Kconfig | 17 +++
Makefile | 1
ipt_TARPIT.c | 296 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 314 insertions(+)
diff -Nur --exclude '*.orig' linux.org/net/ipv4/netfilter/Kconfig linux/net/ipv4/netfilter/Kconfig
--- linux.org/net/ipv4/netfilter/Kconfig 2006-05-02 23:38:44.000000000 +0200
+++ linux/net/ipv4/netfilter/Kconfig 2006-05-04 11:21:59.000000000 +0200
@@ -606,5 +606,22 @@
Allows altering the ARP packet payload: source and destination
hardware and network addresses.
+config IP_NF_TARGET_TARPIT
+ tristate 'TARPIT target support'
+ depends on IP_NF_FILTER
+ 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
+ but doesn't require dedicated
+ hardware or IPs. Any TCP port that you would normally DROP or REJECT
+ can instead become a tarpit.
+
endmenu
diff -Nur --exclude '*.orig' linux.org/net/ipv4/netfilter/Makefile linux/net/ipv4/netfilter/Makefile
--- linux.org/net/ipv4/netfilter/Makefile 2006-05-02 23:38:44.000000000 +0200
+++ linux/net/ipv4/netfilter/Makefile 2006-05-04 11:21:59.000000000 +0200
@@ -0,0 +0,1 @@
+obj-$(CONFIG_IP_NF_TARGET_TARPIT) += ipt_TARPIT.o
diff -Nur --exclude '*.orig' linux.org/net/ipv4/netfilter/ipt_TARPIT.c linux/net/ipv4/netfilter/ipt_TARPIT.c
--- linux.org/net/ipv4/netfilter/ipt_TARPIT.c 1970-01-01 01:00:00.000000000 +0100
+++ linux/net/ipv4/netfilter/ipt_TARPIT.c 2006-05-04 11:21:59.000000000 +0200
@@ -0,0 +1,296 @@
+/*
+ * 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 .
+ *
+ * Copyright (c) 2002 Aaron Hopkins
+ *
+ * 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
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+struct in_device;
+#include
+#include
+#include
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(format, args...)
+#endif
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Aaron Hopkins ");
+
+/* Stolen from ip_finish_output2 */
+static int ip_direct_send(struct sk_buff *skb)
+{
+ struct dst_entry *dst = skb->dst;
+ struct hh_cache *hh = dst->hh;
+
+ if (hh) {
+ read_lock_bh(&hh->hh_lock);
+ memcpy(skb->data - 16, hh->hh_data, 16);
+ read_unlock_bh(&hh->hh_lock);
+ skb_push(skb, hh->hh_len);
+ return hh->hh_output(skb);
+ } else if (dst->neighbour)
+ return dst->neighbour->output(skb);
+
+ if (net_ratelimit())
+ printk(KERN_DEBUG "TARPIT ip_direct_send: no header cache and no neighbor!\n");
+ kfree_skb(skb);
+ return -EINVAL;
+}
+
+
+/* Send reply */
+static void tarpit_tcp(struct sk_buff *oskb,struct rtable *ort,int local)
+{
+ struct sk_buff *nskb;
+ struct rtable *nrt;
+ struct tcphdr *otcph, *ntcph;
+ struct flowi fl = {};
+ unsigned int otcplen;
+ u_int16_t tmp;
+
+ /* A truncated TCP header isn't going to be useful */
+ if (oskb->len < (oskb->nh.iph->ihl*4) + sizeof(struct tcphdr))
+ return;
+
+ otcph = (struct tcphdr *)((u_int32_t*)oskb->nh.iph
+ + oskb->nh.iph->ihl);
+ otcplen = oskb->len - oskb->nh.iph->ihl*4;
+
+ /* No replies for RST or FIN */
+ if (otcph->rst || otcph->fin)
+ return;
+
+ /* No reply to !SYN,!ACK. Rate-limit replies to !SYN,ACKs */
+ if (!otcph->syn && (!otcph->ack || !xrlim_allow(&ort->u.dst, 1*HZ)))
+ return;
+
+ /* Check checksum. */
+ if (tcp_v4_check(otcph, otcplen, oskb->nh.iph->saddr,
+ oskb->nh.iph->daddr,
+ csum_partial((char *)otcph, otcplen, 0)) != 0)
+ return;
+
+ /* Copy skb (even if skb is about to be dropped, we can't just
+ clone it because there may be other things, such as tcpdump,
+ interested in it) */
+ nskb = skb_copy(oskb, GFP_ATOMIC);
+ if (!nskb)
+ return;
+
+ /* This packet will not be the same as the other: clear nf fields */
+ nf_conntrack_put(nskb->nfct);
+ nskb->nfct = NULL;
+#ifdef CONFIG_NETFILTER_DEBUG
+ nskb->nf_debug = 0;
+#endif
+
+ ntcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
+
+ /* Truncate to length (no data) */
+ ntcph->doff = sizeof(struct tcphdr)/4;
+ skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
+ nskb->nh.iph->tot_len = htons(nskb->len);
+
+ /* Swap source and dest */
+ nskb->nh.iph->daddr = xchg(&nskb->nh.iph->saddr, nskb->nh.iph->daddr);
+ tmp = ntcph->source;
+ ntcph->source = ntcph->dest;
+ ntcph->dest = tmp;
+
+ /* Use supplied sequence number or make a new one */
+ ntcph->seq = otcph->ack ? otcph->ack_seq
+ : htonl(secure_tcp_sequence_number(nskb->nh.iph->saddr,
+ nskb->nh.iph->daddr,
+ ntcph->source,
+ ntcph->dest));
+
+ /* Our SYN-ACKs must have a >0 window */
+ ntcph->window = (otcph->syn && !otcph->ack) ? htons(5) : 0;
+
+ ntcph->urg_ptr = 0;
+
+ /* Reset flags */
+ ((u_int8_t *)ntcph)[13] = 0;
+
+ if (otcph->syn && otcph->ack) {
+ ntcph->rst = 1;
+ ntcph->ack_seq = 0;
+ } else {
+ ntcph->syn = otcph->syn;
+ ntcph->ack = 1;
+ ntcph->ack_seq = htonl(ntohl(otcph->seq) + otcph->syn);
+ }
+
+ /* Adjust TCP checksum */
+ ntcph->check = 0;
+ ntcph->check = tcp_v4_check(ntcph, sizeof(struct tcphdr),
+ nskb->nh.iph->saddr,
+ nskb->nh.iph->daddr,
+ csum_partial((char *)ntcph,
+ sizeof(struct tcphdr), 0));
+
+ fl.nl_u.ip4_u.daddr = nskb->nh.iph->daddr;
+ fl.nl_u.ip4_u.saddr = local ? nskb->nh.iph->saddr : 0;
+ fl.nl_u.ip4_u.tos = RT_TOS(nskb->nh.iph->tos) | RTO_CONN;
+ fl.oif = 0;
+
+ if (ip_route_output_key(&nrt, &fl))
+ goto free_nskb;
+
+ dst_release(nskb->dst);
+ nskb->dst = &nrt->u.dst;
+
+ /* Adjust IP TTL */
+ nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
+
+ /* Set DF, id = 0 */
+ nskb->nh.iph->frag_off = htons(IP_DF);
+ nskb->nh.iph->id = 0;
+
+ /* Adjust IP checksum */
+ nskb->nh.iph->check = 0;
+ nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
+ nskb->nh.iph->ihl);
+
+ /* "Never happens" */
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,12)
+ if (nskb->len > dst_mtu(nskb->dst))
+#else
+ if (nskb->len > dst_pmtu(nskb->dst))
+#endif
+ goto free_nskb;
+
+ ip_direct_send (nskb);
+
+ return;
+
+ free_nskb:
+ kfree_skb(nskb);
+}
+
+
+static unsigned int tarpit(struct sk_buff **pskb,
+ const struct net_device *in,
+ const struct net_device *out,
+ unsigned int hooknum,
+ const void *targinfo,
+ void *userinfo)
+{
+ struct sk_buff *skb = *pskb;
+ struct rtable *rt = (struct rtable*)skb->dst;
+
+ /* Do we have an input route cache entry? */
+ if (!rt)
+ return NF_DROP;
+
+ /* No replies to physical multicast/broadcast */
+ if (skb->pkt_type != PACKET_HOST && skb->pkt_type != PACKET_OTHERHOST)
+ return NF_DROP;
+
+ /* Now check at the protocol level */
+ if (rt->rt_flags&(RTCF_BROADCAST|RTCF_MULTICAST))
+ return NF_DROP;
+
+ /* Our naive response construction doesn't deal with IP
+ options, and probably shouldn't try. */
+ if (skb->nh.iph->ihl*4 != sizeof(struct iphdr))
+ return NF_DROP;
+
+ /* We aren't interested in fragments */
+ if (skb->nh.iph->frag_off & htons(IP_OFFSET))
+ return NF_DROP;
+
+ tarpit_tcp(skb,rt,hooknum == NF_IP_LOCAL_IN);
+
+ return NF_DROP;
+}
+
+
+static int check(const char *tablename,
+ const void *e_void,
+ void *targinfo,
+ unsigned int targinfosize,
+ unsigned int hook_mask)
+{
+ const struct ipt_entry *e = e_void;
+
+ /* Only allow these for input/forward packet filtering. */
+ if (strcmp(tablename, "filter") != 0) {
+ DEBUGP("TARPIT: bad table %s'.\n", tablename);
+ return 0;
+ }
+ if ((hook_mask & ~((1 << NF_IP_LOCAL_IN)
+ | (1 << NF_IP_FORWARD))) != 0) {
+ DEBUGP("TARPIT: bad hook mask %X\n", hook_mask);
+ return 0;
+ }
+
+ /* Must specify that it's a TCP packet */
+ if (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & IPT_INV_PROTO)) {
+ DEBUGP("TARPIT: not valid for non-tcp\n");
+ return 0;
+ }
+
+ return 1;
+}
+
+static struct ipt_target ipt_tarpit_reg = {
+ .name = "TARPIT",
+ .target = tarpit,
+ .checkentry = check,
+ .me = THIS_MODULE
+};
+
+static int __init init(void)
+{
+ return ipt_register_target(&ipt_tarpit_reg);
+}
+
+static void __exit fini(void)
+{
+ ipt_unregister_target(&ipt_tarpit_reg);
+}
+
+module_init(init);
+module_exit(fini);