From: "Jason A. Donenfeld" Jason@zx2c4.com
commit 246c03dd899164d0186b6d685d6387f228c28d93 upstream.
In preparation for separating responsibilities, break out the entropy count management part of crng_reseed() into its own function.
No functional changes.
Cc: Theodore Ts'o tytso@mit.edu Reviewed-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 | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-)
--- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -261,6 +261,7 @@ 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);
@@ -506,23 +507,13 @@ static void crng_slow_load(const void *c static void crng_reseed(void) { unsigned long flags; - int entropy_count; unsigned long next_gen; u8 key[CHACHA20_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, @@ -950,6 +941,25 @@ static void extract_entropy(void *buf, s 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))