netdev - [PATCH RFC bpf-next 6/9] bpf: Make bpf_skb_adjust

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Message-Id: <20250929-skb-meta-rx-path-v1-6-de700a7ab1cb@cloudflare.com>
Date: Mon, 29 Sep 2025 16:09:11 +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 6/9] bpf: Make bpf_skb_adjust_room
 metadata-safe

bpf_skb_adjust_room() may push or pull bytes from skb->data. In both cases,
skb metadata must be moved accordingly to stay accessible.

Replace existing memmove() calls, which only move payload, with a helper
that also handles metadata. Reserve enough space for metadata to fit after
skb_push.

Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 net/core/filter.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 2af0a5f1d748..030349179b5a 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3251,11 +3251,11 @@ static void bpf_skb_change_protocol(struct sk_buff *skb, u16 proto)
 
 static int bpf_skb_generic_push(struct sk_buff *skb, u32 off, u32 len)
 {
-	/* Caller already did skb_cow() with len as headroom,
+	/* Caller already did skb_cow() with meta_len+len as headroom,
 	 * so no need to do it here.
 	 */
 	skb_push(skb, len);
-	memmove(skb->data, skb->data + len, off);
+	skb_postpush_data_move(skb, len, off);
 	memset(skb->data + off, 0, len);
 
 	/* No skb_postpush_rcsum(skb, skb->data + off, len)
@@ -3279,7 +3279,7 @@ static int bpf_skb_generic_pop(struct sk_buff *skb, u32 off, u32 len)
 	old_data = skb->data;
 	__skb_pull(skb, len);
 	skb_postpull_rcsum(skb, old_data + off, len);
-	memmove(skb->data, old_data, off);
+	skb_postpull_data_move(skb, len, off);
 
 	return 0;
 }
@@ -3487,6 +3487,7 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
 	u8 inner_mac_len = flags >> BPF_ADJ_ROOM_ENCAP_L2_SHIFT;
 	bool encap = flags & BPF_F_ADJ_ROOM_ENCAP_L3_MASK;
 	u16 mac_len = 0, inner_net = 0, inner_trans = 0;
+	const u8 meta_len = skb_metadata_len(skb);
 	unsigned int gso_type = SKB_GSO_DODGY;
 	int ret;
 
@@ -3497,7 +3498,7 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
 			return -ENOTSUPP;
 	}
 
-	ret = skb_cow_head(skb, len_diff);
+	ret = skb_cow_head(skb, meta_len + len_diff);
 	if (unlikely(ret < 0))
 		return ret;
 

-- 
2.43.0