netdev - [PATCH net-next] samples/bpf: Fix MAC address swapping in xdp2

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Message-Id: <20221015213050.65222-1-gerhard@engleder-embedded.com>
Date:   Sat, 15 Oct 2022 23:30:50 +0200
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     andrew.gospodarek@...adcom.com, ast@...nel.org,
        daniel@...earbox.net, davem@...emloft.net, kuba@...nel.org,
        hawk@...nel.org, john.fastabend@...il.com
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Gerhard Engleder <gerhard@...leder-embedded.com>
Subject: [PATCH net-next] samples/bpf: Fix MAC address swapping in xdp2_kern

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@...leder-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