netfilter: nat: merge nf_nat_ipv4,6 into nat core

before:
   text    data     bss     dec     hex filename
  16566    1576    4136   22278    5706 nf_nat.ko
   3598	    844	      0	   4442	   115a	nf_nat_ipv6.ko
   3187	    844	      0	   4031	    fbf	nf_nat_ipv4.ko

after:
   text    data     bss     dec     hex filename
  22948    1612    4136   28696    7018 nf_nat.ko

... with ipv4/v6 nat now provided directly via nf_nat.ko.

Also changes:
       ret = nf_nat_ipv4_fn(priv, skb, state);
       if (ret != NF_DROP && ret != NF_STOLEN &&
into
	if (ret != NF_ACCEPT)
		return ret;

everywhere.

The nat hooks never should return anything other than
ACCEPT or DROP (and the latter only in rare error cases).

The original code uses multi-line ANDing including assignment-in-if:
        if (ret != NF_DROP && ret != NF_STOLEN &&
           !(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
            (ct = nf_ct_get(skb, &ctinfo)) != NULL) {

I removed this while moving, breaking those in separate conditionals
and moving the assignments into extra lines.

checkpatch still generates some warnings:
 1. Overly long lines (of moved code).
    Breaking them is even more ugly. so I kept this as-is.
 2. use of extern function declarations in a .c file.
    This is necessary evil, we must call
    nf_nat_l3proto_register() from the nat core now.
    All l3proto related functions are removed later in this series,
    those prototypes are then removed as well.

v2: keep empty nf_nat_ipv6_csum_update stub for CONFIG_IPV6=n case.
v3: remove IS_ENABLED(NF_NAT_IPV4/6) tests, NF_NAT_IPVx toggles
    are removed here.
v4: also get rid of the assignments in conditionals.

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

3 files changed, 2 insertions, 346 deletions

diff --git a/net/ipv4/netfilter/Kconfig b/net/ipv4/netfilter/Kconfig
index db05a835748a..8688461ed077 100644
--- a/net/ipv4/netfilter/Kconfig
+++ b/net/ipv4/netfilter/Kconfig
@@ -94,17 +94,7 @@ config NF_REJECT_IPV4
 	tristate "IPv4 packet rejection"
 	default m if NETFILTER_ADVANCED=n
 
-config NF_NAT_IPV4
-	tristate "IPv4 NAT"
-	depends on NF_CONNTRACK
-	default m if NETFILTER_ADVANCED=n
-	select NF_NAT
-	help
-	  The IPv4 NAT option allows masquerading, port forwarding and other
-	  forms of full Network Address Port Translation. This can be
-	  controlled by iptables or nft.
-
-if NF_NAT_IPV4
+if NF_NAT
 
 if NF_TABLES
 config NFT_CHAIN_NAT_IPV4
@@ -163,7 +153,7 @@ config NF_NAT_H323
 	depends on NF_CONNTRACK
 	default NF_CONNTRACK_H323
 
-endif # NF_NAT_IPV4
+endif # NF_NAT
 
 config IP_NF_IPTABLES
 	tristate "IP tables support (required for filtering/masq/NAT)"
@@ -260,7 +250,6 @@ config IP_NF_NAT
 	depends on NF_CONNTRACK
 	default m if NETFILTER_ADVANCED=n
 	select NF_NAT
-	select NF_NAT_IPV4
 	select NETFILTER_XT_NAT
 	help
 	  This enables the `nat' table in iptables. This allows masquerading,
diff --git a/net/ipv4/netfilter/Makefile b/net/ipv4/netfilter/Makefile
index ddeb35ab8bdb..b2cdf705fdf1 100644
--- a/net/ipv4/netfilter/Makefile
+++ b/net/ipv4/netfilter/Makefile
@@ -3,9 +3,6 @@
 # Makefile for the netfilter modules on top of IPv4.
 #
 
-nf_nat_ipv4-y		:= nf_nat_l3proto_ipv4.o
-obj-$(CONFIG_NF_NAT_IPV4) += nf_nat_ipv4.o
-
 # defrag
 obj-$(CONFIG_NF_DEFRAG_IPV4) += nf_defrag_ipv4.o
 
diff --git a/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c b/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c
deleted file mode 100644
index 36b4f9659ffa..000000000000
--- a/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c
+++ /dev/null
@@ -1,330 +0,0 @@
-/*
- * (C) 1999-2001 Paul `Rusty' Russell
- * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
- * (C) 2011 Patrick McHardy <kaber@trash.net>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- */
-
-#include <linux/types.h>
-#include <linux/module.h>
-#include <linux/skbuff.h>
-#include <linux/ip.h>
-#include <linux/icmp.h>
-#include <linux/netfilter.h>
-#include <linux/netfilter_ipv4.h>
-#include <net/secure_seq.h>
-#include <net/checksum.h>
-#include <net/route.h>
-#include <net/ip.h>
-
-#include <net/netfilter/nf_conntrack_core.h>
-#include <net/netfilter/nf_conntrack.h>
-#include <net/netfilter/nf_nat_core.h>
-#include <net/netfilter/nf_nat_l3proto.h>
-#include <net/netfilter/nf_nat_l4proto.h>
-
-static const struct nf_nat_l3proto nf_nat_l3proto_ipv4;
-
-static bool nf_nat_ipv4_manip_pkt(struct sk_buff *skb,
-				  unsigned int iphdroff,
-				  const struct nf_conntrack_tuple *target,
-				  enum nf_nat_manip_type maniptype)
-{
-	struct iphdr *iph;
-	unsigned int hdroff;
-
-	if (!skb_make_writable(skb, iphdroff + sizeof(*iph)))
-		return false;
-
-	iph = (void *)skb->data + iphdroff;
-	hdroff = iphdroff + iph->ihl * 4;
-
-	if (!nf_nat_l4proto_manip_pkt(skb, &nf_nat_l3proto_ipv4, iphdroff,
-				      hdroff, target, maniptype))
-		return false;
-	iph = (void *)skb->data + iphdroff;
-
-	if (maniptype == NF_NAT_MANIP_SRC) {
-		csum_replace4(&iph->check, iph->saddr, target->src.u3.ip);
-		iph->saddr = target->src.u3.ip;
-	} else {
-		csum_replace4(&iph->check, iph->daddr, target->dst.u3.ip);
-		iph->daddr = target->dst.u3.ip;
-	}
-	return true;
-}
-
-static void nf_nat_ipv4_csum_update(struct sk_buff *skb,
-				    unsigned int iphdroff, __sum16 *check,
-				    const struct nf_conntrack_tuple *t,
-				    enum nf_nat_manip_type maniptype)
-{
-	struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
-	__be32 oldip, newip;
-
-	if (maniptype == NF_NAT_MANIP_SRC) {
-		oldip = iph->saddr;
-		newip = t->src.u3.ip;
-	} else {
-		oldip = iph->daddr;
-		newip = t->dst.u3.ip;
-	}
-	inet_proto_csum_replace4(check, skb, oldip, newip, true);
-}
-
-static void nf_nat_ipv4_csum_recalc(struct sk_buff *skb,
-				    u8 proto, void *data, __sum16 *check,
-				    int datalen, int oldlen)
-{
-	if (skb->ip_summed != CHECKSUM_PARTIAL) {
-		const struct iphdr *iph = ip_hdr(skb);
-
-		skb->ip_summed = CHECKSUM_PARTIAL;
-		skb->csum_start = skb_headroom(skb) + skb_network_offset(skb) +
-			ip_hdrlen(skb);
-		skb->csum_offset = (void *)check - data;
-		*check = ~csum_tcpudp_magic(iph->saddr, iph->daddr, datalen,
-					    proto, 0);
-	} else
-		inet_proto_csum_replace2(check, skb,
-					 htons(oldlen), htons(datalen), true);
-}
-
-static const struct nf_nat_l3proto nf_nat_l3proto_ipv4 = {
-	.l3proto		= NFPROTO_IPV4,
-	.manip_pkt		= nf_nat_ipv4_manip_pkt,
-	.csum_update		= nf_nat_ipv4_csum_update,
-	.csum_recalc		= nf_nat_ipv4_csum_recalc,
-};
-
-int nf_nat_icmp_reply_translation(struct sk_buff *skb,
-				  struct nf_conn *ct,
-				  enum ip_conntrack_info ctinfo,
-				  unsigned int hooknum)
-{
-	struct {
-		struct icmphdr	icmp;
-		struct iphdr	ip;
-	} *inside;
-	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
-	enum nf_nat_manip_type manip = HOOK2MANIP(hooknum);
-	unsigned int hdrlen = ip_hdrlen(skb);
-	struct nf_conntrack_tuple target;
-	unsigned long statusbit;
-
-	WARN_ON(ctinfo != IP_CT_RELATED && ctinfo != IP_CT_RELATED_REPLY);
-
-	if (!skb_make_writable(skb, hdrlen + sizeof(*inside)))
-		return 0;
-	if (nf_ip_checksum(skb, hooknum, hdrlen, 0))
-		return 0;
-
-	inside = (void *)skb->data + hdrlen;
-	if (inside->icmp.type == ICMP_REDIRECT) {
-		if ((ct->status & IPS_NAT_DONE_MASK) != IPS_NAT_DONE_MASK)
-			return 0;
-		if (ct->status & IPS_NAT_MASK)
-			return 0;
-	}
-
-	if (manip == NF_NAT_MANIP_SRC)
-		statusbit = IPS_SRC_NAT;
-	else
-		statusbit = IPS_DST_NAT;
-
-	/* Invert if this is reply direction */
-	if (dir == IP_CT_DIR_REPLY)
-		statusbit ^= IPS_NAT_MASK;
-
-	if (!(ct->status & statusbit))
-		return 1;
-
-	if (!nf_nat_ipv4_manip_pkt(skb, hdrlen + sizeof(inside->icmp),
-				   &ct->tuplehash[!dir].tuple, !manip))
-		return 0;
-
-	if (skb->ip_summed != CHECKSUM_PARTIAL) {
-		/* Reloading "inside" here since manip_pkt may reallocate */
-		inside = (void *)skb->data + hdrlen;
-		inside->icmp.checksum = 0;
-		inside->icmp.checksum =
-			csum_fold(skb_checksum(skb, hdrlen,
-					       skb->len - hdrlen, 0));
-	}
-
-	/* Change outer to look like the reply to an incoming packet */
-	nf_ct_invert_tuple(&target, &ct->tuplehash[!dir].tuple);
-	target.dst.protonum = IPPROTO_ICMP;
-	if (!nf_nat_ipv4_manip_pkt(skb, 0, &target, manip))
-		return 0;
-
-	return 1;
-}
-EXPORT_SYMBOL_GPL(nf_nat_icmp_reply_translation);
-
-static unsigned int
-nf_nat_ipv4_fn(void *priv, struct sk_buff *skb,
-	       const struct nf_hook_state *state)
-{
-	struct nf_conn *ct;
-	enum ip_conntrack_info ctinfo;
-
-	ct = nf_ct_get(skb, &ctinfo);
-	if (!ct)
-		return NF_ACCEPT;
-
-	if (ctinfo == IP_CT_RELATED || ctinfo == IP_CT_RELATED_REPLY) {
-		if (ip_hdr(skb)->protocol == IPPROTO_ICMP) {
-			if (!nf_nat_icmp_reply_translation(skb, ct, ctinfo,
-							   state->hook))
-				return NF_DROP;
-			else
-				return NF_ACCEPT;
-		}
-	}
-
-	return nf_nat_inet_fn(priv, skb, state);
-}
-
-static unsigned int
-nf_nat_ipv4_in(void *priv, struct sk_buff *skb,
-	       const struct nf_hook_state *state)
-{
-	unsigned int ret;
-	__be32 daddr = ip_hdr(skb)->daddr;
-
-	ret = nf_nat_ipv4_fn(priv, skb, state);
-	if (ret != NF_DROP && ret != NF_STOLEN &&
-	    daddr != ip_hdr(skb)->daddr)
-		skb_dst_drop(skb);
-
-	return ret;
-}
-
-static unsigned int
-nf_nat_ipv4_out(void *priv, struct sk_buff *skb,
-		const struct nf_hook_state *state)
-{
-#ifdef CONFIG_XFRM
-	const struct nf_conn *ct;
-	enum ip_conntrack_info ctinfo;
-	int err;
-#endif
-	unsigned int ret;
-
-	ret = nf_nat_ipv4_fn(priv, skb, state);
-#ifdef CONFIG_XFRM
-	if (ret != NF_DROP && ret != NF_STOLEN &&
-	    !(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
-	    (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
-		enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
-
-		if ((ct->tuplehash[dir].tuple.src.u3.ip !=
-		     ct->tuplehash[!dir].tuple.dst.u3.ip) ||
-		    (ct->tuplehash[dir].tuple.dst.protonum != IPPROTO_ICMP &&
-		     ct->tuplehash[dir].tuple.src.u.all !=
-		     ct->tuplehash[!dir].tuple.dst.u.all)) {
-			err = nf_xfrm_me_harder(state->net, skb, AF_INET);
-			if (err < 0)
-				ret = NF_DROP_ERR(err);
-		}
-	}
-#endif
-	return ret;
-}
-
-static unsigned int
-nf_nat_ipv4_local_fn(void *priv, struct sk_buff *skb,
-		     const struct nf_hook_state *state)
-{
-	const struct nf_conn *ct;
-	enum ip_conntrack_info ctinfo;
-	unsigned int ret;
-	int err;
-
-	ret = nf_nat_ipv4_fn(priv, skb, state);
-	if (ret != NF_DROP && ret != NF_STOLEN &&
-	    (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
-		enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
-
-		if (ct->tuplehash[dir].tuple.dst.u3.ip !=
-		    ct->tuplehash[!dir].tuple.src.u3.ip) {
-			err = ip_route_me_harder(state->net, skb, RTN_UNSPEC);
-			if (err < 0)
-				ret = NF_DROP_ERR(err);
-		}
-#ifdef CONFIG_XFRM
-		else if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
-			 ct->tuplehash[dir].tuple.dst.protonum != IPPROTO_ICMP &&
-			 ct->tuplehash[dir].tuple.dst.u.all !=
-			 ct->tuplehash[!dir].tuple.src.u.all) {
-			err = nf_xfrm_me_harder(state->net, skb, AF_INET);
-			if (err < 0)
-				ret = NF_DROP_ERR(err);
-		}
-#endif
-	}
-	return ret;
-}
-
-static const struct nf_hook_ops nf_nat_ipv4_ops[] = {
-	/* Before packet filtering, change destination */
-	{
-		.hook		= nf_nat_ipv4_in,
-		.pf		= NFPROTO_IPV4,
-		.hooknum	= NF_INET_PRE_ROUTING,
-		.priority	= NF_IP_PRI_NAT_DST,
-	},
-	/* After packet filtering, change source */
-	{
-		.hook		= nf_nat_ipv4_out,
-		.pf		= NFPROTO_IPV4,
-		.hooknum	= NF_INET_POST_ROUTING,
-		.priority	= NF_IP_PRI_NAT_SRC,
-	},
-	/* Before packet filtering, change destination */
-	{
-		.hook		= nf_nat_ipv4_local_fn,
-		.pf		= NFPROTO_IPV4,
-		.hooknum	= NF_INET_LOCAL_OUT,
-		.priority	= NF_IP_PRI_NAT_DST,
-	},
-	/* After packet filtering, change source */
-	{
-		.hook		= nf_nat_ipv4_fn,
-		.pf		= NFPROTO_IPV4,
-		.hooknum	= NF_INET_LOCAL_IN,
-		.priority	= NF_IP_PRI_NAT_SRC,
-	},
-};
-
-int nf_nat_l3proto_ipv4_register_fn(struct net *net, const struct nf_hook_ops *ops)
-{
-	return nf_nat_register_fn(net, ops, nf_nat_ipv4_ops, ARRAY_SIZE(nf_nat_ipv4_ops));
-}
-EXPORT_SYMBOL_GPL(nf_nat_l3proto_ipv4_register_fn);
-
-void nf_nat_l3proto_ipv4_unregister_fn(struct net *net, const struct nf_hook_ops *ops)
-{
-	nf_nat_unregister_fn(net, ops, ARRAY_SIZE(nf_nat_ipv4_ops));
-}
-EXPORT_SYMBOL_GPL(nf_nat_l3proto_ipv4_unregister_fn);
-
-static int __init nf_nat_l3proto_ipv4_init(void)
-{
-	return nf_nat_l3proto_register(&nf_nat_l3proto_ipv4);
-}
-
-static void __exit nf_nat_l3proto_ipv4_exit(void)
-{
-	nf_nat_l3proto_unregister(&nf_nat_l3proto_ipv4);
-}
-
-MODULE_LICENSE("GPL");
-MODULE_ALIAS("nf-nat-" __stringify(AF_INET));
-
-module_init(nf_nat_l3proto_ipv4_init);
-module_exit(nf_nat_l3proto_ipv4_exit);