1 /* 2 * lib/krb5/os/dnssrv.c 3 * 4 * Copyright 1990,2000,2001,2002,2003 by the Massachusetts Institute of Technology. 5 * All Rights Reserved. 6 * 7 * Export of this software from the United States of America may 8 * require a specific license from the United States Government. 9 * It is the responsibility of any person or organization contemplating 10 * export to obtain such a license before exporting. 11 * 12 * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and 13 * distribute this software and its documentation for any purpose and 14 * without fee is hereby granted, provided that the above copyright 15 * notice appear in all copies and that both that copyright notice and 16 * this permission notice appear in supporting documentation, and that 17 * the name of M.I.T. not be used in advertising or publicity pertaining 18 * to distribution of the software without specific, written prior 19 * permission. Furthermore if you modify this software you must label 20 * your software as modified software and not distribute it in such a 21 * fashion that it might be confused with the original M.I.T. software. 22 * M.I.T. makes no representations about the suitability of 23 * this software for any purpose. It is provided "as is" without express 24 * or implied warranty. 25 * 26 * 27 * do DNS SRV RR queries 28 */ 29 30 #include "autoconf.h" 31 #ifdef KRB5_DNS_LOOKUP 32 33 #include "dnsglue.h" 34 35 /* 36 * Lookup a KDC via DNS SRV records 37 */ 38 39 void krb5int_free_srv_dns_data (struct srv_dns_entry *p) 40 { 41 struct srv_dns_entry *next; 42 while (p) { 43 next = p->next; 44 free(p->host); 45 free(p); 46 p = next; 47 } 48 } 49 50 /* Do DNS SRV query, return results in *answers. 51 52 Make best effort to return all the data we can. On memory or 53 decoding errors, just return what we've got. Always return 0, 54 currently. */ 55 56 krb5_error_code 57 krb5int_make_srv_query_realm(const krb5_data *realm, 58 const char *service, 59 const char *protocol, 60 struct srv_dns_entry **answers) 61 { 62 const unsigned char *p = NULL, *base = NULL; 63 char host[MAXDNAME], *h; 64 int size, ret, rdlen, nlen; 65 unsigned short priority, weight, port; 66 struct krb5int_dns_state *ds = NULL; 67 68 struct srv_dns_entry *head = NULL; 69 struct srv_dns_entry *srv = NULL, *entry = NULL; 70 71 /* 72 * First off, build a query of the form: 73 * 74 * service.protocol.realm 75 * 76 * which will most likely be something like: 77 * 78 * _kerberos._udp.REALM 79 * 80 */ 81 82 if (memchr(realm->data, 0, realm->length)) 83 return 0; 84 if ( strlen(service) + strlen(protocol) + realm->length + 6 85 > MAXDNAME ) 86 return 0; 87 sprintf(host, "%s.%s.%.*s", service, protocol, (int) realm->length, 88 realm->data); 89 90 /* Realm names don't (normally) end with ".", but if the query 91 doesn't end with "." and doesn't get an answer as is, the 92 resolv code will try appending the local domain. Since the 93 realm names are absolutes, let's stop that. 94 95 But only if a name has been specified. If we are performing 96 a search on the prefix alone then the intention is to allow 97 the local domain or domain search lists to be expanded. */ 98 99 h = host + strlen (host); 100 if ((h[-1] != '.') && ((h - host + 1) < sizeof(host))) 101 strcpy (h, "."); 102 103 #ifdef TEST 104 fprintf (stderr, "sending DNS SRV query for %s\n", host); 105 #endif 106 107 size = krb5int_dns_init(&ds, host, C_IN, T_SRV); 108 if (size < 0) 109 goto out; 110 111 for (;;) { 112 ret = krb5int_dns_nextans(ds, &base, &rdlen); 113 if (ret < 0 || base == NULL) 114 goto out; 115 116 p = base; 117 118 SAFE_GETUINT16(base, rdlen, p, 2, priority, out); 119 SAFE_GETUINT16(base, rdlen, p, 2, weight, out); 120 SAFE_GETUINT16(base, rdlen, p, 2, port, out); 121 122 /* 123 * RFC 2782 says the target is never compressed in the reply; 124 * do we believe that? We need to flatten it anyway, though. 125 */ 126 nlen = krb5int_dns_expand(ds, p, host, sizeof(host)); 127 if (nlen < 0 || !INCR_OK(base, rdlen, p, nlen)) 128 goto out; 129 130 /* 131 * We got everything! Insert it into our list, but make sure 132 * it's in the right order. Right now we don't do anything 133 * with the weight field 134 */ 135 136 srv = (struct srv_dns_entry *) malloc(sizeof(struct srv_dns_entry)); 137 if (srv == NULL) 138 goto out; 139 140 srv->priority = priority; 141 srv->weight = weight; 142 srv->port = port; 143 /* The returned names are fully qualified. Don't let the 144 local resolver code do domain search path stuff. */ 145 if (strlen(host) + 2 < sizeof(host)) 146 strcat(host, "."); 147 srv->host = strdup(host); 148 if (srv->host == NULL) { 149 free(srv); 150 goto out; 151 } 152 153 if (head == NULL || head->priority > srv->priority) { 154 srv->next = head; 155 head = srv; 156 } else { 157 /* 158 * This is confusing. Only insert an entry into this 159 * spot if: 160 * The next person has a higher priority (lower priorities 161 * are preferred). 162 * Or 163 * There is no next entry (we're at the end) 164 */ 165 for (entry = head; entry != NULL; entry = entry->next) { 166 if ((entry->next && 167 entry->next->priority > srv->priority) || 168 entry->next == NULL) { 169 srv->next = entry->next; 170 entry->next = srv; 171 break; 172 } 173 } 174 } 175 } 176 177 out: 178 if (ds != NULL) { 179 krb5int_dns_fini(ds); 180 ds = NULL; 181 } 182 *answers = head; 183 return 0; 184 } 185 #endif 186