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.
local gettime = require "util.time".now
local setmetatable = setmetatable;
local _ENV = nil;
-- luacheck: std none
local throttle = {};
local throttle_mt = { __index = throttle };
function throttle:update()
local newt = gettime();
local elapsed = newt - self.t;
self.t = newt;
local balance = (self.rate * elapsed) + self.balance;
if balance > self.max then
self.balance = self.max;
else
self.balance = balance;
end
return self.balance;
end
function throttle:peek(cost)
cost = cost or 1;
return self.balance >= cost or self:update() >= cost;
end
function throttle:poll(cost, split)
if self:peek(cost) then
self.balance = self.balance - cost;
return true;
else
local balance = self.balance;
if split then
self.balance = 0;
end
return false, balance, (cost-balance);
end
end
local function create(max, period)
return setmetatable({ rate = max / period, max = max, t = gettime(), balance = max }, throttle_mt);
end
return {
create = create;
};