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);