1 /* $NetBSD: get_host_realm.c,v 1.2 2017/01/28 21:31:49 christos Exp $ */
2
3 /*
4 * Copyright (c) 1997 - 2005 Kungliga Tekniska Högskolan
5 * (Royal Institute of Technology, Stockholm, Sweden).
6 * All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 *
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 *
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 *
19 * 3. Neither the name of the Institute nor the names of its contributors
20 * may be used to endorse or promote products derived from this software
21 * without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 */
35
36 #include "krb5_locl.h"
37 #include <krb5/resolve.h>
38
39 /* To automagically find the correct realm of a host (without
40 * [domain_realm] in krb5.conf) add a text record for your domain with
41 * the name of your realm, like this:
42 *
43 * _kerberos IN TXT "FOO.SE"
44 *
45 * The search is recursive, so you can add entries for specific
46 * hosts. To find the realm of host a.b.c, it first tries
47 * _kerberos.a.b.c, then _kerberos.b.c and so on.
48 *
49 * This method is described in draft-ietf-cat-krb-dns-locate-03.txt.
50 *
51 */
52
53 static int
copy_txt_to_realms(krb5_context context,const char * domain,struct rk_resource_record * head,krb5_realm ** realms)54 copy_txt_to_realms(krb5_context context,
55 const char *domain,
56 struct rk_resource_record *head,
57 krb5_realm **realms)
58 {
59 struct rk_resource_record *rr;
60 unsigned int n, i;
61
62 for(n = 0, rr = head; rr; rr = rr->next)
63 if (rr->type == rk_ns_t_txt)
64 ++n;
65
66 if (n == 0)
67 return -1;
68
69 *realms = malloc ((n + 1) * sizeof(krb5_realm));
70 if (*realms == NULL)
71 return krb5_enomem(context);;
72
73 for (i = 0; i < n + 1; ++i)
74 (*realms)[i] = NULL;
75
76 for (i = 0, rr = head; rr; rr = rr->next) {
77 if (rr->type == rk_ns_t_txt) {
78 char *tmp = NULL;
79 int invalid_tld = 1;
80
81 /* Check for a gTLD controlled interruption */
82 if (strcmp("Your DNS configuration needs immediate "
83 "attention see https://icann.org/namecollision",
84 rr->u.txt) != 0) {
85 invalid_tld = 0;
86 tmp = strdup(rr->u.txt);
87 }
88 if (tmp == NULL) {
89 for (i = 0; i < n; ++i)
90 free ((*realms)[i]);
91 free (*realms);
92 if (invalid_tld) {
93 krb5_warnx(context,
94 "Realm lookup failed: "
95 "Domain '%s' needs immediate attention "
96 "see https://icann.org/namecollision",
97 domain);
98 return KRB5_KDC_UNREACH;
99 }
100 return krb5_enomem(context);;
101 }
102 (*realms)[i] = tmp;
103 ++i;
104 }
105 }
106 return 0;
107 }
108
109 static int
dns_find_realm(krb5_context context,const char * domain,krb5_realm ** realms)110 dns_find_realm(krb5_context context,
111 const char *domain,
112 krb5_realm **realms)
113 {
114 static const char *default_labels[] = { "_kerberos", NULL };
115 char dom[MAXHOSTNAMELEN];
116 struct rk_dns_reply *r;
117 const char **labels;
118 char **config_labels;
119 int i, ret = 0;
120
121 config_labels = krb5_config_get_strings(context, NULL, "libdefaults",
122 "dns_lookup_realm_labels", NULL);
123 if(config_labels != NULL)
124 labels = (const char **)config_labels;
125 else
126 labels = default_labels;
127 if(*domain == '.')
128 domain++;
129 for (i = 0; labels[i] != NULL; i++) {
130 ret = snprintf(dom, sizeof(dom), "%s.%s.", labels[i], domain);
131 if(ret < 0 || (size_t)ret >= sizeof(dom)) {
132 ret = krb5_enomem(context);
133 goto out;
134 }
135 r = rk_dns_lookup(dom, "TXT");
136 if(r != NULL) {
137 ret = copy_txt_to_realms(context, domain, r->head, realms);
138 rk_dns_free_data(r);
139 if(ret == 0)
140 goto out;
141 }
142 }
143 krb5_set_error_message(context, KRB5_KDC_UNREACH,
144 "Realm lookup failed: "
145 "No DNS TXT record for %s",
146 domain);
147 ret = KRB5_KDC_UNREACH;
148 out:
149 if (config_labels)
150 krb5_config_free_strings(config_labels);
151 return ret;
152 }
153
154 /*
155 * Try to figure out what realms host in `domain' belong to from the
156 * configuration file.
157 */
158
159 static int
config_find_realm(krb5_context context,const char * domain,krb5_realm ** realms)160 config_find_realm(krb5_context context,
161 const char *domain,
162 krb5_realm **realms)
163 {
164 char **tmp = krb5_config_get_strings (context, NULL,
165 "domain_realm",
166 domain,
167 NULL);
168
169 if (tmp == NULL)
170 return -1;
171 *realms = tmp;
172 return 0;
173 }
174
175 /*
176 * This function assumes that `host' is a FQDN (and doesn't handle the
177 * special case of host == NULL either).
178 * Try to find mapping in the config file or DNS and it that fails,
179 * fall back to guessing
180 */
181
182 KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
_krb5_get_host_realm_int(krb5_context context,const char * host,krb5_boolean use_dns,krb5_realm ** realms)183 _krb5_get_host_realm_int(krb5_context context,
184 const char *host,
185 krb5_boolean use_dns,
186 krb5_realm **realms)
187 {
188 const char *p, *q;
189 const char *port;
190 krb5_boolean dns_locate_enable;
191 krb5_error_code ret = 0;
192
193 /* Strip off any trailing ":port" suffix. */
194 port = strchr(host, ':');
195 if (port != NULL) {
196 host = strndup(host, port - host);
197 if (host == NULL)
198 return krb5_enomem(context);
199 }
200
201 dns_locate_enable = krb5_config_get_bool_default(context, NULL, TRUE,
202 "libdefaults", "dns_lookup_realm", NULL);
203 for (p = host; p != NULL; p = strchr (p + 1, '.')) {
204 if (config_find_realm(context, p, realms) == 0) {
205 if (strcasecmp(*realms[0], "dns_locate") != 0)
206 break;
207 krb5_free_host_realm(context, *realms);
208 *realms = NULL;
209 if (!use_dns)
210 continue;
211 for (q = host; q != NULL; q = strchr(q + 1, '.'))
212 if (dns_find_realm(context, q, realms) == 0)
213 break;
214 if (q)
215 break;
216 } else if (use_dns && dns_locate_enable) {
217 if (dns_find_realm(context, p, realms) == 0)
218 break;
219 }
220 }
221
222 /*
223 * If 'p' is NULL, we did not find an explicit realm mapping in either the
224 * configuration file or DNS. Try the hostname suffix as a last resort.
225 *
226 * XXX: If we implement a KDC-specific variant of this function just for
227 * referrals, we could check whether we have a cross-realm TGT for the
228 * realm in question, and if not try the parent (loop again).
229 */
230 if (p == NULL) {
231 p = strchr(host, '.');
232 if (p != NULL) {
233 p++;
234 *realms = malloc(2 * sizeof(krb5_realm));
235 if (*realms != NULL &&
236 ((*realms)[0] = strdup(p)) != NULL) {
237 strupr((*realms)[0]);
238 (*realms)[1] = NULL;
239 } else {
240 free(*realms);
241 ret = krb5_enomem(context);
242 }
243 } else {
244 krb5_set_error_message(context, KRB5_ERR_HOST_REALM_UNKNOWN,
245 N_("unable to find realm of host %s", ""),
246 host);
247 ret = KRB5_ERR_HOST_REALM_UNKNOWN;
248 }
249 }
250
251 /* If 'port' is not NULL, we have a copy of 'host' to free. */
252 if (port)
253 free((void *)host);
254 return ret;
255 }
256
257 /*
258 * Return the realm(s) of `host' as a NULL-terminated list in
259 * `realms'. Free `realms' with krb5_free_host_realm().
260 */
261
262 KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
krb5_get_host_realm(krb5_context context,const char * targethost,krb5_realm ** realms)263 krb5_get_host_realm(krb5_context context,
264 const char *targethost,
265 krb5_realm **realms)
266 {
267 const char *host = targethost;
268 char hostname[MAXHOSTNAMELEN];
269 krb5_error_code ret;
270 int use_dns;
271
272 if (host == NULL) {
273 if (gethostname (hostname, sizeof(hostname))) {
274 *realms = NULL;
275 return errno;
276 }
277 host = hostname;
278 }
279
280 /*
281 * If our local hostname is without components, don't even try to dns.
282 */
283
284 use_dns = (strchr(host, '.') != NULL);
285
286 ret = _krb5_get_host_realm_int (context, host, use_dns, realms);
287 if (ret && targethost != NULL) {
288 /*
289 * If there was no realm mapping for the host (and we wasn't
290 * looking for ourself), guess at the local realm, maybe our
291 * KDC knows better then we do and we get a referral back.
292 */
293 ret = krb5_get_default_realms(context, realms);
294 if (ret) {
295 krb5_set_error_message(context, KRB5_ERR_HOST_REALM_UNKNOWN,
296 N_("Unable to find realm of host %s", ""),
297 host);
298 return KRB5_ERR_HOST_REALM_UNKNOWN;
299 }
300 }
301 return ret;
302 }
303