[PATCH 4.9 117/264] random: fix locking in crng_fast_load()

Greg Kroah-Hartman
2022-06-23T16:55:03Z

From: Dominik Brodowski <linux@dominikbrodowski.net>

commit 7c2fe2b32bf76441ff5b7a425b384e5f75aa530a upstream.

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@dominikbrodowski.net>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -647,12 +647,13 @@ static size_t crng_fast_load(const u8 *c
p[crng_init_cnt % CHACHA20_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;
}