[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20200921075857.4424-6-nstange@suse.de>
Date: Mon, 21 Sep 2020 09:58:21 +0200
From: Nicolai Stange <nstange@...e.de>
To: "Theodore Y. Ts'o" <tytso@....edu>
Cc: linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
"Alexander E. Patrakov" <patrakov@...il.com>,
"Ahmed S. Darwish" <darwish.07@...il.com>,
Willy Tarreau <w@....eu>,
Matthew Garrett <mjg59@...f.ucam.org>,
Vito Caputo <vcaputo@...garu.com>,
Andreas Dilger <adilger.kernel@...ger.ca>,
Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
William Jon McCann <mccann@....edu>,
zhangjs <zachary@...shancloud.com>,
Andy Lutomirski <luto@...nel.org>,
Florian Weimer <fweimer@...hat.com>,
Lennart Poettering <mzxreary@...inter.de>,
Peter Matthias <matthias.peter@....bund.de>,
Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
Roman Drahtmueller <draht@...altsekun.de>,
Neil Horman <nhorman@...hat.com>,
Randy Dunlap <rdunlap@...radead.org>,
Julia Lawall <julia.lawall@...ia.fr>,
Dan Carpenter <dan.carpenter@...cle.com>,
Andy Lavr <andy.lavr@...il.com>,
Eric Biggers <ebiggers@...nel.org>,
"Jason A. Donenfeld" <Jason@...c4.com>,
Stephan Müller <smueller@...onox.de>,
Torsten Duwe <duwe@...e.de>, Petr Tesarik <ptesarik@...e.cz>,
Nicolai Stange <nstange@...e.de>
Subject: [RFC PATCH 05/41] random: don't reset entropy to zero on overflow
credit_entropy_bits() adds one or more positive values to the signed
entropy_count and checks if the result is negative afterwards. Note that
because the initial value of entropy_count is positive, a negative result
can happen only on overflow.
However, if the final entropy_count is found to have overflown, a WARN()
is emitted and the entropy_store's entropy count reset to zero. Even
though this case should never happen, it is better to retain previously
available entropy as this will facilitate a future change factoring out
that approximation of the exponential.
Make credit_entropy_bits() tp reset entropy_count to the original value
rather than zero on overflow.
Signed-off-by: Nicolai Stange <nstange@...e.de>
---
drivers/char/random.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 35e381be20fe..6adac462aa0d 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -706,7 +706,7 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
if (WARN_ON(entropy_count < 0)) {
pr_warn("negative entropy/overflow: pool %s count %d\n",
r->name, entropy_count);
- entropy_count = 0;
+ entropy_count = orig;
} else if (entropy_count > pool_size)
entropy_count = pool_size;
if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
--
2.26.2
Powered by blists - more mailing lists