Fix HKDF implementation to prevent buffer overrun when compiled with NX_SECURE_KEY_CLEAR

[sjscymru]

The _nx_crypto_method_hkdf_cleanup method is passing the incorrect pointer to the HMAC method cleanup when NetX is compiled with NX_SECURE_KEY_CLEAR.

When NX_SECURE_KEY_CLEAR defined, calling _nx_crypto_method_hkdf_cleanup will result in a subsequent call to the HMAC method (if one is set) cleanup function. However the incorrect parameter is being passed, currently HKDF passes in the a pointer to the NX_CRYPTO_METHOD structure of the HMAC method, which is 32 bytes in size.

status = hmac_method -> nx_crypto_cleanup(hmac_method);

But the HMAC cleanup method is calling NX_CRYPTO_MEMSET() on the provided pointer using sizeof(NX_CRYPTO_HMAC) which is 292 bytes is size:

/* Clean up the crypto metadata.  */
NX_CRYPTO_MEMSET(crypto_metadata, 0, sizeof(NX_CRYPTO_HMAC));

This leads to a buffer overflow of 260 bytes. The actual amount can vary depending of the exact HMAC method being used.

[fdesbiens]

Thank you for this contribution, @sjscymru.

@eclipse-threadx/iot-threadx-committers: Please review.