xref: /openbsd-src/usr.bin/ssh/ssh-keysign.c (revision 33b4f39fbeffad07bc3206f173cff9f3c9901cd1)
1 /*
2  * Copyright (c) 2002 Markus Friedl.  All rights reserved.
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
7  * 1. Redistributions of source code must retain the above copyright
8  *    notice, this list of conditions and the following disclaimer.
9  * 2. Redistributions in binary form must reproduce the above copyright
10  *    notice, this list of conditions and the following disclaimer in the
11  *    documentation and/or other materials provided with the distribution.
12  *
13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23  */
24 #include "includes.h"
25 RCSID("$OpenBSD: ssh-keysign.c,v 1.16 2004/04/18 23:10:26 djm Exp $");
26 
27 #include <openssl/evp.h>
28 #include <openssl/rand.h>
29 #include <openssl/rsa.h>
30 
31 #include "log.h"
32 #include "key.h"
33 #include "ssh.h"
34 #include "ssh2.h"
35 #include "misc.h"
36 #include "xmalloc.h"
37 #include "buffer.h"
38 #include "bufaux.h"
39 #include "authfile.h"
40 #include "msg.h"
41 #include "canohost.h"
42 #include "pathnames.h"
43 #include "readconf.h"
44 
45 /* XXX readconf.c needs these */
46 uid_t original_real_uid;
47 
48 static int
49 valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
50     u_int datalen)
51 {
52 	Buffer b;
53 	Key *key = NULL;
54 	u_char *pkblob;
55 	u_int blen, len;
56 	char *pkalg, *p;
57 	int pktype, fail;
58 
59 	fail = 0;
60 
61 	buffer_init(&b);
62 	buffer_append(&b, data, datalen);
63 
64 	/* session id, currently limited to SHA1 (20 bytes) */
65 	p = buffer_get_string(&b, &len);
66 	if (len != 20)
67 		fail++;
68 	xfree(p);
69 
70 	if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
71 		fail++;
72 
73 	/* server user */
74 	buffer_skip_string(&b);
75 
76 	/* service */
77 	p = buffer_get_string(&b, NULL);
78 	if (strcmp("ssh-connection", p) != 0)
79 		fail++;
80 	xfree(p);
81 
82 	/* method */
83 	p = buffer_get_string(&b, NULL);
84 	if (strcmp("hostbased", p) != 0)
85 		fail++;
86 	xfree(p);
87 
88 	/* pubkey */
89 	pkalg = buffer_get_string(&b, NULL);
90 	pkblob = buffer_get_string(&b, &blen);
91 
92 	pktype = key_type_from_name(pkalg);
93 	if (pktype == KEY_UNSPEC)
94 		fail++;
95 	else if ((key = key_from_blob(pkblob, blen)) == NULL)
96 		fail++;
97 	else if (key->type != pktype)
98 		fail++;
99 	xfree(pkalg);
100 	xfree(pkblob);
101 
102 	/* client host name, handle trailing dot */
103 	p = buffer_get_string(&b, &len);
104 	debug2("valid_request: check expect chost %s got %s", host, p);
105 	if (strlen(host) != len - 1)
106 		fail++;
107 	else if (p[len - 1] != '.')
108 		fail++;
109 	else if (strncasecmp(host, p, len - 1) != 0)
110 		fail++;
111 	xfree(p);
112 
113 	/* local user */
114 	p = buffer_get_string(&b, NULL);
115 
116 	if (strcmp(pw->pw_name, p) != 0)
117 		fail++;
118 	xfree(p);
119 
120 	/* end of message */
121 	if (buffer_len(&b) != 0)
122 		fail++;
123 	buffer_free(&b);
124 
125 	debug3("valid_request: fail %d", fail);
126 
127 	if (fail && key != NULL)
128 		key_free(key);
129 	else
130 		*ret = key;
131 
132 	return (fail ? -1 : 0);
133 }
134 
135 int
136 main(int argc, char **argv)
137 {
138 	Buffer b;
139 	Options options;
140 	Key *keys[2], *key;
141 	struct passwd *pw;
142 	int key_fd[2], i, found, version = 2, fd;
143 	u_char *signature, *data;
144 	char *host;
145 	u_int slen, dlen;
146 	u_int32_t rnd[256];
147 
148 	key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
149 	key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
150 
151 	seteuid(getuid());
152 	setuid(getuid());
153 
154 #ifdef DEBUG_SSH_KEYSIGN
155 	log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
156 #endif
157 
158 	/* verify that ssh-keysign is enabled by the admin */
159 	original_real_uid = getuid();	/* XXX readconf.c needs this */
160 	initialize_options(&options);
161 	(void)read_config_file(_PATH_HOST_CONFIG_FILE, "", &options, 0);
162 	fill_default_options(&options);
163 	if (options.enable_ssh_keysign != 1)
164 		fatal("ssh-keysign not enabled in %s",
165 		    _PATH_HOST_CONFIG_FILE);
166 
167 	if (key_fd[0] == -1 && key_fd[1] == -1)
168 		fatal("could not open any host key");
169 
170 	if ((pw = getpwuid(getuid())) == NULL)
171 		fatal("getpwuid failed");
172 	pw = pwcopy(pw);
173 
174 	SSLeay_add_all_algorithms();
175 	for (i = 0; i < 256; i++)
176 		rnd[i] = arc4random();
177 	RAND_seed(rnd, sizeof(rnd));
178 
179 	found = 0;
180 	for (i = 0; i < 2; i++) {
181 		keys[i] = NULL;
182 		if (key_fd[i] == -1)
183 			continue;
184 		keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC,
185 		    NULL, NULL);
186 		close(key_fd[i]);
187 		if (keys[i] != NULL)
188 			found = 1;
189 	}
190 	if (!found)
191 		fatal("no hostkey found");
192 
193 	buffer_init(&b);
194 	if (ssh_msg_recv(STDIN_FILENO, &b) < 0)
195 		fatal("ssh_msg_recv failed");
196 	if (buffer_get_char(&b) != version)
197 		fatal("bad version");
198 	fd = buffer_get_int(&b);
199 	if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO))
200 		fatal("bad fd");
201 	if ((host = get_local_name(fd)) == NULL)
202 		fatal("cannot get sockname for fd");
203 
204 	data = buffer_get_string(&b, &dlen);
205 	if (valid_request(pw, host, &key, data, dlen) < 0)
206 		fatal("not a valid request");
207 	xfree(host);
208 
209 	found = 0;
210 	for (i = 0; i < 2; i++) {
211 		if (keys[i] != NULL &&
212 		    key_equal(key, keys[i])) {
213 			found = 1;
214 			break;
215 		}
216 	}
217 	if (!found)
218 		fatal("no matching hostkey found");
219 
220 	if (key_sign(keys[i], &signature, &slen, data, dlen) != 0)
221 		fatal("key_sign failed");
222 	xfree(data);
223 
224 	/* send reply */
225 	buffer_clear(&b);
226 	buffer_put_string(&b, signature, slen);
227 	if (ssh_msg_send(STDOUT_FILENO, version, &b) == -1)
228 		fatal("ssh_msg_send failed");
229 
230 	return (0);
231 }
232