From 1eb0dc458b6e8efc3a9cf02ec3ccd0f20576910e Mon Sep 17 00:00:00 2001 From: Pablo Neira Ayuso Date: Thu, 30 Apr 2026 16:49:48 +0200 Subject: [PATCH] netfilter: flowtable: ensure sufficient headroom in xmit path commit ef4f741e8627512cb8c82f59a1fc7aacd854aadf upstream. Check for headroom and call skb_expand_head() like in the IP output path to ensure there is sufficient headroom for the mac header when forwarding this packet as suggested by sashiko. Fixes: b5964aac51e0 ("netfilter: flowtable: consolidate xmit path") Signed-off-by: Pablo Neira Ayuso Signed-off-by: Greg Kroah-Hartman --- net/netfilter/nf_flow_table_ip.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c index 4dcc30e7f9e5..1be506a175af 100644 --- a/net/netfilter/nf_flow_table_ip.c +++ b/net/netfilter/nf_flow_table_ip.c @@ -343,8 +343,17 @@ struct nf_flow_xmit { static unsigned int nf_flow_queue_xmit(struct net *net, struct sk_buff *skb, struct nf_flow_xmit *xmit) { - skb->dev = xmit->outdev; - dev_hard_header(skb, skb->dev, ntohs(skb->protocol), + struct net_device *dev = xmit->outdev; + unsigned int hh_len = LL_RESERVED_SPACE(dev); + + if (unlikely(skb_headroom(skb) < hh_len && dev->header_ops)) { + skb = skb_expand_head(skb, hh_len); + if (!skb) + return NF_STOLEN; + } + + skb->dev = dev; + dev_hard_header(skb, dev, ntohs(skb->protocol), xmit->dest, xmit->source, skb->len); dev_queue_xmit(skb);