Fake Root?

local Root = "path/to/sandbox/" -- Need trailing slash for it to work

local function SanitisePath(Path)
  --Get rid of ../ es
  local Path = fs.combine('/', Path):gsub('%.%./?', '')
  local Path = fs.combine(Root, Path)

  --If it doesn''t start with root then:
  if string.sub(Path, 1, string.len(Root)) ~= Root then
    error("Bluuuuuuuuuurgh")
  end

  return Path
end

local Environment = {
  ['fs'] = {
    ['open'] = function(Path, Type)
      return fs.open(SanitisePath(Path), Type)
    end
    --And so on for all other functions
  }

  --Might want to include shell and os.run as they also use these.
}
--Might want to do this so they can access everything
setmetatable(Environment, { __index = getfenv() } )

--Fail safe
Environment._G = Environment

local Func = loadfile("ToSandbox.lua")
setfenv(Func, Environment)
Func()

local ParentEnv = getfenv(fs.open)
--I can now open files in the root directory!
local Handle = ParentEnv.fs.open("startup", "w")

SquidDev, on 13 July 2014 - 03:41 PM said:

Hmmm. This code does the sandboxing bit:

Spoiler

 local Root = "path/to/sandbox/" -- Need trailing slash for it to work local function SanitisePath(Path) --Get rid of ../ es local Path = fs.combine('/', Path):gsub('%.%./?', '') local Path = fs.combine(Root, Path) --If it doesn''t start with root then: if string.sub(Path, 1, string.len(Root)) ~= Root then error("Bluuuuuuuuuurgh") end return Path end local Environment = { ['fs'] = { ['open'] = function(Path, Type) return fs.open(SanitisePath(Path), Type) end --And so on for all other functions } --Might want to include shell and os.run as they also use these. } --Might want to do this so they can access everything setmetatable(Environment, { __index = getfenv() } ) --Fail safe Environment._G = Environment local Func = loadfile("ToSandbox.lua") setfenv(Func, Environment) Func() 

However getfenv does always end up ruining your sandbox:

 local ParentEnv = getfenv(fs.open) --I can now open files in the root directory! local Handle = ParentEnv.fs.open("startup", "w") 

I've never been able to get beyond this step (Ok, I haven't tried much). It is very hard to prevent getfenv being able to at least get a hint of the parent environment and so be able to access the original file system (or whatever).