[Patches] Patch to make tempfile return random filenames

[Guido van Rossum]

> 1. the path.exist part does not solve the problem. It causes a racing
> condition that is not very hard to get around, by having a program
> creating and deleting the file at maximum speed. It will have a 50%
> chance of breaking your program.

I'm not sure where you get the 50% chance from.  It would seem to
depend on how often the kernel switches between processes.  I'd like
to see you create a test to decide how big the probability *really*
is.

> 2. O_EXCL does not always work. E.g. it does not work over NFS - there
> are probably other broken implementations too.

But who puts their /tmp directory on NFS?

> 3. Even if mktemp.TemporaryFile had been sufficient, providing mktemp in
> this dangerous way is not good. Many are likely to use it either not
> thinking about the problem at all, or assuming it's solved in the
> module.

I have always assumed this is only really an issue with set-uid
programs.  If I write a simple script, why would it be vulnerable?
(There's still the PID in the name too.)

> 4. The problems you describe can easily be overcome. I removed the
> counter and the file-exist check because I figgured they were no longer
> needed. I was wrong. Either a larger number should be used and/or
> counter and or file-exist check. Personally I would want the random part
> to bee large enough not have to worry about collisions either by chance,
> after a fork, or by deliberate attack.

do you know enough about random number generators to know how to
generate really truly random numbers?  randrange(sys.maxint) doesn't
really help...

> Do you want a new patch that adresses theese problems better?

I'm still not convinced that this is really a vulnerability, and that
you aren't simply translating a known C vulnerability to Python
without knowing that the same vulnerability exists there.  I'm also
not convinced that you are enough of a security expert that I should
trust your recommendations.  What are your credentials?

--Guido van Rossum (home page: http://www.python.org/~guido/)