linux-kernel - [PATCH 4.13 026/160] net: change skb->mac_header when Generic XDP calls adjust

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Date:   Tue, 10 Oct 2017 21:49:14 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Edward Cree <ecree@...arflare.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.13 026/160] net: change skb->mac_header when Generic XDP calls adjust_head

4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Edward Cree <ecree@...arflare.com>

[ Upstream commit 92dd5452c1be873a1193561f4f691763103d22ac ]

Since XDP's view of the packet includes the MAC header, moving the start-
 of-packet with bpf_xdp_adjust_head needs to also update the offset of the
 MAC header (which is relative to skb->head, not to the skb->data that was
 changed).
Without this, tcpdump sees packets starting from the old MAC header rather
 than the new one, at least in my tests on the loopback device.

Fixes: b5cdae3291f7 ("net: Generic XDP")
Signed-off-by: Edward Cree <ecree@...arflare.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/dev.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4408,6 +4408,7 @@ static u32 netif_receive_generic_xdp(str
 		__skb_pull(skb, off);
 	else if (off < 0)
 		__skb_push(skb, -off);
+	skb->mac_header += off;

 	switch (act) {
 	case XDP_TX: