From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: George Spelvin <lkml@SDF.ORG>
Cc: David Laight <David.Laight@ACULAB.COM>,
Dan Williams <dan.j.williams@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Qian Cai <cai@lca.pw>, Kees Cook <keescook@chromium.org>,
Michal Hocko <mhocko@suse.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>
Subject: Re: [RFC PATCH v1 00/52] Audit kernel random number use
Date: Sun, 29 Mar 2020 17:42:14 -0400 [thread overview]
Message-ID: <20200329214214.GB768293@mit.edu> (raw)
In-Reply-To: <20200329174122.GD4675@SDF.ORG>
On Sun, Mar 29, 2020 at 05:41:22PM +0000, George Spelvin wrote:
> > Using xor was particularly stupid.
> > The whole generator was then linear and trivially reversable.
> > Just using addition would have made it much stronger.
>
> I considered changing it to addition (actually, add pairs and XOR the
> sums), but that would break its self-test. And once I'd done that,
> there are much better possibilities.
>
> Actually, addition doesn't make it *much* stronger. To start
> with, addition and xor are the same thing at the lsbit, so
> observing 113 lsbits gives you a linear decoding problem.
David,
If anyone is trying to rely on prandom_u32() as being "strong" in any
sense of the word in terms of being reversable by attacker --- they
shouldn't be using prandom_u32(). That's going to be true no matter
*what* algorithm we use.
Better distribution? Sure. Making prandom_u32() faster? Absolutely;
that's its primary Raison d'Etre.
George,
Did you send the full set of patches to a single mailing list? Or can
you make it available on a git tree somewhere? I've y seen this
message plus the ext4 related change, and I can't find the full patch
series anywhere. If you can send the next version such that it's
fully cc'ed to linux-kernel, that would be really helpful.
Thanks!!
- Ted
next prev parent reply other threads:[~2020-03-29 21:42 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-03 9:51 [RFC PATCH v1 46/50] mm/shuffle.c: use get_random_max() George Spelvin
2020-03-28 18:23 ` Dan Williams
2020-03-28 18:28 ` [RFC PATCH v1 00/52] Audit kernel random number use George Spelvin
2020-03-29 12:21 ` David Laight
2020-03-29 17:41 ` George Spelvin
2020-03-29 21:42 ` Theodore Y. Ts'o [this message]
2020-03-30 9:27 ` David Laight
2020-04-01 5:17 ` lib/random32.c security George Spelvin
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