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- /* 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
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