hostfile.c revision 264377 
1/* $OpenBSD: hostfile.c,v 1.55 2014/01/31 16:39:19 tedu Exp $ */
2/*
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 *                    All rights reserved
6 * Functions for manipulating the known hosts files.
7 *
8 * As far as I am concerned, the code I have written for this software
9 * can be used freely for any purpose.  Any derived versions of this
10 * software must be clearly marked as such, and if the derived work is
11 * incompatible with the protocol description in the RFC file, it must be
12 * called by a name other than "ssh" or "Secure Shell".
13 *
14 *
15 * Copyright (c) 1999, 2000 Markus Friedl.  All rights reserved.
16 * Copyright (c) 1999 Niels Provos.  All rights reserved.
17 *
18 * Redistribution and use in source and binary forms, with or without
19 * modification, are permitted provided that the following conditions
20 * are met:
21 * 1. Redistributions of source code must retain the above copyright
22 *    notice, this list of conditions and the following disclaimer.
23 * 2. Redistributions in binary form must reproduce the above copyright
24 *    notice, this list of conditions and the following disclaimer in the
25 *    documentation and/or other materials provided with the distribution.
26 *
27 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
28 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
29 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
30 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
31 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
32 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
33 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
34 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
35 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
36 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
37 */
38
39#include "includes.h"
40
41#include <sys/types.h>
42
43#include <netinet/in.h>
44
45#include <resolv.h>
46#include <stdarg.h>
47#include <stdio.h>
48#include <stdlib.h>
49#include <string.h>
50
51#include "xmalloc.h"
52#include "match.h"
53#include "key.h"
54#include "hostfile.h"
55#include "log.h"
56#include "misc.h"
57#include "digest.h"
58#include "hmac.h"
59
60struct hostkeys {
61	struct hostkey_entry *entries;
62	u_int num_entries;
63};
64
65static int
66extract_salt(const char *s, u_int l, u_char *salt, size_t salt_len)
67{
68	char *p, *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, salt, salt_len);
98	free(b64salt);
99	if (ret == -1) {
100		debug2("extract_salt: salt decode error");
101		return (-1);
102	}
103	if (ret != (int)ssh_hmac_bytes(SSH_DIGEST_SHA1)) {
104		debug2("extract_salt: expected salt len %zd, got %d",
105		    ssh_hmac_bytes(SSH_DIGEST_SHA1), ret);
106		return (-1);
107	}
108
109	return (0);
110}
111
112char *
113host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
114{
115	struct ssh_hmac_ctx *ctx;
116	u_char salt[256], result[256];
117	char uu_salt[512], uu_result[512];
118	static char encoded[1024];
119	u_int i, len;
120
121	len = ssh_digest_bytes(SSH_DIGEST_SHA1);
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	if ((ctx = ssh_hmac_start(SSH_DIGEST_SHA1)) == NULL ||
135	    ssh_hmac_init(ctx, salt, len) < 0 ||
136	    ssh_hmac_update(ctx, host, strlen(host)) < 0 ||
137	    ssh_hmac_final(ctx, result, sizeof(result)))
138		fatal("%s: ssh_hmac failed", __func__);
139	ssh_hmac_free(ctx);
140
141	if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
142	    __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
143		fatal("%s: __b64_ntop failed", __func__);
144
145	snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
146	    HASH_DELIM, uu_result);
147
148	return (encoded);
149}
150
151/*
152 * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
153 * pointer over the key.  Skips any whitespace at the beginning and at end.
154 */
155
156int
157hostfile_read_key(char **cpp, int *bitsp, Key *ret)
158{
159	char *cp;
160
161	/* Skip leading whitespace. */
162	for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
163		;
164
165	if (key_read(ret, &cp) != 1)
166		return 0;
167
168	/* Skip trailing whitespace. */
169	for (; *cp == ' ' || *cp == '\t'; cp++)
170		;
171
172	/* Return results. */
173	*cpp = cp;
174	if (bitsp != NULL) {
175		if ((*bitsp = key_size(ret)) <= 0)
176			return 0;
177	}
178	return 1;
179}
180
181static int
182hostfile_check_key(int bits, const Key *key, const char *host,
183    const char *filename, u_long linenum)
184{
185	if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
186		return 1;
187	if (bits != BN_num_bits(key->rsa->n)) {
188		logit("Warning: %s, line %lu: keysize mismatch for host %s: "
189		    "actual %d vs. announced %d.",
190		    filename, linenum, host, BN_num_bits(key->rsa->n), bits);
191		logit("Warning: replace %d with %d in %s, line %lu.",
192		    bits, BN_num_bits(key->rsa->n), filename, linenum);
193	}
194	return 1;
195}
196
197static HostkeyMarker
198check_markers(char **cpp)
199{
200	char marker[32], *sp, *cp = *cpp;
201	int ret = MRK_NONE;
202
203	while (*cp == '@') {
204		/* Only one marker is allowed */
205		if (ret != MRK_NONE)
206			return MRK_ERROR;
207		/* Markers are terminated by whitespace */
208		if ((sp = strchr(cp, ' ')) == NULL &&
209		    (sp = strchr(cp, '\t')) == NULL)
210			return MRK_ERROR;
211		/* Extract marker for comparison */
212		if (sp <= cp + 1 || sp >= cp + sizeof(marker))
213			return MRK_ERROR;
214		memcpy(marker, cp, sp - cp);
215		marker[sp - cp] = '\0';
216		if (strcmp(marker, CA_MARKER) == 0)
217			ret = MRK_CA;
218		else if (strcmp(marker, REVOKE_MARKER) == 0)
219			ret = MRK_REVOKE;
220		else
221			return MRK_ERROR;
222
223		/* Skip past marker and any whitespace that follows it */
224		cp = sp;
225		for (; *cp == ' ' || *cp == '\t'; cp++)
226			;
227	}
228	*cpp = cp;
229	return ret;
230}
231
232struct hostkeys *
233init_hostkeys(void)
234{
235	struct hostkeys *ret = xcalloc(1, sizeof(*ret));
236
237	ret->entries = NULL;
238	return ret;
239}
240
241void
242load_hostkeys(struct hostkeys *hostkeys, const char *host, const char *path)
243{
244	FILE *f;
245	char line[8192];
246	u_long linenum = 0, num_loaded = 0;
247	char *cp, *cp2, *hashed_host;
248	HostkeyMarker marker;
249	Key *key;
250	int kbits;
251
252	if ((f = fopen(path, "r")) == NULL)
253		return;
254	debug3("%s: loading entries for host \"%.100s\" from file \"%s\"",
255	    __func__, host, path);
256	while (read_keyfile_line(f, path, line, sizeof(line), &linenum) == 0) {
257		cp = line;
258
259		/* Skip any leading whitespace, comments and empty lines. */
260		for (; *cp == ' ' || *cp == '\t'; cp++)
261			;
262		if (!*cp || *cp == '#' || *cp == '\n')
263			continue;
264
265		if ((marker = check_markers(&cp)) == MRK_ERROR) {
266			verbose("%s: invalid marker at %s:%lu",
267			    __func__, path, linenum);
268			continue;
269		}
270
271		/* Find the end of the host name portion. */
272		for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
273			;
274
275		/* Check if the host name matches. */
276		if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
277			if (*cp != HASH_DELIM)
278				continue;
279			hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
280			if (hashed_host == NULL) {
281				debug("Invalid hashed host line %lu of %s",
282				    linenum, path);
283				continue;
284			}
285			if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
286				continue;
287		}
288
289		/* Got a match.  Skip host name. */
290		cp = cp2;
291
292		/*
293		 * Extract the key from the line.  This will skip any leading
294		 * whitespace.  Ignore badly formatted lines.
295		 */
296		key = key_new(KEY_UNSPEC);
297		if (!hostfile_read_key(&cp, &kbits, key)) {
298			key_free(key);
299			key = key_new(KEY_RSA1);
300			if (!hostfile_read_key(&cp, &kbits, key)) {
301				key_free(key);
302				continue;
303			}
304		}
305		if (!hostfile_check_key(kbits, key, host, path, linenum))
306			continue;
307
308		debug3("%s: found %skey type %s in file %s:%lu", __func__,
309		    marker == MRK_NONE ? "" :
310		    (marker == MRK_CA ? "ca " : "revoked "),
311		    key_type(key), path, linenum);
312		hostkeys->entries = xrealloc(hostkeys->entries,
313		    hostkeys->num_entries + 1, sizeof(*hostkeys->entries));
314		hostkeys->entries[hostkeys->num_entries].host = xstrdup(host);
315		hostkeys->entries[hostkeys->num_entries].file = xstrdup(path);
316		hostkeys->entries[hostkeys->num_entries].line = linenum;
317		hostkeys->entries[hostkeys->num_entries].key = key;
318		hostkeys->entries[hostkeys->num_entries].marker = marker;
319		hostkeys->num_entries++;
320		num_loaded++;
321	}
322	debug3("%s: loaded %lu keys", __func__, num_loaded);
323	fclose(f);
324	return;
325}
326
327void
328free_hostkeys(struct hostkeys *hostkeys)
329{
330	u_int i;
331
332	for (i = 0; i < hostkeys->num_entries; i++) {
333		free(hostkeys->entries[i].host);
334		free(hostkeys->entries[i].file);
335		key_free(hostkeys->entries[i].key);
336		explicit_bzero(hostkeys->entries + i, sizeof(*hostkeys->entries));
337	}
338	free(hostkeys->entries);
339	explicit_bzero(hostkeys, sizeof(*hostkeys));
340	free(hostkeys);
341}
342
343static int
344check_key_not_revoked(struct hostkeys *hostkeys, Key *k)
345{
346	int is_cert = key_is_cert(k);
347	u_int i;
348
349	for (i = 0; i < hostkeys->num_entries; i++) {
350		if (hostkeys->entries[i].marker != MRK_REVOKE)
351			continue;
352		if (key_equal_public(k, hostkeys->entries[i].key))
353			return -1;
354		if (is_cert &&
355		    key_equal_public(k->cert->signature_key,
356		    hostkeys->entries[i].key))
357			return -1;
358	}
359	return 0;
360}
361
362/*
363 * Match keys against a specified key, or look one up by key type.
364 *
365 * If looking for a keytype (key == NULL) and one is found then return
366 * HOST_FOUND, otherwise HOST_NEW.
367 *
368 * If looking for a key (key != NULL):
369 *  1. If the key is a cert and a matching CA is found, return HOST_OK
370 *  2. If the key is not a cert and a matching key is found, return HOST_OK
371 *  3. If no key matches but a key with a different type is found, then
372 *     return HOST_CHANGED
373 *  4. If no matching keys are found, then return HOST_NEW.
374 *
375 * Finally, check any found key is not revoked.
376 */
377static HostStatus
378check_hostkeys_by_key_or_type(struct hostkeys *hostkeys,
379    Key *k, int keytype, const struct hostkey_entry **found)
380{
381	u_int i;
382	HostStatus end_return = HOST_NEW;
383	int want_cert = key_is_cert(k);
384	HostkeyMarker want_marker = want_cert ? MRK_CA : MRK_NONE;
385	int proto = (k ? k->type : keytype) == KEY_RSA1 ? 1 : 2;
386
387	if (found != NULL)
388		*found = NULL;
389
390	for (i = 0; i < hostkeys->num_entries; i++) {
391		if (proto == 1 && hostkeys->entries[i].key->type != KEY_RSA1)
392			continue;
393		if (proto == 2 && hostkeys->entries[i].key->type == KEY_RSA1)
394			continue;
395		if (hostkeys->entries[i].marker != want_marker)
396			continue;
397		if (k == NULL) {
398			if (hostkeys->entries[i].key->type != keytype)
399				continue;
400			end_return = HOST_FOUND;
401			if (found != NULL)
402				*found = hostkeys->entries + i;
403			k = hostkeys->entries[i].key;
404			break;
405		}
406		if (want_cert) {
407			if (key_equal_public(k->cert->signature_key,
408			    hostkeys->entries[i].key)) {
409				/* A matching CA exists */
410				end_return = HOST_OK;
411				if (found != NULL)
412					*found = hostkeys->entries + i;
413				break;
414			}
415		} else {
416			if (key_equal(k, hostkeys->entries[i].key)) {
417				end_return = HOST_OK;
418				if (found != NULL)
419					*found = hostkeys->entries + i;
420				break;
421			}
422			/* A non-maching key exists */
423			end_return = HOST_CHANGED;
424			if (found != NULL)
425				*found = hostkeys->entries + i;
426		}
427	}
428	if (check_key_not_revoked(hostkeys, k) != 0) {
429		end_return = HOST_REVOKED;
430		if (found != NULL)
431			*found = NULL;
432	}
433	return end_return;
434}
435
436HostStatus
437check_key_in_hostkeys(struct hostkeys *hostkeys, Key *key,
438    const struct hostkey_entry **found)
439{
440	if (key == NULL)
441		fatal("no key to look up");
442	return check_hostkeys_by_key_or_type(hostkeys, key, 0, found);
443}
444
445int
446lookup_key_in_hostkeys_by_type(struct hostkeys *hostkeys, int keytype,
447    const struct hostkey_entry **found)
448{
449	return (check_hostkeys_by_key_or_type(hostkeys, NULL, keytype,
450	    found) == HOST_FOUND);
451}
452
453/*
454 * Appends an entry to the host file.  Returns false if the entry could not
455 * be appended.
456 */
457
458int
459add_host_to_hostfile(const char *filename, const char *host, const Key *key,
460    int store_hash)
461{
462	FILE *f;
463	int success = 0;
464	char *hashed_host = NULL;
465
466	if (key == NULL)
467		return 1;	/* XXX ? */
468	f = fopen(filename, "a");
469	if (!f)
470		return 0;
471
472	if (store_hash) {
473		if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
474			error("add_host_to_hostfile: host_hash failed");
475			fclose(f);
476			return 0;
477		}
478	}
479	fprintf(f, "%s ", store_hash ? hashed_host : host);
480
481	if (key_write(key, f)) {
482		success = 1;
483	} else {
484		error("add_host_to_hostfile: saving key in %s failed", filename);
485	}
486	fprintf(f, "\n");
487	fclose(f);
488	return success;
489}
490