linux-kernel - [PATCH] random: throttle hwrng writes if no entropy is credited

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Message-Id: <20220920141438.2782446-1-Jason@zx2c4.com>
Date:   Tue, 20 Sep 2022 16:14:38 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: [PATCH] random: throttle hwrng writes if no entropy is credited

This value is currently never set to zero, because the hwrng thread only
runs if it's going to be non-zero. This is an oversight, however, that
Dominik is working on fixing. In preparation for this, and so that
there's less coordination required between my tree and Herbert's, make
this currently useless, but not harmful, change here now, in hopes that
Dominik can make the corresponding change in the hwrng core later.

Cc: Dominik Brodowski <linux@...inikbrodowski.net>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 drivers/char/random.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 16e0c5f6cf2f..520a385c7dab 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -865,9 +865,9 @@ void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy)
 
 	/*
 	 * Throttle writing to once every reseed interval, unless we're not yet
-	 * initialized.
+	 * initialized or no entropy is credited.
 	 */
-	if (!kthread_should_stop() && crng_ready())
+	if (!kthread_should_stop() && (crng_ready() || !entropy))
 		schedule_timeout_interruptible(crng_reseed_interval());
 }
 EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
-- 
2.37.3