1 /*
2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4 * All rights reserved
5 * Functions for manipulating the known hosts files.
6 *
7 * As far as I am concerned, the code I have written for this software
8 * can be used freely for any purpose. Any derived versions of this
9 * software must be clearly marked as such, and if the derived work is
10 * incompatible with the protocol description in the RFC file, it must be
11 * called by a name other than "ssh" or "Secure Shell".
12 *
13 *
14 * Copyright (c) 1999, 2000 Markus Friedl. All rights reserved.
15 * Copyright (c) 1999 Niels Provos. All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions
19 * are met:
20 * 1. Redistributions of source code must retain the above copyright
21 * notice, this list of conditions and the following disclaimer.
22 * 2. Redistributions in binary form must reproduce the above copyright
23 * notice, this list of conditions and the following disclaimer in the
24 * documentation and/or other materials provided with the distribution.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36 */
37
38 /* $OpenBSD: hostfile.c,v 1.45 2006/08/03 03:34:42 deraadt Exp $ */
39
40 #pragma ident "%Z%%M% %I% %E% SMI"
41
42 #include "includes.h"
43
44 #include <openssl/opensslconf.h>
45 #include <openssl/hmac.h>
46 #include <openssl/sha.h>
47
48 #include "packet.h"
49 #include "xmalloc.h"
50 #include "match.h"
51 #include "key.h"
52 #include "hostfile.h"
53 #include "log.h"
54
55 /*
56 * Format of a hashed hostname is <MAGIC><SALT>|<HASHED_HOSTNAME>. <MAGIC> is
57 * "|1|". As in non-hashed hostnames this whole string is then followed by a
58 * space, a key type and the key (which is out of scope of this function).
59 *
60 * Example what can be in 's':
61 *
62 * |1|t17NtsuXSLwP0H0eYdd8vJeNakM=|9XFVPh3jZUrfY6YCWn8Ua5eGZtA=
63 */
64 static int
65 extract_salt(const char *s, u_int l, char *salt, size_t salt_len)
66 {
67 char *p;
68 u_char *b64salt;
69 u_int b64len;
70 int ret;
71
72 if (l < sizeof(HASH_MAGIC) - 1) {
73 debug2("extract_salt: string too short");
74 return (-1);
75 }
76 if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
77 debug2("extract_salt: invalid magic identifier");
78 return (-1);
79 }
80 s += sizeof(HASH_MAGIC) - 1;
81 l -= sizeof(HASH_MAGIC) - 1;
82 if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
83 debug2("extract_salt: missing salt termination character");
84 return (-1);
85 }
86
87 b64len = p - s;
88 /* Sanity check */
89 if (b64len == 0 || b64len > 1024) {
90 debug2("extract_salt: bad encoded salt length %u", b64len);
91 return (-1);
92 }
93 b64salt = xmalloc(1 + b64len);
94 memcpy(b64salt, s, b64len);
95 b64salt[b64len] = '\0';
96
97 ret = __b64_pton(b64salt, (u_char *) salt, salt_len);
98 xfree(b64salt);
99 if (ret == -1) {
100 debug2("extract_salt: salt decode error");
101 return (-1);
102 }
103 if (ret != SHA_DIGEST_LENGTH) {
104 debug2("extract_salt: expected salt len %d, got %d",
105 SHA_DIGEST_LENGTH, ret);
106 return (-1);
107 }
108
109 return (0);
110 }
111
112 char *
113 host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
114 {
115 const EVP_MD *md = EVP_sha1();
116 HMAC_CTX mac_ctx;
117 char salt[256], result[256], uu_salt[512], uu_result[512];
118 static char encoded[1024];
119 u_int i, len;
120
121 len = EVP_MD_size(md);
122
123 if (name_from_hostfile == NULL) {
124 /* Create new salt */
125 for (i = 0; i < len; i++)
126 salt[i] = arc4random();
127 } else {
128 /* Extract salt from known host entry */
129 if (extract_salt(name_from_hostfile, src_len, salt,
130 sizeof(salt)) == -1)
131 return (NULL);
132 }
133
134 HMAC_Init(&mac_ctx, salt, len, md);
135 HMAC_Update(&mac_ctx, (u_char *) host, strlen(host));
136 HMAC_Final(&mac_ctx, (u_char *) result, NULL);
137 HMAC_cleanup(&mac_ctx);
138
139 if (__b64_ntop((u_char *) salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
140 __b64_ntop((u_char *) result, len, uu_result, sizeof(uu_result)) == -1)
141 fatal("host_hash: __b64_ntop failed");
142
143 snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
144 HASH_DELIM, uu_result);
145
146 return (encoded);
147 }
148
149 /*
150 * Parses an RSA (number of bits, e, n) or DSA key from a string. Moves the
151 * pointer over the key. Skips any whitespace at the beginning and at end.
152 */
153
154 int
155 hostfile_read_key(char **cpp, u_int *bitsp, Key *ret)
156 {
157 char *cp;
158
159 /* Skip leading whitespace. */
160 for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
161 ;
162
163 if (key_read(ret, &cp) != 1)
164 return 0;
165
166 /* Skip trailing whitespace. */
167 for (; *cp == ' ' || *cp == '\t'; cp++)
168 ;
169
170 /* Return results. */
171 *cpp = cp;
172 *bitsp = key_size(ret);
173 return 1;
174 }
175
176 static int
177 hostfile_check_key(int bits, const Key *key, const char *host, const char *filename, int linenum)
178 {
179 if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
180 return 1;
181 if (bits != BN_num_bits(key->rsa->n)) {
182 log("Warning: %s, line %d: keysize mismatch for host %s: "
183 "actual %d vs. announced %d.",
184 filename, linenum, host, BN_num_bits(key->rsa->n), bits);
185 log("Warning: replace %d with %d in %s, line %d.",
186 bits, BN_num_bits(key->rsa->n), filename, linenum);
187 }
188 return 1;
189 }
190
191 /*
192 * Checks whether the given host (which must be in all lowercase) is already
193 * in the list of our known hosts. Returns HOST_OK if the host is known and
194 * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
195 * if the host is known but used to have a different host key.
196 *
197 * If no 'key' has been specified and a key of type 'keytype' is known
198 * for the specified host, then HOST_FOUND is returned.
199 */
200
201 static HostStatus
202 check_host_in_hostfile_by_key_or_type(const char *filename,
203 const char *host, const Key *key, int keytype, Key *found, int *numret)
204 {
205 FILE *f;
206 char line[8192];
207 int linenum = 0;
208 u_int kbits;
209 char *cp, *cp2, *hashed_host;
210 HostStatus end_return;
211
212 debug3("check_host_in_hostfile: filename %s", filename);
213
214 /* Open the file containing the list of known hosts. */
215 f = fopen(filename, "r");
216 if (!f)
217 return HOST_NEW;
218
219 /*
220 * Return value when the loop terminates. This is set to
221 * HOST_CHANGED if we have seen a different key for the host and have
222 * not found the proper one.
223 */
224 end_return = HOST_NEW;
225
226 /* Go through the file. */
227 while (fgets(line, sizeof(line), f)) {
228 cp = line;
229 linenum++;
230
231 /* Skip any leading whitespace, comments and empty lines. */
232 for (; *cp == ' ' || *cp == '\t'; cp++)
233 ;
234 if (!*cp || *cp == '#' || *cp == '\n')
235 continue;
236
237 /* Find the end of the host name portion. */
238 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
239 ;
240
241 /* Check if the host name matches. */
242 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
243 if (*cp != HASH_DELIM)
244 continue;
245 hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
246 if (hashed_host == NULL) {
247 debug("Invalid hashed host line %d of %s",
248 linenum, filename);
249 continue;
250 }
251 if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
252 continue;
253 }
254
255 /* Got a match. Skip host name. */
256 cp = cp2;
257
258 /*
259 * Extract the key from the line. This will skip any leading
260 * whitespace. Ignore badly formatted lines.
261 */
262 if (!hostfile_read_key(&cp, &kbits, found))
263 continue;
264
265 if (numret != NULL)
266 *numret = linenum;
267
268 if (key == NULL) {
269 /* we found a key of the requested type */
270 if (found->type == keytype) {
271 fclose(f);
272 return HOST_FOUND;
273 }
274 continue;
275 }
276
277 if (!hostfile_check_key(kbits, found, host, filename, linenum))
278 continue;
279
280 /* Check if the current key is the same as the given key. */
281 if (key_equal(key, found)) {
282 /* Ok, they match. */
283 debug3("check_host_in_hostfile: match line %d", linenum);
284 fclose(f);
285 return HOST_OK;
286 }
287 /*
288 * They do not match. We will continue to go through the
289 * file; however, we note that we will not return that it is
290 * new.
291 */
292 end_return = HOST_CHANGED;
293 }
294 /* Clear variables and close the file. */
295 fclose(f);
296
297 /*
298 * Return either HOST_NEW or HOST_CHANGED, depending on whether we
299 * saw a different key for the host.
300 */
301 return end_return;
302 }
303
304 HostStatus
305 check_host_in_hostfile(const char *filename, const char *host, const Key *key,
306 Key *found, int *numret)
307 {
308 if (key == NULL)
309 fatal("no key to look up");
310 return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
311 found, numret));
312 }
313
314 int
315 lookup_key_in_hostfile_by_type(const char *filename, const char *host,
316 int keytype, Key *found, int *numret)
317 {
318 return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
319 keytype, found, numret) == HOST_FOUND);
320 }
321
322 /*
323 * Appends an entry to the host file. Returns false if the entry could not
324 * be appended.
325 */
326
327 int
328 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
329 int store_hash)
330 {
331 FILE *f;
332 int success = 0;
333 char *hashed_host = NULL;
334
335 if (key == NULL)
336 return 1; /* XXX ? */
337 f = fopen(filename, "a");
338 if (!f)
339 return 0;
340
341 if (store_hash) {
342 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
343 error("add_host_to_hostfile: host_hash failed");
344 fclose(f);
345 return 0;
346 }
347 }
348 fprintf(f, "%s ", store_hash ? hashed_host : host);
349
350 if (key_write(key, f)) {
351 success = 1;
352 } else {
353 error("add_host_to_hostfile: saving key in %s failed", filename);
354 }
355 fprintf(f, "\n");
356 fclose(f);
357 return success;
358 }