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

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>

diff --git a/net/core/dev.c b/net/core/dev.c
index fb766d906148e7d1e85a654eaf6048c1cdf49364..9a2254f9802f325de65fa569ceeaa5411a31dfcc 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3892,6 +3892,7 @@ 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_REDIRECT: