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/* dns.c
* (c) Jonas Gunz, 2019
* License: MIT
* */
#include "dns.h"
int dns_construct_header ( struct dns_header* _header, char* _buffer, int _bufflen )
{
if ( !_buffer || !_header || _bufflen < 12 )
return -1;
*((uint16_t*)_buffer) = _header->id; //Since only copied, no flipping necessary
_buffer[2] =
((_header->QR & 0x01) << 7) |
((_header->OPCODE & 0x0F) << 3) |
((_header->AA & 0x01) << 2) |
((_header->TC & 0x01) << 1) |
( _header->RD & 0x01);
_buffer[3] =
((_header->RA & 0x01) << 7) |
((_header->Z & 0x07) << 4) |
( _header->RCODE & 0x0F);
*((uint16_t*)(_buffer + 4 )) = FLIP_BYTES(_header->question_count);
*((uint16_t*)(_buffer + 6 )) = FLIP_BYTES(_header->answer_count);
*((uint16_t*)(_buffer + 8 )) = FLIP_BYTES(_header->authorative_count);
*((uint16_t*)(_buffer + 10)) = FLIP_BYTES(_header->additional_count);
return 12;
}
int dns_destroy_struct ( struct dns_message* _msg )
{
if ( !_msg )
return -1;
if ( _msg->question_count > 0 && _msg->question) {
free ( _msg->question );
_msg->question = NULL;
}
if ( _msg->answer_count > 0 && _msg->answer) {
free ( _msg->answer );
_msg->answer = NULL;
}
return 0;
}
int dns_parse_packet ( char* _buffer, int _bufflen, struct dns_message* _msg )
{
//TODO refactor
if ( !_buffer || !_bufflen || !_msg )
return 1; //Invalid input
if ( _bufflen < 12 )
return 1; //Too short to contain a DNS header
//TODO test
_msg->header.id = *( (uint16_t*) _buffer );
_msg->header.QR = ( 0x80 & *( (uint8_t*) (_buffer + 2)) ) >> 7;
_msg->header.OPCODE = (0x78 & *( (uint8_t*) (_buffer + 2))) >> 3;
_msg->header.AA = (0x04 & *( (uint8_t*) (_buffer + 2))) >> 2;
_msg->header.TC = (0x02 & *( (uint8_t*) (_buffer + 2))) >> 1;
_msg->header.RD = (0x01 & *( (uint8_t*) (_buffer + 2)));
_msg->header.RA = (0x80 & *( (uint8_t*) (_buffer + 3))) >> 7;
_msg->header.Z = (0x70 & *( (uint8_t*) (_buffer + 3))) >> 4;
_msg->header.RCODE = (0x0F & *( (uint8_t*) (_buffer + 3)));
_msg->question_count = _msg->header.question_count = (*((uint8_t*) (_buffer + 4 )) << 8) | *((uint8_t*) (_buffer + 5 ));
_msg->answer_count = _msg->header.answer_count = (*((uint8_t*) (_buffer + 6 )) << 8) | *((uint8_t*) (_buffer + 7 ));
_msg->header.authorative_count = (*((uint8_t*) (_buffer + 8 )) << 8) | *((uint8_t*) (_buffer + 9 ));
_msg->header.additional_count = (*((uint8_t*) (_buffer + 10)) << 8) | *((uint8_t*) (_buffer + 11));
//TODO remove
printf("ANSWER %i\n", _msg->header.answer_count);
printf("QUESTI %i\n", _msg->header.question_count);
printf("AUTHOR %i\n", _msg->header.authorative_count);
printf("ADDITI %i\n", _msg->header.additional_count);
//Check for sensible QD, AN, NS and ARCOUNTS before massive memory allocation
if( _msg->header.question_count > 4 ||
_msg->header.answer_count > 32 ||
_msg->header.authorative_count > 32 ||
_msg->header.additional_count > 32 ) {
return 1;
}
//Allocate question array
//TODO Only implements question section.
size_t qsize = sizeof(typeof(*(_msg->question))) * _msg->question_count;
_msg->question_count = _msg->header.question_count;
_msg->question = malloc ( qsize );
memset( _msg->question, 0, qsize );
if (!_msg->question) //malloc failed
return 1;
int ptr = 12; //byte counter
for (int i = 0; i < _msg->question_count; i++) {
int qname_len = qname_check ( (_buffer + ptr), _bufflen - ptr);
if (qname_len <= 0) //Check for faulty QNAME
return 1;
_msg->question[i].qname = _buffer + ptr;
ptr += qname_len;
if( ptr >= (_bufflen - 4) ) //Out of bounds check
return 1;
_msg->question[i].qtype = ((uint8_t)*(_buffer + ptr) << 8) | ((uint8_t)*(_buffer + ptr + 1));
ptr += 2;
_msg->question[i].qclass = ((uint8_t)*(_buffer + ptr) << 8) | ((uint8_t)*(_buffer + ptr + 1));
ptr += 2;
}
return 0;
}
int fqdn_to_qname( char* _source, int _sourcelen, char* _sink ,int _sinklen )
{
int i;
int lastdot = 0;
if (_sourcelen < 1 || _sinklen < 1)
return -1;
_sink[0] = ' '; //Set to known value
for(i = 0; ((i < _sourcelen) && (i < (_sinklen - 1))); i++) { //Copy offset 1
if(! _source[i])
break;
_sink[i+1] = _source[i];
}
if( _source[i] ) // _source not terminated, thus no valid string
return -1;
for (int o = 0; o < i; o++) {
if( _sink[o] == '.') {
_sink[lastdot] = o - lastdot - 1;
lastdot = o;
}
}
_sink[lastdot] = i - lastdot;
_sink[i + 1] = 0;
return i+2;
}
int qname_to_fqdn( char* _source, int _sourcelen, char* _sink, int _sinklen )
{
if ( !_sourcelen || !_sinklen ) {
return -1;
}
unsigned int next_dot = _source[0] + 1;
int i = 1;
for(i = 1; i < _sourcelen; i++) {
if( i > _sinklen){ //Output too small. Not >= bc sink[i-1] is used
return -1;
}
if ( !_source[i] ) {
_sink[i-1] = '\0';
break;
} else if (i == next_dot) {
_sink[i-1]='.';
next_dot = _source[i] + i + 1;
} else {
_sink[i-1] = _source[i];
}
}
return i-1;
}
int qname_check( char* _source, int _sourcelen )
{
if (!_sourcelen)
return -1;
int next_dot = 0;
//TODO questionable control flow
//TODO add ASCII prrintable check
for (int i = 0; i < _sourcelen; i++) {
if ( i == next_dot ) {
if (_source[i]) { //Not last dot
next_dot = _source[i] + i + 1;
} else { //last dot
return i+1;
}
} else if (!_source[i]) { //Unexpected \0
return -1;
}
}
return -1;
}
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