1 /* $OpenBSD: ssh-keysign.c,v 1.67 2021/07/05 01:16:46 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 <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,u_char * data,size_t datalen)65 valid_request(struct passwd *pw, char *host, struct sshkey **ret,
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 fail = 0;
79
80 if ((b = sshbuf_from(data, datalen)) == NULL)
81 fatal_f("sshbuf_from failed");
82
83 /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
84 if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
85 fatal_fr(r, "parse session ID");
86 if (len != 20 && len != 32)
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 free(pkalg);
126 free(pkblob);
127
128 /* client host name, handle trailing dot */
129 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
130 fatal_fr(r, "parse hostname");
131 debug2_f("check expect chost %s got %s", host, p);
132 if (strlen(host) != len - 1)
133 fail++;
134 else if (p[len - 1] != '.')
135 fail++;
136 else if (strncasecmp(host, p, len - 1) != 0)
137 fail++;
138 free(p);
139
140 /* local user */
141 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
142 fatal_fr(r, "parse luser");
143
144 if (strcmp(pw->pw_name, luser) != 0)
145 fail++;
146 free(luser);
147
148 /* end of message */
149 if (sshbuf_len(b) != 0)
150 fail++;
151 sshbuf_free(b);
152
153 debug3_f("fail %d", fail);
154
155 if (fail)
156 sshkey_free(key);
157 else if (ret != NULL)
158 *ret = key;
159
160 return (fail ? -1 : 0);
161 }
162
163 int
main(int argc,char ** argv)164 main(int argc, char **argv)
165 {
166 struct sshbuf *b;
167 Options options;
168 #define NUM_KEYTYPES 5
169 struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
170 struct passwd *pw;
171 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
172 u_char *signature, *data, rver;
173 char *host, *fp;
174 size_t slen, dlen;
175
176 if (pledge("stdio rpath getpw dns id", NULL) != 0)
177 fatal("%s: pledge: %s", __progname, strerror(errno));
178
179 /* Ensure that stdin and stdout are connected */
180 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
181 exit(1);
182 /* Leave /dev/null fd iff it is attached to stderr */
183 if (fd > 2)
184 close(fd);
185
186 i = 0;
187 /* XXX This really needs to read sshd_config for the paths */
188 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
189 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
190 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
191 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY);
192 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
193
194 if ((pw = getpwuid(getuid())) == NULL)
195 fatal("getpwuid failed");
196 pw = pwcopy(pw);
197
198 permanently_set_uid(pw);
199
200 seed_rng();
201
202 #ifdef DEBUG_SSH_KEYSIGN
203 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
204 #endif
205
206 /* verify that ssh-keysign is enabled by the admin */
207 initialize_options(&options);
208 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "",
209 &options, 0, NULL);
210 (void)fill_default_options(&options);
211 if (options.enable_ssh_keysign != 1)
212 fatal("ssh-keysign not enabled in %s",
213 _PATH_HOST_CONFIG_FILE);
214
215 for (i = found = 0; i < NUM_KEYTYPES; i++) {
216 if (key_fd[i] != -1)
217 found = 1;
218 }
219 if (found == 0)
220 fatal("could not open any host key");
221
222 found = 0;
223 for (i = 0; i < NUM_KEYTYPES; i++) {
224 keys[i] = NULL;
225 if (key_fd[i] == -1)
226 continue;
227 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
228 NULL, &key, NULL);
229 close(key_fd[i]);
230 if (r != 0)
231 debug_r(r, "parse key %d", i);
232 else if (key != NULL) {
233 keys[i] = key;
234 found = 1;
235 }
236 }
237 if (!found)
238 fatal("no hostkey found");
239
240 if (pledge("stdio dns", NULL) != 0)
241 fatal("%s: pledge: %s", __progname, strerror(errno));
242
243 if ((b = sshbuf_new()) == NULL)
244 fatal("%s: sshbuf_new failed", __progname);
245 if (ssh_msg_recv(STDIN_FILENO, b) < 0)
246 fatal("%s: ssh_msg_recv failed", __progname);
247 if ((r = sshbuf_get_u8(b, &rver)) != 0)
248 fatal_r(r, "%s: buffer error", __progname);
249 if (rver != version)
250 fatal("%s: bad version: received %d, expected %d",
251 __progname, rver, version);
252 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
253 fatal_r(r, "%s: buffer error", __progname);
254 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
255 fatal("%s: bad fd = %d", __progname, fd);
256 if ((host = get_local_name(fd)) == NULL)
257 fatal("%s: cannot get local name for fd", __progname);
258
259 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
260 fatal_r(r, "%s: buffer error", __progname);
261 if (valid_request(pw, host, &key, data, dlen) < 0)
262 fatal("%s: not a valid request", __progname);
263 free(host);
264
265 found = 0;
266 for (i = 0; i < NUM_KEYTYPES; i++) {
267 if (keys[i] != NULL &&
268 sshkey_equal_public(key, keys[i])) {
269 found = 1;
270 break;
271 }
272 }
273 if (!found) {
274 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
275 SSH_FP_DEFAULT)) == NULL)
276 fatal("%s: sshkey_fingerprint failed", __progname);
277 fatal("%s: no matching hostkey found for key %s %s", __progname,
278 sshkey_type(key), fp ? fp : "");
279 }
280
281 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen,
282 NULL, NULL, NULL, 0)) != 0)
283 fatal_r(r, "%s: sshkey_sign failed", __progname);
284 free(data);
285
286 /* send reply */
287 sshbuf_reset(b);
288 if ((r = sshbuf_put_string(b, signature, slen)) != 0)
289 fatal_r(r, "%s: buffer error", __progname);
290 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
291 fatal("%s: ssh_msg_send failed", __progname);
292
293 return (0);
294 }
295