1/*-
2 * SPDX-License-Identifier: BSD-2-Clause
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#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] = arc4random_uniform(d[i]->weight * 100 /
100			    totalweight);
101			for (j = 0; j < i; j++) {
102				if (chosen[i] == chosen[j])
103					break;
104			}
105			if (j == i) {
106				d[i]->finalweight = chosen[i];
107				break;
108			}
109		}
110	}
111
112	free(chosen);
113}
114
115struct dns_srvinfo *
116dns_getsrvinfo(const char *zone)
117{
118	struct dns_srvinfo **res, *first;
119	unsigned char *end, *p;
120	char host[MAXHOSTNAMELEN];
121	dns_query q;
122	int len, qdcount, ancount, n, i, f, l;
123	unsigned int type, class, ttl, priority, weight, port;
124
125	if ((len = res_query(zone, C_IN, T_SRV, q.buf, sizeof(q.buf))) == -1 ||
126	    len < (int)sizeof(HEADER))
127		return (NULL);
128
129	qdcount = ntohs(q.hdr.qdcount);
130	ancount = ntohs(q.hdr.ancount);
131
132	end = q.buf + len;
133	p = q.buf + sizeof(HEADER);
134
135	while(qdcount > 0 && p < end) {
136		qdcount--;
137		if((len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN)) < 0)
138			return (NULL);
139		p += len + NS_QFIXEDSZ;
140	}
141
142	res = calloc(ancount, sizeof(struct dns_srvinfo *));
143	if (res == NULL)
144		return (NULL);
145
146	n = 0;
147	while (ancount > 0 && p < end) {
148		ancount--;
149		len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
150		if (len < 0) {
151			for (i = 0; i < n; i++)
152				free(res[i]);
153			free(res);
154			return NULL;
155		}
156
157		p += len;
158
159		NS_GET16(type, p);
160		NS_GET16(class, p);
161		NS_GET32(ttl, p);
162		NS_GET16(len, p);
163
164		if (type != T_SRV) {
165			p += len;
166			continue;
167		}
168
169		NS_GET16(priority, p);
170		NS_GET16(weight, p);
171		NS_GET16(port, p);
172
173		len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
174		if (len < 0) {
175			for (i = 0; i < n; i++)
176				free(res[i]);
177			free(res);
178			return (NULL);
179		}
180
181		res[n] = malloc(sizeof(struct dns_srvinfo));
182		if (res[n] == NULL) {
183			for (i = 0; i < n; i++)
184				free(res[i]);
185			free(res);
186			return (NULL);
187		}
188		res[n]->type = type;
189		res[n]->class = class;
190		res[n]->ttl = ttl;
191		res[n]->priority = priority;
192		res[n]->weight = weight;
193		res[n]->port = port;
194		res[n]->next = NULL;
195		strlcpy(res[n]->host, host, MAXHOSTNAMELEN);
196
197		p += len;
198		n++;
199	}
200
201	qsort(res, n, sizeof(res[0]), srv_priority_cmp);
202
203	priority = f = l = 0;
204	for (i = 0; i < n; i++) {
205		if (res[i]->priority != priority) {
206			if (f != l)
207				compute_weight(res, f, l);
208			f = i;
209			priority = res[i]->priority;
210		}
211		l = i;
212	}
213
214	qsort(res, n, sizeof(res[0]), srv_final_cmp);
215
216	for (i = 0; i < n - 1; i++)
217		res[i]->next = res[i + 1];
218
219	first = res[0];
220	free(res);
221
222	return (first);
223}
224