macvtap: make sure neighbour code can push ethernet header
[ Upstream commit 2f1d8b9e ] Brian reported crashes using IPv6 traffic with macvtap/veth combo. I tracked the crashes in neigh_hh_output() -> memcpy(skb->data - HH_DATA_MOD, hh->hh_data, HH_DATA_MOD); Neighbour code assumes headroom to push Ethernet header is at least 16 bytes. It appears macvtap has only 14 bytes available on arches where NET_IP_ALIGN is 0 (like x86) Effect is a corruption of 2 bytes right before skb->head, and possible crashes if accessing non existing memory. This fix should also increase IPv4 performance, as paranoid code in ip_finish_output2() wont have to call skb_realloc_headroom() Reported-by: Brian Rak <brak@vultr.com> Tested-by: Brian Rak <brak@vultr.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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