[PATCH net-next] samples/bpf: Fix MAC address swapping in xdp2_kern

[PATCH net-next] samples/bpf: Fix MAC address swapping in xdp2_kern

[Gerhard Engleder]

xdp2_kern rewrites and forwards packets out on the same interface.
Forwarding still works but rewrite got broken when xdp multibuffer
support has been added.

With xdp multibuffer a local copy of the packet has been introduced. The
MAC address is now swapped in the local copy, but the local copy in not
written back.

Fix MAC address swapping be adding write back of modified packet.

Fixes: 772251742262 ("samples/bpf: fixup some tools to be able to support xdp multibuffer")
Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
---
 samples/bpf/xdp2_kern.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/samples/bpf/xdp2_kern.c b/samples/bpf/xdp2_kern.c
index 3332ba6bb95f..67804ecf7ce3 100644
--- a/samples/bpf/xdp2_kern.c
+++ b/samples/bpf/xdp2_kern.c
@@ -112,6 +112,10 @@ int xdp_prog1(struct xdp_md *ctx)
 
 	if (ipproto == IPPROTO_UDP) {
 		swap_src_dst_mac(data);
+
+		if (bpf_xdp_store_bytes(ctx, 0, pkt, sizeof(pkt)))
+			return rc;
+
 		rc = XDP_TX;
 	}
 
-- 
2.30.2

Re: [PATCH net-next] samples/bpf: Fix MAC address swapping in xdp2_kern

[Andy Gospodarek]

On Sat, Oct 15, 2022 at 11:30:50PM +0200, Gerhard Engleder wrote:
> xdp2_kern rewrites and forwards packets out on the same interface.
> Forwarding still works but rewrite got broken when xdp multibuffer
> support has been added.
> 
> With xdp multibuffer a local copy of the packet has been introduced. The
> MAC address is now swapped in the local copy, but the local copy in not
> written back.
> 
> Fix MAC address swapping be adding write back of modified packet.
> 

Nice catch!  Thanks for posting this.

> Fixes: 772251742262 ("samples/bpf: fixup some tools to be able to support xdp multibuffer")
> Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Reviewed-by: Andy Gospodarek <gospo@broadcom.com>

> ---
>  samples/bpf/xdp2_kern.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/samples/bpf/xdp2_kern.c b/samples/bpf/xdp2_kern.c
> index 3332ba6bb95f..67804ecf7ce3 100644
> --- a/samples/bpf/xdp2_kern.c
> +++ b/samples/bpf/xdp2_kern.c
> @@ -112,6 +112,10 @@ int xdp_prog1(struct xdp_md *ctx)
>  
>  	if (ipproto == IPPROTO_UDP) {
>  		swap_src_dst_mac(data);
> +
> +		if (bpf_xdp_store_bytes(ctx, 0, pkt, sizeof(pkt)))
> +			return rc;
> +
>  		rc = XDP_TX;
>  	}
>  
> -- 
> 2.30.2
> 

Re: [PATCH net-next] samples/bpf: Fix MAC address swapping in xdp2_kern

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Martin KaFai Lau <martin.lau@kernel.org>:

On Sat, 15 Oct 2022 23:30:50 +0200 you wrote:
> xdp2_kern rewrites and forwards packets out on the same interface.
> Forwarding still works but rewrite got broken when xdp multibuffer
> support has been added.
> 
> With xdp multibuffer a local copy of the packet has been introduced. The
> MAC address is now swapped in the local copy, but the local copy in not
> written back.
> 
> [...]

Here is the summary with links:
  - [net-next] samples/bpf: Fix MAC address swapping in xdp2_kern
    https://git.kernel.org/bpf/bpf-next/c/7a698edf954c

You are awesome, thank you!
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