net: change skb->mac_header when Generic XDP calls adjust_head

[ 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@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/core/dev.c b/net/core/dev.c
index 86b4b0a79e7abb6554af07ed81a7b91e2f8762bf..6fa30a4c60eff0efa046b3c69ba7b0b2c21a4b5f 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4408,6 +4408,7 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
                __skb_pull(skb, off);
        else if (off < 0)
                __skb_push(skb, -off);
+       skb->mac_header += off;
 
        switch (act) {
        case XDP_TX: