dns_utils.c revision 302408 
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: stable/11/usr.sbin/pkg/dns_utils.c 287193 2015-08-27 06:28:42Z delphij $");
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
37typedef union {
38	HEADER hdr;
39	unsigned char buf[1024];
40} dns_query;
41
42static int
43srv_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
57static int
58srv_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
81static void
82compute_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
114struct dns_srvinfo *
115dns_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