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 debug = require "util.debug";
-- Helper functions for debugging
local log = require "util.logger".init("util.debug");
local function log_events(events, name, logger)
local f = events.fire_event;
if not f then
error("Object does not appear to be a util.events object");
end
logger = logger or log;
name = name or tostring(events);
function events.fire_event(event, ...)
logger("debug", "%s firing event: %s", name, event);
return f(event, ...);
end
events[events.fire_event] = f;
return events;
end
local function revert_log_events(events)
events.fire_event, events[events.fire_event] = events[events.fire_event], nil; -- :))
end
local function log_host_events(host)
return log_events(prosody.hosts[host].events, host);
end
local function revert_log_host_events(host)
return revert_log_events(prosody.hosts[host].events);
end
local function show_events(events, specific_event)
local event_handlers = events._handlers;
local events_array = {};
local event_handler_arrays = {};
for event, priorities in pairs(events._event_map) do
local handlers = event_handlers[event];
if handlers and (event == specific_event or not specific_event) then
table.insert(events_array, event);
local handler_strings = {};
for i, handler in ipairs(handlers) do
local upvals = debug.string_from_var_table(debug.get_upvalues_table(handler));
handler_strings[i] = " "..(priorities[handler] or "?")..": "..tostring(handler)..(upvals and ("\n "..upvals) or "");
end
event_handler_arrays[event] = handler_strings;
end
end
table.sort(events_array);
local i = 1;
while i <= #events_array do
local handlers = event_handler_arrays[events_array[i]];
for j=#handlers, 1, -1 do
table.insert(events_array, i+1, handlers[j]);
end
if i > 1 then events_array[i] = "\n"..events_array[i]; end
i = i + #handlers + 1
end
return table.concat(events_array, "\n");
end
local function get_upvalue(f, get_name)
local i, name, value = 0;
repeat
i = i + 1;
name, value = debug.getupvalue(f, i);
until name == get_name or name == nil;
return value;
end
return {
log_host_events = log_host_events;
revert_log_host_events = revert_log_host_events;
log_events = log_events;
revert_log_events = revert_log_events;
show_events = show_events;
get_upvalue = get_upvalue;
};