-- mod_s2s_auth_dane
-- Copyright (C) 2013-2014 Kim Alvefur
--
-- This file is MIT/X11 licensed.
--
-- In your DNS, put
-- _xmpp-server.example.com. IN TLSA 3 0 1 <sha256 hash of certificate>
--
-- Known issues:
-- Race condition
-- Could be done much cleaner if mod_s2s was using util.async
--
-- TODO Things to test/handle:
-- Negative or bogus answers
-- No encryption offered
-- Different hostname before and after STARTTLS - mod_s2s should complain
-- Interaction with Dialback
module:set_global();
local type = type;
local t_insert = table.insert;
local set = require"util.set";
local dns_lookup = require"net.adns".lookup;
local hashes = require"util.hashes";
local base64 = require"util.encodings".base64;
local idna_to_ascii = require "util.encodings".idna.to_ascii;
if not dns_lookup.types or not dns_lookup.types.TLSA then
module:log("error", "No TLSA support available, DANE will not be supported");
return
end
local s2sout = module:depends"s2s".route_to_new_session.s2sout;
local pat = "%-%-%-%-%-BEGIN ([A-Z ]+)%-%-%-%-%-\r?\n"..
"([0-9A-Za-z=+/\r\n]*)\r?\n%-%-%-%-%-END %1%-%-%-%-%-";
local function pem2der(pem)
local typ, data = pem:match(pat);
if typ and data then
return base64.decode(data), typ;
end
end
local use_map = { ["DANE-EE"] = 3; ["DANE-TA"] = 2; ["PKIX-EE"] = 1; ["PKIX-CA"] = 0 }
local implemented_uses = set.new { "DANE-EE", "PKIX-EE" };
local configured_uses = module:get_option_set("dane_uses", { "DANE-EE" });
local enabled_uses = set.intersection(implemented_uses, configured_uses) / function(use) return use_map[use] end;
local function dane_lookup(host_session, cb, a,b,c,e)
if host_session.dane ~= nil then return end
if host_session.direction == "incoming" then
local name = idna_to_ascii(host_session.from_host);
if not name then return end
host_session.dane = dns_lookup(function (answer)
if not answer.secure then
if cb then return cb(a,b,c,e); end
return;
end
local n = #answer
if n == 0 then if cb then return cb(a,b,c,e); end return end
if n == 1 and answer[1].srv.target == '.' then return end
local srv_hosts = { answer = answer };
local dane = {};
host_session.dane = dane;
host_session.srv_hosts = srv_hosts;
for _, record in ipairs(answer) do
t_insert(srv_hosts, record.srv);
dns_lookup(function(dane_answer)
n = n - 1;
if dane_answer.bogus then
t_insert(dane, { bogus = dane_answer.bogus });
elseif dane_answer.secure then
for _, record in ipairs(dane_answer) do
t_insert(dane, record);
end
end
if n == 0 and cb then return cb(a,b,c,e); end
end, ("_%d._tcp.%s."):format(record.srv.port, record.srv.target), "TLSA");
end
end, "_xmpp-server._tcp."..name..".", "SRV");
return true;
elseif host_session.direction == "outgoing" then
if not host_session.srv_hosts then return end
local srv_choice = host_session.srv_hosts[host_session.srv_choice];
host_session.dane = dns_lookup(function(answer)
if answer and (answer.secure and #answer > 0) or answer.bogus then
srv_choice.dane = answer;
else
srv_choice.dane = false;
end
host_session.dane = srv_choice.dane;
if cb then return cb(a,b,c,e); end
end, ("_%d._tcp.%s."):format(srv_choice.port, srv_choice.target), "TLSA");
return true;
end
end
local _try_connect = s2sout.try_connect;
function s2sout.try_connect(host_session, connect_host, connect_port, err)
if not err and dane_lookup(host_session, _try_connect, host_session, connect_host, connect_port, err) then
return true;
end
return _try_connect(host_session, connect_host, connect_port, err);
end
function module.add_host(module)
module:hook("s2s-stream-features", function(event)
-- dane_lookup(origin, origin.from_host);
dane_lookup(event.origin);
end, 1);
module:hook("s2s-authenticated", function(event)
local session = event.session;
if session.dane and not session.secure then
-- TLSA record but no TLS, not ok.
-- TODO Optional?
-- Bogus replies should trigger this path
-- How does this interact with Dialback?
session:close({
condition = "policy-violation",
text = "Encrypted server-to-server communication is required but was not "
..((session.direction == "outgoing" and "offered") or "used")
});
return false;
end
end);
end
module:hook("s2s-check-certificate", function(event)
local session, cert = event.session, event.cert;
local dane = session.dane;
if type(dane) == "table" then
local use, select, match, tlsa, certdata, match_found, supported_found;
for i = 1, #dane do
tlsa = dane[i].tlsa;
module:log("debug", "TLSA %s %s %s %d bytes of data", tlsa:getUsage(), tlsa:getSelector(), tlsa:getMatchType(), #tlsa.data);
use, select, match, certdata = tlsa.use, tlsa.select, tlsa.match;
if enabled_uses:contains(use) then
-- PKIX-EE or DANE-EE
if use == 1 or use == 3 then
supported_found = true
if select == 0 then
certdata = pem2der(cert:pem());
elseif select == 1 and cert.pubkey then
certdata = pem2der(cert:pubkey()); -- Not supported in stock LuaSec
else
module:log("warn", "DANE selector %s is unsupported", tlsa:getSelector() or select);
end
if match == 1 then
certdata = certdata and hashes.sha256(certdata);
elseif match == 2 then
certdata = certdata and hashes.sha512(certdata);
elseif match ~= 0 then
module:log("warn", "DANE match rule %s is unsupported", tlsa:getMatchType() or match);
certdata = nil;
end
-- Should we check if the cert subject matches?
if certdata and certdata == tlsa.data then
(session.log or module._log)("info", "DANE validation successful");
session.cert_identity_status = "valid";
if use == 3 then -- DANE-EE, chain status equals DNSSEC chain status
session.cert_chain_status = "valid";
-- for usage 1, PKIX-EE, the chain has to be valid already
end
match_found = true;
break;
end
end
end
end
if supported_found and not match_found or dane.bogus then
-- No TLSA matched or response was bogus
(session.log or module._log)("warn", "DANE validation failed");
session.cert_identity_status = "invalid";
session.cert_chain_status = "invalid";
end
end
end);
function module.unload()
-- Restore the original try_connect function
s2sout.try_connect = _try_connect;
end