netfilter: refactor NAT redirect IPv4 to use it from nf_tables

This patch refactors the IPv4 code so it can be usable both from xt and
nf_tables.

A similar patch follows-up to handle IPv6.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 89 insertions, 0 deletions

diff --git a/net/ipv4/netfilter/Kconfig b/net/ipv4/netfilter/Kconfig
index 4c019d5c3f57..a300e2c32b26 100644
--- a/net/ipv4/netfilter/Kconfig
+++ b/net/ipv4/netfilter/Kconfig
@@ -104,6 +104,12 @@ config NF_NAT_MASQUERADE_IPV4
           This is the kernel functionality to provide NAT in the masquerade
           flavour (automatic source address selection).
 
+config NF_NAT_REDIRECT_IPV4
+        tristate "IPv4 redirect support"
+        help
+          This is the kernel functionality to provide NAT in the redirect
+          flavour (redirect packets to local machine).
+
 config NFT_MASQ_IPV4
         tristate "IPv4 masquerading support for nf_tables"
         depends on NF_TABLES_IPV4
diff --git a/net/ipv4/netfilter/Makefile b/net/ipv4/netfilter/Makefile
index f4cef5af0969..34e436c92015 100644
--- a/net/ipv4/netfilter/Makefile
+++ b/net/ipv4/netfilter/Makefile
@@ -31,6 +31,7 @@ obj-$(CONFIG_NF_NAT_H323) += nf_nat_h323.o
 obj-$(CONFIG_NF_NAT_PPTP) += nf_nat_pptp.o
 obj-$(CONFIG_NF_NAT_SNMP_BASIC) += nf_nat_snmp_basic.o
 obj-$(CONFIG_NF_NAT_MASQUERADE_IPV4) += nf_nat_masquerade_ipv4.o
+obj-$(CONFIG_NF_NAT_REDIRECT_IPV4) += nf_nat_redirect_ipv4.o
 
 # NAT protocols (nf_nat)
 obj-$(CONFIG_NF_NAT_PROTO_GRE) += nf_nat_proto_gre.o
diff --git a/net/ipv4/netfilter/nf_nat_redirect_ipv4.c b/net/ipv4/netfilter/nf_nat_redirect_ipv4.c
new file mode 100644
index 000000000000..a220552fc532
--- /dev/null
+++ b/net/ipv4/netfilter/nf_nat_redirect_ipv4.c
@@ -0,0 +1,82 @@
+/*
+ * (C) 1999-2001 Paul `Rusty' Russell
+ * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
+ * Copyright (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.
+ *
+ * Based on Rusty Russell's IPv4 REDIRECT target. Development of IPv6
+ * NAT funded by Astaro.
+ */
+
+#include <linux/if.h>
+#include <linux/inetdevice.h>
+#include <linux/ip.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <linux/netfilter.h>
+#include <linux/types.h>
+#include <linux/netfilter_ipv4.h>
+#include <linux/netfilter/x_tables.h>
+#include <net/addrconf.h>
+#include <net/checksum.h>
+#include <net/protocol.h>
+#include <net/netfilter/nf_nat.h>
+#include <net/netfilter/ipv4/nf_nat_redirect.h>
+
+unsigned int
+nf_nat_redirect_ipv4(struct sk_buff *skb,
+                     const struct nf_nat_ipv4_multi_range_compat *mr,
+                     unsigned int hooknum)
+{
+        struct nf_conn *ct;
+        enum ip_conntrack_info ctinfo;
+        __be32 newdst;
+        struct nf_nat_range newrange;
+
+        NF_CT_ASSERT(hooknum == NF_INET_PRE_ROUTING ||
+                     hooknum == NF_INET_LOCAL_OUT);
+
+        ct = nf_ct_get(skb, &ctinfo);
+        NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED));
+
+        /* Local packets: make them go to loopback */
+        if (hooknum == NF_INET_LOCAL_OUT) {
+                newdst = htonl(0x7F000001);
+        } else {
+                struct in_device *indev;
+                struct in_ifaddr *ifa;
+
+                newdst = 0;
+
+                rcu_read_lock();
+                indev = __in_dev_get_rcu(skb->dev);
+                if (indev != NULL) {
+                        ifa = indev->ifa_list;
+                        newdst = ifa->ifa_local;
+                }
+                rcu_read_unlock();
+
+                if (!newdst)
+                        return NF_DROP;
+        }
+
+        /* Transfer from original range. */
+        memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
+        memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
+        newrange.flags       = mr->range[0].flags | NF_NAT_RANGE_MAP_IPS;
+        newrange.min_addr.ip = newdst;
+        newrange.max_addr.ip = newdst;
+        newrange.min_proto   = mr->range[0].min;
+        newrange.max_proto   = mr->range[0].max;
+
+        /* Hand modified range to generic setup. */
+        return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_DST);
+}
+EXPORT_SYMBOL_GPL(nf_nat_redirect_ipv4);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");