[PATCH v12 net-next 4/5] selftests/net: Add bpf skb forwarding program

Wei Wang
2026-05-01T17:55:51Z

Add nk_redirect.bpf.c, a BPF program that forwards skbs matching some IPv6
prefix received on eth0 ifindex to a specified dev ifindex.
bpf_redirect_neigh() is used to make sure neighbor lookup is performed
and proper MAC addr is being used.

Signed-off-by: Wei Wang <weibunny@fb.com>
Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
Tested-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
.../drivers/net/hw/nk_redirect.bpf.c | 60 +++++++++++++++++++
1 file changed, 60 insertions(+)
create mode 100644 tools/testing/selftests/drivers/net/hw/nk_redirect.bpf.c

diff --git a/tools/testing/selftests/drivers/net/hw/nk_redirect.bpf.c b/tools/testing/selftests/drivers/net/hw/nk_redirect.bpf.c
new file mode 100644
index 000000000000..7ac9ffd50f15
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/hw/nk_redirect.bpf.c
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * BPF program for redirecting traffic using bpf_redirect_neigh().
+ * Unlike bpf_redirect() which preserves L2 headers, bpf_redirect_neigh()
+ * performs neighbor lookup and fills in the correct L2 addresses for the
+ * target interface. This is necessary when redirecting across different
+ * device types (e.g., from netdevsim to netkit).
+ */
+#include <linux/bpf.h>
+#include <linux/pkt_cls.h>
+#include <linux/if_ether.h>
+#include <linux/ipv6.h>
+#include <linux/in6.h>
+#include <bpf/bpf_endian.h>
+#include <bpf/bpf_helpers.h>
+
+#define TC_ACT_OK 0
+#define ETH_P_IPV6 0x86DD
+
+#define ctx_ptr(field) ((void *)(long)(field))
+
+#define v6_p64_equal(a, b) (a.s6_addr32[0] == b.s6_addr32[0] && \
+ a.s6_addr32[1] == b.s6_addr32[1])
+
+volatile __u32 redirect_ifindex;
+volatile __u8 ipv6_prefix[16];
+
+SEC("tc/ingress")
+int tc_redirect(struct __sk_buff *skb)
+{
+ void *data_end = ctx_ptr(skb->data_end);
+ void *data = ctx_ptr(skb->data);
+ struct in6_addr *match_prefix;
+ struct ipv6hdr *ip6h;
+ struct ethhdr *eth;
+
+ match_prefix = (struct in6_addr *)ipv6_prefix;
+
+ if (skb->protocol != bpf_htons(ETH_P_IPV6))
+ return TC_ACT_OK;
+
+ eth = data;
+ if ((void *)(eth + 1) > data_end)
+ return TC_ACT_OK;
+
+ ip6h = data + sizeof(struct ethhdr);
+ if ((void *)(ip6h + 1) > data_end)
+ return TC_ACT_OK;
+
+ if (!v6_p64_equal(ip6h->daddr, (*match_prefix)))
+ return TC_ACT_OK;
+
+ /*
+ * Use bpf_redirect_neigh() to perform neighbor lookup and fill in
+ * correct L2 addresses for the target interface.
+ */
+ return bpf_redirect_neigh(redirect_ifindex, NULL, 0, 0);
+}
+
+char __license[] SEC("license") = "GPL";
--
2.52.0