xref: /freebsd/usr.sbin/pkg/dns_utils.c (revision 640235e2c2ba32947f7c59d168437ffa1280f1e6)
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
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
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
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 *
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