Re: [RFC PATCH] net act_vlan: use correct len in skb_pull

[Zahari Doychev <zahari.doychev@linux.com>]

On Thu, Feb 14, 2019 at 06:16:12PM +0900, Toshiaki Makita wrote:
> On 2019/02/14 4:51, Zahari Doychev wrote:
> > The bridge and VLAN code expects that skb->data points to the start of the
> > VLAN header instead of the next (network) header. Currently after
> > tcf_vlan_act() on ingress filter skb->data points to the next network
> > header. In this case the Linux bridge does not forward correctly double
> > tagged VLAN packets added using tc vlan action as the outer vlan tag from
> > the skb is inserted at the wrong offset after the vlan tag in the payload.
> > Making skb->data to point to the VLAN header in tcf_vlan_act() by using
> > ETH_HLEN in skb_pull_rcsum() fixes the problem.
> > 
> > The following commands were used for testing:
> > 
> > ip link add name br0 type bridge vlan_filtering 1
> > ip link set dev br0 up
> > 
> > ip link set dev net0 up
> > ip link set dev net0 master br0
> > 
> > ip link set dev net1 up
> > ip link set dev net1 master br0
> > 
> > bridge vlan add dev net0 vid 100 master
> > bridge vlan add dev br0 vid 100 self
> > bridge vlan add dev net1 vid 100 master
> > 
> > tc qdisc add dev net0 handle ffff: clsact
> > tc qdisc add dev net1 handle ffff: clsact
> > 
> > tc filter add dev net0 ingress pref 1 protocol all flower \
> >                   action vlan push id 10 pipe action vlan push id 100
> > 
> > tc filter add dev net0 egress pref 1 protocol 802.1q flower \
> >                   vlan_id 100 vlan_ethtype 802.1q cvlan_id 10 \
> >                   action vlan pop pipe action vlan pop
> > 
> > Signed-off-by: Zahari Doychev <zahari.doychev@linux.com>
> > ---
> >  net/sched/act_vlan.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/sched/act_vlan.c b/net/sched/act_vlan.c
> > index 93fdaf707313..308d7d89f925 100644
> > --- a/net/sched/act_vlan.c
> > +++ b/net/sched/act_vlan.c
> > @@ -86,7 +86,7 @@ static int tcf_vlan_act(struct sk_buff *skb, const struct tc_action *a,
> >  
> >  out:
> >  	if (skb_at_tc_ingress(skb))
> > -		skb_pull_rcsum(skb, skb->mac_len);
> > +		skb_pull_rcsum(skb, ETH_HLEN);
> 
> As I said before, it would be safer to remember mac_len and use it later.
> 
> 	__u16 mac_len = skb->mac_len;
> ...
> 	err = skb_vlan_push(...)
> ...
> 	if (skb_at_tc_ingress(skb))
> 		skb_pull_rcsum(skb, mac_len);
> 

sorry, I misunderstood it. I will send an update.

Zahari

> 
> -- 
> Toshiaki Makita
>