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)