#include <ctype.h>
25#include <errno.h>
26#include <fcntl.h>
27#include <paths.h>
28#include <pwd.h>
29#include <readpassphrase.h>
30#include <signal.h>
31#include <stdio.h>
32#include <stdlib.h>
33#include <string.h>
34#include <syslog.h>
35#include <unistd.h>
36#include <limits.h>
37
38#include <login_cap.h>
39#include <bsd_auth.h>
40#include <skey.h>
41
42#define	MODE_LOGIN	0
43#define	MODE_CHALLENGE	1
44#define	MODE_RESPONSE	2
45
46void quit(int);
47void send_fd(int);
48void suspend(int);
49
50volatile sig_atomic_t resumed;
51struct skey skey;
52
53int
54main(int argc, char *argv[])
55{
56	FILE *back = NULL;
57	char *user = NULL, *cp, *ep;
58	char challenge[SKEY_MAX_CHALLENGE+17], response[SKEY_MAX_PW_LEN+1];
59	const char *errstr;
60	int ch, fd = -1, haskey = 0, mode = MODE_LOGIN;
61
62	(void)signal(SIGINT, quit);
63	(void)signal(SIGQUIT, quit);
64	(void)signal(SIGALRM, quit);
65	(void)signal(SIGTSTP, suspend);
66	(void)setpriority(PRIO_PROCESS, 0, 0);
67
68	openlog(NULL, LOG_ODELAY, LOG_AUTH);
69
70	while ((ch = getopt(argc, argv, "ds:v:")) != -1) {
71		switch (ch) {
72		case 'd':
73			back = stdout;
74			break;
75		case 's':	/* service */
76			if (strcmp(optarg, "login") == 0)
77				mode = MODE_LOGIN;
78			else if (strcmp(optarg, "challenge") == 0)
79				mode = MODE_CHALLENGE;
80			else if (strcmp(optarg, "response") == 0)
81				mode = MODE_RESPONSE;
82			else {
83				syslog(LOG_ERR, "%s: invalid service", optarg);
84				exit(1);
85			}
86			break;
87		case 'v':
88			if (strncmp(optarg, "fd=", 3) == 0) {
89				fd = strtonum(optarg + 3, 0, INT_MAX, &errstr);
90				if (errstr != NULL) {
91					syslog(LOG_ERR, "fd is %s: %s",
92					    errstr, optarg + 3);
93					fd = -1;
94				}
95			}
96			/* silently ignore unsupported variables */
97			break;
98		default:
99			syslog(LOG_ERR, "usage error");
100			exit(1);
101		}
102	}
103	argc -= optind;
104	argv += optind;
105
106	switch (argc) {
107	case 2:	/* silently ignore class */
108	case 1:
109		user = *argv;
110		break;
111	default:
112		syslog(LOG_ERR, "usage error");
113		exit(1);
114	}
115
116	if (back == NULL && (back = fdopen(3, "r+")) == NULL)  {
117		syslog(LOG_ERR, "reopening back channel: %m");
118		exit(1);
119	}
120
121	/*
122	 * Note: our skeychallenge2() will always fill in the challenge,
123	 *       even if it has to create a fake one.
124	 */
125	switch (mode) {
126	case MODE_LOGIN:
127		haskey = (skeychallenge2(fd, &skey, user, challenge) == 0);
128		strlcat(challenge, "\nS/Key Password:", sizeof(challenge));
129
130		/* time out getting passphrase after 2 minutes to avoid a DoS */
131		if (haskey)
132			alarm(120);
133		resumed = 0;
134		if (!readpassphrase(challenge, response, sizeof(response), 0))
135			exit(1);
136		if (response[0] == '\0')
137			readpassphrase("S/Key Password [echo on]: ",
138			    response, sizeof(response), RPP_ECHO_ON);
139		alarm(0);
140		if (resumed) {
141			/*
142			 * We were suspended by the user.  Our lock is
143			 * no longer valid so we must regain it so
144			 * an attacker cannot do a partial guess of
145			 * an S/Key response already in progress.
146			 */
147			haskey = (skeylookup(&skey, user) == 0);
148		}
149		break;
150
151	case MODE_CHALLENGE:
152		haskey = (skeychallenge2(fd, &skey, user, challenge) == 0);
153		strlcat(challenge, "\nS/Key Password:", sizeof(challenge));
154		fprintf(back, BI_VALUE " challenge %s\n",
155		    auth_mkvalue(challenge));
156		fprintf(back, BI_CHALLENGE "\n");
157		fprintf(back, BI_FDPASS "\n");
158		fflush(back);
159		send_fd(fileno(back));
160		exit(0);
161
162	case MODE_RESPONSE:
163		/* read challenge */
164		mode = -1;
165		cp = challenge;
166		ep = challenge + sizeof(challenge);
167		while (cp < ep && read(fileno(back), cp, 1) == 1) {
168			if (*cp++ == '\0') {
169				mode = MODE_CHALLENGE;
170				break;
171			}
172		}
173		if (mode != MODE_CHALLENGE) {
174			syslog(LOG_ERR,
175			    "protocol error: bad/missing challenge");
176			exit(1);
177		}
178
179		/* read response */
180		cp = response;
181		ep = response + sizeof(response);
182		while (cp < ep && read(fileno(back), cp, 1) == 1) {
183			if (*cp++ == '\0') {
184				mode = MODE_RESPONSE;
185				break;
186			}
187		}
188		if (mode != MODE_RESPONSE) {
189			syslog(LOG_ERR,
190			    "protocol error: bad/missing response");
191			exit(1);
192		}
193
194		/*
195		 * Since the entry is locked we do not need to compare
196		 * the passed in challenge to the S/Key database but
197		 * maybe we should anyway?
198		 */
199		haskey = (skeychallenge2(fd, &skey, user, challenge) == 0);
200		break;
201	}
202
203	/*
204	 * Ignore keyboard interrupt/suspend during database update.
205	 */
206	signal(SIGINT, SIG_IGN);
207	signal(SIGQUIT, SIG_IGN);
208	signal(SIGTSTP, SIG_IGN);
209
210	if (haskey && skeyverify(&skey, response) == 0) {
211		if (mode == MODE_LOGIN) {
212			if (skey.n <= 1)
213				printf("Warning! You MUST change your "
214				    "S/Key password now!\n");
215			else if (skey.n < 5)
216				printf("Warning! Change S/Key password soon\n");
217		}
218		fprintf(back, BI_AUTH "\n");
219		fprintf(back, BI_SECURE "\n");
220		exit(0);
221	}
222	fprintf(back, BI_REJECT "\n");
223	exit(1);
224}
225
226/* ARGSUSED */
227void
228quit(int signo)
229{
230
231	_exit(1);
232}
233
234/* ARGSUSED */
235void
236suspend(int signo)
237{
238	sigset_t nset;
239	int save_errno = errno;
240
241	/*
242	 * Unlock the skey record so we don't sleep holding the lock.
243	 * Unblock SIGTSTP, set it to the default action and then
244	 * resend it so we are suspended properly.
245	 * When we resume, reblock SIGTSTP, reset the signal handler,
246	 * set a flag and restore errno.
247	 */
248	alarm(0);
249	skey_unlock(&skey);
250	(void)signal(signo, SIG_DFL);
251	(void)sigemptyset(&nset);
252	(void)sigaddset(&nset, signo);
253	(void)sigprocmask(SIG_UNBLOCK, &nset, NULL);
254	(void)kill(getpid(), signo);
255	(void)sigprocmask(SIG_BLOCK, &nset, NULL);
256	(void)signal(signo, suspend);
257	resumed = 1;
258	errno = save_errno;
259}
260
261void
262send_fd(int sock)
263{
264	struct msghdr msg;
265	struct cmsghdr *cmp;
266	union {
267		struct cmsghdr hdr;
268		char buf[CMSG_SPACE(sizeof(int))];
269	} cmsgbuf;
270
271	memset(&msg, 0, sizeof(msg));
272	msg.msg_control = &cmsgbuf.buf;
273	msg.msg_controllen = sizeof(cmsgbuf.buf);
274
275	cmp = CMSG_FIRSTHDR(&msg);
276	cmp->cmsg_len = CMSG_LEN(sizeof(int));
277	cmp->cmsg_level = SOL_SOCKET;
278	cmp->cmsg_type = SCM_RIGHTS;
279
280	*(int *)CMSG_DATA(cmp) = fileno(skey.keyfile);
281
282	if (sendmsg(sock, &msg, 0) < 0)
283		syslog(LOG_ERR, "sendmsg: %m");
284}
285