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mod_saslauth: Derive hash from certificate per tls-server-end-point

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This originally used a WIP implementation of cert:sigalg(), a method to
retrieve certificate signature algorithm, but it was never submitted
upstream. https://github.com/Zash/luasec/tree/zash/sigalg

cert:getsignaturename() was merged in
de393417b7

XEP-0440 v0.3.0 made implementing tls-server-end-point a MUST
This commit is contained in:
Kim Alvefur 2021-06-29 00:22:36 +02:00
parent f11fca3cef
commit c6b7b011c0
1 changed files with 34 additions and 0 deletions
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34
plugins/mod_saslauth.lua
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@ -15,6 +15,9 @@ local base64 = require "prosody.util.encodings".base64;
local set = require "prosody.util.set";
local errors = require "prosody.util.error";
local hex = require "prosody.util.hex";
local pem2der = require"util.x509".pem2der;
local hashes = require"util.hashes";
local ssl = require "ssl"; -- FIXME Isolate LuaSec from the rest of the code
local usermanager_get_sasl_handler = require "prosody.core.usermanager".get_sasl_handler;
@ -260,6 +263,30 @@ end
local function tls_server_end_point(self)
local cert_hash = self.userdata["tls-server-end-point"];
if cert_hash then return hex.from(cert_hash); end
-- Hash function selection, see RFC 5929 §4.1
local certfile = self.userdata["tls-server-end-point-cert"];
if not certfile then return end
local f = io.open(certfile);
if not f then return end
local hash = hashes.sha256;
-- FIXME TOCTOU
-- We don't know that this is the right cert, it could have been replaced on
-- disk since we started. Best would be if we could extract the cert used
-- from the SSL context.
local certdata = f:read("*");
local cert = ssl.loadcertificate(certdata);
if cert.getsignaturename then
local sigalg = cert:getsignaturename():lower():match("sha%d+");
if sigalg and sigalg ~= "sha1" and hashes[sigalg] then
-- This should have ruled out MD5 and SHA1
hash = hashes[sigalg];
end
end
return hash(pem2der(cert));
end
local mechanisms_attr = { xmlns='urn:ietf:params:xml:ns:xmpp-sasl' };
@ -295,14 +322,21 @@ module:hook("stream-features", function(event)
else
log("debug", "Channel binding 'tls-unique' not supported (by LuaSec?)");
end
local certfile = origin.ssl_cfg and origin.ssl_cfg.certificate;
-- FIXME .ssl_cfg is set by mod_tls and thus only available with starttls
if tls_server_end_point_hash then
log("debug", "Channel binding 'tls-server-end-point' can be offered with the configured certificate hash");
sasl_handler:add_cb_handler("tls-server-end-point", tls_server_end_point);
channel_bindings:add("tls-server-end-point");
elseif certfile then
log("debug", "Channel binding 'tls-server-end-point' can be offered based on the certificate used");
sasl_handler:add_cb_handler("tls-server-end-point", tls_server_end_point);
channel_bindings:add("tls-server-end-point");
end
sasl_handler["userdata"] = {
["tls-unique"] = origin.conn;
["tls-exporter"] = origin.conn;
["tls-server-end-point-cert"] = certfile;
["tls-server-end-point"] = tls_server_end_point_hash;
};
else