1 /* $OpenBSD: ssh-keysign.c,v 1.55 2018/07/27 05:34:42 dtucker 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 <stdlib.h>
35 #include <string.h>
36 #include <unistd.h>
37 #include <errno.h>
38
39 #ifdef WITH_OPENSSL
40 #include <openssl/evp.h>
41 #include <openssl/rand.h>
42 #include <openssl/rsa.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 "sshkey.h"
59 #include "ssherr.h"
60
61 struct ssh *active_state = NULL; /* XXX needed for linking */
62
63 extern char *__progname;
64
65 static int
valid_request(struct passwd * pw,char * host,struct sshkey ** ret,u_char * data,size_t datalen)66 valid_request(struct passwd *pw, char *host, struct sshkey **ret,
67 u_char *data, size_t datalen)
68 {
69 struct sshbuf *b;
70 struct sshkey *key = NULL;
71 u_char type, *pkblob;
72 char *p;
73 size_t blen, len;
74 char *pkalg, *luser;
75 int r, pktype, fail;
76
77 if (ret != NULL)
78 *ret = NULL;
79 fail = 0;
80
81 if ((b = sshbuf_from(data, datalen)) == NULL)
82 fatal("%s: sshbuf_from failed", __func__);
83
84 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
85 if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
86 fatal("%s: buffer error: %s", __func__, ssh_err(r));
87 if (len != 20 && len != 32)
88 fail++;
89
90 if ((r = sshbuf_get_u8(b, &type)) != 0)
91 fatal("%s: buffer error: %s", __func__, ssh_err(r));
92 if (type != SSH2_MSG_USERAUTH_REQUEST)
93 fail++;
94
95 /* server user */
96 if ((r = sshbuf_skip_string(b)) != 0)
97 fatal("%s: buffer error: %s", __func__, ssh_err(r));
98
99 /* service */
100 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
101 fatal("%s: buffer error: %s", __func__, ssh_err(r));
102 if (strcmp("ssh-connection", p) != 0)
103 fail++;
104 free(p);
105
106 /* method */
107 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
108 fatal("%s: buffer error: %s", __func__, ssh_err(r));
109 if (strcmp("hostbased", p) != 0)
110 fail++;
111 free(p);
112
113 /* pubkey */
114 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
115 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
116 fatal("%s: buffer error: %s", __func__, ssh_err(r));
117
118 pktype = sshkey_type_from_name(pkalg);
119 if (pktype == KEY_UNSPEC)
120 fail++;
121 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
122 error("%s: bad key blob: %s", __func__, ssh_err(r));
123 fail++;
124 } else if (key->type != pktype)
125 fail++;
126 free(pkalg);
127 free(pkblob);
128
129 /* client host name, handle trailing dot */
130 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
131 fatal("%s: buffer error: %s", __func__, ssh_err(r));
132 debug2("%s: check expect chost %s got %s", __func__, host, p);
133 if (strlen(host) != len - 1)
134 fail++;
135 else if (p[len - 1] != '.')
136 fail++;
137 else if (strncasecmp(host, p, len - 1) != 0)
138 fail++;
139 free(p);
140
141 /* local user */
142 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
143 fatal("%s: buffer error: %s", __func__, ssh_err(r));
144
145 if (strcmp(pw->pw_name, luser) != 0)
146 fail++;
147 free(luser);
148
149 /* end of message */
150 if (sshbuf_len(b) != 0)
151 fail++;
152 sshbuf_free(b);
153
154 debug3("%s: fail %d", __func__, fail);
155
156 if (fail)
157 sshkey_free(key);
158 else if (ret != NULL)
159 *ret = key;
160
161 return (fail ? -1 : 0);
162 }
163
164 int
main(int argc,char ** argv)165 main(int argc, char **argv)
166 {
167 struct sshbuf *b;
168 Options options;
169 #define NUM_KEYTYPES 5
170 struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
171 struct passwd *pw;
172 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
173 u_char *signature, *data, rver;
174 char *host, *fp;
175 size_t slen, dlen;
176 #ifdef WITH_OPENSSL
177 u_int32_t rnd[256];
178 #endif
179
180 ssh_malloc_init(); /* must be called before any mallocs */
181 if (pledge("stdio rpath getpw dns id", NULL) != 0)
182 fatal("%s: pledge: %s", __progname, strerror(errno));
183
184 /* Ensure that stdin and stdout are connected */
185 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
186 exit(1);
187 /* Leave /dev/null fd iff it is attached to stderr */
188 if (fd > 2)
189 close(fd);
190
191 i = 0;
192 /* XXX This really needs to read sshd_config for the paths */
193 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
194 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
195 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
196 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY);
197 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
198
199 if ((pw = getpwuid(getuid())) == NULL)
200 fatal("getpwuid failed");
201 pw = pwcopy(pw);
202
203 permanently_set_uid(pw);
204
205 seed_rng();
206
207 #ifdef DEBUG_SSH_KEYSIGN
208 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
209 #endif
210
211 /* verify that ssh-keysign is enabled by the admin */
212 initialize_options(&options);
213 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", &options, 0);
214 fill_default_options(&options);
215 if (options.enable_ssh_keysign != 1)
216 fatal("ssh-keysign not enabled in %s",
217 _PATH_HOST_CONFIG_FILE);
218
219 for (i = found = 0; i < NUM_KEYTYPES; i++) {
220 if (key_fd[i] != -1)
221 found = 1;
222 }
223 if (found == 0)
224 fatal("could not open any host key");
225
226 #ifdef WITH_OPENSSL
227 OpenSSL_add_all_algorithms();
228 arc4random_buf(rnd, sizeof(rnd));
229 RAND_seed(rnd, sizeof(rnd));
230 #endif
231
232 found = 0;
233 for (i = 0; i < NUM_KEYTYPES; i++) {
234 keys[i] = NULL;
235 if (key_fd[i] == -1)
236 continue;
237 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
238 NULL, &key, NULL);
239 close(key_fd[i]);
240 if (r != 0)
241 debug("parse key %d: %s", i, ssh_err(r));
242 else if (key != NULL) {
243 keys[i] = key;
244 found = 1;
245 }
246 }
247 if (!found)
248 fatal("no hostkey found");
249
250 if (pledge("stdio dns", NULL) != 0)
251 fatal("%s: pledge: %s", __progname, strerror(errno));
252
253 if ((b = sshbuf_new()) == NULL)
254 fatal("%s: sshbuf_new failed", __progname);
255 if (ssh_msg_recv(STDIN_FILENO, b) < 0)
256 fatal("ssh_msg_recv failed");
257 if ((r = sshbuf_get_u8(b, &rver)) != 0)
258 fatal("%s: buffer error: %s", __progname, ssh_err(r));
259 if (rver != version)
260 fatal("bad version: received %d, expected %d", rver, version);
261 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
262 fatal("%s: buffer error: %s", __progname, ssh_err(r));
263 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
264 fatal("bad fd");
265 if ((host = get_local_name(fd)) == NULL)
266 fatal("cannot get local name for fd");
267
268 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
269 fatal("%s: buffer error: %s", __progname, ssh_err(r));
270 if (valid_request(pw, host, &key, data, dlen) < 0)
271 fatal("not a valid request");
272 free(host);
273
274 found = 0;
275 for (i = 0; i < NUM_KEYTYPES; i++) {
276 if (keys[i] != NULL &&
277 sshkey_equal_public(key, keys[i])) {
278 found = 1;
279 break;
280 }
281 }
282 if (!found) {
283 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
284 SSH_FP_DEFAULT)) == NULL)
285 fatal("%s: sshkey_fingerprint failed", __progname);
286 fatal("no matching hostkey found for key %s %s",
287 sshkey_type(key), fp ? fp : "");
288 }
289
290 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, NULL, 0))
291 != 0)
292 fatal("sshkey_sign failed: %s", ssh_err(r));
293 free(data);
294
295 /* send reply */
296 sshbuf_reset(b);
297 if ((r = sshbuf_put_string(b, signature, slen)) != 0)
298 fatal("%s: buffer error: %s", __progname, ssh_err(r));
299 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
300 fatal("ssh_msg_send failed");
301
302 return (0);
303 }
304