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 /* To automagically find the correct realm of a host (without
  38  * [domain_realm] in krb5.conf) add a text record for your domain with
  39  * the name of your realm, like this:
  40  *
  41  * _kerberos    IN      TXT     "FOO.SE"
  42  *
  43  * The search is recursive, so you can add entries for specific
  44  * hosts. To find the realm of host a.b.c, it first tries
  45  * _kerberos.a.b.c, then _kerberos.b.c and so on.
  46  *
  47  * This method is described in draft-ietf-cat-krb-dns-locate-03.txt.
  48  *
  49  */
  50
  51 static int
  52 copy_txt_to_realms (struct rk_resource_record *head,
  53                     krb5_realm **realms)
  54 {
  55     struct rk_resource_record *rr;
  56     unsigned int n, i;
  57
  58     for(n = 0, rr = head; rr; rr = rr->next)
  59         if (rr->type == rk_ns_t_txt)
  60             ++n;
  61
  62     if (n == 0)
  63         return -1;
  64
  65     *realms = malloc ((n + 1) * sizeof(krb5_realm));
  66     if (*realms == NULL)
  67         return -1;
  68
  69     for (i = 0; i < n + 1; ++i)
  70         (*realms)[i] = NULL;
  71
  72     for (i = 0, rr = head; rr; rr = rr->next) {
  73         if (rr->type == rk_ns_t_txt) {
  74             char *tmp;
  75
  76             tmp = strdup(rr->u.txt);
  77             if (tmp == NULL) {
  78                 for (i = 0; i < n; ++i)
  79                     free ((*realms)[i]);
  80                 free (*realms);
  81                 return -1;
  82             }
  83             (*realms)[i] = tmp;
  84             ++i;
  85         }
  86     }
  87     return 0;
  88 }
  89
  90 static int
  91 dns_find_realm(krb5_context context,
  92                const char *domain,
  93                krb5_realm **realms)
  94 {
  95     static const char *default_labels[] = { "_kerberos", NULL };
  96     char dom[MAXHOSTNAMELEN];
  97     struct rk_dns_reply *r;
  98     const char **labels;
  99     char **config_labels;
 100     int i, ret;
 101
 102     config_labels = krb5_config_get_strings(context, NULL, "libdefaults",
 103                                             "dns_lookup_realm_labels", NULL);
 104     if(config_labels != NULL)
 105         labels = (const char **)config_labels;
 106     else
 107         labels = default_labels;
 108     if(*domain == '.')
 109         domain++;
 110     for (i = 0; labels[i] != NULL; i++) {
 111         ret = snprintf(dom, sizeof(dom), "%s.%s.", labels[i], domain);
 112         if(ret < 0 || ret >= sizeof(dom)) {
 113             if (config_labels)
 114                 krb5_config_free_strings(config_labels);
 115             return -1;
 116         }
 117         r = rk_dns_lookup(dom, "TXT");
 118         if(r != NULL) {
 119             ret = copy_txt_to_realms (r->head, realms);
 120             rk_dns_free_data(r);
 121             if(ret == 0) {
 122                 if (config_labels)
 123                     krb5_config_free_strings(config_labels);
 124                 return 0;
 125             }
 126         }
 127     }
 128     if (config_labels)
 129         krb5_config_free_strings(config_labels);
 130     return -1;
 131 }
 132
 133 /*
 134  * Try to figure out what realms host in `domain' belong to from the
 135  * configuration file.
 136  */
 137
 138 static int
 139 config_find_realm(krb5_context context,
 140                   const char *domain,
 141                   krb5_realm **realms)
 142 {
 143     char **tmp = krb5_config_get_strings (context, NULL,
 144                                           "domain_realm",
 145                                           domain,
 146                                           NULL);
 147
 148     if (tmp == NULL)
 149         return -1;
 150     *realms = tmp;
 151     return 0;
 152 }
 153
 154 /*
 155  * This function assumes that `host' is a FQDN (and doesn't handle the
 156  * special case of host == NULL either).
 157  * Try to find mapping in the config file or DNS and it that fails,
 158  * fall back to guessing
 159  */
 160
 161 krb5_error_code KRB5_LIB_FUNCTION
 162 _krb5_get_host_realm_int (krb5_context context,
 163                           const char *host,
 164                           krb5_boolean use_dns,
 165                           krb5_realm **realms)
 166 {
 167     const char *p, *q;
 168     krb5_boolean dns_locate_enable;
 169
 170     dns_locate_enable = krb5_config_get_bool_default(context, NULL, TRUE,
 171         "libdefaults", "dns_lookup_realm", NULL);
 172     for (p = host; p != NULL; p = strchr (p + 1, '.')) {
 173         if(config_find_realm(context, p, realms) == 0) {
 174             if(strcasecmp(*realms[0], "dns_locate") == 0) {
 175                 if(use_dns)
 176                     for (q = host; q != NULL; q = strchr(q + 1, '.'))
 177                         if(dns_find_realm(context, q, realms) == 0)
 178                             return 0;
 179                 continue;
 180             } else
 181                 return 0;
 182         }
 183         else if(use_dns && dns_locate_enable) {
 184             if(dns_find_realm(context, p, realms) == 0)
 185                 return 0;
 186         }
 187     }
 188     p = strchr(host, '.');
 189     if(p != NULL) {
 190         p++;
 191         *realms = malloc(2 * sizeof(krb5_realm));
 192         if (*realms == NULL) {
 193             krb5_set_error_message(context, ENOMEM, N_("malloc: out of memory", ""));
 194             return ENOMEM;
 195         }
 196
 197         (*realms)[0] = strdup(p);
 198         if((*realms)[0] == NULL) {
 199             free(*realms);
 200             krb5_set_error_message(context, ENOMEM, N_("malloc: out of memory", ""));
 201             return ENOMEM;
 202         }
 203         strupr((*realms)[0]);
 204         (*realms)[1] = NULL;
 205         return 0;
 206     }
 207     krb5_set_error_message(context, KRB5_ERR_HOST_REALM_UNKNOWN,
 208                            N_("unable to find realm of host %s", ""),
 209                            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_message(context, KRB5_ERR_HOST_REALM_UNKNOWN,
 252                                    N_("Unable to find realm of host %s", ""),
 253                                    host);
 254             return KRB5_ERR_HOST_REALM_UNKNOWN;
 255         }
 256     }
 257     return ret;
 258 }