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net: Helper to move packet data and metadata after skb_push/pull

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Lay groundwork for fixing BPF helpers available to TC(X) programs.

When skb_push() or skb_pull() is called in a TC(X) ingress BPF program, the
skb metadata must be kept in front of the MAC header. Otherwise, BPF
programs using the __sk_buff->data_meta pseudo-pointer lose access to it.

Introduce a helper that moves both metadata and a specified number of
packet data bytes together, suitable as a drop-in replacement for
memmove().

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20251105-skb-meta-rx-path-v4-1-5ceb08a9b37b@cloudflare.com
This commit is contained in:
Jakub Sitnicki
2025-11-05 21:19:38 +01:00
committed by Martin KaFai Lau
parent a0c3aefb08
commit 8989d328df
1 changed files with 75 additions and 0 deletions
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75
include/linux/skbuff.h
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@@ -4564,6 +4564,81 @@ static inline void skb_metadata_clear(struct sk_buff *skb)
skb_metadata_set(skb, 0);
}
/**
* skb_data_move - Move packet data and metadata after skb_push() or skb_pull().
* @skb: packet to operate on
* @len: number of bytes pushed or pulled from &sk_buff->data
* @n: number of bytes to memmove() from pre-push/pull &sk_buff->data
*
* Moves @n bytes of packet data, can be zero, and all bytes of skb metadata.
*
* Assumes metadata is located immediately before &sk_buff->data prior to the
* push/pull, and that sufficient headroom exists to hold it after an
* skb_push(). Otherwise, metadata is cleared and a one-time warning is issued.
*
* Prefer skb_postpull_data_move() or skb_postpush_data_move() to calling this
* helper directly.
*/
static inline void skb_data_move(struct sk_buff *skb, const int len,
const unsigned int n)
{
const u8 meta_len = skb_metadata_len(skb);
u8 *meta, *meta_end;
if (!len || (!n && !meta_len))
return;
if (!meta_len)
goto no_metadata;
meta_end = skb_metadata_end(skb);
meta = meta_end - meta_len;
if (WARN_ON_ONCE(meta_end + len != skb->data ||
meta_len > skb_headroom(skb))) {
skb_metadata_clear(skb);
goto no_metadata;
}
memmove(meta + len, meta, meta_len + n);
return;
no_metadata:
memmove(skb->data, skb->data - len, n);
}
/**
* skb_postpull_data_move - Move packet data and metadata after skb_pull().
* @skb: packet to operate on
* @len: number of bytes pulled from &sk_buff->data
* @n: number of bytes to memmove() from pre-pull &sk_buff->data
*
* See skb_data_move() for details.
*/
static inline void skb_postpull_data_move(struct sk_buff *skb,
const unsigned int len,
const unsigned int n)
{
DEBUG_NET_WARN_ON_ONCE(len > INT_MAX);
skb_data_move(skb, len, n);
}
/**
* skb_postpush_data_move - Move packet data and metadata after skb_push().
* @skb: packet to operate on
* @len: number of bytes pushed onto &sk_buff->data
* @n: number of bytes to memmove() from pre-push &sk_buff->data
*
* See skb_data_move() for details.
*/
static inline void skb_postpush_data_move(struct sk_buff *skb,
const unsigned int len,
const unsigned int n)
{
DEBUG_NET_WARN_ON_ONCE(len > INT_MAX);
skb_data_move(skb, -len, n);
}
struct sk_buff *skb_clone_sk(struct sk_buff *skb);
#ifdef CONFIG_NETWORK_PHY_TIMESTAMPING