netdev - Re: [PATCH net 2/4] bridge: Handle priority-tagged frames properly

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Date:	Wed, 11 Sep 2013 16:00:32 +0900
From:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:	vyasevic@...hat.com
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net 2/4] bridge: Handle priority-tagged frames properly

On Tue, 2013-09-10 at 10:03 -0400, Vlad Yasevich wrote:
> On 09/10/2013 06:34 AM, Toshiaki Makita wrote:
> > IEEE 802.1Q says that when we receive priority-tagged (VID 0) frames
> > use the PVID for the port as its VID.
> > (See IEEE 802.1Q-2005 6.7.1 and Table 9-2)
> >
> > Apply the PVID to not only untagged frames but also priority-tagged frames.
> >
> > Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
> > ---
> >   net/bridge/br_vlan.c | 27 ++++++++++++++++++++-------
> >   1 file changed, 20 insertions(+), 7 deletions(-)
> >
> > diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
> > index 21b6d21..5a9c44a 100644
> > --- a/net/bridge/br_vlan.c
> > +++ b/net/bridge/br_vlan.c
> > @@ -189,6 +189,8 @@ out:
> >   bool br_allowed_ingress(struct net_bridge *br, struct net_port_vlans *v,
> >   			struct sk_buff *skb, u16 *vid)
> >   {
> > +	int err;
> > +
> >   	/* If VLAN filtering is disabled on the bridge, all packets are
> >   	 * permitted.
> >   	 */
> > @@ -201,20 +203,31 @@ bool br_allowed_ingress(struct net_bridge *br, struct net_port_vlans *v,
> >   	if (!v)
> >   		return false;
> >
> > -	if (br_vlan_get_tag(skb, vid)) {
> > +	err = br_vlan_get_tag(skb, vid);
> > +	if (!*vid) {
> >   		u16 pvid = br_get_pvid(v);
> >
> > -		/* Frame did not have a tag.  See if pvid is set
> > -		 * on this port.  That tells us which vlan untagged
> > -		 * traffic belongs to.
> > +		/* Frame had a tag with VID 0 or did not have a tag.
> > +		 * See if pvid is set on this port.  That tells us which
> > +		 * vlan untagged or priority-tagged traffic belongs to.
> >   		 */
> >   		if (pvid == VLAN_N_VID)
> >   			return false;
> >
> > -		/* PVID is set on this port.  Any untagged ingress
> > -		 * frame is considered to belong to this vlan.
> > +		/* PVID is set on this port.  Any untagged or priority-tagged
> > +		 * ingress frame is considered to belong to this vlan.
> >   		 */
> > -		__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), pvid);
> > +		if (likely(err))
> > +			/* Untagged Frame. */
> > +			__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), pvid);
> > +		else
> > +			/* Priority-tagged Frame.
> > +			 * At this point, We know that skb->vlan_tci had
> > +			 * VLAN_TAG_PRESENT bit and its VID field was 0x000.
> > +			 * We update only VID field and preserve PCP field.
> > +			 */
> > +			skb->vlan_tci |= pvid;
> > +
> 
> In the case of a priority tagged frame, we should unroll the 
> modification above and restore the VID field to 0.  Otherwise, you
> may end up either stripping the vlan header completely or forwarding
> with pvid of the ingress port.

Thank you for reviewing.

It is my intended behavior that an incoming priority-tagged frame is
forwarded as a frame untagged or tagged with pvid.

IEEE 802.1Q-2011:

  section 8.1.7 Conversion of frame formats

  NOTE - As all incoming frames, including priority-tagged frames, are
  classified as belonging to a VLAN, the transmitting Port transmits
  VLAN-tagged frames or untagged frames. Hence, a station sending a
  priority-tagged frame via a Bridge will receive a response that is
  either VLAN-tagged or untagged, as described in 8.5.

  3. Definitions

  3.132 Priority-tagged frame: A tagged frame whose tag header carries
  priority information but carries no VLAN identification information.

  3.203 VLAN-tagged frame: A VLAN-tagged frame is a tagged frame whose
  tag header carries *both* VLAN identification and priority
  information.

Toshiaki Makita

> 
> -vlad
> >   		return true;
> >   	}
> >
> >


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