1272343Sngie/* $NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $ */ 2272343Sngie 3272343Sngie/*- 4272343Sngie * Copyright (c) 2013 The NetBSD Foundation, Inc. 5272343Sngie * All rights reserved. 6272343Sngie * 7272343Sngie * This code is derived from software contributed to The NetBSD Foundation 8272343Sngie * by Andreas Gustafsson. 9272343Sngie * 10272343Sngie * Redistribution and use in source and binary forms, with or without 11272343Sngie * modification, are permitted provided that the following conditions 12272343Sngie * are met: 13272343Sngie * 1. Redistributions of source code must retain the above copyright 14272343Sngie * notice, this list of conditions and the following disclaimer. 15272343Sngie * 2. Redistributions in binary form must reproduce the above copyright 16272343Sngie * notice, this list of conditions and the following disclaimer in the 17272343Sngie * documentation and/or other materials provided with the distribution. 18272343Sngie * 19272343Sngie * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20272343Sngie * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21272343Sngie * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22272343Sngie * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23272343Sngie * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24272343Sngie * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25272343Sngie * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26272343Sngie * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27272343Sngie * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28272343Sngie * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29272343Sngie * POSSIBILITY OF SUCH DAMAGE. 30272343Sngie */ 31272343Sngie 32272343Sngie/* 33272343Sngie * A minimal DNS server capable of providing canned answers to the 34272343Sngie * specific queries issued by t_hostent.sh and nothing more. 35272343Sngie */ 36272343Sngie 37272343Sngie#include <sys/cdefs.h> 38272343Sngie__RCSID("$NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $"); 39272343Sngie 40272343Sngie#include <ctype.h> 41272343Sngie#include <err.h> 42272343Sngie#include <errno.h> 43272343Sngie#include <fcntl.h> 44272343Sngie#include <memory.h> 45272343Sngie#include <stdio.h> 46272343Sngie#include <stdlib.h> 47272343Sngie#include <unistd.h> 48272343Sngie 49272343Sngie#include <sys/socket.h> 50272343Sngie 51272343Sngie#include <netinet/in.h> 52276478Sngie#ifdef __NetBSD__ 53272343Sngie#include <netinet6/in6.h> 54276478Sngie#endif 55272343Sngie 56276478Sngie#ifdef __FreeBSD__ 57276478Sngie#include <paths.h> 58276478Sngie#endif 59276478Sngie 60272343Sngieunion sockaddr_either { 61272343Sngie struct sockaddr s; 62272343Sngie struct sockaddr_in sin; 63272343Sngie struct sockaddr_in6 sin6; 64272343Sngie}; 65272343Sngie 66272343Sngie#ifdef DEBUG 67272343Sngie#define DPRINTF(...) fprintf(stderr, __VA_ARGS__) 68272343Sngie#else 69272343Sngie#define DPRINTF(...) 70272343Sngie#endif 71272343Sngie 72272343Sngie/* A DNS question and its corresponding answer */ 73272343Sngie 74272343Sngiestruct dns_data { 75272343Sngie size_t qname_size; 76272343Sngie const char *qname; /* Wire-encode question name */ 77272343Sngie int qtype; 78272343Sngie size_t answer_size; 79272343Sngie const char *answer; /* One wire-encoded answer RDATA */ 80272343Sngie}; 81272343Sngie 82272343Sngie/* Convert C string constant to length + data pair */ 83272343Sngie#define STR_DATA(s) sizeof(s) - 1, s 84272343Sngie 85272343Sngie/* Canned DNS queestion-answer pairs */ 86272343Sngiestruct dns_data data[] = { 87272343Sngie /* Forward mappings */ 88272343Sngie /* localhost IN A -> 127.0.0.1 */ 89272343Sngie { STR_DATA("\011localhost\000"), 1, 90272343Sngie STR_DATA("\177\000\000\001") }, 91272343Sngie /* localhost IN AAAA -> ::1 */ 92272343Sngie { STR_DATA("\011localhost\000"), 28, 93272343Sngie STR_DATA("\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001") }, 94272343Sngie /* sixthavenue.astron.com IN A -> 38.117.134.16 */ 95272343Sngie { STR_DATA("\013sixthavenue\006astron\003com\000"), 1, 96272343Sngie STR_DATA("\046\165\206\020") }, 97272343Sngie /* sixthavenue.astron.com IN AAAA -> 2620:106:3003:1f00:3e4a:92ff:fef4:e180 */ 98272343Sngie { STR_DATA("\013sixthavenue\006astron\003com\000"), 28, 99272343Sngie STR_DATA("\x26\x20\x01\x06\x30\x03\x1f\x00\x3e\x4a\x92\xff\xfe\xf4\xe1\x80") }, 100272343Sngie /* Reverse mappings */ 101272343Sngie { STR_DATA("\0011\0010\0010\003127\007in-addr\004arpa\000"), 12, 102272343Sngie STR_DATA("\011localhost\000") }, 103272343Sngie { STR_DATA("\0011\0010\0010\0010\0010\0010\0010\0010" 104272343Sngie "\0010\0010\0010\0010\0010\0010\0010\0010" 105272343Sngie "\0010\0010\0010\0010\0010\0010\0010\0010" 106272343Sngie "\0010\0010\0010\0010\0010\0010\0010\0010" 107272343Sngie "\003ip6\004arpa\000"), 12, 108272343Sngie STR_DATA("\011localhost\000") }, 109272343Sngie { STR_DATA("\00216\003134\003117\00238" 110272343Sngie "\007in-addr\004arpa\000"), 12, 111272343Sngie STR_DATA("\013sixthavenue\006astron\003com\000") }, 112272343Sngie { STR_DATA("\0010\0018\0011\001e\0014\001f\001e\001f" 113272343Sngie "\001f\001f\0012\0019\001a\0014\001e\0013" 114272343Sngie "\0010\0010\001f\0011\0013\0010\0010\0013" 115272343Sngie "\0016\0010\0011\0010\0010\0012\0016\0012" 116272343Sngie "\003ip6\004arpa\000"), 12, 117272343Sngie STR_DATA("\013sixthavenue\006astron\003com\000") }, 118272343Sngie /* End marker */ 119272343Sngie { STR_DATA(""), 0, STR_DATA("") } 120272343Sngie}; 121272343Sngie 122272343Sngie/* 123272343Sngie * Compare two DNS names for equality. If equal, return their 124272343Sngie * length, and if not, return zero. Does not handle compression. 125272343Sngie */ 126272343Sngiestatic int 127272343Sngiename_eq(const unsigned char *a, const unsigned char *b) { 128272343Sngie const unsigned char *a_save = a; 129272343Sngie for (;;) { 130272343Sngie int i; 131272343Sngie int lena = *a++; 132272343Sngie int lenb = *b++; 133272343Sngie if (lena != lenb) 134272343Sngie return 0; 135272343Sngie if (lena == 0) 136272343Sngie return a - a_save; 137272343Sngie for (i = 0; i < lena; i++) 138272343Sngie if (tolower(a[i]) != tolower(b[i])) 139272343Sngie return 0; 140272343Sngie a += lena; 141272343Sngie b += lena; 142272343Sngie } 143272343Sngie} 144272343Sngie 145272343Sngie#ifdef DEBUG 146272343Sngiestatic char * 147272343Sngiename2str(const void *v, char *buf, size_t buflen) { 148272343Sngie const unsigned char *a = v; 149272343Sngie char *b = buf; 150272343Sngie char *eb = buf + buflen; 151272343Sngie 152272343Sngie#define ADDC(c) do { \ 153272343Sngie if (b < eb) \ 154272343Sngie *b++ = c; \ 155272343Sngie else \ 156272343Sngie return NULL; \ 157272343Sngie } while (/*CONSTCOND*/0) 158272343Sngie for (int did = 0;; did++) { 159272343Sngie int lena = *a++; 160272343Sngie if (lena == 0) { 161272343Sngie ADDC('\0'); 162272343Sngie return buf; 163272343Sngie } 164272343Sngie if (did) 165272343Sngie ADDC('.'); 166272343Sngie for (int i = 0; i < lena; i++) 167272343Sngie ADDC(a[i]); 168272343Sngie a += lena; 169272343Sngie } 170272343Sngie} 171272343Sngie#endif 172272343Sngie 173276478Sngie#ifdef __FreeBSD__ 174276478Sngie/* XXX the daemon2_* functions should be in a library */ 175276478Sngie 176276478Sngieint __daemon2_detach_pipe[2]; 177276478Sngie 178276478Sngiestatic int 179276478Sngiedaemon2_fork(void) 180276478Sngie{ 181276478Sngie int r; 182276478Sngie int fd; 183276478Sngie int i; 184276478Sngie 185276478Sngie /* 186276478Sngie * Set up the pipe, making sure the write end does not 187276478Sngie * get allocated one of the file descriptors that will 188276478Sngie * be closed in daemon2_detach(). 189276478Sngie */ 190276478Sngie for (i = 0; i < 3; i++) { 191276478Sngie r = pipe(__daemon2_detach_pipe); 192276478Sngie if (r < 0) 193276478Sngie return -1; 194276478Sngie if (__daemon2_detach_pipe[1] <= STDERR_FILENO && 195276478Sngie (fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) { 196276478Sngie (void)dup2(fd, __daemon2_detach_pipe[0]); 197276478Sngie (void)dup2(fd, __daemon2_detach_pipe[1]); 198276478Sngie if (fd > STDERR_FILENO) 199276478Sngie (void)close(fd); 200276478Sngie continue; 201276478Sngie } 202276478Sngie break; 203276478Sngie } 204276478Sngie 205276478Sngie r = fork(); 206276478Sngie if (r < 0) { 207276478Sngie return -1; 208276478Sngie } else if (r == 0) { 209276478Sngie /* child */ 210276478Sngie close(__daemon2_detach_pipe[0]); 211276478Sngie return 0; 212276478Sngie } 213276478Sngie /* Parent */ 214276478Sngie 215276478Sngie (void) close(__daemon2_detach_pipe[1]); 216276478Sngie 217276478Sngie for (;;) { 218276478Sngie char dummy; 219276478Sngie r = read(__daemon2_detach_pipe[0], &dummy, 1); 220276478Sngie if (r < 0) { 221276478Sngie if (errno == EINTR) 222276478Sngie continue; 223276478Sngie _exit(1); 224276478Sngie } else if (r == 0) { 225276478Sngie _exit(1); 226276478Sngie } else { /* r > 0 */ 227276478Sngie _exit(0); 228276478Sngie } 229276478Sngie } 230276478Sngie} 231276478Sngie 232276478Sngiestatic int 233276478Sngiedaemon2_detach(int nochdir, int noclose) 234276478Sngie{ 235276478Sngie int r; 236276478Sngie int fd; 237276478Sngie 238276478Sngie if (setsid() == -1) 239276478Sngie return -1; 240276478Sngie 241276478Sngie if (!nochdir) 242276478Sngie (void)chdir("/"); 243276478Sngie 244276478Sngie if (!noclose && (fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) { 245276478Sngie (void)dup2(fd, STDIN_FILENO); 246276478Sngie (void)dup2(fd, STDOUT_FILENO); 247276478Sngie (void)dup2(fd, STDERR_FILENO); 248276478Sngie if (fd > STDERR_FILENO) 249276478Sngie (void)close(fd); 250276478Sngie } 251276478Sngie 252276478Sngie while (1) { 253276478Sngie r = write(__daemon2_detach_pipe[1], "", 1); 254276478Sngie if (r < 0) { 255276478Sngie if (errno == EINTR) 256276478Sngie continue; 257276478Sngie /* May get "broken pipe" here if parent is killed */ 258276478Sngie return -1; 259276478Sngie } else if (r == 0) { 260276478Sngie /* Should not happen */ 261276478Sngie return -1; 262276478Sngie } else { 263276478Sngie break; 264276478Sngie } 265276478Sngie } 266276478Sngie 267276478Sngie (void) close(__daemon2_detach_pipe[1]); 268276478Sngie 269276478Sngie return 0; 270276478Sngie} 271276478Sngie#endif 272276478Sngie 273272343Sngieint main(int argc, char **argv) { 274272343Sngie int s, r, protocol; 275272343Sngie union sockaddr_either saddr; 276272343Sngie struct dns_data *dp; 277272343Sngie unsigned char *p; 278272343Sngie char pidfile_name[40]; 279272343Sngie FILE *f; 280272343Sngie int one = 1; 281272343Sngie#ifdef DEBUG 282272343Sngie char buf1[1024], buf2[1024]; 283272343Sngie#endif 284272343Sngie 285276478Sngie#ifdef __FreeBSD__ 286276478Sngie daemon2_fork(); 287276478Sngie#endif 288272343Sngie if (argc < 2 || ((protocol = argv[1][0]) != '4' && protocol != '6')) 289272343Sngie errx(1, "usage: dns_server 4 | 6"); 290272343Sngie s = socket(protocol == '4' ? PF_INET : PF_INET6, SOCK_DGRAM, IPPROTO_UDP); 291272343Sngie if (s < 0) 292272343Sngie err(1, "socket"); 293272343Sngie if (protocol == '4') { 294272343Sngie memset(&saddr.sin, 0, sizeof(saddr.sin)); 295272343Sngie saddr.sin.sin_family = AF_INET; 296272343Sngie saddr.sin.sin_len = sizeof(saddr.sin); 297272343Sngie saddr.sin.sin_port = htons(53); 298272343Sngie saddr.sin.sin_addr.s_addr = INADDR_ANY; 299272343Sngie } else { 300272343Sngie static struct in6_addr loopback = IN6ADDR_LOOPBACK_INIT; 301272343Sngie memset(&saddr.sin6, 0, sizeof(saddr.sin6)); 302272343Sngie saddr.sin6.sin6_family = AF_INET6; 303272343Sngie saddr.sin6.sin6_len = sizeof(saddr.sin6); 304272343Sngie saddr.sin6.sin6_port = htons(53); 305272343Sngie saddr.sin6.sin6_addr = loopback; 306272343Sngie } 307272343Sngie 308272343Sngie r = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one); 309272343Sngie if (r < 0) 310272343Sngie err(1, "setsockopt"); 311272343Sngie 312272343Sngie r = bind(s, 313272343Sngie (struct sockaddr *) &saddr, 314272343Sngie protocol == '4' ? sizeof(struct sockaddr_in) : 315272343Sngie sizeof(struct sockaddr_in6)); 316272343Sngie if (r < 0) 317272343Sngie err(1, "bind"); 318272343Sngie 319272343Sngie snprintf(pidfile_name, sizeof pidfile_name, 320272343Sngie "dns_server_%c.pid", protocol); 321272343Sngie f = fopen(pidfile_name, "w"); 322272343Sngie fprintf(f, "%d", getpid()); 323272343Sngie fclose(f); 324276478Sngie#ifdef __FreeBSD__ 325272343Sngie#ifdef DEBUG 326276478Sngie daemon2_detach(0, 1); 327276478Sngie#else 328276478Sngie daemon2_detach(0, 0); 329276478Sngie#endif 330276478Sngie#else 331276478Sngie#ifdef DEBUG 332272343Sngie daemon(0, 1); 333272343Sngie#else 334272343Sngie daemon(0, 0); 335272343Sngie#endif 336276478Sngie#endif 337272343Sngie 338272343Sngie for (;;) { 339272343Sngie unsigned char buf[512]; 340272343Sngie union sockaddr_either from; 341272343Sngie ssize_t nrecv, nsent; 342272343Sngie socklen_t fromlen = 343272343Sngie protocol == '4' ? sizeof(struct sockaddr_in) : 344272343Sngie sizeof(struct sockaddr_in6); 345272343Sngie memset(buf, 0, sizeof buf); 346272343Sngie nrecv = recvfrom(s, buf, sizeof buf, 0, &from.s, &fromlen); 347272343Sngie if (nrecv < 0) 348272343Sngie err(1, "recvfrom"); 349272343Sngie if (nrecv < 12) { 350272343Sngie DPRINTF("Too short %zd\n", nrecv); 351272343Sngie continue; 352272343Sngie } 353272343Sngie if ((buf[2] & 0x80) != 0) { 354272343Sngie DPRINTF("Not a query 0x%x\n", buf[2]); 355272343Sngie continue; 356272343Sngie } 357272343Sngie if (!(buf[4] == 0 && buf[5] == 1)) { 358272343Sngie DPRINTF("QCOUNT is not 1 0x%x 0x%x\n", buf[4], buf[5]); 359272343Sngie continue; /* QDCOUNT is not 1 */ 360272343Sngie } 361272343Sngie 362272343Sngie for (dp = data; dp->qname_size != 0; dp++) { 363272343Sngie int qtype, qclass; 364272343Sngie p = buf + 12; /* Point to QNAME */ 365272343Sngie int n = name_eq(p, (const unsigned char *) dp->qname); 366272343Sngie if (n == 0) { 367272343Sngie DPRINTF("no match name %s != %s\n", 368272343Sngie name2str(p, buf1, sizeof(buf1)), 369272343Sngie name2str(dp->qname, buf2, sizeof(buf2))); 370272343Sngie continue; /* Name does not match */ 371272343Sngie } 372272343Sngie DPRINTF("match name %s\n", 373272343Sngie name2str(p, buf1, sizeof(buf1))); 374272343Sngie p += n; /* Skip QNAME */ 375272343Sngie qtype = *p++ << 8; 376272343Sngie qtype |= *p++; 377272343Sngie if (qtype != dp->qtype) { 378272343Sngie DPRINTF("no match name 0x%x != 0x%x\n", 379272343Sngie qtype, dp->qtype); 380272343Sngie continue; 381272343Sngie } 382272343Sngie DPRINTF("match type 0x%x\n", qtype); 383272343Sngie qclass = *p++ << 8; 384272343Sngie qclass |= *p++; 385272343Sngie if (qclass != 1) { /* IN */ 386272343Sngie DPRINTF("no match class %d != 1\n", qclass); 387272343Sngie continue; 388272343Sngie } 389272343Sngie DPRINTF("match class %d\n", qclass); 390272343Sngie goto found; 391272343Sngie } 392272343Sngie continue; 393272343Sngie found: 394272343Sngie buf[2] |= 0x80; /* QR */ 395272343Sngie buf[3] |= 0x80; /* RA */ 396272343Sngie memset(buf + 6, 0, 6); /* Clear ANCOUNT, NSCOUNT, ARCOUNT */ 397272343Sngie buf[7] = 1; /* ANCOUNT */ 398272343Sngie memcpy(p, dp->qname, dp->qname_size); 399272343Sngie p += dp->qname_size; 400272343Sngie *p++ = dp->qtype >> 8; 401272343Sngie *p++ = dp->qtype & 0xFF; 402272343Sngie *p++ = 0; 403272343Sngie *p++ = 1; /* IN */ 404272343Sngie memset(p, 0, 4); /* TTL = 0 */ 405272343Sngie p += 4; 406272343Sngie *p++ = 0; /* RDLENGTH MSB */ 407272343Sngie *p++ = dp->answer_size; /* RDLENGTH LSB */ 408272343Sngie memcpy(p, dp->answer, dp->answer_size); 409272343Sngie p += dp->answer_size; 410272343Sngie nsent = sendto(s, buf, p - buf, 0, &from.s, fromlen); 411272343Sngie DPRINTF("sent %zd\n", nsent); 412272343Sngie if (nsent != p - buf) 413272343Sngie warn("sendto"); 414272343Sngie } 415272343Sngie} 416