xref: /netbsd-src/crypto/external/bsd/openssh/dist/ssh-keysign.c (revision 1c7715dda22cf2bd169e2f84953c050393e8fe9c)
1 /*	$NetBSD: ssh-keysign.c,v 1.26 2024/07/08 22:33:44 christos Exp $	*/
2 /* $OpenBSD: ssh-keysign.c,v 1.74 2024/04/30 05:53:03 djm Exp $ */
3 
4 /*
5  * Copyright (c) 2002 Markus Friedl.  All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  *
16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26  */
27 
28 #include "includes.h"
29 __RCSID("$NetBSD: ssh-keysign.c,v 1.26 2024/07/08 22:33:44 christos Exp $");
30 #include <sys/types.h>
31 
32 #ifdef WITH_OPENSSL
33 #include <openssl/evp.h>
34 #endif
35 
36 #include <fcntl.h>
37 #include <paths.h>
38 #include <pwd.h>
39 #include <stdarg.h>
40 #include <stdio.h>
41 #include <stdlib.h>
42 #include <string.h>
43 #include <unistd.h>
44 #include <errno.h>
45 
46 #include "xmalloc.h"
47 #include "log.h"
48 #include "sshkey.h"
49 #include "ssh.h"
50 #include "ssh2.h"
51 #include "misc.h"
52 #include "sshbuf.h"
53 #include "authfile.h"
54 #include "msg.h"
55 #include "canohost.h"
56 #include "pathnames.h"
57 #include "readconf.h"
58 #include "uidswap.h"
59 #include "ssherr.h"
60 
61 extern char *__progname;
62 
63 static int
valid_request(struct passwd * pw,char * host,struct sshkey ** ret,char ** pkalgp,u_char * data,size_t datalen)64 valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp,
65     u_char *data, size_t datalen)
66 {
67 	struct sshbuf *b;
68 	struct sshkey *key = NULL;
69 	u_char type, *pkblob;
70 	char *p;
71 	size_t blen, len;
72 	char *pkalg, *luser;
73 	int r, pktype, fail;
74 
75 	if (ret != NULL)
76 		*ret = NULL;
77 	if (pkalgp != NULL)
78 		*pkalgp = NULL;
79 	fail = 0;
80 
81 	if ((b = sshbuf_from(data, datalen)) == NULL)
82 		fatal_f("sshbuf_from failed");
83 
84 	/* session id */
85 	if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
86 		fatal_fr(r, "parse session ID");
87 	if (len != 20 && /* SHA1 */
88 	    len != 32 && /* SHA256 */
89 	    len != 48 && /* SHA384 */
90 	    len != 64)   /* SHA512 */
91 		fail++;
92 
93 	if ((r = sshbuf_get_u8(b, &type)) != 0)
94 		fatal_fr(r, "parse type");
95 	if (type != SSH2_MSG_USERAUTH_REQUEST)
96 		fail++;
97 
98 	/* server user */
99 	if ((r = sshbuf_skip_string(b)) != 0)
100 		fatal_fr(r, "parse user");
101 
102 	/* service */
103 	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
104 		fatal_fr(r, "parse service");
105 	if (strcmp("ssh-connection", p) != 0)
106 		fail++;
107 	free(p);
108 
109 	/* method */
110 	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
111 		fatal_fr(r, "parse method");
112 	if (strcmp("hostbased", p) != 0)
113 		fail++;
114 	free(p);
115 
116 	/* pubkey */
117 	if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
118 	    (r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
119 		fatal_fr(r, "parse pk");
120 
121 	pktype = sshkey_type_from_name(pkalg);
122 	if (pktype == KEY_UNSPEC)
123 		fail++;
124 	else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
125 		error_fr(r, "decode key");
126 		fail++;
127 	} else if (key->type != pktype)
128 		fail++;
129 
130 	/* client host name, handle trailing dot */
131 	if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
132 		fatal_fr(r, "parse hostname");
133 	debug2_f("check expect chost %s got %s", host, p);
134 	if (strlen(host) != len - 1)
135 		fail++;
136 	else if (p[len - 1] != '.')
137 		fail++;
138 	else if (strncasecmp(host, p, len - 1) != 0)
139 		fail++;
140 	free(p);
141 
142 	/* local user */
143 	if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
144 		fatal_fr(r, "parse luser");
145 
146 	if (strcmp(pw->pw_name, luser) != 0)
147 		fail++;
148 	free(luser);
149 
150 	/* end of message */
151 	if (sshbuf_len(b) != 0)
152 		fail++;
153 	sshbuf_free(b);
154 
155 	debug3_f("fail %d", fail);
156 
157 	if (!fail) {
158 		if (ret != NULL) {
159 			*ret = key;
160 			key = NULL;
161 		}
162 		if (pkalgp != NULL) {
163 			*pkalgp = pkalg;
164 			pkalg = NULL;
165 		}
166 	}
167 	sshkey_free(key);
168 	free(pkalg);
169 	free(pkblob);
170 
171 	return (fail ? -1 : 0);
172 }
173 
174 int
main(int argc,char ** argv)175 main(int argc, char **argv)
176 {
177 	struct sshbuf *b;
178 	Options options;
179 #define NUM_KEYTYPES 5
180 	struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
181 	struct passwd *pw;
182 	int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
183 	u_char *signature, *data, rver;
184 	char *host, *fp, *pkalg;
185 	size_t slen, dlen;
186 
187 #ifdef __OpenBSD__
188 	if (pledge("stdio rpath getpw dns id", NULL) != 0)
189 		fatal("%s: pledge: %s", __progname, strerror(errno));
190 #endif
191 
192 	/* Ensure that stdin and stdout are connected */
193 	if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
194 		exit(1);
195 	/* Leave /dev/null fd iff it is attached to stderr */
196 	if (fd > 2)
197 		close(fd);
198 
199 	for (i = 0; i < NUM_KEYTYPES; i++)
200 		key_fd[i] = -1;
201 
202 	i = 0;
203 	/* XXX This really needs to read sshd_config for the paths */
204 #ifdef WITH_DSA
205 	key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
206 #endif
207 	key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
208 	key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
209 	key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY);
210 	key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
211 
212 	if ((pw = getpwuid(getuid())) == NULL)
213 		fatal("getpwuid failed");
214 	pw = pwcopy(pw);
215 
216 	permanently_set_uid(pw);
217 
218 #ifdef DEBUG_SSH_KEYSIGN
219 	log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
220 #endif
221 
222 	/* verify that ssh-keysign is enabled by the admin */
223 	initialize_options(&options);
224 	(void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "",
225 	    &options, 0, NULL);
226 	(void)fill_default_options(&options);
227 	if (options.enable_ssh_keysign != 1)
228 		fatal("ssh-keysign not enabled in %s",
229 		    _PATH_HOST_CONFIG_FILE);
230 
231 #ifdef __OpenBSD__
232 	if (pledge("stdio dns", NULL) != 0)
233 		fatal("%s: pledge: %s", __progname, strerror(errno));
234 #endif
235 
236 	for (i = found = 0; i < NUM_KEYTYPES; i++) {
237 		if (key_fd[i] != -1)
238 			found = 1;
239 	}
240 	if (found == 0)
241 		fatal("could not open any host key");
242 
243 #ifdef WITH_OPENSSL
244 	OpenSSL_add_all_algorithms();
245 #endif
246 
247 	found = 0;
248 	for (i = 0; i < NUM_KEYTYPES; i++) {
249 		keys[i] = NULL;
250 		if (key_fd[i] == -1)
251 			continue;
252 		r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
253 		    NULL, &key, NULL);
254 		close(key_fd[i]);
255 		if (r != 0)
256 			debug_r(r, "parse key %d", i);
257 		else if (key != NULL) {
258 			keys[i] = key;
259 			found = 1;
260 		}
261 	}
262 	if (!found)
263 		fatal("no hostkey found");
264 
265 	if ((b = sshbuf_new()) == NULL)
266 		fatal("%s: sshbuf_new failed", __progname);
267 	if (ssh_msg_recv(STDIN_FILENO, b) < 0)
268 		fatal("%s: ssh_msg_recv failed", __progname);
269 	if ((r = sshbuf_get_u8(b, &rver)) != 0)
270 		fatal_r(r, "%s: buffer error", __progname);
271 	if (rver != version)
272 		fatal("%s: bad version: received %d, expected %d",
273 		    __progname, rver, version);
274 	if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
275 		fatal_r(r, "%s: buffer error", __progname);
276 	if (fd <= STDERR_FILENO)
277 		fatal("%s: bad fd = %d", __progname, fd);
278 	if ((host = get_local_name(fd)) == NULL)
279 		fatal("%s: cannot get local name for fd", __progname);
280 
281 	if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
282 		fatal_r(r, "%s: buffer error", __progname);
283 	if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0)
284 		fatal("%s: not a valid request", __progname);
285 	free(host);
286 
287 	found = 0;
288 	for (i = 0; i < NUM_KEYTYPES; i++) {
289 		if (keys[i] != NULL &&
290 		    sshkey_equal_public(key, keys[i])) {
291 			found = 1;
292 			break;
293 		}
294 	}
295 	if (!found) {
296 		if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
297 		    SSH_FP_DEFAULT)) == NULL)
298 			fatal("%s: sshkey_fingerprint failed", __progname);
299 		fatal("%s: no matching hostkey found for key %s %s", __progname,
300 		    sshkey_type(key), fp ? fp : "");
301 	}
302 
303 	if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen,
304 	    pkalg, NULL, NULL, 0)) != 0)
305 		fatal_r(r, "%s: sshkey_sign failed", __progname);
306 	free(data);
307 
308 	/* send reply */
309 	sshbuf_reset(b);
310 	if ((r = sshbuf_put_string(b, signature, slen)) != 0)
311 		fatal_r(r, "%s: buffer error", __progname);
312 	if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
313 		fatal("%s: ssh_msg_send failed", __progname);
314 
315 	return (0);
316 }
317