hmac_drbg_free() called too often and too early inside benchmark.c

[TrinityTonic]

Description

• Type: Bug
• Priority: Minor

There's a bug in the mbedTLS benchmark program. When HMAC_DRBG_C is tested, two configurations, namely with SHA1 and with SHA256 are tested. However for both configurations mbedtls_hmac_drbg_free() is called, which means that the context is freed too early although it is being used later. mbedtls_hmac_drbg_free() should only be called at the end of the
#if defined(MBEDTLS_HMAC_DRBG_C) - code.

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Bug

mbed TLS build:
Version: 2.6.0

[RonEld]

Hi @TrinityTonic Thank you for reporting this
Although I agree that this is confusing that mbedtls_hmac_drbg_free() is called after every operation, it is not a major bug, as the mbedtls_hmac_drbg_free() only clears the context from its internal data.
I agree it might cause a problem when MBEDTLS_THREADING_C is defined, or when there will be an alternative implementation support for HMAC DRBG in the future.

[TrinityTonic]

@RonEld Yea, I was noticing the problem with MBEDTLS_THREADING_C as my (alternative) Mutex is freed when hmac_drbg_free() is called and later on the the code tried to lock the mutex it had freed before.

[ciarmcom]

ARM Internal Ref: IOTSSL-1761