Use whitelist instead of a blacklist and allow only a small set of
fields that might be relevant in the context of flow dissector:
* data
* data_end
* flow_keys
This is required for the eth_get_headlen case where we have only a
chunk of data to dissect (i.e. trying to read the other skb fields
doesn't make sense).
Note, that it is a breaking API change! However, we've provided
flow_keys->n_proto as a substitute for skb->protocol; and there is
no need to manually handle skb->vlan_present. So even if we
break somebody, the migration is trivial. Unfortunately, we can't
support eth_get_headlen use-case without those breaking changes.
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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