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mesecons
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Disable JIT optimization for user code and allow string.find in plain mode 

Disabling LuaJIT for user code enables normal working of debug.sethook() even for loops. The drawback is that that code will run more slowly.

The fourth parameter of string.find indicates whether the second parameter should be interpreted literally (true) or as a pattern (false). Allowing patterns enables DoS attacks, but it's possible to
allow literal matching with little effort, by disallowing the function only if the fourth parameter (plain mode) is not `true`.
This commit is contained in:
Pedro Gimeno 2016-03-14 14:29:34 +01:00 committed by Jeija
parent 72e513ecbd
commit b487783c23
1 changed files with 21 additions and 35 deletions
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56
mesecons_luacontroller/init.lua
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@ -216,6 +216,17 @@ local function safe_string_rep(str, n)
return string.rep(str, n)
end
-- string.find with a pattern can be used to DoS the server.
-- Therefore, limit string.find to patternless matching.
local function safe_string_find(...)
if (select(4, ...)) ~= true then
debug.sethook() -- Clear hook
error("string.find: 'plain' (fourth parameter) must always be true in a LuaController")
end
return string.find(...)
end
local function remove_functions(x)
local tp = type(x)
if tp == "table" then
@ -292,6 +303,7 @@ local function create_environment(pos, mem, event)
rep = safe_string_rep,
reverse = string.reverse,
sub = string.sub,
find = safe_string_find,
},
math = {
abs = math.abs,
@ -354,22 +366,6 @@ local function timeout()
end
local function code_prohibited(code)
-- LuaJIT doesn't increment the instruction counter when running
-- loops, so we have to sanitize inputs if we're using LuaJIT.
if not rawget(_G, "jit") then
return false
end
local prohibited = {"while", "for", "repeat", "until", "goto"}
code = " "..code.." "
for _, p in ipairs(prohibited) do
if string.find(code, "[^%w_]"..p.."[^%w_]") then
return "Prohibited command: "..p
end
end
end
local function create_sandbox(code, env)
if code:byte(1) == 27 then
return nil, "Binary code prohibited."
@ -378,24 +374,17 @@ local function create_sandbox(code, env)
if not f then return nil, msg end
setfenv(f, env)
-- Turn off JIT optimization for user code so that count
-- events are generated when adding debug hooks
if rawget(_G, "jit") then
jit.off(f, true)
end
return function(...)
-- Normal Lua: Use instruction counter to stop execution
-- after luacontroller_maxevents.
-- LuaJIT: Count function calls instead of instructions, allows usage
-- of function keyword. However, LuaJIT still doesn't trigger
-- lines events when using infinite loops.
-- Use instruction counter to stop execution
-- after luacontroller_maxevents
local maxevents = mesecon.setting("luacontroller_maxevents", 10000)
if not rawget(_G, "jit") then
debug.sethook(timeout, "", maxevents)
else
local events = 0
debug.sethook(function ()
events = events + 1
if events > maxevents then
timeout()
end
end, "c")
end
debug.sethook(timeout, "", maxevents)
local ok, ret = pcall(f, ...)
debug.sethook() -- Clear hook
if not ok then error(ret, 0) end
@ -432,9 +421,6 @@ local function run(pos, event)
local mem = load_memory(meta)
local code = meta:get_string("code")
local err = code_prohibited(code)
if err then return err end
-- Create environment
local env = create_environment(pos, mem, event)