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    SubjectRe: [PATCH] random: add blocking facility to urandom
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    On Wed, 2011-09-07 at 16:02 -0400, Steve Grubb wrote:
    > On Wednesday, September 07, 2011 03:27:37 PM 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.
    >
    > The only time this kicks in is when a system is under attack. If you have set this and
    > the system is running as normal, you will never notice it even there. Almost all uses
    > of urandom grab 4 bytes and seed openssl or libgcrypt or nss. It then uses those
    > libraries. There are the odd cases where something uses urandom to generate a key or
    > otherwise grab a chunk of bytes, but these are still small reads in the scheme of
    > things. Can you think of any legitimate use of urandom that grabs 100K or 1M from
    > urandom? Even those numbers still won't hit the sysctl on a normally function system.
    >

    As far as I remember, several wipe utilities are using /dev/urandom to
    overwrite disks (possibly several times).

    Something similar probably happens for getting junk on disks before
    creating an encrypted filesystem on top of them.

    --

    Sasha.



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