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 chosen = malloc(sizeof(int) * (last - first + 1));
88 totalweight = 0;
89
90 for (i = 0; i <= last; i++)
91 totalweight += d[i]->weight;
92
93 if (totalweight == 0)
94 return;
95
96 for (i = 0; i <= last; i++) {
97 for (;;) {
98 chosen[i] = random() % (d[i]->weight * 100 / totalweight);
99 for (j = 0; j < i; j++) {
100 if (chosen[i] == chosen[j])
101 break;
102 }
103 if (j == i) {
104 d[i]->finalweight = chosen[i];
105 break;
106 }
107 }
108 }
109
110 free(chosen);
111 }
112
113 struct dns_srvinfo *
dns_getsrvinfo(const char * zone)114 dns_getsrvinfo(const char *zone)
115 {
116 struct dns_srvinfo **res, *first;
117 unsigned char *end, *p;
118 char host[MAXHOSTNAMELEN];
119 dns_query q;
120 int len, qdcount, ancount, n, i, f, l;
121 unsigned int type, class, ttl, priority, weight, port;
122
123 if ((len = res_query(zone, C_IN, T_SRV, q.buf, sizeof(q.buf))) == -1 ||
124 len < (int)sizeof(HEADER))
125 return (NULL);
126
127 qdcount = ntohs(q.hdr.qdcount);
128 ancount = ntohs(q.hdr.ancount);
129
130 end = q.buf + len;
131 p = q.buf + sizeof(HEADER);
132
133 while(qdcount > 0 && p < end) {
134 qdcount--;
135 if((len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN)) < 0)
136 return (NULL);
137 p += len + NS_QFIXEDSZ;
138 }
139
140 res = calloc(ancount, sizeof(struct dns_srvinfo *));
141 if (res == NULL)
142 return (NULL);
143
144 n = 0;
145 while (ancount > 0 && p < end) {
146 ancount--;
147 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
148 if (len < 0) {
149 for (i = 0; i < n; i++)
150 free(res[i]);
151 free(res);
152 return NULL;
153 }
154
155 p += len;
156
157 NS_GET16(type, p);
158 NS_GET16(class, p);
159 NS_GET32(ttl, p);
160 NS_GET16(len, p);
161
162 if (type != T_SRV) {
163 p += len;
164 continue;
165 }
166
167 NS_GET16(priority, p);
168 NS_GET16(weight, p);
169 NS_GET16(port, p);
170
171 len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
172 if (len < 0) {
173 for (i = 0; i < n; i++)
174 free(res[i]);
175 free(res);
176 return (NULL);
177 }
178
179 res[n] = malloc(sizeof(struct dns_srvinfo));
180 if (res[n] == NULL) {
181 for (i = 0; i < n; i++)
182 free(res[i]);
183 free(res);
184 return (NULL);
185 }
186 res[n]->type = type;
187 res[n]->class = class;
188 res[n]->ttl = ttl;
189 res[n]->priority = priority;
190 res[n]->weight = weight;
191 res[n]->port = port;
192 res[n]->next = NULL;
193 strlcpy(res[n]->host, host, MAXHOSTNAMELEN);
194
195 p += len;
196 n++;
197 }
198
199 qsort(res, n, sizeof(res[0]), srv_priority_cmp);
200
201 priority = f = l = 0;
202 for (i = 0; i < n; i++) {
203 if (res[i]->priority != priority) {
204 if (f != l)
205 compute_weight(res, f, l);
206 f = i;
207 priority = res[i]->priority;
208 }
209 l = i;
210 }
211
212 qsort(res, n, sizeof(res[0]), srv_final_cmp);
213
214 for (i = 0; i < n - 1; i++)
215 res[i]->next = res[i + 1];
216
217 first = res[0];
218 free(res);
219
220 return (first);
221 }
222