From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
commit fed7ef061686cc813b1f3d8d0edc6c35b4d3537b upstream.
Since all changes of crng_init now go through credit_init_bits(), we can
fix a long standing race in which two concurrent callers of
credit_init_bits() have the new bit count >= some threshold, but are
doing so with crng_init as a lower threshold, checked outside of a lock,
resulting in crng_reseed() or similar being called twice.
In order to fix this, we can use the original cmpxchg value of the bit
count, and only change crng_init when the bit count transitions from
below a threshold to meeting the threshold.
Reviewed-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/random.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -823,7 +823,7 @@ static void extract_entropy(void *buf, s
static void credit_init_bits(size_t nbits)
{
- unsigned int init_bits, orig, add;
+ unsigned int new, orig, add;
unsigned long flags;
if (crng_ready() || !nbits)
@@ -833,12 +833,12 @@ static void credit_init_bits(size_t nbit
do {
orig = READ_ONCE(input_pool.init_bits);
- init_bits = min_t(unsigned int, POOL_BITS, orig + add);
- } while (cmpxchg(&input_pool.init_bits, orig, init_bits) != orig);
+ new = min_t(unsigned int, POOL_BITS, orig + add);
+ } while (cmpxchg(&input_pool.init_bits, orig, new) != orig);
- if (!crng_ready() && init_bits >= POOL_READY_BITS)
+ if (orig < POOL_READY_BITS && new >= POOL_READY_BITS)
crng_reseed();
- else if (unlikely(crng_init == CRNG_EMPTY && init_bits >= POOL_EARLY_BITS)) {
+ else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) {
spin_lock_irqsave(&base_crng.lock, flags);
if (crng_init == CRNG_EMPTY) {
extract_entropy(base_crng.key, sizeof(base_crng.key));
