1 /* $OpenBSD: ssh-keysign.c,v 1.80 2026/03/19 02:36:28 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 #include <paths.h>
30 #include <pwd.h>
31 #include <stdarg.h>
32 #include <stdio.h>
33 #include <stdlib.h>
34 #include <string.h>
35 #include <unistd.h>
36 #include <errno.h>
37
38 #ifdef WITH_OPENSSL
39 #include <openssl/evp.h>
40 #include <openssl/rand.h>
41 #include <openssl/rsa.h>
42 #include "openbsd-compat/openssl-compat.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 "ssherr.h"
59
60 extern char *__progname;
61
62 static int
valid_request(struct passwd * pw,char * host,struct sshkey ** ret,char ** pkalgp,u_char * data,size_t datalen)63 valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp,
64 u_char *data, size_t datalen)
65 {
66 struct sshbuf *b;
67 struct sshkey *key = NULL;
68 u_char type, *pkblob;
69 char *p;
70 size_t blen, len;
71 char *pkalg, *luser;
72 int r, pktype, fail;
73
74 if (ret != NULL)
75 *ret = NULL;
76 if (pkalgp != NULL)
77 *pkalgp = NULL;
78 fail = 0;
79
80 if ((b = sshbuf_from(data, datalen)) == NULL)
81 fatal_f("sshbuf_from failed");
82
83 /* session id */
84 if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
85 fatal_fr(r, "parse session ID");
86 if (len != 20 && /* SHA1 */
87 len != 32 && /* SHA256 */
88 len != 48 && /* SHA384 */
89 len != 64) /* SHA512 */
90 fail++;
91
92 if ((r = sshbuf_get_u8(b, &type)) != 0)
93 fatal_fr(r, "parse type");
94 if (type != SSH2_MSG_USERAUTH_REQUEST)
95 fail++;
96
97 /* server user */
98 if ((r = sshbuf_skip_string(b)) != 0)
99 fatal_fr(r, "parse user");
100
101 /* service */
102 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
103 fatal_fr(r, "parse service");
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_fr(r, "parse method");
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_fr(r, "parse pk");
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_fr(r, "decode key");
125 fail++;
126 } else if (key->type != pktype)
127 fail++;
128
129 /* client host name, handle trailing dot */
130 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
131 fatal_fr(r, "parse hostname");
132 debug2_f("check expect chost \"%s\" got \"%s\"", host, p);
133 if (len == 0)
134 fail++;
135 else 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
175 int
main(int argc,char ** argv)176 main(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 /* Ensure that stdin and stdout are connected */
189 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
190 exit(1);
191 /* Leave /dev/null fd iff it is attached to stderr */
192 if (fd > 2)
193 close(fd);
194
195 if (pledge("stdio rpath getpw dns id", NULL) != 0)
196 fatal("%s: pledge: %s", __progname, strerror(errno));
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 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
204 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
205 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
206
207 if ((pw = getpwuid(getuid())) == NULL)
208 fatal("getpwuid failed");
209 pw = pwcopy(pw);
210
211 permanently_set_uid(pw);
212
213 seed_rng();
214
215 #ifdef DEBUG_SSH_KEYSIGN
216 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
217 #endif
218
219 /* verify that ssh-keysign is enabled by the admin */
220 initialize_options(&options);
221 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", "",
222 &options, 0, NULL);
223 (void)fill_default_options(&options);
224 if (options.enable_ssh_keysign != 1)
225 fatal("ssh-keysign not enabled in %s",
226 _PATH_HOST_CONFIG_FILE);
227
228 if (pledge("stdio dns", NULL) != 0)
229 fatal("%s: pledge: %s", __progname, strerror(errno));
230
231 for (i = found = 0; i < NUM_KEYTYPES; i++) {
232 if (key_fd[i] != -1)
233 found = 1;
234 }
235 if (found == 0)
236 fatal("could not open any host key");
237
238 found = 0;
239 for (i = 0; i < NUM_KEYTYPES; i++) {
240 keys[i] = NULL;
241 if (key_fd[i] == -1)
242 continue;
243 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
244 NULL, &key, NULL);
245 close(key_fd[i]);
246 if (r != 0)
247 debug_r(r, "parse key %d", i);
248 else if (key != NULL) {
249 keys[i] = key;
250 found = 1;
251 }
252 }
253 if (!found)
254 fatal("no hostkey found");
255
256 if ((b = sshbuf_new()) == NULL)
257 fatal("%s: sshbuf_new failed", __progname);
258 if (ssh_msg_recv(STDIN_FILENO, b) < 0)
259 fatal("%s: ssh_msg_recv failed", __progname);
260 if ((r = sshbuf_get_u8(b, &rver)) != 0)
261 fatal_r(r, "%s: buffer error", __progname);
262 if (rver != version)
263 fatal("%s: bad version: received %d, expected %d",
264 __progname, rver, version);
265 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
266 fatal_r(r, "%s: buffer error", __progname);
267 if (fd <= STDERR_FILENO)
268 fatal("%s: bad fd = %d", __progname, fd);
269 if ((host = get_local_name(fd)) == NULL)
270 fatal("%s: cannot get local name for fd", __progname);
271
272 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
273 fatal_r(r, "%s: buffer error", __progname);
274 if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0)
275 fatal("%s: not a valid request", __progname);
276 free(host);
277
278 found = 0;
279 for (i = 0; i < NUM_KEYTYPES; i++) {
280 if (keys[i] != NULL &&
281 sshkey_equal_public(key, keys[i])) {
282 found = 1;
283 break;
284 }
285 }
286 if (!found) {
287 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
288 SSH_FP_DEFAULT)) == NULL)
289 fatal("%s: sshkey_fingerprint failed", __progname);
290 fatal("%s: no matching hostkey found for key %s %s", __progname,
291 sshkey_type(key), fp ? fp : "");
292 }
293
294 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen,
295 pkalg, NULL, NULL, 0)) != 0)
296 fatal_r(r, "%s: sshkey_sign failed", __progname);
297 free(data);
298
299 /* send reply */
300 sshbuf_reset(b);
301 if ((r = sshbuf_put_string(b, signature, slen)) != 0)
302 fatal_r(r, "%s: buffer error", __progname);
303 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
304 fatal("%s: ssh_msg_send failed", __progname);
305
306 return (0);
307 }
308