/* resolv.c: DNS Resolver * * Copyright (C) 1998 Kenneth Albanowski <kjahds@kjahds.com>, * The Silver Hammer Group, Ltd. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Library General Public * License as published by the Free Software Foundation; either * version 2 of the License, or (at your option) any later version. * * 5-Oct-2000 W. Greathouse wgreathouse@smva.com * Fix memory leak and memory corruption. * -- Every name resolution resulted in * a new parse of resolv.conf and new * copy of nameservers allocated by * strdup. * -- Every name resolution resulted in * a new read of resolv.conf without * resetting index from prior read... * resulting in exceeding array bounds. * * Limit nameservers read from resolv.conf * * Add "search" domains from resolv.conf * * Some systems will return a security * signature along with query answer for * dynamic DNS entries. * -- skip/ignore this answer * * Include arpa/nameser.h for defines. * * General cleanup * */ #include <string.h> #include <stdio.h> #include <signal.h> #include <errno.h> #include <sys/socket.h> #include <sys/types.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdlib.h> #include <unistd.h> #include <cfgfile.h> #include <resolv.h> #include <arpa/nameser.h> #define MAX_RECURSE 5 #define REPLY_TIMEOUT 10 #define MAX_RETRIES 15 #define MAX_SERVERS 3 #define MAX_SEARCH 4 #undef DEBUG #ifdef DEBUG static inline void DPRINTF(const char *format, ...) { va_list args; va_start(args, format); vfprintf(stderr, format, args); va_end(args); } #else static inline void DPRINTF(const char *format, ...) { } #endif #ifdef L_encodeh int encode_header(struct resolv_header *h, unsigned char *dest, int maxlen) { if (maxlen < HFIXEDSZ) return -1; dest[0] = (h->id & 0xff00) >> 8; dest[1] = (h->id & 0x00ff) >> 0; dest[2] = (h->qr ? 0x80 : 0) | ((h->opcode & 0x0f) << 3) | (h->aa ? 0x04 : 0) | (h->tc ? 0x02 : 0) | (h->rd ? 0x01 : 0); dest[3] = (h->ra ? 0x80 : 0) | (h->rcode & 0x0f); dest[4] = (h->qdcount & 0xff00) >> 8; dest[5] = (h->qdcount & 0x00ff) >> 0; dest[6] = (h->ancount & 0xff00) >> 8; dest[7] = (h->ancount & 0x00ff) >> 0; dest[8] = (h->nscount & 0xff00) >> 8; dest[9] = (h->nscount & 0x00ff) >> 0; dest[10] = (h->arcount & 0xff00) >> 8; dest[11] = (h->arcount & 0x00ff) >> 0; return HFIXEDSZ; } #endif #ifdef L_decodeh int decode_header(unsigned char *data, struct resolv_header *h) { h->id = (data[0] << 8) | data[1]; h->qr = (data[2] & 0x80) ? 1 : 0; h->opcode = (data[2] >> 3) & 0x0f; h->aa = (data[2] & 0x04) ? 1 : 0; h->tc = (data[2] & 0x02) ? 1 : 0; h->rd = (data[2] & 0x01) ? 1 : 0; h->ra = (data[3] & 0x80) ? 1 : 0; h->rcode = data[3] & 0x0f; h->qdcount = (data[4] << 8) | data[5]; h->ancount = (data[6] << 8) | data[7]; h->nscount = (data[8] << 8) | data[9]; h->arcount = (data[10] << 8) | data[11]; return HFIXEDSZ; } #endif #ifdef L_encoded /* Encode a dotted string into nameserver transport-level encoding. This routine is fairly dumb, and doesn't attempt to compress the data */ int encode_dotted(const char *dotted, unsigned char *dest, int maxlen) { int used = 0; while (dotted && *dotted) { char *c = strchr(dotted, '.'); int l = c ? c - dotted : strlen(dotted); if (l >= (maxlen - used - 1)) return -1; dest[used++] = l; memcpy(dest + used, dotted, l); used += l; if (c) dotted = c + 1; else break; } if (maxlen < 1) return -1; dest[used++] = 0; return used; } #endif #ifdef L_decoded /* Decode a dotted string from nameserver transport-level encoding. This routine understands compressed data. */ int decode_dotted(const unsigned char *data, int offset, char *dest, int maxlen) { int l; int measure = 1; int total = 0; int used = 0; if (!data) return -1; while ((l = data[offset++])) { if (measure && total++) break; if ((l & 0xc0) == (0xc0)) { if (measure) total++; /* compressed item, redirect */ offset = ((l & 0x3f) << 8) | data[offset]; measure = 0; continue; } if ((used + l + 1) >= maxlen) return -1; memcpy(dest + used, data + offset, l); offset += l; used += l; if (measure) total += l; if (data[offset] != 0) dest[used++] = '.'; else dest[used++] = '\0'; } DPRINTF("Total decode len = %d\n", total); return total; } #endif #ifdef L_lengthd int length_dotted(const unsigned char *data, int offset) { int orig_offset = offset; int l; if (!data) return -1; while ((l = data[offset++])) { if ((l & 0xc0) == (0xc0)) { offset++; break; } offset += l; } return offset - orig_offset; } #endif #ifdef L_encodeq int encode_question(struct resolv_question *q, unsigned char *dest, int maxlen) { int i; i = encode_dotted(q->dotted, dest, maxlen); if (i < 0) return i; dest += i; maxlen -= i; if (maxlen < 4) return -1; dest[0] = (q->qtype & 0xff00) >> 8; dest[1] = (q->qtype & 0x00ff) >> 0; dest[2] = (q->qclass & 0xff00) >> 8; dest[3] = (q->qclass & 0x00ff) >> 0; return i + 4; } #endif #ifdef L_decodeq int decode_question(unsigned char *message, int offset, struct resolv_question *q) { char temp[256]; int i; i = decode_dotted(message, offset, temp, sizeof(temp)); if (i < 0) return i; offset += i; q->dotted = strdup(temp); q->qtype = (message[offset + 0] << 8) | message[offset + 1]; q->qclass = (message[offset + 2] << 8) | message[offset + 3]; return i + 4; } #endif #ifdef L_lengthq int length_question(unsigned char *message, int offset) { int i; i = length_dotted(message, offset); if (i < 0) return i; return i + 4; } #endif #ifdef L_encodea int encode_answer(struct resolv_answer *a, unsigned char *dest, int maxlen) { int i; i = encode_dotted(a->dotted, dest, maxlen); if (i < 0) return i; dest += i; maxlen -= i; if (maxlen < (RRFIXEDSZ+a->rdlength)) return -1; *dest++ = (a->atype & 0xff00) >> 8; *dest++ = (a->atype & 0x00ff) >> 0; *dest++ = (a->aclass & 0xff00) >> 8; *dest++ = (a->aclass & 0x00ff) >> 0; *dest++ = (a->ttl & 0xff000000) >> 24; *dest++ = (a->ttl & 0x00ff0000) >> 16; *dest++ = (a->ttl & 0x0000ff00) >> 8; *dest++ = (a->ttl & 0x000000ff) >> 0; *dest++ = (a->rdlength & 0xff00) >> 8; *dest++ = (a->rdlength & 0x00ff) >> 0; memcpy(dest, a->rdata, a->rdlength); return i + RRFIXEDSZ + a->rdlength; } #endif #ifdef L_decodea int decode_answer(unsigned char *message, int offset, struct resolv_answer *a) { char temp[256]; int i; i = decode_dotted(message, offset, temp, sizeof(temp)); if (i < 0) return i; message += offset + i; a->dotted = strdup(temp); a->atype = (message[0] << 8) | message[1]; message += 2; a->aclass = (message[0] << 8) | message[1]; message += 2; a->ttl = (message[0] << 24) | (message[1] << 16) | (message[2] << 8) | (message[3] << 0); message += 4; a->rdlength = (message[0] << 8) | message[1]; message += 2; a->rdata = message; a->rdoffset = offset + i + RRFIXEDSZ; DPRINTF("i=%d,rdlength=%d\n", i, a->rdlength); return i + RRFIXEDSZ + a->rdlength; } #endif #ifdef L_encodep int encode_packet(struct resolv_header *h, struct resolv_question **q, struct resolv_answer **an, struct resolv_answer **ns, struct resolv_answer **ar, unsigned char *dest, int maxlen) { int i, total = 0; int j; i = encode_header(h, dest, maxlen); if (i < 0) return i; dest += i; maxlen -= i; total += i; for (j = 0; j < h->qdcount; j++) { i = encode_question(q[j], dest, maxlen); if (i < 0) return i; dest += i; maxlen -= i; total += i; } for (j = 0; j < h->ancount; j++) { i = encode_answer(an[j], dest, maxlen); if (i < 0) return i; dest += i; maxlen -= i; total += i; } for (j = 0; j < h->nscount; j++) { i = encode_answer(ns[j], dest, maxlen); if (i < 0) return i; dest += i; maxlen -= i; total += i; } for (j = 0; j < h->arcount; j++) { i = encode_answer(ar[j], dest, maxlen); if (i < 0) return i; dest += i; maxlen -= i; total += i; } return total; } #endif #ifdef L_decodep int decode_packet(unsigned char *data, struct resolv_header *h) { return decode_header(data, h); } #endif #ifdef L_formquery int form_query(int id, const char *name, int type, unsigned char *packet, int maxlen) { struct resolv_header h; struct resolv_question q; int i, j; memset(&h, 0, sizeof(h)); h.id = id; h.qdcount = 1; q.dotted = (char *) name; q.qtype = type; q.qclass = C_IN; /* CLASS_IN */ i = encode_header(&h, packet, maxlen); if (i < 0) return i; j = encode_question(&q, packet + i, maxlen - i); if (j < 0) return j; return i + j; } #endif #ifdef L_dnslookup int dns_caught_signal = 0; void dns_catch_signal(int signo) { dns_caught_signal = 1; } int dns_lookup(const char *name, int type, int nscount, const char **nsip, unsigned char **outpacket, struct resolv_answer *a) { static int id = 1; int i, j, len, fd, pos; static int ns = 0; struct sockaddr_in sa; int oldalarm; __sighandler_t oldhandler; struct resolv_header h; struct resolv_question q; int retries = 0; unsigned char * packet = malloc(PACKETSZ); unsigned char * lookup = malloc(MAXDNAME); int variant = 0; extern int searchdomains; extern const char * searchdomain[MAX_SEARCH]; fd = -1; if (!packet || !lookup || !nscount) goto fail; DPRINTF("Looking up type %d answer for '%s'\n", type, name); ns %= nscount; while (retries++ < MAX_RETRIES) { if (fd != -1) close(fd); fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); if (fd == -1) goto fail; memset(packet, 0, PACKETSZ); memset(&h, 0, sizeof(h)); h.id = ++id; h.qdcount = 1; h.rd = 1; DPRINTF("encoding header\n", h.rd); i = encode_header(&h, packet, PACKETSZ); if (i < 0) goto fail; strncpy(lookup,name,MAXDNAME); if (variant < searchdomains) { strncat(lookup,".", MAXDNAME); strncat(lookup,searchdomain[variant], MAXDNAME); } DPRINTF("lookup name: %s\n", lookup); q.dotted = (char *)lookup; q.qtype = type; q.qclass = C_IN; /* CLASS_IN */ j = encode_question(&q, packet+i, PACKETSZ-i); if (j < 0) goto fail; len = i + j; DPRINTF("On try %d, sending query to port %d of machine %s\n", retries, NAMESERVER_PORT, nsip[ns]); sa.sin_family = AF_INET; sa.sin_port = htons(NAMESERVER_PORT); sa.sin_addr.s_addr = inet_addr(nsip[ns]); if (connect(fd, (struct sockaddr *) &sa, sizeof(sa)) == -1) { if (errno == ENETUNREACH) { /* routing error, presume not transient */ goto tryall; } else /* retry */ continue; } DPRINTF("Transmitting packet of length %d, id=%d, qr=%d\n", len, h.id, h.qr); send(fd, packet, len, 0); dns_caught_signal = 0; oldalarm = alarm(REPLY_TIMEOUT); oldhandler = signal(SIGALRM, dns_catch_signal); i = recv(fd, packet, PACKETSZ, 0); alarm(0); signal(SIGALRM, oldhandler); alarm(oldalarm); DPRINTF("Timeout=%d, len=%d\n", dns_caught_signal, i); if (dns_caught_signal) /* timed out, so retry send and receive, to next nameserver on queue */ goto again; if (i < HFIXEDSZ) /* too short ! */ goto again; decode_header(packet, &h); DPRINTF("id = %d, qr = %d\n", h.id, h.qr); if ((h.id != id) || (!h.qr)) /* unsolicited */ goto again; DPRINTF("Got response %s\n", "(i think)!"); DPRINTF("qrcount=%d,ancount=%d,nscount=%d,arcount=%d\n", h.qdcount, h.ancount, h.nscount, h.arcount); DPRINTF("opcode=%d,aa=%d,tc=%d,rd=%d,ra=%d,rcode=%d\n", h.opcode, h.aa, h.tc, h.rd, h.ra, h.rcode); if ((h.rcode) || (h.ancount < 1)) { /* negative result, not present */ goto again; } pos = HFIXEDSZ; for (j = 0; j < h.qdcount; j++) { DPRINTF("Skipping question %d at %d\n", j, pos); i = length_question(packet, pos); DPRINTF("Length of question %d is %d\n", j, i); if (i < 0) goto again; pos += i; } DPRINTF("Decoding answer at pos %d\n", pos); for (j=0;j<h.ancount;j++) { i = decode_answer(packet, pos, a); if (i<0) { DPRINTF("failed decode %d\n", i); goto again; } /* For all but T_SIG, accept first answer */ if (a->atype != T_SIG) break; DPRINTF("skipping T_SIG %d\n", i); free(a->dotted); pos += i; } DPRINTF("Answer name = |%s|\n", a->dotted); DPRINTF("Answer type = |%d|\n", a->atype); close(fd); if (outpacket) *outpacket = packet; else free(packet); return (0); /* success! */ tryall: /* if there are other nameservers, give them a go, otherwise return with error */ variant = 0; if (retries >= nscount*(searchdomains+1)) goto fail; again: /* if there are searchdomains, try them or fallback as passed */ if (variant < searchdomains) { /* next search */ variant++; } else { /* next server, first search */ ns = (ns + 1) % nscount; variant = 0; } } fail: if (fd != -1) close(fd); if (lookup) free(lookup); if (packet) free(packet); return -1; } #endif #ifdef L_resolveaddress int resolve_address(const char *address, int nscount, const char **nsip, struct in_addr *in) { unsigned char *packet; struct resolv_answer a; char temp[256]; int i; int nest = 0; if (!address || !in) return -1; strncpy(temp, address, sizeof(temp)); for (;;) { i = dns_lookup(temp, T_A, nscount, nsip, &packet, &a); if (i < 0) return -1; free(a.dotted); if (a.atype == T_CNAME) { /* CNAME */ i = decode_dotted(packet, a.rdoffset, temp, sizeof(temp)); free(packet); if (i < 0) return -1; if (++nest > MAX_RECURSE) return -1; continue; } else if (a.atype == T_A) { /* ADDRESS */ free(packet); break; } else { free(packet); return -1; } } if (in) memcpy(in, a.rdata, INADDRSZ); /* IPv4 T_A */ return 0; } #endif #ifdef L_resolvemailbox int resolve_mailbox(const char *address, int nscount, const char **nsip, struct in_addr *in) { struct resolv_answer a; unsigned char *packet; char temp[256]; int nest = 0; int i; if (!address || !in) return -1; /* look up mail exchange */ i = dns_lookup(address, T_MX, nscount, nsip, &packet, &a); strncpy(temp, address, sizeof(temp)); if (i >= 0) { i = decode_dotted(packet, a.rdoffset+2, temp, sizeof(temp)); free(packet); } for (;;) { i = dns_lookup(temp, T_A, nscount, nsip, &packet, &a); if (i < 0) return -1; free(a.dotted); if (a.atype == T_CNAME) { /* CNAME */ i = decode_dotted(packet, a.rdoffset, temp, sizeof(temp)); free(packet); if (i < 0) return i; if (++nest > MAX_RECURSE) return -1; continue; } else if (a.atype == T_A) { /* ADDRESS */ free(packet); break; } else { free(packet); return -1; } } if (in) memcpy(in, a.rdata, INADDRSZ); /* IPv4 */ return 0; } #endif extern int nameservers; extern const char * nameserver[MAX_SERVERS]; extern int searchdomains; extern const char * searchdomain[MAX_SEARCH]; #ifdef L_opennameservers int nameservers; const char * nameserver[MAX_SERVERS]; int searchdomains; const char * searchdomain[MAX_SEARCH]; int open_nameservers() { FILE *fp; char **arg; int i; if (nameservers > 0) return 0; if ((fp = fopen("/etc/resolv.conf", "r"))) { if (0 != (arg = cfgfind(fp, "nameserver"))) { for (i=1; arg[i] && nameservers <= MAX_SERVERS; i++) { nameserver[nameservers++] = strdup(arg[i]); DPRINTF("adding nameserver %s\n",arg[i]); } } if (0 != (arg = cfgfind(fp, "search"))) { for (i=1; arg[i] && searchdomains <= MAX_SEARCH; i++) { searchdomain[searchdomains++] = strdup(arg[i]); DPRINTF("adding search %s\n",arg[i]); } } fclose(fp); } else { DPRINTF("failed to open %s\n", "resolv.conf"); } DPRINTF("nameservers = %d\n", nameservers); return 0; } #endif #ifdef L_closenameservers void close_nameservers(void) { while (nameservers > 0) free((void*)nameserver[--nameservers]); } #endif #ifdef L_resolvename const char *resolve_name(const char *name, int mailbox) { struct in_addr in; int i; /* shortcut: is it a valid IP address to begin with? */ if (inet_aton(name, &in)) return name; open_nameservers(); DPRINTF("looking up '%s', mailbox=%d, nameservers=%d\n", name, mailbox, nameservers); if (mailbox) i = resolve_mailbox(name, nameservers, nameserver, &in); else i = resolve_address(name, nameservers, nameserver, &in); if (i < 0) return 0; DPRINTF("success = '%s'\n", inet_ntoa(in)); return inet_ntoa(in); } #endif #ifdef L_gethostbyname struct hostent *gethostbyname(const char *name) { static struct hostent h; static char namebuf[256]; static struct in_addr in; static struct in_addr *addr_list[2]; unsigned char *packet; struct resolv_answer a; int i; int nest = 0; open_nameservers(); if (!name) return 0; memset(&h, 0, sizeof(h)); addr_list[0] = ∈ addr_list[1] = 0; strcpy(namebuf, name); for (;;) { i = dns_lookup(namebuf, 1, nameservers, nameserver, &packet, &a); if (i < 0) return 0; strncpy(namebuf, a.dotted, sizeof(namebuf)); free(a.dotted); if (a.atype == T_CNAME) { /* CNAME */ i = decode_dotted(packet, a.rdoffset, namebuf, sizeof(namebuf)); free(packet); if (i < 0) return 0; if (++nest > MAX_RECURSE) return 0; continue; } else if (a.atype == T_A) { /* ADDRESS */ memcpy(&in, a.rdata, sizeof(in)); h.h_name = namebuf; h.h_addrtype = AF_INET; h.h_length = sizeof(in); h.h_addr_list = (char **) addr_list; free(packet); break; } else { free(packet); return 0; } } return &h; } #endif #ifdef L_gethostbyaddr struct hostent *gethostbyaddr(const char *addr, int len, int type) { static struct hostent h; static char namebuf[256]; static struct in_addr in; static struct in_addr *addr_list[2]; unsigned char *packet; struct resolv_answer a; int i; int nest = 0; if (!addr || (len != sizeof(in)) || (type != AF_INET)) return 0; memcpy(&in.s_addr, addr, len); open_nameservers(); memset(&h, 0, sizeof(h)); addr_list[0] = ∈ addr_list[1] = 0; sprintf(namebuf, "%d.%d.%d.%d.in-addr.arpa", (in.s_addr >> 24) & 0xff, (in.s_addr >> 16) & 0xff, (in.s_addr >> 8) & 0xff, (in.s_addr >> 0) & 0xff); for (;;) { i = dns_lookup(namebuf, T_PTR, nameservers, nameserver, &packet, &a); if (i < 0) return 0; strncpy(namebuf, a.dotted, sizeof(namebuf)); free(a.dotted); if (a.atype == T_CNAME) { /* CNAME */ i = decode_dotted(packet, a.rdoffset, namebuf, sizeof(namebuf)); free(packet); if (i < 0) return 0; if (++nest > MAX_RECURSE) return 0; continue; } else if (a.atype == T_PTR) { /* ADDRESS */ i = decode_dotted(packet, a.rdoffset, namebuf, sizeof(namebuf)); free(packet); h.h_name = namebuf; h.h_addrtype = AF_INET; h.h_length = sizeof(in); h.h_addr_list = (char **) addr_list; break; } else { free(packet); return 0; } } return &h; } #endif