Bug 962035 (CVE-2013-2065)

Aaron Patterson (tenderlove) reports:

Object taint bypassing in DL and Fiddle in Ruby

There is a vulnerability in DL and Fiddle in Ruby where tainted strings can be
used by system calls regardless of the $SAFE level set in Ruby. This
vulnerability has been assigned the CVE identifier CVE-2013-2065.

Versions Affected:  1.9.3-pX, 2.0.0-p0
Not affected:       1.8.X
Fixed Versions:     1.9.3-pX, 2.0.0-pX

Impact 
------
Native functions exposed to Ruby with DL or Fiddle do not check the taint
values set on the objects passed in.  This can result in tainted objects being
accepted as input when a SecurityError exception should be raised.

Impacted DL code will look something like this:

    def my_function(user_input)
      handle    = DL.dlopen(nil)
      sys_cfunc = DL::CFunc.new(handle['system'], DL::TYPE_INT, 'system')
      sys       = DL::Function.new(sys_cfunc, [DL::TYPE_VOIDP])
      sys.call user_input
    end
    
    $SAFE = 1
    my_function "uname -rs".taint

Impacted Fiddle code will look something like this:

    def my_function(user_input)
      handle    = DL.dlopen(nil)
      sys = Fiddle::Function.new(handle['system'],
                              [Fiddle::TYPE_VOIDP], Fiddle::TYPE_INT)
      sys.call user_input
    end
    
    $SAFE = 1
    my_function "uname -rs".taint

All users running an affected release should either upgrade or use one of the
work arounds immediately. 

Note that this *does not* prevent numeric memory offsets from being used as
pointer values.  Numbers cannot be tainted, so code passing a numeric memory
offset cannot be checked.  For example:

    def my_function(input)
      handle    = DL.dlopen(nil)
      sys = Fiddle::Function.new(handle['system'],
                              [Fiddle::TYPE_VOIDP], Fiddle::TYPE_INT)
      sys.call input
    end
    
    $SAFE = 1
    user_input = "uname -rs".taint
    my_function DL::CPtr[user_input].to_i

In this case, the memory location is passed, and taintedness of the object
cannot be determined by DL / Fiddle.  In this case, please check the tainting
of the user input before passing the memory location:

    user_input = "uname -rs".taint
    raise if $SAFE >= 1 && user_input.tainted?
    my_function DL::CPtr[user_input].to_i


Releases 
-------- 
The FIXED releases are available at the normal locations. 

Workarounds 
----------- 
This monkey patch can be used as a workaround:

    class Fiddle::Function
      alias :old_call :call
      def call(*args)
        if $SAFE >= 1 && args.any? { |x| x.tainted? }
          raise SecurityError, "tainted parameter not allowed"
        end
        old_call(*args)
      end
    end

Patches 
------- 
To aid users who aren't able to upgrade immediately we have provided patches
for the two supported release series.  They are in git-am format and consist
of a single changeset.

* 1-9-fiddle-tainting.patch - Patch for 1.9 series 
* 2-0-fiddle-tainting.patch - Patch for 2.0 series