1/* $OpenBSD: ssh-keysign.c,v 1.73 2024/01/11 01:51:16 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 <stdio.h>
35#include <stdlib.h>
36#include <string.h>
37#include <unistd.h>
38#include <errno.h>
39
40#ifdef WITH_OPENSSL
41#include <openssl/evp.h>
42#include <openssl/rand.h>
43#include <openssl/rsa.h>
44#include "openbsd-compat/openssl-compat.h"
45#endif
46
47#include "xmalloc.h"
48#include "log.h"
49#include "sshkey.h"
50#include "ssh.h"
51#include "ssh2.h"
52#include "misc.h"
53#include "sshbuf.h"
54#include "authfile.h"
55#include "msg.h"
56#include "canohost.h"
57#include "pathnames.h"
58#include "readconf.h"
59#include "uidswap.h"
60#include "ssherr.h"
61
62extern char *__progname;
63
64static int
65valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp,
66    u_char *data, size_t datalen)
67{
68	struct sshbuf *b;
69	struct sshkey *key = NULL;
70	u_char type, *pkblob;
71	char *p;
72	size_t blen, len;
73	char *pkalg, *luser;
74	int r, pktype, fail;
75
76	if (ret != NULL)
77		*ret = NULL;
78	if (pkalgp != NULL)
79		*pkalgp = NULL;
80	fail = 0;
81
82	if ((b = sshbuf_from(data, datalen)) == NULL)
83		fatal_f("sshbuf_from failed");
84
85	/* session id */
86	if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
87		fatal_fr(r, "parse session ID");
88	if (len != 20 && /* SHA1 */
89	    len != 32 && /* SHA256 */
90	    len != 48 && /* SHA384 */
91	    len != 64)   /* SHA512 */
92		fail++;
93
94	if ((r = sshbuf_get_u8(b, &type)) != 0)
95		fatal_fr(r, "parse type");
96	if (type != SSH2_MSG_USERAUTH_REQUEST)
97		fail++;
98
99	/* server user */
100	if ((r = sshbuf_skip_string(b)) != 0)
101		fatal_fr(r, "parse user");
102
103	/* service */
104	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
105		fatal_fr(r, "parse service");
106	if (strcmp("ssh-connection", p) != 0)
107		fail++;
108	free(p);
109
110	/* method */
111	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
112		fatal_fr(r, "parse method");
113	if (strcmp("hostbased", p) != 0)
114		fail++;
115	free(p);
116
117	/* pubkey */
118	if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
119	    (r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
120		fatal_fr(r, "parse pk");
121
122	pktype = sshkey_type_from_name(pkalg);
123	if (pktype == KEY_UNSPEC)
124		fail++;
125	else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
126		error_fr(r, "decode key");
127		fail++;
128	} else if (key->type != pktype)
129		fail++;
130
131	/* client host name, handle trailing dot */
132	if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
133		fatal_fr(r, "parse hostname");
134	debug2_f("check expect chost %s got %s", 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_fr(r, "parse luser");
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_f("fail %d", fail);
157
158	if (!fail) {
159		if (ret != NULL) {
160			*ret = key;
161			key = NULL;
162		}
163		if (pkalgp != NULL) {
164			*pkalgp = pkalg;
165			pkalg = NULL;
166		}
167	}
168	sshkey_free(key);
169	free(pkalg);
170	free(pkblob);
171
172	return (fail ? -1 : 0);
173}
174
175int
176main(int argc, char **argv)
177{
178	struct sshbuf *b;
179	Options options;
180#define NUM_KEYTYPES 5
181	struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
182	struct passwd *pw;
183	int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
184	u_char *signature, *data, rver;
185	char *host, *fp, *pkalg;
186	size_t slen, dlen;
187
188	if (pledge("stdio rpath getpw dns id", NULL) != 0)
189		fatal("%s: pledge: %s", __progname, strerror(errno));
190
191	/* Ensure that stdin and stdout are connected */
192	if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
193		exit(1);
194	/* Leave /dev/null fd iff it is attached to stderr */
195	if (fd > 2)
196		close(fd);
197
198	for (i = 0; i < NUM_KEYTYPES; i++)
199		key_fd[i] = -1;
200
201	i = 0;
202	/* XXX This really needs to read sshd_config for the paths */
203#ifdef WITH_DSA
204	key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
205#endif
206	key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
207	key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
208	key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY);
209	key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
210
211	if ((pw = getpwuid(getuid())) == NULL)
212		fatal("getpwuid failed");
213	pw = pwcopy(pw);
214
215	permanently_set_uid(pw);
216
217	seed_rng();
218
219#ifdef DEBUG_SSH_KEYSIGN
220	log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
221#endif
222
223	/* verify that ssh-keysign is enabled by the admin */
224	initialize_options(&options);
225	(void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "",
226	    &options, 0, NULL);
227	(void)fill_default_options(&options);
228	if (options.enable_ssh_keysign != 1)
229		fatal("ssh-keysign not enabled in %s",
230		    _PATH_HOST_CONFIG_FILE);
231
232	if (pledge("stdio dns", NULL) != 0)
233		fatal("%s: pledge: %s", __progname, strerror(errno));
234
235	for (i = found = 0; i < NUM_KEYTYPES; i++) {
236		if (key_fd[i] != -1)
237			found = 1;
238	}
239	if (found == 0)
240		fatal("could not open any host key");
241
242	found = 0;
243	for (i = 0; i < NUM_KEYTYPES; i++) {
244		keys[i] = NULL;
245		if (key_fd[i] == -1)
246			continue;
247		r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
248		    NULL, &key, NULL);
249		close(key_fd[i]);
250		if (r != 0)
251			debug_r(r, "parse key %d", i);
252		else if (key != NULL) {
253			keys[i] = key;
254			found = 1;
255		}
256	}
257	if (!found)
258		fatal("no hostkey found");
259
260	if ((b = sshbuf_new()) == NULL)
261		fatal("%s: sshbuf_new failed", __progname);
262	if (ssh_msg_recv(STDIN_FILENO, b) < 0)
263		fatal("%s: ssh_msg_recv failed", __progname);
264	if ((r = sshbuf_get_u8(b, &rver)) != 0)
265		fatal_r(r, "%s: buffer error", __progname);
266	if (rver != version)
267		fatal("%s: bad version: received %d, expected %d",
268		    __progname, rver, version);
269	if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
270		fatal_r(r, "%s: buffer error", __progname);
271	if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
272		fatal("%s: bad fd = %d", __progname, fd);
273	if ((host = get_local_name(fd)) == NULL)
274		fatal("%s: cannot get local name for fd", __progname);
275
276	if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
277		fatal_r(r, "%s: buffer error", __progname);
278	if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0)
279		fatal("%s: not a valid request", __progname);
280	free(host);
281
282	found = 0;
283	for (i = 0; i < NUM_KEYTYPES; i++) {
284		if (keys[i] != NULL &&
285		    sshkey_equal_public(key, keys[i])) {
286			found = 1;
287			break;
288		}
289	}
290	if (!found) {
291		if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
292		    SSH_FP_DEFAULT)) == NULL)
293			fatal("%s: sshkey_fingerprint failed", __progname);
294		fatal("%s: no matching hostkey found for key %s %s", __progname,
295		    sshkey_type(key), fp ? fp : "");
296	}
297
298	if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen,
299	    pkalg, NULL, NULL, 0)) != 0)
300		fatal_r(r, "%s: sshkey_sign failed", __progname);
301	free(data);
302
303	/* send reply */
304	sshbuf_reset(b);
305	if ((r = sshbuf_put_string(b, signature, slen)) != 0)
306		fatal_r(r, "%s: buffer error", __progname);
307	if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
308		fatal("%s: ssh_msg_send failed", __progname);
309
310	return (0);
311}
312