summaryrefslogtreecommitdiffstats
path: root/modules/renumber/renumber.lua
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--modules/renumber/renumber.lua181
1 files changed, 181 insertions, 0 deletions
diff --git a/modules/renumber/renumber.lua b/modules/renumber/renumber.lua
new file mode 100644
index 0000000..60803d5
--- /dev/null
+++ b/modules/renumber/renumber.lua
@@ -0,0 +1,181 @@
+-- SPDX-License-Identifier: GPL-3.0-or-later
+-- Module interface
+local ffi = require('ffi')
+local prefixes_global = {}
+
+-- get address from config: either subnet prefix or fixed endpoint
+local function extract_address(target)
+ local idx = string.find(target, "!", 1, true)
+ if idx == nil then
+ return target, false
+ end
+ if idx ~= #target then
+ error("[renumber] \"!\" symbol in target is only accepted at the end of address")
+ end
+ return string.sub(target, 1, idx - 1), true
+end
+
+-- Create bitmask from integer mask for single octet: 2 -> 11000000
+local function getOctetBitmask(intMask)
+ return bit.lshift(bit.rshift(255, 8 - intMask), 8 - intMask)
+end
+
+-- Merge ipNet with ipHost, using intMask
+local function mergeIps(ipNet, ipHost, intMask)
+ local octetMask
+ local result = ""
+
+ if #ipNet ~= #ipHost then
+ return nil
+ end
+
+ if intMask == nil then
+ return ipNet
+ end
+
+ for currentOctetNo = 1, #ipNet do
+ if intMask >= 8 then
+ result = result .. ipNet:sub(currentOctetNo,currentOctetNo)
+ elseif (intMask <= 0) then
+ result = result .. ipHost:sub(currentOctetNo,currentOctetNo)
+ else
+ octetMask = getOctetBitmask(intMask)
+ result = result .. string.char(bit.bor(
+ bit.band(string.byte(ipNet:sub(currentOctetNo,currentOctetNo)), octetMask),
+ bit.band(string.byte(ipHost:sub(currentOctetNo,currentOctetNo)), bit.bnot(octetMask))
+ ))
+ end
+ intMask = intMask - 8
+ end
+
+ return result
+end
+
+-- Create subnet prefix rule
+local function matchprefix(subnet, addr)
+ local is_exact
+ addr, is_exact = extract_address(addr)
+ local target = kres.str2ip(addr)
+ if target == nil then error('[renumber] invalid address: '..addr) end
+ local addrtype = string.find(addr, ':', 1, true) and kres.type.AAAA or kres.type.A
+ local subnet_cd = ffi.new('char[16]')
+ local bitlen = ffi.C.kr_straddr_subnet(subnet_cd, subnet)
+ if bitlen < 0 then error('[renumber] invalid subnet: '..subnet) end
+ return {subnet_cd, bitlen, target, addrtype, is_exact}
+end
+
+-- Create name match rule
+local function matchname(name, addr)
+ local is_exact
+ addr, is_exact = extract_address(addr) -- though matchname() always leads to replacing whole address
+ local target = kres.str2ip(addr)
+ if target == nil then error('[renumber] invalid address: '..addr) end
+ local owner = todname(name)
+ if not name then error('[renumber] invalid name: '..name) end
+ local addrtype = string.find(addr, ':', 1, true) and kres.type.AAAA or kres.type.A
+ return {owner, nil, target, addrtype, is_exact}
+end
+
+-- Add subnet prefix rewrite rule
+local function add_prefix(subnet, addr)
+ local prefix = matchprefix(subnet, addr)
+ table.insert(prefixes_global, prefix)
+end
+
+-- Match IP against given subnet or record owner
+local function match_subnet(subnet, bitlen, addrtype, rr)
+ local addr = rr.rdata
+ return addrtype == rr.type and
+ ((bitlen and (#addr >= bitlen / 8) and (ffi.C.kr_bitcmp(subnet, addr, bitlen) == 0)) or subnet == rr.owner)
+end
+
+-- Renumber address record
+local function renumber_record(tbl, rr)
+ for i = 1, #tbl do
+ local prefix = tbl[i]
+ local subnet = prefix[1]
+ local bitlen = prefix[2]
+ local target = prefix[3]
+ local addrtype = prefix[4]
+ local is_exact = prefix[5]
+
+ -- Match record type to address family and record address to given subnet
+ -- If provided, compare record owner to prefix name
+ if match_subnet(subnet, bitlen, addrtype, rr) then
+ if is_exact then
+ rr.rdata = target
+ else
+ local mergedHost = mergeIps(target, rr.rdata, bitlen)
+ if mergedHost ~= nil then rr.rdata = mergedHost end
+ end
+
+ return rr
+ end
+ end
+ return nil
+end
+
+-- Renumber addresses based on config
+local function rule(prefixes)
+ return function (state, req)
+ if state == kres.FAIL then return state end
+ local pkt = req.answer
+ -- Only successful answers
+ local records = pkt:section(kres.section.ANSWER)
+ local ancount = #records
+ if ancount == 0 then return state end
+ -- Find renumber candidates
+ local changed = false
+ for i = 1, ancount do
+ local rr = records[i]
+ if rr.type == kres.type.A or rr.type == kres.type.AAAA then
+ local new_rr = renumber_record(prefixes, rr)
+ if new_rr ~= nil then
+ records[i] = new_rr
+ changed = true
+ end
+ end
+ end
+ -- If not rewritten, chain action
+ if not changed then return state end
+ -- Replace section if renumbering
+ local qname = pkt:qname()
+ local qclass = pkt:qclass()
+ local qtype = pkt:qtype()
+ pkt:recycle()
+ pkt:question(qname, qclass, qtype)
+ for i = 1, ancount do
+ local rr = records[i]
+ -- Strip signatures as rewritten data cannot be validated
+ if rr.type ~= kres.type.RRSIG then
+ pkt:put(rr.owner, rr.ttl, rr.class, rr.type, rr.rdata)
+ end
+ end
+ req:set_extended_error(kres.extended_error.FORGED, "DUQR")
+ return state
+ end
+end
+
+-- Export module interface
+local M = {
+ prefix = matchprefix,
+ name = matchname,
+ rule = rule,
+ match_subnet = match_subnet,
+}
+
+-- Config
+function M.config (conf)
+ if conf == nil then return end
+ if type(conf) ~= 'table' or type(conf[1]) ~= 'table' then
+ error('[renumber] expected { {prefix, target}, ... }')
+ end
+ for i = 1, #conf do add_prefix(conf[i][1], conf[i][2]) end
+end
+
+-- Layers
+M.layer = {
+ finish = rule(prefixes_global),
+}
+
+return M