linux-kernel - [PATCH 2/2] random: fix locking for crng_init in crng

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Message-Id: <20220205103458.133386-3-linux@dominikbrodowski.net>
Date:   Sat,  5 Feb 2022 11:34:58 +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 2/2] 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 crng_finalize_init(),
and split out the parts which can be delayed to crng_late_init().

If crng_finalize_init() cannot proceed due to workqueues not yet
being available, it is called again in rand_initialize(). Then, we
do not need to call crng_late_init(): At this time, the boot
process is still so early that there are no other processes to wake
up.

Signed-off-by: Dominik Brodowski <linux@...inikbrodowski.net>
---
 drivers/char/random.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 2df08d05e850..c70a9abbd8cb 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -557,19 +557,24 @@ static void __init crng_initialize_primary(void)
 	primary_crng.init_time = jiffies - CRNG_RESEED_INTERVAL - 1;
 }
 
-static void crng_finalize_init(void)
+static bool crng_finalize_init(void)
 {
 	if (!system_wq) {
 		/* We can't call numa_crng_init until we have workqueues,
 		 * so mark this for processing later. */
 		crng_need_final_init = true;
-		return;
+		return false;
 	}
 
 	invalidate_batched_entropy();
 	numa_crng_init();
 	crng_init = 2;
 	crng_need_final_init = false;
+	return true;
+}
+
+static void crng_late_init(void)
+{
 	process_random_ready_list();
 	wake_up_interruptible(&crng_init_wait);
 	kill_fasync(&fasync, SIGIO, POLL_IN);
@@ -710,6 +715,7 @@ static int crng_slow_load(const u8 *cp, size_t len)
 
 static void crng_reseed(struct crng_state *crng)
 {
+	bool needs_late_init = false;
 	unsigned long flags;
 	int i;
 	union {
@@ -744,9 +750,11 @@ static void crng_reseed(struct crng_state *crng)
 	}
 	memzero_explicit(&buf, sizeof(buf));
 	WRITE_ONCE(crng->init_time, jiffies);
-	spin_unlock_irqrestore(&crng->lock, flags);
 	if (crng == &primary_crng && crng_init < 2)
-		crng_finalize_init();
+		needs_late_init = crng_finalize_init();
+	spin_unlock_irqrestore(&crng->lock, flags);
+	if (needs_late_init)
+		crng_late_init();
 }
 
 static void _extract_crng(struct crng_state *crng, u8 out[CHACHA_BLOCK_SIZE])
@@ -1383,8 +1391,10 @@ static void __init init_std_data(void)
 int __init rand_initialize(void)
 {
 	init_std_data();
-	if (crng_need_final_init)
+	if (crng_need_final_init) {
 		crng_finalize_init();
+		pr_notice("crng init done\n");
+	}
 	crng_initialize_primary();
 	crng_global_init_time = jiffies;
 	if (ratelimit_disable) {
-- 
2.35.1