netdev - [PATCH RFC bpf-next 5/9] bpf: Make bpf_skb_vlan

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Message-Id: <20250929-skb-meta-rx-path-v1-5-de700a7ab1cb@cloudflare.com>
Date: Mon, 29 Sep 2025 16:09:10 +0200
From: Jakub Sitnicki <jakub@...udflare.com>
To: bpf@...r.kernel.org
Cc: netdev@...r.kernel.org, kernel-team@...udflare.com
Subject: [PATCH RFC bpf-next 5/9] bpf: Make bpf_skb_vlan_push helper
 metadata-safe

Use the metadata-aware helper to move packet bytes after skb_push(),
ensuring metadata remains valid after calling the BPF helper.

Also, take care to reserve sufficient headroom for metadata to fit.

Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 include/linux/if_vlan.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 4ecc2509b0d4..b0e1f57d51aa 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -355,16 +355,17 @@ static inline int __vlan_insert_inner_tag(struct sk_buff *skb,
 					  __be16 vlan_proto, u16 vlan_tci,
 					  unsigned int mac_len)
 {
+	const u8 meta_len = mac_len > ETH_HLEN ? skb_metadata_len(skb) : 0;
 	struct vlan_ethhdr *veth;
 
-	if (skb_cow_head(skb, VLAN_HLEN) < 0)
+	if (skb_cow_head(skb, meta_len + VLAN_HLEN) < 0)
 		return -ENOMEM;
 
 	skb_push(skb, VLAN_HLEN);
 
 	/* Move the mac header sans proto to the beginning of the new header. */
 	if (likely(mac_len > ETH_TLEN))
-		memmove(skb->data, skb->data + VLAN_HLEN, mac_len - ETH_TLEN);
+		skb_postpush_data_move(skb, VLAN_HLEN, mac_len - ETH_TLEN);
 	if (skb_mac_header_was_set(skb))
 		skb->mac_header -= VLAN_HLEN;
 

-- 
2.43.0