vavrusa

var net = require('net');
var dgram = require('dgram');

function ntohs(arr) {
  return ((arr[0] & 0xFF) << 8) | (arr[1] & 0xFF);
}

function parse_name(data, pos)
{
  for (base = pos; pos < data.length;) {

vavrusa

vavrusa

## How it deals with bad CDNs

The query is `who.ami.here.com. A`

1. It's going to ask at `.` to `com. NS` and get a referral
2. it's going to ask `com.` nameserver about `here.com. NS` and get a referral

... see the pattern, it just appends labels, but bear with me

3. We're asking `here.com` nameserver about `ami.here.com. NS` , but he's a prick and tells us 'NXDOMAIN'.

vavrusa

Near-stretch ideas
------------------

* I *quite* like how it's built, but it's too much *PowerDNS*-y, hacking on it is a pain (if you work on cheap virtuals like me) because of long build times and dependencies (I know, but try it yourself on the budget DigitalOcean droplet...), I'd say lose the legacy and make it really a standalone thing.
* The configuration is sometimes confusing, like if I set it up to listen on local interfaces, it happily does so but it silently drops all queries because the ACL allows localhost only (uhm, maybe it needs to say something in verbose mode or documentation update).
* The config format for IPv6 has a poor choice of ':' as a separator, it's not possible to forward to IPv6 address on a custom port.

Far-stretch ideas
-----------------

vavrusa

local slowdrip = {
  tracked = {},
  blocked = {},
  window = 60,     -- Length of the tracking window
  threshold = 100, -- Number of NXDOMAINs before blocking
  -- Track suffixes of names leading to NXDOMAIN
  layer = {
    finish = function(state, req, answer)
      local parent = answer:qname()
      parent = parent:sub(parent:find('.',0,true), -1)

vavrusa

#include <stdio.h>
#include <string.h>
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
#include <arpa/inet.h>

/* Get/set opcode */
static int msg_op(lua_State *L)
{

vavrusa

-- C definitions
local ffi = require('ffi')
local csym = ffi.C
ffi.cdef[[
/* DHCP header format */
struct __attribute__((packed)) dhcp_msg {
	/* Header */
	uint8_t op;
	uint8_t htype;
	uint8_t hlen;

vavrusa

local mod = {}
mod.layer = {
	consume = function (state, req, answer)
		if state == kres.FAIL then
			return state
		end
		answer = kres.pkt_t(answer)
		req = kres.request_t(req)
		if answer:qtype() == kres.type.NS then
			local qry = req:push(answer:qname(), kres.type.SOA, kres.class.IN)

vavrusa

Mitigating with local resolver

There are two preconditions for the attack:

1. One of the queries results in 2k valid answer
2. One of the queries soft-fails and will be retried

Mitigating (1) with UDP is simple: set maximum UDP buffer size to <2048B [1] That leaves TCP.

vavrusa

#!/usr/bin/python
#
# Copyright 2016 Google Inc
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#