Re: /proc/sys/kernel/pid_max issues

From: William Lee Irwin III (wli_at_holomorphy.com)
Date: 09/13/04

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    Date:	Mon, 13 Sep 2004 07:27:52 -0700
To: Albert Cahalan <albert@users.sf.net>

    On Mon, 2004-09-13 at 03:42, William Lee Irwin III wrote:
    >> The resource tracking and locking implications of this are disturbing.
    >> Would fully pseudorandom allocation be acceptable?

    On Mon, Sep 13, 2004 at 10:11:29AM -0400, Albert Cahalan wrote:
    > There's no point.
    > LRU reduces accidents that don't involve an attacker.
    > Strong crypto random can make some attacks a bit harder.
    > OpenBSD does this. It doesn't work well enough to bother
    > with if the implementation is problematic; there's not
    > much you can do while avoiding 64-bit or 128-bit PIDs.
    > Pseudorandom is 100% useless.
    > Per-user PID recycling would make it much harder for
    > an attacker to grab a specific PID. Perhaps the attacker
    > knows that a sched_setscheduler call is coming, and he
    > has a way to make the right process restart or crash.
    > Normally, this lets him get SCHED_FIFO or somesuch.
    > With per-user PID recycling, it would be difficult for
    > him to grab the desired PID.

    I'd suggest pushing for 64-bit+ pid's, then. IIRC most of the work
    there is in userspace (the in-kernel part is trivial).

    -- wli
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