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 #ifdef __NetBSD__ 53 #include <netinet6/in6.h> 54 #endif 55 56 #ifdef __FreeBSD__ 57 #include <paths.h> 58 #endif 59 60 union sockaddr_either { 61 struct sockaddr s; 62 struct sockaddr_in sin; 63 struct sockaddr_in6 sin6; 64 }; 65 66 #ifdef DEBUG 67 #define DPRINTF(...) fprintf(stderr, __VA_ARGS__) 68 #else 69 #define DPRINTF(...) 70 #endif 71 72 /* A DNS question and its corresponding answer */ 73 74 struct dns_data { 75 size_t qname_size; 76 const char *qname; /* Wire-encode question name */ 77 int qtype; 78 size_t answer_size; 79 const char *answer; /* One wire-encoded answer RDATA */ 80 }; 81 82 /* Convert C string constant to length + data pair */ 83 #define STR_DATA(s) sizeof(s) - 1, s 84 85 /* Canned DNS queestion-answer pairs */ 86 struct dns_data data[] = { 87 /* Forward mappings */ 88 /* localhost IN A -> 127.0.0.1 */ 89 { STR_DATA("\011localhost\000"), 1, 90 STR_DATA("\177\000\000\001") }, 91 /* localhost IN AAAA -> ::1 */ 92 { STR_DATA("\011localhost\000"), 28, 93 STR_DATA("\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001") }, 94 /* sixthavenue.astron.com IN A -> 38.117.134.16 */ 95 { STR_DATA("\013sixthavenue\006astron\003com\000"), 1, 96 STR_DATA("\046\165\206\020") }, 97 /* sixthavenue.astron.com IN AAAA -> 2620:106:3003:1f00:3e4a:92ff:fef4:e180 */ 98 { STR_DATA("\013sixthavenue\006astron\003com\000"), 28, 99 STR_DATA("\x26\x20\x01\x06\x30\x03\x1f\x00\x3e\x4a\x92\xff\xfe\xf4\xe1\x80") }, 100 /* Reverse mappings */ 101 { STR_DATA("\0011\0010\0010\003127\007in-addr\004arpa\000"), 12, 102 STR_DATA("\011localhost\000") }, 103 { STR_DATA("\0011\0010\0010\0010\0010\0010\0010\0010" 104 "\0010\0010\0010\0010\0010\0010\0010\0010" 105 "\0010\0010\0010\0010\0010\0010\0010\0010" 106 "\0010\0010\0010\0010\0010\0010\0010\0010" 107 "\003ip6\004arpa\000"), 12, 108 STR_DATA("\011localhost\000") }, 109 { STR_DATA("\00216\003134\003117\00238" 110 "\007in-addr\004arpa\000"), 12, 111 STR_DATA("\013sixthavenue\006astron\003com\000") }, 112 { STR_DATA("\0010\0018\0011\001e\0014\001f\001e\001f" 113 "\001f\001f\0012\0019\001a\0014\001e\0013" 114 "\0010\0010\001f\0011\0013\0010\0010\0013" 115 "\0016\0010\0011\0010\0010\0012\0016\0012" 116 "\003ip6\004arpa\000"), 12, 117 STR_DATA("\013sixthavenue\006astron\003com\000") }, 118 /* End marker */ 119 { STR_DATA(""), 0, STR_DATA("") } 120 }; 121 122 /* 123 * Compare two DNS names for equality. If equal, return their 124 * length, and if not, return zero. Does not handle compression. 125 */ 126 static int 127 name_eq(const unsigned char *a, const unsigned char *b) { 128 const unsigned char *a_save = a; 129 for (;;) { 130 int i; 131 int lena = *a++; 132 int lenb = *b++; 133 if (lena != lenb) 134 return 0; 135 if (lena == 0) 136 return a - a_save; 137 for (i = 0; i < lena; i++) 138 if (tolower(a[i]) != tolower(b[i])) 139 return 0; 140 a += lena; 141 b += lena; 142 } 143 } 144 145 #ifdef DEBUG 146 static char * 147 name2str(const void *v, char *buf, size_t buflen) { 148 const unsigned char *a = v; 149 char *b = buf; 150 char *eb = buf + buflen; 151 152 #define ADDC(c) do { \ 153 if (b < eb) \ 154 *b++ = c; \ 155 else \ 156 return NULL; \ 157 } while (/*CONSTCOND*/0) 158 for (int did = 0;; did++) { 159 int lena = *a++; 160 if (lena == 0) { 161 ADDC('\0'); 162 return buf; 163 } 164 if (did) 165 ADDC('.'); 166 for (int i = 0; i < lena; i++) 167 ADDC(a[i]); 168 a += lena; 169 } 170 } 171 #endif 172 173 #ifdef __FreeBSD__ 174 /* XXX the daemon2_* functions should be in a library */ 175 176 int __daemon2_detach_pipe[2]; 177 178 static int 179 daemon2_fork(void) 180 { 181 int r; 182 int fd; 183 int i; 184 185 /* 186 * Set up the pipe, making sure the write end does not 187 * get allocated one of the file descriptors that will 188 * be closed in daemon2_detach(). 189 */ 190 for (i = 0; i < 3; i++) { 191 r = pipe(__daemon2_detach_pipe); 192 if (r < 0) 193 return -1; 194 if (__daemon2_detach_pipe[1] <= STDERR_FILENO && 195 (fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) { 196 (void)dup2(fd, __daemon2_detach_pipe[0]); 197 (void)dup2(fd, __daemon2_detach_pipe[1]); 198 if (fd > STDERR_FILENO) 199 (void)close(fd); 200 continue; 201 } 202 break; 203 } 204 205 r = fork(); 206 if (r < 0) { 207 return -1; 208 } else if (r == 0) { 209 /* child */ 210 close(__daemon2_detach_pipe[0]); 211 return 0; 212 } 213 /* Parent */ 214 215 (void) close(__daemon2_detach_pipe[1]); 216 217 for (;;) { 218 char dummy; 219 r = read(__daemon2_detach_pipe[0], &dummy, 1); 220 if (r < 0) { 221 if (errno == EINTR) 222 continue; 223 _exit(1); 224 } else if (r == 0) { 225 _exit(1); 226 } else { /* r > 0 */ 227 _exit(0); 228 } 229 } 230 } 231 232 static int 233 daemon2_detach(int nochdir, int noclose) 234 { 235 int r; 236 int fd; 237 238 if (setsid() == -1) 239 return -1; 240 241 if (!nochdir) 242 (void)chdir("/"); 243 244 if (!noclose && (fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) { 245 (void)dup2(fd, STDIN_FILENO); 246 (void)dup2(fd, STDOUT_FILENO); 247 (void)dup2(fd, STDERR_FILENO); 248 if (fd > STDERR_FILENO) 249 (void)close(fd); 250 } 251 252 while (1) { 253 r = write(__daemon2_detach_pipe[1], "", 1); 254 if (r < 0) { 255 if (errno == EINTR) 256 continue; 257 /* May get "broken pipe" here if parent is killed */ 258 return -1; 259 } else if (r == 0) { 260 /* Should not happen */ 261 return -1; 262 } else { 263 break; 264 } 265 } 266 267 (void) close(__daemon2_detach_pipe[1]); 268 269 return 0; 270 } 271 #endif 272 273 int main(int argc, char **argv) { 274 int s, r, protocol; 275 union sockaddr_either saddr; 276 struct dns_data *dp; 277 unsigned char *p; 278 char pidfile_name[40]; 279 FILE *f; 280 int one = 1; 281 #ifdef DEBUG 282 char buf1[1024], buf2[1024]; 283 #endif 284 285 #ifdef __FreeBSD__ 286 daemon2_fork(); 287 #endif 288 if (argc < 2 || ((protocol = argv[1][0]) != '4' && protocol != '6')) 289 errx(1, "usage: dns_server 4 | 6"); 290 s = socket(protocol == '4' ? PF_INET : PF_INET6, SOCK_DGRAM, IPPROTO_UDP); 291 if (s < 0) 292 err(1, "socket"); 293 if (protocol == '4') { 294 memset(&saddr.sin, 0, sizeof(saddr.sin)); 295 saddr.sin.sin_family = AF_INET; 296 saddr.sin.sin_len = sizeof(saddr.sin); 297 saddr.sin.sin_port = htons(53); 298 saddr.sin.sin_addr.s_addr = INADDR_ANY; 299 } else { 300 static struct in6_addr loopback = IN6ADDR_LOOPBACK_INIT; 301 memset(&saddr.sin6, 0, sizeof(saddr.sin6)); 302 saddr.sin6.sin6_family = AF_INET6; 303 saddr.sin6.sin6_len = sizeof(saddr.sin6); 304 saddr.sin6.sin6_port = htons(53); 305 saddr.sin6.sin6_addr = loopback; 306 } 307 308 r = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one); 309 if (r < 0) 310 err(1, "setsockopt"); 311 312 r = bind(s, 313 (struct sockaddr *) &saddr, 314 protocol == '4' ? sizeof(struct sockaddr_in) : 315 sizeof(struct sockaddr_in6)); 316 if (r < 0) 317 err(1, "bind"); 318 319 snprintf(pidfile_name, sizeof pidfile_name, 320 "dns_server_%c.pid", protocol); 321 f = fopen(pidfile_name, "w"); 322 fprintf(f, "%d", getpid()); 323 fclose(f); 324 #ifdef __FreeBSD__ 325 #ifdef DEBUG 326 daemon2_detach(0, 1); 327 #else 328 daemon2_detach(0, 0); 329 #endif 330 #else 331 #ifdef DEBUG 332 daemon(0, 1); 333 #else 334 daemon(0, 0); 335 #endif 336 #endif 337 338 for (;;) { 339 unsigned char buf[512]; 340 union sockaddr_either from; 341 ssize_t nrecv, nsent; 342 socklen_t fromlen = 343 protocol == '4' ? sizeof(struct sockaddr_in) : 344 sizeof(struct sockaddr_in6); 345 memset(buf, 0, sizeof buf); 346 nrecv = recvfrom(s, buf, sizeof buf, 0, &from.s, &fromlen); 347 if (nrecv < 0) 348 err(1, "recvfrom"); 349 if (nrecv < 12) { 350 DPRINTF("Too short %zd\n", nrecv); 351 continue; 352 } 353 if ((buf[2] & 0x80) != 0) { 354 DPRINTF("Not a query 0x%x\n", buf[2]); 355 continue; 356 } 357 if (!(buf[4] == 0 && buf[5] == 1)) { 358 DPRINTF("QCOUNT is not 1 0x%x 0x%x\n", buf[4], buf[5]); 359 continue; /* QDCOUNT is not 1 */ 360 } 361 362 for (dp = data; dp->qname_size != 0; dp++) { 363 int qtype, qclass; 364 p = buf + 12; /* Point to QNAME */ 365 int n = name_eq(p, (const unsigned char *) dp->qname); 366 if (n == 0) { 367 DPRINTF("no match name %s != %s\n", 368 name2str(p, buf1, sizeof(buf1)), 369 name2str(dp->qname, buf2, sizeof(buf2))); 370 continue; /* Name does not match */ 371 } 372 DPRINTF("match name %s\n", 373 name2str(p, buf1, sizeof(buf1))); 374 p += n; /* Skip QNAME */ 375 qtype = *p++ << 8; 376 qtype |= *p++; 377 if (qtype != dp->qtype) { 378 DPRINTF("no match name 0x%x != 0x%x\n", 379 qtype, dp->qtype); 380 continue; 381 } 382 DPRINTF("match type 0x%x\n", qtype); 383 qclass = *p++ << 8; 384 qclass |= *p++; 385 if (qclass != 1) { /* IN */ 386 DPRINTF("no match class %d != 1\n", qclass); 387 continue; 388 } 389 DPRINTF("match class %d\n", qclass); 390 goto found; 391 } 392 continue; 393 found: 394 buf[2] |= 0x80; /* QR */ 395 buf[3] |= 0x80; /* RA */ 396 memset(buf + 6, 0, 6); /* Clear ANCOUNT, NSCOUNT, ARCOUNT */ 397 buf[7] = 1; /* ANCOUNT */ 398 memcpy(p, dp->qname, dp->qname_size); 399 p += dp->qname_size; 400 *p++ = dp->qtype >> 8; 401 *p++ = dp->qtype & 0xFF; 402 *p++ = 0; 403 *p++ = 1; /* IN */ 404 memset(p, 0, 4); /* TTL = 0 */ 405 p += 4; 406 *p++ = 0; /* RDLENGTH MSB */ 407 *p++ = dp->answer_size; /* RDLENGTH LSB */ 408 memcpy(p, dp->answer, dp->answer_size); 409 p += dp->answer_size; 410 nsent = sendto(s, buf, p - buf, 0, &from.s, fromlen); 411 DPRINTF("sent %zd\n", nsent); 412 if (nsent != p - buf) 413 warn("sendto"); 414 } 415 } 416