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SubjectRe: RFC/PATCH: Random pid generation

On 13 Jan 2000, Peter Samuelson wrote:

> [Alan Cox]
> > > Random pids just slow the process down. Its an argument for writing
> > > decent code.
>
> Chris Evans <chris@ferret.lmh.ox.ac.uk> writes:
> > Random pids in a 32 bit space would take an average of ~1 random
> > number generation to calculate per fork. That can't be too slow can
> > it?
>
> By "slow the process down" Alan was referring to the process of
> exploiting a /tmp race. You didn't eliminate the race, in other words,
> you just obfuscated it.

Ah, thank you.

Obfuscation is not to be discounted, however. Imagine a 64 bit pid_t. Now,
the race would, on average, take longer than the remaining lifetime of the
universe to exploit.

A 32 bit pid_t is more interesting (and plausible). Assuming a _signed_
pid_t, a rather high rate of 1000 exploit attempts/second, and a 100% race
success when the right pid is guessed

.. you take on average 11.5 days to exploit. At 100% CPU. That's not going
to go unnoticed.

Cheers
Chris


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