netfilter: nfnetlink_queue: fix OOB when mac header was cleared

stable inclusion
from linux-4.19.218
commit 779e36a18ecca58ad1637680feb7ca431458506b

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

[ Upstream commit 5648b5e1 ]

On 64bit platforms the MAC header is set to 0xffff on allocation and
also when a helper like skb_unset_mac_header() is called.

dev_parse_header may call skb_mac_header() which assumes valid mac offset:

 BUG: KASAN: use-after-free in eth_header_parse+0x75/0x90
 Read of size 6 at addr ffff8881075a5c05 by task nf-queue/1364
 Call Trace:
  memcpy+0x20/0x60
  eth_header_parse+0x75/0x90
  __nfqnl_enqueue_packet+0x1a61/0x3380
  __nf_queue+0x597/0x1300
  nf_queue+0xf/0x40
  nf_hook_slow+0xed/0x190
  nf_hook+0x184/0x440
  ip_output+0x1c0/0x2a0
  nf_reinject+0x26f/0x700
  nfqnl_recv_verdict+0xa16/0x18b0
  nfnetlink_rcv_msg+0x506/0xe70

The existing code only works if the skb has a mac header.

Fixes: 2c38de4c ("netfilter: fix looped (broad|multi)cast's MAC handling")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>