From: Eric Biggers <ebiggers@xxxxxxxxxx>
_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@xxxxxxxxxxxxxxx
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
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
