netdev - Re: [PATCH net-next 2/2] openvswitch: Fix skb->protocol for vlan frames.

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Message-Id: <76814927-D373-4C3A-BC85-5771304235A7@ovn.org>
Date:   Mon, 28 Nov 2016 14:29:39 -0800
From:   Jarno Rajahalme <jarno@....org>
To:     Jiri Benc <jbenc@...hat.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] openvswitch: Fix skb->protocol for vlan frames.


> On Nov 24, 2016, at 8:10 AM, Jiri Benc <jbenc@...hat.com> wrote:
> 
> On Tue, 22 Nov 2016 20:09:34 -0800, Jarno Rajahalme wrote:
>> Do not set skb->protocol to be the ethertype of the L3 header, unless
>> the packet only has the L3 header.  For a non-hardware offloaded VLAN
>> frame skb->protocol needs to be one of the VLAN ethertypes.
>> 
>> Any VLAN offloading is undone on the OVS netlink interface.  Due to
>> this all VLAN packets sent to openvswitch module from userspace are
>> non-offloaded.
> 
> This is exactly why I wanted to always accelerate the vlan tag, the
> same way it is done in other parts of the networking stack: to prevent
> all those weird corner cases.
> 
> Looks to me this is the only real way forward.
> 

I’m not sure what you suggest here. Obviously the kernel ABI can not be changed as existing userspace code expects upcalled packets to be non-accelerated. Also, if userspace pushes vlan headers, the packet will actually have them.

> This patch is wrong, it would leave skb->protocol as ETH_P_TEB for L2
> frames received via ARPHRD_NONE interface.
> 

Would this incremental fix this:

diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index 9be9fda..37f1bb9 100644
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -354,6 +354,8 @@ static int parse_vlan(struct sk_buff *skb, struct sw_flow_key *key)
 		res = parse_vlan_tag(skb, &key->eth.vlan);
 		if (res <= 0)
 			return res;
+		if (skb->protocol == htons(ETH_P_TEB))
+			skb->protocol = key->eth.vlan.tpid;
 	}
 
 	/* Parse inner vlan tag. */


  Jarno