Annotation of src/usr.bin/ssh/dns.c, Revision 1.27
1.27 ! djm 1: /* $OpenBSD: dns.c,v 1.26 2010/02/26 20:29:54 djm 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: */
1.20 stevesk 27:
28: #include <sys/types.h>
29: #include <sys/socket.h>
1.1 jakob 30:
31: #include <netdb.h>
1.22 stevesk 32: #include <stdio.h>
1.21 stevesk 33: #include <string.h>
1.1 jakob 34:
35: #include "xmalloc.h"
36: #include "key.h"
37: #include "dns.h"
38: #include "log.h"
39:
40: static const char *errset_text[] = {
41: "success", /* 0 ERRSET_SUCCESS */
42: "out of memory", /* 1 ERRSET_NOMEMORY */
43: "general failure", /* 2 ERRSET_FAIL */
44: "invalid parameter", /* 3 ERRSET_INVAL */
45: "name does not exist", /* 4 ERRSET_NONAME */
46: "data does not exist", /* 5 ERRSET_NODATA */
47: };
48:
49: static const char *
1.10 avsm 50: dns_result_totext(unsigned int res)
1.1 jakob 51: {
1.10 avsm 52: switch (res) {
1.1 jakob 53: case ERRSET_SUCCESS:
54: return errset_text[ERRSET_SUCCESS];
55: case ERRSET_NOMEMORY:
56: return errset_text[ERRSET_NOMEMORY];
57: case ERRSET_FAIL:
58: return errset_text[ERRSET_FAIL];
59: case ERRSET_INVAL:
60: return errset_text[ERRSET_INVAL];
61: case ERRSET_NONAME:
62: return errset_text[ERRSET_NONAME];
63: case ERRSET_NODATA:
64: return errset_text[ERRSET_NODATA];
65: default:
66: return "unknown error";
67: }
68: }
69:
70: /*
71: * Read SSHFP parameters from key buffer.
72: */
73: static int
74: dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
1.26 djm 75: u_char **digest, u_int *digest_len, Key *key)
1.1 jakob 76: {
77: int success = 0;
78:
79: switch (key->type) {
80: case KEY_RSA:
1.3 jakob 81: *algorithm = SSHFP_KEY_RSA;
1.1 jakob 82: break;
83: case KEY_DSA:
1.3 jakob 84: *algorithm = SSHFP_KEY_DSA;
1.1 jakob 85: break;
1.27 ! djm 86: /* XXX KEY_ECDSA */
1.1 jakob 87: default:
1.14 stevesk 88: *algorithm = SSHFP_KEY_RESERVED; /* 0 */
1.1 jakob 89: }
90:
91: if (*algorithm) {
1.3 jakob 92: *digest_type = SSHFP_HASH_SHA1;
1.1 jakob 93: *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
1.14 stevesk 94: if (*digest == NULL)
95: fatal("dns_read_key: null from key_fingerprint_raw()");
1.1 jakob 96: success = 1;
97: } else {
1.3 jakob 98: *digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 99: *digest = NULL;
100: *digest_len = 0;
101: success = 0;
102: }
103:
104: return success;
105: }
106:
107: /*
108: * Read SSHFP parameters from rdata buffer.
109: */
110: static int
111: dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
112: u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
113: {
114: int success = 0;
115:
1.3 jakob 116: *algorithm = SSHFP_KEY_RESERVED;
117: *digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 118:
119: if (rdata_len >= 2) {
120: *algorithm = rdata[0];
121: *digest_type = rdata[1];
122: *digest_len = rdata_len - 2;
123:
124: if (*digest_len > 0) {
125: *digest = (u_char *) xmalloc(*digest_len);
126: memcpy(*digest, rdata + 2, *digest_len);
127: } else {
1.18 deraadt 128: *digest = (u_char *)xstrdup("");
1.1 jakob 129: }
130:
131: success = 1;
132: }
133:
134: return success;
135: }
136:
1.11 jakob 137: /*
138: * Check if hostname is numerical.
139: * Returns -1 if hostname is numeric, 0 otherwise
140: */
141: static int
142: is_numeric_hostname(const char *hostname)
143: {
144: struct addrinfo hints, *ai;
145:
1.25 dtucker 146: /*
147: * We shouldn't ever get a null host but if we do then log an error
148: * and return -1 which stops DNS key fingerprint processing.
149: */
150: if (hostname == NULL) {
151: error("is_numeric_hostname called with NULL hostname");
152: return -1;
153: }
154:
1.11 jakob 155: memset(&hints, 0, sizeof(hints));
156: hints.ai_socktype = SOCK_DGRAM;
157: hints.ai_flags = AI_NUMERICHOST;
158:
1.25 dtucker 159: if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
1.11 jakob 160: freeaddrinfo(ai);
161: return -1;
162: }
163:
164: return 0;
165: }
1.1 jakob 166:
167: /*
168: * Verify the given hostname, address and host key using DNS.
1.9 djm 169: * Returns 0 if lookup succeeds, -1 otherwise
1.1 jakob 170: */
171: int
172: verify_host_key_dns(const char *hostname, struct sockaddr *address,
1.26 djm 173: Key *hostkey, int *flags)
1.1 jakob 174: {
1.12 djm 175: u_int counter;
1.1 jakob 176: int result;
1.4 jakob 177: struct rrsetinfo *fingerprints = NULL;
1.1 jakob 178:
179: u_int8_t hostkey_algorithm;
180: u_int8_t hostkey_digest_type;
181: u_char *hostkey_digest;
182: u_int hostkey_digest_len;
183:
184: u_int8_t dnskey_algorithm;
185: u_int8_t dnskey_digest_type;
186: u_char *dnskey_digest;
187: u_int dnskey_digest_len;
188:
1.8 jakob 189: *flags = 0;
1.1 jakob 190:
1.16 stevesk 191: debug3("verify_host_key_dns");
1.1 jakob 192: if (hostkey == NULL)
193: fatal("No key to look up!");
1.11 jakob 194:
195: if (is_numeric_hostname(hostname)) {
196: debug("skipped DNS lookup for numerical hostname");
197: return -1;
198: }
1.1 jakob 199:
200: result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
1.4 jakob 201: DNS_RDATATYPE_SSHFP, 0, &fingerprints);
1.1 jakob 202: if (result) {
203: verbose("DNS lookup error: %s", dns_result_totext(result));
1.8 jakob 204: return -1;
1.1 jakob 205: }
206:
1.8 jakob 207: if (fingerprints->rri_flags & RRSET_VALIDATED) {
208: *flags |= DNS_VERIFY_SECURE;
209: debug("found %d secure fingerprints in DNS",
210: fingerprints->rri_nrdatas);
211: } else {
212: debug("found %d insecure fingerprints in DNS",
213: fingerprints->rri_nrdatas);
1.1 jakob 214: }
215:
216: /* Initialize host key parameters */
217: if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
218: &hostkey_digest, &hostkey_digest_len, hostkey)) {
219: error("Error calculating host key fingerprint.");
1.5 jakob 220: freerrset(fingerprints);
1.8 jakob 221: return -1;
1.1 jakob 222: }
223:
1.8 jakob 224: if (fingerprints->rri_nrdatas)
225: *flags |= DNS_VERIFY_FOUND;
226:
1.24 stevesk 227: for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
1.1 jakob 228: /*
229: * Extract the key from the answer. Ignore any badly
1.4 jakob 230: * formatted fingerprints.
1.1 jakob 231: */
232: if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
233: &dnskey_digest, &dnskey_digest_len,
1.4 jakob 234: fingerprints->rri_rdatas[counter].rdi_data,
235: fingerprints->rri_rdatas[counter].rdi_length)) {
1.1 jakob 236: verbose("Error parsing fingerprint from DNS.");
237: continue;
238: }
239:
240: /* Check if the current key is the same as the given key */
241: if (hostkey_algorithm == dnskey_algorithm &&
242: hostkey_digest_type == dnskey_digest_type) {
243:
244: if (hostkey_digest_len == dnskey_digest_len &&
245: memcmp(hostkey_digest, dnskey_digest,
246: hostkey_digest_len) == 0) {
247:
1.8 jakob 248: *flags |= DNS_VERIFY_MATCH;
1.1 jakob 249: }
250: }
1.14 stevesk 251: xfree(dnskey_digest);
1.1 jakob 252: }
253:
1.14 stevesk 254: xfree(hostkey_digest); /* from key_fingerprint_raw() */
1.4 jakob 255: freerrset(fingerprints);
1.1 jakob 256:
1.8 jakob 257: if (*flags & DNS_VERIFY_FOUND)
258: if (*flags & DNS_VERIFY_MATCH)
259: debug("matching host key fingerprint found in DNS");
260: else
261: debug("mismatching host key fingerprint found in DNS");
262: else
263: debug("no host key fingerprint found in DNS");
1.1 jakob 264:
1.8 jakob 265: return 0;
1.1 jakob 266: }
267:
268: /*
269: * Export the fingerprint of a key as a DNS resource record
270: */
271: int
1.26 djm 272: export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
1.1 jakob 273: {
274: u_int8_t rdata_pubkey_algorithm = 0;
1.3 jakob 275: u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
1.1 jakob 276: u_char *rdata_digest;
277: u_int rdata_digest_len;
278:
1.12 djm 279: u_int i;
1.1 jakob 280: int success = 0;
281:
282: if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
1.16 stevesk 283: &rdata_digest, &rdata_digest_len, key)) {
1.1 jakob 284:
285: if (generic)
286: fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
287: DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
288: rdata_pubkey_algorithm, rdata_digest_type);
289: else
290: fprintf(f, "%s IN SSHFP %d %d ", hostname,
291: rdata_pubkey_algorithm, rdata_digest_type);
292:
293: for (i = 0; i < rdata_digest_len; i++)
294: fprintf(f, "%02x", rdata_digest[i]);
295: fprintf(f, "\n");
1.14 stevesk 296: xfree(rdata_digest); /* from key_fingerprint_raw() */
1.1 jakob 297: success = 1;
298: } else {
1.16 stevesk 299: error("export_dns_rr: unsupported algorithm");
1.1 jakob 300: }
301:
302: return success;
303: }
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