How To/Restrict lua script access to a base dir (base dir restriction)

Put the following source at the beginning of your source to enable the base dir restriction in lua.

You need LuaFileSystem installed.

do
	local oldOpen = io.open
	io.open = function (filename, mode)
		require "lfs"
		local currentdir=lfs.currentdir()
		-- On Windows, wrong drive
		if (string.sub(filename,2,2)==':' and string.sub(filename,1,1)~=string.sub(currentdir,1,1)) then
			return nil, "access denied"
		end
		
		-- If this is no windows drive location and no *nix root -> append it
		if (string.sub(filename,2,2)~=':' and string.sub(filename,1,1)~='/') then
			filename=currentdir..[[\]]..filename
		end
		local strlenbefore=string.len(filename)+1
		while ( strlenbefore>string.len(filename) ) do
			strlenbefore=string.len(filename)
			-- Clean on windows from the ...
			filename=string.gsub(filename,[[([^%/]+)%\([^%/]+)%\%.%.]],"%1")
			--Clean on linux from the ...
			filename=string.gsub(filename,[[([^%/]-)%/%.%.]],"")
		end
		if (string.sub(filename,1,string.len(currentdir))~=currentdir) then
			return nil, "access denied"
		end 
		return oldOpen(filename, mode)
	end
end