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authorEric Biggers <ebiggers@google.com>2021-12-21 01:41:57 +0300
committerJason A. Donenfeld <Jason@zx2c4.com>2022-01-07 02:25:25 +0300
commit009ba8568be497c640cab7571f7bfd18345d7b24 (patch)
tree1adc5b2e17ac2cbce18f6a1cd2a42078225769bb /drivers/char
parent5d73d1e320c3fd94ea15ba5f79301da9a8bcc7de (diff)
downloadlinux-009ba8568be497c640cab7571f7bfd18345d7b24.tar.xz
random: fix data race on crng init time
_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> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Diffstat (limited to 'drivers/char')
-rw-r--r--drivers/char/random.c17
1 files changed, 10 insertions, 7 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 5e3046606640..13c968b950c5 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -991,7 +991,7 @@ 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();
@@ -1017,12 +1017,15 @@ 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;
@@ -1962,7 +1965,7 @@ 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;