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(krb5_context context,
  53                    const char *domain,
  54                    struct rk_resource_record *head,
  55                    krb5_realm **realms)
  56 {
  57     struct rk_resource_record *rr;
  58     unsigned int n, i;
  59
  60     for(n = 0, rr = head; rr; rr = rr->next)
  61         if (rr->type == rk_ns_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 krb5_enomem(context);;
  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 == rk_ns_t_txt) {
  76             char *tmp = NULL;
  77             int invalid_tld = 1;
  78
  79             /* Check for a gTLD controlled interruption */
  80             if (strcmp("Your DNS configuration needs immediate "
  81                         "attention see https://icann.org/namecollision",
  82                         rr->u.txt) != 0) {
  83                 invalid_tld = 0;
  84                 tmp = strdup(rr->u.txt);
  85             }
  86             if (tmp == NULL) {
  87                 for (i = 0; i < n; ++i)
  88                     free ((*realms)[i]);
  89                 free (*realms);
  90                 if (invalid_tld) {
  91                     krb5_warnx(context,
  92                                "Realm lookup failed: "
  93                                "Domain '%s' needs immediate attention "
  94                                "see https://icann.org/namecollision",
  95                                 domain);
  96                     return KRB5_KDC_UNREACH;
  97                 }
  98                 return krb5_enomem(context);;
  99             }
 100             (*realms)[i] = tmp;
 101             ++i;
 102         }
 103     }
 104     return 0;
 105 }
 106
 107 static int
 108 dns_find_realm(krb5_context context,
 109                const char *domain,
 110                krb5_realm **realms)
 111 {
 112     static const char *default_labels[] = { "_kerberos", NULL };
 113     char dom[MAXHOSTNAMELEN];
 114     struct rk_dns_reply *r;
 115     const char **labels;
 116     char **config_labels;
 117     int i, ret = 0;
 118
 119     config_labels = krb5_config_get_strings(context, NULL, "libdefaults",
 120                                             "dns_lookup_realm_labels", NULL);
 121     if(config_labels != NULL)
 122         labels = (const char **)config_labels;
 123     else
 124         labels = default_labels;
 125     if(*domain == '.')
 126         domain++;
 127     for (i = 0; labels[i] != NULL; i++) {
 128         ret = snprintf(dom, sizeof(dom), "%s.%s.", labels[i], domain);
 129         if(ret < 0 || (size_t)ret >= sizeof(dom)) {
 130             ret = krb5_enomem(context);
 131             goto out;
 132         }
 133         r = rk_dns_lookup(dom, "TXT");
 134         if(r != NULL) {
 135             ret = copy_txt_to_realms(context, domain, r->head, realms);
 136             rk_dns_free_data(r);
 137             if(ret == 0)
 138                 goto out;
 139         }
 140     }
 141     krb5_set_error_message(context, KRB5_KDC_UNREACH,
 142                             "Realm lookup failed: "
 143                             "No DNS TXT record for %s",
 144                             domain);
 145     ret = KRB5_KDC_UNREACH;
 146 out:
 147     if (config_labels)
 148         krb5_config_free_strings(config_labels);
 149     return ret;
 150 }
 151
 152 /*
 153  * Try to figure out what realms host in `domain' belong to from the
 154  * configuration file.
 155  */
 156
 157 static int
 158 config_find_realm(krb5_context context,
 159                   const char *domain,
 160                   krb5_realm **realms)
 161 {
 162     char **tmp = krb5_config_get_strings (context, NULL,
 163                                           "domain_realm",
 164                                           domain,
 165                                           NULL);
 166
 167     if (tmp == NULL)
 168         return -1;
 169     *realms = tmp;
 170     return 0;
 171 }
 172
 173 /*
 174  * This function assumes that `host' is a FQDN (and doesn't handle the
 175  * special case of host == NULL either).
 176  * Try to find mapping in the config file or DNS and it that fails,
 177  * fall back to guessing
 178  */
 179
 180 KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
 181 _krb5_get_host_realm_int(krb5_context context,
 182                          const char *host,
 183                          krb5_boolean use_dns,
 184                          krb5_realm **realms)
 185 {
 186     const char *p, *q;
 187     const char *port;
 188     krb5_boolean dns_locate_enable;
 189     krb5_error_code ret = 0;
 190
 191     /* Strip off any trailing ":port" suffix. */
 192     port = strchr(host, ':');
 193     if (port != NULL) {
 194         host = strndup(host, port - host);
 195         if (host == NULL)
 196             return krb5_enomem(context);
 197     }
 198
 199     dns_locate_enable = krb5_config_get_bool_default(context, NULL, TRUE,
 200         "libdefaults", "dns_lookup_realm", NULL);
 201     for (p = host; p != NULL; p = strchr (p + 1, '.')) {
 202         if (config_find_realm(context, p, realms) == 0) {
 203             if (strcasecmp(*realms[0], "dns_locate") != 0)
 204                 break;
 205             krb5_free_host_realm(context, *realms);
 206             *realms = NULL;
 207             if (!use_dns)
 208                 continue;
 209             for (q = host; q != NULL; q = strchr(q + 1, '.'))
 210                 if (dns_find_realm(context, q, realms) == 0)
 211                     break;
 212             if (q)
 213                 break;
 214         } else if (use_dns && dns_locate_enable) {
 215             if (dns_find_realm(context, p, realms) == 0)
 216                 break;
 217         }
 218     }
 219
 220     /*
 221      * If 'p' is NULL, we did not find an explicit realm mapping in either the
 222      * configuration file or DNS.  Try the hostname suffix as a last resort.
 223      *
 224      * XXX: If we implement a KDC-specific variant of this function just for
 225      * referrals, we could check whether we have a cross-realm TGT for the
 226      * realm in question, and if not try the parent (loop again).
 227      */
 228     if (p == NULL) {
 229         p = strchr(host, '.');
 230         if (p != NULL) {
 231             p++;
 232             *realms = malloc(2 * sizeof(krb5_realm));
 233             if (*realms != NULL &&
 234                 ((*realms)[0] = strdup(p)) != NULL) {
 235                 strupr((*realms)[0]);
 236                 (*realms)[1] = NULL;
 237             } else {
 238                 free(*realms);
 239                 ret = krb5_enomem(context);
 240             }
 241         } else {
 242             krb5_set_error_message(context, KRB5_ERR_HOST_REALM_UNKNOWN,
 243                                    N_("unable to find realm of host %s", ""),
 244                                    host);
 245             ret = KRB5_ERR_HOST_REALM_UNKNOWN;
 246         }
 247     }
 248
 249     /* If 'port' is not NULL, we have a copy of 'host' to free. */
 250     if (port)
 251         free((void *)host);
 252     return ret;
 253 }
 254
 255 /*
 256  * Return the realm(s) of `host' as a NULL-terminated list in
 257  * `realms'. Free `realms' with krb5_free_host_realm().
 258  */
 259
 260 KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
 261 krb5_get_host_realm(krb5_context context,
 262                     const char *targethost,
 263                     krb5_realm **realms)
 264 {
 265     const char *host = targethost;
 266     char hostname[MAXHOSTNAMELEN];
 267     krb5_error_code ret;
 268     int use_dns;
 269
 270     if (host == NULL) {
 271         if (gethostname (hostname, sizeof(hostname))) {
 272             *realms = NULL;
 273             return errno;
 274         }
 275         host = hostname;
 276     }
 277
 278     /*
 279      * If our local hostname is without components, don't even try to dns.
 280      */
 281
 282     use_dns = (strchr(host, '.') != NULL);
 283
 284     ret = _krb5_get_host_realm_int (context, host, use_dns, realms);
 285     if (ret && targethost != NULL) {
 286         /*
 287          * If there was no realm mapping for the host (and we wasn't
 288          * looking for ourself), guess at the local realm, maybe our
 289          * KDC knows better then we do and we get a referral back.
 290          */
 291         ret = krb5_get_default_realms(context, realms);
 292         if (ret) {
 293             krb5_set_error_message(context, KRB5_ERR_HOST_REALM_UNKNOWN,
 294                                    N_("Unable to find realm of host %s", ""),
 295                                    host);
 296             return KRB5_ERR_HOST_REALM_UNKNOWN;
 297         }
 298     }
 299     return ret;
 300 }