dnsd: fix a number of bugs. Ideas by Ming-Ching Tiew (mctiew AT yahoo.com)
function old new delta undot - 42 +42 dnsd_main 1394 1213 -181 ------------------------------------------------------------------------------ (add/remove: 1/0 grow/shrink: 0/1 up/down: 42/-181) Total: -139 bytes
This commit is contained in:
Denis Vlasenko
parent
135cecbbce
commit
ddbf3bf35f
@ -24,73 +24,63 @@
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#define DEBUG 0
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enum {
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MAX_HOST_LEN = 16, // longest host name allowed is 15
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IP_STRING_LEN = 18, // .xxx.xxx.xxx.xxx\0
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/* Can tweak this */
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DEFAULT_TTL = 120,
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//must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
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MAX_NAME_LEN = (IP_STRING_LEN + 13),
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/* Cannot get bigger packets than 512 per RFC1035
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In practice this can be set considerably smaller:
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Length of response packet is header (12B) + 2*type(4B) + 2*class(4B) +
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ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
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2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
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*/
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/* Cannot get bigger packets than 512 per RFC1035.
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* In practice this can be set considerably smaller:
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* Length of response packet is header (12B) + 2*type(4B) + 2*class(4B) +
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* ttl(4B) + rlen(2B) + r (MAX_NAME_LEN = 21B) +
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* 2*querystring (2 MAX_NAME_LEN = 42B), all together 90 Bytes
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*/
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MAX_PACK_LEN = 512,
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DEFAULT_TTL = 30, // increase this when not testing?
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IP_STRING_LEN = sizeof(".xxx.xxx.xxx.xxx"),
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MAX_NAME_LEN = IP_STRING_LEN - 1 + sizeof(".in-addr.arpa"),
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REQ_A = 1,
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REQ_PTR = 12
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REQ_PTR = 12,
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};
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struct dns_head { // the message from client and first part of response mag
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/* the message from client and first part of response msg */
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struct dns_head {
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uint16_t id;
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uint16_t flags;
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uint16_t nquer; // accepts 0
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uint16_t nansw; // 1 in response
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uint16_t nauth; // 0
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uint16_t nadd; // 0
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uint16_t nquer;
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uint16_t nansw;
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uint16_t nauth;
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uint16_t nadd;
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};
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struct dns_prop {
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uint16_t type;
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uint16_t class;
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};
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struct dns_entry { // element of known name, ip address and reversed ip address
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/* element of known name, ip address and reversed ip address */
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struct dns_entry {
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struct dns_entry *next;
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char ip[IP_STRING_LEN]; // dotted decimal IP
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char rip[IP_STRING_LEN]; // length decimal reversed IP
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char name[MAX_HOST_LEN];
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uint32_t ip;
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char rip[IP_STRING_LEN]; /* length decimal reversed IP */
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char name[1];
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};
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#define OPT_verbose (option_mask32)
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/*
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* Convert host name from C-string to dns length/string.
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*/
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static void convname(char *a, uint8_t *q)
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{
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int i = (q[0] == '.') ? 0 : 1;
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for (; i < MAX_HOST_LEN-1 && *q; i++, q++)
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a[i] = tolower(*q);
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a[0] = i - 1;
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a[i] = 0;
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}
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/*
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* Insert length of substrings instead of dots
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*/
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static void undot(uint8_t *rip)
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static void undot(char *rip)
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{
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int i = 0, s = 0;
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int i = 0;
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int s = 0;
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while (rip[i])
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i++;
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for (--i; i >= 0; i--) {
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if (rip[i] == '.') {
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rip[i] = s;
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s = 0;
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} else s++;
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} else {
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s++;
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}
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}
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}
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@ -101,199 +91,369 @@ static struct dns_entry *parse_conf_file(const char *fileconf)
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{
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char *token[2];
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parser_t *parser;
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struct dns_entry *m, *prev, *conf_data;
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struct dns_entry *m, *conf_data;
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struct dns_entry **nextp;
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conf_data = NULL;
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nextp = &conf_data;
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prev = conf_data = NULL;
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parser = config_open(fileconf);
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while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) {
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unsigned a, b, c, d;
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/*
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* Assumes all host names are lower case only
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* Hostnames with more than one label are not handled correctly.
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* Presently the dot is copied into name without
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* converting to a length/string substring for that label.
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*/
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// if (!token[1] || sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
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if (sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
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continue;
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struct in_addr ip;
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uint32_t v32;
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m = xzalloc(sizeof(*m));
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/*m->next = NULL;*/
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sprintf(m->ip, ".%u.%u.%u.%u"+1, a, b, c, d);
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sprintf(m->rip, ".%u.%u.%u.%u", d, c, b, a);
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undot((uint8_t*)m->rip);
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convname(m->name, (uint8_t*)token[0]);
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if (inet_aton(token[1], &ip) == 0) {
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bb_error_msg("error at line %u, skipping", parser->lineno);
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continue;
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}
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if (OPT_verbose)
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bb_error_msg("name:%s, ip:%s", &(m->name[1]), m->ip);
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bb_error_msg("name:%s, ip:%s", token[0], token[1]);
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if (prev == NULL)
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conf_data = m;
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else
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prev->next = m;
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prev = m;
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/* sizeof(*m) includes 1 byte for m->name[0] */
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m = xzalloc(sizeof(*m) + strlen(token[0]) + 1);
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/*m->next = NULL;*/
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*nextp = m;
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nextp = &m->next;
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m->name[0] = '.';
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strcpy(m->name + 1, token[0]);
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undot(m->name);
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m->ip = ip.s_addr; /* in network order */
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v32 = ntohl(m->ip);
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/* inverted order */
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sprintf(m->rip, ".%u.%u.%u.%u",
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(uint8_t)(v32),
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(uint8_t)(v32 >> 8),
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(uint8_t)(v32 >> 16),
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(v32 >> 24)
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);
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undot(m->rip);
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}
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config_close(parser);
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return conf_data;
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}
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/*
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* Look query up in dns records and return answer if found
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* qs is the query string, first byte the string length
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* Look query up in dns records and return answer if found.
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* qs is the query string.
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*/
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static int table_lookup(struct dns_entry *d, uint16_t type, uint8_t *as, uint8_t *qs)
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static int table_lookup(uint8_t *as, struct dns_entry *d, uint16_t type, uint8_t *qs)
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{
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int i;
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do {
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while (d) {
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unsigned len = d->name[0];
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/* d->name[len] is the last (non NUL) char */
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#if DEBUG
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char *p, *q;
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q = (char *)&(qs[1]);
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p = &(d->name[1]);
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fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d",
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__FUNCTION__, (int)strlen(p), (int)(d->name[0]),
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p, q, (int)strlen(q));
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fprintf(stderr, "%d/%d p:%s q:%s %d\n",
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(int)strlen(p), len,
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p, q, (int)strlen(q)
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);
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#endif
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if (type == REQ_A) {
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if (type == htons(REQ_A)) {
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/* search by host name */
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for (i = 1; i <= (int)(d->name[0]); i++)
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if (tolower(qs[i]) != d->name[i])
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break;
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if (i > (int)(d->name[0])
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|| (d->name[0] == 1 && d->name[1] == '*')
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) {
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strcpy((char *)as, d->ip);
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if (len != 1 || d->name[1] != '*') {
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if (strcasecmp(d->name, (char*)qs) != 0)
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goto next;
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}
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move_to_unaligned32((uint32_t *)as, d->ip);
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#if DEBUG
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fprintf(stderr, " OK as:%s\n", as);
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fprintf(stderr, "OK as:%x\n", (int)d->ip);
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#endif
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return 0;
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}
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} else if (type == REQ_PTR) {
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/* search by IP-address */
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if ((d->name[0] != 1 || d->name[1] != '*')
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&& !strncmp(d->rip + 1, (char*)qs + 1, strlen(d->rip)-1)
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) {
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strcpy((char *)as, d->name);
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return 0;
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}
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return 0;
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}
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/* search by IP-address */
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if ((len != 1 || d->name[1] != '*')
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/* assume (do not check) that qs ends in ".in-addr.arpa" */
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&& strncmp(d->rip, (char*)qs, strlen(d->rip)) == 0
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) {
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strcpy((char *)as, d->name);
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#if DEBUG
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fprintf(stderr, "OK as:%s\n", as);
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#endif
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return 0;
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}
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next:
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d = d->next;
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} while (d);
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}
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return -1;
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}
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/*
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* Decode message and generate answer
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*/
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/* RFC 1035
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...
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Whenever an octet represents a numeric quantity, the left most bit
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in the diagram is the high order or most significant bit.
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That is, the bit labeled 0 is the most significant bit.
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...
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4.1.1. Header section format
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1 1 1 1 1 1
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| ID |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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|QR| OPCODE |AA|TC|RD|RA| Z | RCODE |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| QDCOUNT |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| ANCOUNT |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| NSCOUNT |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| ARCOUNT |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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ID 16 bit random identifier assigned by query.
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Used to match query/response.
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QR message is a query (0), or a response (1).
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OPCODE 0 standard query (QUERY)
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1 inverse query (IQUERY)
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2 server status request (STATUS)
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AA Authoritative Answer - this bit is valid in responses,
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and specifies that the responding name server is an
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authority for the domain name in question section.
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Note that the contents of the answer section may have
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multiple owner names because of aliases. The AA bit
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corresponds to the name which matches the query name, or
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the first owner name in the answer section.
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TC TrunCation - specifies that this message was truncated.
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RD Recursion Desired - this bit may be set in a query and
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is copied into the response. If RD is set, it directs
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the name server to pursue the query recursively.
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Recursive query support is optional.
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RA Recursion Available - this be is set or cleared in a
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response, and denotes whether recursive query support is
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available in the name server.
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Z Reserved for future use. Must be zero.
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RCODE Response code.
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0 No error condition
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1 Format error
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2 Server failure - The name server was
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unable to process this query due to a
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problem with the name server.
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3 Name Error - Meaningful only for
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responses from an authoritative name
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server, this code signifies that the
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domain name referenced in the query does
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not exist.
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4 Not Implemented.
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5 Refused.
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QDCOUNT number of entries in the question section.
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ANCOUNT number of resource records in the answer section.
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NSCOUNT number of name server resource records in the authority records section.
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ARCOUNT number of resource records in the additional records section.
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4.1.2. Question section format
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The section contains QDCOUNT (usually 1) entries, each of the following format:
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1 1 1 1 1 1
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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/ QNAME /
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/ /
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| QTYPE |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| QCLASS |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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QNAME a domain name represented as a sequence of labels, where
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each label consists of a length octet followed by that
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number of octets. The domain name terminates with the
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zero length octet for the null label of the root. Note
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that this field may be an odd number of octets; no
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padding is used.
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QTYPE a two octet type of the query.
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1 a host address [REQ_A const]
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2 an authoritative name server
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3 a mail destination (Obsolete - use MX)
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4 a mail forwarder (Obsolete - use MX)
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5 the canonical name for an alias
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6 marks the start of a zone of authority
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7 a mailbox domain name (EXPERIMENTAL)
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8 a mail group member (EXPERIMENTAL)
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9 a mail rename domain name (EXPERIMENTAL)
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10 a null RR (EXPERIMENTAL)
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11 a well known service description
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12 a domain name pointer [REQ_PTR const]
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13 host information
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14 mailbox or mail list information
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15 mail exchange
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16 text strings
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0x1c IPv6?
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252 a request for a transfer of an entire zone
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253 a request for mailbox-related records (MB, MG or MR)
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254 a request for mail agent RRs (Obsolete - see MX)
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255 a request for all records
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QCLASS a two octet code that specifies the class of the query.
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1 the Internet
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(others are historic only)
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255 any class
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4.1.3. Resource record format
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The answer, authority, and additional sections all share the same
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format: a variable number of resource records, where the number of
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records is specified in the corresponding count field in the header.
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Each resource record has the following format:
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1 1 1 1 1 1
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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/ /
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/ NAME /
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| TYPE |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| CLASS |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| TTL |
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| |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| RDLENGTH |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
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/ RDATA /
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/ /
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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NAME a domain name to which this resource record pertains.
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TYPE two octets containing one of the RR type codes. This
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field specifies the meaning of the data in the RDATA
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field.
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CLASS two octets which specify the class of the data in the
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RDATA field.
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TTL a 32 bit unsigned integer that specifies the time
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interval (in seconds) that the resource record may be
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cached before it should be discarded. Zero values are
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interpreted to mean that the RR can only be used for the
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transaction in progress, and should not be cached.
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RDLENGTH an unsigned 16 bit integer that specifies the length in
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octets of the RDATA field.
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RDATA a variable length string of octets that describes the
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resource. The format of this information varies
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according to the TYPE and CLASS of the resource record.
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For example, if the TYPE is A and the CLASS is IN,
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the RDATA field is a 4 octet ARPA Internet address.
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4.1.4. Message compression
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In order to reduce the size of messages, the domain system utilizes a
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compression scheme which eliminates the repetition of domain names in a
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message. In this scheme, an entire domain name or a list of labels at
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the end of a domain name is replaced with a pointer to a prior occurance
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of the same name.
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The pointer takes the form of a two octet sequence:
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 1 1| OFFSET |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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The first two bits are ones. This allows a pointer to be distinguished
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from a label, since the label must begin with two zero bits because
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labels are restricted to 63 octets or less. The OFFSET field specifies
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an offset from the start of the message (i.e., the first octet
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of the ID field in the domain header).
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A zero offset specifies the first byte of the ID field, etc.
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The compression scheme allows a domain name in a message to be
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represented as either:
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- a sequence of labels ending in a zero octet
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- a pointer
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- a sequence of labels ending with a pointer
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*/
|
||||
static int process_packet(struct dns_entry *conf_data, uint32_t conf_ttl, uint8_t *buf)
|
||||
{
|
||||
uint8_t answstr[MAX_NAME_LEN + 1];
|
||||
struct dns_head *head;
|
||||
struct dns_prop *qprop;
|
||||
struct dns_prop *unaligned_qprop;
|
||||
uint8_t *from, *answb;
|
||||
uint16_t outr_rlen;
|
||||
uint16_t outr_flags;
|
||||
uint16_t flags;
|
||||
int lookup_result, type, packet_len;
|
||||
uint16_t type;
|
||||
uint16_t class;
|
||||
int querystr_len;
|
||||
|
||||
answstr[0] = '\0';
|
||||
|
||||
head = (struct dns_head *)buf;
|
||||
if (head->nquer == 0) {
|
||||
bb_error_msg("no queries");
|
||||
bb_error_msg("packet has 0 queries, ignored");
|
||||
return -1;
|
||||
}
|
||||
|
||||
if (head->flags & 0x8000) {
|
||||
bb_error_msg("ignoring response packet");
|
||||
if (head->flags & htons(0x8000)) { /* QR bit */
|
||||
bb_error_msg("response packet, ignored");
|
||||
return -1;
|
||||
}
|
||||
|
||||
from = (void *)&head[1]; // start of query string
|
||||
//FIXME: strlen of untrusted data??!
|
||||
querystr_len = strlen((char *)from) + 1 + sizeof(struct dns_prop);
|
||||
answb = from + querystr_len; // where to append answer block
|
||||
/* start of query string */
|
||||
from = (void *)(head + 1);
|
||||
/* caller guarantees strlen is <= MAX_PACK_LEN */
|
||||
querystr_len = strlen((char *)from) + 1;
|
||||
/* may be unaligned! */
|
||||
unaligned_qprop = (void *)(from + querystr_len);
|
||||
/* where to append answer block */
|
||||
answb = (void *)(unaligned_qprop + 1);
|
||||
|
||||
outr_rlen = 0;
|
||||
outr_flags = 0;
|
||||
/* QR = 1 "response", RCODE = 4 "Not Implemented" */
|
||||
outr_flags = htons(0x8000 | 4);
|
||||
|
||||
qprop = (struct dns_prop *)(answb - 4);
|
||||
type = ntohs(qprop->type);
|
||||
|
||||
// only let REQ_A and REQ_PTR pass
|
||||
if (!(type == REQ_A || type == REQ_PTR)) {
|
||||
goto empty_packet; /* we can't handle the query type */
|
||||
}
|
||||
|
||||
if (ntohs(qprop->class) != 1 /* class INET */ ) {
|
||||
outr_flags = 4; /* not supported */
|
||||
move_from_unaligned16(type, &unaligned_qprop->type);
|
||||
if (type != htons(REQ_A) && type != htons(REQ_PTR)) {
|
||||
/* we can't handle the query type */
|
||||
goto empty_packet;
|
||||
}
|
||||
/* we only support standard queries */
|
||||
|
||||
if ((ntohs(head->flags) & 0x7800) != 0)
|
||||
move_from_unaligned16(class, &unaligned_qprop->class);
|
||||
if (class != htons(1)) { /* not class INET? */
|
||||
goto empty_packet;
|
||||
}
|
||||
/* OPCODE != 0 "standard query" ? */
|
||||
if ((head->flags & htons(0x7800)) != 0) {
|
||||
goto empty_packet;
|
||||
}
|
||||
|
||||
// We have a standard query
|
||||
bb_info_msg("%s", (char *)from);
|
||||
lookup_result = table_lookup(conf_data, type, answstr, from);
|
||||
if (lookup_result != 0) {
|
||||
outr_flags = 3 | 0x0400; // name do not exist and auth
|
||||
if (table_lookup(answstr, conf_data, type, from) != 0) {
|
||||
/* QR = 1 "response"
|
||||
* AA = 1 "Authoritative Answer"
|
||||
* RCODE = 3 "Name Error" */
|
||||
outr_flags = htons(0x8000 | 0x0400 | 3);
|
||||
goto empty_packet;
|
||||
}
|
||||
if (type == REQ_A) { // return an address
|
||||
struct in_addr a; // NB! its "struct { unsigned __long__ s_addr; }"
|
||||
uint32_t v32;
|
||||
if (!inet_aton((char*)answstr, &a)) { //dotted dec to long conv
|
||||
outr_flags = 1; /* Frmt err */
|
||||
goto empty_packet;
|
||||
}
|
||||
v32 = a.s_addr; /* in case long != int */
|
||||
move_to_unaligned32(answstr, v32);
|
||||
outr_rlen = 4; // uint32_t IP
|
||||
} else
|
||||
outr_rlen = strlen((char *)answstr) + 1; // a host name
|
||||
outr_flags |= 0x0400; /* authority-bit */
|
||||
// we have an answer
|
||||
/* return an address */
|
||||
outr_rlen = 4;
|
||||
if (type == htons(REQ_PTR)) {
|
||||
/* return a host name */
|
||||
outr_rlen = strlen((char *)answstr) + 1;
|
||||
}
|
||||
/* QR = 1 "response",
|
||||
* AA = 1 "Authoritative Answer",
|
||||
* RCODE = 0 "success" */
|
||||
outr_flags = htons(0x8000 | 0x0400 | 0);
|
||||
/* we have one answer */
|
||||
head->nansw = htons(1);
|
||||
|
||||
// copy query block to answer block
|
||||
/* copy query block to answer block */
|
||||
querystr_len += sizeof(unaligned_qprop);
|
||||
memcpy(answb, from, querystr_len);
|
||||
answb += querystr_len;
|
||||
|
||||
// and append answer rr
|
||||
// FIXME: unaligned accesses??
|
||||
*(uint32_t *) answb = htonl(conf_ttl);
|
||||
/* append answer Resource Record */
|
||||
move_to_unaligned32((uint32_t *)answb, htonl(conf_ttl));
|
||||
answb += 4;
|
||||
*(uint16_t *) answb = htons(outr_rlen);
|
||||
move_to_unaligned32((uint16_t *)answb, htons(outr_rlen));
|
||||
answb += 2;
|
||||
memcpy(answb, answstr, outr_rlen);
|
||||
answb += outr_rlen;
|
||||
|
||||
empty_packet:
|
||||
|
||||
flags = ntohs(head->flags);
|
||||
// clear rcode and RA, set responsebit and our new flags
|
||||
flags |= (outr_flags & 0xff80) | 0x8000;
|
||||
head->flags = htons(flags);
|
||||
head->flags |= outr_flags;
|
||||
head->nauth = head->nadd = 0;
|
||||
head->nquer = htons(1);
|
||||
head->nquer = htons(1); // why???
|
||||
|
||||
packet_len = answb - buf;
|
||||
return packet_len;
|
||||
return answb - buf;
|
||||
}
|
||||
|
||||
/*
|
||||
* Exit on signal
|
||||
*/
|
||||
//static void interrupt(int sig)
|
||||
//{
|
||||
// /* unlink("/var/run/dnsd.lock"); */
|
||||
// bb_error_msg("interrupt, exiting\n");
|
||||
// kill_myself_with_sig(sig);
|
||||
//}
|
||||
|
||||
int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
|
||||
int dnsd_main(int argc UNUSED_PARAM, char **argv)
|
||||
{
|
||||
@ -328,7 +488,6 @@ int dnsd_main(int argc UNUSED_PARAM, char **argv)
|
||||
|
||||
conf_data = parse_conf_file(fileconf);
|
||||
|
||||
// signal(SIGINT, interrupt); - just for one message?
|
||||
bb_signals(0
|
||||
/* why? + (1 << SIGPIPE) */
|
||||
+ (1 << SIGHUP)
|
||||
@ -348,8 +507,11 @@ int dnsd_main(int argc UNUSED_PARAM, char **argv)
|
||||
from = xzalloc(lsa_size);
|
||||
to = xzalloc(lsa_size);
|
||||
|
||||
bb_info_msg("Accepting UDP packets on %s",
|
||||
xmalloc_sockaddr2dotted(&lsa->u.sa));
|
||||
{
|
||||
char *p = xmalloc_sockaddr2dotted(&lsa->u.sa);
|
||||
bb_info_msg("Accepting UDP packets on %s", p);
|
||||
free(p);
|
||||
}
|
||||
|
||||
while (1) {
|
||||
int r;
|
||||
@ -361,7 +523,7 @@ int dnsd_main(int argc UNUSED_PARAM, char **argv)
|
||||
memcpy(to, lsa, lsa_size);
|
||||
r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len);
|
||||
if (r < 12 || r > MAX_PACK_LEN) {
|
||||
bb_error_msg("invalid packet size");
|
||||
bb_error_msg("packet size %d, ignored", r);
|
||||
continue;
|
||||
}
|
||||
if (OPT_verbose)
|
||||
|
||||
Loading…
Reference in New Issue
Block a user