lib/krb5/get_host_realm.c

   1 /*
   2  * Copyright (c) 1997 - 2005 Kungliga Tekniska Högskolan
   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("$Id$");
  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 }