Am Montag, 25. Oktober 2021, 11:25:21 CEST schrieb Nicolai Stange: Hi Nicolai, > 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@xxxxxxx> Reviewed-by: Stephan Müller <smueller@xxxxxxxxxx> Ciao Stephan
