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.
-- Prosody IM
-- Copyright (C) 2008-2010 Matthew Wild
-- Copyright (C) 2008-2010 Waqas Hussain
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--
local pairs = pairs;
local t_insert = table.insert;
local t_remove = table.remove;
local t_sort = table.sort;
local setmetatable = setmetatable;
local next = next;
local _ENV = nil;
-- luacheck: std none
local function new()
-- Map event name to ordered list of handlers (lazily built): handlers[event_name] = array_of_handler_functions
local handlers = {};
-- Array of wrapper functions that wrap all events (nil if empty)
local global_wrappers;
-- Per-event wrappers: wrappers[event_name] = wrapper_function
local wrappers = {};
-- Event map: event_map[handler_function] = priority_number
local event_map = {};
-- Called on-demand to build handlers entries
local function _rebuild_index(self, event)
local _handlers = event_map[event];
if not _handlers or next(_handlers) == nil then return; end
local index = {};
for handler in pairs(_handlers) do
t_insert(index, handler);
end
t_sort(index, function(a, b) return _handlers[a] > _handlers[b]; end);
self[event] = index;
return index;
end;
setmetatable(handlers, { __index = _rebuild_index });
local function add_handler(event, handler, priority)
local map = event_map[event];
if map then
map[handler] = priority or 0;
else
map = {[handler] = priority or 0};
event_map[event] = map;
end
handlers[event] = nil;
end;
local function remove_handler(event, handler)
local map = event_map[event];
if map then
map[handler] = nil;
handlers[event] = nil;
if next(map) == nil then
event_map[event] = nil;
end
end
end;
local function get_handlers(event)
return handlers[event];
end;
local function add_handlers(self)
for event, handler in pairs(self) do
add_handler(event, handler);
end
end;
local function remove_handlers(self)
for event, handler in pairs(self) do
remove_handler(event, handler);
end
end;
local function _fire_event(event_name, event_data)
local h = handlers[event_name];
if h then
for i=1,#h do
local ret = h[i](event_data);
if ret ~= nil then return ret; end
end
end
end;
local function fire_event(event_name, event_data)
-- luacheck: ignore 432/event_name 432/event_data
local w = wrappers[event_name] or global_wrappers;
if w then
local curr_wrapper = #w;
local function c(event_name, event_data)
curr_wrapper = curr_wrapper - 1;
if curr_wrapper == 0 then
if global_wrappers == nil or w == global_wrappers then
return _fire_event(event_name, event_data);
end
w, curr_wrapper = global_wrappers, #global_wrappers;
return w[curr_wrapper](c, event_name, event_data);
else
return w[curr_wrapper](c, event_name, event_data);
end
end
return w[curr_wrapper](c, event_name, event_data);
end
return _fire_event(event_name, event_data);
end
local function add_wrapper(event_name, wrapper)
local w;
if event_name == false then
w = global_wrappers;
if not w then
w = {};
global_wrappers = w;
end
else
w = wrappers[event_name];
if not w then
w = {};
wrappers[event_name] = w;
end
end
w[#w+1] = wrapper;
end
local function remove_wrapper(event_name, wrapper)
local w;
if event_name == false then
w = global_wrappers;
else
w = wrappers[event_name];
end
if not w then return; end
for i = #w, 1, -1 do
if w[i] == wrapper then
t_remove(w, i);
end
end
if #w == 0 then
if event_name == false then
global_wrappers = nil;
else
wrappers[event_name] = nil;
end
end
end
return {
add_handler = add_handler;
remove_handler = remove_handler;
add_handlers = add_handlers;
remove_handlers = remove_handlers;
get_handlers = get_handlers;
wrappers = {
add_handler = add_wrapper;
remove_handler = remove_wrapper;
};
add_wrapper = add_wrapper;
remove_wrapper = remove_wrapper;
fire_event = fire_event;
_handlers = handlers;
_event_map = event_map;
};
end
return {
new = new;
};