C/C++ Dereference error: Dereference before null check - c++

Question

In the function below I am facing a Dereference error before null check. In the line
SEC_KM_KEKColumn_t *pAdmin1KEKs = pTCGKS->keySet[SEC_KM_Admin1].kc;
There is an error which states directly dereferencing pointer pTCGKS. And also in the line
SEC_ASSERT_MODEL(pDefaultKS != NULL && pTCGKS != NULL);
there is an error which states Dereference before null check (REVERSE_INULL)
check_after_deref: Null-checking pTCGKS suggests that it may be null, but it has already been dereferenced on all paths leading to the check.
Stat_t SEC_COD_SLOW SEC_KM_TCG_Activ(SEC_KM_TCGKeySet_t *pTCGKS, uint32_t rangesSUM, SEC_KM_DefaultKeySet_t *pDefaultKS)
{
Status_t status = STATUS_OK;
uint32_t rangeIndex = 0;
const SEC_KM_KDF_t *pDigestNID = SEC_KM_GetAnybodyDigest();
SEC_KM_KEKColumn_t *pAdmin1KEKs = pTCGKS->keySet[SEC_KM_Admin1].kc;
const SEC_KM_KDF_t *pDigestAID = SEC_KM_TCG_GetSessionCredentials();
SEC_ASSERT_DEBUG(SEC_KM_TCG_GetSessionUserID() == SEC_KM_Admin1);
SEC_ASSERT_MODEL(pDefaultKS != NULL && pTCGKS != NULL);
// Generate Key Chains for all TCG authorities for Original Opal scheme
status = SEC_KM_TCG_Generate(pTCGKS, pDigestNID, pDigestAID);
if (status != STATUS_OK)
{
return status;
}
// Rewrap SDEK from default key storage into Global Range of TCG
status = SEC_KM_RewrapSDEK(&pDefaultKS->SDEKw, &pDefaultKS->keySet.RKEKw, &pDefaultKS->keySet.PKEKw, pDigestNID,
&pTCGKS->DEK[GDEK].SDEK.w, &pAdmin1KEKs[RKEKG].w, &pAdmin1KEKs[PKEK].w, pDigestAID);
if (status != STATUS_OK)
{
return status;
}
status = SEC_KM_TCG_ConvertToSUM(pTCGKS, pDigestNID, rangesSUM);
if (status != STATUS_OK)
{
return status;
}
// After Activation all ranges are unlocked. So unwrap all SDEKs.
for (rangeIndex = 0; rangeIndex < TCG_MAX_RANGE_KEYS; rangeIndex++)
{
status = SEC_KM_TCG_UnwrapUnlockedSDEK(pTCGKS, rangeIndex);
if (status != STATUS_OK)
{
return status;
}
}
return status;
}

Answer 1

It's exactly what it says.
First you dereference pTCGKS, then you check that it isn't null.
Compilers can (and will) optimise out a "late" null check as being effectively redundant for any well-defined program, making your assertion potentially useless.
Move it to before your dereference.

Answer 2

The SEC_ASSERT_MODEL checks for NULL after the line that references it. If pTCGKS is null a runtime error will occur before that check, so it serves no useful purpose.
I assume SEC_ASSERT_MODEL is a precondition check macro - if that is the case you need to perform those checks before using the checked parameters:
SEC_ASSERT_DEBUG(SEC_KM_TCG_GetSessionUserID() == SEC_KM_Admin1);
SEC_ASSERT_MODEL(pDefaultKS != NULL && pTCGKS != NULL);
Status_t status = STATUS_OK;
uint32_t rangeIndex = 0;
const SEC_KM_KDF_t *pDigestNID = SEC_KM_GetAnybodyDigest();
SEC_KM_KEKColumn_t *pAdmin1KEKs = pTCGKS->keySet[SEC_KM_Admin1].kc;
const SEC_KM_KDF_t *pDigestAID = SEC_KM_TCG_GetSessionCredentials();