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[79.184.211.13]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-63e7ef6c061sm4172035a12.0.2025.10.26.07.18.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 26 Oct 2025 07:18:37 -0700 (PDT) From: Jakub Sitnicki Date: Sun, 26 Oct 2025 15:18:21 +0100 Subject: [PATCH bpf-next v3 01/16] net: Helper to move packet data and metadata after skb_push/pull Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251026-skb-meta-rx-path-v3-1-37cceebb95d3@cloudflare.com> References: <20251026-skb-meta-rx-path-v3-0-37cceebb95d3@cloudflare.com> In-Reply-To: <20251026-skb-meta-rx-path-v3-0-37cceebb95d3@cloudflare.com> To: bpf@vger.kernel.org Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Martin KaFai Lau , Daniel Borkmann , John Fastabend , Stanislav Fomichev , Alexei Starovoitov , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Hao Luo , Jiri Olsa , Arthur Fabre , Jesper Dangaard Brouer , netdev@vger.kernel.org, kernel-team@cloudflare.com X-Mailer: b4 0.15-dev-07fe9 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 --- include/linux/skbuff.h | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index fb3fec9affaa..41365de55e69 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -4561,6 +4561,81 @@ 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 -- 2.43.0