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