1/* $OpenBSD: ssh-keysign.c,v 1.74 2024/04/30 05:53:03 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 <sys/types.h>
27
28#ifdef WITH_OPENSSL
29#include <openssl/evp.h>
30#endif
31
32#include <fcntl.h>
33#include <paths.h>
34#include <pwd.h>
35#include <stdarg.h>
36#include <stdio.h>
37#include <stdlib.h>
38#include <string.h>
39#include <unistd.h>
40#include <errno.h>
41
42#include "xmalloc.h"
43#include "log.h"
44#include "sshkey.h"
45#include "ssh.h"
46#include "ssh2.h"
47#include "misc.h"
48#include "sshbuf.h"
49#include "authfile.h"
50#include "msg.h"
51#include "canohost.h"
52#include "pathnames.h"
53#include "readconf.h"
54#include "uidswap.h"
55#include "ssherr.h"
56
57extern char *__progname;
58
59static int
60valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp,
61    u_char *data, size_t datalen)
62{
63	struct sshbuf *b;
64	struct sshkey *key = NULL;
65	u_char type, *pkblob;
66	char *p;
67	size_t blen, len;
68	char *pkalg, *luser;
69	int r, pktype, fail;
70
71	if (ret != NULL)
72		*ret = NULL;
73	if (pkalgp != NULL)
74		*pkalgp = NULL;
75	fail = 0;
76
77	if ((b = sshbuf_from(data, datalen)) == NULL)
78		fatal_f("sshbuf_from failed");
79
80	/* session id */
81	if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
82		fatal_fr(r, "parse session ID");
83	if (len != 20 && /* SHA1 */
84	    len != 32 && /* SHA256 */
85	    len != 48 && /* SHA384 */
86	    len != 64)   /* SHA512 */
87		fail++;
88
89	if ((r = sshbuf_get_u8(b, &type)) != 0)
90		fatal_fr(r, "parse type");
91	if (type != SSH2_MSG_USERAUTH_REQUEST)
92		fail++;
93
94	/* server user */
95	if ((r = sshbuf_skip_string(b)) != 0)
96		fatal_fr(r, "parse user");
97
98	/* service */
99	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
100		fatal_fr(r, "parse service");
101	if (strcmp("ssh-connection", p) != 0)
102		fail++;
103	free(p);
104
105	/* method */
106	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
107		fatal_fr(r, "parse method");
108	if (strcmp("hostbased", p) != 0)
109		fail++;
110	free(p);
111
112	/* pubkey */
113	if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
114	    (r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
115		fatal_fr(r, "parse pk");
116
117	pktype = sshkey_type_from_name(pkalg);
118	if (pktype == KEY_UNSPEC)
119		fail++;
120	else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
121		error_fr(r, "decode key");
122		fail++;
123	} else if (key->type != pktype)
124		fail++;
125
126	/* client host name, handle trailing dot */
127	if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
128		fatal_fr(r, "parse hostname");
129	debug2_f("check expect chost %s got %s", host, p);
130	if (strlen(host) != len - 1)
131		fail++;
132	else if (p[len - 1] != '.')
133		fail++;
134	else if (strncasecmp(host, p, len - 1) != 0)
135		fail++;
136	free(p);
137
138	/* local user */
139	if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
140		fatal_fr(r, "parse luser");
141
142	if (strcmp(pw->pw_name, luser) != 0)
143		fail++;
144	free(luser);
145
146	/* end of message */
147	if (sshbuf_len(b) != 0)
148		fail++;
149	sshbuf_free(b);
150
151	debug3_f("fail %d", fail);
152
153	if (!fail) {
154		if (ret != NULL) {
155			*ret = key;
156			key = NULL;
157		}
158		if (pkalgp != NULL) {
159			*pkalgp = pkalg;
160			pkalg = NULL;
161		}
162	}
163	sshkey_free(key);
164	free(pkalg);
165	free(pkblob);
166
167	return (fail ? -1 : 0);
168}
169
170int
171main(int argc, char **argv)
172{
173	struct sshbuf *b;
174	Options options;
175#define NUM_KEYTYPES 5
176	struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
177	struct passwd *pw;
178	int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
179	u_char *signature, *data, rver;
180	char *host, *fp, *pkalg;
181	size_t slen, dlen;
182
183	if (pledge("stdio rpath getpw dns id", NULL) != 0)
184		fatal("%s: pledge: %s", __progname, strerror(errno));
185
186	/* Ensure that stdin and stdout are connected */
187	if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
188		exit(1);
189	/* Leave /dev/null fd iff it is attached to stderr */
190	if (fd > 2)
191		close(fd);
192
193	for (i = 0; i < NUM_KEYTYPES; i++)
194		key_fd[i] = -1;
195
196	i = 0;
197	/* XXX This really needs to read sshd_config for the paths */
198#ifdef WITH_DSA
199	key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
200#endif
201	key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
202	key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
203	key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY);
204	key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
205
206	if ((pw = getpwuid(getuid())) == NULL)
207		fatal("getpwuid failed");
208	pw = pwcopy(pw);
209
210	permanently_set_uid(pw);
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, "", "",
219	    &options, 0, NULL);
220	(void)fill_default_options(&options);
221	if (options.enable_ssh_keysign != 1)
222		fatal("ssh-keysign not enabled in %s",
223		    _PATH_HOST_CONFIG_FILE);
224
225	if (pledge("stdio dns", NULL) != 0)
226		fatal("%s: pledge: %s", __progname, strerror(errno));
227
228	for (i = found = 0; i < NUM_KEYTYPES; i++) {
229		if (key_fd[i] != -1)
230			found = 1;
231	}
232	if (found == 0)
233		fatal("could not open any host key");
234
235#ifdef WITH_OPENSSL
236	OpenSSL_add_all_algorithms();
237#endif
238
239	found = 0;
240	for (i = 0; i < NUM_KEYTYPES; i++) {
241		keys[i] = NULL;
242		if (key_fd[i] == -1)
243			continue;
244		r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
245		    NULL, &key, NULL);
246		close(key_fd[i]);
247		if (r != 0)
248			debug_r(r, "parse key %d", i);
249		else if (key != NULL) {
250			keys[i] = key;
251			found = 1;
252		}
253	}
254	if (!found)
255		fatal("no hostkey found");
256
257	if ((b = sshbuf_new()) == NULL)
258		fatal("%s: sshbuf_new failed", __progname);
259	if (ssh_msg_recv(STDIN_FILENO, b) < 0)
260		fatal("%s: ssh_msg_recv failed", __progname);
261	if ((r = sshbuf_get_u8(b, &rver)) != 0)
262		fatal_r(r, "%s: buffer error", __progname);
263	if (rver != version)
264		fatal("%s: bad version: received %d, expected %d",
265		    __progname, rver, version);
266	if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
267		fatal_r(r, "%s: buffer error", __progname);
268	if (fd <= STDERR_FILENO)
269		fatal("%s: bad fd = %d", __progname, fd);
270	if ((host = get_local_name(fd)) == NULL)
271		fatal("%s: cannot get local name for fd", __progname);
272
273	if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
274		fatal_r(r, "%s: buffer error", __progname);
275	if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0)
276		fatal("%s: not a valid request", __progname);
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("%s: no matching hostkey found for key %s %s", __progname,
292		    sshkey_type(key), fp ? fp : "");
293	}
294
295	if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen,
296	    pkalg, NULL, NULL, 0)) != 0)
297		fatal_r(r, "%s: sshkey_sign failed", __progname);
298	free(data);
299
300	/* send reply */
301	sshbuf_reset(b);
302	if ((r = sshbuf_put_string(b, signature, slen)) != 0)
303		fatal_r(r, "%s: buffer error", __progname);
304	if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
305		fatal("%s: ssh_msg_send failed", __progname);
306
307	return (0);
308}
309