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

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Date:	Wed, 14 Oct 2015 11:10:47 -0700
From:	Joe Stringer <joestringer@...ira.com>
To:	netdev@...r.kernel.org, pshelar@...ira.com
Cc:	tgraf@...g.ch, hannes@...hat.com, jesse@...ira.com
Subject: [PATCH net] openvswitch: Scrub skb between namespaces

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)) {
+		skb_scrub_packet(skb, true);
+		tun_info = NULL;
+	}
+	skb->mark = mark;
+
 	/* Extract flow from 'skb' into 'key'. */
 	error = ovs_flow_key_extract(tun_info, skb, &key);
 	if (unlikely(error)) {
-- 
2.1.4

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