get_host_realm.c revision 1.2 
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 H��gskolan
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
53static int
54copy_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
109static int
110dns_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;
148out:
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
159static int
160config_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
182KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
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
262KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
263krb5_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