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
krb5int_free_srv_dns_data(struct srv_dns_entry * p)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
krb5int_make_srv_query_realm(const krb5_data * realm,const char * service,const char * protocol,struct srv_dns_entry ** answers)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