+++ /dev/null
---- a/net/netfilter/Kconfig
-+++ b/net/netfilter/Kconfig
-@@ -469,6 +469,23 @@ 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
-+ ---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 (IPV6 || IPV6=n)
---- a/net/netfilter/Makefile
-+++ b/net/netfilter/Makefile
-@@ -51,6 +51,7 @@ 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
---- /dev/null
-+++ b/net/netfilter/xt_TARPIT.c
-@@ -0,0 +1,279 @@
-+/*
-+ * 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(&init_net, &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 *skb,
-+ const struct net_device *in,
-+ const struct net_device *out,
-+ unsigned int hooknum,
-+ const struct xt_target *target,
-+ const void *targinfo)
-+{
-+ 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_INET_LOCAL_IN);
-+ return NF_DROP;
-+}
-+
-+static bool 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_INET_PRE_ROUTING)
-+ return true;
-+ if (strcmp(tablename, "filter") != 0)
-+ return false;
-+ invalid = hook_mask & ~((1 << NF_INET_LOCAL_IN) | (1 << NF_INET_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.git / commitdiff