1/*
2 * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
3 * Use is subject to license terms.
4 */
5/*
6 * Copyright (c) 2002 Markus Friedl.  All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28#include "includes.h"
29RCSID("$OpenBSD: ssh-keysign.c,v 1.7 2002/07/03 14:21:05 markus Exp $");
30
31#pragma ident	"%Z%%M%	%I%	%E% SMI"
32
33#include <unistd.h>
34
35#include <openssl/evp.h>
36#include <openssl/rand.h>
37#include <openssl/rsa.h>
38
39#include "log.h"
40#include "key.h"
41#include "ssh.h"
42#include "ssh2.h"
43#include "misc.h"
44#include "xmalloc.h"
45#include "buffer.h"
46#include "bufaux.h"
47#include "authfile.h"
48#include "msg.h"
49#include "canohost.h"
50#include "pathnames.h"
51#include "readconf.h"
52
53uid_t original_real_uid;	/* XXX readconf.c needs this */
54
55#ifdef HAVE___PROGNAME
56extern char *__progname;
57#else
58#ifndef lint
59char *__progname;
60#endif /* lint */
61#endif
62
63static int
64valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
65    u_int datalen)
66{
67	Buffer b;
68	Key *key;
69	u_char *pkblob;
70	u_int blen, len;
71	char *pkalg, *p;
72	int pktype, fail;
73
74	fail = 0;
75
76	buffer_init(&b);
77	buffer_append(&b, data, datalen);
78
79	/* session id, currently limited to SHA1 (20 bytes) */
80	p = buffer_get_string(&b, &len);
81	if (len != 20)
82		fail++;
83	xfree(p);
84
85	if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
86		fail++;
87
88	/* server user */
89	buffer_skip_string(&b);
90
91	/* service */
92	p = buffer_get_string(&b, NULL);
93	if (strcmp("ssh-connection", p) != 0)
94		fail++;
95	xfree(p);
96
97	/* method */
98	p = buffer_get_string(&b, NULL);
99	if (strcmp("hostbased", p) != 0)
100		fail++;
101	xfree(p);
102
103	/* pubkey */
104	pkalg = buffer_get_string(&b, NULL);
105	pkblob = buffer_get_string(&b, &blen);
106
107	pktype = key_type_from_name(pkalg);
108	if (pktype == KEY_UNSPEC)
109		fail++;
110	else if ((key = key_from_blob(pkblob, blen)) == NULL)
111		fail++;
112	else if (key->type != pktype)
113		fail++;
114	xfree(pkalg);
115	xfree(pkblob);
116
117	/* client host name, handle trailing dot */
118	p = buffer_get_string(&b, &len);
119	debug2("valid_request: check expect chost %s got %s", host, p);
120	if (strlen(host) != len - 1)
121		fail++;
122	else if (p[len - 1] != '.')
123		fail++;
124	else if (strncasecmp(host, p, len - 1) != 0)
125		fail++;
126	xfree(p);
127
128	/* local user */
129	p = buffer_get_string(&b, NULL);
130
131	if (strcmp(pw->pw_name, p) != 0)
132		fail++;
133	xfree(p);
134
135	/* end of message */
136	if (buffer_len(&b) != 0)
137		fail++;
138
139	debug3("valid_request: fail %d", fail);
140
141	if (fail && key != NULL)
142		key_free(key);
143	else
144		*ret = key;
145
146	return (fail ? -1 : 0);
147}
148
149int
150main(int argc, char **argv)
151{
152	Buffer b;
153	Options options;
154	Key *keys[2], *key;
155	struct passwd *pw;
156	int key_fd[2], i, found, version = 2, fd;
157	u_char *signature, *data;
158	char *host;
159	u_int slen, dlen;
160	u_int32_t rnd[256];
161
162	/*
163	 * Since these two open()s are all that's done here before
164	 * dropping privileges with setreuid(), and since having been
165	 * privileged protects ssh-keysign from core dumps and tracing,
166	 * there's no need to use Least Privilege interfaces like
167	 * setppriv(2).
168	 */
169	key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
170	key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
171
172	(void) setreuid(getuid(), getuid());
173
174	(void) g11n_setlocale(LC_ALL, "");
175
176	init_rng();
177	seed_rng();
178	arc4random_stir();
179
180#ifdef DEBUG_SSH_KEYSIGN
181	log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
182#endif
183
184	/* verify that ssh-keysign is enabled by the admin */
185	original_real_uid = getuid();	/* XXX readconf.c needs this */
186	initialize_options(&options);
187	(void)read_config_file(_PATH_HOST_CONFIG_FILE, "", &options);
188	fill_default_options(&options);
189	if (options.hostbased_authentication != 1)
190		fatal("Hostbased authentication not enabled in %s",
191		    _PATH_HOST_CONFIG_FILE);
192
193	if (key_fd[0] == -1 && key_fd[1] == -1)
194		fatal("could not open any host key");
195
196	if ((pw = getpwuid(getuid())) == NULL)
197		fatal("getpwuid failed");
198	pw = pwcopy(pw);
199
200	SSLeay_add_all_algorithms();
201	for (i = 0; i < 256; i++)
202		rnd[i] = arc4random();
203	RAND_seed(rnd, sizeof(rnd));
204
205	found = 0;
206	for (i = 0; i < 2; i++) {
207		keys[i] = NULL;
208		if (key_fd[i] == -1)
209			continue;
210		keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC,
211		    NULL, NULL);
212		(void) close(key_fd[i]);
213		if (keys[i] != NULL && keys[i]->type == KEY_RSA) {
214			if (RSA_blinding_on(keys[i]->rsa, NULL) != 1) {
215				error("RSA_blinding_on failed");
216				key_free(keys[i]);
217				keys[i] = NULL;
218			}
219		}
220		if (keys[i] != NULL)
221			found = 1;
222	}
223	if (!found)
224		fatal("no hostkey found");
225
226	buffer_init(&b);
227	if (ssh_msg_recv(STDIN_FILENO, &b) < 0)
228		fatal("ssh_msg_recv failed");
229	if (buffer_get_char(&b) != version)
230		fatal("bad version");
231	fd = buffer_get_int(&b);
232	if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO))
233		fatal("bad fd");
234	if ((host = get_local_name(fd)) == NULL)
235		fatal("cannot get sockname for fd");
236
237	data = buffer_get_string(&b, &dlen);
238	if (valid_request(pw, host, &key, data, dlen) < 0)
239		fatal("not a valid request");
240	xfree(host);
241
242	found = 0;
243	for (i = 0; i < 2; i++) {
244		if (keys[i] != NULL &&
245		    key_equal(key, keys[i])) {
246			found = 1;
247			break;
248		}
249	}
250	if (!found)
251		fatal("no matching hostkey found");
252
253	if (key_sign(keys[i], &signature, &slen, data, dlen) != 0)
254		fatal("key_sign failed");
255	xfree(data);
256
257	/* send reply */
258	buffer_clear(&b);
259	buffer_put_string(&b, signature, slen);
260	ssh_msg_send(STDOUT_FILENO, version, &b);
261
262	return (0);
263}
264