1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2012-2013 Baptiste Daroussin <bapt@FreeBSD.org>
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 #include <stdlib.h>
31 #include <string.h>
32 #include <netinet/in.h>
33 #include <resolv.h>
34
35 #include "dns_utils.h"
36
37 typedef union {
38 HEADER hdr;
39 unsigned char buf[1024];
40 } dns_query;
41
42 static int
srv_priority_cmp(const void * a,const void * b)43 srv_priority_cmp(const void *a, const void *b)
44 {
45 const struct dns_srvinfo *da, *db;
46 unsigned int r, l;
47
48 da = *(struct dns_srvinfo * const *)a;
49 db = *(struct dns_srvinfo * const *)b;
50
51 l = da->priority;
52 r = db->priority;
53
54 return ((l > r) - (l < r));
55 }
56
57 static int
srv_final_cmp(const void * a,const void * b)58 srv_final_cmp(const void *a, const void *b)
59 {
60 const struct dns_srvinfo *da, *db;
61 unsigned int r, l, wr, wl;
62 int res;
63
64 da = *(struct dns_srvinfo * const *)a;
65 db = *(struct dns_srvinfo * const *)b;
66
67 l = da->priority;
68 r = db->priority;
69
70 res = ((l > r) - (l < r));
71
72 if (res == 0) {
73 wl = da->finalweight;
74 wr = db->finalweight;
75 res = ((wr > wl) - (wr < wl));
76 }
77
78 return (res);
79 }
80
81 static void
compute_weight(struct dns_srvinfo ** d,int first,int last)82 compute_weight(struct dns_srvinfo **d, int first, int last)
83 {
84 int i, j, totalweight;
85 int *chosen;
86
87 totalweight = 0;
88
89 for (i = 0; i <= last; i++)
90 totalweight += d[i]->weight;
91
92 if (totalweight == 0)
93 return;
94
95 chosen = malloc(sizeof(int) * (last - first + 1));
96
97 for (i = 0; i <= last; i++) {
98 for (;;) {
99 chosen[i] = arc4random_uniform(d[i]->weight * 100 /
100 totalweight);
101 for (j = 0; j < i; j++) {
102 if (chosen[i] == chosen[j])
103 break;
104 }
105 if (j == i) {
106 d[i]->finalweight = chosen[i];
107 break;
108 }
109 }
110 }
111
112 free(chosen);
113 }
114
115 struct dns_srvinfo *
dns_getsrvinfo(const char * zone)116 dns_getsrvinfo(const char *zone)
117 {
118 struct dns_srvinfo **res, *first;
119 unsigned char *end, *p;
120 char host[MAXHOSTNAMELEN];
121 dns_query q;
122 int len, qdcount, ancount, n, i, f, l;
123 unsigned int type, class, ttl, priority, weight, port;
124
125 if ((len = res_query(zone, C_IN, T_SRV, q.buf, sizeof(q.buf))) == -1 ||
126 len < (int)sizeof(HEADER))
127 return (NULL);
128
129 qdcount = ntohs(q.hdr.qdcount);
130 ancount = ntohs(q.hdr.ancount);
131
132 end = q.buf + len;
133 p = q.buf + sizeof(HEADER);
134
135 while(qdcount > 0 && p < end) {
136 qdcount--;
137 if((len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN)) < 0)
138 return (NULL);
139 p += len + NS_QFIXEDSZ;
140 }
141
142 res = calloc(ancount, sizeof(struct dns_srvinfo *));
143 if (res == NULL)
144 return (NULL);
145
146 n = 0;
147 while (ancount > 0 && p < end) {
148 ancount--;
149 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
150 if (len < 0) {
151 for (i = 0; i < n; i++)
152 free(res[i]);
153 free(res);
154 return NULL;
155 }
156
157 p += len;
158
159 NS_GET16(type, p);
160 NS_GET16(class, p);
161 NS_GET32(ttl, p);
162 NS_GET16(len, p);
163
164 if (type != T_SRV) {
165 p += len;
166 continue;
167 }
168
169 NS_GET16(priority, p);
170 NS_GET16(weight, p);
171 NS_GET16(port, p);
172
173 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
174 if (len < 0) {
175 for (i = 0; i < n; i++)
176 free(res[i]);
177 free(res);
178 return (NULL);
179 }
180
181 res[n] = malloc(sizeof(struct dns_srvinfo));
182 if (res[n] == NULL) {
183 for (i = 0; i < n; i++)
184 free(res[i]);
185 free(res);
186 return (NULL);
187 }
188 res[n]->type = type;
189 res[n]->class = class;
190 res[n]->ttl = ttl;
191 res[n]->priority = priority;
192 res[n]->weight = weight;
193 res[n]->port = port;
194 res[n]->next = NULL;
195 strlcpy(res[n]->host, host, MAXHOSTNAMELEN);
196
197 p += len;
198 n++;
199 }
200
201 qsort(res, n, sizeof(res[0]), srv_priority_cmp);
202
203 priority = f = l = 0;
204 for (i = 0; i < n; i++) {
205 if (res[i]->priority != priority) {
206 if (f != l)
207 compute_weight(res, f, l);
208 f = i;
209 priority = res[i]->priority;
210 }
211 l = i;
212 }
213
214 qsort(res, n, sizeof(res[0]), srv_final_cmp);
215
216 for (i = 0; i < n - 1; i++)
217 res[i]->next = res[i + 1];
218
219 first = res[0];
220 free(res);
221
222 return (first);
223 }
224