linux-kernel - hid-u2fzero.c - hw_random quality set to 1?

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Message-ID: <Ye8W6bOh85JILMrp@owl.dominikbrodowski.net>
Date:   Mon, 24 Jan 2022 22:15:21 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     andrew.shadura@...labora.co.uk
Cc:     jikos@...nel.org, benjamin.tissoires@...hat.com,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, herbert@...dor.apana.org.au
Subject: hid-u2fzero.c - hw_random quality set to 1?

Hi,

is there any specific rationale why the quality of the hid-u2fzero.c hw
rng is set to 1, meaning that only 1 bit of entrop is added per 1024 bits
of input (see drivers/char/hw_random/core.c)? That actually means that
currently no entropy is credited at all, as this driver will return not
more than 64 bytes (= rc), and then

	rc * current_quality * 8 >> 10

evaluates to 0. While this is addressed by a patch I just submitted,[*]
I'd like to know whether this low quality setting is correct.

Thanks,
	Dominik

[*] https://lore.kernel.org/linux-crypto/20220124202951.28579-6-linux@dominikbrodowski.net/