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LookupServer: Randomize the 0x20 bit in DNS request ASCII characters

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This adds a bit of extra entropy to DNS requests, making it harder to
spoof a valid response.

Suggested by @zecke in #10.
This commit is contained in:
Andreas Kling 2020-01-26 13:04:06 +01:00
parent 02be23cf81
commit b4d55b16b6
1 changed files with 23 additions and 1 deletions
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24
Servers/LookupServer/DNSRequest.cpp
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@ -1,7 +1,9 @@
#include "DNSRequest.h"
#include "DNSPacket.h"
#include <AK/BufferStream.h>
#include <AK/StringBuilder.h>
#include <arpa/inet.h>
#include <ctype.h>
#include <stdlib.h>
#define C_IN 1
@ -14,7 +16,27 @@ DNSRequest::DNSRequest()
void DNSRequest::add_question(const String& name, u16 record_type)
{
ASSERT(m_questions.size() <= UINT16_MAX);
m_questions.empend(name, record_type, C_IN);
if (name.is_empty())
return;
// Randomize the 0x20 bit in every ASCII character.
StringBuilder builder;
for (size_t i = 0; i < name.length(); ++i) {
u8 ch = name[i];
if (isalpha(ch)) {
if (arc4random_uniform(2))
ch |= 0x20;
else
ch &= ~0x20;
}
builder.append(ch);
}
if (name[name.length() - 1] != '.')
builder.append('.');
m_questions.empend(builder.to_string(), record_type, C_IN);
}
ByteBuffer DNSRequest::to_byte_buffer() const