linux-kernel - [PATCH] random: fix locking for crng_init in crng

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Message-ID: <YgQOgqWr0nwqZCh6@owl.dominikbrodowski.net>
Date:   Wed, 9 Feb 2022 19:57:06 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A . Donenfeld" <Jason@...c4.com>, tytso@....edu
Cc:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: [PATCH] random: fix locking for crng_init in crng_reseed()

crng_init is protected by primary_crng->lock. Therefore, we need
to hold this lock when increasing crng_init to 2. As we shouldn't
hold this lock for too long, only hold it for those parts which
require protection.

Signed-off-by: Dominik Brodowski <linux@...inikbrodowski.net>
---
 drivers/char/random.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index cc4d9d414df2..aee56032ebb4 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -497,6 +497,7 @@ static void crng_slow_load(const void *cp, unsigned int len)

 static void crng_reseed(void)
 {
+	bool complete_init = false;
 	unsigned long flags;
 	int entropy_count;
 	unsigned long next_gen;
@@ -526,12 +527,14 @@ static void crng_reseed(void)
 		++next_gen;
 	WRITE_ONCE(base_crng.generation, next_gen);
 	base_crng.birth = jiffies;
-	spin_unlock_irqrestore(&base_crng.lock, flags);
-	memzero_explicit(key, sizeof(key));
-
 	if (crng_init < 2) {
 		invalidate_batched_entropy();
 		crng_init = 2;
+		complete_init = true;
+	}
+	spin_unlock_irqrestore(&base_crng.lock, flags);
+	memzero_explicit(key, sizeof(key));
+	if (complete_init) {
 		process_random_ready_list();
 		wake_up_interruptible(&crng_init_wait);
 		kill_fasync(&fasync, SIGIO, POLL_IN);