/* $NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $ */ /*- * Copyright (c) 2013 The NetBSD Foundation, Inc. * All rights reserved. * * This code is derived from software contributed to The NetBSD Foundation * by Andreas Gustafsson. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */ /* * A minimal DNS server capable of providing canned answers to the * specific queries issued by t_hostent.sh and nothing more. */ #include __RCSID("$NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $"); #include #include #include #include #include #include #include #include #include #include #include union sockaddr_either { struct sockaddr s; struct sockaddr_in sin; struct sockaddr_in6 sin6; }; #ifdef DEBUG #define DPRINTF(...) fprintf(stderr, __VA_ARGS__) #else #define DPRINTF(...) #endif /* A DNS question and its corresponding answer */ struct dns_data { size_t qname_size; const char *qname; /* Wire-encode question name */ int qtype; size_t answer_size; const char *answer; /* One wire-encoded answer RDATA */ }; /* Convert C string constant to length + data pair */ #define STR_DATA(s) sizeof(s) - 1, s /* Canned DNS queestion-answer pairs */ struct dns_data data[] = { /* Forward mappings */ /* localhost IN A -> 127.0.0.1 */ { STR_DATA("\011localhost\000"), 1, STR_DATA("\177\000\000\001") }, /* localhost IN AAAA -> ::1 */ { STR_DATA("\011localhost\000"), 28, STR_DATA("\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001") }, /* sixthavenue.astron.com IN A -> 38.117.134.16 */ { STR_DATA("\013sixthavenue\006astron\003com\000"), 1, STR_DATA("\046\165\206\020") }, /* sixthavenue.astron.com IN AAAA -> 2620:106:3003:1f00:3e4a:92ff:fef4:e180 */ { STR_DATA("\013sixthavenue\006astron\003com\000"), 28, STR_DATA("\x26\x20\x01\x06\x30\x03\x1f\x00\x3e\x4a\x92\xff\xfe\xf4\xe1\x80") }, /* Reverse mappings */ { STR_DATA("\0011\0010\0010\003127\007in-addr\004arpa\000"), 12, STR_DATA("\011localhost\000") }, { STR_DATA("\0011\0010\0010\0010\0010\0010\0010\0010" "\0010\0010\0010\0010\0010\0010\0010\0010" "\0010\0010\0010\0010\0010\0010\0010\0010" "\0010\0010\0010\0010\0010\0010\0010\0010" "\003ip6\004arpa\000"), 12, STR_DATA("\011localhost\000") }, { STR_DATA("\00216\003134\003117\00238" "\007in-addr\004arpa\000"), 12, STR_DATA("\013sixthavenue\006astron\003com\000") }, { STR_DATA("\0010\0018\0011\001e\0014\001f\001e\001f" "\001f\001f\0012\0019\001a\0014\001e\0013" "\0010\0010\001f\0011\0013\0010\0010\0013" "\0016\0010\0011\0010\0010\0012\0016\0012" "\003ip6\004arpa\000"), 12, STR_DATA("\013sixthavenue\006astron\003com\000") }, /* End marker */ { STR_DATA(""), 0, STR_DATA("") } }; /* * Compare two DNS names for equality. If equal, return their * length, and if not, return zero. Does not handle compression. */ static int name_eq(const unsigned char *a, const unsigned char *b) { const unsigned char *a_save = a; for (;;) { int i; int lena = *a++; int lenb = *b++; if (lena != lenb) return 0; if (lena == 0) return a - a_save; for (i = 0; i < lena; i++) if (tolower(a[i]) != tolower(b[i])) return 0; a += lena; b += lena; } } #ifdef DEBUG static char * name2str(const void *v, char *buf, size_t buflen) { const unsigned char *a = v; char *b = buf; char *eb = buf + buflen; #define ADDC(c) do { \ if (b < eb) \ *b++ = c; \ else \ return NULL; \ } while (/*CONSTCOND*/0) for (int did = 0;; did++) { int lena = *a++; if (lena == 0) { ADDC('\0'); return buf; } if (did) ADDC('.'); for (int i = 0; i < lena; i++) ADDC(a[i]); a += lena; } } #endif int main(int argc, char **argv) { int s, r, protocol; union sockaddr_either saddr; struct dns_data *dp; unsigned char *p; char pidfile_name[40]; FILE *f; int one = 1; #ifdef DEBUG char buf1[1024], buf2[1024]; #endif if (argc < 2 || ((protocol = argv[1][0]) != '4' && protocol != '6')) errx(1, "usage: dns_server 4 | 6"); s = socket(protocol == '4' ? PF_INET : PF_INET6, SOCK_DGRAM, IPPROTO_UDP); if (s < 0) err(1, "socket"); if (protocol == '4') { memset(&saddr.sin, 0, sizeof(saddr.sin)); saddr.sin.sin_family = AF_INET; saddr.sin.sin_len = sizeof(saddr.sin); saddr.sin.sin_port = htons(53); saddr.sin.sin_addr.s_addr = INADDR_ANY; } else { static struct in6_addr loopback = IN6ADDR_LOOPBACK_INIT; memset(&saddr.sin6, 0, sizeof(saddr.sin6)); saddr.sin6.sin6_family = AF_INET6; saddr.sin6.sin6_len = sizeof(saddr.sin6); saddr.sin6.sin6_port = htons(53); saddr.sin6.sin6_addr = loopback; } r = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one); if (r < 0) err(1, "setsockopt"); r = bind(s, (struct sockaddr *) &saddr, protocol == '4' ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6)); if (r < 0) err(1, "bind"); snprintf(pidfile_name, sizeof pidfile_name, "dns_server_%c.pid", protocol); f = fopen(pidfile_name, "w"); fprintf(f, "%d", getpid()); fclose(f); #ifdef DEBUG daemon(0, 1); #else daemon(0, 0); #endif for (;;) { unsigned char buf[512]; union sockaddr_either from; ssize_t nrecv, nsent; socklen_t fromlen = protocol == '4' ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6); memset(buf, 0, sizeof buf); nrecv = recvfrom(s, buf, sizeof buf, 0, &from.s, &fromlen); if (nrecv < 0) err(1, "recvfrom"); if (nrecv < 12) { DPRINTF("Too short %zd\n", nrecv); continue; } if ((buf[2] & 0x80) != 0) { DPRINTF("Not a query 0x%x\n", buf[2]); continue; } if (!(buf[4] == 0 && buf[5] == 1)) { DPRINTF("QCOUNT is not 1 0x%x 0x%x\n", buf[4], buf[5]); continue; /* QDCOUNT is not 1 */ } for (dp = data; dp->qname_size != 0; dp++) { int qtype, qclass; p = buf + 12; /* Point to QNAME */ int n = name_eq(p, (const unsigned char *) dp->qname); if (n == 0) { DPRINTF("no match name %s != %s\n", name2str(p, buf1, sizeof(buf1)), name2str(dp->qname, buf2, sizeof(buf2))); continue; /* Name does not match */ } DPRINTF("match name %s\n", name2str(p, buf1, sizeof(buf1))); p += n; /* Skip QNAME */ qtype = *p++ << 8; qtype |= *p++; if (qtype != dp->qtype) { DPRINTF("no match name 0x%x != 0x%x\n", qtype, dp->qtype); continue; } DPRINTF("match type 0x%x\n", qtype); qclass = *p++ << 8; qclass |= *p++; if (qclass != 1) { /* IN */ DPRINTF("no match class %d != 1\n", qclass); continue; } DPRINTF("match class %d\n", qclass); goto found; } continue; found: buf[2] |= 0x80; /* QR */ buf[3] |= 0x80; /* RA */ memset(buf + 6, 0, 6); /* Clear ANCOUNT, NSCOUNT, ARCOUNT */ buf[7] = 1; /* ANCOUNT */ memcpy(p, dp->qname, dp->qname_size); p += dp->qname_size; *p++ = dp->qtype >> 8; *p++ = dp->qtype & 0xFF; *p++ = 0; *p++ = 1; /* IN */ memset(p, 0, 4); /* TTL = 0 */ p += 4; *p++ = 0; /* RDLENGTH MSB */ *p++ = dp->answer_size; /* RDLENGTH LSB */ memcpy(p, dp->answer, dp->answer_size); p += dp->answer_size; nsent = sendto(s, buf, p - buf, 0, &from.s, fromlen); DPRINTF("sent %zd\n", nsent); if (nsent != p - buf) warn("sendto"); } }