[ovs-dev] [PATCH] datapath: Backport "openvswitch: Zero flows on allocation."

Jesse Gross jesse at nicira.com
Thu Sep 24 03:12:58 UTC 2015


On Wed, Sep 23, 2015 at 7:43 PM, Pravin Shelar <pshelar at nicira.com> wrote:
> On Tue, Sep 22, 2015 at 6:17 PM, Jesse Gross <jesse at nicira.com> wrote:
>> Upstream commit:
>>     openvswitch: Zero flows on allocation.
>>
>>     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 at nicira.com>
>>     Acked-by: Pravin B Shelar <pshelar at nicira.com>
>>     Signed-off-by: David S. Miller <davem at davemloft.net>
>>
>> Upstream: ae5f2fb1 ("openvswitch: Zero flows on allocation.")
>> Signed-off-by: Jesse Gross <jesse at nicira.com>
>
> Acked-by: Pravin B Shelar <pshelar at nicira.com>

Thanks, applied to master, branch-2.4 and branch-2.3.



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