netdev - [PATCH bpf-next v2 05/15] bpf: Make bpf_skb_vlan

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Message-Id: <20251019-skb-meta-rx-path-v2-5-f9a58f3eb6d6@cloudflare.com>
Date: Sun, 19 Oct 2025 14:45:29 +0200
From: Jakub Sitnicki <jakub@...udflare.com>
To: bpf@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Daniel Borkmann <daniel@...earbox.net>, 
 John Fastabend <john.fastabend@...il.com>, 
 Stanislav Fomichev <sdf@...ichev.me>, Alexei Starovoitov <ast@...nel.org>, 
 Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>, 
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, 
 KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>, 
 Jiri Olsa <jolsa@...nel.org>, Arthur Fabre <arthur@...hurfabre.com>, 
 netdev@...r.kernel.org, kernel-team@...udflare.com
Subject: [PATCH bpf-next v2 05/15] 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..f7f34eb15e06 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_TLEN ? 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