vhost/crypto: fix possible TOCTOU attack

vhost/crypto: fix possible TOCTOU attack

This patch fixes the possible time-of-check to time-of-use (TOCTOU)
attack problem by copying request data and descriptor index to local
variable prior to process.

Also the original sequential read of descriptors may lead to TOCTOU
attack. This patch fixes the problem by loading all descriptors of a
request to local buffer before processing.

CVE-2020-14375
Fixes: 3bb595ecd682 ("vhost/crypto: add request handler")
Cc: stable@dpdk.org
Signed-off-by: Fan Zhang <roy.fan.zhang@intel.com>
Acked-by: Chenbo Xia <chenbo.xia@intel.com>