2005-04-16 22:20:36 +00:00
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/*
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* This is a module which is used for rejecting packets.
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* Added support for customized reject packets (Jozsef Kadlecsik).
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* Added support for ICMP type-3-code-13 (Maciej Soltysiak). [RFC 1812]
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*/
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/* (C) 1999-2001 Paul `Rusty' Russell
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* (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/config.h>
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/ip.h>
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#include <linux/udp.h>
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#include <linux/icmp.h>
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#include <net/icmp.h>
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#include <net/ip.h>
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#include <net/tcp.h>
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#include <net/route.h>
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#include <net/dst.h>
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#include <linux/netfilter_ipv4/ip_tables.h>
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#include <linux/netfilter_ipv4/ipt_REJECT.h>
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#ifdef CONFIG_BRIDGE_NETFILTER
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#include <linux/netfilter_bridge.h>
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#endif
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
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MODULE_DESCRIPTION("iptables REJECT target module");
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#if 0
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#define DEBUGP printk
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#else
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#define DEBUGP(format, args...)
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#endif
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static inline struct rtable *route_reverse(struct sk_buff *skb,
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struct tcphdr *tcph, int hook)
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{
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struct iphdr *iph = skb->nh.iph;
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struct dst_entry *odst;
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struct flowi fl = {};
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struct rtable *rt;
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/* We don't require ip forwarding to be enabled to be able to
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* send a RST reply for bridged traffic. */
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if (hook != NF_IP_FORWARD
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#ifdef CONFIG_BRIDGE_NETFILTER
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|| (skb->nf_bridge && skb->nf_bridge->mask & BRNF_BRIDGED)
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#endif
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) {
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fl.nl_u.ip4_u.daddr = iph->saddr;
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if (hook == NF_IP_LOCAL_IN)
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fl.nl_u.ip4_u.saddr = iph->daddr;
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fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
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if (ip_route_output_key(&rt, &fl) != 0)
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return NULL;
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} else {
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/* non-local src, find valid iif to satisfy
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* rp-filter when calling ip_route_input. */
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fl.nl_u.ip4_u.daddr = iph->daddr;
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if (ip_route_output_key(&rt, &fl) != 0)
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return NULL;
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odst = skb->dst;
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if (ip_route_input(skb, iph->saddr, iph->daddr,
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RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
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dst_release(&rt->u.dst);
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return NULL;
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}
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dst_release(&rt->u.dst);
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rt = (struct rtable *)skb->dst;
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skb->dst = odst;
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fl.nl_u.ip4_u.daddr = iph->saddr;
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fl.nl_u.ip4_u.saddr = iph->daddr;
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fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
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}
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if (rt->u.dst.error) {
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dst_release(&rt->u.dst);
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return NULL;
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}
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fl.proto = IPPROTO_TCP;
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fl.fl_ip_sport = tcph->dest;
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fl.fl_ip_dport = tcph->source;
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2005-09-08 22:11:55 +00:00
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xfrm_lookup((struct dst_entry **)&rt, &fl, NULL, 0);
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2005-04-16 22:20:36 +00:00
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return rt;
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}
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/* Send RST reply */
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static void send_reset(struct sk_buff *oldskb, int hook)
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{
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struct sk_buff *nskb;
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2005-06-21 21:03:46 +00:00
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struct iphdr *iph = oldskb->nh.iph;
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2005-04-16 22:20:36 +00:00
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struct tcphdr _otcph, *oth, *tcph;
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struct rtable *rt;
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u_int16_t tmp_port;
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u_int32_t tmp_addr;
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2005-06-21 21:03:46 +00:00
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unsigned int tcplen;
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2005-04-16 22:20:36 +00:00
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int needs_ack;
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int hh_len;
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/* IP header checks: fragment. */
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if (oldskb->nh.iph->frag_off & htons(IP_OFFSET))
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return;
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oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4,
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sizeof(_otcph), &_otcph);
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if (oth == NULL)
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return;
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/* No RST for RST. */
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if (oth->rst)
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return;
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2005-06-21 21:03:46 +00:00
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/* Check checksum */
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tcplen = oldskb->len - iph->ihl * 4;
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if (((hook != NF_IP_LOCAL_IN && oldskb->ip_summed != CHECKSUM_HW) ||
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(hook == NF_IP_LOCAL_IN &&
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oldskb->ip_summed != CHECKSUM_UNNECESSARY)) &&
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csum_tcpudp_magic(iph->saddr, iph->daddr, tcplen, IPPROTO_TCP,
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oldskb->ip_summed == CHECKSUM_HW ? oldskb->csum :
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skb_checksum(oldskb, iph->ihl * 4, tcplen, 0)))
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return;
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2005-04-16 22:20:36 +00:00
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if ((rt = route_reverse(oldskb, oth, hook)) == NULL)
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return;
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hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);
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/* We need a linear, writeable skb. We also need to expand
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headroom in case hh_len of incoming interface < hh_len of
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outgoing interface */
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nskb = skb_copy_expand(oldskb, hh_len, skb_tailroom(oldskb),
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GFP_ATOMIC);
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if (!nskb) {
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dst_release(&rt->u.dst);
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return;
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}
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dst_release(nskb->dst);
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nskb->dst = &rt->u.dst;
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/* This packet will not be the same as the other: clear nf fields */
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nf_reset(nskb);
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nskb->nfmark = 0;
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#ifdef CONFIG_BRIDGE_NETFILTER
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nf_bridge_put(nskb->nf_bridge);
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nskb->nf_bridge = NULL;
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#endif
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tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
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/* Swap source and dest */
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tmp_addr = nskb->nh.iph->saddr;
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nskb->nh.iph->saddr = nskb->nh.iph->daddr;
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nskb->nh.iph->daddr = tmp_addr;
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tmp_port = tcph->source;
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tcph->source = tcph->dest;
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tcph->dest = tmp_port;
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/* Truncate to length (no data) */
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tcph->doff = sizeof(struct tcphdr)/4;
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skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
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nskb->nh.iph->tot_len = htons(nskb->len);
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if (tcph->ack) {
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needs_ack = 0;
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tcph->seq = oth->ack_seq;
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tcph->ack_seq = 0;
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} else {
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needs_ack = 1;
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tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
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+ oldskb->len - oldskb->nh.iph->ihl*4
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- (oth->doff<<2));
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tcph->seq = 0;
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}
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/* Reset flags */
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((u_int8_t *)tcph)[13] = 0;
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tcph->rst = 1;
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tcph->ack = needs_ack;
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tcph->window = 0;
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tcph->urg_ptr = 0;
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/* Adjust TCP checksum */
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tcph->check = 0;
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tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
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nskb->nh.iph->saddr,
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nskb->nh.iph->daddr,
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csum_partial((char *)tcph,
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sizeof(struct tcphdr), 0));
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/* Adjust IP TTL, DF */
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nskb->nh.iph->ttl = MAXTTL;
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/* Set DF, id = 0 */
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nskb->nh.iph->frag_off = htons(IP_DF);
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nskb->nh.iph->id = 0;
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/* Adjust IP checksum */
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nskb->nh.iph->check = 0;
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nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
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nskb->nh.iph->ihl);
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/* "Never happens" */
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if (nskb->len > dst_mtu(nskb->dst))
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goto free_nskb;
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nf_ct_attach(nskb, oldskb);
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NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
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dst_output);
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return;
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free_nskb:
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kfree_skb(nskb);
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}
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static inline void send_unreach(struct sk_buff *skb_in, int code)
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{
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icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
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}
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static unsigned int reject(struct sk_buff **pskb,
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const struct net_device *in,
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const struct net_device *out,
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unsigned int hooknum,
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const void *targinfo,
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void *userinfo)
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{
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const struct ipt_reject_info *reject = targinfo;
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/* Our naive response construction doesn't deal with IP
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options, and probably shouldn't try. */
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if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
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return NF_DROP;
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/* WARNING: This code causes reentry within iptables.
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This means that the iptables jump stack is now crap. We
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must return an absolute verdict. --RR */
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switch (reject->with) {
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case IPT_ICMP_NET_UNREACHABLE:
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send_unreach(*pskb, ICMP_NET_UNREACH);
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break;
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case IPT_ICMP_HOST_UNREACHABLE:
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send_unreach(*pskb, ICMP_HOST_UNREACH);
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break;
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case IPT_ICMP_PROT_UNREACHABLE:
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send_unreach(*pskb, ICMP_PROT_UNREACH);
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break;
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case IPT_ICMP_PORT_UNREACHABLE:
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send_unreach(*pskb, ICMP_PORT_UNREACH);
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break;
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case IPT_ICMP_NET_PROHIBITED:
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send_unreach(*pskb, ICMP_NET_ANO);
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break;
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case IPT_ICMP_HOST_PROHIBITED:
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send_unreach(*pskb, ICMP_HOST_ANO);
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break;
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case IPT_ICMP_ADMIN_PROHIBITED:
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send_unreach(*pskb, ICMP_PKT_FILTERED);
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break;
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case IPT_TCP_RESET:
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send_reset(*pskb, hooknum);
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case IPT_ICMP_ECHOREPLY:
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/* Doesn't happen. */
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break;
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}
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return NF_DROP;
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}
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static int check(const char *tablename,
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const struct ipt_entry *e,
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void *targinfo,
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unsigned int targinfosize,
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unsigned int hook_mask)
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{
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const struct ipt_reject_info *rejinfo = targinfo;
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if (targinfosize != IPT_ALIGN(sizeof(struct ipt_reject_info))) {
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DEBUGP("REJECT: targinfosize %u != 0\n", targinfosize);
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return 0;
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}
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/* Only allow these for packet filtering. */
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if (strcmp(tablename, "filter") != 0) {
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DEBUGP("REJECT: bad table `%s'.\n", tablename);
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return 0;
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}
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if ((hook_mask & ~((1 << NF_IP_LOCAL_IN)
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| (1 << NF_IP_FORWARD)
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| (1 << NF_IP_LOCAL_OUT))) != 0) {
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DEBUGP("REJECT: bad hook mask %X\n", hook_mask);
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return 0;
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}
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if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
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printk("REJECT: ECHOREPLY no longer supported.\n");
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return 0;
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} else if (rejinfo->with == IPT_TCP_RESET) {
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/* Must specify that it's a TCP packet */
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if (e->ip.proto != IPPROTO_TCP
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|| (e->ip.invflags & IPT_INV_PROTO)) {
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DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
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return 0;
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}
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}
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return 1;
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}
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static struct ipt_target ipt_reject_reg = {
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.name = "REJECT",
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.target = reject,
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.checkentry = check,
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.me = THIS_MODULE,
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};
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static int __init init(void)
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{
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return ipt_register_target(&ipt_reject_reg);
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}
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static void __exit fini(void)
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{
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ipt_unregister_target(&ipt_reject_reg);
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}
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module_init(init);
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module_exit(fini);
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