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1 | /* $OpenBSD: dns.c,v 1.11 2005/04/20 10:05:45 jakob Exp $ */ | |
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 | ||
29 | #include "includes.h" | |
30 | ||
31 | #include <openssl/bn.h> | |
32 | #ifdef LWRES | |
33 | #include <lwres/netdb.h> | |
34 | #include <dns/result.h> | |
35 | #else /* LWRES */ | |
36 | #include <netdb.h> | |
37 | #endif /* LWRES */ | |
38 | ||
39 | #include "xmalloc.h" | |
40 | #include "key.h" | |
41 | #include "dns.h" | |
42 | #include "log.h" | |
43 | #include "uuencode.h" | |
44 | ||
45 | extern char *__progname; | |
46 | RCSID("$OpenBSD: dns.c,v 1.11 2005/04/20 10:05:45 jakob Exp $"); | |
47 | ||
48 | #ifndef LWRES | |
49 | static const char *errset_text[] = { | |
50 | "success", /* 0 ERRSET_SUCCESS */ | |
51 | "out of memory", /* 1 ERRSET_NOMEMORY */ | |
52 | "general failure", /* 2 ERRSET_FAIL */ | |
53 | "invalid parameter", /* 3 ERRSET_INVAL */ | |
54 | "name does not exist", /* 4 ERRSET_NONAME */ | |
55 | "data does not exist", /* 5 ERRSET_NODATA */ | |
56 | }; | |
57 | ||
58 | static const char * | |
59 | dns_result_totext(unsigned int res) | |
60 | { | |
61 | switch (res) { | |
62 | case ERRSET_SUCCESS: | |
63 | return errset_text[ERRSET_SUCCESS]; | |
64 | case ERRSET_NOMEMORY: | |
65 | return errset_text[ERRSET_NOMEMORY]; | |
66 | case ERRSET_FAIL: | |
67 | return errset_text[ERRSET_FAIL]; | |
68 | case ERRSET_INVAL: | |
69 | return errset_text[ERRSET_INVAL]; | |
70 | case ERRSET_NONAME: | |
71 | return errset_text[ERRSET_NONAME]; | |
72 | case ERRSET_NODATA: | |
73 | return errset_text[ERRSET_NODATA]; | |
74 | default: | |
75 | return "unknown error"; | |
76 | } | |
77 | } | |
78 | #endif /* LWRES */ | |
79 | ||
80 | ||
81 | /* | |
82 | * Read SSHFP parameters from key buffer. | |
83 | */ | |
84 | static int | |
85 | dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type, | |
86 | u_char **digest, u_int *digest_len, const Key *key) | |
87 | { | |
88 | int success = 0; | |
89 | ||
90 | switch (key->type) { | |
91 | case KEY_RSA: | |
92 | *algorithm = SSHFP_KEY_RSA; | |
93 | break; | |
94 | case KEY_DSA: | |
95 | *algorithm = SSHFP_KEY_DSA; | |
96 | break; | |
97 | default: | |
98 | *algorithm = SSHFP_KEY_RESERVED; | |
99 | } | |
100 | ||
101 | if (*algorithm) { | |
102 | *digest_type = SSHFP_HASH_SHA1; | |
103 | *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len); | |
104 | success = 1; | |
105 | } else { | |
106 | *digest_type = SSHFP_HASH_RESERVED; | |
107 | *digest = NULL; | |
108 | *digest_len = 0; | |
109 | success = 0; | |
110 | } | |
111 | ||
112 | return success; | |
113 | } | |
114 | ||
115 | /* | |
116 | * Read SSHFP parameters from rdata buffer. | |
117 | */ | |
118 | static int | |
119 | dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, | |
120 | u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) | |
121 | { | |
122 | int success = 0; | |
123 | ||
124 | *algorithm = SSHFP_KEY_RESERVED; | |
125 | *digest_type = SSHFP_HASH_RESERVED; | |
126 | ||
127 | if (rdata_len >= 2) { | |
128 | *algorithm = rdata[0]; | |
129 | *digest_type = rdata[1]; | |
130 | *digest_len = rdata_len - 2; | |
131 | ||
132 | if (*digest_len > 0) { | |
133 | *digest = (u_char *) xmalloc(*digest_len); | |
134 | memcpy(*digest, rdata + 2, *digest_len); | |
135 | } else { | |
136 | *digest = NULL; | |
137 | } | |
138 | ||
139 | success = 1; | |
140 | } | |
141 | ||
142 | return success; | |
143 | } | |
144 | ||
145 | /* | |
146 | * Check if hostname is numerical. | |
147 | * Returns -1 if hostname is numeric, 0 otherwise | |
148 | */ | |
149 | static int | |
150 | is_numeric_hostname(const char *hostname) | |
151 | { | |
152 | struct addrinfo hints, *ai; | |
153 | ||
154 | memset(&hints, 0, sizeof(hints)); | |
155 | hints.ai_socktype = SOCK_DGRAM; | |
156 | hints.ai_flags = AI_NUMERICHOST; | |
157 | ||
158 | if (getaddrinfo(hostname, "0", &hints, &ai) == 0) { | |
159 | freeaddrinfo(ai); | |
160 | return -1; | |
161 | } | |
162 | ||
163 | return 0; | |
164 | } | |
165 | ||
166 | /* | |
167 | * Verify the given hostname, address and host key using DNS. | |
168 | * Returns 0 if lookup succeeds, -1 otherwise | |
169 | */ | |
170 | int | |
171 | verify_host_key_dns(const char *hostname, struct sockaddr *address, | |
172 | const Key *hostkey, int *flags) | |
173 | { | |
174 | int counter; | |
175 | int result; | |
176 | struct rrsetinfo *fingerprints = NULL; | |
177 | ||
178 | u_int8_t hostkey_algorithm; | |
179 | u_int8_t hostkey_digest_type; | |
180 | u_char *hostkey_digest; | |
181 | u_int hostkey_digest_len; | |
182 | ||
183 | u_int8_t dnskey_algorithm; | |
184 | u_int8_t dnskey_digest_type; | |
185 | u_char *dnskey_digest; | |
186 | u_int dnskey_digest_len; | |
187 | ||
188 | *flags = 0; | |
189 | ||
190 | debug3("verify_hostkey_dns"); | |
191 | if (hostkey == NULL) | |
192 | fatal("No key to look up!"); | |
193 | ||
194 | if (is_numeric_hostname(hostname)) { | |
195 | debug("skipped DNS lookup for numerical hostname"); | |
196 | return -1; | |
197 | } | |
198 | ||
199 | result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, | |
200 | DNS_RDATATYPE_SSHFP, 0, &fingerprints); | |
201 | if (result) { | |
202 | verbose("DNS lookup error: %s", dns_result_totext(result)); | |
203 | return -1; | |
204 | } | |
205 | ||
206 | if (fingerprints->rri_flags & RRSET_VALIDATED) { | |
207 | *flags |= DNS_VERIFY_SECURE; | |
208 | debug("found %d secure fingerprints in DNS", | |
209 | fingerprints->rri_nrdatas); | |
210 | } else { | |
211 | debug("found %d insecure fingerprints in DNS", | |
212 | fingerprints->rri_nrdatas); | |
213 | } | |
214 | ||
215 | /* Initialize host key parameters */ | |
216 | if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, | |
217 | &hostkey_digest, &hostkey_digest_len, hostkey)) { | |
218 | error("Error calculating host key fingerprint."); | |
219 | freerrset(fingerprints); | |
220 | return -1; | |
221 | } | |
222 | ||
223 | if (fingerprints->rri_nrdatas) | |
224 | *flags |= DNS_VERIFY_FOUND; | |
225 | ||
226 | for (counter = 0 ; counter < fingerprints->rri_nrdatas ; counter++) { | |
227 | /* | |
228 | * Extract the key from the answer. Ignore any badly | |
229 | * formatted fingerprints. | |
230 | */ | |
231 | if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, | |
232 | &dnskey_digest, &dnskey_digest_len, | |
233 | fingerprints->rri_rdatas[counter].rdi_data, | |
234 | fingerprints->rri_rdatas[counter].rdi_length)) { | |
235 | verbose("Error parsing fingerprint from DNS."); | |
236 | continue; | |
237 | } | |
238 | ||
239 | /* Check if the current key is the same as the given key */ | |
240 | if (hostkey_algorithm == dnskey_algorithm && | |
241 | hostkey_digest_type == dnskey_digest_type) { | |
242 | ||
243 | if (hostkey_digest_len == dnskey_digest_len && | |
244 | memcmp(hostkey_digest, dnskey_digest, | |
245 | hostkey_digest_len) == 0) { | |
246 | ||
247 | *flags |= DNS_VERIFY_MATCH; | |
248 | } | |
249 | } | |
250 | } | |
251 | ||
252 | freerrset(fingerprints); | |
253 | ||
254 | if (*flags & DNS_VERIFY_FOUND) | |
255 | if (*flags & DNS_VERIFY_MATCH) | |
256 | debug("matching host key fingerprint found in DNS"); | |
257 | else | |
258 | debug("mismatching host key fingerprint found in DNS"); | |
259 | else | |
260 | debug("no host key fingerprint found in DNS"); | |
261 | ||
262 | return 0; | |
263 | } | |
264 | ||
265 | ||
266 | /* | |
267 | * Export the fingerprint of a key as a DNS resource record | |
268 | */ | |
269 | int | |
270 | export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic) | |
271 | { | |
272 | u_int8_t rdata_pubkey_algorithm = 0; | |
273 | u_int8_t rdata_digest_type = SSHFP_HASH_SHA1; | |
274 | u_char *rdata_digest; | |
275 | u_int rdata_digest_len; | |
276 | ||
277 | int i; | |
278 | int success = 0; | |
279 | ||
280 | if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, | |
281 | &rdata_digest, &rdata_digest_len, key)) { | |
282 | ||
283 | if (generic) | |
284 | fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname, | |
285 | DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len, | |
286 | rdata_pubkey_algorithm, rdata_digest_type); | |
287 | else | |
288 | fprintf(f, "%s IN SSHFP %d %d ", hostname, | |
289 | rdata_pubkey_algorithm, rdata_digest_type); | |
290 | ||
291 | for (i = 0; i < rdata_digest_len; i++) | |
292 | fprintf(f, "%02x", rdata_digest[i]); | |
293 | fprintf(f, "\n"); | |
294 | success = 1; | |
295 | } else { | |
296 | error("dns_export_rr: unsupported algorithm"); | |
297 | } | |
298 | ||
299 | return success; | |
300 | } |