mod_s2s_auth_dane: Fix potential traceback in logging if SRV target fails nameprep
-- mod_s2s_auth_dane
-- Copyright (C) 2013-2014 Kim Alvefur
--
-- This file is MIT/X11 licensed.
--
-- Implements DANE and Secure Delegation using DNS SRV as described in
-- http://tools.ietf.org/html/draft-miller-xmpp-dnssec-prooftype
--
-- Known issues:
-- 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;
local idna_to_unicode = require"util.encodings".idna.to_unicode;
local nameprep = require"util.encodings".stringprep.nameprep;
local cert_verify_identity = require "util.x509".verify_identity;
do
local net_dns = require"net.dns";
if not net_dns.types or not net_dns.types[52] then
module:log("error", "No TLSA support available, DANE will not be supported");
return
end
end
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" };
if debug.getregistry()["SSL:Certificate"].__index.issued then
-- Need cert:issued() for these
implemented_uses:add("DANE-TA");
implemented_uses:add("PKIX-CA");
else
module:log("warn", "Unable to support DANE-TA and PKIX-CA");
end
local configured_uses = module:get_option_set("dane_uses", { "DANE-EE", "DANE-TA" });
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 = host_session.from_host and idna_to_ascii(host_session.from_host);
if not name then return end
host_session.dane = dns_lookup(function (answer)
host_session.dane = false;
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
-- How to handle this?
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
local srv_hosts = host_session.srv_hosts;
if not ( srv_hosts and srv_hosts.answer and srv_hosts.answer.secure ) then return end
local srv_choice = 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
function module.add_host(module)
local function on_new_s2s(event)
local host_session = event.origin;
if host_session.type == "s2sout" or host_session.type == "s2sin" or host_session.dane ~= nil then return end -- Already authenticated
host_session.log("debug", "Pausing connection until DANE lookup is completed");
host_session.conn:pause()
local function resume()
host_session.log("debug", "DANE lookup completed, resuming connection");
host_session.conn:resume()
end
if not dane_lookup(host_session, resume) then
resume();
end
end
-- New outgoing connections
module:hook("stanza/http://etherx.jabber.org/streams:features", on_new_s2s, 501);
module:hook("s2sout-authenticate-legacy", on_new_s2s, 200);
-- New incoming connections
module:hook("s2s-stream-features", on_new_s2s, 10);
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
-- Cleanup
session.dane = nil;
session.srv_hosts = nil;
end);
end
local function one_dane_check(tlsa, cert)
local select, match, certdata = tlsa.select, tlsa.match;
if select == 0 then
certdata = pem2der(cert:pem());
elseif select == 1 and cert.pubkey then
certdata = pem2der(cert:pubkey());
else
module:log("warn", "DANE selector %s is unsupported", tlsa:getSelector() or select);
return;
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 %s is unsupported", tlsa:getMatchType() or match);
return;
end
return certdata == tlsa.data;
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, tlsa, match_found, supported_found, chain, leafcert, cacert, is_match;
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 = tlsa.use;
if enabled_uses:contains(use) then
-- PKIX-EE or DANE-EE
if use == 1 or use == 3 then
-- Should we check if the cert subject matches?
is_match = one_dane_check(tlsa, cert);
if is_match ~= nil then
supported_found = true;
end
if is_match 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
elseif use == 0 or use == 2 then
supported_found = true;
if chain == nil then
chain = session.conn:socket():getpeerchain();
end
for i = 2, #chain do
cacert, leafcert = chain[i], chain[i-1];
is_match = one_dane_check(tlsa, cacert);
if is_match ~= nil then
supported_found = true;
end
if use == 2 and not cacert:issued(leafcert or cacert) then
module:log("debug", "Broken chain");
break;
end
if is_match then
(session.log or module._log)("info", "DANE validation successful");
if use == 2 then -- DANE-TA
session.cert_identity_status = "valid";
session.cert_chain_status = "valid";
-- for usage 0, PKIX-CA, identity and chain has to be valid already
end
match_found = true;
break;
end
end
if match_found then 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
else
if session.cert_chain_status == "valid" and session.cert_identity_status ~= "valid"
and session.srv_hosts and session.srv_hosts.answer and session.srv_hosts.answer.secure then
local srv_hosts, srv_choice, srv_target = session.srv_hosts, session.srv_choice;
for i = srv_choice or 1, srv_choice or #srv_hosts do
srv_target = session.srv_hosts[i].target:gsub("%.?$","");
(session.log or module._log)("debug", "Comparing certificate with Secure SRV target %s", srv_target);
srv_target = nameprep(idna_to_unicode());
if srv_target and cert_verify_identity(srv_target, "xmpp-server", cert) then
(session.log or module._log)("info", "Certificate matches Secure SRV target %s", srv_target);
session.cert_identity_status = "valid";
return;
end
end
end
end
end);