netfilter: nft_inner: validate mandatory meta and payload

[ Upstream commit c4ab9da8 ]

Check for mandatory netlink attributes in payload and meta expression
when used embedded from the inner expression, otherwise NULL pointer
dereference is possible from userspace.

Fixes: a150d122 ("netfilter: nft_meta: add inner match support")
Fixes: 3a07327d ("netfilter: nft_inner: support for inner tunnel header matching")
Signed-off-by: Davide Ornaghi <d.ornaghi97@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>