PowerDNS DNSdist: forward/reverse DNS lookup from ISC Kea DHCP leases

dnsdist.conf

package.path = package.path .. ";" .. "/path/to/dir/containing/this/script/" .. "?.lua"

require "kea"

local dhcpDomains = newSuffixMatchNode()
dhcpDomains:add("8.b.d.0.1.0.0.2.ip6.arpa")
dhcpDomains:add("0.2.0.192.in-addr.arpa.")
dhcpDomains:add("example.net")

local nmg = newNMG()
nmg:addMask("192.0.2.0/24")
nmg:addMask("2001:0bd8::/32")

addAction(AndRule({NetmaskGroupRule(nmg), SuffixMatchNodeRule(dhcpDomains)}), LuaAction(dhcpLookup))

kea.lua

-- without this dnsdist cannot find some modules
package.path = package.path .. ";" .. "/usr/lib/lua/" .. "?.lua"


local cjson = require("cjson")
local http = require("socket.http")
local ltn12 = require("ltn12")


local keaCtrlAgentUrl = "http://localhost:8000"

local dhcpPostLease4GetAll = {
        command = "lease4-get-all",
        service = {"dhcp4"}
}

local dhcpPostLease6GetAll = {
        command = "lease6-get-all",
        service = {"dhcp6"}
}


local function keaCtrlAgentPost(data)
	local jsonData = cjson.encode(data)
	local response = {}
	local res, code, headers, status = http.request {
		headers = {
			["Content-Type"] = "application/json",
			-- Kea control agent does not support chunked transfer encoding
			-- set the Content-Length header to disable it
			["Content-Length"] = string.len(jsonData),
		},
		method = "POST",
		sink = ltn12.sink.table(response),
		source = ltn12.source.string(jsonData),
		url = keaCtrlAgentUrl,
	}

	-- print("keaCtrlAgentPost: " .. jsonData)

	if code == 200 then
		response = table.concat(response)
		return cjson.decode(response)
	else
		return {}
	end
end

local function compressip6(addr)
	local result = table.concat(addr, ":")
	local max_start, max_zeros, zero_count, zero_start = 0, 0, 0, 0

	for i, group in ipairs(addr) do
		if group == "0" then
			if zero_start == 0 then
				zero_start = i
			end
			zero_count = zero_count + 1
		else
			if zero_count > max_zeros then
				max_zeros = zero_count
				max_start = zero_start
			end
			zero_start = 0
			zero_count = 0
		end

	end

	if zero_count > max_zeros then
		max_zeros = zero_count
		max_start = zero_start
	end

	if max_zeros > 1 then
		local after, before = "", ""
		if max_start + max_zeros <= #addr then
			after = table.concat(addr, ":", max_start + max_zeros)
		end
		if max_start > 1 then
			before = table.concat(addr, ":", 1, max_start - 1)
		end
		result = before .. "::" .. after
	end

	return result
end

local function reverse4(record)
	local result = {}
	for octet in record:gmatch("%d+") do
		table.insert(result, octet)
	end
	return result[4] .. "." .. result[3] .. "." .. result[2] .. "." .. result[1]
end

local function reverse6(record)
	local result = {}
	record = string.gsub(record, "%.ip6.arpa%.*$", "")
	record = string.gsub(record, "%.", "")
	record = string.reverse(record)

	for word in record:gmatch("%x%x%x%x") do
		table.insert(result, string.format("%0x", tonumber(word, 16)))
	end

	result = compressip6(result)
	return result
end

local function lookupForward(leases, hostname)
	for _, entry in pairs(leases) do
		for _, lease in pairs(entry.arguments.leases) do
			-- print(lease.hostname)
			if lease.hostname == hostname or lease.hostname .. "." == hostname then
				return lease["ip-address"]
			end
		end
	end

	return nil
end

local function lookupReverse(leases, ip)
	-- print("lookupReverse(): ip: " .. ip)
	for _, entry in pairs(leases) do
		for _, lease in pairs(entry.arguments.leases) do
			-- print(lease.hostname)
			if lease["ip-address"] == ip then
				return lease["hostname"]
			end
		end
	end

	return nil
end


function dhcpLookup(dq)
	if dq == nil then
		-- print("dhcpLookup() called with nil argument")
		return
	end

	local qname = dq.qname:toString()
	local response = nil
	-- print("dhcpLookup(): " .. qname)

	if dq.qtype == DNSQType.A then
		-- print("dhcpLookup() A " .. qname)
		local dhcpLeases4 = keaCtrlAgentPost(dhcpPostLease4GetAll)
		response = lookupForward(dhcpLeases4, qname)
	elseif dq.qtype == DNSQType.AAAA then
		-- print("dhcpLookup() AAAA " .. qname)
		local dhcpLeases6 = keaCtrlAgentPost(dhcpPostLease6GetAll)
		response = lookupForward(dhcpLeases6, qname)
	elseif dq.qtype == DNSQType.PTR then
		-- print("dhcpLookup() PTR " .. qname)
		if string.match(qname, "in-addr.arpa.") ~= nil then
			-- print("dhcpLook() PTR IPv4")
			local dhcpLeases4 = keaCtrlAgentPost(dhcpPostLease4GetAll)
			response = lookupReverse(dhcpLeases4, reverse4(qname))
		elseif qname:gmatch("ip6.arpa.") then
			-- print("dhcpLook() PTR IPv6")
			local dhcpLeases6 = keaCtrlAgentPost(dhcpPostLease6GetAll)
			response = lookupReverse(dhcpLeases6, reverse6(qname))
		else
			-- print("dhcpLook() PTR invalid")
		end
	else
		-- print("not A nor AAAA but " .. dq.qtype)
		return DNSAction.None
	end

	if response == nil then
		return DNSAction.Nxdomain
	else
		return DNSAction.Spoof, response
	end
end