netfilter: iptables TPROXY target

The TPROXY target implements redirection of non-local TCP/UDP traffic to local
sockets. Additionally, it's possible to manipulate the packet mark if and only
if a socket has been found. (We need this because we cannot use multiple
targets in the same iptables rule.)

Signed-off-by: KOVACS Krisztian <hidden@sch.bme.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>

4 files changed, 142 insertions, 0 deletions

diff --git a/include/linux/netfilter/xt_TPROXY.h b/include/linux/netfilter/xt_TPROXY.h
new file mode 100644
index 000000000000..152e8f97132b
--- /dev/null
+++ b/include/linux/netfilter/xt_TPROXY.h
@@ -0,0 +1,14 @@
+#ifndef _XT_TPROXY_H_target
+#define _XT_TPROXY_H_target
+
+/* TPROXY target is capable of marking the packet to perform
+ * redirection. We can get rid of that whenever we get support for
+ * mutliple targets in the same rule. */
+struct xt_tproxy_target_info {
+        u_int32_t mark_mask;
+        u_int32_t mark_value;
+        __be32 laddr;
+        __be16 lport;
+};
+
+#endif /* _XT_TPROXY_H_target */
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index f6c807299487..de18bba619f2 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -421,6 +421,21 @@ config NETFILTER_XT_TARGET_RATEEST
 
           To compile it as a module, choose M here.  If unsure, say N.
 
+config NETFILTER_XT_TARGET_TPROXY
+        tristate '"TPROXY" target support (EXPERIMENTAL)'
+        depends on EXPERIMENTAL
+        depends on NETFILTER_TPROXY
+        depends on NETFILTER_XTABLES
+        depends on NETFILTER_ADVANCED
+        select NF_DEFRAG_IPV4
+        help
+          This option adds a `TPROXY' target, which is somewhat similar to
+          REDIRECT.  It can only be used in the mangle table and is useful
+          to redirect traffic to a transparent proxy.  It does _not_ depend
+          on Netfilter connection tracking and NAT, unlike REDIRECT.
+
+          To compile it as a module, choose M here.  If unsure, say N.
+
 config NETFILTER_XT_TARGET_TRACE
         tristate  '"TRACE" target support'
         depends on NETFILTER_XTABLES
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 1cdc3a13d01f..8ce67665882d 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -51,6 +51,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_NFQUEUE) += xt_NFQUEUE.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_NOTRACK) += xt_NOTRACK.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_RATEEST) += xt_RATEEST.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_SECMARK) += xt_SECMARK.o
+obj-$(CONFIG_NETFILTER_XT_TARGET_TPROXY) += xt_TPROXY.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_TCPMSS) += xt_TCPMSS.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_TCPOPTSTRIP) += xt_TCPOPTSTRIP.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_TRACE) += xt_TRACE.o
diff --git a/net/netfilter/xt_TPROXY.c b/net/netfilter/xt_TPROXY.c
new file mode 100644
index 000000000000..183f251d2f06
--- /dev/null
+++ b/net/netfilter/xt_TPROXY.c
@@ -0,0 +1,112 @@
+/*
+ * Transparent proxy support for Linux/iptables
+ *
+ * Copyright (c) 2006-2007 BalaBit IT Ltd.
+ * Author: Balazs Scheidler, Krisztian Kovacs
+ *
+ * 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/module.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+#include <net/checksum.h>
+#include <net/udp.h>
+#include <net/inet_sock.h>
+
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter_ipv4/ip_tables.h>
+#include <linux/netfilter/xt_TPROXY.h>
+
+#include <net/netfilter/ipv4/nf_defrag_ipv4.h>
+#include <net/netfilter/nf_tproxy_core.h>
+
+static unsigned int
+tproxy_tg(struct sk_buff *skb,
+          const struct net_device *in,
+          const struct net_device *out,
+          unsigned int hooknum,
+          const struct xt_target *target,
+          const void *targinfo)
+{
+        const struct iphdr *iph = ip_hdr(skb);
+        const struct xt_tproxy_target_info *tgi = targinfo;
+        struct udphdr _hdr, *hp;
+        struct sock *sk;
+
+        hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
+        if (hp == NULL)
+                return NF_DROP;
+
+        sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
+                                   iph->saddr, tgi->laddr ? tgi->laddr : iph->daddr,
+                                   hp->source, tgi->lport ? tgi->lport : hp->dest,
+                                   in, true);
+
+        /* NOTE: assign_sock consumes our sk reference */
+        if (sk && nf_tproxy_assign_sock(skb, sk)) {
+                /* This should be in a separate target, but we don't do multiple
+                   targets on the same rule yet */
+                skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;
+
+                pr_debug("redirecting: proto %u %08x:%u -> %08x:%u, mark: %x\n",
+                         iph->protocol, ntohl(iph->daddr), ntohs(hp->dest),
+                         ntohl(tgi->laddr), ntohs(tgi->lport), skb->mark);
+                return NF_ACCEPT;
+        }
+
+        pr_debug("no socket, dropping: proto %u %08x:%u -> %08x:%u, mark: %x\n",
+                 iph->protocol, ntohl(iph->daddr), ntohs(hp->dest),
+                 ntohl(tgi->laddr), ntohs(tgi->lport), skb->mark);
+        return NF_DROP;
+}
+
+static bool
+tproxy_tg_check(const char *tablename,
+                const void *entry,
+                const struct xt_target *target,
+                void *targetinfo,
+                unsigned int hook_mask)
+{
+        const struct ipt_ip *i = entry;
+
+        if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
+            && !(i->invflags & IPT_INV_PROTO))
+                return true;
+
+        pr_info("xt_TPROXY: Can be used only in combination with "
+                "either -p tcp or -p udp\n");
+        return false;
+}
+
+static struct xt_target tproxy_tg_reg __read_mostly = {
+        .name           = "TPROXY",
+        .family         = AF_INET,
+        .table          = "mangle",
+        .target         = tproxy_tg,
+        .targetsize     = sizeof(struct xt_tproxy_target_info),
+        .checkentry     = tproxy_tg_check,
+        .hooks          = 1 << NF_INET_PRE_ROUTING,
+        .me             = THIS_MODULE,
+};
+
+static int __init tproxy_tg_init(void)
+{
+        nf_defrag_ipv4_enable();
+        return xt_register_target(&tproxy_tg_reg);
+}
+
+static void __exit tproxy_tg_exit(void)
+{
+        xt_unregister_target(&tproxy_tg_reg);
+}
+
+module_init(tproxy_tg_init);
+module_exit(tproxy_tg_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Krisztian Kovacs");
+MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module.");
+MODULE_ALIAS("ipt_TPROXY");