[Sorry for the inconvenience: I just noticed that Gmail has a bad
formatting. I resend the patch hoping that now things are right.]
Kernel module to capture and hold incoming TCP connections sending a
zero window packet to slow down the worm action.
More informations and newer version at:
http://npadovano.altervista.org/tarpit.html (or in the source code
comments)
Below you can find the patch and the relative userspace library
(compile it and put the .so output in /lib/xtables)
----tarpit-2.6.35.7.patch----
diff -rupN linux-2.6.35.7.orig/drivers/char/random.c
linux-2.6.35.7/drivers/char/random.c
--- linux-2.6.35.7.orig/drivers/char/random.c 2010-09-29
03:09:08.000000000 +0200
+++ linux-2.6.35.7/drivers/char/random.c 2010-10-08
02:51:35.000000000 +0200
@@ -1514,6 +1514,8 @@ __u32 secure_ip_id(__be32 daddr)
return half_md4_transform(hash, keyptr->secret);
}
+EXPORT_SYMBOL(secure_ip_id);
+
#ifdef CONFIG_INET
__u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
@@ -1551,6 +1553,8 @@ __u32 secure_tcp_sequence_number(__be32
return seq;
}
+EXPORT_SYMBOL(secure_tcp_sequence_number);
+
/* Generate secure starting point for ephemeral IPV4 transport port
search */
u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
{
diff -rupN linux-2.6.35.7.orig/net/netfilter/Kconfig
linux-2.6.35.7/net/netfilter/Kconfig
--- linux-2.6.35.7.orig/net/netfilter/Kconfig 2010-09-29
03:09:08.000000000 +0200
+++ linux-2.6.35.7/net/netfilter/Kconfig 2010-10-08
12:51:07.000000000 +0200
@@ -548,6 +548,32 @@ config NETFILTER_XT_TARGET_SECMARK
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
+ default m if NETFILTER_ADVANCED=n
+ ---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 (with a probe packet).
+ Attempts to close the connection are ignored, forcing the remote
+ side to time out the connection in 12-24 minutes. Any TCP port that
+ you would normally DROP or REJECT can instead become a tarpit.
+ Example:
+
+ 1) iptables -A INPUT -p tcp --dport 1111 -j TARPIT
+ 2) iptables -A FORWARD -p tcp -s x.y.z.k --dport 1111 -j TARPIT
+
+ In the first example all the incoming TCP packets sent to the port
+ 1111 will be tarpitted. In the second one, we're tarpitting all the
+ forwarded packets sent to the host x.y.z.k on the port 1111.
+
+ You can find more informations and newer versions at:
+ <http://npadovano.altervista.org/tarpit.html>. Reporting bugs and
+ improvements are welcome.
+
config NETFILTER_XT_TARGET_TCPMSS
tristate '"TCPMSS" target support'
depends on (IPV6 || IPV6=n)
diff -rupN linux-2.6.35.7.orig/net/netfilter/Makefile
linux-2.6.35.7/net/netfilter/Makefile
--- linux-2.6.35.7.orig/net/netfilter/Makefile 2010-09-29
03:09:08.000000000 +0200
+++ linux-2.6.35.7/net/netfilter/Makefile 2010-10-08
02:53:44.000000000 +0200
@@ -56,6 +56,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_NFQUEUE
obj-$(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-$(CONFIG_NETFILTER_XT_TARGET_TARPIT) += xt_TARPIT.o
obj-$(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
diff -rupN linux-2.6.35.7.orig/net/netfilter/xt_TARPIT.c
linux-2.6.35.7/net/netfilter/xt_TARPIT.c
--- linux-2.6.35.7.orig/net/netfilter/xt_TARPIT.c 1970-01-01
01:00:00.000000000 +0100
+++ linux-2.6.35.7/net/netfilter/xt_TARPIT.c 2010-10-08
13:27:54.000000000 +0200
@@ -0,0 +1,304 @@
+/*
+ * 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://labrea.sourceforge.net/>.
+ *
+ * Original idea of:
+ * Aaron Hopkins, <tools@xxxxxxx>
+ *
+ * Version 2.6.35.7 kernel release, written by:
+ * Nicola Padovano, <nicola.padovano@xxxxxxxxx>
+ *
+ * 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 60-240 seconds.
+ * - Prevent spoofing (don't allow the victim to connect with server worm)
+ * - 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,!RST,!FIN with ACK, window 0 bytes, rate-limited
+ * - Reply to TCP SYN,ACK,!RST,!FIN with RST to prevent spoofing
+ * - No reply to TCP RST or FIN
+ *
+ * More informations and newer versions at:
+ * <http://npadovano.altervista.com/tarpit.html>
+ */
+
+#include <linux/version.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+#include <net/ip.h>
+#include <net/tcp.h>
+#include <net/icmp.h>
+#include <net/route.h>
+#include <linux/random.h>
+#include <linux/netfilter_ipv4/ip_tables.h>
+
+
+MODULE_DESCRIPTION("TARPIT iptables target, info at: "
+ "http://npadovano.altervista.org/tarpit.html";);
+MODULE_AUTHOR("Nicola Padovano <nicola.padovano@xxxxxxxxx>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("xt_TARPIT");
+
+/*
+ * send a packet (to L2 output processing function)
+ *
+ * Note: there is also rtable* argument: it's only
+ * used for debugging reason. Delete it if
+ * you're sure things work.
+ */
+static int ip_direct_send(struct sk_buff* skb)
+{
+ /* get skb dst_entry pointer */
+ struct dst_entry* dst = skb_dst(skb);
+
+ /* if we already sent a packet to our neighbour */
+ if (dst->hh != NULL)
+ return neigh_hh_output(dst->hh,skb);
+
+ /* if there isn't header cache, send our packet with simple output
function */
+ else if (dst->neighbour != NULL)
+ return dst->neighbour->output(skb);
+
+ /* no neighbour, no header cache: it's impossible send the packet */
+ if (net_ratelimit())
+ printk(KERN_DEBUG "TARPIT> ip_direct_send: no neighbour, no header
cache\n");
+
+ kfree_skb(skb);
+
+ return -EINVAL;
+}
+
+/*
+ * tarpit service routine: it accepts a pointer to
+ * sk_buff (the received packet) and its (input)
+ * cache entry.
+ * Note: the received packet it's called "old" in
+ * the comments below. The packet to send
+ * it's called "new".
+ */
+static void tarpit_tcp(const struct sk_buff *oskb,
+ struct rtable *ort)
+{
+ struct iphdr *oiph; /* old ip header pointer */
+ struct tcphdr *otcph; /* old tcp header pointer */
+ unsigned int oiphlen; /* old ip header len */
+ unsigned int otcplen; /* old tcp (payload + header) len */
+
+ struct sk_buff *nskb; /* new skb buffer */
+ struct iphdr *niph; /* new ip header pointer */
+ struct tcphdr *ntcph; /* new tcp header pointer */
+ struct rtable *nrt; /* new routing table */
+
+ struct flowi fl = {}; /* search key used for the cache
lookups */
+
+ u_int32_t tmp32; /* swapping variables*/
+ u_int16_t tmp16;
+
+ /* fill old structs */
+ oiph = ip_hdr(oskb); /* get old ip header pointer */
+ oiphlen = ip_hdrlen(oskb);
+ otcph = (void*)oiph + oiphlen; /* do not use
skb_transport_header! */
+ otcplen = oskb->len - oiphlen;
+
+ /* packets to drop */
+ if ( (oskb->len < oiphlen + sizeof(struct tcphdr))
|| /* truncate tcp header: 1st too fragmented packet...*/
+ (otcph->fin || otcph->rst)
|| /* RST or FIN packet*/
+ (!otcph->ack && !otcph->syn)
|| /* !ACK,!SYN packet */
+ (tcp_v4_check(otcplen, oiph->saddr,
oiph->daddr, /* bad tcp checksum e ip checksum */
+ csum_partial((char *)otcph, otcplen, 0))) ||
+ (oiph->frag_off & htons(IP_OFFSET))
|| /* fragment packets (after the first one) */
+ (!otcph->syn && otcph->ack && !xrlim_allow(&ort->u.dst,HZ))
|| /* rate-limit answer to SYN,ACK packets */
+ (ort == NULL)
|| /* check for an
input routing cache entry */
+ (oskb->pkt_type != PACKET_HOST
&& /* no replies to physical
multi/broadcast */
+ oskb->pkt_type != PACKET_OTHERHOST) ||
+ (ort->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
) /* check IP multi/broadcast */
+ return;
+
+
+ if (!(nskb = skb_copy(oskb, GFP_ATOMIC))) /* we start with a
yet-prepared buffer */
+ return; /* return if there's
an error in copy */
+
+ /* 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
+
+ skb_trim(nskb, ip_hdrlen(nskb) + sizeof(struct tcphdr)); /* trim
skb size to IP LEN + TCP LEN*/
+ niph = (struct iphdr*)skb_network_header(nskb);
+ ntcph = (void*)niph + ip_hdrlen(nskb);
+
+ /* set new ip header */
+ tmp32 = niph->saddr;
+ niph->saddr = niph->daddr;
+ niph->daddr = tmp32;
+
+ niph->tot_len = htons(nskb->len);
+ niph->id = htons(secure_ip_id(niph->daddr));
+
+ niph->frag_off = htons(IP_DF); /* set don't frag flag */
+ niph->ttl = (u32)64;
+
+ niph->check = 0;
+ niph->check = ip_fast_csum((unsigned char*)niph ,niph->ihl);
+
+ /* set new tcp header */
+ tmp16 = ntcph->source;
+ ntcph->source = ntcph->dest;
+ ntcph->dest = tmp16;
+
+ ntcph->doff = sizeof(struct tcphdr)/4; /* 20bytes, doff is a
4bit variable */
+
+ ((u_int8_t*)ntcph)[13] = 0; /* reset all flag */
+ ntcph->urg_ptr = 0;
+
+ /* 1st goal: new tcp connection */
+ if (otcph->syn && !otcph->ack)
+ {
+ ntcph->syn = 1;
+ ntcph->ack = 1;
+ ntcph->seq = htonl(secure_tcp_sequence_number(niph->saddr,
+ niph->daddr,
+ ntcph->source,
+ ntcph->dest));
+ ntcph->ack_seq = htonl(ntohl(otcph->seq) + 1);
+ ntcph->window = htons(5);
+ }
+
+ /* 2nd goal: RST tcp: RST+ACK */
+ else if (otcph->syn && otcph->ack)
+ {
+ ntcph->syn = 0;
+ ntcph->ack = 1;
+ ntcph->rst = 1;
+
+ ntcph->seq = otcph->ack_seq;
+ ntcph->ack_seq = 0;
+ }
+
+ /* 3rd goal: 0 byte window */
+ else if (!otcph->syn && otcph->ack)
+ {
+ ntcph->syn = 0;
+ ntcph->ack = 1;
+ ntcph->window = 0;
+ ntcph->seq = otcph->ack_seq;
+ ntcph->ack_seq = otcph->seq; /* it's saying: "i'm not received
anything" */
+ }
+ else /* unacknowledged packet: drop it*/
+ return;
+
+ ntcph->check = 0;
+ ntcph->check = tcp_v4_check(sizeof(struct tcphdr),
+ niph->saddr,
+ niph->daddr,
+ csum_partial((char *)ntcph,
+ sizeof(struct tcphdr), 0));
+
+
+ /* create a search key to find packet route in cache*/
+ fl.nl_u.ip4_u.daddr = niph->daddr;
+ fl.nl_u.ip4_u.saddr = 0;
+ fl.nl_u.ip4_u.tos = RT_TOS(niph->tos) | RTO_CONN;
+ fl.oif = 0;
+
+ if (ip_route_output_key(&init_net, &nrt, &fl)) /* fill
nrt struct */
+ goto free_nskb; /* exit if
errors in filling*/
+
+ dst_release(skb_dst(nskb));
+ nskb->_skb_refdst = ((unsigned long)&(nrt->u.dst));
+
+ ip_direct_send(nskb); /* send
the packet */
+
+ return;
+
+ free_nskb:
+ kfree_skb(nskb);
+}
+
+
+/*
+ * target function, called everyone the rule is satisfied
+ * standard behaviour: NF_DROP
+ */
+static unsigned int xt_tarpit_target(struct sk_buff *skb,
+ const struct xt_target_param *par)
+{
+ struct rtable *rt = (void *)skb->_skb_refdst;
+ tarpit_tcp(skb,rt);
+ return NF_DROP;
+}
+
+/*
+ * xt_tarpit_check allows only:
+ * 1. raw table & PRE_ROUTING hook or
+ * 2. filter table & (LOCAL_IN or FORWARD) hook
+ * Note: for new kernels version: returns _false_
+ * if checking is OK, otherwise returns _true_
+ */
+static bool xt_tarpit_check(const struct xt_mtchk_param *par)
+{
+ if (!strcmp(par->table, "raw") &&
+ par->hook_mask == NF_INET_PRE_ROUTING)
+ return false;
+
+ if (strcmp(par->table, "filter"))
+ return true;
+
+ return (par->hook_mask & ~((1 << NF_INET_LOCAL_IN) |
+ (1 << NF_INET_FORWARD)));
+}
+
+
+static struct xt_target xt_tar_reg = {
+ .name = "TARPIT", /* target name */
+ .family = AF_INET, /* level 3 protocol */
+ .proto = IPPROTO_TCP, /* we recognize only tcp protocol */
+ .target = xt_tarpit_target, /* pointer to target function */
+ .checkentry = xt_tarpit_check, /* pointer to check-entry function */
+ .me = THIS_MODULE,
+};
+
+/*
+ * initing module function
+ */
+static int __init xt_tarpit_init(void)
+{
+ return xt_register_target(&xt_tar_reg);
+}
+
+/*
+ * delete module
+ */
+static void __exit xt_tarpit_exit(void)
+{
+ xt_unregister_target(&xt_tar_reg);
+}
+
+module_init(xt_tarpit_init);
+module_exit(xt_tarpit_exit);
----libxt_TARPIT.c----
#include <stdio.h>
#include <getopt.h>
#include <xtables.h>
static void tarpit_tg_help(void)
{
printf("TARPIT takes no options\n\n");
}
static int tarpit_tg_parse(int c, char **argv, int invert, unsigned int
*flags,
const void *entry, struct xt_entry_target
**target)
{
return 0;
}
static void tarpit_tg_check(unsigned int flags)
{
}
static struct xtables_target tarpit_tg_reg = {
.version = XTABLES_VERSION,
.name = "TARPIT",
.family = AF_INET,
.help = tarpit_tg_help,
.parse = tarpit_tg_parse,
.final_check = tarpit_tg_check,
};
static __attribute__((constructor)) void tarpit_tg_ldr(void)
{
xtables_register_target(&tarpit_tg_reg);
}
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