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1 | /* $OpenBSD: ssh-keysign.c,v 1.29 2006/08/03 03:34:42 deraadt 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 | #include <openssl/evp.h> | |
39 | #include <openssl/rand.h> | |
40 | #include <openssl/rsa.h> | |
41 | ||
42 | #include "xmalloc.h" | |
43 | #include "log.h" | |
44 | #include "key.h" | |
45 | #include "ssh.h" | |
46 | #include "ssh2.h" | |
47 | #include "misc.h" | |
48 | #include "buffer.h" | |
49 | #include "authfile.h" | |
50 | #include "msg.h" | |
51 | #include "canohost.h" | |
52 | #include "pathnames.h" | |
53 | #include "readconf.h" | |
54 | #include "uidswap.h" | |
55 | ||
56 | /* XXX readconf.c needs these */ | |
57 | uid_t original_real_uid; | |
58 | ||
59 | extern char *__progname; | |
60 | ||
61 | static int | |
62 | valid_request(struct passwd *pw, char *host, Key **ret, u_char *data, | |
63 | u_int datalen) | |
64 | { | |
65 | Buffer b; | |
66 | Key *key = NULL; | |
67 | u_char *pkblob; | |
68 | u_int blen, len; | |
69 | char *pkalg, *p; | |
70 | int pktype, fail; | |
71 | ||
72 | fail = 0; | |
73 | ||
74 | buffer_init(&b); | |
75 | buffer_append(&b, data, datalen); | |
76 | ||
77 | /* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */ | |
78 | p = buffer_get_string(&b, &len); | |
79 | if (len != 20 && len != 32) | |
80 | fail++; | |
81 | xfree(p); | |
82 | ||
83 | if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST) | |
84 | fail++; | |
85 | ||
86 | /* server user */ | |
87 | buffer_skip_string(&b); | |
88 | ||
89 | /* service */ | |
90 | p = buffer_get_string(&b, NULL); | |
91 | if (strcmp("ssh-connection", p) != 0) | |
92 | fail++; | |
93 | xfree(p); | |
94 | ||
95 | /* method */ | |
96 | p = buffer_get_string(&b, NULL); | |
97 | if (strcmp("hostbased", p) != 0) | |
98 | fail++; | |
99 | xfree(p); | |
100 | ||
101 | /* pubkey */ | |
102 | pkalg = buffer_get_string(&b, NULL); | |
103 | pkblob = buffer_get_string(&b, &blen); | |
104 | ||
105 | pktype = key_type_from_name(pkalg); | |
106 | if (pktype == KEY_UNSPEC) | |
107 | fail++; | |
108 | else if ((key = key_from_blob(pkblob, blen)) == NULL) | |
109 | fail++; | |
110 | else if (key->type != pktype) | |
111 | fail++; | |
112 | xfree(pkalg); | |
113 | xfree(pkblob); | |
114 | ||
115 | /* client host name, handle trailing dot */ | |
116 | p = buffer_get_string(&b, &len); | |
117 | debug2("valid_request: check expect chost %s got %s", host, p); | |
118 | if (strlen(host) != len - 1) | |
119 | fail++; | |
120 | else if (p[len - 1] != '.') | |
121 | fail++; | |
122 | else if (strncasecmp(host, p, len - 1) != 0) | |
123 | fail++; | |
124 | xfree(p); | |
125 | ||
126 | /* local user */ | |
127 | p = buffer_get_string(&b, NULL); | |
128 | ||
129 | if (strcmp(pw->pw_name, p) != 0) | |
130 | fail++; | |
131 | xfree(p); | |
132 | ||
133 | /* end of message */ | |
134 | if (buffer_len(&b) != 0) | |
135 | fail++; | |
136 | buffer_free(&b); | |
137 | ||
138 | debug3("valid_request: fail %d", fail); | |
139 | ||
140 | if (fail && key != NULL) | |
141 | key_free(key); | |
142 | else | |
143 | *ret = key; | |
144 | ||
145 | return (fail ? -1 : 0); | |
146 | } | |
147 | ||
148 | int | |
149 | main(int argc, char **argv) | |
150 | { | |
151 | Buffer b; | |
152 | Options options; | |
153 | Key *keys[2], *key = NULL; | |
154 | struct passwd *pw; | |
155 | int key_fd[2], i, found, version = 2, fd; | |
156 | u_char *signature, *data; | |
157 | char *host; | |
158 | u_int slen, dlen; | |
159 | u_int32_t rnd[256]; | |
160 | ||
161 | /* Ensure that stdin and stdout are connected */ | |
162 | if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) | |
163 | exit(1); | |
164 | /* Leave /dev/null fd iff it is attached to stderr */ | |
165 | if (fd > 2) | |
166 | close(fd); | |
167 | ||
168 | key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); | |
169 | key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); | |
170 | ||
171 | original_real_uid = getuid(); /* XXX readconf.c needs this */ | |
172 | if ((pw = getpwuid(original_real_uid)) == NULL) | |
173 | fatal("getpwuid failed"); | |
174 | pw = pwcopy(pw); | |
175 | ||
176 | permanently_set_uid(pw); | |
177 | ||
178 | init_rng(); | |
179 | seed_rng(); | |
180 | arc4random_stir(); | |
181 | ||
182 | #ifdef DEBUG_SSH_KEYSIGN | |
183 | log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); | |
184 | #endif | |
185 | ||
186 | /* verify that ssh-keysign is enabled by the admin */ | |
187 | initialize_options(&options); | |
188 | (void)read_config_file(_PATH_HOST_CONFIG_FILE, "", &options, 0); | |
189 | fill_default_options(&options); | |
190 | if (options.enable_ssh_keysign != 1) | |
191 | fatal("ssh-keysign not enabled in %s", | |
192 | _PATH_HOST_CONFIG_FILE); | |
193 | ||
194 | if (key_fd[0] == -1 && key_fd[1] == -1) | |
195 | fatal("could not open any host key"); | |
196 | ||
197 | SSLeay_add_all_algorithms(); | |
198 | for (i = 0; i < 256; i++) | |
199 | rnd[i] = arc4random(); | |
200 | RAND_seed(rnd, sizeof(rnd)); | |
201 | ||
202 | found = 0; | |
203 | for (i = 0; i < 2; i++) { | |
204 | keys[i] = NULL; | |
205 | if (key_fd[i] == -1) | |
206 | continue; | |
207 | keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC, | |
208 | NULL, NULL); | |
209 | close(key_fd[i]); | |
210 | if (keys[i] != NULL) | |
211 | found = 1; | |
212 | } | |
213 | if (!found) | |
214 | fatal("no hostkey found"); | |
215 | ||
216 | buffer_init(&b); | |
217 | if (ssh_msg_recv(STDIN_FILENO, &b) < 0) | |
218 | fatal("ssh_msg_recv failed"); | |
219 | if (buffer_get_char(&b) != version) | |
220 | fatal("bad version"); | |
221 | fd = buffer_get_int(&b); | |
222 | if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO)) | |
223 | fatal("bad fd"); | |
224 | if ((host = get_local_name(fd)) == NULL) | |
225 | fatal("cannot get sockname for fd"); | |
226 | ||
227 | data = buffer_get_string(&b, &dlen); | |
228 | if (valid_request(pw, host, &key, data, dlen) < 0) | |
229 | fatal("not a valid request"); | |
230 | xfree(host); | |
231 | ||
232 | found = 0; | |
233 | for (i = 0; i < 2; i++) { | |
234 | if (keys[i] != NULL && | |
235 | key_equal(key, keys[i])) { | |
236 | found = 1; | |
237 | break; | |
238 | } | |
239 | } | |
240 | if (!found) | |
241 | fatal("no matching hostkey found"); | |
242 | ||
243 | if (key_sign(keys[i], &signature, &slen, data, dlen) != 0) | |
244 | fatal("key_sign failed"); | |
245 | xfree(data); | |
246 | ||
247 | /* send reply */ | |
248 | buffer_clear(&b); | |
249 | buffer_put_string(&b, signature, slen); | |
250 | if (ssh_msg_send(STDOUT_FILENO, version, &b) == -1) | |
251 | fatal("ssh_msg_send failed"); | |
252 | ||
253 | return (0); | |
254 | } |