1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
|
/* 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;
}
|