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] = arc4random_uniform(d[i]->weight * 100 /
102 totalweight);
103 for (j = 0; j < i; j++) {
104 if (chosen[i] == chosen[j])
105 break;
106 }
107 if (j == i) {
108 d[i]->finalweight = chosen[i];
109 break;
110 }
111 }
112 }
113
114 free(chosen);
115 }
116
117 struct dns_srvinfo *
dns_getsrvinfo(const char * zone)118 dns_getsrvinfo(const char *zone)
119 {
120 struct dns_srvinfo **res, *first;
121 unsigned char *end, *p;
122 char host[MAXHOSTNAMELEN];
123 dns_query q;
124 int len, qdcount, ancount, n, i, f, l;
125 unsigned int type, class, ttl, priority, weight, port;
126
127 if ((len = res_query(zone, C_IN, T_SRV, q.buf, sizeof(q.buf))) == -1 ||
128 len < (int)sizeof(HEADER))
129 return (NULL);
130
131 qdcount = ntohs(q.hdr.qdcount);
132 ancount = ntohs(q.hdr.ancount);
133
134 end = q.buf + len;
135 p = q.buf + sizeof(HEADER);
136
137 while(qdcount > 0 && p < end) {
138 qdcount--;
139 if((len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN)) < 0)
140 return (NULL);
141 p += len + NS_QFIXEDSZ;
142 }
143
144 res = calloc(ancount, sizeof(struct dns_srvinfo *));
145 if (res == NULL)
146 return (NULL);
147
148 n = 0;
149 while (ancount > 0 && p < end) {
150 ancount--;
151 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
152 if (len < 0) {
153 for (i = 0; i < n; i++)
154 free(res[i]);
155 free(res);
156 return NULL;
157 }
158
159 p += len;
160
161 NS_GET16(type, p);
162 NS_GET16(class, p);
163 NS_GET32(ttl, p);
164 NS_GET16(len, p);
165
166 if (type != T_SRV) {
167 p += len;
168 continue;
169 }
170
171 NS_GET16(priority, p);
172 NS_GET16(weight, p);
173 NS_GET16(port, p);
174
175 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
176 if (len < 0) {
177 for (i = 0; i < n; i++)
178 free(res[i]);
179 free(res);
180 return (NULL);
181 }
182
183 res[n] = malloc(sizeof(struct dns_srvinfo));
184 if (res[n] == NULL) {
185 for (i = 0; i < n; i++)
186 free(res[i]);
187 free(res);
188 return (NULL);
189 }
190 res[n]->type = type;
191 res[n]->class = class;
192 res[n]->ttl = ttl;
193 res[n]->priority = priority;
194 res[n]->weight = weight;
195 res[n]->port = port;
196 res[n]->next = NULL;
197 strlcpy(res[n]->host, host, MAXHOSTNAMELEN);
198
199 p += len;
200 n++;
201 }
202
203 qsort(res, n, sizeof(res[0]), srv_priority_cmp);
204
205 priority = f = l = 0;
206 for (i = 0; i < n; i++) {
207 if (res[i]->priority != priority) {
208 if (f != l)
209 compute_weight(res, f, l);
210 f = i;
211 priority = res[i]->priority;
212 }
213 l = i;
214 }
215
216 qsort(res, n, sizeof(res[0]), srv_final_cmp);
217
218 for (i = 0; i < n - 1; i++)
219 res[i]->next = res[i + 1];
220
221 first = res[0];
222 free(res);
223
224 return (first);
225 }
226