diff options
Diffstat (limited to 'drivers/char/random.c')
| -rw-r--r-- | drivers/char/random.c | 36 |
1 files changed, 23 insertions, 13 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index e7571de3d91a..d9a31ac10daf 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -260,6 +260,7 @@ static struct { }; static void extract_entropy(void *buf, size_t nbytes); +static bool drain_entropy(void *buf, size_t nbytes); static void crng_reseed(void); @@ -456,23 +457,13 @@ static void crng_slow_load(const void *cp, size_t len) static void crng_reseed(void) { unsigned long flags; - int entropy_count; unsigned long next_gen; u8 key[CHACHA_KEY_SIZE]; bool finalize_init = false; - /* - * First we make sure we have POOL_MIN_BITS of entropy in the pool, - * and then we drain all of it. Only then can we extract a new key. - */ - do { - entropy_count = READ_ONCE(input_pool.entropy_count); - if (entropy_count < POOL_MIN_BITS) - return; - } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); - extract_entropy(key, sizeof(key)); - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); + /* Only reseed if we can, to prevent brute forcing a small amount of new bits. */ + if (!drain_entropy(key, sizeof(key))) + return; /* * We copy the new key into the base_crng, overwriting the old one, @@ -900,6 +891,25 @@ static void extract_entropy(void *buf, size_t nbytes) memzero_explicit(&block, sizeof(block)); } +/* + * First we make sure we have POOL_MIN_BITS of entropy in the pool, and then we + * set the entropy count to zero (but don't actually touch any data). Only then + * can we extract a new key with extract_entropy(). + */ +static bool drain_entropy(void *buf, size_t nbytes) +{ + unsigned int entropy_count; + do { + entropy_count = READ_ONCE(input_pool.entropy_count); + if (entropy_count < POOL_MIN_BITS) + return false; + } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); + extract_entropy(buf, nbytes); + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + return true; +} + #define warn_unseeded_randomness(previous) \ _warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous)) |