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/* dns.c
* (c) Jonas Gunz, 2019
* License: MIT
* */
#include "dns.h"
int dns_construct_header ( char* _buffer, int _bufflen, dns_header_t* _header )
{
if ( !_buffer || !_header || _bufflen < 12 )
return -1;
*((uint16_t*)_buffer) = _header->id; /* Since only copied, no flipping necessary */
_buffer[2] =
(char)((_header->QR & 0x01) << 7) |
(char)((_header->OPCODE & 0x0F) << 3) |
(char)((_header->AA & 0x01) << 2) |
(char)((_header->TC & 0x01) << 1) |
(char)( _header->RD & 0x01);
_buffer[3] =
(char)((_header->RA & 0x01) << 7) |
(char)((_header->Z & 0x07) << 4) |
(char)( _header->RCODE & 0x0F);
*((uint16_t*)(_buffer + 4 )) = (uint16_t)FLIP_BYTES(_header->question_count);
*((uint16_t*)(_buffer + 6 )) = (uint16_t)FLIP_BYTES(_header->answer_count);
*((uint16_t*)(_buffer + 8 )) = (uint16_t)FLIP_BYTES(_header->authorative_count);
*((uint16_t*)(_buffer + 10)) = (uint16_t)FLIP_BYTES(_header->additional_count);
return DNS_HEADER_LEN;
}
int dns_construct_answer (
char* _buffer,
int _bufflen,
dns_answer_t* _answer
) {
int ret = 0;
if ( !_buffer || _bufflen <= 0 || !_answer )
return -1;
/* Check buffer size */
if ( _answer->qname_len + _answer->rdlength + 10 > _bufflen )
return -1;
memcpy( _buffer, _answer->qname, (unsigned)_answer->qname_len );
ret += _answer->qname_len;
*((uint16_t*)(_buffer + ret + 0 )) = (uint16_t)FLIP_BYTES(_answer->type);
*((uint16_t*)(_buffer + ret + 2 )) = (uint16_t)FLIP_BYTES(_answer->class);
*((uint16_t*)(_buffer + ret + 4 )) = (uint16_t)FLIP_BYTES((uint16_t)((_answer->ttl << 16) & 0xffff));
*((uint16_t*)(_buffer + ret + 6 )) = (uint16_t)FLIP_BYTES((uint16_t)(_answer->ttl & 0xffff));
*((uint16_t*)(_buffer + ret + 8 )) = (uint16_t)FLIP_BYTES(_answer->rdlength);
ret += 10;
memcpy( _buffer + ret, _answer->rdata, _answer->rdlength );
ret += _answer->rdlength;
return ret;
}
int dns_construct_questoin (
char* _buffer,
int _bufflen,
dns_question_t* _question
) {
/* TODO Test */
int ret = 0;
if ( !_buffer || _bufflen <= 0 || !_question )
return -1;
/* Check buffer size */
if ( _question->qname_len + 4 > _bufflen )
return -1;
memcpy( _buffer, _question->qname, (unsigned)_question->qname_len );
ret += _question->qname_len;
*((uint16_t*)(_buffer + ret + 0 )) = (uint16_t)FLIP_BYTES(_question->qtype);
*((uint16_t*)(_buffer + ret + 2 )) = (uint16_t)FLIP_BYTES(_question->qclass);
ret += 4;
return ret;
}
/* Question and answer count come from header */
int dns_construct_packet (
char* _buffer,
int _bufflen,
dns_message_t* _message
) {
return -1;
}
int dns_destroy_struct ( dns_message_t* _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, dns_message_t* _msg )
{
int i = 0;
size_t qsize;
int ptr;
/* 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 = (uint16_t)(*((uint8_t*) (_buffer + 4 )) << 8) | *((uint8_t*) (_buffer + 5 ));
_msg->answer_count = _msg->header.answer_count = (uint16_t)(*((uint8_t*) (_buffer + 6 )) << 8) | *((uint8_t*) (_buffer + 7 ));
_msg->header.authorative_count = (uint16_t)(*((uint8_t*) (_buffer + 8 )) << 8) | *((uint8_t*) (_buffer + 9 ));
_msg->header.additional_count = (uint16_t)(*((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.
*/
qsize = sizeof(*(_msg->question)) * (unsigned)_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;
ptr = 12; /* byte counter */
/* TODO refactor */
for ( 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;
_msg->question[i].qname_len = qname_len;
ptr += qname_len;
if( ptr >= (_bufflen - 4) ) /* Out of bounds check */
return 1;
_msg->question[i].qtype = (uint16_t)((uint8_t)*(_buffer + ptr) << 8) | ((uint8_t)*(_buffer + ptr + 1));
ptr += 2;
_msg->question[i].qclass = (uint16_t)((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, o;
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] ) {
_sink[0] = 0; /* ensure _sink is terminated */
return -1;
}
for (o = 0; o < i; o++) {
if( _sink[o] == '.') {
_sink[lastdot] = (char)(o - lastdot - 1);
lastdot = o;
}
}
_sink[lastdot] = (char)(i - lastdot);
_sink[i + 1] = 0;
return i+2;
}
int qname_to_fqdn( char* _source, int _sourcelen, char* _sink, int _sinklen )
{
unsigned int next_dot;
unsigned int i = 1;
if ( !_sourcelen || !_sinklen ) {
return -1;
}
next_dot = (unsigned)_source[0] + 1;
for(i = 1; i < (unsigned)_sourcelen; i++) {
if( i > (unsigned)_sinklen){ /* Output too small. Not >= bc sink[i-1] is used */
_sink[0] = 0; /* ensure _sink is terminated */
return -1;
}
if ( !_source[i] ) {
_sink[i-1] = '\0';
break;
} else if (i == next_dot) {
_sink[i-1]='.';
next_dot = (unsigned)_source[i] + i + 1;
} else {
_sink[i-1] = _source[i];
}
}
return (signed)i-1;
}
int qname_check( char* _source, int _sourcelen )
{
int next_dot = 0;
int i = 0;
if (!_sourcelen)
return -1;
/* TODO questionable control flow */
for (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;
} else if (
!(_source[i]>='0' && _source[i]<='9') &&
!(_source[i]>='A' && _source[i]<='Z') &&
!(_source[i]>='a' && _source[i]<='z') &&
!(_source[i]== '-') && !(_source[i]=='_')
) {
return -1;
}
}
return -1;
}
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