Mailing List Archive

Along comes a new version of xt_TARPIT.

---
net/netfilter/Kconfig | 17 +++
net/netfilter/Makefile | 1
net/netfilter/xt_TARPIT.c | 246 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 264 insertions(+)

Index: linux-2.6.22.1/net/netfilter/Kconfig
===================================================================
--- linux-2.6.22.1.orig/net/netfilter/Kconfig
+++ linux-2.6.22.1/net/netfilter/Kconfig
@@ -375,6 +375,23 @@ config NETFILTER_XT_TARGET_CONNSECMARK

To compile it as a module, choose M here. If unsure, say N.

+config NETFILTER_XT_TARGET_TARPIT
+ tristate '"TARPIT" target support'
+ depends on NETFILTER_XTABLES
+ ---help---
+ Adds a TARPIT target to iptables, which captures and holds
+ incoming TCP connections using no local per-connection resources.
+ Connections are accepted, but immediately switched to the persist
+ state (0 byte window), in which the remote side stops sending data
+ and asks to continue every 60-240 seconds. Attempts to close the
+ connection are ignored, forcing the remote side to time out the
+ connection in 12-24 minutes.
+
+ This offers similar functionality to LaBrea
+ <http://www.hackbusters.net/LaBrea/>, but does not require dedicated
+ hardware or IPs. Any TCP port that you would normally DROP or REJECT
+ can instead become a tarpit.
+
config NETFILTER_XT_TARGET_TCPMSS
tristate '"TCPMSS" target support'
depends on NETFILTER_XTABLES && (IPV6 || IPV6=n)
Index: linux-2.6.22.1/net/netfilter/Makefile
===================================================================
--- linux-2.6.22.1.orig/net/netfilter/Makefile
+++ linux-2.6.22.1/net/netfilter/Makefile
@@ -46,6 +46,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_NFLOG)
obj-$(CONFIG_NETFILTER_XT_TARGET_NOTRACK) += xt_NOTRACK.o
obj-$(CONFIG_NETFILTER_XT_TARGET_TRACE) += xt_TRACE.o
obj-$(CONFIG_NETFILTER_XT_TARGET_SECMARK) += xt_SECMARK.o
+obj-$(CONFIG_NETFILTER_XT_TARGET_TARPIT) += xt_TARPIT.o
obj-$(CONFIG_NETFILTER_XT_TARGET_TCPMSS) += xt_TCPMSS.o
obj-$(CONFIG_NETFILTER_XT_TARGET_CONNSECMARK) += xt_CONNSECMARK.o

Index: linux-2.6.22.1/net/netfilter/xt_TARPIT.c
===================================================================
--- /dev/null
+++ linux-2.6.22.1/net/netfilter/xt_TARPIT.c
@@ -0,0 +1,246 @@
+/*
+ * Kernel module to capture and hold incoming TCP connections using
+ * no local per-connection resources.
+ *
+ * Based on ipt_REJECT.c and offering functionality similar to
+ * LaBrea <http://www.hackbusters.net/LaBrea/>.
+ *
+ * Copyright (c) 2002 Aaron Hopkins <tools@die.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * Goal:
+ * - Allow incoming TCP connections to be established.
+ * - Passing data should result in the connection being switched to the
+ * persist state (0 byte window), in which the remote side stops sending
+ * data and asks to continue every 60 seconds.
+ * - Attempts to shut down the connection should be ignored completely, so
+ * the remote side ends up having to time it out.
+ *
+ * This means:
+ * - Reply to TCP SYN,!ACK,!RST,!FIN with SYN-ACK, window 5 bytes
+ * - Reply to TCP SYN,ACK,!RST,!FIN with RST to prevent spoofing
+ * - Reply to TCP !SYN,!RST,!FIN with ACK, window 0 bytes, rate-limited
+ */
+
+/*
+#include <net/ip.h>
+#include <net/icmp.h>
+#include <linux/random.h>
+*/
+
+#include <linux/ip.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/netfilter/x_tables.h>
+#ifdef CONFIG_BRIDGE_NETFILTER
+# include <linux/netfilter_bridge.h>
+#endif
+#include <net/route.h>
+#include <net/tcp.h>
+
+/* Send reply */
+static inline void tarpit_tcp(struct sk_buff *oldskb, unsigned int hook)
+{
+ struct tcphdr _otcph, *oth, *tcph;
+ unsigned int addr_type;
+ struct sk_buff *nskb;
+ struct iphdr *niph;
+ u_int16_t tmp;
+
+ /* A truncated TCP header is not going to be useful */
+ if (oldskb->len < ip_hdrlen(oldskb) + sizeof(struct tcphdr))
+ return;
+
+ oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
+ sizeof(_otcph), &_otcph);
+ if (oth == NULL)
+ return;
+
+ /* No replies for RST, FIN or !SYN,!ACK */
+ if (oth->rst || oth->fin || (!oth->syn && !oth->ack))
+ return;
+
+ /* Rate-limit replies to !SYN,ACKs */
+ /*
+ if (!oth->syn && oth->ack)
+ if (!xrlim_allow(&ort->u.dst, HZ))
+ return;
+ */
+
+ /* Check checksum. */
+ if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
+ return;
+
+ /*
+ * Copy skb (even if skb is about to be dropped, we cannot just
+ * clone it because there may be other things, such as tcpdump,
+ * interested in it)
+ */
+ nskb = skb_copy_expand(oldskb, LL_MAX_HEADER,
+ skb_tailroom(oldskb), GFP_ATOMIC);
+ if (nskb == NULL)
+ return;
+
+ /* This packet will not be the same as the other: clear nf fields */
+ nf_reset(nskb);
+ nskb->mark = 0;
+ skb_init_secmark(nskb);
+
+ skb_shinfo(nskb)->gso_size = 0;
+ skb_shinfo(nskb)->gso_segs = 0;
+ skb_shinfo(nskb)->gso_type = 0;
+
+ tcph = (struct tcphdr *)(skb_network_header(nskb) + ip_hdrlen(nskb));
+
+ /* Swap source and dest */
+ niph = ip_hdr(nskb);
+ niph->daddr = xchg(&niph->saddr, niph->daddr);
+ tmp = tcph->source;
+ tcph->source = tcph->dest;
+ tcph->dest = tmp;
+
+ /* Truncate to length (no data) */
+ tcph->doff = sizeof(struct tcphdr) / 4;
+ skb_trim(nskb, ip_hdrlen(nskb) + sizeof(struct tcphdr));
+ niph->tot_len = htons(nskb->len);
+
+ /* Use supplied sequence number or make a new one */
+ tcph->seq = oth->ack ? oth->ack_seq : 0;
+
+ /* Our SYN-ACKs must have a >0 window */
+ tcph->window = (oth->syn && !oth->ack) ? htons(5) : 0;
+ tcph->urg_ptr = 0;
+
+ /* Reset flags */
+ ((u_int8_t *)tcph)[13] = 0;
+
+ if (oth->syn && oth->ack) {
+ tcph->rst = true;
+ tcph->ack_seq = false;
+ } else {
+ tcph->syn = oth->syn;
+ tcph->ack = 1;
+ tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn);
+ }
+
+ /* Adjust TCP checksum */
+ tcph->check = 0;
+ tcph->check = tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
+ niph->daddr, csum_partial((char *)tcph,
+ sizeof(struct tcphdr), 0));
+
+ /* Set DF, id = 0 */
+ niph->frag_off = htons(IP_DF);
+ niph->id = 0;
+
+#ifdef CONFIG_BRIDGE_NETFILTER
+ if (hook != NF_IP_FORWARD || (nskb->nf_bridge != NULL &&
+ nskb->nf_bridge->mask & BRNF_BRIDGED))
+#else
+ if (hook != NF_IP_FORWARD)
+#endif
+ addr_type = RTN_LOCAL;
+
+ if (ip_route_me_harder(&nskb, addr_type))
+ goto free_nskb;
+
+ nskb->ip_summed = CHECKSUM_NONE;
+
+ /* Adjust IP TTL */
+ niph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
+
+ /* Adjust IP checksum */
+ niph->check = 0;
+ niph->check = ip_fast_csum(skb_network_header(nskb), niph->ihl);
+
+ /* "Never happens" */
+ if (nskb->len > dst_mtu(nskb->dst))
+ goto free_nskb;
+
+ nf_ct_attach(nskb, oldskb);
+
+ NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
+ dst_output);
+ return;
+
+ free_nskb:
+ kfree_skb(nskb);
+}
+
+static unsigned int xt_tarpit_target(struct sk_buff **pskb,
+ const struct net_device *in,
+ const struct net_device *out,
+ unsigned int hooknum,
+ const struct xt_target *target,
+ const void *targinfo)
+{
+ struct sk_buff *skb = *pskb;
+ const struct iphdr *iph = ip_hdr(skb);
+ const struct rtable *rt = (const void *)skb->dst;
+
+ /* Do we have an input route cache entry? (Not in PREROUTING.) */
+ if (rt == NULL)
+ return NF_DROP;
+
+ /* No replies to physical multicast/broadcast */
+ /* skb != PACKET_OTHERHOST handled by ip_rcv() */
+ if (skb->pkt_type != PACKET_HOST)
+ return NF_DROP;
+
+ /* Now check at the protocol level */
+ if (rt->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
+ return NF_DROP;
+
+ /*
+ * Our naive response construction does not deal with IP
+ * options, and probably should not try.
+ */
+ if (ip_hdrlen(skb) != sizeof(struct iphdr))
+ return NF_DROP;
+
+ /* We are not interested in fragments */
+ if (iph->frag_off & htons(IP_OFFSET))
+ return NF_DROP;
+
+ tarpit_tcp(skb, hooknum);
+ return NF_DROP;
+}
+
+static struct xt_target xt_tarpit_reg __read_mostly = {
+ .name = "TARPIT",
+ .family = AF_INET,
+ .table = "filter",
+ .hooks = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD),
+ .proto = IPPROTO_TCP,
+ .target = xt_tarpit_target,
+ .me = THIS_MODULE,
+};
+
+static int __init xt_tarpit_init(void)
+{
+ return xt_register_target(&xt_tarpit_reg);
+}
+
+static void __exit xt_tarpit_exit(void)
+{
+ xt_unregister_target(&xt_tarpit_reg);
+}
+
+module_init(xt_tarpit_init);
+module_exit(xt_tarpit_exit);
+MODULE_DESCRIPTION("netfilter xt_TARPIT target module");
+MODULE_AUTHOR("Jan Engelhardt <jengelh@computergmbh.de>");
+MODULE_LICENSE("GPL");