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crypto: drbg - move dynamic ->reseed_threshold adjustments to __drbg_seed()

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commit 262d83a4290c331cd4f617a457408bdb82fbb738 upstream.

Since commit 42ea507fae ("crypto: drbg - reseed often if seedsource is
degraded"), the maximum seed lifetime represented by ->reseed_threshold
gets temporarily lowered if the get_random_bytes() source cannot provide
sufficient entropy yet, as is common during boot, and restored back to
the original value again once that has changed.

More specifically, if the add_random_ready_callback() invoked from
drbg_prepare_hrng() in the course of DRBG instantiation does not return
-EALREADY, that is, if get_random_bytes() has not been fully initialized
at this point yet, drbg_prepare_hrng() will lower ->reseed_threshold
to a value of 50. The drbg_async_seed() scheduled from said
random_ready_callback will eventually restore the original value.

A future patch will replace the random_ready_callback based notification
mechanism and thus, there will be no add_random_ready_callback() return
value anymore which could get compared to -EALREADY.

However, there's __drbg_seed() which gets invoked in the course of both,
the DRBG instantiation as well as the eventual reseeding from
get_random_bytes() in aforementioned drbg_async_seed(), if any. Moreover,
it knows about the get_random_bytes() initialization state by the time the
seed data had been obtained from it: the new_seed_state argument introduced
with the previous patch would get set to DRBG_SEED_STATE_PARTIAL in case
get_random_bytes() had not been fully initialized yet and to
DRBG_SEED_STATE_FULL otherwise. Thus, __drbg_seed() provides a convenient
alternative for managing that ->reseed_threshold lowering and restoring at
a central place.

Move all ->reseed_threshold adjustment code from drbg_prepare_hrng() and
drbg_async_seed() respectively to __drbg_seed(). Make __drbg_seed()
lower the ->reseed_threshold to 50 in case its new_seed_state argument
equals DRBG_SEED_STATE_PARTIAL and let it restore the original value
otherwise.

There is no change in behaviour.

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>
This commit is contained in:
Nicolai Stange 2022-06-02 22:22:31 +02:00 committed by Greg Kroah-Hartman
parent 54700e82a7
commit e744e34a3c
1 changed files with 21 additions and 9 deletions
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30
crypto/drbg.c
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@ -1046,6 +1046,27 @@ static inline int __drbg_seed(struct drbg_state *drbg, struct list_head *seed,
/* 10.1.1.2 / 10.1.1.3 step 5 */ /* 10.1.1.2 / 10.1.1.3 step 5 */
drbg->reseed_ctr = 1; drbg->reseed_ctr = 1;
switch (drbg->seeded) {
case DRBG_SEED_STATE_UNSEEDED:
/* Impossible, but handle it to silence compiler warnings. */
fallthrough;
case DRBG_SEED_STATE_PARTIAL:
/*
* Require frequent reseeds until the seed source is
* fully initialized.
*/
drbg->reseed_threshold = 50;
break;
case DRBG_SEED_STATE_FULL:
/*
* Seed source has become fully initialized, frequent
* reseeds no longer required.
*/
drbg->reseed_threshold = drbg_max_requests(drbg);
break;
}
return ret; return ret;
} }
@ -1094,9 +1115,6 @@ static void drbg_async_seed(struct work_struct *work)
__drbg_seed(drbg, &seedlist, true, DRBG_SEED_STATE_FULL); __drbg_seed(drbg, &seedlist, true, DRBG_SEED_STATE_FULL);
if (drbg->seeded == DRBG_SEED_STATE_FULL)
drbg->reseed_threshold = drbg_max_requests(drbg);
unlock: unlock:
mutex_unlock(&drbg->drbg_mutex); mutex_unlock(&drbg->drbg_mutex);
@ -1532,12 +1550,6 @@ static int drbg_prepare_hrng(struct drbg_state *drbg)
return err; return err;
} }
/*
* Require frequent reseeds until the seed source is fully
* initialized.
*/
drbg->reseed_threshold = 50;
return err; return err;
} }