From: Nicolai Stange nstange@suse.de
commit 262d83a4290c331cd4f617a457408bdb82fbb738 upstream.
Since commit 42ea507fae1a ("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 --- crypto/drbg.c | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-)
--- a/crypto/drbg.c +++ b/crypto/drbg.c @@ -1046,6 +1046,27 @@ static inline int __drbg_seed(struct drb /* 10.1.1.2 / 10.1.1.3 step 5 */ 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; }
@@ -1094,9 +1115,6 @@ static void drbg_async_seed(struct work_
__drbg_seed(drbg, &seedlist, true, DRBG_SEED_STATE_FULL);
- if (drbg->seeded == DRBG_SEED_STATE_FULL) - drbg->reseed_threshold = drbg_max_requests(drbg); - unlock: mutex_unlock(&drbg->drbg_mutex);
@@ -1532,12 +1550,6 @@ static int drbg_prepare_hrng(struct drbg return err; }
- /* - * Require frequent reseeds until the seed source is fully - * initialized. - */ - drbg->reseed_threshold = 50; - return err; }