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LookupServer: Retry with 0x20 randomization turned off on EREFUSED

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Apparently some authoritative servers don't handle 0x20 randomization
well and may send EREFUSED. Retry with randomization turned off then.

Reference: https://github.com/dns-violations/dns-violations/blob/master/2017/DVE-2017-0006.md

More work towards #10.
This commit is contained in:
Andreas Kling 2020-01-26 13:45:15 +01:00
parent 00be9b33b1
commit a9ec2225a5
6 changed files with 48 additions and 11 deletions
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16
Servers/LookupServer/DNSRequest.cpp
View file

@ -13,22 +13,24 @@ DNSRequest::DNSRequest()
{
}
void DNSRequest::add_question(const String& name, u16 record_type)
void DNSRequest::add_question(const String& name, u16 record_type, ShouldRandomizeCase should_randomize_case)
{
ASSERT(m_questions.size() <= UINT16_MAX);
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;
if (should_randomize_case == ShouldRandomizeCase::Yes) {
// Randomize the 0x20 bit in every ASCII character.
if (isalpha(ch)) {
if (arc4random_uniform(2))
ch |= 0x20;
else
ch &= ~0x20;
}
}
builder.append(ch);
}