1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * Mini nslookup implementation for busybox
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4 | *
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5 | * Copyright (C) 1999,2000 by Lineo, inc. and John Beppu
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6 | * Copyright (C) 1999,2000,2001 by John Beppu <beppu@codepoet.org>
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7 | *
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8 | * Correct default name server display and explicit name server option
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9 | * added by Ben Zeckel <bzeckel@hmc.edu> June 2001
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10 | *
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11 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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12 | */
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13 |
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14 | //usage:#define nslookup_trivial_usage
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15 | //usage: "[HOST] [SERVER]"
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16 | //usage:#define nslookup_full_usage "\n\n"
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17 | //usage: "Query the nameserver for the IP address of the given HOST\n"
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18 | //usage: "optionally using a specified DNS server"
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19 | //usage:
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20 | //usage:#define nslookup_example_usage
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21 | //usage: "$ nslookup localhost\n"
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22 | //usage: "Server: default\n"
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23 | //usage: "Address: default\n"
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24 | //usage: "\n"
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25 | //usage: "Name: debian\n"
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26 | //usage: "Address: 127.0.0.1\n"
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27 |
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28 | #include <resolv.h>
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29 | #include "libbb.h"
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30 |
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31 | /*
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32 | * I'm only implementing non-interactive mode;
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33 | * I totally forgot nslookup even had an interactive mode.
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34 | *
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35 | * This applet is the only user of res_init(). Without it,
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36 | * you may avoid pulling in _res global from libc.
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37 | */
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38 |
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39 | /* Examples of 'standard' nslookup output
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40 | * $ nslookup yahoo.com
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41 | * Server: 128.193.0.10
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42 | * Address: 128.193.0.10#53
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43 | *
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44 | * Non-authoritative answer:
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45 | * Name: yahoo.com
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46 | * Address: 216.109.112.135
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47 | * Name: yahoo.com
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48 | * Address: 66.94.234.13
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49 | *
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50 | * $ nslookup 204.152.191.37
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51 | * Server: 128.193.4.20
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52 | * Address: 128.193.4.20#53
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53 | *
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54 | * Non-authoritative answer:
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55 | * 37.191.152.204.in-addr.arpa canonical name = 37.32-27.191.152.204.in-addr.arpa.
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56 | * 37.32-27.191.152.204.in-addr.arpa name = zeus-pub2.kernel.org.
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57 | *
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58 | * Authoritative answers can be found from:
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59 | * 32-27.191.152.204.in-addr.arpa nameserver = ns1.kernel.org.
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60 | * 32-27.191.152.204.in-addr.arpa nameserver = ns2.kernel.org.
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61 | * 32-27.191.152.204.in-addr.arpa nameserver = ns3.kernel.org.
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62 | * ns1.kernel.org internet address = 140.211.167.34
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63 | * ns2.kernel.org internet address = 204.152.191.4
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64 | * ns3.kernel.org internet address = 204.152.191.36
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65 | */
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66 |
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67 | static int print_host(const char *hostname, const char *header)
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68 | {
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69 | /* We can't use xhost2sockaddr() - we want to get ALL addresses,
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70 | * not just one */
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71 | struct addrinfo *result = NULL;
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72 | int rc;
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73 | struct addrinfo hint;
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74 |
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75 | memset(&hint, 0 , sizeof(hint));
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76 | /* hint.ai_family = AF_UNSPEC; - zero anyway */
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77 | /* Needed. Or else we will get each address thrice (or more)
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78 | * for each possible socket type (tcp,udp,raw...): */
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79 | hint.ai_socktype = SOCK_STREAM;
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80 | // hint.ai_flags = AI_CANONNAME;
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81 | rc = getaddrinfo(hostname, NULL /*service*/, &hint, &result);
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82 |
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83 | if (rc == 0) {
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84 | struct addrinfo *cur = result;
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85 | unsigned cnt = 0;
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86 |
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87 | printf("%-10s %s\n", header, hostname);
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88 | // puts(cur->ai_canonname); ?
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89 | while (cur) {
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90 | char *dotted, *revhost;
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91 | dotted = xmalloc_sockaddr2dotted_noport(cur->ai_addr);
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92 | revhost = xmalloc_sockaddr2hostonly_noport(cur->ai_addr);
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93 |
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94 | printf("Address %u: %s%c", ++cnt, dotted, revhost ? ' ' : '\n');
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95 | if (revhost) {
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96 | puts(revhost);
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97 | if (ENABLE_FEATURE_CLEAN_UP)
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98 | free(revhost);
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99 | }
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100 | if (ENABLE_FEATURE_CLEAN_UP)
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101 | free(dotted);
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102 | cur = cur->ai_next;
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103 | }
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104 | } else {
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105 | #if ENABLE_VERBOSE_RESOLUTION_ERRORS
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106 | bb_error_msg("can't resolve '%s': %s", hostname, gai_strerror(rc));
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107 | #else
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108 | bb_error_msg("can't resolve '%s'", hostname);
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109 | #endif
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110 | }
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111 | if (ENABLE_FEATURE_CLEAN_UP && result)
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112 | freeaddrinfo(result);
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113 | return (rc != 0);
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114 | }
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115 |
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116 | /* lookup the default nameserver and display it */
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117 | static void server_print(void)
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118 | {
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119 | char *server;
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120 | struct sockaddr *sa;
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121 |
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122 | #if ENABLE_FEATURE_IPV6
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123 | sa = (struct sockaddr*)_res._u._ext.nsaddrs[0];
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124 | if (!sa)
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125 | #endif
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126 | sa = (struct sockaddr*)&_res.nsaddr_list[0];
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127 | server = xmalloc_sockaddr2dotted_noport(sa);
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128 |
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129 | print_host(server, "Server:");
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130 | if (ENABLE_FEATURE_CLEAN_UP)
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131 | free(server);
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132 | bb_putchar('\n');
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133 | }
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134 |
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135 | /* alter the global _res nameserver structure to use
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136 | an explicit dns server instead of what is in /etc/resolv.conf */
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137 | static void set_default_dns(const char *server)
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138 | {
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139 | len_and_sockaddr *lsa;
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140 |
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141 | if (!server)
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142 | return;
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143 |
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144 | /* NB: this works even with, say, "[::1]:5353"! :) */
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145 | lsa = xhost2sockaddr(server, 53);
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146 |
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147 | if (lsa->u.sa.sa_family == AF_INET) {
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148 | _res.nscount = 1;
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149 | /* struct copy */
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150 | _res.nsaddr_list[0] = lsa->u.sin;
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151 | }
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152 | #if ENABLE_FEATURE_IPV6
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153 | /* Hoped libc can cope with IPv4 address there too.
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154 | * No such luck, glibc 2.4 segfaults even with IPv6,
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155 | * maybe I misunderstand how to make glibc use IPv6 addr?
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156 | * (uclibc 0.9.31+ should work) */
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157 | if (lsa->u.sa.sa_family == AF_INET6) {
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158 | // glibc neither SEGVs nor sends any dgrams with this
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159 | // (strace shows no socket ops):
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160 | //_res.nscount = 0;
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161 | _res._u._ext.nscount = 1;
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162 | /* store a pointer to part of malloc'ed lsa */
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163 | _res._u._ext.nsaddrs[0] = &lsa->u.sin6;
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164 | /* must not free(lsa)! */
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165 | }
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166 | #endif
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167 | }
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168 |
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169 | int nslookup_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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170 | int nslookup_main(int argc, char **argv)
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171 | {
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172 | /* We allow 1 or 2 arguments.
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173 | * The first is the name to be looked up and the second is an
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174 | * optional DNS server with which to do the lookup.
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175 | * More than 3 arguments is an error to follow the pattern of the
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176 | * standard nslookup */
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177 | if (!argv[1] || argv[1][0] == '-' || argc > 3)
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178 | bb_show_usage();
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179 |
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180 | /* initialize DNS structure _res used in printing the default
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181 | * name server and in the explicit name server option feature. */
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182 | res_init();
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183 | /* rfc2133 says this enables IPv6 lookups */
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184 | /* (but it also says "may be enabled in /etc/resolv.conf") */
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185 | /*_res.options |= RES_USE_INET6;*/
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186 |
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187 | set_default_dns(argv[2]);
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188 |
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189 | server_print();
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190 |
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191 | /* getaddrinfo and friends are free to request a resolver
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192 | * reinitialization. Just in case, set_default_dns() again
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193 | * after getaddrinfo (in server_print). This reportedly helps
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194 | * with bug 675 "nslookup does not properly use second argument"
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195 | * at least on Debian Wheezy and Openwrt AA (eglibc based).
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196 | */
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197 | set_default_dns(argv[2]);
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198 |
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199 | return print_host(argv[1], "Name:");
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200 | }
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