Re: [Qemu-devel] [PATCH for-2.8] virtio-crypto: zeroize the key material before free

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Dec 06, 2016 at 05:29:13PM +0800, Gonglei wrote:
> Zeroize the memory of CryptoDevBackendSymOpInfo structure pointed
> for key material security.
> 
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
>  hw/virtio/virtio-crypto.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/virtio-crypto.c b/hw/virtio/virtio-crypto.c
> index 2f2467e..ecb19b6 100644
> --- a/hw/virtio/virtio-crypto.c
> +++ b/hw/virtio/virtio-crypto.c
> @@ -337,7 +337,18 @@ static void virtio_crypto_free_request(VirtIOCryptoReq *req)
>  {
>      if (req) {
>          if (req->flags == CRYPTODEV_BACKEND_ALG_SYM) {
> -            g_free(req->u.sym_op_info);
> +            size_t max_len;
> +            CryptoDevBackendSymOpInfo *op_info = req->u.sym_op_info;
> +
> +            max_len = op_info->iv_len +
> +                      op_info->aad_len +
> +                      op_info->src_len +
> +                      op_info->dst_len +
> +                      op_info->digest_result_len;
> +
> +            /* Zeroize and free request data structure */
> +            memset(op_info, 0, sizeof(*op_info) + max_len);
> +            g_free(op_info);

Write into memory, then free it?  This looks rather strange. Why are we
doing this?

>          }
>          g_free(req);
>      }
> -- 
> 1.8.3.1
>