Re: [PATCH 1/5] selftests/sgx: Fix uninitialized pointer dereference in error path.

[Huang, Kai]

On Mon, 2023-07-24 at 18:58 +0200, Jo Van Bulck wrote:
> Ensure ctx is zero-initialized, such that the encl_measure function will
> not call EVP_MD_CTX_destroy with an uninitialized ctx pointer in case of an
> early error during key generation.
> 
> Signed-off-by: Jo Van Bulck <jo.vanbulck@xxxxxxxxxxxxxx>
> ---
>  tools/testing/selftests/sgx/sigstruct.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/sgx/sigstruct.c b/tools/testing/selftests/sgx/sigstruct.c
> index a07896a46364..dd1fdab90e26 100644
> --- a/tools/testing/selftests/sgx/sigstruct.c
> +++ b/tools/testing/selftests/sgx/sigstruct.c
> @@ -318,9 +318,9 @@ bool encl_measure(struct encl *encl)
>  	struct sgx_sigstruct *sigstruct = &encl->sigstruct;
>  	struct sgx_sigstruct_payload payload;
>  	uint8_t digest[SHA256_DIGEST_LENGTH];
> +	EVP_MD_CTX *ctx = NULL;
>  	unsigned int siglen;
>  	RSA *key = NULL;
> -	EVP_MD_CTX *ctx;
>  	int i;
>  
>  	memset(sigstruct, 0, sizeof(*sigstruct));

Is it safe to assume EVP_MD_CTX_destroy() can always handle a NULL ctx?

The manpage says:

EVP_MD_CTX_destroy() cleans up digest context ctx and frees up the space
allocated to it, it should be called only on a context created using
EVP_MD_CTX_create().