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net: xdp: pull ethernet header off packet after computing skb->protocol 

When an XDP program changes the ethernet header protocol field,
eth_type_trans is used to recalculate skb->protocol. In order for
eth_type_trans to work correctly, the ethernet header must actually be
part of the skb data segment, so the code first pushes that onto the
head of the skb. However, it subsequently forgets to pull it back off,
making the behavior of the passed-on packet inconsistent between the
protocol modifying case and the static protocol case. This patch fixes
the issue by simply pulling the ethernet header back off of the skb
head.

Fixes: 2972495699 ("net: fix generic XDP to handle if eth header was mangled")
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason A. Donenfeld 2020-08-15 09:29:30 +02:00 committed by David S. Miller
parent d0f5c7076e
commit f8414a8d88
1 changed files with 1 additions and 0 deletions
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1
net/core/dev.c
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@ -4676,6 +4676,7 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
(orig_bcast != is_multicast_ether_addr_64bits(eth->h_dest))) {
__skb_push(skb, ETH_HLEN);
skb->protocol = eth_type_trans(skb, skb->dev);
__skb_pull(skb, ETH_HLEN);
}
switch (act) {