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

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Message-ID: <88eb26eb-b3a8-40e7-5c47-f832b3b0a627@cs.kuleuven.be>
Date:   Mon, 7 Aug 2023 08:15:06 +0200
From:   Jo Van Bulck <jo.vanbulck@...kuleuven.be>
To:     "Huang, Kai" <kai.huang@...el.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 1/5] selftests/sgx: Fix uninitialized pointer dereference
 in error path.

On 03.08.23 05:51, Huang, Kai wrote:
> 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().

Thank you for pointing this out. Afais the implementations I've seen can 
handle NULL, and similar error-handling paths exists where 
EVP_MD_CTX_destroy() is called with a NULL pointer exist in several 
places in the openSSL code.

That being said, this indeed not explicit in the specification (unlike 
RSA_free() which is called just after and explicitly specifies that NULL 
is okay). So you're probably right that it's generally safer to not call 
EVP_MD_CTX_destroy() with a NULL pointer.

I'll include an extra check for this in the next patch revision.