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
62 extern char *__progname;
63
64 static int
valid_request(struct passwd * pw,char * host,struct sshkey ** ret,char ** pkalgp,u_char * data,size_t datalen)65 valid_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
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 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