tpm2-provider-cipher: Fix potential allocator–deallocator inconsistency for IV buffers

[hyperfinitism]

Issue

In tpm2-provider-cipher.c, cctx->ivector is initially allocated using OPENSSL_zalloc and finally deallocated using OPENSSL_clear_free().

In the tpm2_cipher_process_buffer/update_stream() functions, the IV buffer cctx->ivector will be replaced with the IV buffer ivector allocated in encrypt_decrypt(); this may happen allocator–deallocator inconsistency.

tpm2-tss internally uses the standard malloc/free(), while OpenSSL uses the OPENSSL_malloc/free(); the latter may internally use custom allocator/reallocator/deallocator set via CRYPTO_set_mem_functions().

Fix

This commit resolves this potential inconsistency as follows:

• Before
  1. cleanse and free cctx->ivector
  2. cctx->ivector = ivector
• After
  1. memcpy ivector to cctx->ivector
  2. cleanse and free ivector

Test

I have confirmed that make check completed successfully.

[gotthardp]

Thank you very much for your contribution. Also in relation to #164 I prefer to have an equivalent for OPENSSL_clear_free, so I created cleanse_free and used it to fix this issue.

If you agree, I suggest to cancel this PR and use the PR #168 instead. I added you there as the co-author.

[gotthardp]

I suggest #168 instead.

[hyperfinitism]

Thanks for the review and for pointing out the alternative approach.

I agree that the solution proposed in the other PR provides a clearer and more appropriate fix. In comparison, my change is more of a workaround and does not address the underlying issue as cleanly.

I will close this PR and follow the other one instead.

Thanks again for the feedback.