[PATCH net 4/6] net: stmmac: copy XDP metadata in AF_XDP zero-copy RX

[Lorenzo Bianconi <lorenzo.bianconi@oss.qualcomm.com>]

stmmac_construct_skb_zc() reserves headroom for the XDP metadata and
records the length reported by the XDP program, but only copies the
packet data starting at xdp->data. The bytes in
[xdp->data_meta, xdp->data) are never copied into the new skb, so the
skb advertises metadata that is not there: after eth_type_trans()
anchors mac_header, data_meta points at uninitialized headroom instead
of what the program wrote.

Copy the metadata together with the packet data starting at
xdp->data_meta, leaving skb->data at the start of the frame and the
metadata immediately before it, and record its length. This keeps
data_meta valid for the stack and TC BPF, and keeps the metadata aligned
when stmmac_rx_vlan() relocates it with the MAC header while stripping a
tag.

Fixes: bba2556efad6 ("net: stmmac: Enable RX via AF_XDP zero-copy")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@oss.qualcomm.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 30a2774d722b..8a2faf50d695 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5519,7 +5519,8 @@ static struct sk_buff *stmmac_construct_skb_zc(struct stmmac_channel *ch,
 		return NULL;
 
 	skb_reserve(skb, xdp->data - xdp->data_hard_start);
-	memcpy(__skb_put(skb, datasize), xdp->data, datasize);
+	__skb_put(skb, datasize);
+	memcpy(skb->data - metasize, xdp->data_meta, datasize + metasize);
 	if (metasize)
 		skb_metadata_set(skb, metasize);
 

-- 
2.56.0