1/*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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__FBSDID("$FreeBSD$");
31
32#include <stdlib.h>
33#include <string.h>
34#include <netinet/in.h>
35#include <resolv.h>
36
37#include "dns_utils.h"
38
39typedef union {
40	HEADER hdr;
41	unsigned char buf[1024];
42} dns_query;
43
44static int
45srv_priority_cmp(const void *a, const void *b)
46{
47	const struct dns_srvinfo *da, *db;
48	unsigned int r, l;
49
50	da = *(struct dns_srvinfo * const *)a;
51	db = *(struct dns_srvinfo * const *)b;
52
53	l = da->priority;
54	r = db->priority;
55
56	return ((l > r) - (l < r));
57}
58
59static int
60srv_final_cmp(const void *a, const void *b)
61{
62	const struct dns_srvinfo *da, *db;
63	unsigned int r, l, wr, wl;
64	int res;
65
66	da = *(struct dns_srvinfo * const *)a;
67	db = *(struct dns_srvinfo * const *)b;
68
69	l = da->priority;
70	r = db->priority;
71
72	res = ((l > r) - (l < r));
73
74	if (res == 0) {
75		wl = da->finalweight;
76		wr = db->finalweight;
77		res = ((wr > wl) - (wr < wl));
78	}
79
80	return (res);
81}
82
83static void
84compute_weight(struct dns_srvinfo **d, int first, int last)
85{
86	int i, j, totalweight;
87	int *chosen;
88
89	totalweight = 0;
90
91	for (i = 0; i <= last; i++)
92		totalweight += d[i]->weight;
93
94	if (totalweight == 0)
95		return;
96
97	chosen = malloc(sizeof(int) * (last - first + 1));
98
99	for (i = 0; i <= last; i++) {
100		for (;;) {
101			chosen[i] = arc4random_uniform(d[i]->weight * 100 /
102			    totalweight);
103			for (j = 0; j < i; j++) {
104				if (chosen[i] == chosen[j])
105					break;
106			}
107			if (j == i) {
108				d[i]->finalweight = chosen[i];
109				break;
110			}
111		}
112	}
113
114	free(chosen);
115}
116
117struct dns_srvinfo *
118dns_getsrvinfo(const char *zone)
119{
120	struct dns_srvinfo **res, *first;
121	unsigned char *end, *p;
122	char host[MAXHOSTNAMELEN];
123	dns_query q;
124	int len, qdcount, ancount, n, i, f, l;
125	unsigned int type, class, ttl, priority, weight, port;
126
127	if ((len = res_query(zone, C_IN, T_SRV, q.buf, sizeof(q.buf))) == -1 ||
128	    len < (int)sizeof(HEADER))
129		return (NULL);
130
131	qdcount = ntohs(q.hdr.qdcount);
132	ancount = ntohs(q.hdr.ancount);
133
134	end = q.buf + len;
135	p = q.buf + sizeof(HEADER);
136
137	while(qdcount > 0 && p < end) {
138		qdcount--;
139		if((len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN)) < 0)
140			return (NULL);
141		p += len + NS_QFIXEDSZ;
142	}
143
144	res = calloc(ancount, sizeof(struct dns_srvinfo *));
145	if (res == NULL)
146		return (NULL);
147
148	n = 0;
149	while (ancount > 0 && p < end) {
150		ancount--;
151		len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
152		if (len < 0) {
153			for (i = 0; i < n; i++)
154				free(res[i]);
155			free(res);
156			return NULL;
157		}
158
159		p += len;
160
161		NS_GET16(type, p);
162		NS_GET16(class, p);
163		NS_GET32(ttl, p);
164		NS_GET16(len, p);
165
166		if (type != T_SRV) {
167			p += len;
168			continue;
169		}
170
171		NS_GET16(priority, p);
172		NS_GET16(weight, p);
173		NS_GET16(port, p);
174
175		len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
176		if (len < 0) {
177			for (i = 0; i < n; i++)
178				free(res[i]);
179			free(res);
180			return (NULL);
181		}
182
183		res[n] = malloc(sizeof(struct dns_srvinfo));
184		if (res[n] == NULL) {
185			for (i = 0; i < n; i++)
186				free(res[i]);
187			free(res);
188			return (NULL);
189		}
190		res[n]->type = type;
191		res[n]->class = class;
192		res[n]->ttl = ttl;
193		res[n]->priority = priority;
194		res[n]->weight = weight;
195		res[n]->port = port;
196		res[n]->next = NULL;
197		strlcpy(res[n]->host, host, MAXHOSTNAMELEN);
198
199		p += len;
200		n++;
201	}
202
203	qsort(res, n, sizeof(res[0]), srv_priority_cmp);
204
205	priority = f = l = 0;
206	for (i = 0; i < n; i++) {
207		if (res[i]->priority != priority) {
208			if (f != l)
209				compute_weight(res, f, l);
210			f = i;
211			priority = res[i]->priority;
212		}
213		l = i;
214	}
215
216	qsort(res, n, sizeof(res[0]), srv_final_cmp);
217
218	for (i = 0; i < n - 1; i++)
219		res[i]->next = res[i + 1];
220
221	first = res[0];
222	free(res);
223
224	return (first);
225}
226