1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
|
/* $OpenBSD: ssh-keysign.c,v 1.26 2006/07/17 01:31:10 stevesk Exp $ */
/*
* Copyright (c) 2002 Markus Friedl. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "includes.h"
#include <sys/types.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/rsa.h>
#include <fcntl.h>
#include <paths.h>
#include <pwd.h>
#include <unistd.h>
#include "log.h"
#include "key.h"
#include "ssh.h"
#include "ssh2.h"
#include "misc.h"
#include "xmalloc.h"
#include "buffer.h"
#include "bufaux.h"
#include "authfile.h"
#include "msg.h"
#include "canohost.h"
#include "pathnames.h"
#include "readconf.h"
#include "uidswap.h"
/* XXX readconf.c needs these */
uid_t original_real_uid;
static int
valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
u_int datalen)
{
Buffer b;
Key *key = NULL;
u_char *pkblob;
u_int blen, len;
char *pkalg, *p;
int pktype, fail;
fail = 0;
buffer_init(&b);
buffer_append(&b, data, datalen);
/* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
p = buffer_get_string(&b, &len);
if (len != 20 && len != 32)
fail++;
xfree(p);
if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
fail++;
/* server user */
buffer_skip_string(&b);
/* service */
p = buffer_get_string(&b, NULL);
if (strcmp("ssh-connection", p) != 0)
fail++;
xfree(p);
/* method */
p = buffer_get_string(&b, NULL);
if (strcmp("hostbased", p) != 0)
fail++;
xfree(p);
/* pubkey */
pkalg = buffer_get_string(&b, NULL);
pkblob = buffer_get_string(&b, &blen);
pktype = key_type_from_name(pkalg);
if (pktype == KEY_UNSPEC)
fail++;
else if ((key = key_from_blob(pkblob, blen)) == NULL)
fail++;
else if (key->type != pktype)
fail++;
xfree(pkalg);
xfree(pkblob);
/* client host name, handle trailing dot */
p = buffer_get_string(&b, &len);
debug2("valid_request: check expect chost %s got %s", host, p);
if (strlen(host) != len - 1)
fail++;
else if (p[len - 1] != '.')
fail++;
else if (strncasecmp(host, p, len - 1) != 0)
fail++;
xfree(p);
/* local user */
p = buffer_get_string(&b, NULL);
if (strcmp(pw->pw_name, p) != 0)
fail++;
xfree(p);
/* end of message */
if (buffer_len(&b) != 0)
fail++;
buffer_free(&b);
debug3("valid_request: fail %d", fail);
if (fail && key != NULL)
key_free(key);
else
*ret = key;
return (fail ? -1 : 0);
}
int
main(int argc, char **argv)
{
Buffer b;
Options options;
Key *keys[2], *key;
struct passwd *pw;
int key_fd[2], i, found, version = 2, fd;
u_char *signature, *data;
char *host;
u_int slen, dlen;
u_int32_t rnd[256];
/* Ensure that stdin and stdout are connected */
if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
exit(1);
/* Leave /dev/null fd iff it is attached to stderr */
if (fd > 2)
close(fd);
key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
original_real_uid = getuid(); /* XXX readconf.c needs this */
if ((pw = getpwuid(original_real_uid)) == NULL)
fatal("getpwuid failed");
pw = pwcopy(pw);
permanently_set_uid(pw);
#ifdef DEBUG_SSH_KEYSIGN
log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
#endif
/* verify that ssh-keysign is enabled by the admin */
initialize_options(&options);
(void)read_config_file(_PATH_HOST_CONFIG_FILE, "", &options, 0);
fill_default_options(&options);
if (options.enable_ssh_keysign != 1)
fatal("ssh-keysign not enabled in %s",
_PATH_HOST_CONFIG_FILE);
if (key_fd[0] == -1 && key_fd[1] == -1)
fatal("could not open any host key");
SSLeay_add_all_algorithms();
for (i = 0; i < 256; i++)
rnd[i] = arc4random();
RAND_seed(rnd, sizeof(rnd));
found = 0;
for (i = 0; i < 2; i++) {
keys[i] = NULL;
if (key_fd[i] == -1)
continue;
keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC,
NULL, NULL);
close(key_fd[i]);
if (keys[i] != NULL)
found = 1;
}
if (!found)
fatal("no hostkey found");
buffer_init(&b);
if (ssh_msg_recv(STDIN_FILENO, &b) < 0)
fatal("ssh_msg_recv failed");
if (buffer_get_char(&b) != version)
fatal("bad version");
fd = buffer_get_int(&b);
if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO))
fatal("bad fd");
if ((host = get_local_name(fd)) == NULL)
fatal("cannot get sockname for fd");
data = buffer_get_string(&b, &dlen);
if (valid_request(pw, host, &key, data, dlen) < 0)
fatal("not a valid request");
xfree(host);
found = 0;
for (i = 0; i < 2; i++) {
if (keys[i] != NULL &&
key_equal(key, keys[i])) {
found = 1;
break;
}
}
if (!found)
fatal("no matching hostkey found");
if (key_sign(keys[i], &signature, &slen, data, dlen) != 0)
fatal("key_sign failed");
xfree(data);
/* send reply */
buffer_clear(&b);
buffer_put_string(&b, signature, slen);
if (ssh_msg_send(STDOUT_FILENO, version, &b) == -1)
fatal("ssh_msg_send failed");
return (0);
}
|
