Users may want to monitor the traffic of multiple remote systems at a
single location while both filtering to monitor only certain traffic, and
preserving the original packet.
This extension for iptables/xtables add the ability to clone and encapsulate
any packet matched with iptables, and send it to a specified remote destination.
Signed-off-by: Colin Zeidler <czeidler@xxxxxxxxxxxxxxxxxx>
---
include/uapi/linux/netfilter/xt_RMIRROR.h | 16 ++
net/netfilter/Kconfig | 9 ++
net/netfilter/Makefile | 1 +
net/netfilter/xt_RMIRROR.c | 246 ++++++++++++++++++++++++++++++
4 files changed, 272 insertions(+)
create mode 100644 include/uapi/linux/netfilter/xt_RMIRROR.h
create mode 100644 net/netfilter/xt_RMIRROR.c
diff --git a/include/uapi/linux/netfilter/xt_RMIRROR.h b/include/uapi/linux/netfilter/xt_RMIRROR.h
new file mode 100644
index 0000000..479bf33
--- /dev/null
+++ b/include/uapi/linux/netfilter/xt_RMIRROR.h
@@ -0,0 +1,16 @@
+/*
+ * Author Colin Zeidler <czeidler@xxxxxxxxxxxxxxxxxx>
+ *
+ * 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.
+ */
+#ifndef _LINUX_NETFILTER_XT_RMIRROR_H
+#define _LINUX_NETFILTER_XT_RMIRROR_H
+
+struct xt_rmirror_tginfo {
+ union nf_inet_addr dst;
+ unsigned int len;
+};
+
+#endif /* _LINUX_NETFILTER_XT_RMIRROR_H */
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index e4a13cc..e7455c5 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -945,6 +945,15 @@ config NETFILTER_XT_TARGET_REDIRECT
To compile it as a module, choose M here. If unsure, say N.
+config NETFILTER_XT_TARGET_RMIRROR
+ tristate '"RMIRROR" - packet mirroring over GRE'
+ depends on NETFILTER_ADVANCED
+ depends on !NF_CONNTRACK || NF_CONNTRACK
+ select NF_DUP_IPV4
+ ---help---
+ This option adds a "RMIRROR" target which can clone a packet and
+ encapsulate the clone in a GRE tunnel to a remote destination.
+
config NETFILTER_XT_TARGET_TEE
tristate '"TEE" - packet cloning to alternate destination'
depends on NETFILTER_ADVANCED
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index f78ed24..12805ad 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -132,6 +132,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_NFLOG) += xt_NFLOG.o
obj-$(CONFIG_NETFILTER_XT_TARGET_NFQUEUE) += xt_NFQUEUE.o
obj-$(CONFIG_NETFILTER_XT_TARGET_RATEEST) += xt_RATEEST.o
obj-$(CONFIG_NETFILTER_XT_TARGET_REDIRECT) += xt_REDIRECT.o
+obj-$(CONFIG_NETFILTER_XT_TARGET_RMIRROR) += xt_RMIRROR.o
obj-$(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
diff --git a/net/netfilter/xt_RMIRROR.c b/net/netfilter/xt_RMIRROR.c
new file mode 100644
index 0000000..09d9d49
--- /dev/null
+++ b/net/netfilter/xt_RMIRROR.c
@@ -0,0 +1,246 @@
+/*
+ * Author Colin Zeidler <czeidler@xxxxxxxxxxxxxxxxxx>
+ *
+ * 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/version.h>
+#include <linux/ip.h>
+#include <linux/inetdevice.h>
+#include <linux/skbuff.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/percpu.h>
+#include <linux/route.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter_ipv4.h>
+#include <linux/netdevice.h>
+#include <net/ip.h>
+#include <net/gre.h>
+#include <net/checksum.h>
+#include <net/route.h>
+#include <net/neighbour.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/if_ether.h>
+
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+#define WITH_CONNTRACK 1
+#include <net/netfilter/nf_conntrack.h>
+#endif
+
+#include <linux/netfilter/xt_RMIRROR.h>
+
+static DEFINE_PER_CPU(bool, rmirror_active);
+
+struct rmirror_hdr {
+ struct iphdr ip;
+ struct gre_base_hdr gre;
+};
+
+static struct rmirror_hdr new_rmirror = {
+ .ip = {
+ .version = 4,
+ .ihl = 5,
+ .tos = 0,
+ .frag_off = 0,
+ .ttl = 0xff,
+ .protocol = 0x2F, // GRE
+ },
+ .gre = {
+ .flags = 0,
+ .protocol = htons(0x6558),
+ },
+};
+
+static const char zeromac[6] = { 0, 0, 0, 0, 0, 0};
+
+/* Apply routing information to skb,
+ * so it can be sent with ip_local_out()
+ *
+ * Based on net/netfilter/xt_TEE.c, tee_tg_route4
+ */
+bool rmirror_tg_route4(struct sk_buff *skb, __be32 ip)
+{
+ const struct iphdr *iph = ip_hdr(skb);
+ struct net *net = &init_net;
+ struct rtable *rt;
+ struct flowi4 fl4;
+
+ memset(&fl4, 0, sizeof(fl4));
+
+ fl4.daddr = ip;
+ fl4.flowi4_tos = RT_TOS(iph->tos);
+ fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
+ fl4.flowi4_flags = FLOWI_FLAG_KNOWN_NH;
+ rt = ip_route_output_key(net, &fl4);
+ if (IS_ERR(rt))
+ return false;
+
+ skb_dst_drop(skb);
+ skb_dst_set(skb, &rt->dst);
+ skb->dev = rt->dst.dev;
+ skb->protocol = htons(ETH_P_TEB);
+ return true;
+}
+
+/* Create new skb that encapsulates data of original
+ * skb with GRE
+ */
+bool encap_packet4(struct sk_buff *skb, const struct xt_rmirror_tginfo *info)
+{
+ struct rmirror_hdr *rmh;
+ struct iphdr *iph;
+ struct ethhdr *ehdr;
+ struct ethhdr *datamac;
+ bool mac_needed = false;
+
+ /* add extra size as we include MAC Header and IP Header */
+ int extra_header = sizeof(new_rmirror);
+
+ /* If the skb did not have a mac header, i.e. new outgoing skb
+ * create the mac header for the skb we cloned
+ * as if it had progressed through the stack
+ */
+ if (!skb_mac_header_was_set(skb)) {
+ if (!skb->dev) {
+ iph = ip_hdr(skb);
+ rmirror_tg_route4(skb, iph->daddr);
+ }
+ if (skb->dev) {
+ dev_hard_header(skb,
+ skb->dev,
+ ETH_P_IP,
+ &zeromac,
+ NULL,
+ skb->len);
+ mac_needed = true;
+ }
+
+ if (skb_headroom(skb) < extra_header)
+ pskb_expand_head(skb, extra_header, 0, GFP_ATOMIC);
+ } else if (skb_mac_header_was_set(skb)) {
+ ehdr = eth_hdr(skb);
+ extra_header = extra_header + sizeof(*ehdr);
+ if (skb_headroom(skb) < extra_header)
+ pskb_expand_head(skb, extra_header, 0, GFP_ATOMIC);
+ datamac = (struct ethhdr *)skb_push(skb, sizeof(*ehdr));
+ memcpy(datamac, ehdr, sizeof(*ehdr));
+ }
+
+ skb->encapsulation = 1;
+
+ skb_reset_inner_headers(skb);
+
+ rmh = (struct rmirror_hdr *)skb_push(skb, sizeof(*rmh));
+ memcpy(rmh, &new_rmirror, sizeof(*rmh));
+
+ if (info->len > 0)
+ skb_trim(skb, sizeof(*rmh) + info->len);
+
+ iph = &rmh->ip;
+ iph->daddr = info->dst.ip;
+ iph->tot_len = htons(skb->len);
+ __ip_select_ident(&init_net, iph, 1);
+ ip_send_check(iph);
+ skb_reset_network_header(skb);
+
+ return mac_needed;
+}
+
+unsigned int rmirror_tg4(struct sk_buff *skb,
+ const struct xt_action_param *par
+ )
+{
+ const struct xt_rmirror_tginfo *info = par->targinfo;
+ struct dst_entry *inner_dst;
+ __be32 inner_daddr;
+ bool mac_needed;
+
+ if (__this_cpu_read(rmirror_active))
+ return XT_CONTINUE;
+
+ skb = skb_clone(skb, GFP_ATOMIC);
+#ifdef WITH_CONNTRACK
+ nf_reset(skb);
+ nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
+#endif //WITH CONNTRACK
+ inner_daddr = ip_hdr(skb)->daddr;
+
+ mac_needed = encap_packet4(skb, info);
+
+ if (mac_needed)
+ inner_dst = skb_dst(skb);
+
+ // Send the cloned skb
+ if (rmirror_tg_route4(skb, info->dst.ip)) {
+ // set saddr based on output device
+ struct in_device *idev = rcu_dereference(skb->dev->ip_ptr);
+ struct iphdr *iph = ip_hdr(skb);
+
+ iph->saddr = idev->ifa_list->ifa_address;
+
+ if (mac_needed) {
+ struct neighbour *n;
+ struct ethhdr *inner_eh;
+
+ inner_eh = (struct ethhdr *)((char *)iph + sizeof(new_rmirror));
+ n = dst_neigh_lookup(inner_dst, &inner_daddr);
+ if (n)
+ memcpy(inner_eh->h_dest,
+ n->ha,
+ sizeof(char) * 6);
+ else
+ memcpy(inner_eh->h_dest,
+ zeromac,
+ sizeof(char) * 6);
+ }
+
+ __this_cpu_write(rmirror_active, true);
+ ip_local_out(&init_net, skb->sk, skb);
+ __this_cpu_write(rmirror_active, false);
+ } else {
+ kfree_skb(skb);
+ }
+
+ return XT_CONTINUE;
+}
+
+static int rmirror_tg_check(const struct xt_tgchk_param *par)
+{
+ struct xt_rmirror_tginfo *info = par->targinfo;
+
+ return 0;
+}
+
+static struct xt_target rmirror_tg_reg[] __read_mostly = {
+ {
+ .name = "RMIRROR",
+ .revision = 0,
+ .family = NFPROTO_IPV4,
+ .target = rmirror_tg4,
+ .targetsize = sizeof(struct xt_rmirror_tginfo),
+ .checkentry = rmirror_tg_check,
+ .me = THIS_MODULE,
+ },
+};
+
+static int __init rmirror_tg_init(void)
+{
+ return xt_register_targets(rmirror_tg_reg, ARRAY_SIZE(rmirror_tg_reg));
+}
+
+static void __exit rmirror_tg_exit(void)
+{
+ xt_unregister_targets(rmirror_tg_reg, ARRAY_SIZE(rmirror_tg_reg));
+}
+
+module_init(rmirror_tg_init);
+module_exit(rmirror_tg_exit);
+
+MODULE_ALIAS("ipt_RMIRROR");
+
+MODULE_AUTHOR("Colin Zeidler, czeidler@xxxxxxxxxxxxxxxxxx");
+MODULE_DESCRIPTION("Xtables: clone and send packet with GRE");
+MODULE_LICENSE("GPL");
+
--
2.1.4
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