linux-kernel - Re: [PATCH net] net: sched: act_mirred: drop skb's dst

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Message-ID: <2ad15b96-156d-7b71-0e37-74ceeacade35@cogentembedded.com>
Date:   Sat, 12 Oct 2019 22:34:50 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Zhiyuan Hou <zhiyuan2048@...ux.alibaba.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S . Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: sched: act_mirred: drop skb's dst_entry in
 ingress redirection

Hello!

On 10/12/2019 10:16 AM, Zhiyuan Hou wrote:

> In act_mirred's ingress redirection, if the skb's dst_entry is valid
> when call function netif_receive_skb, the fllowing l3 stack process

  Following or flowing?

> (ip_rcv_finish_core) will check dst_entry and skip the routing
> decision. Using the old dst_entry is unexpected and may discard the
> skb in some case. For example dst->dst_input points to dst_discard.
> 
> This patch drops the skb's dst_entry before calling netif_receive_skb
> so that the skb can be made routing decision like a normal ingress
> skb.
> 
> Signed-off-by: Zhiyuan Hou <zhiyuan2048@...ux.alibaba.com>
> ---
>  net/sched/act_mirred.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
> index 9ce073a05414..6108a64c0cd5 100644
> --- a/net/sched/act_mirred.c
> +++ b/net/sched/act_mirred.c
[...]
> @@ -298,8 +299,10 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
>  
>  	if (!want_ingress)
>  		err = dev_queue_xmit(skb2);
> -	else
> +	else {
> +		skb_dst_drop(skb2);
>  		err = netif_receive_skb(skb2);
> +	}

   If you introduce {} in one *if* branch, {} should be added to the other branches as well,
says CodingStyle.

[...]

MBR, Sergei