linux-kernel - Reading large amounts from /dev/urandom broken

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Message-ID: <CANZNk81nyws__swPUoxz912wi5PJ2CBXbiLpJ-Jc4oLcX+J8vw@mail.gmail.com>
Date:	Wed, 23 Jul 2014 16:52:21 +0300
From:	Andrey Utkin <andrey.krieger.utkin@...il.com>
To:	tytso@....edu, hannes@...essinduktion.org
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Reading large amounts from /dev/urandom broken

Dear developers, please check bugzilla ticket
https://bugzilla.kernel.org/show_bug.cgi?id=80981 (not the initial
issue, but starting with comment#3.

Reading from /dev/urandom gives EOF after 33554431 bytes.  I believe
it is introduced by commit 79a8468747c5f95ed3d5ce8376a3e82e0c5857fc,
with the chunk

nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3));

which is described in commit message as "additional paranoia check to
prevent overly large count values to be passed into urandom_read()".

I don't know why people pull such large amounts of data from urandom,
but given today there are two bugreports regarding problems doing
that, i consider that this is practiced.

-- 
Andrey Utkin
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