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Date:   Fri, 6 May 2022 11:23:50 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Cc:     herbert@gondor.apana.org.au, linux-crypto@vger.kernel.org,
        qat-linux@intel.com, vdronov@redhat.com, stable@vger.kernel.org,
        Adam Guerin <adam.guerin@intel.com>,
        Wojciech Ziemba <wojciech.ziemba@intel.com>
Subject: Re: [PATCH 07/12] crypto: qat - set to zero DH parameters before free
Message-ID: <YnTpJkTXwmYyE9lQ@kroah.com>
References: <20220506082327.21605-1-giovanni.cabiddu@intel.com>
 <20220506082327.21605-8-giovanni.cabiddu@intel.com>
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On Fri, May 06, 2022 at 09:23:22AM +0100, Giovanni Cabiddu wrote:
> Set to zero the DH context buffers containing the DH key before they are
> freed.

That says what, but not why.

> Cc: stable@vger.kernel.org
> Fixes: c9839143ebbf ("crypto: qat - Add DH support")
> Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
> Reviewed-by: Adam Guerin <adam.guerin@intel.com>
> Reviewed-by: Wojciech Ziemba <wojciech.ziemba@intel.com>
> ---
>  drivers/crypto/qat/qat_common/qat_asym_algs.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/crypto/qat/qat_common/qat_asym_algs.c b/drivers/crypto/qat/qat_common/qat_asym_algs.c
> index d75eb77c9fb9..2fec89b8a188 100644
> --- a/drivers/crypto/qat/qat_common/qat_asym_algs.c
> +++ b/drivers/crypto/qat/qat_common/qat_asym_algs.c
> @@ -421,14 +421,17 @@ static int qat_dh_set_params(struct qat_dh_ctx *ctx, struct dh *params)
>  static void qat_dh_clear_ctx(struct device *dev, struct qat_dh_ctx *ctx)
>  {
>  	if (ctx->g) {
> +		memzero_explicit(ctx->g, ctx->p_size);
>  		dma_free_coherent(dev, ctx->p_size, ctx->g, ctx->dma_g);

Why is a memset() not sufficient here?
And what is this solving?  Who would get this stale data?

thanks,

greg k-h