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[69.172.89.235]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35e4e2dbf47sm8084388a91.0.2026.04.13.01.49.30 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 13 Apr 2026 01:49:32 -0700 (PDT) From: Dudu Lu To: netdev@vger.kernel.org Cc: jhs@mojatatu.com, jiri@resnulli.us, Dudu Lu Subject: [PATCH] net/sched: act_mirred: fix wrong device for mac_header_xmit check in tcf_blockcast_redir Date: Mon, 13 Apr 2026 16:49:27 +0800 Message-Id: <20260413084927.71353-1-phx0fer@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-145) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In tcf_blockcast_redir(), when iterating block ports to redirect packets to multiple devices, the mac_header_xmit flag is queried from the wrong device. The loop sends to dev_prev but queries dev_is_mac_header_xmit(dev) — which is the NEXT device in the iteration, not the one being sent to. This causes tcf_mirred_to_dev() to make incorrect decisions about whether to push or pull the MAC header. When the block contains mixed device types (e.g., an ethernet veth and a tunnel device), intermediate devices get the wrong mac_header_xmit flag, leading to skb header corruption. In the worst case, skb_push_rcsum with an incorrect mac_len can exhaust headroom and panic. The last device in the loop is handled correctly (line 365-366 uses dev_is_mac_header_xmit(dev_prev)), confirming this is a copy-paste oversight for the intermediate devices. Fix by using dev_prev instead of dev for the mac_header_xmit query, consistent with the device actually being sent to. Fixes: 42f39036cda8 ("net/sched: act_mirred: Allow mirred to block") Signed-off-by: Dudu Lu --- net/sched/act_mirred.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c index 05e0b14b5773..2c5a7a321a94 100644 --- a/net/sched/act_mirred.c +++ b/net/sched/act_mirred.c @@ -354,7 +354,7 @@ static int tcf_blockcast_redir(struct sk_buff *skb, struct tcf_mirred *m, goto assign_prev; tcf_mirred_to_dev(skb, m, dev_prev, - dev_is_mac_header_xmit(dev), + dev_is_mac_header_xmit(dev_prev), mirred_eaction, retval); assign_prev: dev_prev = dev; -- 2.39.3 (Apple Git-145)