linux-kernel - (Small) bias in generation of random passkeys for pairing

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Date:   Wed, 19 Jun 2019 18:24:56 +0200
From:   Pavel Machek <pavel@....cz>
To:     kernel list <linux-kernel@...r.kernel.org>, security@...nel.org,
        linux-bluetooth@...r.kernel.org, johan.hedberg@...il.com,
        marcel@...tmann.org
Subject: (Small) bias in generation of random passkeys for pairing

Hi!

There's a (small) bias in passkey generation in bluetooth:

                get_random_bytes(&passkey, sizeof(passkey));
 		passkey %= 1000000;
		put_unaligned_le32(passkey, smp->tk);

(there are at least two places doing this).

All passkeys are not of same probability, passkey "000000" is more
probable than "999999", but difference is small.

Do we care?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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