Commit b8ec5ba4 authored by Stephan Mueller's avatar Stephan Mueller Committed by Herbert Xu
Browse files

crypto: drbg - use Jitter RNG to obtain seed 



During initialization, the DRBG now tries to allocate a handle of the
Jitter RNG. If such a Jitter RNG is available during seeding, the DRBG
pulls the required entropy/nonce string from get_random_bytes and
concatenates it with a string of equal size from the Jitter RNG. That
combined string is now the seed for the DRBG.

Written differently, the initial seed of the DRBG is now:

get_random_bytes(entropy/nonce) || jitterentropy (entropy/nonce)

If the Jitter RNG is not available, the DRBG only seeds from
get_random_bytes.

CC: Andreas Steffen <andreas.steffen@strongswan.org>
CC: Theodore Ts'o <tytso@mit.edu>
CC: Sandy Harris <sandyinchina@gmail.com>
Signed-off-by: default avatarStephan Mueller <smueller@chronox.de>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 4c787990

crypto/drbg.c

+45 −7
Original line number Diff line number Diff line
@@ -1062,13 +1062,18 @@ static void drbg_async_seed(struct work_struct *work) 
	LIST_HEAD(seedlist);

	struct drbg_state *drbg = container_of(work, struct drbg_state,

					       seed_work);

	int ret;



	get_blocking_random_bytes(drbg->seed_buf, drbg->seed_buf_len);



	drbg_string_fill(&data, drbg->seed_buf, drbg->seed_buf_len);

	list_add_tail(&data.list, &seedlist);

	mutex_lock(&drbg->drbg_mutex);

	__drbg_seed(drbg, &seedlist, true);

	ret = __drbg_seed(drbg, &seedlist, true);

	if (!ret && drbg->jent) {

		crypto_free_rng(drbg->jent);

		drbg->jent = NULL;

	}

	memzero_explicit(drbg->seed_buf, drbg->seed_buf_len);

	mutex_unlock(&drbg->drbg_mutex);

}
@@ -1103,10 +1108,24 @@ static int drbg_seed(struct drbg_state *drbg, struct drbg_string *pers, 
				 drbg->test_data.len);

		pr_devel("DRBG: using test entropy\n");

	} else {

		/* Get seed from in-kernel /dev/urandom */

		get_random_bytes(drbg->seed_buf, drbg->seed_buf_len);



		/* Get seed from Jitter RNG */

		if (!drbg->jent ||

		    crypto_rng_get_bytes(drbg->jent,

					 drbg->seed_buf + drbg->seed_buf_len,

					 drbg->seed_buf_len)) {

			drbg_string_fill(&data1, drbg->seed_buf,

					 drbg->seed_buf_len);

			pr_devel("DRBG: (re)seeding with %zu bytes of entropy\n",

				 drbg->seed_buf_len);

		get_random_bytes(drbg->seed_buf, drbg->seed_buf_len);

		drbg_string_fill(&data1, drbg->seed_buf, drbg->seed_buf_len);

		} else {

			drbg_string_fill(&data1, drbg->seed_buf,

					 drbg->seed_buf_len * 2);

			pr_devel("DRBG: (re)seeding with %zu bytes of entropy\n",

				 drbg->seed_buf_len * 2);

		}

	}

	list_add_tail(&data1.list, &seedlist);
@@ -1131,7 +1150,7 @@ static int drbg_seed(struct drbg_state *drbg, struct drbg_string *pers, 
	 * Clear the initial entropy buffer as the async call may not overwrite

	 * that buffer for quite some time.

	 */

	memzero_explicit(drbg->seed_buf, drbg->seed_buf_len);

	memzero_explicit(drbg->seed_buf, drbg->seed_buf_len * 2);

	if (ret)

		goto out;

	/*
@@ -1171,6 +1190,10 @@ static inline void drbg_dealloc_state(struct drbg_state *drbg) 
#endif

	kzfree(drbg->seed_buf);

	drbg->seed_buf = NULL;

	if (drbg->jent) {

		crypto_free_rng(drbg->jent);

		drbg->jent = NULL;

	}

}



/*
@@ -1246,14 +1269,29 @@ static inline int drbg_alloc_state(struct drbg_state *drbg) 
		ret = -EFAULT;

		goto err;

	}

	/* ensure we have sufficient buffer space for initial seed */

	/*

	 * Ensure we have sufficient buffer space for initial seed which

	 * consists of the seed from get_random_bytes and the Jitter RNG.

	 */

	drbg->seed_buf_len = ((drbg->seed_buf_len + 1) / 2) * 3;

	drbg->seed_buf = kzalloc(drbg->seed_buf_len, GFP_KERNEL);

	drbg->seed_buf = kzalloc(drbg->seed_buf_len * 2, GFP_KERNEL);

	if (!drbg->seed_buf)

		goto err;



	INIT_WORK(&drbg->seed_work, drbg_async_seed);



	drbg->jent = crypto_alloc_rng("jitterentropy_rng", 0, 0);

	if(IS_ERR(drbg->jent))

	{

		pr_info("DRBG: could not allocate Jitter RNG handle for seeding\n");

		/*

		 * As the Jitter RNG is a module that may not be present, we

		 * continue with the operation and do not fully tie the DRBG

		 * to the Jitter RNG.

		 */

		drbg->jent = NULL;

	}



	return 0;



err:

include/crypto/drbg.h

+1 −0
Original line number Diff line number Diff line
@@ -123,6 +123,7 @@ struct drbg_state { 
	struct work_struct seed_work;	/* asynchronous seeding support */

	u8 *seed_buf;			/* buffer holding the seed */

	size_t seed_buf_len;

	struct crypto_rng *jent;

	const struct drbg_state_ops *d_ops;

	const struct drbg_core *core;

	struct drbg_string test_data;

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