netfilter: xtables: allow xtables-nft only builds

Add hidden IP(6)_NF_IPTABLES_LEGACY symbol.

When any of the "old" builtin tables are enabled the "old" iptables
interface will be supported.

To disable the old set/getsockopt interface the existing options
for the builtin tables need to be turned off:

CONFIG_IP_NF_IPTABLES=m
CONFIG_IP_NF_FILTER is not set
CONFIG_IP_NF_NAT is not set
CONFIG_IP_NF_MANGLE is not set
CONFIG_IP_NF_RAW is not set
CONFIG_IP_NF_SECURITY is not set

Same for CONFIG_IP6_NF_ variants.

This allows to build a kernel that only supports ip(6)tables-nft
(iptables-over-nftables api).

In the future the _LEGACY symbol will become visible and the select
statements will be turned into 'depends on', but for now be on safe side
so "make oldconfig" won't break things.

Signed-off-by: Florian Westphal <fw@strlen.de>

2 files changed, 13 insertions, 4 deletions

diff --git a/net/ipv4/netfilter/Kconfig b/net/ipv4/netfilter/Kconfig
index 070475392236f..7835230872818 100644
--- a/net/ipv4/netfilter/Kconfig
+++ b/net/ipv4/netfilter/Kconfig
@@ -10,6 +10,10 @@ config NF_DEFRAG_IPV4
 	tristate
 	default n
 
+# old sockopt interface and eval loop
+config IP_NF_IPTABLES_LEGACY
+	tristate
+
 config NF_SOCKET_IPV4
 	tristate "IPv4 socket lookup support"
 	help
@@ -152,7 +156,7 @@ config IP_NF_MATCH_ECN
 config IP_NF_MATCH_RPFILTER
 	tristate '"rpfilter" reverse path filter match support'
 	depends on NETFILTER_ADVANCED
-	depends on IP_NF_MANGLE || IP_NF_RAW
+	depends on IP_NF_MANGLE || IP_NF_RAW || NFT_COMPAT
 	help
 	  This option allows you to match packets whose replies would
 	  go out via the interface the packet came in.
@@ -173,6 +177,7 @@ config IP_NF_MATCH_TTL
 config IP_NF_FILTER
 	tristate "Packet filtering"
 	default m if NETFILTER_ADVANCED=n
+	select IP_NF_IPTABLES_LEGACY
 	help
 	  Packet filtering defines a table `filter', which has a series of
 	  rules for simple packet filtering at local input, forwarding and
@@ -182,7 +187,7 @@ config IP_NF_FILTER
 
 config IP_NF_TARGET_REJECT
 	tristate "REJECT target support"
-	depends on IP_NF_FILTER
+	depends on IP_NF_FILTER || NFT_COMPAT
 	select NF_REJECT_IPV4
 	default m if NETFILTER_ADVANCED=n
 	help
@@ -212,6 +217,7 @@ config IP_NF_NAT
 	default m if NETFILTER_ADVANCED=n
 	select NF_NAT
 	select NETFILTER_XT_NAT
+	select IP6_NF_IPTABLES_LEGACY
 	help
 	  This enables the `nat' table in iptables. This allows masquerading,
 	  port forwarding and other forms of full Network Address Port
@@ -252,6 +258,7 @@ endif # IP_NF_NAT
 config IP_NF_MANGLE
 	tristate "Packet mangling"
 	default m if NETFILTER_ADVANCED=n
+	select IP_NF_IPTABLES_LEGACY
 	help
 	  This option adds a `mangle' table to iptables: see the man page for
 	  iptables(8).  This table is used for various packet alterations
@@ -261,7 +268,7 @@ config IP_NF_MANGLE
 
 config IP_NF_TARGET_ECN
 	tristate "ECN target support"
-	depends on IP_NF_MANGLE
+	depends on IP_NF_MANGLE || NFT_COMPAT
 	depends on NETFILTER_ADVANCED
 	help
 	  This option adds a `ECN' target, which can be used in the iptables mangle
@@ -286,6 +293,7 @@ config IP_NF_TARGET_TTL
 # raw + specific targets
 config IP_NF_RAW
 	tristate  'raw table support (required for NOTRACK/TRACE)'
+	select IP_NF_IPTABLES_LEGACY
 	help
 	  This option adds a `raw' table to iptables. This table is the very
 	  first in the netfilter framework and hooks in at the PREROUTING
@@ -299,6 +307,7 @@ config IP_NF_SECURITY
 	tristate "Security table"
 	depends on SECURITY
 	depends on NETFILTER_ADVANCED
+	select IP_NF_IPTABLES_LEGACY
 	help
 	  This option adds a `security' table to iptables, for use
 	  with Mandatory Access Control (MAC) policy.
diff --git a/net/ipv4/netfilter/Makefile b/net/ipv4/netfilter/Makefile
index 5a26f9de1ab92..85502d4dfbb4d 100644
--- a/net/ipv4/netfilter/Makefile
+++ b/net/ipv4/netfilter/Makefile
@@ -25,7 +25,7 @@ obj-$(CONFIG_NFT_FIB_IPV4) += nft_fib_ipv4.o
 obj-$(CONFIG_NFT_DUP_IPV4) += nft_dup_ipv4.o
 
 # generic IP tables
-obj-$(CONFIG_IP_NF_IPTABLES) += ip_tables.o
+obj-$(CONFIG_IP_NF_IPTABLES_LEGACY) += ip_tables.o
 
 # the three instances of ip_tables
 obj-$(CONFIG_IP_NF_FILTER) += iptable_filter.o