diff options
Diffstat (limited to 'modules/dns64')
| -rw-r--r-- | modules/dns64/README.rst | 26 | ||||
| -rw-r--r-- | modules/dns64/dns64.lua | 103 | ||||
| -rw-r--r-- | modules/dns64/dns64.mk | 2 | ||||
| -rw-r--r-- | modules/dns64/dns64.test.lua | 52 |
4 files changed, 183 insertions, 0 deletions
diff --git a/modules/dns64/README.rst b/modules/dns64/README.rst new file mode 100644 index 0000000..047443f --- /dev/null +++ b/modules/dns64/README.rst @@ -0,0 +1,26 @@ +.. _mod-dns64: + +DNS64 +----- + +The module for :rfc:`6147` DNS64 AAAA-from-A record synthesis, it is used to enable client-server communication between an IPv6-only client and an IPv4-only server. See the well written `introduction`_ in the PowerDNS documentation. +If no address is passed (i.e. ``nil``), the well-known prefix ``64:ff9b::`` is used. + +.. warning:: The module currently won't work well with :ref:`policy.STUB <mod-policy>`. + Also, the IPv6 passed in configuration is assumed to be ``/96``, and + PTR synthesis and "exclusion prefixes" aren't implemented. + +.. tip:: The A record sub-requests will be DNSSEC secured, but the synthetic AAAA records can't be. Make sure the last mile between stub and resolver is secure to avoid spoofing. + +Example configuration +^^^^^^^^^^^^^^^^^^^^^ + +.. code-block:: lua + + -- Load the module with a NAT64 address + modules = { dns64 = 'fe80::21b:77ff:0:0' } + -- Reconfigure later + dns64.config('fe80::21b:aabb:0:0') + + +.. _introduction: https://doc.powerdns.com/md/recursor/dns64 diff --git a/modules/dns64/dns64.lua b/modules/dns64/dns64.lua new file mode 100644 index 0000000..8e3eaa0 --- /dev/null +++ b/modules/dns64/dns64.lua @@ -0,0 +1,103 @@ +-- Module interface +local ffi = require('ffi') +local M = {} +local addr_buf = ffi.new('char[16]') + +--[[ +Missing parts of the RFC: + > The implementation SHOULD support mapping of separate IPv4 address + > ranges to separate IPv6 prefixes for AAAA record synthesis. This + > allows handling of special use IPv4 addresses [RFC5735]. + + Also the exclusion prefixes are not implemented, sec. 5.1.4 (MUST). + + TODO: support different prefix lengths, defaulting to /96 if not specified + https://tools.ietf.org/html/rfc6052#section-2.2 + + PTR queries aren't supported (MUST), sec. 5.3.1.2 +]] + +-- Config +function M.config (confstr) + M.proxy = kres.str2ip(confstr or '64:ff9b::') + if M.proxy == nil then error('[dns64] "'..confstr..'" is not a valid address') end +end + +-- Layers +M.layer = { } +function M.layer.consume(state, req, pkt) + if state == kres.FAIL then return state end + pkt = kres.pkt_t(pkt) + req = kres.request_t(req) + local qry = req:current() + -- Observe only final answers in IN class where request has no CD flag. + if M.proxy == nil or not qry.flags.RESOLVED + or pkt:qclass() ~= kres.class.IN or req.answer:cd() then + return state + end + -- Synthetic AAAA from marked A responses + local answer = pkt:section(kres.section.ANSWER) + + -- Observe final AAAA NODATA responses to the current SNAME. + local is_nodata = pkt:rcode() == kres.rcode.NOERROR and #answer == 0 + if pkt:qtype() == kres.type.AAAA and is_nodata and pkt:qname() == qry:name() + and qry.flags.RESOLVED and not qry.flags.CNAME and qry.parent == nil then + -- Start a *marked* corresponding A sub-query. + local extraFlags = kres.mk_qflags({}) + extraFlags.DNSSEC_WANT = qry.flags.DNSSEC_WANT + extraFlags.AWAIT_CUT = true + extraFlags.DNS64_MARK = true + req:push(pkt:qname(), kres.type.A, kres.class.IN, extraFlags, qry) + return state + end + + + -- Observe answer to the marked sub-query, and convert all A records in ANSWER + -- to corresponding AAAA records to be put into the request's answer. + if not qry.flags.DNS64_MARK then return state end + -- Find rank for the NODATA answer. + -- That will result into corresponding AD flag. See RFC 6147 5.5.2. + local neg_rank + if qry.parent.flags.DNSSEC_WANT and not qry.parent.flags.DNSSEC_INSECURE + then neg_rank = ffi.C.KR_RANK_SECURE + else neg_rank = ffi.C.KR_RANK_INSECURE + end + -- Find TTL bound from SOA, according to RFC 6147 5.1.7.4. + local max_ttl = 600 + for i = 1, tonumber(req.auth_selected.len) do + local entry = req.auth_selected.at[i - 1] + if entry.qry_uid == qry.parent.uid and entry.rr + and entry.rr.type == kres.type.SOA + and entry.rr.rclass == kres.class.IN then + max_ttl = entry.rr:ttl() + end + end + -- Find the As and do the conversion itself. + for i = 1, tonumber(req.answ_selected.len) do + local orig = req.answ_selected.at[i - 1] + if orig.qry_uid == qry.uid and orig.rr.type == kres.type.A then + local rank = neg_rank + if orig.rank < rank then rank = orig.rank end + -- Disable GC, as this object doesn't own owner or RDATA, it's just a reference + local ttl = orig.rr:ttl() + if ttl > max_ttl then ttl = max_ttl end + local rrs = ffi.gc(kres.rrset(nil, kres.type.AAAA, orig.rr.rclass, ttl), nil) + rrs._owner = orig.rr._owner + for k = 1, orig.rr.rrs.count do + local rdata = orig.rr:rdata( k - 1 ) + ffi.copy(addr_buf, M.proxy, 12) + ffi.copy(addr_buf + 12, rdata, 4) + ffi.C.knot_rrset_add_rdata(rrs, ffi.string(addr_buf, 16), 16, req.pool) + end + ffi.C.kr_ranked_rrarray_add( + req.answ_selected, + rrs, + rank, + true, + qry.uid, + req.pool) + end + end +end + +return M diff --git a/modules/dns64/dns64.mk b/modules/dns64/dns64.mk new file mode 100644 index 0000000..948188c --- /dev/null +++ b/modules/dns64/dns64.mk @@ -0,0 +1,2 @@ +dns64_SOURCES := dns64.lua +$(call make_lua_module,dns64) diff --git a/modules/dns64/dns64.test.lua b/modules/dns64/dns64.test.lua new file mode 100644 index 0000000..1798ccd --- /dev/null +++ b/modules/dns64/dns64.test.lua @@ -0,0 +1,52 @@ +local condition = require('cqueues.condition') + +-- setup resolver +modules = { 'hints', 'dns64' } +hints['dns64.example'] = '192.168.1.1' +hints.use_nodata(true) -- Respond NODATA to AAAA query +dns64.config('fe80::21b:77ff:0:0') + +-- helper to wait for query resolution +local function wait_resolve(qname, qtype) + local waiting, done, cond = false, false, condition.new() + local rcode, answers = kres.rcode.SERVFAIL, {} + resolve { + name = qname, + type = qtype, + finish = function (answer, _) + answer = kres.pkt_t(answer) + rcode = answer:rcode() + answers = answer:section(kres.section.ANSWER) + -- Signal as completed + if waiting then + cond:signal() + end + done = true + end, + } + -- Wait if it didn't finish immediately + if not done then + waiting = true + cond:wait() + end + return rcode, answers +end + +-- test builtin rules +local function test_builtin_rules() + local rcode, answers = wait_resolve('dns64.example', kres.type.AAAA) + same(rcode, kres.rcode.NOERROR, 'dns64.example returns NOERROR') + same(#answers, 1, 'dns64.example synthesised answer') + local expect = {'dns64.example.', '0', 'AAAA', 'fe80::21b:77ff:c0a8:101'} + if #answers > 0 then + local rr = {kres.rr2str(answers[1]):match('(%S+)%s+(%S+)%s+(%S+)%s+(%S+)')} + same(rr, expect, 'dns64.example synthesised correct AAAA record') + end +end + +-- plan tests +local tests = { + test_builtin_rules, +} + +return tests
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