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Mon, 16 Mar 2026 14:11:12 -0700 (PDT) Received: from majuu.waya ([70.50.89.69]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-89c53374573sm27356266d6.7.2026.03.16.14.11.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Mar 2026 14:11:11 -0700 (PDT) From: Jamal Hadi Salim To: netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, jiri@resnulli.us, stephen@networkplumber.org, victor@mojatatu.com, will@willsroot.io, xmei5@asu.edu, pctammela@mojatatu.com, savy@syst3mfailure.io, kuniyu@google.com, toke@toke.dk, willemdebruijnkernel@gmail.com, Jamal Hadi Salim Subject: [PATCH net v2 2/6] net/sched: Fix ethx:ingress -> ethy:egress -> ethx:ingress mirred loop Date: Mon, 16 Mar 2026 17:10:48 -0400 Message-Id: <20260316211052.332383-3-jhs@mojatatu.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260316211052.332383-1-jhs@mojatatu.com> References: <20260316211052.332383-1-jhs@mojatatu.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When mirred redirects to ingress (from either ingress or egress) the loop state from sched_mirred_dev array dev is lost because of 1) the packet deferral into the backlog and 2) the fact the sched_mirred_dev array is cleared. In such cases, if there was a loop we won't discover it. Here's a simple test to reproduce: ip a add dev port0 10.10.10.11/24 tc qdisc add dev port0 clsact tc filter add dev port0 egress protocol ip \ prio 10 matchall action mirred ingress redirect dev port1 tc qdisc add dev port1 clsact tc filter add dev port1 ingress protocol ip \ prio 10 matchall action mirred egress redirect dev port0 ping -c 1 -W0.01 10.10.10.10 Another bug fixed here is a false positive, example current code will claim this is a loop when its not: tc qdisc add dev port0 clsact tc qdisc add dev port1 clsact # port0 ingress --> port1 ingress tc filter add dev port0 ingress protocol ip \ prio 10 matchall action mirred ingress redirect dev port1 # port1 ingress --> port1 egress tc filter add dev port1 ingress protocol ip \ prio 10 matchall action mirred egress redirect dev port1 #port1 egress --> port0 egress tc filter add dev port1 egress protocol ip \ prio 11 matchall action mirred egress redirect dev port0 ping -c 1 -W0.01 10.10.10.10 And see the ping fail Fixes: fe946a751d9b ("net/sched: act_mirred: add loop detection") Signed-off-by: Jamal Hadi Salim --- net/sched/act_mirred.c | 45 ++++++++++++++++++++++++++---------------- 1 file changed, 28 insertions(+), 17 deletions(-) diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c index 05e0b14b5773..9ef261e19e40 100644 --- a/net/sched/act_mirred.c +++ b/net/sched/act_mirred.c @@ -26,6 +26,8 @@ #include #include +#define MIRRED_DEFER_LIMIT 3 + static LIST_HEAD(mirred_list); static DEFINE_SPINLOCK(mirred_list_lock); @@ -234,12 +236,15 @@ tcf_mirred_forward(bool at_ingress, bool want_ingress, struct sk_buff *skb) { int err; - if (!want_ingress) + if (!want_ingress) { err = tcf_dev_queue_xmit(skb, dev_queue_xmit); - else if (!at_ingress) - err = netif_rx(skb); - else - err = netif_receive_skb(skb); + } else { + skb->ttl++; + if (!at_ingress) + err = netif_rx(skb); + else + err = netif_receive_skb(skb); + } return err; } @@ -426,6 +431,7 @@ TC_INDIRECT_SCOPE int tcf_mirred_act(struct sk_buff *skb, struct netdev_xmit *xmit; bool m_mac_header_xmit; struct net_device *dev; + bool want_ingress; int i, m_eaction; u32 blockid; @@ -434,7 +440,8 @@ TC_INDIRECT_SCOPE int tcf_mirred_act(struct sk_buff *skb, #else xmit = this_cpu_ptr(&softnet_data.xmit); #endif - if (unlikely(xmit->sched_mirred_nest >= MIRRED_NEST_LIMIT)) { + if (unlikely(xmit->sched_mirred_nest >= MIRRED_NEST_LIMIT || + skb->ttl >= MIRRED_DEFER_LIMIT)) { net_warn_ratelimited("Packet exceeded mirred recursion limit on dev %s\n", netdev_name(skb->dev)); return TC_ACT_SHOT; @@ -453,23 +460,27 @@ TC_INDIRECT_SCOPE int tcf_mirred_act(struct sk_buff *skb, tcf_action_inc_overlimit_qstats(&m->common); return retval; } - for (i = 0; i < xmit->sched_mirred_nest; i++) { - if (xmit->sched_mirred_dev[i] != dev) - continue; - pr_notice_once("tc mirred: loop on device %s\n", - netdev_name(dev)); - tcf_action_inc_overlimit_qstats(&m->common); - return retval; - } - xmit->sched_mirred_dev[xmit->sched_mirred_nest++] = dev; + m_eaction = READ_ONCE(m->tcfm_eaction); + want_ingress = tcf_mirred_act_wants_ingress(m_eaction); + if (!want_ingress) { + for (i = 0; i < xmit->sched_mirred_nest; i++) { + if (xmit->sched_mirred_dev[i] != dev) + continue; + pr_notice_once("tc mirred: loop on device %s\n", + netdev_name(dev)); + tcf_action_inc_overlimit_qstats(&m->common); + return retval; + } + xmit->sched_mirred_dev[xmit->sched_mirred_nest++] = dev; + } m_mac_header_xmit = READ_ONCE(m->tcfm_mac_header_xmit); - m_eaction = READ_ONCE(m->tcfm_eaction); retval = tcf_mirred_to_dev(skb, m, dev, m_mac_header_xmit, m_eaction, retval); - xmit->sched_mirred_nest--; + if (!want_ingress) + xmit->sched_mirred_nest--; return retval; } -- 2.34.1