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Commit 0b553acf authored by Jason A. Donenfeld's avatar Jason A. Donenfeld Committed by Greg Kroah-Hartman
Browse files

random: introduce drain_entropy() helper to declutter crng_reseed() 



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: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: default avatarEric Biggers <ebiggers@google.com>
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 5401246c

drivers/char/random.c

+23 −13
Original line number Diff line number Diff line
@@ -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 *cp, size_t len) 
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)

	/* Only reseed if we can, to prevent brute forcing a small amount of new bits. */

	if (!drain_entropy(key, sizeof(key)))

		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);



	/*

	 * We copy the new key into the base_crng, overwriting the old one,
@@ -950,6 +941,25 @@ 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))