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From: "Theodore Ts'o" <tytso@mit.edu>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: linux-kernel@vger.kernel.org,
	Hannes Frederic Sowa <hannes@stressinduktion.org>,
	Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH 1/2] random: use chacha20 for get_random_int/long
Date: Tue, 17 Jan 2017 22:49:07 -0500	[thread overview]
Message-ID: <20170118034907.spozwf4erlvx5s4x@thunk.org> (raw)
In-Reply-To: <20170106183202.5035-1-Jason@zx2c4.com>

Hi Jason,

I've been taking a look at your patch, and i think it's... problematic.

You're using a union for the entropy_u64 and entropy_u32 arrays, and
the position field is used to indexed into those two arrays.

So if the first caller calls get_random_u64 with position=0, it will
get the first 64 bits out of the batched entropy, and increment the
position to 1.  If the second caller calls get_random_u32 with
position=1... it will get the second of the 32-bit chunks in the
batched entropy array --- which will include the 64 bits returned to
the first caller.

That's not very random.   :-(

						- Ted

  parent reply	other threads:[~2017-01-18  4:50 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-06 18:32 Jason A. Donenfeld
2017-01-06 18:32 ` [PATCH 2/2] random: convert get_random_int/long into get_random_u32/u64 Jason A. Donenfeld
2017-01-18  3:49 ` Theodore Ts'o [this message]
2017-01-20  5:27   ` [PATCH 1/2] random: use chacha20 for get_random_int/long Jason A. Donenfeld
2017-01-20 14:28     ` Theodore Ts'o
2017-01-20 15:38       ` Jason A. Donenfeld
2017-01-21  0:10         ` Theodore Ts'o
2017-01-21  0:13           ` Jason A. Donenfeld
2017-01-20 15:47       ` Jason A. Donenfeld
2017-01-21  0:15         ` Theodore Ts'o
2017-01-21  0:16           ` Jason A. Donenfeld
2017-01-21  6:24             ` Theodore Ts'o
2017-01-21 14:08               ` Jason A. Donenfeld
2017-01-22 11:24                 ` Greg Kroah-Hartman
2017-01-22 12:21                   ` Jason A. Donenfeld
2017-01-22 15:20                     ` Greg Kroah-Hartman
2017-01-22 15:34                       ` Jason A. Donenfeld
2017-01-22 15:34                         ` [PATCH 2/2] random: convert get_random_int/long into get_random_u32/u64 Jason A. Donenfeld
2017-01-22 22:28                       ` [PATCH 1/2] random: use chacha20 for get_random_int/long Theodore Ts'o
2017-01-22 22:49                         ` Jason A. Donenfeld
2017-01-23  0:33                           ` Theodore Ts'o
2017-01-23  8:12                         ` Greg Kroah-Hartman
  -- strict thread matches above, loose matches on Subject: below --
2016-12-22 18:07 Jason A. Donenfeld

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