mod_s2s_auth_dane: Invalidate trust if there are TLSA records but no matches, or bogus results
-- mod_s2s_auth_dane
--
-- Between the DNS lookup and the chertificate validation, there is a race condition.
-- Solving that probably requires changes to mod_s2s, like using util.async
module:set_global();
local dns_lookup = require"net.adns".lookup;
local hashes = require"util.hashes";
local base64 = require"util.encodings".base64;
local s2sout = module:depends"s2s".route_to_new_session.s2sout;
local _try_connect = s2sout.try_connect
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
-- TODO Things to test/handle:
-- Negative or bogus answers
-- No SRV records
function s2sout.try_connect(host_session, connect_host, connect_port, err)
local srv_hosts = host_session.srv_hosts;
local srv_choice = host_session.srv_choice;
if srv_hosts and srv_hosts.answer.secure and not srv_hosts[srv_choice].dane then
dns_lookup(function(answer)
if answer and ( #answer > 0 or answer.bogus ) then
srv_hosts[srv_choice].dane = answer;
for i, tlsa in ipairs(answer) do
module:log("debug", "TLSA %s", tostring(tlsa));
end
end
end, ("_%d._tcp.%s"):format(connect_port, connect_host), "TLSA")
end
return _try_connect(host_session, connect_host, connect_port, err)
end
module:hook("s2s-check-certificate", function(event)
local session, cert = event.session, event.cert;
local srv_hosts = session.srv_hosts;
local srv_choice = session.srv_choice;
local choosen = srv_hosts and srv_hosts[srv_choice];
if choosen and choosen.dane then
local use, select, match, tlsa, certdata, match_found
for i, rr in ipairs(choosen.dane) do
tlsa = rr.tlsa
module:log("debug", "TLSA %s", tostring(tlsa));
use, select, match, certdata = tlsa.use, tlsa.select, tlsa.match;
if use == 1 or use == 3 then
if select == 0 then
certdata = pem2der(cert:pem());
elseif select == 1 then
certdata = pem2der(cert:pubkey());
else
module:log("warn", "DANE selector %d is unsupported", select);
end
if match == 1 then
certdata = hashes.sha256(certdata);
elseif match == 2 then
certdata = hashes.sha512(certdata);
elseif match ~= 0 then
module:log("warn", "DANE match rule %d is unsupported", 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
session.cert_chain_status = "valid"
-- for usage 1 the chain has to be valid already
end
match_found = true
break;
end
else
module:log("warn", "DANE %s is unsupported", tlsa:getUsage() or ("usage "..tostring(use)));
-- TODO Ca checks needs to loop over the chain and stuff
end
end
if not match_found then
(session.log or module._log)("info", "DANE validation successful");
session.cert_identity_status = "invalid";
session.cert_chain_status = "invalid";
end
end
end);
function module.unload()
s2sout.try_connect = _try_connect;
end