Annotation of src/usr.bin/ssh/dns.c, Revision 1.40
1.40 ! dtucker 1: /* $OpenBSD: dns.c,v 1.39 2020/10/18 11:32:01 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>
1.40 ! dtucker 32: #include <stdarg.h>
1.22 stevesk 33: #include <stdio.h>
1.21 stevesk 34: #include <string.h>
1.31 djm 35: #include <stdlib.h>
1.1 jakob 36:
37: #include "xmalloc.h"
1.33 djm 38: #include "sshkey.h"
39: #include "ssherr.h"
1.1 jakob 40: #include "dns.h"
41: #include "log.h"
1.32 djm 42: #include "digest.h"
1.1 jakob 43:
44: static const char *errset_text[] = {
45: "success", /* 0 ERRSET_SUCCESS */
46: "out of memory", /* 1 ERRSET_NOMEMORY */
47: "general failure", /* 2 ERRSET_FAIL */
48: "invalid parameter", /* 3 ERRSET_INVAL */
49: "name does not exist", /* 4 ERRSET_NONAME */
50: "data does not exist", /* 5 ERRSET_NODATA */
51: };
52:
53: static const char *
1.10 avsm 54: dns_result_totext(unsigned int res)
1.1 jakob 55: {
1.10 avsm 56: switch (res) {
1.1 jakob 57: case ERRSET_SUCCESS:
58: return errset_text[ERRSET_SUCCESS];
59: case ERRSET_NOMEMORY:
60: return errset_text[ERRSET_NOMEMORY];
61: case ERRSET_FAIL:
62: return errset_text[ERRSET_FAIL];
63: case ERRSET_INVAL:
64: return errset_text[ERRSET_INVAL];
65: case ERRSET_NONAME:
66: return errset_text[ERRSET_NONAME];
67: case ERRSET_NODATA:
68: return errset_text[ERRSET_NODATA];
69: default:
70: return "unknown error";
71: }
72: }
73:
74: /*
75: * Read SSHFP parameters from key buffer.
76: */
77: static int
78: dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
1.33 djm 79: u_char **digest, size_t *digest_len, struct sshkey *key)
1.1 jakob 80: {
1.33 djm 81: int r, success = 0;
1.32 djm 82: int fp_alg = -1;
1.1 jakob 83:
84: switch (key->type) {
85: case KEY_RSA:
1.3 jakob 86: *algorithm = SSHFP_KEY_RSA;
1.28 djm 87: if (!*digest_type)
88: *digest_type = SSHFP_HASH_SHA1;
1.1 jakob 89: break;
90: case KEY_DSA:
1.3 jakob 91: *algorithm = SSHFP_KEY_DSA;
1.28 djm 92: if (!*digest_type)
93: *digest_type = SSHFP_HASH_SHA1;
94: break;
95: case KEY_ECDSA:
96: *algorithm = SSHFP_KEY_ECDSA;
1.30 logan 97: if (!*digest_type)
98: *digest_type = SSHFP_HASH_SHA256;
99: break;
100: case KEY_ED25519:
101: *algorithm = SSHFP_KEY_ED25519;
1.38 markus 102: if (!*digest_type)
103: *digest_type = SSHFP_HASH_SHA256;
104: break;
105: case KEY_XMSS:
106: *algorithm = SSHFP_KEY_XMSS;
1.28 djm 107: if (!*digest_type)
108: *digest_type = SSHFP_HASH_SHA256;
1.1 jakob 109: break;
110: default:
1.14 stevesk 111: *algorithm = SSHFP_KEY_RESERVED; /* 0 */
1.28 djm 112: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
113: }
114:
115: switch (*digest_type) {
116: case SSHFP_HASH_SHA1:
1.32 djm 117: fp_alg = SSH_DIGEST_SHA1;
1.28 djm 118: break;
119: case SSHFP_HASH_SHA256:
1.32 djm 120: fp_alg = SSH_DIGEST_SHA256;
1.28 djm 121: break;
122: default:
123: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
1.1 jakob 124: }
125:
1.28 djm 126: if (*algorithm && *digest_type) {
1.33 djm 127: if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
128: digest_len)) != 0)
1.39 djm 129: fatal_fr(r, "sshkey_fingerprint_raw");
1.1 jakob 130: success = 1;
131: } else {
132: *digest = NULL;
133: *digest_len = 0;
134: success = 0;
135: }
136:
137: return success;
138: }
139:
140: /*
141: * Read SSHFP parameters from rdata buffer.
142: */
143: static int
144: dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
1.33 djm 145: u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
1.1 jakob 146: {
147: int success = 0;
148:
1.3 jakob 149: *algorithm = SSHFP_KEY_RESERVED;
150: *digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 151:
152: if (rdata_len >= 2) {
153: *algorithm = rdata[0];
154: *digest_type = rdata[1];
155: *digest_len = rdata_len - 2;
156:
157: if (*digest_len > 0) {
1.35 deraadt 158: *digest = xmalloc(*digest_len);
1.1 jakob 159: memcpy(*digest, rdata + 2, *digest_len);
160: } else {
1.18 deraadt 161: *digest = (u_char *)xstrdup("");
1.1 jakob 162: }
163:
164: success = 1;
165: }
166:
167: return success;
168: }
169:
1.11 jakob 170: /*
171: * Check if hostname is numerical.
172: * Returns -1 if hostname is numeric, 0 otherwise
173: */
174: static int
175: is_numeric_hostname(const char *hostname)
176: {
177: struct addrinfo hints, *ai;
178:
1.25 dtucker 179: /*
180: * We shouldn't ever get a null host but if we do then log an error
181: * and return -1 which stops DNS key fingerprint processing.
182: */
183: if (hostname == NULL) {
184: error("is_numeric_hostname called with NULL hostname");
185: return -1;
186: }
187:
1.11 jakob 188: memset(&hints, 0, sizeof(hints));
189: hints.ai_socktype = SOCK_DGRAM;
190: hints.ai_flags = AI_NUMERICHOST;
191:
1.25 dtucker 192: if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
1.11 jakob 193: freeaddrinfo(ai);
194: return -1;
195: }
196:
197: return 0;
198: }
1.1 jakob 199:
200: /*
201: * Verify the given hostname, address and host key using DNS.
1.9 djm 202: * Returns 0 if lookup succeeds, -1 otherwise
1.1 jakob 203: */
204: int
205: verify_host_key_dns(const char *hostname, struct sockaddr *address,
1.33 djm 206: struct sshkey *hostkey, int *flags)
1.1 jakob 207: {
1.12 djm 208: u_int counter;
1.1 jakob 209: int result;
1.4 jakob 210: struct rrsetinfo *fingerprints = NULL;
1.1 jakob 211:
212: u_int8_t hostkey_algorithm;
1.28 djm 213: u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 214: u_char *hostkey_digest;
1.33 djm 215: size_t hostkey_digest_len;
1.1 jakob 216:
217: u_int8_t dnskey_algorithm;
218: u_int8_t dnskey_digest_type;
219: u_char *dnskey_digest;
1.33 djm 220: size_t dnskey_digest_len;
1.1 jakob 221:
1.8 jakob 222: *flags = 0;
1.1 jakob 223:
1.16 stevesk 224: debug3("verify_host_key_dns");
1.1 jakob 225: if (hostkey == NULL)
226: fatal("No key to look up!");
1.11 jakob 227:
228: if (is_numeric_hostname(hostname)) {
229: debug("skipped DNS lookup for numerical hostname");
230: return -1;
231: }
1.1 jakob 232:
233: result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
1.4 jakob 234: DNS_RDATATYPE_SSHFP, 0, &fingerprints);
1.1 jakob 235: if (result) {
236: verbose("DNS lookup error: %s", dns_result_totext(result));
1.8 jakob 237: return -1;
1.1 jakob 238: }
239:
1.8 jakob 240: if (fingerprints->rri_flags & RRSET_VALIDATED) {
241: *flags |= DNS_VERIFY_SECURE;
242: debug("found %d secure fingerprints in DNS",
243: fingerprints->rri_nrdatas);
244: } else {
245: debug("found %d insecure fingerprints in DNS",
246: fingerprints->rri_nrdatas);
1.1 jakob 247: }
248:
1.28 djm 249: /* Initialize default host key parameters */
1.1 jakob 250: if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
251: &hostkey_digest, &hostkey_digest_len, hostkey)) {
252: error("Error calculating host key fingerprint.");
1.5 jakob 253: freerrset(fingerprints);
1.8 jakob 254: return -1;
1.1 jakob 255: }
256:
1.8 jakob 257: if (fingerprints->rri_nrdatas)
258: *flags |= DNS_VERIFY_FOUND;
259:
1.24 stevesk 260: for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
1.1 jakob 261: /*
262: * Extract the key from the answer. Ignore any badly
1.4 jakob 263: * formatted fingerprints.
1.1 jakob 264: */
265: if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
266: &dnskey_digest, &dnskey_digest_len,
1.4 jakob 267: fingerprints->rri_rdatas[counter].rdi_data,
268: fingerprints->rri_rdatas[counter].rdi_length)) {
1.1 jakob 269: verbose("Error parsing fingerprint from DNS.");
270: continue;
271: }
272:
1.28 djm 273: if (hostkey_digest_type != dnskey_digest_type) {
274: hostkey_digest_type = dnskey_digest_type;
1.29 djm 275: free(hostkey_digest);
1.28 djm 276:
277: /* Initialize host key parameters */
278: if (!dns_read_key(&hostkey_algorithm,
279: &hostkey_digest_type, &hostkey_digest,
280: &hostkey_digest_len, hostkey)) {
281: error("Error calculating key fingerprint.");
282: freerrset(fingerprints);
283: return -1;
284: }
285: }
286:
1.1 jakob 287: /* Check if the current key is the same as the given key */
288: if (hostkey_algorithm == dnskey_algorithm &&
289: hostkey_digest_type == dnskey_digest_type) {
290: if (hostkey_digest_len == dnskey_digest_len &&
1.28 djm 291: timingsafe_bcmp(hostkey_digest, dnskey_digest,
292: hostkey_digest_len) == 0)
1.8 jakob 293: *flags |= DNS_VERIFY_MATCH;
1.1 jakob 294: }
1.29 djm 295: free(dnskey_digest);
1.1 jakob 296: }
297:
1.37 djm 298: free(hostkey_digest); /* from sshkey_fingerprint_raw() */
299: freerrset(fingerprints);
300:
301: if (*flags & DNS_VERIFY_FOUND)
1.8 jakob 302: if (*flags & DNS_VERIFY_MATCH)
303: debug("matching host key fingerprint found in DNS");
304: else
305: debug("mismatching host key fingerprint found in DNS");
1.37 djm 306: else
1.8 jakob 307: debug("no host key fingerprint found in DNS");
1.1 jakob 308:
1.8 jakob 309: return 0;
1.1 jakob 310: }
311:
312: /*
313: * Export the fingerprint of a key as a DNS resource record
314: */
315: int
1.33 djm 316: export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
1.1 jakob 317: {
318: u_int8_t rdata_pubkey_algorithm = 0;
1.28 djm 319: u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
320: u_int8_t dtype;
1.1 jakob 321: u_char *rdata_digest;
1.33 djm 322: size_t i, rdata_digest_len;
1.1 jakob 323: int success = 0;
324:
1.28 djm 325: for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
326: rdata_digest_type = dtype;
327: if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
328: &rdata_digest, &rdata_digest_len, key)) {
329: if (generic) {
1.33 djm 330: fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
1.28 djm 331: hostname, DNS_RDATATYPE_SSHFP,
332: 2 + rdata_digest_len,
333: rdata_pubkey_algorithm, rdata_digest_type);
334: } else {
335: fprintf(f, "%s IN SSHFP %d %d ", hostname,
336: rdata_pubkey_algorithm, rdata_digest_type);
337: }
338: for (i = 0; i < rdata_digest_len; i++)
339: fprintf(f, "%02x", rdata_digest[i]);
340: fprintf(f, "\n");
1.34 djm 341: free(rdata_digest); /* from sshkey_fingerprint_raw() */
1.28 djm 342: success = 1;
343: }
344: }
1.1 jakob 345:
1.28 djm 346: /* No SSHFP record was generated at all */
347: if (success == 0) {
1.39 djm 348: error_f("unsupported algorithm and/or digest_type");
1.1 jakob 349: }
350:
351: return success;
352: }
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