netdev - Re: [PATCH] net: core: set skb useful vars in __bpf_tx

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Date:   Tue, 2 Nov 2021 09:58:09 +0800
From:   Tonghao Zhang <xiangxia.m.yue@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH] net: core: set skb useful vars in __bpf_tx_skb

On Tue, Nov 2, 2021 at 5:46 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 10/29/21 3:54 AM, xiangxia.m.yue@...il.com wrote:
> [...]
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 4bace37a6a44..2dbff0944768 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -2107,9 +2107,19 @@ static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb)
> >               return -ENETDOWN;
> >       }
> >
> > -     skb->dev = dev;
> > +     /* The target netdevice (e.g. ifb) may use the:
> > +      * - skb_iif
> > +      * - redirected
> > +      * - from_ingress
> > +      */
> > +     skb->skb_iif = skb->dev->ifindex;
>
> This doesn't look right to me to set it unconditionally in tx path, isn't ifb_ri_tasklet()
> setting skb->skb_iif in this case (or __netif_receive_skb_core() in main rx path)?
Hi
the act_mirred set the skb->skb_iif, redirected and from_ingress. and
__netif_receive_skb_core also set skb->skb_iif.
so we can use the act_mirred to ifb in ingress or egress path.
For ingress, when we use the bpf_redirct to ifb, we should set
redirected, and from_ingress.
For egress, when we use the bpf_redirct to ifb, we should skb_iif ,
set redirected, and from_ingress.

> Also, I would suggest to add a proper BPF selftest which outlines the issue you're solving
> in here.
Ok, thanks.
> > +#ifdef CONFIG_NET_CLS_ACT
> > +     skb_set_redirected(skb, skb->tc_at_ingress);
> > +#else
> >       skb->tstamp = 0;
> > +#endif
> >
> > +     skb->dev = dev;
> >       dev_xmit_recursion_inc();
> >       ret = dev_queue_xmit(skb);
> >       dev_xmit_recursion_dec();
> >
>


-- 
Best regards, Tonghao