ssh-keysign.c revision 295367 
1/* $OpenBSD: ssh-keysign.c,v 1.49 2015/07/03 03:56:25 djm Exp $ */
2/*
3 * Copyright (c) 2002 Markus Friedl.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#include "includes.h"
27
28#include <fcntl.h>
29#ifdef HAVE_PATHS_H
30#include <paths.h>
31#endif
32#include <pwd.h>
33#include <stdarg.h>
34#include <stdlib.h>
35#include <string.h>
36#include <unistd.h>
37
38#ifdef WITH_OPENSSL
39#include <openssl/evp.h>
40#include <openssl/rand.h>
41#include <openssl/rsa.h>
42#endif
43
44#include "xmalloc.h"
45#include "log.h"
46#include "sshkey.h"
47#include "ssh.h"
48#include "ssh2.h"
49#include "misc.h"
50#include "sshbuf.h"
51#include "authfile.h"
52#include "msg.h"
53#include "canohost.h"
54#include "pathnames.h"
55#include "readconf.h"
56#include "uidswap.h"
57#include "sshkey.h"
58#include "ssherr.h"
59
60struct ssh *active_state = NULL; /* XXX needed for linking */
61
62/* XXX readconf.c needs these */
63uid_t original_real_uid;
64
65extern char *__progname;
66
67static int
68valid_request(struct passwd *pw, char *host, struct sshkey **ret,
69    u_char *data, size_t datalen)
70{
71	struct sshbuf *b;
72	struct sshkey *key = NULL;
73	u_char type, *pkblob;
74	char *p;
75	size_t blen, len;
76	char *pkalg, *luser;
77	int r, pktype, fail;
78
79	if (ret != NULL)
80		*ret = NULL;
81	fail = 0;
82
83	if ((b = sshbuf_from(data, datalen)) == NULL)
84		fatal("%s: sshbuf_from failed", __func__);
85
86	/* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
87	if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
88		fatal("%s: buffer error: %s", __func__, ssh_err(r));
89	if (len != 20 && len != 32)
90		fail++;
91
92	if ((r = sshbuf_get_u8(b, &type)) != 0)
93		fatal("%s: buffer error: %s", __func__, ssh_err(r));
94	if (type != SSH2_MSG_USERAUTH_REQUEST)
95		fail++;
96
97	/* server user */
98	if ((r = sshbuf_skip_string(b)) != 0)
99		fatal("%s: buffer error: %s", __func__, ssh_err(r));
100
101	/* service */
102	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
103		fatal("%s: buffer error: %s", __func__, ssh_err(r));
104	if (strcmp("ssh-connection", p) != 0)
105		fail++;
106	free(p);
107
108	/* method */
109	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
110		fatal("%s: buffer error: %s", __func__, ssh_err(r));
111	if (strcmp("hostbased", p) != 0)
112		fail++;
113	free(p);
114
115	/* pubkey */
116	if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
117	    (r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
118		fatal("%s: buffer error: %s", __func__, ssh_err(r));
119
120	pktype = sshkey_type_from_name(pkalg);
121	if (pktype == KEY_UNSPEC)
122		fail++;
123	else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
124		error("%s: bad key blob: %s", __func__, ssh_err(r));
125		fail++;
126	} else if (key->type != pktype)
127		fail++;
128	free(pkalg);
129	free(pkblob);
130
131	/* client host name, handle trailing dot */
132	if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
133		fatal("%s: buffer error: %s", __func__, ssh_err(r));
134	debug2("%s: check expect chost %s got %s", __func__, host, p);
135	if (strlen(host) != len - 1)
136		fail++;
137	else if (p[len - 1] != '.')
138		fail++;
139	else if (strncasecmp(host, p, len - 1) != 0)
140		fail++;
141	free(p);
142
143	/* local user */
144	if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
145		fatal("%s: buffer error: %s", __func__, ssh_err(r));
146
147	if (strcmp(pw->pw_name, luser) != 0)
148		fail++;
149	free(luser);
150
151	/* end of message */
152	if (sshbuf_len(b) != 0)
153		fail++;
154	sshbuf_free(b);
155
156	debug3("%s: fail %d", __func__, fail);
157
158	if (fail && key != NULL)
159		sshkey_free(key);
160	else if (ret != NULL)
161		*ret = key;
162
163	return (fail ? -1 : 0);
164}
165
166int
167main(int argc, char **argv)
168{
169	struct sshbuf *b;
170	Options options;
171#define NUM_KEYTYPES 4
172	struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
173	struct passwd *pw;
174	int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
175	u_char *signature, *data, rver;
176	char *host, *fp;
177	size_t slen, dlen;
178#ifdef WITH_OPENSSL
179	u_int32_t rnd[256];
180#endif
181
182	/* Ensure that stdin and stdout are connected */
183	if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
184		exit(1);
185	/* Leave /dev/null fd iff it is attached to stderr */
186	if (fd > 2)
187		close(fd);
188
189	i = 0;
190	/* XXX This really needs to read sshd_config for the paths */
191	key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
192	key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
193	key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
194	key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
195
196	original_real_uid = getuid();	/* XXX readconf.c needs this */
197	if ((pw = getpwuid(original_real_uid)) == NULL)
198		fatal("getpwuid failed");
199	pw = pwcopy(pw);
200
201	permanently_set_uid(pw);
202
203	seed_rng();
204
205#ifdef DEBUG_SSH_KEYSIGN
206	log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
207#endif
208
209	/* verify that ssh-keysign is enabled by the admin */
210	initialize_options(&options);
211	(void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", &options, 0);
212	fill_default_options(&options);
213	if (options.enable_ssh_keysign != 1)
214		fatal("ssh-keysign not enabled in %s",
215		    _PATH_HOST_CONFIG_FILE);
216
217	for (i = found = 0; i < NUM_KEYTYPES; i++) {
218		if (key_fd[i] != -1)
219			found = 1;
220	}
221	if (found == 0)
222		fatal("could not open any host key");
223
224#ifdef WITH_OPENSSL
225	OpenSSL_add_all_algorithms();
226	arc4random_buf(rnd, sizeof(rnd));
227	RAND_seed(rnd, sizeof(rnd));
228#endif
229
230	found = 0;
231	for (i = 0; i < NUM_KEYTYPES; i++) {
232		keys[i] = NULL;
233		if (key_fd[i] == -1)
234			continue;
235		r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
236		    NULL, &key, NULL);
237		close(key_fd[i]);
238		if (r != 0)
239			debug("parse key %d: %s", i, ssh_err(r));
240		else if (key != NULL) {
241			keys[i] = key;
242			found = 1;
243		}
244	}
245	if (!found)
246		fatal("no hostkey found");
247
248	if ((b = sshbuf_new()) == NULL)
249		fatal("%s: sshbuf_new failed", __func__);
250	if (ssh_msg_recv(STDIN_FILENO, b) < 0)
251		fatal("ssh_msg_recv failed");
252	if ((r = sshbuf_get_u8(b, &rver)) != 0)
253		fatal("%s: buffer error: %s", __func__, ssh_err(r));
254	if (rver != version)
255		fatal("bad version: received %d, expected %d", rver, version);
256	if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
257		fatal("%s: buffer error: %s", __func__, ssh_err(r));
258	if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
259		fatal("bad fd");
260	if ((host = get_local_name(fd)) == NULL)
261		fatal("cannot get local name for fd");
262
263	if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
264		fatal("%s: buffer error: %s", __func__, ssh_err(r));
265	if (valid_request(pw, host, &key, data, dlen) < 0)
266		fatal("not a valid request");
267	free(host);
268
269	found = 0;
270	for (i = 0; i < NUM_KEYTYPES; i++) {
271		if (keys[i] != NULL &&
272		    sshkey_equal_public(key, keys[i])) {
273			found = 1;
274			break;
275		}
276	}
277	if (!found) {
278		if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
279		    SSH_FP_DEFAULT)) == NULL)
280			fatal("%s: sshkey_fingerprint failed", __func__);
281		fatal("no matching hostkey found for key %s %s",
282		    sshkey_type(key), fp ? fp : "");
283	}
284
285	if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, 0)) != 0)
286		fatal("sshkey_sign failed: %s", ssh_err(r));
287	free(data);
288
289	/* send reply */
290	sshbuf_reset(b);
291	if ((r = sshbuf_put_string(b, signature, slen)) != 0)
292		fatal("%s: buffer error: %s", __func__, ssh_err(r));
293	if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
294		fatal("ssh_msg_send failed");
295
296	return (0);
297}
298