netfilter: nf_tables: nft_fib: consistent l3mdev handling

netfilter: nf_tables: nft_fib: consistent l3mdev handling

fib has two modes:
1. Obtain output device according to source or destination address
2. Obtain the type of the address, e.g. local, unicast, multicast.

'fib daddr type' should return 'local' if the address is configured
in this netns or unicast otherwise.

'fib daddr . iif type' should return 'local' if the address is configured
on the input interface or unicast otherwise, i.e. more restrictive.

However, if the interface is part of a VRF, then 'fib daddr type'
returns unicast even if the address is configured on the incoming
interface.

This is broken for both ipv4 and ipv6.

In the ipv4 case, inet_dev_addr_type must only be used if the
'iif' or 'oif' (strict mode) was requested.

Else inet_addr_type_dev_table() needs to be used and the correct
dev argument must be passed as well so the correct fib (vrf) table
is used.

In the ipv6 case, the bug is similar, without strict mode, dev is NULL
so .flowi6_l3mdev will be set to 0.

Add a new 'nft_fib_l3mdev_master_ifindex_rcu()' helper and use that
to init the .l3mdev structure member.

For ipv6, use it from nft_fib6_flowi_init() which gets called from
both the 'type' and the 'route' mode eval functions.

This provides consistent behaviour for all modes for both ipv4 and ipv6:
If strict matching is requested, the input respectively output device
of the netfilter hooks is used.

Otherwise, use skb->dev to obtain the l3mdev ifindex.

Without this, most type checks in updated nft_fib.sh selftest fail:

  FAIL: did not find veth0 . 10.9.9.1 . local in fibtype4
  FAIL: did not find veth0 . dead:1::1 . local in fibtype6
  FAIL: did not find veth0 . dead:9::1 . local in fibtype6
  FAIL: did not find tvrf . 10.0.1.1 . local in fibtype4
  FAIL: did not find tvrf . 10.9.9.1 . local in fibtype4
  FAIL: did not find tvrf . dead:1::1 . local in fibtype6
  FAIL: did not find tvrf . dead:9::1 . local in fibtype6
  FAIL: fib expression address types match (iif in vrf)

(fib errounously returns 'unicast' for all of them, even
 though all of these addresses are local to the vrf).

Fixes: f6d0cbcf09c5 ("netfilter: nf_tables: add fib expression")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>