linux-kernel - Re: random: /dev/random often returns short reads

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Message-ID: <20170117171539.dadciiz2kfjtqrfk@thunk.org>
Date:   Tue, 17 Jan 2017 12:15:39 -0500
From:   Theodore Ts'o <tytso@....edu>
To:     Denys Vlasenko <vda.linux@...glemail.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: random: /dev/random often returns short reads

On Tue, Jan 17, 2017 at 09:21:31AM +0100, Denys Vlasenko wrote:
> > If someone wants to send me a patch, I'll happily take a look at it,
> 
> Will something along these lines be accepted?

The problem is that this won't work.  In the cases that we're talking
about, the entropy counter in the secondary pool is not zero, but
close to zero, we'll still have short reads.  And that's going to
happen a fair amount of the time.

Perhaps the best *hacky* solution would be to say, ok if the entropy
count is less than some threshold, don't use the correct entropy
calculation, but rather assume that all of the new bits won't land on
top of existing entropy bits.  It undoes some of Peter's very careful
and accurate calculations (so I'd like Peter's thoughts), but in
reality, very few people use /dev/random these days except for GPG and
people hacking OpenSSL for FIPS certification so they can feed at at
the US Federal Government's trough.

I'm not sure I care *that* much, but then I think FIPS certification
is a complete waste of Taxpayer dollars, so it's not something I care
a whole lot about fixing, either.  :-)

						- Ted