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#75, update dns parsing

This commit is contained in:
Erik Ekman 2009-09-20 15:11:12 +00:00
parent 3940f4e5ff
commit bd4a4eb24c
1 changed files with 154 additions and 30 deletions
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176
src/dns.c
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@ -39,6 +39,8 @@
#include "encoding.h"
#include "read.h"
#define CHECKLEN(x) if (buflen - (p-buf) < (x)) return 0
int
dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_t datalen)
{
@ -47,6 +49,9 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_
char *p;
int len;
if (buflen < sizeof(HEADER))
return 0;
memset(buf, 0, buflen);
header = (HEADER*)buf;
@ -68,29 +73,80 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_
name = 0xc000 | ((p - buf) & 0x3fff);
putname(&p, sizeof(q->name), q->name);
/* Question section */
putname(&p, buflen - (p - buf), q->name);
CHECKLEN(4);
putshort(&p, q->type);
putshort(&p, C_IN);
/* Answer section */
CHECKLEN(10);
putshort(&p, name);
if (q->type == T_A)
putshort(&p, T_CNAME); /* answer CNAME to A question */
else
putshort(&p, q->type);
putshort(&p, C_IN);
putlong(&p, 0);
putlong(&p, 0); /* TTL */
if (q->type == T_CNAME || q->type == T_A || q->type == T_MX)
{
/* data is expected to be like "Hblabla.host.name.com\0" */
char *startp = p;
int namelen;
p += 2; /* skip 2 bytes length */
CHECKLEN(2);
if (q->type == T_MX)
putshort(&p, 10); /* preference */
putname(&p, buflen - (p - buf), data);
CHECKLEN(0);
namelen = p - startp;
namelen -= 2;
putshort(&startp, namelen);
}
else if (q->type == T_TXT)
{
/* TXT has binary or base-X data */
char *startp = p;
int txtlen;
p += 2; /* skip 2 bytes length */
puttxtbin(&p, buflen - (p - buf), data, datalen);
CHECKLEN(0);
txtlen = p - startp;
txtlen -= 2;
putshort(&startp, txtlen);
}
else
{
/* NULL has raw binary data */
datalen = MIN(datalen, buflen - (p - buf));
CHECKLEN(2);
putshort(&p, datalen);
CHECKLEN(datalen);
putdata(&p, data, datalen);
CHECKLEN(0);
}
break;
case QR_QUERY:
/* Note that iodined also uses this for forward queries */
header->qdcount = htons(1);
header->arcount = htons(1);
putname(&p, datalen, data);
putname(&p, buflen - (p - buf), data);
CHECKLEN(4);
putshort(&p, q->type);
putshort(&p, C_IN);
/* EDNS0 */
/* EDNS0 to advertise maximum response length
(even CNAME/A/MX, 255+255+header would be >512) */
CHECKLEN(11);
putbyte(&p, 0x00); /* Root */
putshort(&p, 0x0029); /* OPT */
putshort(&p, 0x1000); /* Payload size: 4096 */
@ -107,6 +163,7 @@ dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_
int
dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomain)
/* Only used when iodined gets an NS type query */
{
HEADER *header;
int len;
@ -117,6 +174,9 @@ dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomai
int domain_len;
char *p;
if (buflen < sizeof(HEADER))
return 0;
memset(buf, 0, buflen);
header = (HEADER*)buf;
@ -148,33 +208,38 @@ dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomai
topname = 0xc000 | ((p - buf + domain_len) & 0x3fff);
/* Query section */
putname(&p, sizeof(q->name), q->name); /* Name */
putname(&p, buflen - (p - buf), q->name); /* Name */
CHECKLEN(4);
putshort(&p, q->type); /* Type */
putshort(&p, C_IN); /* Class */
/* Answer section */
CHECKLEN(12);
putshort(&p, name); /* Name */
putshort(&p, q->type); /* Type */
putshort(&p, C_IN); /* Class */
putlong(&p, 0x3ea7d011); /* TTL */
putlong(&p, 3600); /* TTL */
putshort(&p, 5); /* Data length */
/* pointer to ns.topdomain */
nsname = 0xc000 | ((p - buf) & 0x3fff);
CHECKLEN(5);
putbyte(&p, 2);
putbyte(&p, 'n');
putbyte(&p, 's');
putshort(&p, topname); /* Name Server */
/* Additional data (A-record of NS server) */
CHECKLEN(12);
putshort(&p, nsname); /* Name Server */
putshort(&p, T_A); /* Type */
putshort(&p, C_IN); /* Class */
putlong(&p, 0x3ea7d011); /* TTL */
putlong(&p, 3600); /* TTL */
putshort(&p, 4); /* Data length */
/* ugly hack to output IP address */
domain = (char *) &q->destination;
CHECKLEN(4);
putbyte(&p, *domain++);
putbyte(&p, *domain++);
putbyte(&p, *domain++);
@ -184,6 +249,8 @@ dns_encode_ns_response(char *buf, size_t buflen, struct query *q, char *topdomai
return len;
}
#undef CHECKLEN
unsigned short
dns_get_id(char *packet, size_t packetlen)
{
@ -196,6 +263,8 @@ dns_get_id(char *packet, size_t packetlen)
return ntohs(header->id);
}
#define CHECKLEN(x) if (packetlen - (data-packet) < (x)) return 0
int
dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, size_t packetlen)
{
@ -235,27 +304,50 @@ dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, siz
switch (qr) {
case QR_ANSWER:
if(qdcount != 1 || ancount != 1) {
if(qdcount < 1 || ancount < 1) {
/* We may get both CNAME and A, then ancount=2 */
switch (header->rcode) {
case REFUSED:
case NOERROR: /* 0 */
if (header->tc)
warnx("Got TRUNCATION as reply: response too long for DNS path");
else
warnx("Got reply without error, but also without question and/or answer");
break;
case FORMERR: /* 1 */
warnx("Got FORMERR as reply: server does not understand our request");
break;
case SERVFAIL: /* 2 */
if (qdcount >= 1
&& packetlen >= sizeof(HEADER) + 2
&& (data[1] == 'r' || data[1] == 'R'))
warnx("Got SERVFAIL as reply on earlier fragsize autoprobe");
else if (qdcount >= 1
&& packetlen >= sizeof(HEADER) + 2
&& (data[1] < '0' || data[1] > '9')
&& (data[1] < 'a' || data[1] > 'f')
&& (data[1] < 'A' || data[1] > 'F')
&& data[1] != 'p' && data[1] != 'P')
warnx("Got SERVFAIL as reply on earlier config setting");
else
warnx("Got SERVFAIL as reply: server failed or recursion timeout");
break;
case NXDOMAIN: /* 3 */
warnx("Got NXDOMAIN as reply: domain does not exist");
break;
case NOTIMP: /* 4 */
warnx("Got NOTIMP as reply: server does not support our request");
break;
case REFUSED: /* 5 */
warnx("Got REFUSED as reply");
break;
case NOTIMP:
warnx("Got NOTIMP as reply");
break;
case NXDOMAIN:
warnx("Got NXDOMAIN as reply");
break;
case SERVFAIL:
warnx("Got SERVFAIL as reply");
break;
case NOERROR:
default:
warnx("no query or answer in reply packet");
warnx("Got RCODE %u as reply", (unsigned int) header->rcode);
break;
}
return -1;
@ -265,33 +357,65 @@ dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, siz
q->id = id;
readname(packet, packetlen, &data, name, sizeof(name));
CHECKLEN(4);
readshort(packet, &data, &type);
readshort(packet, &data, &class);
/* Assume that first answer is NULL/CNAME that we wanted */
readname(packet, packetlen, &data, name, sizeof(name));
CHECKLEN(10);
readshort(packet, &data, &type);
readshort(packet, &data, &class);
readlong(packet, &data, &ttl);
readshort(packet, &data, &rlen);
if (type == T_NULL) {
rv = MIN(rlen, sizeof(rdata));
rv = readdata(packet, &data, rdata, rv);
if(type == T_NULL && rv >= 2 && buf) {
if (rv >= 2 && buf) {
rv = MIN(rv, buflen);
memcpy(buf, rdata, rv);
}
/* "else rv=0;" here? */
}
if ((type == T_CNAME || type == T_MX) && buf) {
if (type == T_MX)
data += 2; /* skip preference */
memset(name, 0, sizeof(name));
readname(packet, packetlen, &data, name, sizeof(name) - 1);
name[sizeof(name)-1] = '\0';
strncpy(buf, name, buflen);
buf[buflen - 1] = '\0';
rv = strlen(buf);
}
if (type == T_TXT && buf) {
rv = readtxtbin(packet, &data, rlen, rdata, sizeof(rdata));
if (rv >= 1) {
rv = MIN(rv, buflen);
memcpy(buf, rdata, rv);
}
}
if (q != NULL)
q->type = type;
break;
case QR_QUERY:
if (qdcount != 1) {
if (qdcount < 1) {
warnx("no question section in name query");
return -1;
}
memset(name, 0, sizeof(name));
readname(packet, packetlen, &data, name, sizeof(name) - 1);
name[sizeof(name)-1] = '\0';
CHECKLEN(4);
readshort(packet, &data, &type);
readshort(packet, &data, &class);
if (q == NULL) {
rv = 0;
break;
}
strncpy(q->name, name, sizeof(q->name));
q->name[sizeof(q->name) - 1] = '\0';
q->type = type;