1/* vi: set sw=4 ts=4: */
2/*
3 * Mini nslookup implementation for busybox
4 *
5 * Copyright (C) 1999,2000 by Lineo, inc. and John Beppu
6 * Copyright (C) 1999,2000,2001 by John Beppu <beppu@codepoet.org>
7 *
8 * Correct default name server display and explicit name server option
9 * added by Ben Zeckel <bzeckel@hmc.edu> June 2001
10 *
11 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
12 */
13
14#include <resolv.h>
15#include "libbb.h"
16
17/*
18 * I'm only implementing non-interactive mode;
19 * I totally forgot nslookup even had an interactive mode.
20 *
21 * This applet is the only user of res_init(). Without it,
22 * you may avoid pulling in _res global from libc.
23 */
24
25/* Examples of 'standard' nslookup output
26 * $ nslookup yahoo.com
27 * Server:         128.193.0.10
28 * Address:        128.193.0.10#53
29 *
30 * Non-authoritative answer:
31 * Name:   yahoo.com
32 * Address: 216.109.112.135
33 * Name:   yahoo.com
34 * Address: 66.94.234.13
35 *
36 * $ nslookup 204.152.191.37
37 * Server:         128.193.4.20
38 * Address:        128.193.4.20#53
39 *
40 * Non-authoritative answer:
41 * 37.191.152.204.in-addr.arpa     canonical name = 37.32-27.191.152.204.in-addr.arpa.
42 * 37.32-27.191.152.204.in-addr.arpa       name = zeus-pub2.kernel.org.
43 *
44 * Authoritative answers can be found from:
45 * 32-27.191.152.204.in-addr.arpa  nameserver = ns1.kernel.org.
46 * 32-27.191.152.204.in-addr.arpa  nameserver = ns2.kernel.org.
47 * 32-27.191.152.204.in-addr.arpa  nameserver = ns3.kernel.org.
48 * ns1.kernel.org  internet address = 140.211.167.34
49 * ns2.kernel.org  internet address = 204.152.191.4
50 * ns3.kernel.org  internet address = 204.152.191.36
51 */
52
53static int print_host(const char *hostname, const char *header)
54{
55	/* We can't use xhost2sockaddr() - we want to get ALL addresses,
56	 * not just one */
57	struct addrinfo *result = NULL;
58	int rc;
59	struct addrinfo hint;
60
61	memset(&hint, 0 , sizeof(hint));
62	/* hint.ai_family = AF_UNSPEC; - zero anyway */
63	/* Needed. Or else we will get each address thrice (or more)
64	 * for each possible socket type (tcp,udp,raw...): */
65	hint.ai_socktype = SOCK_STREAM;
66	// hint.ai_flags = AI_CANONNAME;
67	rc = getaddrinfo(hostname, NULL /*service*/, &hint, &result);
68
69	if (rc == 0) {
70		struct addrinfo *cur = result;
71		unsigned cnt = 0;
72
73		printf("%-10s %s\n", header, hostname);
74		// puts(cur->ai_canonname); ?
75		while (cur) {
76			char *dotted, *revhost;
77			dotted = xmalloc_sockaddr2dotted_noport(cur->ai_addr);
78			revhost = xmalloc_sockaddr2hostonly_noport(cur->ai_addr);
79
80			printf("Address %u: %s%c", ++cnt, dotted, revhost ? ' ' : '\n');
81			if (revhost) {
82				puts(revhost);
83				if (ENABLE_FEATURE_CLEAN_UP)
84					free(revhost);
85			}
86			if (ENABLE_FEATURE_CLEAN_UP)
87				free(dotted);
88			cur = cur->ai_next;
89		}
90	} else {
91#if ENABLE_VERBOSE_RESOLUTION_ERRORS
92		bb_error_msg("can't resolve '%s': %s", hostname, gai_strerror(rc));
93#else
94		bb_error_msg("can't resolve '%s'", hostname);
95#endif
96	}
97	if (ENABLE_FEATURE_CLEAN_UP && result)
98		freeaddrinfo(result);
99	return (rc != 0);
100}
101
102/* lookup the default nameserver and display it */
103static void server_print(void)
104{
105	char *server;
106	struct sockaddr *sa;
107
108#if ENABLE_FEATURE_IPV6
109	sa = (struct sockaddr*)_res._u._ext.nsaddrs[0];
110	if (!sa)
111#endif
112		sa = (struct sockaddr*)&_res.nsaddr_list[0];
113	server = xmalloc_sockaddr2dotted_noport(sa);
114
115	print_host(server, "Server:");
116	if (ENABLE_FEATURE_CLEAN_UP)
117		free(server);
118	bb_putchar('\n');
119}
120
121/* alter the global _res nameserver structure to use
122   an explicit dns server instead of what is in /etc/resolv.conf */
123static void set_default_dns(const char *server)
124{
125	len_and_sockaddr *lsa;
126
127	if (!server)
128		return;
129
130	/* NB: this works even with, say, "[::1]:5353"! :) */
131	lsa = xhost2sockaddr(server, 53);
132
133	if (lsa->u.sa.sa_family == AF_INET) {
134		_res.nscount = 1;
135		/* struct copy */
136		_res.nsaddr_list[0] = lsa->u.sin;
137	}
138#if ENABLE_FEATURE_IPV6
139	/* Hoped libc can cope with IPv4 address there too.
140	 * No such luck, glibc 2.4 segfaults even with IPv6,
141	 * maybe I misunderstand how to make glibc use IPv6 addr?
142	 * (uclibc 0.9.31+ should work) */
143	if (lsa->u.sa.sa_family == AF_INET6) {
144		// glibc neither SEGVs nor sends any dgrams with this
145		// (strace shows no socket ops):
146		//_res.nscount = 0;
147		_res._u._ext.nscount = 1;
148		/* store a pointer to part of malloc'ed lsa */
149		_res._u._ext.nsaddrs[0] = &lsa->u.sin6;
150		/* must not free(lsa)! */
151	}
152#endif
153}
154
155int nslookup_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
156int nslookup_main(int argc, char **argv)
157{
158	/* We allow 1 or 2 arguments.
159	 * The first is the name to be looked up and the second is an
160	 * optional DNS server with which to do the lookup.
161	 * More than 3 arguments is an error to follow the pattern of the
162	 * standard nslookup */
163	if (!argv[1] || argv[1][0] == '-' || argc > 3)
164		bb_show_usage();
165
166	/* initialize DNS structure _res used in printing the default
167	 * name server and in the explicit name server option feature. */
168	res_init();
169	/* rfc2133 says this enables IPv6 lookups */
170	/* (but it also says "may be enabled in /etc/resolv.conf") */
171	/*_res.options |= RES_USE_INET6;*/
172
173	set_default_dns(argv[2]);
174
175	server_print();
176
177	/* getaddrinfo and friends are free to request a resolver
178	 * reinitialization. Just in case, set_default_dns() again
179	 * after getaddrinfo (in server_print). This reportedly helps
180	 * with bug 675 "nslookup does not properly use second argument"
181	 * at least on Debian Wheezy and Openwrt AA (eglibc based).
182	 */
183	set_default_dns(argv[2]);
184
185	return print_host(argv[1], "Name:");
186}
187