xref: /freebsd/crypto/heimdal/lib/krb5/get_host_realm.c (revision 7aa383846770374466b1dcb2cefd71bde9acf463)
1 /*
2  * Copyright (c) 1997 - 2005 Kungliga Tekniska H�gskolan
3  * (Royal Institute of Technology, Stockholm, Sweden).
4  * All rights reserved.
5  *
6  * Redistribution and use in source and binary forms, with or without
7  * modification, are permitted provided that the following conditions
8  * are met:
9  *
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  *
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  *
17  * 3. Neither the name of the Institute nor the names of its contributors
18  *    may be used to endorse or promote products derived from this software
19  *    without specific prior written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  */
33 
34 #include "krb5_locl.h"
35 #include <resolve.h>
36 
37 RCSID("$Id: get_host_realm.c 18541 2006-10-17 19:28:36Z lha $");
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
54 copy_txt_to_realms (struct resource_record *head,
55 		    krb5_realm **realms)
56 {
57     struct resource_record *rr;
58     int n, i;
59 
60     for(n = 0, rr = head; rr; rr = rr->next)
61 	if (rr->type == T_TXT)
62 	    ++n;
63 
64     if (n == 0)
65 	return -1;
66 
67     *realms = malloc ((n + 1) * sizeof(krb5_realm));
68     if (*realms == NULL)
69 	return -1;
70 
71     for (i = 0; i < n + 1; ++i)
72 	(*realms)[i] = NULL;
73 
74     for (i = 0, rr = head; rr; rr = rr->next) {
75 	if (rr->type == T_TXT) {
76 	    char *tmp;
77 
78 	    tmp = strdup(rr->u.txt);
79 	    if (tmp == NULL) {
80 		for (i = 0; i < n; ++i)
81 		    free ((*realms)[i]);
82 		free (*realms);
83 		return -1;
84 	    }
85 	    (*realms)[i] = tmp;
86 	    ++i;
87 	}
88     }
89     return 0;
90 }
91 
92 static int
93 dns_find_realm(krb5_context context,
94 	       const char *domain,
95 	       krb5_realm **realms)
96 {
97     static const char *default_labels[] = { "_kerberos", NULL };
98     char dom[MAXHOSTNAMELEN];
99     struct dns_reply *r;
100     const char **labels;
101     char **config_labels;
102     int i, ret;
103 
104     config_labels = krb5_config_get_strings(context, NULL, "libdefaults",
105 					    "dns_lookup_realm_labels", NULL);
106     if(config_labels != NULL)
107 	labels = (const char **)config_labels;
108     else
109 	labels = default_labels;
110     if(*domain == '.')
111 	domain++;
112     for (i = 0; labels[i] != NULL; i++) {
113 	ret = snprintf(dom, sizeof(dom), "%s.%s.", labels[i], domain);
114 	if(ret < 0 || ret >= sizeof(dom)) {
115 	    if (config_labels)
116 		krb5_config_free_strings(config_labels);
117 	    return -1;
118 	}
119     	r = dns_lookup(dom, "TXT");
120     	if(r != NULL) {
121 	    ret = copy_txt_to_realms (r->head, realms);
122 	    dns_free_data(r);
123 	    if(ret == 0) {
124 		if (config_labels)
125 		    krb5_config_free_strings(config_labels);
126 		return 0;
127 	    }
128 	}
129     }
130     if (config_labels)
131 	krb5_config_free_strings(config_labels);
132     return -1;
133 }
134 
135 /*
136  * Try to figure out what realms host in `domain' belong to from the
137  * configuration file.
138  */
139 
140 static int
141 config_find_realm(krb5_context context,
142 		  const char *domain,
143 		  krb5_realm **realms)
144 {
145     char **tmp = krb5_config_get_strings (context, NULL,
146 					  "domain_realm",
147 					  domain,
148 					  NULL);
149 
150     if (tmp == NULL)
151 	return -1;
152     *realms = tmp;
153     return 0;
154 }
155 
156 /*
157  * This function assumes that `host' is a FQDN (and doesn't handle the
158  * special case of host == NULL either).
159  * Try to find mapping in the config file or DNS and it that fails,
160  * fall back to guessing
161  */
162 
163 krb5_error_code KRB5_LIB_FUNCTION
164 _krb5_get_host_realm_int (krb5_context context,
165 			  const char *host,
166 			  krb5_boolean use_dns,
167 			  krb5_realm **realms)
168 {
169     const char *p, *q;
170     krb5_boolean dns_locate_enable;
171 
172     dns_locate_enable = krb5_config_get_bool_default(context, NULL, TRUE,
173 	"libdefaults", "dns_lookup_realm", NULL);
174     for (p = host; p != NULL; p = strchr (p + 1, '.')) {
175 	if(config_find_realm(context, p, realms) == 0) {
176 	    if(strcasecmp(*realms[0], "dns_locate") == 0) {
177 		if(use_dns)
178 		    for (q = host; q != NULL; q = strchr(q + 1, '.'))
179 			if(dns_find_realm(context, q, realms) == 0)
180 			    return 0;
181 		continue;
182 	    } else
183 	    	return 0;
184 	}
185 	else if(use_dns && dns_locate_enable) {
186 	    if(dns_find_realm(context, p, realms) == 0)
187 		return 0;
188 	}
189     }
190     p = strchr(host, '.');
191     if(p != NULL) {
192 	p++;
193 	*realms = malloc(2 * sizeof(krb5_realm));
194 	if (*realms == NULL) {
195 	    krb5_set_error_string(context, "malloc: out of memory");
196 	    return ENOMEM;
197 	}
198 
199 	(*realms)[0] = strdup(p);
200 	if((*realms)[0] == NULL) {
201 	    free(*realms);
202 	    krb5_set_error_string(context, "malloc: out of memory");
203 	    return ENOMEM;
204 	}
205 	strupr((*realms)[0]);
206 	(*realms)[1] = NULL;
207 	return 0;
208     }
209     krb5_set_error_string(context, "unable to find realm of host %s", host);
210     return KRB5_ERR_HOST_REALM_UNKNOWN;
211 }
212 
213 /*
214  * Return the realm(s) of `host' as a NULL-terminated list in
215  * `realms'. Free `realms' with krb5_free_host_realm().
216  */
217 
218 krb5_error_code KRB5_LIB_FUNCTION
219 krb5_get_host_realm(krb5_context context,
220 		    const char *targethost,
221 		    krb5_realm **realms)
222 {
223     const char *host = targethost;
224     char hostname[MAXHOSTNAMELEN];
225     krb5_error_code ret;
226     int use_dns;
227 
228     if (host == NULL) {
229 	if (gethostname (hostname, sizeof(hostname))) {
230 	    *realms = NULL;
231 	    return errno;
232 	}
233 	host = hostname;
234     }
235 
236     /*
237      * If our local hostname is without components, don't even try to dns.
238      */
239 
240     use_dns = (strchr(host, '.') != NULL);
241 
242     ret = _krb5_get_host_realm_int (context, host, use_dns, realms);
243     if (ret && targethost != NULL) {
244 	/*
245 	 * If there was no realm mapping for the host (and we wasn't
246 	 * looking for ourself), guess at the local realm, maybe our
247 	 * KDC knows better then we do and we get a referral back.
248 	 */
249 	ret = krb5_get_default_realms(context, realms);
250 	if (ret) {
251 	    krb5_set_error_string(context, "Unable to find realm of host %s",
252 				  host);
253 	    return KRB5_ERR_HOST_REALM_UNKNOWN;
254 	}
255     }
256     return ret;
257 }
258