1 /* $NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $ */ 2 3 /*- 4 * Copyright (c) 2013 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Andreas Gustafsson. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 /* 33 * A minimal DNS server capable of providing canned answers to the 34 * specific queries issued by t_hostent.sh and nothing more. 35 */ 36 37 #include <sys/cdefs.h> 38 __RCSID("$NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $"); 39 40 #include <ctype.h> 41 #include <err.h> 42 #include <errno.h> 43 #include <fcntl.h> 44 #include <memory.h> 45 #include <stdio.h> 46 #include <stdlib.h> 47 #include <unistd.h> 48 49 #include <sys/socket.h> 50 51 #include <netinet/in.h> 52 #include <netinet6/in6.h> 53 54 union sockaddr_either { 55 struct sockaddr s; 56 struct sockaddr_in sin; 57 struct sockaddr_in6 sin6; 58 }; 59 60 #ifdef DEBUG 61 #define DPRINTF(...) fprintf(stderr, __VA_ARGS__) 62 #else 63 #define DPRINTF(...) 64 #endif 65 66 /* A DNS question and its corresponding answer */ 67 68 struct dns_data { 69 size_t qname_size; 70 const char *qname; /* Wire-encode question name */ 71 int qtype; 72 size_t answer_size; 73 const char *answer; /* One wire-encoded answer RDATA */ 74 }; 75 76 /* Convert C string constant to length + data pair */ 77 #define STR_DATA(s) sizeof(s) - 1, s 78 79 /* Canned DNS queestion-answer pairs */ 80 struct dns_data data[] = { 81 /* Forward mappings */ 82 /* localhost IN A -> 127.0.0.1 */ 83 { STR_DATA("\011localhost\000"), 1, 84 STR_DATA("\177\000\000\001") }, 85 /* localhost IN AAAA -> ::1 */ 86 { STR_DATA("\011localhost\000"), 28, 87 STR_DATA("\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001") }, 88 /* sixthavenue.astron.com IN A -> 38.117.134.16 */ 89 { STR_DATA("\013sixthavenue\006astron\003com\000"), 1, 90 STR_DATA("\046\165\206\020") }, 91 /* sixthavenue.astron.com IN AAAA -> 2620:106:3003:1f00:3e4a:92ff:fef4:e180 */ 92 { STR_DATA("\013sixthavenue\006astron\003com\000"), 28, 93 STR_DATA("\x26\x20\x01\x06\x30\x03\x1f\x00\x3e\x4a\x92\xff\xfe\xf4\xe1\x80") }, 94 /* Reverse mappings */ 95 { STR_DATA("\0011\0010\0010\003127\007in-addr\004arpa\000"), 12, 96 STR_DATA("\011localhost\000") }, 97 { STR_DATA("\0011\0010\0010\0010\0010\0010\0010\0010" 98 "\0010\0010\0010\0010\0010\0010\0010\0010" 99 "\0010\0010\0010\0010\0010\0010\0010\0010" 100 "\0010\0010\0010\0010\0010\0010\0010\0010" 101 "\003ip6\004arpa\000"), 12, 102 STR_DATA("\011localhost\000") }, 103 { STR_DATA("\00216\003134\003117\00238" 104 "\007in-addr\004arpa\000"), 12, 105 STR_DATA("\013sixthavenue\006astron\003com\000") }, 106 { STR_DATA("\0010\0018\0011\001e\0014\001f\001e\001f" 107 "\001f\001f\0012\0019\001a\0014\001e\0013" 108 "\0010\0010\001f\0011\0013\0010\0010\0013" 109 "\0016\0010\0011\0010\0010\0012\0016\0012" 110 "\003ip6\004arpa\000"), 12, 111 STR_DATA("\013sixthavenue\006astron\003com\000") }, 112 /* End marker */ 113 { STR_DATA(""), 0, STR_DATA("") } 114 }; 115 116 /* 117 * Compare two DNS names for equality. If equal, return their 118 * length, and if not, return zero. Does not handle compression. 119 */ 120 static int 121 name_eq(const unsigned char *a, const unsigned char *b) { 122 const unsigned char *a_save = a; 123 for (;;) { 124 int i; 125 int lena = *a++; 126 int lenb = *b++; 127 if (lena != lenb) 128 return 0; 129 if (lena == 0) 130 return a - a_save; 131 for (i = 0; i < lena; i++) 132 if (tolower(a[i]) != tolower(b[i])) 133 return 0; 134 a += lena; 135 b += lena; 136 } 137 } 138 139 #ifdef DEBUG 140 static char * 141 name2str(const void *v, char *buf, size_t buflen) { 142 const unsigned char *a = v; 143 char *b = buf; 144 char *eb = buf + buflen; 145 146 #define ADDC(c) do { \ 147 if (b < eb) \ 148 *b++ = c; \ 149 else \ 150 return NULL; \ 151 } while (/*CONSTCOND*/0) 152 for (int did = 0;; did++) { 153 int lena = *a++; 154 if (lena == 0) { 155 ADDC('\0'); 156 return buf; 157 } 158 if (did) 159 ADDC('.'); 160 for (int i = 0; i < lena; i++) 161 ADDC(a[i]); 162 a += lena; 163 } 164 } 165 #endif 166 167 int main(int argc, char **argv) { 168 int s, r, protocol; 169 union sockaddr_either saddr; 170 struct dns_data *dp; 171 unsigned char *p; 172 char pidfile_name[40]; 173 FILE *f; 174 int one = 1; 175 #ifdef DEBUG 176 char buf1[1024], buf2[1024]; 177 #endif 178 179 if (argc < 2 || ((protocol = argv[1][0]) != '4' && protocol != '6')) 180 errx(1, "usage: dns_server 4 | 6"); 181 s = socket(protocol == '4' ? PF_INET : PF_INET6, SOCK_DGRAM, IPPROTO_UDP); 182 if (s < 0) 183 err(1, "socket"); 184 if (protocol == '4') { 185 memset(&saddr.sin, 0, sizeof(saddr.sin)); 186 saddr.sin.sin_family = AF_INET; 187 saddr.sin.sin_len = sizeof(saddr.sin); 188 saddr.sin.sin_port = htons(53); 189 saddr.sin.sin_addr.s_addr = INADDR_ANY; 190 } else { 191 static struct in6_addr loopback = IN6ADDR_LOOPBACK_INIT; 192 memset(&saddr.sin6, 0, sizeof(saddr.sin6)); 193 saddr.sin6.sin6_family = AF_INET6; 194 saddr.sin6.sin6_len = sizeof(saddr.sin6); 195 saddr.sin6.sin6_port = htons(53); 196 saddr.sin6.sin6_addr = loopback; 197 } 198 199 r = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one); 200 if (r < 0) 201 err(1, "setsockopt"); 202 203 r = bind(s, 204 (struct sockaddr *) &saddr, 205 protocol == '4' ? sizeof(struct sockaddr_in) : 206 sizeof(struct sockaddr_in6)); 207 if (r < 0) 208 err(1, "bind"); 209 210 snprintf(pidfile_name, sizeof pidfile_name, 211 "dns_server_%c.pid", protocol); 212 f = fopen(pidfile_name, "w"); 213 fprintf(f, "%d", getpid()); 214 fclose(f); 215 #ifdef DEBUG 216 daemon(0, 1); 217 #else 218 daemon(0, 0); 219 #endif 220 221 for (;;) { 222 unsigned char buf[512]; 223 union sockaddr_either from; 224 ssize_t nrecv, nsent; 225 socklen_t fromlen = 226 protocol == '4' ? sizeof(struct sockaddr_in) : 227 sizeof(struct sockaddr_in6); 228 memset(buf, 0, sizeof buf); 229 nrecv = recvfrom(s, buf, sizeof buf, 0, &from.s, &fromlen); 230 if (nrecv < 0) 231 err(1, "recvfrom"); 232 if (nrecv < 12) { 233 DPRINTF("Too short %zd\n", nrecv); 234 continue; 235 } 236 if ((buf[2] & 0x80) != 0) { 237 DPRINTF("Not a query 0x%x\n", buf[2]); 238 continue; 239 } 240 if (!(buf[4] == 0 && buf[5] == 1)) { 241 DPRINTF("QCOUNT is not 1 0x%x 0x%x\n", buf[4], buf[5]); 242 continue; /* QDCOUNT is not 1 */ 243 } 244 245 for (dp = data; dp->qname_size != 0; dp++) { 246 int qtype, qclass; 247 p = buf + 12; /* Point to QNAME */ 248 int n = name_eq(p, (const unsigned char *) dp->qname); 249 if (n == 0) { 250 DPRINTF("no match name %s != %s\n", 251 name2str(p, buf1, sizeof(buf1)), 252 name2str(dp->qname, buf2, sizeof(buf2))); 253 continue; /* Name does not match */ 254 } 255 DPRINTF("match name %s\n", 256 name2str(p, buf1, sizeof(buf1))); 257 p += n; /* Skip QNAME */ 258 qtype = *p++ << 8; 259 qtype |= *p++; 260 if (qtype != dp->qtype) { 261 DPRINTF("no match name 0x%x != 0x%x\n", 262 qtype, dp->qtype); 263 continue; 264 } 265 DPRINTF("match type 0x%x\n", qtype); 266 qclass = *p++ << 8; 267 qclass |= *p++; 268 if (qclass != 1) { /* IN */ 269 DPRINTF("no match class %d != 1\n", qclass); 270 continue; 271 } 272 DPRINTF("match class %d\n", qclass); 273 goto found; 274 } 275 continue; 276 found: 277 buf[2] |= 0x80; /* QR */ 278 buf[3] |= 0x80; /* RA */ 279 memset(buf + 6, 0, 6); /* Clear ANCOUNT, NSCOUNT, ARCOUNT */ 280 buf[7] = 1; /* ANCOUNT */ 281 memcpy(p, dp->qname, dp->qname_size); 282 p += dp->qname_size; 283 *p++ = dp->qtype >> 8; 284 *p++ = dp->qtype & 0xFF; 285 *p++ = 0; 286 *p++ = 1; /* IN */ 287 memset(p, 0, 4); /* TTL = 0 */ 288 p += 4; 289 *p++ = 0; /* RDLENGTH MSB */ 290 *p++ = dp->answer_size; /* RDLENGTH LSB */ 291 memcpy(p, dp->answer, dp->answer_size); 292 p += dp->answer_size; 293 nsent = sendto(s, buf, p - buf, 0, &from.s, fromlen); 294 DPRINTF("sent %zd\n", nsent); 295 if (nsent != p - buf) 296 warn("sendto"); 297 } 298 } 299
Indexes created Tue Sep 23 22:09:46 GMT 2025