netdev - Re: [net v6 1/2] net: core: set skb useful vars in __bpf_tx

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Date:   Fri, 25 Mar 2022 08:56:28 +0800
From:   Tonghao Zhang <xiangxia.m.yue@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Network Development <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Antoine Tenart <atenart@...nel.org>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Wei Wang <weiwan@...gle.com>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [net v6 1/2] net: core: set skb useful vars in __bpf_tx_skb

On Thu, Mar 24, 2022 at 11:16 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Thu, Mar 24, 2022 at 6:57 AM <xiangxia.m.yue@...il.com> wrote:
> >
> > From: Tonghao Zhang <xiangxia.m.yue@...il.com>
> >
> > We may use bpf_redirect to redirect the packets to other
> > netdevice (e.g. ifb) in ingress or egress path.
> >
> > The target netdevice may check the *skb_iif, *redirected
> > and *from_ingress. For example, if skb_iif or redirected
> > is 0, ifb will drop the packets.
> >
> > Fixes: a70b506efe89 ("bpf: enforce recursion limit on redirects")
> > Cc: "David S. Miller" <davem@...emloft.net>
> > Cc: Jakub Kicinski <kuba@...nel.org>
> > Cc: Alexei Starovoitov <ast@...nel.org>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Cc: Andrii Nakryiko <andrii@...nel.org>
> > Cc: Martin KaFai Lau <kafai@...com>
> > Cc: Song Liu <songliubraving@...com>
> > Cc: Yonghong Song <yhs@...com>
> > Cc: John Fastabend <john.fastabend@...il.com>
> > Cc: KP Singh <kpsingh@...nel.org>
> > Cc: Eric Dumazet <edumazet@...gle.com>
> > Cc: Antoine Tenart <atenart@...nel.org>
> > Cc: Alexander Lobakin <alexandr.lobakin@...el.com>
> > Cc: Wei Wang <weiwan@...gle.com>
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
> > ---
> >  net/core/filter.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index a7044e98765e..c1f45d2e6b0a 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -2107,7 +2107,15 @@ static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb)
> >         }
> >
> >         skb->dev = dev;
> > +       /* The target netdevice (e.g. ifb) may use the:
> > +        * - redirected
> > +        * - from_ingress
> > +        */
> > +#ifdef CONFIG_NET_CLS_ACT
> > +       skb_set_redirected(skb, skb->tc_at_ingress);
> > +#else
> >         skb_clear_tstamp(skb);
> > +#endif
>
> I thought Daniel Nacked it a couple times already.
> Please stop this spam.
Hi
Daniel rejected the 2/3 patch,
https://patchwork.kernel.org/project/netdevbpf/patch/20211208145459.9590-3-xiangxia.m.yue@gmail.com/
The reasons are as follows.
* 2/3 patch adds a check in fastpath.
* on egress, redirect skb to ifb is not useful.
but this patch fixes  redirect skb to ifb on ingress. I think it is
useful for us.

Hi
Daniel, can you review this patch ?

-- 
Best regards, Tonghao