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#75, update dns parsing
This commit is contained in:
Erik Ekman
parent
3940f4e5ff
commit
bd4a4eb24c
1 changed files with 154 additions and 30 deletions
184
src/dns.c
184
src/dns.c
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@ -39,6 +39,8 @@
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#include "encoding.h"
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#include "read.h"
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#define CHECKLEN(x) if (buflen - (p-buf) < (x)) return 0
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int
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dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_t datalen)
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{
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@ -47,6 +49,9 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_
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char *p;
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int len;
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if (buflen < sizeof(HEADER))
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return 0;
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memset(buf, 0, buflen);
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header = (HEADER*)buf;
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@ -68,29 +73,80 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_
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name = 0xc000 | ((p - buf) & 0x3fff);
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putname(&p, sizeof(q->name), q->name);
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/* Question section */
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putname(&p, buflen - (p - buf), q->name);
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CHECKLEN(4);
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putshort(&p, q->type);
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putshort(&p, C_IN);
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/* Answer section */
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CHECKLEN(10);
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putshort(&p, name);
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putshort(&p, q->type);
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if (q->type == T_A)
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putshort(&p, T_CNAME); /* answer CNAME to A question */
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else
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putshort(&p, q->type);
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putshort(&p, C_IN);
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putlong(&p, 0);
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putlong(&p, 0); /* TTL */
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if (q->type == T_CNAME || q->type == T_A || q->type == T_MX)
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{
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/* data is expected to be like "Hblabla.host.name.com\0" */
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char *startp = p;
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int namelen;
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p += 2; /* skip 2 bytes length */
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CHECKLEN(2);
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if (q->type == T_MX)
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putshort(&p, 10); /* preference */
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putname(&p, buflen - (p - buf), data);
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CHECKLEN(0);
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namelen = p - startp;
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namelen -= 2;
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putshort(&startp, namelen);
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}
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else if (q->type == T_TXT)
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{
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/* TXT has binary or base-X data */
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char *startp = p;
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int txtlen;
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p += 2; /* skip 2 bytes length */
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puttxtbin(&p, buflen - (p - buf), data, datalen);
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CHECKLEN(0);
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txtlen = p - startp;
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txtlen -= 2;
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putshort(&startp, txtlen);
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}
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else
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{
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/* NULL has raw binary data */
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datalen = MIN(datalen, buflen - (p - buf));
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CHECKLEN(2);
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putshort(&p, datalen);
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CHECKLEN(datalen);
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putdata(&p, data, datalen);
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CHECKLEN(0);
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}
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break;
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case QR_QUERY:
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/* Note that iodined also uses this for forward queries */
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header->qdcount = htons(1);
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header->arcount = htons(1);
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putname(&p, datalen, data);
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putname(&p, buflen - (p - buf), data);
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CHECKLEN(4);
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putshort(&p, q->type);
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putshort(&p, C_IN);
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/* EDNS0 */
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/* EDNS0 to advertise maximum response length
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(even CNAME/A/MX, 255+255+header would be >512) */
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CHECKLEN(11);
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putbyte(&p, 0x00); /* Root */
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putshort(&p, 0x0029); /* OPT */
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putshort(&p, 0x1000); /* Payload size: 4096 */
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@ -107,6 +163,7 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_
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int
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dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomain)
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/* Only used when iodined gets an NS type query */
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{
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HEADER *header;
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int len;
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@ -117,6 +174,9 @@ dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomai
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int domain_len;
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char *p;
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if (buflen < sizeof(HEADER))
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return 0;
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memset(buf, 0, buflen);
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header = (HEADER*)buf;
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@ -148,33 +208,38 @@ dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomai
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topname = 0xc000 | ((p - buf + domain_len) & 0x3fff);
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/* Query section */
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putname(&p, sizeof(q->name), q->name); /* Name */
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putname(&p, buflen - (p - buf), q->name); /* Name */
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CHECKLEN(4);
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putshort(&p, q->type); /* Type */
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putshort(&p, C_IN); /* Class */
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/* Answer section */
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CHECKLEN(12);
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putshort(&p, name); /* Name */
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putshort(&p, q->type); /* Type */
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putshort(&p, C_IN); /* Class */
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putlong(&p, 0x3ea7d011); /* TTL */
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putlong(&p, 3600); /* TTL */
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putshort(&p, 5); /* Data length */
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/* pointer to ns.topdomain */
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nsname = 0xc000 | ((p - buf) & 0x3fff);
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CHECKLEN(5);
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putbyte(&p, 2);
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putbyte(&p, 'n');
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putbyte(&p, 's');
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putshort(&p, topname); /* Name Server */
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/* Additional data (A-record of NS server) */
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CHECKLEN(12);
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putshort(&p, nsname); /* Name Server */
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putshort(&p, T_A); /* Type */
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putshort(&p, C_IN); /* Class */
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putlong(&p, 0x3ea7d011); /* TTL */
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putlong(&p, 3600); /* TTL */
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putshort(&p, 4); /* Data length */
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/* ugly hack to output IP address */
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domain = (char *) &q->destination;
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CHECKLEN(4);
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putbyte(&p, *domain++);
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putbyte(&p, *domain++);
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putbyte(&p, *domain++);
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@ -184,6 +249,8 @@ dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomai
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return len;
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}
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#undef CHECKLEN
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unsigned short
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dns_get_id(char *packet, size_t packetlen)
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{
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@ -196,6 +263,8 @@ dns_get_id(char *packet, size_t packetlen)
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return ntohs(header->id);
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}
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#define CHECKLEN(x) if (packetlen - (data-packet) < (x)) return 0
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int
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dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, size_t packetlen)
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{
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@ -235,27 +304,50 @@ dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, siz
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switch (qr) {
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case QR_ANSWER:
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if(qdcount != 1 || ancount != 1) {
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if(qdcount < 1 || ancount < 1) {
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/* We may get both CNAME and A, then ancount=2 */
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switch (header->rcode) {
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case REFUSED:
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case NOERROR: /* 0 */
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if (header->tc)
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warnx("Got TRUNCATION as reply: response too long for DNS path");
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else
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warnx("Got reply without error, but also without question and/or answer");
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break;
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case FORMERR: /* 1 */
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warnx("Got FORMERR as reply: server does not understand our request");
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break;
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case SERVFAIL: /* 2 */
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if (qdcount >= 1
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&& packetlen >= sizeof(HEADER) + 2
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&& (data[1] == 'r' || data[1] == 'R'))
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warnx("Got SERVFAIL as reply on earlier fragsize autoprobe");
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else if (qdcount >= 1
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&& packetlen >= sizeof(HEADER) + 2
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&& (data[1] < '0' || data[1] > '9')
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&& (data[1] < 'a' || data[1] > 'f')
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&& (data[1] < 'A' || data[1] > 'F')
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&& data[1] != 'p' && data[1] != 'P')
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warnx("Got SERVFAIL as reply on earlier config setting");
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else
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warnx("Got SERVFAIL as reply: server failed or recursion timeout");
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break;
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case NXDOMAIN: /* 3 */
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warnx("Got NXDOMAIN as reply: domain does not exist");
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break;
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case NOTIMP: /* 4 */
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warnx("Got NOTIMP as reply: server does not support our request");
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break;
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case REFUSED: /* 5 */
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warnx("Got REFUSED as reply");
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break;
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case NOTIMP:
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warnx("Got NOTIMP as reply");
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break;
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case NXDOMAIN:
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warnx("Got NXDOMAIN as reply");
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break;
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case SERVFAIL:
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warnx("Got SERVFAIL as reply");
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break;
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case NOERROR:
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default:
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warnx("no query or answer in reply packet");
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warnx("Got RCODE %u as reply", (unsigned int) header->rcode);
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break;
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}
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return -1;
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@ -265,33 +357,65 @@ dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, siz
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q->id = id;
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readname(packet, packetlen, &data, name, sizeof(name));
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CHECKLEN(4);
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readshort(packet, &data, &type);
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readshort(packet, &data, &class);
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/* Assume that first answer is NULL/CNAME that we wanted */
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readname(packet, packetlen, &data, name, sizeof(name));
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CHECKLEN(10);
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readshort(packet, &data, &type);
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readshort(packet, &data, &class);
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readlong(packet, &data, &ttl);
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readshort(packet, &data, &rlen);
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rv = MIN(rlen, sizeof(rdata));
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rv = readdata(packet, &data, rdata, rv);
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if(type == T_NULL && rv >= 2 && buf) {
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rv = MIN(rv, buflen);
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memcpy(buf, rdata, rv);
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if (type == T_NULL) {
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rv = MIN(rlen, sizeof(rdata));
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rv = readdata(packet, &data, rdata, rv);
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if (rv >= 2 && buf) {
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rv = MIN(rv, buflen);
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memcpy(buf, rdata, rv);
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}
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/* "else rv=0;" here? */
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}
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if ((type == T_CNAME || type == T_MX) && buf) {
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if (type == T_MX)
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data += 2; /* skip preference */
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memset(name, 0, sizeof(name));
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readname(packet, packetlen, &data, name, sizeof(name) - 1);
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name[sizeof(name)-1] = '\0';
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strncpy(buf, name, buflen);
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buf[buflen - 1] = '\0';
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rv = strlen(buf);
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}
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if (type == T_TXT && buf) {
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rv = readtxtbin(packet, &data, rlen, rdata, sizeof(rdata));
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if (rv >= 1) {
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rv = MIN(rv, buflen);
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memcpy(buf, rdata, rv);
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}
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}
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if (q != NULL)
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q->type = type;
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break;
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case QR_QUERY:
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if (qdcount != 1) {
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if (qdcount < 1) {
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warnx("no question section in name query");
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return -1;
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}
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memset(name, 0, sizeof(name));
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readname(packet, packetlen, &data, name, sizeof(name) - 1);
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name[sizeof(name)-1] = '\0';
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CHECKLEN(4);
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readshort(packet, &data, &type);
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readshort(packet, &data, &class);
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if (q == NULL) {
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rv = 0;
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break;
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}
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strncpy(q->name, name, sizeof(q->name));
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q->name[sizeof(q->name) - 1] = '\0';
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q->type = type;
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