netfilter: nf_tables: add fib expression

Add FIB expression, supported for ipv4, ipv6 and inet family (the latter
just dispatches to ipv4 or ipv6 one based on nfproto).

Currently supports fetching output interface index/name and the
rtm_type associated with an address.

This can be used for adding path filtering. rtm_type is useful
to e.g. enforce a strong-end host model where packets
are only accepted if daddr is configured on the interface the
packet arrived on.

The fib expression is a native nftables alternative to the
xtables addrtype and rp_filter matches.

FIB result order for oif/oifname retrieval is as follows:
 - if packet is local (skb has rtable, RTF_LOCAL set, this
   will also catch looped-back multicast packets), set oif to
   the loopback interface.
 - if fib lookup returns an error, or result points to local,
   store zero result.  This means '--local' option of -m rpfilter
   is not supported. It is possible to use 'fib type local' or add
   explicit saddr/daddr matching rules to create exceptions if this
   is really needed.
 - store result in the destination register.
   In case of multiple routes, search set for desired oif in case
   strict matching is requested.

ipv4 and ipv6 behave fib expressions are supposed to behave the same.

[ I have collapsed Arnd Bergmann's ("netfilter: nf_tables: fib warnings")

	http://patchwork.ozlabs.org/patch/688615/

  to address fallout from this patch after rebasing nf-next, that was
  posted to address compilation warnings. --pablo ]

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index e8d56d9..9bcf899 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -581,6 +581,19 @@ config NFT_HASH
 	  This option adds the "hash" expression that you can use to perform
 	  a hash operation on registers.
 
+config NFT_FIB
+	tristate
+
+config NFT_FIB_INET
+	depends on NF_TABLES_INET
+	depends on NFT_FIB_IPV4
+	depends on NFT_FIB_IPV6
+	tristate "Netfilter nf_tables fib inet support"
+	help
+	  This option allows using the FIB expression from the inet table.
+	  The lookup will be delegated to the IPv4 or IPv6 FIB depending
+	  on the protocol of the packet.
+
 if NF_TABLES_NETDEV
 
 config NF_DUP_NETDEV