1 /*-
2 * Copyright (c) 2012-2013 Baptiste Daroussin <bapt@FreeBSD.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer,
10 * without modification, immediately at the beginning of the file.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27 #include <sys/cdefs.h>
28 __FBSDID("$FreeBSD$");
29
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] = random() % (d[i]->weight * 100 / totalweight);
100 for (j = 0; j < i; j++) {
101 if (chosen[i] == chosen[j])
102 break;
103 }
104 if (j == i) {
105 d[i]->finalweight = chosen[i];
106 break;
107 }
108 }
109 }
110
111 free(chosen);
112 }
113
114 struct dns_srvinfo *
dns_getsrvinfo(const char * zone)115 dns_getsrvinfo(const char *zone)
116 {
117 struct dns_srvinfo **res, *first;
118 unsigned char *end, *p;
119 char host[MAXHOSTNAMELEN];
120 dns_query q;
121 int len, qdcount, ancount, n, i, f, l;
122 unsigned int type, class, ttl, priority, weight, port;
123
124 if ((len = res_query(zone, C_IN, T_SRV, q.buf, sizeof(q.buf))) == -1 ||
125 len < (int)sizeof(HEADER))
126 return (NULL);
127
128 qdcount = ntohs(q.hdr.qdcount);
129 ancount = ntohs(q.hdr.ancount);
130
131 end = q.buf + len;
132 p = q.buf + sizeof(HEADER);
133
134 while(qdcount > 0 && p < end) {
135 qdcount--;
136 if((len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN)) < 0)
137 return (NULL);
138 p += len + NS_QFIXEDSZ;
139 }
140
141 res = calloc(ancount, sizeof(struct dns_srvinfo *));
142 if (res == NULL)
143 return (NULL);
144
145 n = 0;
146 while (ancount > 0 && p < end) {
147 ancount--;
148 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
149 if (len < 0) {
150 for (i = 0; i < n; i++)
151 free(res[i]);
152 free(res);
153 return NULL;
154 }
155
156 p += len;
157
158 NS_GET16(type, p);
159 NS_GET16(class, p);
160 NS_GET32(ttl, p);
161 NS_GET16(len, p);
162
163 if (type != T_SRV) {
164 p += len;
165 continue;
166 }
167
168 NS_GET16(priority, p);
169 NS_GET16(weight, p);
170 NS_GET16(port, p);
171
172 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
173 if (len < 0) {
174 for (i = 0; i < n; i++)
175 free(res[i]);
176 free(res);
177 return (NULL);
178 }
179
180 res[n] = malloc(sizeof(struct dns_srvinfo));
181 if (res[n] == NULL) {
182 for (i = 0; i < n; i++)
183 free(res[i]);
184 free(res);
185 return (NULL);
186 }
187 res[n]->type = type;
188 res[n]->class = class;
189 res[n]->ttl = ttl;
190 res[n]->priority = priority;
191 res[n]->weight = weight;
192 res[n]->port = port;
193 res[n]->next = NULL;
194 strlcpy(res[n]->host, host, MAXHOSTNAMELEN);
195
196 p += len;
197 n++;
198 }
199
200 qsort(res, n, sizeof(res[0]), srv_priority_cmp);
201
202 priority = f = l = 0;
203 for (i = 0; i < n; i++) {
204 if (res[i]->priority != priority) {
205 if (f != l)
206 compute_weight(res, f, l);
207 f = i;
208 priority = res[i]->priority;
209 }
210 l = i;
211 }
212
213 qsort(res, n, sizeof(res[0]), srv_final_cmp);
214
215 for (i = 0; i < n - 1; i++)
216 res[i]->next = res[i + 1];
217
218 first = res[0];
219 free(res);
220
221 return (first);
222 }
223