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Message-ID: <20191016151307.40f63896@jimi>
Date: Wed, 16 Oct 2019 15:13:07 +0300
From: Eyal Birger <eyal.birger@...il.com>
To: Zhiyuan Hou <zhiyuan2048@...ux.alibaba.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>,
Jamal Hadi Salim <jhs@...atatu.com>,
Jiri Pirko <jiri@...nulli.us>,
"David S . Miller" <davem@...emloft.net>,
Linux Kernel Network Developers <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>, shmulik.ladkani@...il.com
Subject: Re: [PATCH net] net: sched: act_mirred: drop skb's dst_entry in
ingress redirection
Hi,
On Wed, 16 Oct 2019 01:22:01 +0800
Zhiyuan Hou <zhiyuan2048@...ux.alibaba.com> wrote:
> On 2019/10/15 1:57 上午, Cong Wang wrote:
> > On Sat, Oct 12, 2019 at 12:16 AM Zhiyuan Hou
> > <zhiyuan2048@...ux.alibaba.com> wrote:
> >> 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
> >> @@ -18,6 +18,7 @@
> >> #include <linux/gfp.h>
> >> #include <linux/if_arp.h>
> >> #include <net/net_namespace.h>
> >> +#include <net/dst.h>
> >> #include <net/netlink.h>
> >> #include <net/pkt_sched.h>
> >> #include <net/pkt_cls.h>
> >> @@ -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);
> >> + }
> > Good catch!
Indeed! Thanks for fixing this!
> >
> > I don't want to be picky, but it seems this is only needed
> > when redirecting from egress to ingress, right? That is,
> > ingress to ingress, or ingress to egress is okay? If not,
> > please fix all the cases while you are on it?
> Sure. But I think this patch is also needed when redirecting from
> ingress to ingress. Because we cannot assure that a skb has null dst
> in ingress redirection path. For example, if redirecting a skb from
> loopback's ingress to other device's ingress, the skb will take a
> dst.
>
> As commit logs point out, skb with valid dst cannot be made routing
> decision in following process. original dst may cause skb loss or
> other unexpected behavior.
On the other hand, removing the dst on ingress-to-ingress redirection
may remove LWT information on incoming packets, which may be undesired.
Eyal.
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