linux-kernel - [PATCH 5.15 120/145] random: do not use batches when !crng

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Message-Id: <20220527084905.195699040@linuxfoundation.org>
Date:   Fri, 27 May 2022 10:50:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Theodore Tso <tytso@....edu>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH 5.15 120/145] random: do not use batches when !crng_ready()

From: "Jason A. Donenfeld" <Jason@...c4.com>

commit cbe89e5a375a51bbb952929b93fa973416fea74e upstream.

It's too hard to keep the batches synchronized, and pointless anyway,
since in !crng_ready(), we're updating the base_crng key really often,
where batching only hurts. So instead, if the crng isn't ready, just
call into get_random_bytes(). At this stage nothing is performance
critical anyhow.

Cc: Theodore Ts'o <tytso@....edu>
Reviewed-by: Dominik Brodowski <linux@...inikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/char/random.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -467,10 +467,8 @@ static void crng_pre_init_inject(const v
 
 	if (account) {
 		crng_init_cnt += min_t(size_t, len, CRNG_INIT_CNT_THRESH - crng_init_cnt);
-		if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
-			++base_crng.generation;
+		if (crng_init_cnt >= CRNG_INIT_CNT_THRESH)
 			crng_init = 1;
-		}
 	}
 
 	spin_unlock_irqrestore(&base_crng.lock, flags);
@@ -626,6 +624,11 @@ u64 get_random_u64(void)
 
 	warn_unseeded_randomness(&previous);
 
+	if  (!crng_ready()) {
+		_get_random_bytes(&ret, sizeof(ret));
+		return ret;
+	}
+
 	local_lock_irqsave(&batched_entropy_u64.lock, flags);
 	batch = raw_cpu_ptr(&batched_entropy_u64);
 
@@ -660,6 +663,11 @@ u32 get_random_u32(void)
 
 	warn_unseeded_randomness(&previous);
 
+	if  (!crng_ready()) {
+		_get_random_bytes(&ret, sizeof(ret));
+		return ret;
+	}
+
 	local_lock_irqsave(&batched_entropy_u32.lock, flags);
 	batch = raw_cpu_ptr(&batched_entropy_u32);