fix: zero-init ML-DSA keygen DMA response

[MarkAtwood]

Bug

In _HandleMlDsaKeyGenDma (src/wh_server_crypto.c), the response struct is declared uninitialized:

whMessageCrypto_MlDsaKeyGenDmaResponse res;

Multiple error paths return before res is written — _IsMlDsaLevelSupported failure (WH_ERROR_BADARGS), wc_MlDsaKey_Init/SetParams/MakeKey failure, and DMA WRITE_PRE address-check failure before res.keyId/res.keySize are set. All fall through to wh_MessageCrypto_TranslateMlDsaKeyGenDmaResponse with *outSize = sizeof(res), transmitting indeterminate stack bytes for res.keyId, res.keySize, and res.dmaAddrStatus to the client. (dmaAddrStatus.badAddr is only set on WH_ERROR_ACCESS, so it is garbage for every other error.)

Fix

Zero-initialize the response struct at declaration:

whMessageCrypto_MlDsaKeyGenDmaResponse res = {0};

Error paths now transmit deterministic zeros instead of stack garbage. This matches the sibling DMA handlers, e.g. _HandleAesCtrDma which does memset(&res, 0, sizeof(res)) before any response send.

Build verification

Compiled the translation unit against the standard wolfHSM server + ML-DSA + DMA config on Ubuntu 24.04:

gcc -c -DWOLFHSM_CFG -DWOLFHSM_CFG_ENABLE_SERVER -DWOLFHSM_CFG_DMA -DWOLFSSL_HAVE_MLDSA \
    -I. -Itest/config -I<wolfssl-install>/include src/wh_server_crypto.c

Exit 0, _HandleMlDsaKeyGenDma present as a defined text symbol.

Reported by static analysis (Fenrir finding 463).

[Copilot]

Pull request overview

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This PR fixes an information-leak bug in the ML-DSA key generation DMA handler by ensuring the DMA response struct is deterministically initialized on all error paths.

Changes:

• Zero-initialize whMessageCrypto_MlDsaKeyGenDmaResponse res in _HandleMlDsaKeyGenDma to prevent transmitting uninitialized stack bytes.

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