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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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