Re: [PATCH v2 7/7] fs: HKDF - remove duplicate memory clearing

From: Eric Biggers <ebiggers@kernel.org>
To: "Stephan Müller" <smueller@chronox.de>
Cc: herbert@gondor.apana.org.au, Jarkko Sakkinen <jarkko@kernel.org>,
	mathew.j.martineau@linux.intel.com, dhowells@redhat.com,
	linux-crypto@vger.kernel.org, linux-fscrypt@vger.kernel.org,
	linux-kernel@vger.kernel.org, keyrings@vger.kernel.org,
	simo@redhat.com
Subject: Re: [PATCH v2 7/7] fs: HKDF - remove duplicate memory clearing
Date: Thu, 28 Jan 2021 12:21:21 -0800	[thread overview]
Message-ID: <YBMcwcWFgolygTbs@sol.localdomain> (raw)
In-Reply-To: <8714658.CDJkKcVGEf@positron.chronox.de>

On Sun, Jan 24, 2021 at 03:04:50PM +0100, Stephan Müller wrote:
> The clearing of the OKM memory buffer in case of an error is already
> performed by the HKDF implementation crypto_hkdf_expand. Thus, the
> code clearing is not needed any more in the file system code base.
> 
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> ---
>  fs/crypto/hkdf.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/crypto/hkdf.c b/fs/crypto/hkdf.c
> index ae236b42b1f0..c48dd8ca3a46 100644
> --- a/fs/crypto/hkdf.c
> +++ b/fs/crypto/hkdf.c
> @@ -102,13 +102,10 @@ int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
>  		.iov_base = (u8 *)info,
>  		.iov_len = infolen,
>  	} };
> -	int err = crypto_hkdf_expand(hkdf->hmac_tfm,
> -				     info_iov, ARRAY_SIZE(info_iov),
> -				     okm, okmlen);
>  
> -	if (unlikely(err))
> -		memzero_explicit(okm, okmlen); /* so caller doesn't need to */
> -	return err;
> +	return crypto_hkdf_expand(hkdf->hmac_tfm,
> +				  info_iov, ARRAY_SIZE(info_iov),
> +				  okm, okmlen);
>  }
>  

Shoudn't this just be folded into the previous patch, which converted
fscrypt_hkdf_expand() to use crypto_hkdf_expand() in the first place?

- Eric