1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2012-2013 Baptiste Daroussin <[email protected]>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer,
12 * without modification, immediately at the beginning of the file.
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 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29 #include <sys/cdefs.h>
30 __FBSDID("$FreeBSD$");
31
32 #include <stdlib.h>
33 #include <string.h>
34 #include <netinet/in.h>
35 #include <resolv.h>
36
37 #include "dns_utils.h"
38
39 typedef union {
40 HEADER hdr;
41 unsigned char buf[1024];
42 } dns_query;
43
44 static int
srv_priority_cmp(const void * a,const void * b)45 srv_priority_cmp(const void *a, const void *b)
46 {
47 const struct dns_srvinfo *da, *db;
48 unsigned int r, l;
49
50 da = *(struct dns_srvinfo * const *)a;
51 db = *(struct dns_srvinfo * const *)b;
52
53 l = da->priority;
54 r = db->priority;
55
56 return ((l > r) - (l < r));
57 }
58
59 static int
srv_final_cmp(const void * a,const void * b)60 srv_final_cmp(const void *a, const void *b)
61 {
62 const struct dns_srvinfo *da, *db;
63 unsigned int r, l, wr, wl;
64 int res;
65
66 da = *(struct dns_srvinfo * const *)a;
67 db = *(struct dns_srvinfo * const *)b;
68
69 l = da->priority;
70 r = db->priority;
71
72 res = ((l > r) - (l < r));
73
74 if (res == 0) {
75 wl = da->finalweight;
76 wr = db->finalweight;
77 res = ((wr > wl) - (wr < wl));
78 }
79
80 return (res);
81 }
82
83 static void
compute_weight(struct dns_srvinfo ** d,int first,int last)84 compute_weight(struct dns_srvinfo **d, int first, int last)
85 {
86 int i, j, totalweight;
87 int *chosen;
88
89 totalweight = 0;
90
91 for (i = 0; i <= last; i++)
92 totalweight += d[i]->weight;
93
94 if (totalweight == 0)
95 return;
96
97 chosen = malloc(sizeof(int) * (last - first + 1));
98
99 for (i = 0; i <= last; i++) {
100 for (;;) {
101 chosen[i] = random() % (d[i]->weight * 100 / totalweight);
102 for (j = 0; j < i; j++) {
103 if (chosen[i] == chosen[j])
104 break;
105 }
106 if (j == i) {
107 d[i]->finalweight = chosen[i];
108 break;
109 }
110 }
111 }
112
113 free(chosen);
114 }
115
116 struct dns_srvinfo *
dns_getsrvinfo(const char * zone)117 dns_getsrvinfo(const char *zone)
118 {
119 struct dns_srvinfo **res, *first;
120 unsigned char *end, *p;
121 char host[MAXHOSTNAMELEN];
122 dns_query q;
123 int len, qdcount, ancount, n, i, f, l;
124 unsigned int type, class, ttl, priority, weight, port;
125
126 if ((len = res_query(zone, C_IN, T_SRV, q.buf, sizeof(q.buf))) == -1 ||
127 len < (int)sizeof(HEADER))
128 return (NULL);
129
130 qdcount = ntohs(q.hdr.qdcount);
131 ancount = ntohs(q.hdr.ancount);
132
133 end = q.buf + len;
134 p = q.buf + sizeof(HEADER);
135
136 while(qdcount > 0 && p < end) {
137 qdcount--;
138 if((len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN)) < 0)
139 return (NULL);
140 p += len + NS_QFIXEDSZ;
141 }
142
143 res = calloc(ancount, sizeof(struct dns_srvinfo *));
144 if (res == NULL)
145 return (NULL);
146
147 n = 0;
148 while (ancount > 0 && p < end) {
149 ancount--;
150 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
151 if (len < 0) {
152 for (i = 0; i < n; i++)
153 free(res[i]);
154 free(res);
155 return NULL;
156 }
157
158 p += len;
159
160 NS_GET16(type, p);
161 NS_GET16(class, p);
162 NS_GET32(ttl, p);
163 NS_GET16(len, p);
164
165 if (type != T_SRV) {
166 p += len;
167 continue;
168 }
169
170 NS_GET16(priority, p);
171 NS_GET16(weight, p);
172 NS_GET16(port, p);
173
174 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
175 if (len < 0) {
176 for (i = 0; i < n; i++)
177 free(res[i]);
178 free(res);
179 return (NULL);
180 }
181
182 res[n] = malloc(sizeof(struct dns_srvinfo));
183 if (res[n] == NULL) {
184 for (i = 0; i < n; i++)
185 free(res[i]);
186 free(res);
187 return (NULL);
188 }
189 res[n]->type = type;
190 res[n]->class = class;
191 res[n]->ttl = ttl;
192 res[n]->priority = priority;
193 res[n]->weight = weight;
194 res[n]->port = port;
195 res[n]->next = NULL;
196 strlcpy(res[n]->host, host, MAXHOSTNAMELEN);
197
198 p += len;
199 n++;
200 }
201
202 qsort(res, n, sizeof(res[0]), srv_priority_cmp);
203
204 priority = f = l = 0;
205 for (i = 0; i < n; i++) {
206 if (res[i]->priority != priority) {
207 if (f != l)
208 compute_weight(res, f, l);
209 f = i;
210 priority = res[i]->priority;
211 }
212 l = i;
213 }
214
215 qsort(res, n, sizeof(res[0]), srv_final_cmp);
216
217 for (i = 0; i < n - 1; i++)
218 res[i]->next = res[i + 1];
219
220 first = res[0];
221 free(res);
222
223 return (first);
224 }
225