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Thu, 11 Jun 2026 01:09:13 -0700 (PDT) From: Sun Jian To: bpf@vger.kernel.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, davem@davemloft.net, kuba@kernel.org, hawk@kernel.org, john.fastabend@gmail.com, sdf@fomichev.me, shuah@kernel.org, jiayuan.chen@linux.dev, toke@redhat.com, menglong.dong@linux.dev, emil@etsalapatis.com, Sun Jian Subject: [PATCH bpf v4 1/2] bpf: Run generic devmap egress prog on private skb Date: Thu, 11 Jun 2026 16:08:48 +0800 Message-ID: <20260611080850.536996-2-sun.jian.kdev@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260611080850.536996-1-sun.jian.kdev@gmail.com> References: <20260611080850.536996-1-sun.jian.kdev@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Generic XDP devmap multi redirect uses skb_clone() for intermediate destinations and sends the last destination with the original skb. This can leave multiple destinations sharing the same packet data. This becomes visible after generic devmap egress-program support was added: a devmap egress program may mutate packet data, and another destination sharing the same data can observe that mutation. Native XDP broadcast redirect does not have this issue because xdpf_clone() copies the frame data for each destination. Generic XDP should provide the same per-destination isolation before running a devmap egress program. Fix this by making cloned skbs private before running the generic devmap egress program. Use skb_copy() instead of skb_unshare() so allocation failure does not consume the skb and the existing caller error paths keep their ownership semantics. Fixes: 2ea5eabaf04a ("bpf: devmap: Implement devmap prog execution for generic XDP") Suggested-by: Jiayuan Chen Suggested-by: Jakub Kicinski Reviewed-by: Toke Høiland-Jørgensen Signed-off-by: Sun Jian --- kernel/bpf/devmap.c | 41 +++++++++++++++++++++++++++++++---------- 1 file changed, 31 insertions(+), 10 deletions(-) diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c index cc0a43ebab6b..a3d6c60dbddb 100644 --- a/kernel/bpf/devmap.c +++ b/kernel/bpf/devmap.c @@ -512,35 +512,52 @@ static inline int __xdp_enqueue(struct net_device *dev, struct xdp_frame *xdpf, return 0; } -static u32 dev_map_bpf_prog_run_skb(struct sk_buff *skb, struct bpf_dtab_netdev *dst) +static int dev_map_bpf_prog_run_skb(struct sk_buff **pskb, + struct bpf_dtab_netdev *dst, + u32 *act) { + struct sk_buff *skb = *pskb; struct xdp_txq_info txq = { .dev = dst->dev }; struct xdp_buff xdp; - u32 act; - if (!dst->xdp_prog) - return XDP_PASS; + if (!dst->xdp_prog) { + *act = XDP_PASS; + return 0; + } + + if (skb_cloned(skb)) { + struct sk_buff *nskb; + + nskb = skb_copy(skb, GFP_ATOMIC); + if (!nskb) + return -ENOMEM; + + nskb->mac_len = skb->mac_len; + consume_skb(skb); + skb = nskb; + *pskb = nskb; + } __skb_pull(skb, skb->mac_len); xdp.txq = &txq; - act = bpf_prog_run_generic_xdp(skb, &xdp, dst->xdp_prog); - switch (act) { + *act = bpf_prog_run_generic_xdp(skb, &xdp, dst->xdp_prog); + switch (*act) { case XDP_PASS: __skb_push(skb, skb->mac_len); break; default: - bpf_warn_invalid_xdp_action(NULL, dst->xdp_prog, act); + bpf_warn_invalid_xdp_action(NULL, dst->xdp_prog, *act); fallthrough; case XDP_ABORTED: - trace_xdp_exception(dst->dev, dst->xdp_prog, act); + trace_xdp_exception(dst->dev, dst->xdp_prog, *act); fallthrough; case XDP_DROP: kfree_skb(skb); break; } - return act; + return 0; } int dev_xdp_enqueue(struct net_device *dev, struct xdp_frame *xdpf, @@ -700,6 +717,7 @@ int dev_map_enqueue_multi(struct xdp_frame *xdpf, struct net_device *dev_rx, int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb, const struct bpf_prog *xdp_prog) { + u32 act; int err; err = xdp_ok_fwd_dev(dst->dev, skb->len); @@ -710,7 +728,10 @@ int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb, * return 0 even if packet is dropped. Helper below takes care of * freeing skb. */ - if (dev_map_bpf_prog_run_skb(skb, dst) != XDP_PASS) + err = dev_map_bpf_prog_run_skb(&skb, dst, &act); + if (err) + return err; + if (act != XDP_PASS) return 0; skb->dev = dst->dev; -- 2.43.0