--- /dev/null
+Index: linux-2.6.21.7/net/netfilter/Kconfig
+===================================================================
+--- linux-2.6.21.7.orig/net/netfilter/Kconfig
++++ linux-2.6.21.7/net/netfilter/Kconfig
+@@ -414,6 +414,23 @@ 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-2.6.21.7/net/netfilter/Makefile
+===================================================================
+--- linux-2.6.21.7.orig/net/netfilter/Makefile
++++ linux-2.6.21.7/net/netfilter/Makefile
+@@ -45,6 +45,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_NFQUEUE
+ obj-$(CONFIG_NETFILTER_XT_TARGET_NFLOG) += xt_NFLOG.o
+ obj-$(CONFIG_NETFILTER_XT_TARGET_NOTRACK) += xt_NOTRACK.o
+ obj-$(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-$(CONFIG_NETFILTER_XT_TARGET_CONNSECMARK) += xt_CONNSECMARK.o
+ obj-$(CONFIG_NETFILTER_XT_TARGET_CHAOS) += xt_CHAOS.o
+Index: linux-2.6.21.7/net/netfilter/xt_TARPIT.c
+===================================================================
+--- /dev/null
++++ linux-2.6.21.7/net/netfilter/xt_TARPIT.c
+@@ -0,0 +1,280 @@
++/*
++ * 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 <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>
++struct in_device;
++#include <net/route.h>
++#include <linux/random.h>
++#include <linux/netfilter_ipv4/ip_tables.h>
++
++#if 0
++#define DEBUGP printk
++#else
++#define DEBUGP(format, args...)
++#endif
++
++/* Stolen from ip_finish_output2 */
++static int ip_direct_send(struct sk_buff *skb)
++{
++ struct dst_entry *dst = skb->dst;
++
++ if (dst->hh != NULL)
++ return neigh_hh_output(dst->hh, skb);
++ else if (dst->neighbour != NULL)
++ 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(const struct sk_buff *oskb, struct rtable *ort,
++ unsigned int local)
++{
++ struct sk_buff *nskb;
++ struct rtable *nrt;
++ struct tcphdr *otcph, *ntcph;
++ struct flowi fl = {};
++ unsigned int otcplen;
++ u_int16_t tmp;
++
++ const struct iphdr *oiph = ip_hdr(oskb);
++ struct iphdr *niph;
++
++ /* A truncated TCP header is not going to be useful */
++ if (oskb->len < ip_hdrlen(oskb) + sizeof(struct tcphdr))
++ return;
++
++ otcph = (void *)oiph + ip_hdrlen(oskb);
++ otcplen = oskb->len - ip_hdrlen(oskb);
++
++ /* 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(otcplen, oiph->saddr, oiph->daddr,
++ csum_partial((char *)otcph, otcplen, 0)) != 0)
++ 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(oskb, GFP_ATOMIC);
++ if (nskb == NULL)
++ return;
++
++ niph = ip_hdr(nskb);
++
++ /* 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 = (void *)niph + ip_hdrlen(nskb);
++
++ /* Truncate to length (no data) */
++ ntcph->doff = sizeof(struct tcphdr)/4;
++ skb_trim(nskb, ip_hdrlen(nskb) + sizeof(struct tcphdr));
++ niph->tot_len = htons(nskb->len);
++
++ /* Swap source and dest */
++ niph->daddr = xchg(&niph->saddr, niph->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(niph->saddr,
++ niph->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(sizeof(struct tcphdr),
++ niph->saddr,
++ niph->daddr,
++ csum_partial((char *)ntcph,
++ sizeof(struct tcphdr), 0));
++
++ fl.nl_u.ip4_u.daddr = niph->daddr;
++ fl.nl_u.ip4_u.saddr = local ? niph->saddr : 0;
++ fl.nl_u.ip4_u.tos = RT_TOS(niph->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 */
++ niph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
++
++ /* Set DF, id = 0 */
++ niph->frag_off = htons(IP_DF);
++ niph->id = 0;
++
++ /* Adjust IP checksum */
++ niph->check = 0;
++ niph->check = ip_fast_csum((unsigned char *)niph, niph->ihl);
++
++ /* "Never happens" */
++ if (nskb->len > dst_mtu(nskb->dst))
++ goto free_nskb;
++
++ ip_direct_send(nskb);
++ 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)
++{
++ const struct sk_buff *skb = *pskb;
++ const struct iphdr *iph = ip_hdr(skb);
++ struct rtable *rt = (void *)skb->dst;
++
++ /* Do we have an input route cache entry? */
++ if (rt == NULL)
++ 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 does not deal with IP
++ * options, and probably should not try.
++ */
++ if (iph->ihl * 4 != 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, rt, hooknum == NF_IP_LOCAL_IN);
++ return NF_DROP;
++}
++
++static int xt_tarpit_check(const char *tablename, const void *entry,
++ const struct xt_target *target, void *targinfo,
++ unsigned int hook_mask)
++{
++ bool invalid;
++
++ if (strcmp(tablename, "raw") == 0 && hook_mask == NF_IP_PRE_ROUTING)
++ return true;
++ if (strcmp(tablename, "filter") != 0)
++ return false;
++ invalid = hook_mask & ~((1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD));
++ return !invalid;
++}
++
++static struct xt_target xt_tarpit_reg = {
++ .name = "TARPIT",
++ .family = AF_INET,
++ .proto = IPPROTO_TCP,
++ .target = xt_tarpit_target,
++ .checkentry = xt_tarpit_check,
++ .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@gmx.de>");
++MODULE_LICENSE("GPL");
++MODULE_ALIAS("ipt_TARPIT");
projects / openwrt / openwrt.git / blobdiff