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wolfTPM2: harden PCR/hash wrapper validation #554

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wolfTPM2: harden PCR/hash wrapper validation #554

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17 changes: 15 additions & 2 deletions src/tpm2_wrap.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6695,6 +6695,10 @@ int wolfTPM2_ResetPCR(WOLFTPM2_DEV* dev, int pcrIndex)
{

@aidangarske aidangarske Jul 22, 2026

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🟠 [Medium] New wrapper validation paths are not covered by regression tests · Missing Tests

The PR adds defensive validation to four public PCR/hash wrappers: wolfTPM2_ResetPCR and wolfTPM2_ExtendPCR now reject out-of-range PCR indexes (return BAD_FUNC_ARG), wolfTPM2_ReadPCR now rejects a successful empty PCR response (pcrValues.count == 0 -> TPM_RC_FAILURE) before reading digests[0], and wolfTPM2_HashStart now rejects any algorithm for which TPM2_GetHashDigestSize(hashAlg) == 0. These are observable local wrapper contracts, but the diff changes only src/tpm2_wrap.c and adds no regression tests. The existing tests only exercise happy paths (PCR reset/extend success, HashStart with TPM_ALG_SHA256) and do not assert the new negative paths: invalid PCR indexes, non-hash HashStart input, or an empty PCR read response. Severity views differ: the review mode rated this Medium while review-security rated it Info; keeping the stricter Medium. This is not a blocking security issue in the changed code, but regression coverage would prevent the behavior from being accidentally relaxed later.

Fix: Add focused regression tests in tests/unit_tests.c for the new negative paths: wolfTPM2_ResetPCR(&dev, PCR_LAST + 1) and wolfTPM2_ExtendPCR(&dev, PCR_LAST + 1, ...) returning BAD_FUNC_ARG, wolfTPM2_HashStart(&dev, &hash, TPM_ALG_RSA, NULL, 0) returning BAD_FUNC_ARG, and an empty PCR read response (pcrValues.count == 0 -> TPM_RC_FAILURE) using a harness/backend configuration that can produce or mock that TPM response.

int rc;
PCR_Reset_In pcrReset;

if (pcrIndex < (int)PCR_FIRST || pcrIndex > (int)PCR_LAST)
return BAD_FUNC_ARG;

XMEMSET(&pcrReset, 0, sizeof(pcrReset));
pcrReset.pcrHandle = pcrIndex;
rc = TPM2_PCR_Reset(&pcrReset);
Expand Down Expand Up @@ -6816,6 +6820,12 @@ int wolfTPM2_ReadPCR(WOLFTPM2_DEV* dev, int pcrIndex, int hashAlg, byte* digest,
return rc;
}

/* A successful read must return at least one digest; otherwise the
* digests[0] access below reads uninitialized data. */
if (pcrReadOut.pcrValues.count == 0) {
return TPM_RC_FAILURE;
}

digestLen = (int)pcrReadOut.pcrValues.digests[0].size;
if (digest) {
if (pDigestLen == NULL) {
Expand Down Expand Up @@ -6852,7 +6862,8 @@ int wolfTPM2_ExtendPCR(WOLFTPM2_DEV* dev, int pcrIndex, int hashAlg,
int rc;
PCR_Extend_In pcrExtend;

if (dev == NULL || digestLen < 0 || digestLen > TPM_MAX_DIGEST_SIZE) {
if (dev == NULL || digestLen < 0 || digestLen > TPM_MAX_DIGEST_SIZE ||
pcrIndex < (int)PCR_FIRST || pcrIndex > (int)PCR_LAST) {
return BAD_FUNC_ARG;
}

Expand Down Expand Up @@ -7712,7 +7723,9 @@ int wolfTPM2_HashStart(WOLFTPM2_DEV* dev, WOLFTPM2_HASH* hash,
HashSequenceStart_In in;
HashSequenceStart_Out out;

if (dev == NULL || hash == NULL || hashAlg == TPM_ALG_NULL ||
/* TPM2_GetHashDigestSize() is 0 for any algorithm that is not a hash,
* so this rejects them locally instead of relying on TPM_RC_HASH. */
if (dev == NULL || hash == NULL || TPM2_GetHashDigestSize(hashAlg) == 0 ||
(usageAuthSz > 0 && usageAuth == NULL)) {
return BAD_FUNC_ARG;
}
Expand Down
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