Annotation of src/usr.bin/ssh/dns.c, Revision 1.16
1.16 ! stevesk 1: /* $OpenBSD: dns.c,v 1.15 2005/10/17 14:01:28 stevesk Exp $ */
1.1 jakob 2:
3: /*
4: * Copyright (c) 2003 Wesley Griffin. All rights reserved.
5: * Copyright (c) 2003 Jakob Schlyter. All rights reserved.
6: *
7: * Redistribution and use in source and binary forms, with or without
8: * modification, are permitted provided that the following conditions
9: * are met:
10: * 1. Redistributions of source code must retain the above copyright
11: * notice, this list of conditions and the following disclaimer.
12: * 2. Redistributions in binary form must reproduce the above copyright
13: * notice, this list of conditions and the following disclaimer in the
14: * documentation and/or other materials provided with the distribution.
15: *
16: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26: */
27:
28: #include "includes.h"
1.16 ! stevesk 29: RCSID("$OpenBSD: dns.c,v 1.15 2005/10/17 14:01:28 stevesk Exp $");
1.1 jakob 30:
31: #include <netdb.h>
32:
33: #include "xmalloc.h"
34: #include "key.h"
35: #include "dns.h"
36: #include "log.h"
37:
38: static const char *errset_text[] = {
39: "success", /* 0 ERRSET_SUCCESS */
40: "out of memory", /* 1 ERRSET_NOMEMORY */
41: "general failure", /* 2 ERRSET_FAIL */
42: "invalid parameter", /* 3 ERRSET_INVAL */
43: "name does not exist", /* 4 ERRSET_NONAME */
44: "data does not exist", /* 5 ERRSET_NODATA */
45: };
46:
47: static const char *
1.10 avsm 48: dns_result_totext(unsigned int res)
1.1 jakob 49: {
1.10 avsm 50: switch (res) {
1.1 jakob 51: case ERRSET_SUCCESS:
52: return errset_text[ERRSET_SUCCESS];
53: case ERRSET_NOMEMORY:
54: return errset_text[ERRSET_NOMEMORY];
55: case ERRSET_FAIL:
56: return errset_text[ERRSET_FAIL];
57: case ERRSET_INVAL:
58: return errset_text[ERRSET_INVAL];
59: case ERRSET_NONAME:
60: return errset_text[ERRSET_NONAME];
61: case ERRSET_NODATA:
62: return errset_text[ERRSET_NODATA];
63: default:
64: return "unknown error";
65: }
66: }
67:
68: /*
69: * Read SSHFP parameters from key buffer.
70: */
71: static int
72: dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
1.8 jakob 73: u_char **digest, u_int *digest_len, const Key *key)
1.1 jakob 74: {
75: int success = 0;
76:
77: switch (key->type) {
78: case KEY_RSA:
1.3 jakob 79: *algorithm = SSHFP_KEY_RSA;
1.1 jakob 80: break;
81: case KEY_DSA:
1.3 jakob 82: *algorithm = SSHFP_KEY_DSA;
1.1 jakob 83: break;
84: default:
1.14 stevesk 85: *algorithm = SSHFP_KEY_RESERVED; /* 0 */
1.1 jakob 86: }
87:
88: if (*algorithm) {
1.3 jakob 89: *digest_type = SSHFP_HASH_SHA1;
1.1 jakob 90: *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
1.14 stevesk 91: if (*digest == NULL)
92: fatal("dns_read_key: null from key_fingerprint_raw()");
1.1 jakob 93: success = 1;
94: } else {
1.3 jakob 95: *digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 96: *digest = NULL;
97: *digest_len = 0;
98: success = 0;
99: }
100:
101: return success;
102: }
103:
104: /*
105: * Read SSHFP parameters from rdata buffer.
106: */
107: static int
108: dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
109: u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
110: {
111: int success = 0;
112:
1.3 jakob 113: *algorithm = SSHFP_KEY_RESERVED;
114: *digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 115:
116: if (rdata_len >= 2) {
117: *algorithm = rdata[0];
118: *digest_type = rdata[1];
119: *digest_len = rdata_len - 2;
120:
121: if (*digest_len > 0) {
122: *digest = (u_char *) xmalloc(*digest_len);
123: memcpy(*digest, rdata + 2, *digest_len);
124: } else {
1.14 stevesk 125: *digest = xstrdup("");
1.1 jakob 126: }
127:
128: success = 1;
129: }
130:
131: return success;
132: }
133:
1.11 jakob 134: /*
135: * Check if hostname is numerical.
136: * Returns -1 if hostname is numeric, 0 otherwise
137: */
138: static int
139: is_numeric_hostname(const char *hostname)
140: {
141: struct addrinfo hints, *ai;
142:
143: memset(&hints, 0, sizeof(hints));
144: hints.ai_socktype = SOCK_DGRAM;
145: hints.ai_flags = AI_NUMERICHOST;
146:
147: if (getaddrinfo(hostname, "0", &hints, &ai) == 0) {
148: freeaddrinfo(ai);
149: return -1;
150: }
151:
152: return 0;
153: }
1.1 jakob 154:
155: /*
156: * Verify the given hostname, address and host key using DNS.
1.9 djm 157: * Returns 0 if lookup succeeds, -1 otherwise
1.1 jakob 158: */
159: int
160: verify_host_key_dns(const char *hostname, struct sockaddr *address,
1.8 jakob 161: const Key *hostkey, int *flags)
1.1 jakob 162: {
1.12 djm 163: u_int counter;
1.1 jakob 164: int result;
1.4 jakob 165: struct rrsetinfo *fingerprints = NULL;
1.1 jakob 166:
167: u_int8_t hostkey_algorithm;
168: u_int8_t hostkey_digest_type;
169: u_char *hostkey_digest;
170: u_int hostkey_digest_len;
171:
172: u_int8_t dnskey_algorithm;
173: u_int8_t dnskey_digest_type;
174: u_char *dnskey_digest;
175: u_int dnskey_digest_len;
176:
1.8 jakob 177: *flags = 0;
1.1 jakob 178:
1.16 ! stevesk 179: debug3("verify_host_key_dns");
1.1 jakob 180: if (hostkey == NULL)
181: fatal("No key to look up!");
1.11 jakob 182:
183: if (is_numeric_hostname(hostname)) {
184: debug("skipped DNS lookup for numerical hostname");
185: return -1;
186: }
1.1 jakob 187:
188: result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
1.4 jakob 189: DNS_RDATATYPE_SSHFP, 0, &fingerprints);
1.1 jakob 190: if (result) {
191: verbose("DNS lookup error: %s", dns_result_totext(result));
1.8 jakob 192: return -1;
1.1 jakob 193: }
194:
1.8 jakob 195: if (fingerprints->rri_flags & RRSET_VALIDATED) {
196: *flags |= DNS_VERIFY_SECURE;
197: debug("found %d secure fingerprints in DNS",
198: fingerprints->rri_nrdatas);
199: } else {
200: debug("found %d insecure fingerprints in DNS",
201: fingerprints->rri_nrdatas);
1.1 jakob 202: }
203:
204: /* Initialize host key parameters */
205: if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
206: &hostkey_digest, &hostkey_digest_len, hostkey)) {
207: error("Error calculating host key fingerprint.");
1.5 jakob 208: freerrset(fingerprints);
1.8 jakob 209: return -1;
1.1 jakob 210: }
211:
1.8 jakob 212: if (fingerprints->rri_nrdatas)
213: *flags |= DNS_VERIFY_FOUND;
214:
1.13 stevesk 215: for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
1.1 jakob 216: /*
217: * Extract the key from the answer. Ignore any badly
1.4 jakob 218: * formatted fingerprints.
1.1 jakob 219: */
220: if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
221: &dnskey_digest, &dnskey_digest_len,
1.4 jakob 222: fingerprints->rri_rdatas[counter].rdi_data,
223: fingerprints->rri_rdatas[counter].rdi_length)) {
1.1 jakob 224: verbose("Error parsing fingerprint from DNS.");
225: continue;
226: }
227:
228: /* Check if the current key is the same as the given key */
229: if (hostkey_algorithm == dnskey_algorithm &&
230: hostkey_digest_type == dnskey_digest_type) {
231:
232: if (hostkey_digest_len == dnskey_digest_len &&
233: memcmp(hostkey_digest, dnskey_digest,
234: hostkey_digest_len) == 0) {
235:
1.8 jakob 236: *flags |= DNS_VERIFY_MATCH;
1.1 jakob 237: }
238: }
1.14 stevesk 239: xfree(dnskey_digest);
1.1 jakob 240: }
241:
1.14 stevesk 242: xfree(hostkey_digest); /* from key_fingerprint_raw() */
1.4 jakob 243: freerrset(fingerprints);
1.1 jakob 244:
1.8 jakob 245: if (*flags & DNS_VERIFY_FOUND)
246: if (*flags & DNS_VERIFY_MATCH)
247: debug("matching host key fingerprint found in DNS");
248: else
249: debug("mismatching host key fingerprint found in DNS");
250: else
251: debug("no host key fingerprint found in DNS");
1.1 jakob 252:
1.8 jakob 253: return 0;
1.1 jakob 254: }
255:
256: /*
257: * Export the fingerprint of a key as a DNS resource record
258: */
259: int
1.8 jakob 260: export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic)
1.1 jakob 261: {
262: u_int8_t rdata_pubkey_algorithm = 0;
1.3 jakob 263: u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
1.1 jakob 264: u_char *rdata_digest;
265: u_int rdata_digest_len;
266:
1.12 djm 267: u_int i;
1.1 jakob 268: int success = 0;
269:
270: if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
1.16 ! stevesk 271: &rdata_digest, &rdata_digest_len, key)) {
1.1 jakob 272:
273: if (generic)
274: fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
275: DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
276: rdata_pubkey_algorithm, rdata_digest_type);
277: else
278: fprintf(f, "%s IN SSHFP %d %d ", hostname,
279: rdata_pubkey_algorithm, rdata_digest_type);
280:
281: for (i = 0; i < rdata_digest_len; i++)
282: fprintf(f, "%02x", rdata_digest[i]);
283: fprintf(f, "\n");
1.14 stevesk 284: xfree(rdata_digest); /* from key_fingerprint_raw() */
1.1 jakob 285: success = 1;
286: } else {
1.16 ! stevesk 287: error("export_dns_rr: unsupported algorithm");
1.1 jakob 288: }
289:
290: return success;
291: }
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