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crypto: drbg - track whether DRBG was seeded with !rng_is_initialized()

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commit 2bcd254438 upstream.

Currently, the DRBG implementation schedules asynchronous works from
random_ready_callbacks for reseeding the DRBG instances with output from
get_random_bytes() once the latter has sufficient entropy available.

However, as the get_random_bytes() initialization state can get queried by
means of rng_is_initialized() now, there is no real need for this
asynchronous reseeding logic anymore and it's better to keep things simple
by doing it synchronously when needed instead, i.e. from drbg_generate()
once rng_is_initialized() has flipped to true.

Of course, for this to work, drbg_generate() would need some means by which
it can tell whether or not rng_is_initialized() has flipped to true since
the last seeding from get_random_bytes(). Or equivalently, whether or not
the last seed from get_random_bytes() has happened when
rng_is_initialized() was still evaluating to false.

As it currently stands, enum drbg_seed_state allows for the representation
of two different DRBG seeding states: DRBG_SEED_STATE_UNSEEDED and
DRBG_SEED_STATE_FULL. The former makes drbg_generate() to invoke a full
reseeding operation involving both, the rather expensive jitterentropy as
well as the get_random_bytes() randomness sources. The DRBG_SEED_STATE_FULL
state on the other hand implies that no reseeding at all is required for a
!->pr DRBG variant.

Introduce the new DRBG_SEED_STATE_PARTIAL state to enum drbg_seed_state for
representing the condition that a DRBG was being seeded when
rng_is_initialized() had still been false. In particular, this new state
implies that
- the given DRBG instance has been fully seeded from the jitterentropy
  source (if enabled)
- and drbg_generate() is supposed to reseed from get_random_bytes()
  *only* once rng_is_initialized() turns to true.

Up to now, the __drbg_seed() helper used to set the given DRBG instance's
->seeded state to constant DRBG_SEED_STATE_FULL. Introduce a new argument
allowing for the specification of the to be written ->seeded value instead.
Make the first of its two callers, drbg_seed(), determine the appropriate
value based on rng_is_initialized(). The remaining caller,
drbg_async_seed(), is known to get invoked only once rng_is_initialized()
is true, hence let it pass constant DRBG_SEED_STATE_FULL for the new
argument to __drbg_seed().

There is no change in behaviour, except for that the pr_devel() in
drbg_generate() would now report "unseeded" for ->pr DRBG instances which
had last been seeded when rng_is_initialized() was still evaluating to
false.

Signed-off-by: Nicolai Stange <nstange@suse.de>
Reviewed-by: Stephan Müller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Nicolai Stange 2022-06-02 22:22:30 +02:00 committed by Greg Kroah-Hartman
parent 1b93b302e9
commit babba4bf53
2 changed files with 9 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
crypto/drbg.c
View File

@ -1035,14 +1035,14 @@ static const struct drbg_state_ops drbg_hash_ops = {
******************************************************************/
static inline int __drbg_seed(struct drbg_state *drbg, struct list_head *seed,
int reseed)
int reseed, enum drbg_seed_state new_seed_state)
{
int ret = drbg->d_ops->update(drbg, seed, reseed);
if (ret)
return ret;
drbg->seeded = DRBG_SEED_STATE_FULL;
drbg->seeded = new_seed_state;
/* 10.1.1.2 / 10.1.1.3 step 5 */
drbg->reseed_ctr = 1;
@ -1092,7 +1092,7 @@ static void drbg_async_seed(struct work_struct *work)
*/
drbg->seeded = DRBG_SEED_STATE_UNSEEDED;
__drbg_seed(drbg, &seedlist, true);
__drbg_seed(drbg, &seedlist, true, DRBG_SEED_STATE_FULL);
if (drbg->seeded == DRBG_SEED_STATE_FULL)
drbg->reseed_threshold = drbg_max_requests(drbg);
@ -1122,6 +1122,7 @@ static int drbg_seed(struct drbg_state *drbg, struct drbg_string *pers,
unsigned int entropylen = drbg_sec_strength(drbg->core->flags);
struct drbg_string data1;
LIST_HEAD(seedlist);
enum drbg_seed_state new_seed_state = DRBG_SEED_STATE_FULL;
/* 9.1 / 9.2 / 9.3.1 step 3 */
if (pers && pers->len > (drbg_max_addtl(drbg))) {
@ -1149,6 +1150,9 @@ static int drbg_seed(struct drbg_state *drbg, struct drbg_string *pers,
BUG_ON((entropylen * 2) > sizeof(entropy));
/* Get seed from in-kernel /dev/urandom */
if (!rng_is_initialized())
new_seed_state = DRBG_SEED_STATE_PARTIAL;
ret = drbg_get_random_bytes(drbg, entropy, entropylen);
if (ret)
goto out;
@ -1205,7 +1209,7 @@ static int drbg_seed(struct drbg_state *drbg, struct drbg_string *pers,
memset(drbg->C, 0, drbg_statelen(drbg));
}
ret = __drbg_seed(drbg, &seedlist, reseed);
ret = __drbg_seed(drbg, &seedlist, reseed, new_seed_state);
out:
memzero_explicit(entropy, entropylen * 2);

1
include/crypto/drbg.h
View File

@ -107,6 +107,7 @@ struct drbg_test_data {
enum drbg_seed_state {
DRBG_SEED_STATE_UNSEEDED,
DRBG_SEED_STATE_PARTIAL, /* Seeded with !rng_is_initialized() */
DRBG_SEED_STATE_FULL,
};