[Haskell-cafe] Re: ANN: System.FilePath 0.9

[Chris Kuklewicz]

Stephane Bortzmeyer wrote:
> On Mon, Jul 17, 2006 at 03:07:51AM +0100,
>  Neil Mitchell <ndmitchell at gmail.com> wrote 
>  a message of 64 lines which said:
> 
>> How about adding something like "restrictFilePaths :: FilePath -> IO
>> ()" which will restrict the area that can be played with to that
>> beneath the given FilePath?
> 
> If someone does so, be aware that it is *not* trivial to write it
> securely.
> 
> For instance, many lazy (not in the Haskell meaning) programmers
> believe that the path is safe if it does not include .. but it is
> false (hint: ."."/foo/bar is a legal path on Unix).

That is a legal path if your Haskell program invokes (perhaps indirectly) a Unix 
shell.  But if you can inject strings into a shell invocation then it is 
obviously impossible to do anything about limiting it to be weaker than the IO 
monad.

-- 
Chris