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Date: Sun, 25 Sep 2022 11:00:48 -0700 From: Cong Wang <xiyou.wangcong@...il.com> To: Paul Blakey <paulb@...dia.com> Cc: Daniel Borkmann <daniel@...earbox.net>, Vlad Buslov <vladbu@...dia.com>, Oz Shlomo <ozsh@...dia.com>, Roi Dayan <roid@...dia.com>, netdev@...r.kernel.org, Saeed Mahameed <saeedm@...dia.com>, Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com> Subject: Re: [PATCH net v2 1/2] net: Fix return value of qdisc ingress handling on success On Sun, Sep 25, 2022 at 11:14:21AM +0300, Paul Blakey wrote: > Currently qdisc ingress handling (sch_handle_ingress()) doesn't > set a return value and it is left to the old return value of > the caller (__netif_receive_skb_core()) which is RX drop, so if > the packet is consumed, caller will stop and return this value > as if the packet was dropped. > > This causes a problem in the kernel tcp stack when having a > egress tc rule forwarding to a ingress tc rule. > The tcp stack sending packets on the device having the egress rule > will see the packets as not successfully transmitted (although they > actually were), will not advance it's internal state of sent data, > and packets returning on such tcp stream will be dropped by the tcp > stack with reason ack-of-unsent-data. See reproduction in [0] below. > Hm, but how is this return value propagated to egress? I checked tcf_mirred_act() code, but don't see how it is even used there. 318 err = tcf_mirred_forward(want_ingress, skb2); 319 if (err) { 320 out: 321 tcf_action_inc_overlimit_qstats(&m->common); 322 if (tcf_mirred_is_act_redirect(m_eaction)) 323 retval = TC_ACT_SHOT; 324 } 325 __this_cpu_dec(mirred_rec_level); 326 327 return retval; What am I missing? Also, the offending commit is very old and this configuration is not uncommon at all, how could we even not notice this for such a long time? Thanks.
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