Annotation of src/usr.bin/ssh/dns.c, Revision 1.30
1.30 ! logan 1: /* $OpenBSD: dns.c,v 1.29 2013/05/17 00:13:13 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;
1.28 djm 78: enum fp_type fp_type = 0;
1.1 jakob 79:
80: switch (key->type) {
81: case KEY_RSA:
1.3 jakob 82: *algorithm = SSHFP_KEY_RSA;
1.28 djm 83: if (!*digest_type)
84: *digest_type = SSHFP_HASH_SHA1;
1.1 jakob 85: break;
86: case KEY_DSA:
1.3 jakob 87: *algorithm = SSHFP_KEY_DSA;
1.28 djm 88: if (!*digest_type)
89: *digest_type = SSHFP_HASH_SHA1;
90: break;
91: case KEY_ECDSA:
92: *algorithm = SSHFP_KEY_ECDSA;
1.30 ! logan 93: if (!*digest_type)
! 94: *digest_type = SSHFP_HASH_SHA256;
! 95: break;
! 96: case KEY_ED25519:
! 97: *algorithm = SSHFP_KEY_ED25519;
1.28 djm 98: if (!*digest_type)
99: *digest_type = SSHFP_HASH_SHA256;
1.1 jakob 100: break;
101: default:
1.14 stevesk 102: *algorithm = SSHFP_KEY_RESERVED; /* 0 */
1.28 djm 103: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
104: }
105:
106: switch (*digest_type) {
107: case SSHFP_HASH_SHA1:
108: fp_type = SSH_FP_SHA1;
109: break;
110: case SSHFP_HASH_SHA256:
111: fp_type = SSH_FP_SHA256;
112: break;
113: default:
114: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
1.1 jakob 115: }
116:
1.28 djm 117: if (*algorithm && *digest_type) {
118: *digest = key_fingerprint_raw(key, fp_type, digest_len);
1.14 stevesk 119: if (*digest == NULL)
120: fatal("dns_read_key: null from key_fingerprint_raw()");
1.1 jakob 121: success = 1;
122: } else {
123: *digest = NULL;
124: *digest_len = 0;
125: success = 0;
126: }
127:
128: return success;
129: }
130:
131: /*
132: * Read SSHFP parameters from rdata buffer.
133: */
134: static int
135: dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
136: u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
137: {
138: int success = 0;
139:
1.3 jakob 140: *algorithm = SSHFP_KEY_RESERVED;
141: *digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 142:
143: if (rdata_len >= 2) {
144: *algorithm = rdata[0];
145: *digest_type = rdata[1];
146: *digest_len = rdata_len - 2;
147:
148: if (*digest_len > 0) {
149: *digest = (u_char *) xmalloc(*digest_len);
150: memcpy(*digest, rdata + 2, *digest_len);
151: } else {
1.18 deraadt 152: *digest = (u_char *)xstrdup("");
1.1 jakob 153: }
154:
155: success = 1;
156: }
157:
158: return success;
159: }
160:
1.11 jakob 161: /*
162: * Check if hostname is numerical.
163: * Returns -1 if hostname is numeric, 0 otherwise
164: */
165: static int
166: is_numeric_hostname(const char *hostname)
167: {
168: struct addrinfo hints, *ai;
169:
1.25 dtucker 170: /*
171: * We shouldn't ever get a null host but if we do then log an error
172: * and return -1 which stops DNS key fingerprint processing.
173: */
174: if (hostname == NULL) {
175: error("is_numeric_hostname called with NULL hostname");
176: return -1;
177: }
178:
1.11 jakob 179: memset(&hints, 0, sizeof(hints));
180: hints.ai_socktype = SOCK_DGRAM;
181: hints.ai_flags = AI_NUMERICHOST;
182:
1.25 dtucker 183: if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
1.11 jakob 184: freeaddrinfo(ai);
185: return -1;
186: }
187:
188: return 0;
189: }
1.1 jakob 190:
191: /*
192: * Verify the given hostname, address and host key using DNS.
1.9 djm 193: * Returns 0 if lookup succeeds, -1 otherwise
1.1 jakob 194: */
195: int
196: verify_host_key_dns(const char *hostname, struct sockaddr *address,
1.26 djm 197: Key *hostkey, int *flags)
1.1 jakob 198: {
1.12 djm 199: u_int counter;
1.1 jakob 200: int result;
1.4 jakob 201: struct rrsetinfo *fingerprints = NULL;
1.1 jakob 202:
203: u_int8_t hostkey_algorithm;
1.28 djm 204: u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 205: u_char *hostkey_digest;
206: u_int hostkey_digest_len;
207:
208: u_int8_t dnskey_algorithm;
209: u_int8_t dnskey_digest_type;
210: u_char *dnskey_digest;
211: u_int dnskey_digest_len;
212:
1.8 jakob 213: *flags = 0;
1.1 jakob 214:
1.16 stevesk 215: debug3("verify_host_key_dns");
1.1 jakob 216: if (hostkey == NULL)
217: fatal("No key to look up!");
1.11 jakob 218:
219: if (is_numeric_hostname(hostname)) {
220: debug("skipped DNS lookup for numerical hostname");
221: return -1;
222: }
1.1 jakob 223:
224: result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
1.4 jakob 225: DNS_RDATATYPE_SSHFP, 0, &fingerprints);
1.1 jakob 226: if (result) {
227: verbose("DNS lookup error: %s", dns_result_totext(result));
1.8 jakob 228: return -1;
1.1 jakob 229: }
230:
1.8 jakob 231: if (fingerprints->rri_flags & RRSET_VALIDATED) {
232: *flags |= DNS_VERIFY_SECURE;
233: debug("found %d secure fingerprints in DNS",
234: fingerprints->rri_nrdatas);
235: } else {
236: debug("found %d insecure fingerprints in DNS",
237: fingerprints->rri_nrdatas);
1.1 jakob 238: }
239:
1.28 djm 240: /* Initialize default host key parameters */
1.1 jakob 241: if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
242: &hostkey_digest, &hostkey_digest_len, hostkey)) {
243: error("Error calculating host key fingerprint.");
1.5 jakob 244: freerrset(fingerprints);
1.8 jakob 245: return -1;
1.1 jakob 246: }
247:
1.8 jakob 248: if (fingerprints->rri_nrdatas)
249: *flags |= DNS_VERIFY_FOUND;
250:
1.24 stevesk 251: for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
1.1 jakob 252: /*
253: * Extract the key from the answer. Ignore any badly
1.4 jakob 254: * formatted fingerprints.
1.1 jakob 255: */
256: if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
257: &dnskey_digest, &dnskey_digest_len,
1.4 jakob 258: fingerprints->rri_rdatas[counter].rdi_data,
259: fingerprints->rri_rdatas[counter].rdi_length)) {
1.1 jakob 260: verbose("Error parsing fingerprint from DNS.");
261: continue;
262: }
263:
1.28 djm 264: if (hostkey_digest_type != dnskey_digest_type) {
265: hostkey_digest_type = dnskey_digest_type;
1.29 djm 266: free(hostkey_digest);
1.28 djm 267:
268: /* Initialize host key parameters */
269: if (!dns_read_key(&hostkey_algorithm,
270: &hostkey_digest_type, &hostkey_digest,
271: &hostkey_digest_len, hostkey)) {
272: error("Error calculating key fingerprint.");
273: freerrset(fingerprints);
274: return -1;
275: }
276: }
277:
1.1 jakob 278: /* Check if the current key is the same as the given key */
279: if (hostkey_algorithm == dnskey_algorithm &&
280: hostkey_digest_type == dnskey_digest_type) {
281: if (hostkey_digest_len == dnskey_digest_len &&
1.28 djm 282: timingsafe_bcmp(hostkey_digest, dnskey_digest,
283: hostkey_digest_len) == 0)
1.8 jakob 284: *flags |= DNS_VERIFY_MATCH;
1.1 jakob 285: }
1.29 djm 286: free(dnskey_digest);
1.1 jakob 287: }
288:
1.29 djm 289: free(hostkey_digest); /* from key_fingerprint_raw() */
1.4 jakob 290: freerrset(fingerprints);
1.1 jakob 291:
1.8 jakob 292: if (*flags & DNS_VERIFY_FOUND)
293: if (*flags & DNS_VERIFY_MATCH)
294: debug("matching host key fingerprint found in DNS");
295: else
296: debug("mismatching host key fingerprint found in DNS");
297: else
298: debug("no host key fingerprint found in DNS");
1.1 jakob 299:
1.8 jakob 300: return 0;
1.1 jakob 301: }
302:
303: /*
304: * Export the fingerprint of a key as a DNS resource record
305: */
306: int
1.26 djm 307: export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
1.1 jakob 308: {
309: u_int8_t rdata_pubkey_algorithm = 0;
1.28 djm 310: u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
311: u_int8_t dtype;
1.1 jakob 312: u_char *rdata_digest;
1.28 djm 313: u_int i, rdata_digest_len;
1.1 jakob 314: int success = 0;
315:
1.28 djm 316: for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
317: rdata_digest_type = dtype;
318: if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
319: &rdata_digest, &rdata_digest_len, key)) {
320: if (generic) {
321: fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ",
322: hostname, DNS_RDATATYPE_SSHFP,
323: 2 + rdata_digest_len,
324: rdata_pubkey_algorithm, rdata_digest_type);
325: } else {
326: fprintf(f, "%s IN SSHFP %d %d ", hostname,
327: rdata_pubkey_algorithm, rdata_digest_type);
328: }
329: for (i = 0; i < rdata_digest_len; i++)
330: fprintf(f, "%02x", rdata_digest[i]);
331: fprintf(f, "\n");
1.29 djm 332: free(rdata_digest); /* from key_fingerprint_raw() */
1.28 djm 333: success = 1;
334: }
335: }
1.1 jakob 336:
1.28 djm 337: /* No SSHFP record was generated at all */
338: if (success == 0) {
339: error("%s: unsupported algorithm and/or digest_type", __func__);
1.1 jakob 340: }
341:
342: return success;
343: }
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