netfilter: flowtable: validate vlan header

In the Linux kernel, the following vulnerability has been resolved:

netfilter: flowtable: validate vlan header

Ensure there is sufficient room to access the protocol field of the

VLAN header, validate it once before the flowtable lookup.

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BUG: KMSAN: uninit-value in nf_flow_offload_inet_hook+0x45a/0x5f0 net/netfilter/nf_flow_table_inet.c:32

nf_flow_offload_inet_hook+0x45a/0x5f0 net/netfilter/nf_flow_table_inet.c:32

nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]

nf_hook_slow+0xf4/0x400 net/netfilter/core.c:626

nf_hook_ingress include/linux/netfilter_netdev.h:34 [inline]

nf_ingress net/core/dev.c:5440 [inline]