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LookupServer: Verify that DNS response questions match the request

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To protect against DNS spoof attacks, we now check that the questions
in incoming responses match the questions in the request we sent out.

Suggested by @zecke in #10.
This commit is contained in:
Andreas Kling 2020-01-26 13:06:00 +01:00
parent b4d55b16b6
commit 00be9b33b1
4 changed files with 26 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

10
Servers/LookupServer/DNSQuestion.h
View file

@ -16,6 +16,16 @@ public:
u16 class_code() const { return m_class_code; }
const String& name() const { return m_name; }
bool operator==(const DNSQuestion& other) const
{
return m_name == other.m_name && m_record_type == other.m_record_type && m_class_code == other.m_class_code;
}
bool operator!=(const DNSQuestion& other) const
{
return !(*this == other);
}
private:
String m_name;
u16 m_record_type { 0 };

2
Servers/LookupServer/DNSRequest.h
View file

@ -18,6 +18,8 @@ public:
void add_question(const String& name, u16 record_type);
const Vector<DNSQuestion>& questions() const { return m_questions; }
u16 question_count() const
{
ASSERT(m_questions.size() < UINT16_MAX);

3
Servers/LookupServer/DNSResponse.cpp
View file

@ -28,7 +28,6 @@ private:
static_assert(sizeof(DNSRecordWithoutName) == 10);
Optional<DNSResponse> DNSResponse::from_raw_response(const u8* raw_data, size_t raw_size)
{
if (raw_size < sizeof(DNSPacket)) {
@ -79,7 +78,7 @@ Optional<DNSResponse> DNSResponse::from_raw_response(const u8* raw_data, size_t
// FIXME: Parse some other record types perhaps?
dbg() << " data=(unimplemented record type " << record.type() << ")";
}
dbg() << "Answer #" << i << ": type=" << record.type() << ", ttl=" << record.ttl() << ", length=" << record.data_length() << ", data=_" << data << "_";
dbg() << "Answer #" << i << ": name=_" << name << "_, type=" << record.type() << ", ttl=" << record.ttl() << ", length=" << record.data_length() << ", data=_" << data << "_";
response.m_answers.empend(name, record.type(), record.record_class(), record.ttl(), data);
offset += record.data_length();
}

14
Servers/LookupServer/LookupServer.cpp
View file

@ -216,10 +216,22 @@ Vector<String> LookupServer::lookup(const String& hostname, bool& did_timeout, u
dbgprintf("LookupServer: ID mismatch (%u vs %u) :(\n", response.id(), request.id());
return {};
}
if (response.question_count() != 1) {
if (response.question_count() != request.question_count()) {
dbgprintf("LookupServer: Question count (%u vs %u) :(\n", response.question_count(), request.question_count());
return {};
}
for (size_t i = 0; i < request.question_count(); ++i) {
auto& request_question = request.questions()[i];
auto& response_question = response.questions()[i];
if (request_question != response_question) {
dbg() << "Request and response questions do not match";
dbg() << " Request: {_" << request_question.name() << "_, " << request_question.record_type() << ", " << request_question.class_code() << "}";
dbg() << " Response: {_" << response_question.name() << "_, " << response_question.record_type() << ", " << response_question.class_code() << "}";
return {};
}
}
if (response.answer_count() < 1) {
dbgprintf("LookupServer: Not enough answers (%u) :(\n", response.answer_count());
return {};