ssh-keysign.c revision 296853 
1/* $OpenBSD: ssh-keysign.c,v 1.52 2016/02/15 09:47:49 dtucker 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#include <errno.h>
38
39#ifdef WITH_OPENSSL
40#include <openssl/evp.h>
41#include <openssl/rand.h>
42#include <openssl/rsa.h>
43#endif
44
45#include "xmalloc.h"
46#include "log.h"
47#include "sshkey.h"
48#include "ssh.h"
49#include "ssh2.h"
50#include "misc.h"
51#include "sshbuf.h"
52#include "authfile.h"
53#include "msg.h"
54#include "canohost.h"
55#include "pathnames.h"
56#include "readconf.h"
57#include "uidswap.h"
58#include "sshkey.h"
59#include "ssherr.h"
60
61struct ssh *active_state = NULL; /* XXX needed for linking */
62
63extern char *__progname;
64
65/* XXX readconf.c needs these */
66uid_t original_real_uid;
67
68extern char *__progname;
69
70static int
71valid_request(struct passwd *pw, char *host, struct sshkey **ret,
72    u_char *data, size_t datalen)
73{
74	struct sshbuf *b;
75	struct sshkey *key = NULL;
76	u_char type, *pkblob;
77	char *p;
78	size_t blen, len;
79	char *pkalg, *luser;
80	int r, pktype, fail;
81
82	if (ret != NULL)
83		*ret = NULL;
84	fail = 0;
85
86	if ((b = sshbuf_from(data, datalen)) == NULL)
87		fatal("%s: sshbuf_from failed", __func__);
88
89	/* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
90	if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
91		fatal("%s: buffer error: %s", __func__, ssh_err(r));
92	if (len != 20 && len != 32)
93		fail++;
94
95	if ((r = sshbuf_get_u8(b, &type)) != 0)
96		fatal("%s: buffer error: %s", __func__, ssh_err(r));
97	if (type != SSH2_MSG_USERAUTH_REQUEST)
98		fail++;
99
100	/* server user */
101	if ((r = sshbuf_skip_string(b)) != 0)
102		fatal("%s: buffer error: %s", __func__, ssh_err(r));
103
104	/* service */
105	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
106		fatal("%s: buffer error: %s", __func__, ssh_err(r));
107	if (strcmp("ssh-connection", p) != 0)
108		fail++;
109	free(p);
110
111	/* method */
112	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
113		fatal("%s: buffer error: %s", __func__, ssh_err(r));
114	if (strcmp("hostbased", p) != 0)
115		fail++;
116	free(p);
117
118	/* pubkey */
119	if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
120	    (r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
121		fatal("%s: buffer error: %s", __func__, ssh_err(r));
122
123	pktype = sshkey_type_from_name(pkalg);
124	if (pktype == KEY_UNSPEC)
125		fail++;
126	else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
127		error("%s: bad key blob: %s", __func__, ssh_err(r));
128		fail++;
129	} else if (key->type != pktype)
130		fail++;
131	free(pkalg);
132	free(pkblob);
133
134	/* client host name, handle trailing dot */
135	if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
136		fatal("%s: buffer error: %s", __func__, ssh_err(r));
137	debug2("%s: check expect chost %s got %s", __func__, host, p);
138	if (strlen(host) != len - 1)
139		fail++;
140	else if (p[len - 1] != '.')
141		fail++;
142	else if (strncasecmp(host, p, len - 1) != 0)
143		fail++;
144	free(p);
145
146	/* local user */
147	if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
148		fatal("%s: buffer error: %s", __func__, ssh_err(r));
149
150	if (strcmp(pw->pw_name, luser) != 0)
151		fail++;
152	free(luser);
153
154	/* end of message */
155	if (sshbuf_len(b) != 0)
156		fail++;
157	sshbuf_free(b);
158
159	debug3("%s: fail %d", __func__, fail);
160
161	if (fail && key != NULL)
162		sshkey_free(key);
163	else if (ret != NULL)
164		*ret = key;
165
166	return (fail ? -1 : 0);
167}
168
169int
170main(int argc, char **argv)
171{
172	struct sshbuf *b;
173	Options options;
174#define NUM_KEYTYPES 4
175	struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
176	struct passwd *pw;
177	int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
178	u_char *signature, *data, rver;
179	char *host, *fp;
180	size_t slen, dlen;
181#ifdef WITH_OPENSSL
182	u_int32_t rnd[256];
183#endif
184
185	ssh_malloc_init();	/* must be called before any mallocs */
186	if (pledge("stdio rpath getpw dns id", NULL) != 0)
187		fatal("%s: pledge: %s", __progname, strerror(errno));
188
189	/* Ensure that stdin and stdout are connected */
190	if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
191		exit(1);
192	/* Leave /dev/null fd iff it is attached to stderr */
193	if (fd > 2)
194		close(fd);
195
196	i = 0;
197	/* XXX This really needs to read sshd_config for the paths */
198	key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
199	key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
200	key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
201	key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
202
203	original_real_uid = getuid();	/* XXX readconf.c needs this */
204	if ((pw = getpwuid(original_real_uid)) == NULL)
205		fatal("getpwuid failed");
206	pw = pwcopy(pw);
207
208	permanently_set_uid(pw);
209
210	seed_rng();
211
212#ifdef DEBUG_SSH_KEYSIGN
213	log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
214#endif
215
216	/* verify that ssh-keysign is enabled by the admin */
217	initialize_options(&options);
218	(void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", &options, 0);
219	fill_default_options(&options);
220	if (options.enable_ssh_keysign != 1)
221		fatal("ssh-keysign not enabled in %s",
222		    _PATH_HOST_CONFIG_FILE);
223
224	for (i = found = 0; i < NUM_KEYTYPES; i++) {
225		if (key_fd[i] != -1)
226			found = 1;
227	}
228	if (found == 0)
229		fatal("could not open any host key");
230
231#ifdef WITH_OPENSSL
232	OpenSSL_add_all_algorithms();
233	arc4random_buf(rnd, sizeof(rnd));
234	RAND_seed(rnd, sizeof(rnd));
235#endif
236
237	found = 0;
238	for (i = 0; i < NUM_KEYTYPES; i++) {
239		keys[i] = NULL;
240		if (key_fd[i] == -1)
241			continue;
242		r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
243		    NULL, &key, NULL);
244		close(key_fd[i]);
245		if (r != 0)
246			debug("parse key %d: %s", i, ssh_err(r));
247		else if (key != NULL) {
248			keys[i] = key;
249			found = 1;
250		}
251	}
252	if (!found)
253		fatal("no hostkey found");
254
255	if (pledge("stdio dns", NULL) != 0)
256		fatal("%s: pledge: %s", __progname, strerror(errno));
257
258	if ((b = sshbuf_new()) == NULL)
259		fatal("%s: sshbuf_new failed", __progname);
260	if (ssh_msg_recv(STDIN_FILENO, b) < 0)
261		fatal("ssh_msg_recv failed");
262	if ((r = sshbuf_get_u8(b, &rver)) != 0)
263		fatal("%s: buffer error: %s", __progname, ssh_err(r));
264	if (rver != version)
265		fatal("bad version: received %d, expected %d", rver, version);
266	if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
267		fatal("%s: buffer error: %s", __progname, ssh_err(r));
268	if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
269		fatal("bad fd");
270	if ((host = get_local_name(fd)) == NULL)
271		fatal("cannot get local name for fd");
272
273	if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
274		fatal("%s: buffer error: %s", __progname, ssh_err(r));
275	if (valid_request(pw, host, &key, data, dlen) < 0)
276		fatal("not a valid request");
277	free(host);
278
279	found = 0;
280	for (i = 0; i < NUM_KEYTYPES; i++) {
281		if (keys[i] != NULL &&
282		    sshkey_equal_public(key, keys[i])) {
283			found = 1;
284			break;
285		}
286	}
287	if (!found) {
288		if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
289		    SSH_FP_DEFAULT)) == NULL)
290			fatal("%s: sshkey_fingerprint failed", __progname);
291		fatal("no matching hostkey found for key %s %s",
292		    sshkey_type(key), fp ? fp : "");
293	}
294
295	if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, NULL, 0))
296	    != 0)
297		fatal("sshkey_sign failed: %s", ssh_err(r));
298	free(data);
299
300	/* send reply */
301	sshbuf_reset(b);
302	if ((r = sshbuf_put_string(b, signature, slen)) != 0)
303		fatal("%s: buffer error: %s", __progname, ssh_err(r));
304	if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
305		fatal("ssh_msg_send failed");
306
307	return (0);
308}
309