From: Eric Biggers <ebiggers@kernel.org>
To: Theodore Ts'o <tytso@mit.edu>, "Jason A . Donenfeld " <Jason@zx2c4.com>
Cc: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
"Paul E . McKenney" <paulmck@kernel.org>,
stable@vger.kernel.org
Subject: [PATCH v2 2/2] random: fix data race on crng init time
Date: Mon, 20 Dec 2021 16:41:57 -0600 [thread overview]
Message-ID: <20211220224157.111959-3-ebiggers@kernel.org> (raw)
In-Reply-To: <20211220224157.111959-1-ebiggers@kernel.org>
From: Eric Biggers <ebiggers@google.com>
_extract_crng() does plain loads of crng->init_time and
crng_global_init_time, which causes undefined behavior if
crng_reseed() and RNDRESEEDCRNG modify these corrently.
Use READ_ONCE() and WRITE_ONCE() to make the behavior defined.
Don't fix the race on crng->init_time by protecting it with crng->lock,
since it's not a problem for duplicate reseedings to occur. I.e., the
lockless access with READ_ONCE() is fine.
Fixes: d848e5f8e1eb ("random: add new ioctl RNDRESEEDCRNG")
Fixes: e192be9d9a30 ("random: replace non-blocking pool with a Chacha20-based CRNG")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
drivers/char/random.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 1294b4527cdd..1a7bb66d6a58 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -980,7 +980,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
crng->state[i+4] ^= buf.key[i] ^ rv;
}
memzero_explicit(&buf, sizeof(buf));
- crng->init_time = jiffies;
+ WRITE_ONCE(crng->init_time, jiffies);
spin_unlock_irqrestore(&crng->lock, flags);
if (crng == &primary_crng && crng_init < 2) {
invalidate_batched_entropy();
@@ -1006,12 +1006,15 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
static void _extract_crng(struct crng_state *crng,
__u8 out[CHACHA_BLOCK_SIZE])
{
- unsigned long v, flags;
+ unsigned long v, flags, init_time;
- if (crng_ready() &&
- (time_after(crng_global_init_time, crng->init_time) ||
- time_after(jiffies, crng->init_time + CRNG_RESEED_INTERVAL)))
- crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL);
+ if (crng_ready()) {
+ init_time = READ_ONCE(crng->init_time);
+ if (time_after(READ_ONCE(crng_global_init_time), init_time) ||
+ time_after(jiffies, init_time + CRNG_RESEED_INTERVAL))
+ crng_reseed(crng, crng == &primary_crng ?
+ &input_pool : NULL);
+ }
spin_lock_irqsave(&crng->lock, flags);
if (arch_get_random_long(&v))
crng->state[14] ^= v;
@@ -1951,7 +1954,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
if (crng_init < 2)
return -ENODATA;
crng_reseed(&primary_crng, &input_pool);
- crng_global_init_time = jiffies - 1;
+ WRITE_ONCE(crng_global_init_time, jiffies - 1);
return 0;
default:
return -EINVAL;
--
2.34.1
next prev parent reply other threads:[~2021-12-20 22:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-20 22:41 [PATCH v2 0/2] random: fix some data races Eric Biggers
2021-12-20 22:41 ` [PATCH v2 1/2] random: fix data race on crng_node_pool Eric Biggers
2021-12-20 22:41 ` Eric Biggers [this message]
2021-12-20 23:40 ` [PATCH v2 0/2] random: fix some data races Paul E. McKenney
2021-12-21 12:15 ` Jason A. Donenfeld
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