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 setmetatable = setmetatable;
local math_floor = math.floor;
local t_remove = table.remove;
local function _heap_insert(self, item, sync, item2, index)
local pos = #self + 1;
while true do
local half_pos = math_floor(pos / 2);
if half_pos == 0 or item > self[half_pos] then break; end
self[pos] = self[half_pos];
sync[pos] = sync[half_pos];
index[sync[pos]] = pos;
pos = half_pos;
end
self[pos] = item;
sync[pos] = item2;
index[item2] = pos;
end
local function _percolate_up(self, k, sync, index)
local tmp = self[k];
local tmp_sync = sync[k];
while k ~= 1 do
local parent = math_floor(k/2);
if tmp >= self[parent] then break; end
self[k] = self[parent];
sync[k] = sync[parent];
index[sync[k]] = k;
k = parent;
end
self[k] = tmp;
sync[k] = tmp_sync;
index[tmp_sync] = k;
return k;
end
local function _percolate_down(self, k, sync, index)
local tmp = self[k];
local tmp_sync = sync[k];
local size = #self;
local child = 2*k;
while 2*k <= size do
if child ~= size and self[child] > self[child + 1] then
child = child + 1;
end
if tmp > self[child] then
self[k] = self[child];
sync[k] = sync[child];
index[sync[k]] = k;
else
break;
end
k = child;
child = 2*k;
end
self[k] = tmp;
sync[k] = tmp_sync;
index[tmp_sync] = k;
return k;
end
local function _heap_pop(self, sync, index)
local size = #self;
if size == 0 then return nil; end
local result = self[1];
local result_sync = sync[1];
index[result_sync] = nil;
if size == 1 then
self[1] = nil;
sync[1] = nil;
return result, result_sync;
end
self[1] = t_remove(self);
sync[1] = t_remove(sync);
index[sync[1]] = 1;
_percolate_down(self, 1, sync, index);
return result, result_sync;
end
local indexed_heap = {};
function indexed_heap:insert(item, priority, id)
if id == nil then
id = self.current_id;
self.current_id = id + 1;
end
self.items[id] = item;
_heap_insert(self.priorities, priority, self.ids, id, self.index);
return id;
end
function indexed_heap:pop()
local priority, id = _heap_pop(self.priorities, self.ids, self.index);
if id then
local item = self.items[id];
self.items[id] = nil;
return priority, item, id;
end
end
function indexed_heap:peek()
return self.priorities[1];
end
function indexed_heap:reprioritize(id, priority)
local k = self.index[id];
if k == nil then return; end
self.priorities[k] = priority;
k = _percolate_up(self.priorities, k, self.ids, self.index);
_percolate_down(self.priorities, k, self.ids, self.index);
end
function indexed_heap:remove_index(k)
local result = self.priorities[k];
if result == nil then return; end
local result_sync = self.ids[k];
local item = self.items[result_sync];
local size = #self.priorities;
self.priorities[k] = self.priorities[size];
self.ids[k] = self.ids[size];
self.index[self.ids[k]] = k;
t_remove(self.priorities);
t_remove(self.ids);
self.index[result_sync] = nil;
self.items[result_sync] = nil;
if size > k then
k = _percolate_up(self.priorities, k, self.ids, self.index);
_percolate_down(self.priorities, k, self.ids, self.index);
end
return result, item, result_sync;
end
function indexed_heap:remove(id)
return self:remove_index(self.index[id]);
end
local mt = { __index = indexed_heap };
local _M = {
create = function()
return setmetatable({
ids = {}; -- heap of ids, sync'd with priorities
items = {}; -- map id->items
priorities = {}; -- heap of priorities
index = {}; -- map of id->index of id in ids
current_id = 1.5
}, mt);
end
};
return _M;