1 /* $OpenBSD: ssh-keysign.c,v 1.47 2015/01/28 22:36:00 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 <stdlib.h>
35 #include <string.h>
36 #include <unistd.h>
37 
38 #ifdef WITH_OPENSSL
39 #include <openssl/evp.h>
40 #include <openssl/rand.h>
41 #include <openssl/rsa.h>
42 #endif
43 
44 #include "xmalloc.h"
45 #include "log.h"
46 #include "sshkey.h"
47 #include "ssh.h"
48 #include "ssh2.h"
49 #include "misc.h"
50 #include "sshbuf.h"
51 #include "authfile.h"
52 #include "msg.h"
53 #include "canohost.h"
54 #include "pathnames.h"
55 #include "readconf.h"
56 #include "uidswap.h"
57 #include "sshkey.h"
58 #include "ssherr.h"
59 
60 struct ssh *active_state = NULL; /* XXX needed for linking */
61 
62 /* XXX readconf.c needs these */
63 uid_t original_real_uid;
64 
65 extern char *__progname;
66 
67 static int
valid_request(struct passwd * pw,char * host,struct sshkey ** ret,u_char * data,size_t datalen)68 valid_request(struct passwd *pw, char *host, struct sshkey **ret,
69     u_char *data, size_t datalen)
70 {
71 	struct sshbuf *b;
72 	struct sshkey *key = NULL;
73 	u_char type, *pkblob;
74 	char *p;
75 	size_t blen, len;
76 	char *pkalg, *luser;
77 	int r, pktype, fail;
78 
79 	if (ret != NULL)
80 		*ret = NULL;
81 	fail = 0;
82 
83 	if ((b = sshbuf_from(data, datalen)) == NULL)
84 		fatal("%s: sshbuf_from failed", __func__);
85 
86 	/* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
87 	if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
88 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
89 	if (len != 20 && len != 32)
90 		fail++;
91 
92 	if ((r = sshbuf_get_u8(b, &type)) != 0)
93 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
94 	if (type != SSH2_MSG_USERAUTH_REQUEST)
95 		fail++;
96 
97 	/* server user */
98 	if ((r = sshbuf_skip_string(b)) != 0)
99 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
100 
101 	/* service */
102 	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
103 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
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("%s: buffer error: %s", __func__, ssh_err(r));
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("%s: buffer error: %s", __func__, ssh_err(r));
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("%s: bad key blob: %s", __func__, ssh_err(r));
125 		fail++;
126 	} else if (key->type != pktype)
127 		fail++;
128 	free(pkalg);
129 	free(pkblob);
130 
131 	/* client host name, handle trailing dot */
132 	if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
133 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
134 	debug2("%s: check expect chost %s got %s", __func__, 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("%s: buffer error: %s", __func__, ssh_err(r));
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("%s: fail %d", __func__, fail);
157 
158 	if (fail && key != NULL)
159 		sshkey_free(key);
160 	else
161 		*ret = key;
162 
163 	return (fail ? -1 : 0);
164 }
165 
166 int
main(int argc,char ** argv)167 main(int argc, char **argv)
168 {
169 	struct sshbuf *b;
170 	Options options;
171 #define NUM_KEYTYPES 4
172 	struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
173 	struct passwd *pw;
174 	int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
175 	u_char *signature, *data, rver;
176 	char *host, *fp;
177 	size_t slen, dlen;
178 #ifdef WITH_OPENSSL
179 	u_int32_t rnd[256];
180 #endif
181 
182 	/* Ensure that stdin and stdout are connected */
183 	if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
184 		exit(1);
185 	/* Leave /dev/null fd iff it is attached to stderr */
186 	if (fd > 2)
187 		close(fd);
188 
189 	i = 0;
190 	key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
191 	key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
192 	key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
193 	key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
194 
195 	original_real_uid = getuid();	/* XXX readconf.c needs this */
196 	if ((pw = getpwuid(original_real_uid)) == NULL)
197 		fatal("getpwuid failed");
198 	pw = pwcopy(pw);
199 
200 	permanently_set_uid(pw);
201 
202 	seed_rng();
203 
204 #ifdef DEBUG_SSH_KEYSIGN
205 	log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
206 #endif
207 
208 	/* verify that ssh-keysign is enabled by the admin */
209 	initialize_options(&options);
210 	(void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", &options, 0);
211 	fill_default_options(&options);
212 	if (options.enable_ssh_keysign != 1)
213 		fatal("ssh-keysign not enabled in %s",
214 		    _PATH_HOST_CONFIG_FILE);
215 
216 	for (i = found = 0; i < NUM_KEYTYPES; i++) {
217 		if (key_fd[i] != -1)
218 			found = 1;
219 	}
220 	if (found == 0)
221 		fatal("could not open any host key");
222 
223 #ifdef WITH_OPENSSL
224 	OpenSSL_add_all_algorithms();
225 	arc4random_buf(rnd, sizeof(rnd));
226 	RAND_seed(rnd, sizeof(rnd));
227 #endif
228 
229 	found = 0;
230 	for (i = 0; i < NUM_KEYTYPES; i++) {
231 		keys[i] = NULL;
232 		if (key_fd[i] == -1)
233 			continue;
234 		r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
235 		    NULL, &key, NULL);
236 		close(key_fd[i]);
237 		if (r != 0)
238 			debug("parse key %d: %s", i, ssh_err(r));
239 		else if (key != NULL) {
240 			keys[i] = key;
241 			found = 1;
242 		}
243 	}
244 	if (!found)
245 		fatal("no hostkey found");
246 
247 	if ((b = sshbuf_new()) == NULL)
248 		fatal("%s: sshbuf_new failed", __func__);
249 	if (ssh_msg_recv(STDIN_FILENO, b) < 0)
250 		fatal("ssh_msg_recv failed");
251 	if ((r = sshbuf_get_u8(b, &rver)) != 0)
252 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
253 	if (rver != version)
254 		fatal("bad version: received %d, expected %d", rver, version);
255 	if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
256 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
257 	if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
258 		fatal("bad fd");
259 	if ((host = get_local_name(fd)) == NULL)
260 		fatal("cannot get local name for fd");
261 
262 	if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
263 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
264 	if (valid_request(pw, host, &key, data, dlen) < 0)
265 		fatal("not a valid request");
266 	free(host);
267 
268 	found = 0;
269 	for (i = 0; i < NUM_KEYTYPES; i++) {
270 		if (keys[i] != NULL &&
271 		    sshkey_equal_public(key, keys[i])) {
272 			found = 1;
273 			break;
274 		}
275 	}
276 	if (!found) {
277 		if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
278 		    SSH_FP_DEFAULT)) == NULL)
279 			fatal("%s: sshkey_fingerprint failed", __func__);
280 		fatal("no matching hostkey found for key %s %s",
281 		    sshkey_type(key), fp ? fp : "");
282 	}
283 
284 	if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, 0)) != 0)
285 		fatal("sshkey_sign failed: %s", ssh_err(r));
286 	free(data);
287 
288 	/* send reply */
289 	sshbuf_reset(b);
290 	if ((r = sshbuf_put_string(b, signature, slen)) != 0)
291 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
292 	if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
293 		fatal("ssh_msg_send failed");
294 
295 	return (0);
296 }
297