util.xml: Do not allow doctypes, comments or processing instructions
Yes. This is as bad as it sounds. CVE pending.
In Prosody itself, this only affects mod_websocket, which uses util.xml
to parse the <open/> frame, thus allowing unauthenticated remote DoS
using Billion Laughs. However, third-party modules using util.xml may
also be affected by this.
This commit installs handlers which disallow the use of doctype
declarations and processing instructions without any escape hatch. It,
by default, also introduces such a handler for comments, however, there
is a way to enable comments nontheless.
This is because util.xml is used to parse human-facing data, where
comments are generally a desirable feature, and also because comments
are generally harmless.
module:set_global();
local max_buffer_len = module:get_option_number("multiplex_buffer_size", 1024);
local portmanager = require "core.portmanager";
local available_services = {};
local function add_service(service)
local multiplex_pattern = service.multiplex and service.multiplex.pattern;
if multiplex_pattern then
module:log("debug", "Adding multiplex service %q with pattern %q", service.name, multiplex_pattern);
available_services[service] = multiplex_pattern;
else
module:log("debug", "Service %q is not multiplex-capable", service.name);
end
end
module:hook("service-added", function (event) add_service(event.service); end);
module:hook("service-removed", function (event) available_services[event.service] = nil; end);
for _, services in pairs(portmanager.get_registered_services()) do
for _, service in ipairs(services) do
add_service(service);
end
end
local buffers = {};
local listener = { default_mode = "*a" };
function listener.onconnect()
end
function listener.onincoming(conn, data)
if not data then return; end
local buf = buffers[conn];
buf = buf and buf..data or data;
for service, multiplex_pattern in pairs(available_services) do
if buf:match(multiplex_pattern) then
module:log("debug", "Routing incoming connection to %s", service.name);
local next_listener = service.listener;
conn:setlistener(next_listener);
local onconnect = next_listener.onconnect;
if onconnect then onconnect(conn) end
return next_listener.onincoming(conn, buf);
end
end
if #buf > max_buffer_len then -- Give up
conn:close();
else
buffers[conn] = buf;
end
end
function listener.ondisconnect(conn)
buffers[conn] = nil; -- warn if no buffer?
end
listener.ondetach = listener.ondisconnect;
module:provides("net", {
name = "multiplex";
config_prefix = "";
listener = listener;
});
module:provides("net", {
name = "multiplex_ssl";
config_prefix = "ssl";
encryption = "ssl";
listener = listener;
});