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* This is a module which is used for rejecting packets.
* Added support for customized reject packets (Jozsef Kadlecsik).
* Added support for ICMP type-3-code-13 (Maciej Soltysiak). [RFC 1812]
*/
/* (C) 1999-2001 Paul `Rusty' Russell
* (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/config.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <linux/icmp.h>
#include <net/icmp.h>
#include <net/ip.h>
#include <net/tcp.h>
#include <net/route.h>
#include <net/dst.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv4/ipt_REJECT.h>
#ifdef CONFIG_BRIDGE_NETFILTER
#include <linux/netfilter_bridge.h>
#endif
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
MODULE_DESCRIPTION("iptables REJECT target module");
#if 0
#define DEBUGP printk
#else
#define DEBUGP(format, args...)
#endif
static inline struct rtable *route_reverse(struct sk_buff *skb,
struct tcphdr *tcph, int hook)
{
struct iphdr *iph = skb->nh.iph;
struct dst_entry *odst;
struct flowi fl = {};
struct rtable *rt;
/* We don't require ip forwarding to be enabled to be able to
* send a RST reply for bridged traffic. */
if (hook != NF_IP_FORWARD
#ifdef CONFIG_BRIDGE_NETFILTER
|| (skb->nf_bridge && skb->nf_bridge->mask & BRNF_BRIDGED)
#endif
) {
fl.nl_u.ip4_u.daddr = iph->saddr;
if (hook == NF_IP_LOCAL_IN)
fl.nl_u.ip4_u.saddr = iph->daddr;
fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
if (ip_route_output_key(&rt, &fl) != 0)
return NULL;
} else {
/* non-local src, find valid iif to satisfy
* rp-filter when calling ip_route_input. */
fl.nl_u.ip4_u.daddr = iph->daddr;
if (ip_route_output_key(&rt, &fl) != 0)
return NULL;
odst = skb->dst;
if (ip_route_input(skb, iph->saddr, iph->daddr,
RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
dst_release(&rt->u.dst);
return NULL;
}
dst_release(&rt->u.dst);
rt = (struct rtable *)skb->dst;
skb->dst = odst;
fl.nl_u.ip4_u.daddr = iph->saddr;
fl.nl_u.ip4_u.saddr = iph->daddr;
fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
}
if (rt->u.dst.error) {
dst_release(&rt->u.dst);
return NULL;
}
fl.proto = IPPROTO_TCP;
fl.fl_ip_sport = tcph->dest;
fl.fl_ip_dport = tcph->source;
if (xfrm_lookup((struct dst_entry **)&rt, &fl, NULL, 0)) {
dst_release(&rt->u.dst);
rt = NULL;
}
return rt;
}
/* Send RST reply */
static void send_reset(struct sk_buff *oldskb, int hook)
{
struct sk_buff *nskb;
struct iphdr *iph = oldskb->nh.iph;
struct tcphdr _otcph, *oth, *tcph;
struct rtable *rt;
u_int16_t tmp_port;
u_int32_t tmp_addr;
unsigned int tcplen;
int needs_ack;
int hh_len;
/* IP header checks: fragment. */
if (oldskb->nh.iph->frag_off & htons(IP_OFFSET))
return;
oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4,
sizeof(_otcph), &_otcph);
if (oth == NULL)
return;
/* No RST for RST. */
if (oth->rst)
return;
/* Check checksum */
tcplen = oldskb->len - iph->ihl * 4;
if (((hook != NF_IP_LOCAL_IN && oldskb->ip_summed != CHECKSUM_HW) ||
(hook == NF_IP_LOCAL_IN &&
oldskb->ip_summed != CHECKSUM_UNNECESSARY)) &&
csum_tcpudp_magic(iph->saddr, iph->daddr, tcplen, IPPROTO_TCP,
oldskb->ip_summed == CHECKSUM_HW ? oldskb->csum :
skb_checksum(oldskb, iph->ihl * 4, tcplen, 0)))
return;
if ((rt = route_reverse(oldskb, oth, hook)) == NULL)
return;
hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);
/* We need a linear, writeable skb. We also need to expand
headroom in case hh_len of incoming interface < hh_len of
outgoing interface */
nskb = skb_copy_expand(oldskb, hh_len, skb_tailroom(oldskb),
GFP_ATOMIC);
if (!nskb) {
dst_release(&rt->u.dst);
return;
}
dst_release(nskb->dst);
nskb->dst = &rt->u.dst;
/* This packet will not be the same as the other: clear nf fields */
nf_reset(nskb);
nskb->nfcache = 0;
nskb->nfmark = 0;
#ifdef CONFIG_BRIDGE_NETFILTER
nf_bridge_put(nskb->nf_bridge);
nskb->nf_bridge = NULL;
#endif
tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
/* Swap source and dest */
tmp_addr = nskb->nh.iph->saddr;
nskb->nh.iph->saddr = nskb->nh.iph->daddr;
nskb->nh.iph->daddr = tmp_addr;
tmp_port = tcph->source;
tcph->source = tcph->dest;
tcph->dest = tmp_port;
/* Truncate to length (no data) */
tcph->doff = sizeof(struct tcphdr)/4;
skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
nskb->nh.iph->tot_len = htons(nskb->len);
if (tcph->ack) {
needs_ack = 0;
tcph->seq = oth->ack_seq;
tcph->ack_seq = 0;
} else {
needs_ack = 1;
tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
+ oldskb->len - oldskb->nh.iph->ihl*4
- (oth->doff<<2));
tcph->seq = 0;
}
/* Reset flags */
((u_int8_t *)tcph)[13] = 0;
tcph->rst = 1;
tcph->ack = needs_ack;
tcph->window = 0;
tcph->urg_ptr = 0;
/* Adjust TCP checksum */
tcph->check = 0;
tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
nskb->nh.iph->saddr,
nskb->nh.iph->daddr,
csum_partial((char *)tcph,
sizeof(struct tcphdr), 0));
/* Adjust IP TTL, DF */
nskb->nh.iph->ttl = MAXTTL;
/* 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 (nskb->len > dst_mtu(nskb->dst))
goto free_nskb;
nf_ct_attach(nskb, oldskb);
NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
dst_output);
return;
free_nskb:
kfree_skb(nskb);
}
static inline void send_unreach(struct sk_buff *skb_in, int code)
{
icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
}
static unsigned int reject(struct sk_buff **pskb,
const struct net_device *in,
const struct net_device *out,
unsigned int hooknum,
const void *targinfo,
void *userinfo)
{
const struct ipt_reject_info *reject = targinfo;
/* Our naive response construction doesn't deal with IP
options, and probably shouldn't try. */
if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
return NF_DROP;
/* WARNING: This code causes reentry within iptables.
This means that the iptables jump stack is now crap. We
must return an absolute verdict. --RR */
switch (reject->with) {
case IPT_ICMP_NET_UNREACHABLE:
send_unreach(*pskb, ICMP_NET_UNREACH);
break;
case IPT_ICMP_HOST_UNREACHABLE:
send_unreach(*pskb, ICMP_HOST_UNREACH);
break;
case IPT_ICMP_PROT_UNREACHABLE:
send_unreach(*pskb, ICMP_PROT_UNREACH);
break;
case IPT_ICMP_PORT_UNREACHABLE:
send_unreach(*pskb, ICMP_PORT_UNREACH);
break;
case IPT_ICMP_NET_PROHIBITED:
send_unreach(*pskb, ICMP_NET_ANO);
break;
case IPT_ICMP_HOST_PROHIBITED:
send_unreach(*pskb, ICMP_HOST_ANO);
break;
case IPT_ICMP_ADMIN_PROHIBITED:
send_unreach(*pskb, ICMP_PKT_FILTERED);
break;
case IPT_TCP_RESET:
send_reset(*pskb, hooknum);
case IPT_ICMP_ECHOREPLY:
/* Doesn't happen. */
break;
}
return NF_DROP;
}
static int check(const char *tablename,
const struct ipt_entry *e,
void *targinfo,
unsigned int targinfosize,
unsigned int hook_mask)
{
const struct ipt_reject_info *rejinfo = targinfo;
if (targinfosize != IPT_ALIGN(sizeof(struct ipt_reject_info))) {
DEBUGP("REJECT: targinfosize %u != 0\n", targinfosize);
return 0;
}
/* Only allow these for packet filtering. */
if (strcmp(tablename, "filter") != 0) {
DEBUGP("REJECT: bad table `%s'.\n", tablename);
return 0;
}
if ((hook_mask & ~((1 << NF_IP_LOCAL_IN)
| (1 << NF_IP_FORWARD)
| (1 << NF_IP_LOCAL_OUT))) != 0) {
DEBUGP("REJECT: bad hook mask %X\n", hook_mask);
return 0;
}
if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
printk("REJECT: ECHOREPLY no longer supported.\n");
return 0;
} else if (rejinfo->with == IPT_TCP_RESET) {
/* Must specify that it's a TCP packet */
if (e->ip.proto != IPPROTO_TCP
|| (e->ip.invflags & IPT_INV_PROTO)) {
DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
return 0;
}
}
return 1;
}
static struct ipt_target ipt_reject_reg = {
.name = "REJECT",
.target = reject,
.checkentry = check,
.me = THIS_MODULE,
};
static int __init init(void)
{
return ipt_register_target(&ipt_reject_reg);
}
static void __exit fini(void)
{
ipt_unregister_target(&ipt_reject_reg);
}
module_init(init);
module_exit(fini);
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