netdev - [PATCH net-next 1/2] igc: AF_XDP zero-copy metadata adjust breaks SKBs on XDP

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Date:   Mon, 15 Nov 2021 21:36:25 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <borkmann@...earbox.net>,
        anthony.l.nguyen@...el.com, jesse.brandeburg@...el.com,
        intel-wired-lan@...ts.osuosl.org, magnus.karlsson@...el.com,
        bjorn@...nel.org
Subject: [PATCH net-next 1/2] igc: AF_XDP zero-copy metadata adjust breaks
 SKBs on XDP_PASS

Driver already implicitly supports XDP metadata access in AF_XDP
zero-copy mode, as xsk_buff_pool's xp_alloc() naturally set xdp_buff
data_meta equal data.

This works fine for XDP and AF_XDP, but if a BPF-prog adjust via
bpf_xdp_adjust_meta() and choose to call XDP_PASS, then igc function
igc_construct_skb_zc() will construct an invalid SKB packet. The
function correctly include the xdp->data_meta area in the memcpy, but
forgot to pull header to take metasize into account.

Fixes: fc9df2a0b520 ("igc: Enable RX via AF_XDP zero-copy")
Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 drivers/net/ethernet/intel/igc/igc_main.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 8e448288ee26..76b0a7311369 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -2448,8 +2448,10 @@ static struct sk_buff *igc_construct_skb_zc(struct igc_ring *ring,
 
 	skb_reserve(skb, xdp->data_meta - xdp->data_hard_start);
 	memcpy(__skb_put(skb, totalsize), xdp->data_meta, totalsize);
-	if (metasize)
+	if (metasize) {
 		skb_metadata_set(skb, metasize);
+		__skb_pull(skb, metasize);
+	}
 
 	return skb;
 }