netdev - Re: [Bridge] [PATCH 1/2] net: bridge: fix tc added QinQ forwarding

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Date:   Thu, 17 Jan 2019 11:19:14 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
Cc:     Zahari Doychev <zahari.doychev@...ux.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bridge@...ts.linux-foundation.org,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Johannes Berg <johannes@...solutions.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Bridge] [PATCH 1/2] net: bridge: fix tc added QinQ forwarding

On Thu, Jan 17, 2019 at 12:59 AM Toshiaki Makita
<makita.toshiaki@....ntt.co.jp> wrote:
>
> On 2019/01/17 17:17, Zahari Doychev wrote:
> > On Tue, Jan 15, 2019 at 03:11:28PM +0900, Toshiaki Makita wrote:
> >> On 2019/01/13 22:59, Zahari Doychev wrote:
> >>> Use the skb->mac_len instead of using the ETH_HLEN when pushing the skb
> >>> data pointer. This fixes sending incorrect packets when more than one
> >>> vlan tags are pushed by tc-vlan and the mac header length is bigger than
> >>> ETH_HLEN. In this way the vlan tagged contained in the skb is inserted at
> >>> right offset in the packet payload before sending the packet.
> >>>
> >>> Signed-off-by: Zahari Doychev <zahari.doychev@...ux.com>
> >>> ---
> >>>  net/bridge/br_forward.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
> >>> index 5372e2042adf..55f928043f77 100644
> >>> --- a/net/bridge/br_forward.c
> >>> +++ b/net/bridge/br_forward.c
> >>> @@ -39,7 +39,7 @@ int br_dev_queue_push_xmit(struct net *net, struct sock *sk, struct sk_buff *skb
> >>>     if (!is_skb_forwardable(skb->dev, skb))
> >>>             goto drop;
> >>>
> >>> -   skb_push(skb, ETH_HLEN);
> >>> +   skb_push(skb, skb->mac_len);
> >>>     br_drop_fake_rtable(skb);
> >>>
> >>>     if (skb->ip_summed == CHECKSUM_PARTIAL &&
> >>>
> >>
> >> I guess you mean skb->data points to mac_header + ETH_HLEN + VLAN_HLEN
> >> when bridge receives skbs in br_handle_frame()?
> >
> > yes, this is what I see.
> >
> >> If so, the behavior of act_vlan is odd. Normal double tagged skbs from
> >> hardware devices should have skb->data pointing to mac_header + ETH_HLEN
> >> because they just call eth_type_trans() before entering
> >> netif_receive_skb()...
> >> I think act_vlan needs some fix.
> >
> > The act_valn is using the skb_vlan_push(...) to add the vlan tags and in this
> > way increasing the skb->data and mac_len. So I think I can add a fix there to
> > set the skb->data to point to mac_header + ETH_HLEN when more tags are added.
>
> As skb->data always points to mac_header after calling skb_vlan_push(),
> we probably need to remember mac_len before invocation of it?
>
> The problem should be this part in tcf_vlan_act():
>
> > out:
> >       if (skb_at_tc_ingress(skb))
> >               skb_pull_rcsum(skb, skb->mac_len);
>
> skb->mac_len should not be used here.

I am confused. This code is to push skb->data back to network header.
If skb_vlan_push() pushes skb->data to mac header, then this code
is correct for pulling it back to network header, as skb->mac_len is
updated accordingly inside skb_vlan_push() too.

What goes wrong here? skb->mac_len isn't correct for double tagging?

Thanks.