Re: [PATCH net v2] openvswitch: Zero flows on allocation.

[David Miller <davem@davemloft.net>]

From: Jesse Gross <jesse@nicira.com>
Date: Mon, 21 Sep 2015 20:21:20 -0700

> When support for megaflows was introduced, OVS needed to start
> installing flows with a mask applied to them. Since masking is an
> expensive operation, OVS also had an optimization that would only
> take the parts of the flow keys that were covered by a non-zero
> mask. The values stored in the remaining pieces should not matter
> because they are masked out.
> 
> While this works fine for the purposes of matching (which must always
> look at the mask), serialization to netlink can be problematic. Since
> the flow and the mask are serialized separately, the uninitialized
> portions of the flow can be encoded with whatever values happen to be
> present.
> 
> In terms of functionality, this has little effect since these fields
> will be masked out by definition. However, it leaks kernel memory to
> userspace, which is a potential security vulnerability. It is also
> possible that other code paths could look at the masked key and get
> uninitialized data, although this does not currently appear to be an
> issue in practice.
> 
> This removes the mask optimization for flows that are being installed.
> This was always intended to be the case as the mask optimizations were
> really targetting per-packet flow operations.
> 
> Fixes: 03f0d916 ("openvswitch: Mega flow implementation")
> Signed-off-by: Jesse Gross <jesse@nicira.com>

Applied and queued up for -stable, thanks.