netdev - Re: [PATCH net] openvswitch: Scrub skb between namespaces

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Date:	Fri, 16 Oct 2015 09:05:44 -0700
From:	Joe Stringer <joestringer@...ira.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	netdev <netdev@...r.kernel.org>, Thomas Graf <tgraf@...g.ch>,
	Hannes Sowa <hannes@...hat.com>, Jesse Gross <jesse@...ira.com>
Subject: Re: [PATCH net] openvswitch: Scrub skb between namespaces

On 14 October 2015 at 17:34, Pravin Shelar <pshelar@...ira.com> wrote:
> On Wed, Oct 14, 2015 at 11:10 AM, Joe Stringer <joestringer@...ira.com> wrote:
>> If OVS receives a packet from another namespace, then the packet should
>> be scrubbed. However, people have already begun to rely on the behaviour
>> that skb->mark is preserved across namespaces, so retain this one field.
>>
>> This is mainly to address information leakage between namespaces when
>> using OVS internal ports, but by placing it in ovs_vport_receive() it is
>> more generally applicable, meaning it should not be overlooked if other
>> port types are allowed to be moved into namespaces in future.
>>
>> Signed-off-by: Joe Stringer <joestringer@...ira.com>
>> ---
>> I originally proposed this patch as part of the conntrack changes to OVS,
>> and there was some discussion on that thread, culminating here:
>> http://www.spinics.net/lists/netdev/msg338626.html
>>
>> We also discussed this a bit in Seattle, however I didn't follow up
>> immediately so I don't exactly recall what the consensus was. Following
>> Jesse's direction in the above thread, I'm proposing that we preserve the
>> mark, but scrub the rest. Also fixed the use-after-free bug present in the
>> previous version.
>>
>> I think this is relevant for 'net', because this is the first time that
>> the metadata_dst and nfct are exposed (albeit indirectly) through OVS so it
>> would be nice to get agreement on the expected behaviour.
>> ---
>>  net/openvswitch/vport.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/net/openvswitch/vport.c b/net/openvswitch/vport.c
>> index fc5c0b9ccfe9..70f19ea99b92 100644
>> --- a/net/openvswitch/vport.c
>> +++ b/net/openvswitch/vport.c
>> @@ -440,10 +440,17 @@ int ovs_vport_receive(struct vport *vport, struct sk_buff *skb,
>>                       const struct ip_tunnel_info *tun_info)
>>  {
>>         struct sw_flow_key key;
>> +       u32 mark = skb->mark;
>>         int error;
>>
>>         OVS_CB(skb)->input_vport = vport;
>>         OVS_CB(skb)->mru = 0;
>> +       if (dev_net(skb->dev) != ovs_dp_get_net(vport->dp)) {
> This should be marked as unlikely.

OK.

>> +               skb_scrub_packet(skb, true);
>> +               tun_info = NULL;
>> +       }
>> +       skb->mark = mark;
> Lets move this to skb scrub block. in other cases this not required.

OK, I'll send a v2.
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