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/hmac.h>
45 #include <openssl/sha.h>
46
47 #include "packet.h"
48 #include "xmalloc.h"
49 #include "match.h"
50 #include "key.h"
51 #include "hostfile.h"
52 #include "log.h"
53
54 /*
55 * Format of a hashed hostname is <MAGIC><SALT>|<HASHED_HOSTNAME>. <MAGIC> is
56 * "|1|". As in non-hashed hostnames this whole string is then followed by a
57 * space, a key type and the key (which is out of scope of this function).
58 *
59 * Example what can be in 's':
60 *
61 * |1|t17NtsuXSLwP0H0eYdd8vJeNakM=|9XFVPh3jZUrfY6YCWn8Ua5eGZtA=
62 */
63 static int
extract_salt(const char * s,u_int l,char * salt,size_t salt_len)64 extract_salt(const char *s, u_int l, char *salt, size_t salt_len)
65 {
66 char *p;
67 u_char *b64salt;
68 u_int b64len;
69 int ret;
70
71 if (l < sizeof(HASH_MAGIC) - 1) {
72 debug2("extract_salt: string too short");
73 return (-1);
74 }
75 if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
76 debug2("extract_salt: invalid magic identifier");
77 return (-1);
78 }
79 s += sizeof(HASH_MAGIC) - 1;
80 l -= sizeof(HASH_MAGIC) - 1;
81 if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
82 debug2("extract_salt: missing salt termination character");
83 return (-1);
84 }
85
86 b64len = p - s;
87 /* Sanity check */
88 if (b64len == 0 || b64len > 1024) {
89 debug2("extract_salt: bad encoded salt length %u", b64len);
90 return (-1);
91 }
92 b64salt = xmalloc(1 + b64len);
93 memcpy(b64salt, s, b64len);
94 b64salt[b64len] = '\0';
95
96 ret = __b64_pton(b64salt, (u_char *) salt, salt_len);
97 xfree(b64salt);
98 if (ret == -1) {
99 debug2("extract_salt: salt decode error");
100 return (-1);
101 }
102 if (ret != SHA_DIGEST_LENGTH) {
103 debug2("extract_salt: expected salt len %d, got %d",
104 SHA_DIGEST_LENGTH, ret);
105 return (-1);
106 }
107
108 return (0);
109 }
110
111 char *
host_hash(const char * host,const char * name_from_hostfile,u_int src_len)112 host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
113 {
114 const EVP_MD *md = EVP_sha1();
115 HMAC_CTX mac_ctx;
116 char salt[256], result[256], uu_salt[512], uu_result[512];
117 static char encoded[1024];
118 u_int i, len;
119
120 len = EVP_MD_size(md);
121
122 if (name_from_hostfile == NULL) {
123 /* Create new salt */
124 for (i = 0; i < len; i++)
125 salt[i] = arc4random();
126 } else {
127 /* Extract salt from known host entry */
128 if (extract_salt(name_from_hostfile, src_len, salt,
129 sizeof(salt)) == -1)
130 return (NULL);
131 }
132
133 HMAC_Init(&mac_ctx, salt, len, md);
134 HMAC_Update(&mac_ctx, (u_char *) host, strlen(host));
135 HMAC_Final(&mac_ctx, (u_char *) result, NULL);
136 HMAC_cleanup(&mac_ctx);
137
138 if (__b64_ntop((u_char *) salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
139 __b64_ntop((u_char *) result, len, uu_result, sizeof(uu_result)) == -1)
140 fatal("host_hash: __b64_ntop failed");
141
142 snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
143 HASH_DELIM, uu_result);
144
145 return (encoded);
146 }
147
148 /*
149 * Parses an RSA (number of bits, e, n) or DSA key from a string. Moves the
150 * pointer over the key. Skips any whitespace at the beginning and at end.
151 */
152
153 int
hostfile_read_key(char ** cpp,u_int * bitsp,Key * ret)154 hostfile_read_key(char **cpp, u_int *bitsp, Key *ret)
155 {
156 char *cp;
157
158 /* Skip leading whitespace. */
159 for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
160 ;
161
162 if (key_read(ret, &cp) != 1)
163 return 0;
164
165 /* Skip trailing whitespace. */
166 for (; *cp == ' ' || *cp == '\t'; cp++)
167 ;
168
169 /* Return results. */
170 *cpp = cp;
171 *bitsp = key_size(ret);
172 return 1;
173 }
174
175 static int
hostfile_check_key(int bits,const Key * key,const char * host,const char * filename,int linenum)176 hostfile_check_key(int bits, const Key *key, const char *host, const char *filename, int linenum)
177 {
178 if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
179 return 1;
180 if (bits != BN_num_bits(key->rsa->n)) {
181 log("Warning: %s, line %d: keysize mismatch for host %s: "
182 "actual %d vs. announced %d.",
183 filename, linenum, host, BN_num_bits(key->rsa->n), bits);
184 log("Warning: replace %d with %d in %s, line %d.",
185 bits, BN_num_bits(key->rsa->n), filename, linenum);
186 }
187 return 1;
188 }
189
190 /*
191 * Checks whether the given host (which must be in all lowercase) is already
192 * in the list of our known hosts. Returns HOST_OK if the host is known and
193 * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
194 * if the host is known but used to have a different host key.
195 *
196 * If no 'key' has been specified and a key of type 'keytype' is known
197 * for the specified host, then HOST_FOUND is returned.
198 */
199
200 static HostStatus
check_host_in_hostfile_by_key_or_type(const char * filename,const char * host,const Key * key,int keytype,Key * found,int * numret)201 check_host_in_hostfile_by_key_or_type(const char *filename,
202 const char *host, const Key *key, int keytype, Key *found, int *numret)
203 {
204 FILE *f;
205 char line[8192];
206 int linenum = 0;
207 u_int kbits;
208 char *cp, *cp2, *hashed_host;
209 HostStatus end_return;
210
211 debug3("check_host_in_hostfile: filename %s", filename);
212
213 /* Open the file containing the list of known hosts. */
214 f = fopen(filename, "r");
215 if (!f)
216 return HOST_NEW;
217
218 /*
219 * Return value when the loop terminates. This is set to
220 * HOST_CHANGED if we have seen a different key for the host and have
221 * not found the proper one.
222 */
223 end_return = HOST_NEW;
224
225 /* Go through the file. */
226 while (fgets(line, sizeof(line), f)) {
227 cp = line;
228 linenum++;
229
230 /* Skip any leading whitespace, comments and empty lines. */
231 for (; *cp == ' ' || *cp == '\t'; cp++)
232 ;
233 if (!*cp || *cp == '#' || *cp == '\n')
234 continue;
235
236 /* Find the end of the host name portion. */
237 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
238 ;
239
240 /* Check if the host name matches. */
241 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
242 if (*cp != HASH_DELIM)
243 continue;
244 hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
245 if (hashed_host == NULL) {
246 debug("Invalid hashed host line %d of %s",
247 linenum, filename);
248 continue;
249 }
250 if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
251 continue;
252 }
253
254 /* Got a match. Skip host name. */
255 cp = cp2;
256
257 /*
258 * Extract the key from the line. This will skip any leading
259 * whitespace. Ignore badly formatted lines.
260 */
261 if (!hostfile_read_key(&cp, &kbits, found))
262 continue;
263
264 if (numret != NULL)
265 *numret = linenum;
266
267 if (key == NULL) {
268 /* we found a key of the requested type */
269 if (found->type == keytype) {
270 fclose(f);
271 return HOST_FOUND;
272 }
273 continue;
274 }
275
276 if (!hostfile_check_key(kbits, found, host, filename, linenum))
277 continue;
278
279 /* Check if the current key is the same as the given key. */
280 if (key_equal(key, found)) {
281 /* Ok, they match. */
282 debug3("check_host_in_hostfile: match line %d", linenum);
283 fclose(f);
284 return HOST_OK;
285 }
286 /*
287 * They do not match. We will continue to go through the
288 * file; however, we note that we will not return that it is
289 * new.
290 */
291 end_return = HOST_CHANGED;
292 }
293 /* Clear variables and close the file. */
294 fclose(f);
295
296 /*
297 * Return either HOST_NEW or HOST_CHANGED, depending on whether we
298 * saw a different key for the host.
299 */
300 return end_return;
301 }
302
303 HostStatus
check_host_in_hostfile(const char * filename,const char * host,const Key * key,Key * found,int * numret)304 check_host_in_hostfile(const char *filename, const char *host, const Key *key,
305 Key *found, int *numret)
306 {
307 if (key == NULL)
308 fatal("no key to look up");
309 return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
310 found, numret));
311 }
312
313 int
lookup_key_in_hostfile_by_type(const char * filename,const char * host,int keytype,Key * found,int * numret)314 lookup_key_in_hostfile_by_type(const char *filename, const char *host,
315 int keytype, Key *found, int *numret)
316 {
317 return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
318 keytype, found, numret) == HOST_FOUND);
319 }
320
321 /*
322 * Appends an entry to the host file. Returns false if the entry could not
323 * be appended.
324 */
325
326 int
add_host_to_hostfile(const char * filename,const char * host,const Key * key,int store_hash)327 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
328 int store_hash)
329 {
330 FILE *f;
331 int success = 0;
332 char *hashed_host = NULL;
333
334 if (key == NULL)
335 return 1; /* XXX ? */
336 f = fopen(filename, "a");
337 if (!f)
338 return 0;
339
340 if (store_hash) {
341 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
342 error("add_host_to_hostfile: host_hash failed");
343 fclose(f);
344 return 0;
345 }
346 }
347 fprintf(f, "%s ", store_hash ? hashed_host : host);
348
349 if (key_write(key, f)) {
350 success = 1;
351 } else {
352 error("add_host_to_hostfile: saving key in %s failed", filename);
353 }
354 fprintf(f, "\n");
355 fclose(f);
356 return success;
357 }
358