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crypto: drbg - use Jitter RNG to obtain seed

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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: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Stephan Mueller 2015-05-25 15:09:59 +02:00 committed by Herbert Xu
parent 4c7879907e
commit b8ec5ba42c
2 changed files with 46 additions and 7 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

52
crypto/drbg.c
View file

@ -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 {
pr_devel("DRBG: (re)seeding with %zu bytes of entropy\n",
drbg->seed_buf_len);
/* Get seed from in-kernel /dev/urandom */
get_random_bytes(drbg->seed_buf, drbg->seed_buf_len);
drbg_string_fill(&data1, 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);
} 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:

1
include/crypto/drbg.h
View file

@ -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;