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Improve LuaController security (#393)

Fixes:
1. Lack of 'safe' on minetest.deserialize usage
2. String sandbox bypass via (""):evil()
3. Loss of upcoming digilines messages on server shutdown
4. LCs failing to show information on some errors
5. Interrupt IDs as infinite data storage
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20kdc authored and numberZero committed Jan 22, 2018
1 parent fec82ab commit 065e870349cf394240cf9748db4743c0d6d54461
Showing with 124 additions and 39 deletions.
  1. +124 −39 mesecons_luacontroller/init.lua
@@ -13,8 +13,10 @@
-- newport = merge_port_states(state1, state2): just does result = state1 or state2 for every port
-- set_port(pos, rule, state): activates/deactivates the mesecons according to the port states
-- set_port_states(pos, ports): Applies new port states to a Luacontroller at pos
-- run(pos): runs the code in the controller at pos
-- reset_meta(pos, code, errmsg): performs a software-reset, installs new code and prints error messages
-- run_inner(pos, code, event): runs code on the controller at pos and event
-- reset_formspec(pos, code, errmsg): installs new code and prints error messages, without resetting LCID
-- reset_meta(pos, code, errmsg): performs a software-reset, installs new code and prints error message
-- run(pos, event): a wrapper for run_inner which gets code & handles errors via reset_meta
-- resetn(pos): performs a hardware reset, turns off all ports
--
-- The Sandbox
@@ -141,7 +143,7 @@ local function set_port_states(pos, ports)
-- Solution / Workaround:
-- Remember which output was turned off and ignore next "off" event.
local meta = minetest.get_meta(pos)
local ign = minetest.deserialize(meta:get_string("ignore_offevents")) or {}
local ign = minetest.deserialize(meta:get_string("ignore_offevents"), true) or {}
if ports.a and not vports.a and not mesecon.is_powered(pos, rules.a) then ign.A = true end
if ports.b and not vports.b and not mesecon.is_powered(pos, rules.b) then ign.B = true end
if ports.c and not vports.c and not mesecon.is_powered(pos, rules.c) then ign.C = true end
@@ -183,7 +185,7 @@ end

local function ignore_event(event, meta)
if event.type ~= "off" then return false end
local ignore_offevents = minetest.deserialize(meta:get_string("ignore_offevents")) or {}
local ignore_offevents = minetest.deserialize(meta:get_string("ignore_offevents"), true) or {}
if ignore_offevents[event.pin.name] then
ignore_offevents[event.pin.name] = nil
meta:set_string("ignore_offevents", minetest.serialize(ignore_offevents))
@@ -236,6 +238,7 @@ local function remove_functions(x)
local seen = {}

local function rfuncs(x)
if x == nil then return end
if seen[x] then return end
seen[x] = true
if type(x) ~= "table" then return end
@@ -259,12 +262,27 @@ local function remove_functions(x)
return x
end

local function get_interrupt(pos)
-- itbl: Flat table of functions to run after sandbox cleanup, used to prevent various security hazards
local function get_interrupt(pos, itbl, send_warning)
-- iid = interrupt id
local function interrupt(time, iid)
-- NOTE: This runs within string metatable sandbox, so don't *rely* on anything of the form (""):y
-- Hence the values get moved out. Should take less time than original, so totally compatible
if type(time) ~= "number" then return end
local luac_id = minetest.get_meta(pos):get_int("luac_id")
mesecon.queue:add_action(pos, "lc_interrupt", {luac_id, iid}, time, iid, 1)
table.insert(itbl, function ()
-- Outside string metatable sandbox, can safely run this now
local luac_id = minetest.get_meta(pos):get_int("luac_id")
-- Check if IID is dodgy, so you can't use interrupts to store an infinite amount of data.
-- Note that this is safe from alter-after-free because this code gets run after the sandbox has ended.
-- This runs outside of the timer and *shouldn't* harm perf. unless dodgy data is being sent in the first place
iid = remove_functions(iid)
local msg_ser = minetest.serialize(iid)
if #msg_ser <= mesecon.setting("luacontroller_interruptid_maxlen", 256) then
mesecon.queue:add_action(pos, "lc_interrupt", {luac_id, iid}, time, iid, 1)
else
send_warning("An interrupt ID was too large!")
end
end)
end
return interrupt
end
@@ -357,32 +375,49 @@ local function clean_and_weigh_digiline_message(msg, back_references)
end


local function get_digiline_send(pos)
-- itbl: Flat table of functions to run after sandbox cleanup, used to prevent various security hazards
local function get_digiline_send(pos, itbl, send_warning)
if not minetest.global_exists("digilines") then return end
local chan_maxlen = mesecon.setting("luacontroller_digiline_channel_maxlen", 256)
local maxlen = mesecon.setting("luacontroller_digiline_maxlen", 50000)
return function(channel, msg)
-- NOTE: This runs within string metatable sandbox, so don't *rely* on anything of the form (""):y
-- or via anything that could.
-- Make sure channel is string, number or boolean
if (type(channel) ~= "string" and type(channel) ~= "number" and type(channel) ~= "boolean") then
if type(channel) == "string" then
if #channel > chan_maxlen then
send_warning("Channel string too long.")
return false
end
elseif (type(channel) ~= "string" and type(channel) ~= "number" and type(channel) ~= "boolean") then
send_warning("Channel must be string, number or boolean.")
return false
end

local msg_cost
msg, msg_cost = clean_and_weigh_digiline_message(msg)
if msg == nil or msg_cost > mesecon.setting("luacontroller_digiline_maxlen", 50000) then
if msg == nil or msg_cost > maxlen then
send_warning("Message was too complex, or contained invalid data.")
return false
end

minetest.after(0, digilines.receptor_send, pos, digilines.rules.default, channel, msg)
table.insert(itbl, function ()
-- Runs outside of string metatable sandbox
local luac_id = minetest.get_meta(pos):get_int("luac_id")
mesecon.queue:add_action(pos, "lc_digiline_relay", {channel, luac_id, msg})
end)
return true
end
end


local safe_globals = {
-- Don't add pcall/xpcall unless willing to deal with the consequences (unless very careful, incredibly likely to allow killing server indirectly)
"assert", "error", "ipairs", "next", "pairs", "select",
"tonumber", "tostring", "type", "unpack", "_VERSION"
}

local function create_environment(pos, mem, event)
local function create_environment(pos, mem, event, itbl, send_warning)
-- Gather variables for the environment
local vports = minetest.registered_nodes[minetest.get_node(pos).name].virtual_portstates
local vports_copy = {}
@@ -399,8 +434,8 @@ local function create_environment(pos, mem, event)
heat = mesecon.get_heat(pos),
heat_max = mesecon.setting("overheat_max", 20),
print = safe_print,
interrupt = get_interrupt(pos),
digiline_send = get_digiline_send(pos),
interrupt = get_interrupt(pos, itbl, send_warning),
digiline_send = get_digiline_send(pos, itbl, send_warning),
string = {
byte = string.byte,
char = string.char,
@@ -488,10 +523,11 @@ local function create_sandbox(code, env)
jit.off(f, true)
end

local maxevents = mesecon.setting("luacontroller_maxevents", 10000)
return function(...)
-- NOTE: This runs within string metatable sandbox, so the setting's been moved out for safety
-- Use instruction counter to stop execution
-- after luacontroller_maxevents
local maxevents = mesecon.setting("luacontroller_maxevents", 10000)
debug.sethook(timeout, "", maxevents)
local ok, ret = pcall(f, ...)
debug.sethook() -- Clear hook
@@ -502,7 +538,7 @@ end


local function load_memory(meta)
return minetest.deserialize(meta:get_string("lc_memory")) or {}
return minetest.deserialize(meta:get_string("lc_memory"), true) or {}
end


@@ -519,44 +555,61 @@ local function save_memory(pos, meta, mem)
end
end


local function run(pos, event)
-- Returns success (boolean), errmsg (string)
-- run (as opposed to run_inner) is responsible for setting up meta according to this output
local function run_inner(pos, code, event)
local meta = minetest.get_meta(pos)
if overheat(pos) then return end
if ignore_event(event, meta) then return end
-- Note: These return success, presumably to avoid changing LC ID.
if overheat(pos) then return true, "" end
if ignore_event(event, meta) then return true, "" end

-- Load code & mem from meta
local mem = load_memory(meta)
local code = meta:get_string("code")

-- 'Last warning' label.
local warning = ""
local function send_warning(str)
warning = "Warning: " .. str
end

-- Create environment
local env = create_environment(pos, mem, event)
local itbl = {}
local env = create_environment(pos, mem, event, itbl, send_warning)

-- Create the sandbox and execute code
local f, msg = create_sandbox(code, env)
if not f then return msg end
if not f then return false, msg end
-- Start string true sandboxing
local onetruestring = getmetatable("")
-- If a string sandbox is already up yet inconsistent, something is very wrong
assert(onetruestring.__index == string)
onetruestring.__index = env.string
local success, msg = pcall(f)
if not success then return msg end
onetruestring.__index = string
-- End string true sandboxing
if not success then return false, msg end
if type(env.port) ~= "table" then
return "Ports set are invalid."
return false, "Ports set are invalid."
end

-- Actually set the ports
set_port_states(pos, env.port)

-- Save memory. This may burn the luacontroller if a memory overflow occurs.
save_memory(pos, meta, env.mem)
end

mesecon.queue:add_function("lc_interrupt", function (pos, luac_id, iid)
-- There is no luacontroller anymore / it has been reprogrammed / replaced / burnt
if (minetest.get_meta(pos):get_int("luac_id") ~= luac_id) then return end
if (minetest.registered_nodes[minetest.get_node(pos).name].is_burnt) then return end
run(pos, {type="interrupt", iid = iid})
end)
-- Execute deferred tasks
for _, v in ipairs(itbl) do
local failure = v()
if failure then
return false, failure
end
end
return true, warning
end

local function reset_meta(pos, code, errmsg)
local meta = minetest.get_meta(pos)
local function reset_formspec(meta, code, errmsg)
meta:set_string("code", code)
code = minetest.formspec_escape(code or "")
errmsg = minetest.formspec_escape(tostring(errmsg or ""))
@@ -566,13 +619,50 @@ local function reset_meta(pos, code, errmsg)
"image_button[4.75,8.75;2.5,1;jeija_luac_runbutton.png;program;]"..
"image_button_exit[11.72,-0.25;0.425,0.4;jeija_close_window.png;exit;]"..
"label[0.1,9;"..errmsg.."]")
end

local function reset_meta(pos, code, errmsg)
local meta = minetest.get_meta(pos)
reset_formspec(meta, code, errmsg)
meta:set_int("luac_id", math.random(1, 65535))
end

-- Wraps run_inner with LC-reset-on-error
local function run(pos, event)
local meta = minetest.get_meta(pos)
local code = meta:get_string("code")
local ok, errmsg = run_inner(pos, code, event)
if not ok then
reset_meta(pos, code, errmsg)
else
reset_formspec(meta, code, errmsg)
end
return ok, errmsg
end

local function reset(pos)
set_port_states(pos, {a=false, b=false, c=false, d=false})
end

-----------------------
-- A.Queue callbacks --
-----------------------

mesecon.queue:add_function("lc_interrupt", function (pos, luac_id, iid)
-- There is no luacontroller anymore / it has been reprogrammed / replaced / burnt
if (minetest.get_meta(pos):get_int("luac_id") ~= luac_id) then return end
if (minetest.registered_nodes[minetest.get_node(pos).name].is_burnt) then return end
run(pos, {type="interrupt", iid = iid})
end)

mesecon.queue:add_function("lc_digiline_relay", function (pos, channel, luac_id, msg)
if not digiline then return end
-- This check is only really necessary because in case of server crash, old actions can be thrown into the future
if (minetest.get_meta(pos):get_int("luac_id") ~= luac_id) then return end
if (minetest.registered_nodes[minetest.get_node(pos).name].is_burnt) then return end
-- The actual work
digiline:receptor_send(pos, digiline.rules.default, channel, msg)
end)

-----------------------
-- Node Registration --
@@ -613,12 +703,7 @@ end
local function set_program(pos, code)
reset(pos)
reset_meta(pos, code)
local err = run(pos, {type="program"})
if err then
reset_meta(pos, code, err)
return false, err
end
return true
return run(pos, {type="program"})
end

local function on_receive_fields(pos, form_name, fields, sender)

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