linux-kernel - [PATCH 1/2] random: fix locking in crng_fast

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Date:   Sat,  5 Feb 2022 11:34:57 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A . Donenfeld" <Jason@...c4.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Cc:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: [PATCH 1/2] random: fix locking in crng_fast_load()

crng_init is protected by primary_crng->lock, so keep holding that lock
when incrementing crng_init from 0 to 1 in crng_fast_load(). The call to
pr_notice() can wait until the lock is released; this code path cannot
be reached twice, as crng_fast_load() aborts early if crng_init > 0.

Signed-off-by: Dominik Brodowski <linux@...inikbrodowski.net>
---
 drivers/char/random.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 5d7d6e01bbc4..2df08d05e850 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -653,12 +653,13 @@ static size_t crng_fast_load(const u8 *cp, size_t len)
 		p[crng_init_cnt % CHACHA_KEY_SIZE] ^= *cp;
 		cp++; crng_init_cnt++; len--; ret++;
 	}
-	spin_unlock_irqrestore(&primary_crng.lock, flags);
 	if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
 		invalidate_batched_entropy();
 		crng_init = 1;
-		pr_notice("fast init done\n");
 	}
+	spin_unlock_irqrestore(&primary_crng.lock, flags);
+	if (crng_init == 1)
+		pr_notice("fast init done\n");
 	return ret;
 }
 
-- 
2.35.1