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rand: add a note about a potentially misleading code analyzer warning.

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When seeding from a parent DRBG, the pointer to the child is used as
additional data.  This triggers static code analysers.  Rearrange and
expand the comments to make this more obvious.

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/12724)
This commit is contained in:
Pauli 2020-08-26 23:56:55 +10:00
parent 1d6c86709c
commit edd53e9135
1 changed files with 11 additions and 5 deletions
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16
providers/implementations/rands/drbg.c
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@ -183,17 +183,23 @@ static size_t prov_drbg_get_entropy(PROV_DRBG *drbg, unsigned char **pout,
if (buffer != NULL) {
size_t bytes = 0;
if (drbg->parent_generate == NULL)
goto err;
/*
* Get random data from parent. Include our address as additional input,
* in order to provide some additional distinction between different
* DRBG child instances.
* Our lock is already held, but we need to lock our parent before
* generating bits from it. (Note: taking the lock will be a no-op
* if locking if drbg->parent->lock == NULL.)
*/
if (drbg->parent_generate == NULL)
goto err;
drbg_lock_parent(drbg);
/*
* Get random data from parent. Include our DRBG address as
* additional input, in order to provide a distinction between
* different DRBG child instances.
*
* Note: using the sizeof() operator on a pointer triggers
* a warning in some static code analyzers, but it's
* intentional and correct here.
*/
if (drbg->parent_generate(drbg->parent, buffer, bytes_needed,
drbg->strength, prediction_resistance,
(unsigned char *)&drbg,