Re: [PATCH net-next 8/9] selftests/net: Add bpf skb forwarding program

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Mon, Feb 23, 2026 at 04:24:08PM -0800, Wei Wang wrote:
> 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>
> ---
>  .../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";
> -- 
> 2.47.3
> 

Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
Tested-by: Bobby Eshleman <bobbyeshleman@meta.com>