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
|
use super::Result;
pub struct PacketBuffer {
pub buf: [u8; 512],
pub pos: usize,
}
impl PacketBuffer {
pub fn new() -> PacketBuffer {
PacketBuffer {
buf: [0; 512],
pos: 0,
}
}
pub fn pos(&self) -> usize {
self.pos
}
pub fn step(&mut self, steps: usize) -> Result<()> {
self.pos += steps;
Ok(())
}
pub fn seek(&mut self, pos: usize) -> Result<()> {
self.pos = pos;
Ok(())
}
pub fn read(&mut self) -> Result<u8> {
if self.pos >= 512 {
return Err("End of buffer".into());
}
let res = self.buf[self.pos];
self.pos += 1;
Ok(res)
}
pub fn get(&mut self, pos: usize) -> Result<u8> {
if pos >= 512 {
return Err("End of buffer".into());
}
Ok(self.buf[pos])
}
pub fn get_range(&mut self, start: usize, len: usize) -> Result<&[u8]> {
if start + len >= 512 {
return Err("End of buffer".into());
}
Ok(&self.buf[start..start + len as usize])
}
pub fn read_u16(&mut self) -> Result<u16> {
let res = ((self.read()? as u16) << 8) | (self.read()? as u16);
Ok(res)
}
pub fn read_u32(&mut self) -> Result<u32> {
let res = ((self.read()? as u32) << 24)
| ((self.read()? as u32) << 16)
| ((self.read()? as u32) << 8)
| ((self.read()? as u32) << 0);
Ok(res)
}
pub fn read_qname(&mut self, outstr: &mut String) -> Result<()> {
let mut pos = self.pos();
let mut jumped = false;
let mut delim = "";
let max_jumps = 5;
let mut jumps_performed = 0;
loop {
// Dns Packets are untrusted data, so we need to be paranoid. Someone
// can craft a packet with a cycle in the jump instructions. This guards
// against such packets.
if jumps_performed > max_jumps {
return Err(format!("Limit of {} jumps exceeded", max_jumps).into());
}
let len = self.get(pos)?;
// A two byte sequence, where the two highest bits of the first byte is
// set, represents a offset relative to the start of the buffer. We
// handle this by jumping to the offset, setting a flag to indicate
// that we shouldn't update the shared buffer position once done.
if (len & 0xC0) == 0xC0 {
// When a jump is performed, we only modify the shared buffer
// position once, and avoid making the change later on.
if !jumped {
self.seek(pos + 2)?;
}
let b2 = self.get(pos + 1)? as u16;
let offset = (((len as u16) ^ 0xC0) << 8) | b2;
pos = offset as usize;
jumped = true;
jumps_performed += 1;
continue;
}
pos += 1;
// Names are terminated by an empty label of length 0
if len == 0 {
break;
}
outstr.push_str(delim);
let str_buffer = self.get_range(pos, len as usize)?;
outstr.push_str(&String::from_utf8_lossy(str_buffer).to_lowercase());
delim = ".";
pos += len as usize;
}
if !jumped {
self.seek(pos)?;
}
Ok(())
}
pub fn write(&mut self, val: u8) -> Result<()> {
if self.pos >= 512 {
return Err("End of buffer".into());
}
self.buf[self.pos] = val;
self.pos += 1;
Ok(())
}
pub fn write_u8(&mut self, val: u8) -> Result<()> {
self.write(val)?;
Ok(())
}
pub fn write_u16(&mut self, val: u16) -> Result<()> {
self.write((val >> 8) as u8)?;
self.write((val & 0xFF) as u8)?;
Ok(())
}
pub fn write_u32(&mut self, val: u32) -> Result<()> {
self.write(((val >> 24) & 0xFF) as u8)?;
self.write(((val >> 16) & 0xFF) as u8)?;
self.write(((val >> 8) & 0xFF) as u8)?;
self.write(((val >> 0) & 0xFF) as u8)?;
Ok(())
}
pub fn write_qname(&mut self, qname: &str) -> Result<()> {
for label in qname.split('.') {
let len = label.len();
if len > 0x34 {
return Err("Single label exceeds 63 characters of length".into());
}
self.write_u8(len as u8)?;
for b in label.as_bytes() {
self.write_u8(*b)?;
}
}
self.write_u8(0)?;
Ok(())
}
pub fn set(&mut self, pos: usize, val: u8) -> Result<()> {
self.buf[pos] = val;
Ok(())
}
pub fn set_u16(&mut self, pos: usize, val: u16) -> Result<()> {
self.set(pos, (val >> 8) as u8)?;
self.set(pos + 1, (val & 0xFF) as u8)?;
Ok(())
}
}
|
