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    SubjectRe: [PATCH] random: add blocking facility to urandom
    Ted Ts'o wrote:
    > On Wed, Sep 07, 2011 at 02:26:35PM -0400, Jarod Wilson wrote:
    >> We're looking for a generic solution here that doesn't require
    >> re-educating every single piece of userspace. And anything done in
    >> userspace is going to be full of possible holes -- there needs to be
    >> something in place that actually *enforces* the policy, and
    >> centralized accounting/tracking, lest you wind up with multiple
    >> processes racing to grab the entropy.
    > Yeah, but there are userspace programs that depend on urandom not
    > blocking... so your proposed change would break them.

    But only if you've set the sysctl to a non-zero value, and even then,
    only if someone is actively draining entropy from /dev/random.
    Otherwise, in practice, it behaves the same as always. Granted, I
    haven't tested with all possible userspace to see how it might fall
    down, but suggestions for progs to try would be welcomed.

    But again, I want to stress that out of the box, there's absolutely no
    change to the way urandom behaves, no blocking, this *only* kicks in if
    you twiddle the sysctl because you have some sort of security
    requirement that mandates it.

    Jarod Wilson

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