261 lines
6.3 KiB
C
261 lines
6.3 KiB
C
/*
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* This is a module which is used for rejecting packets.
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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/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/x_tables.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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/* 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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struct iphdr *niph;
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struct tcphdr _otcph, *oth, *tcph;
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__be16 tmp_port;
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__be32 tmp_addr;
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int needs_ack;
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unsigned int addr_type;
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/* IP header checks: fragment. */
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if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
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return;
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oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
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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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/* Check checksum */
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if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
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return;
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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, LL_MAX_HEADER, skb_tailroom(oldskb),
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GFP_ATOMIC);
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if (!nskb)
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return;
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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->mark = 0;
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skb_init_secmark(nskb);
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skb_shinfo(nskb)->gso_size = 0;
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skb_shinfo(nskb)->gso_segs = 0;
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skb_shinfo(nskb)->gso_type = 0;
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tcph = (struct tcphdr *)(skb_network_header(nskb) + ip_hdrlen(nskb));
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/* Swap source and dest */
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niph = ip_hdr(nskb);
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tmp_addr = niph->saddr;
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niph->saddr = niph->daddr;
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niph->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, ip_hdrlen(nskb) + sizeof(struct tcphdr));
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niph->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 - ip_hdrlen(oldskb) -
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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(sizeof(struct tcphdr),
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niph->saddr, niph->daddr,
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csum_partial(tcph,
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sizeof(struct tcphdr), 0));
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/* Set DF, id = 0 */
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niph->frag_off = htons(IP_DF);
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niph->id = 0;
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addr_type = RTN_UNSPEC;
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if (hook != NF_IP_FORWARD
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#ifdef CONFIG_BRIDGE_NETFILTER
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|| (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
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#endif
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)
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addr_type = RTN_LOCAL;
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if (ip_route_me_harder(nskb, addr_type))
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goto free_nskb;
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nskb->ip_summed = CHECKSUM_NONE;
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/* Adjust IP TTL */
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niph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
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/* Adjust IP checksum */
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niph->check = 0;
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niph->check = ip_fast_csum(skb_network_header(nskb), niph->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 *skb,
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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 struct xt_target *target,
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const void *targinfo)
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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 (ip_hdrlen(skb) != 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(skb, ICMP_NET_UNREACH);
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break;
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case IPT_ICMP_HOST_UNREACHABLE:
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send_unreach(skb, ICMP_HOST_UNREACH);
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break;
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case IPT_ICMP_PROT_UNREACHABLE:
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send_unreach(skb, ICMP_PROT_UNREACH);
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break;
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case IPT_ICMP_PORT_UNREACHABLE:
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send_unreach(skb, ICMP_PORT_UNREACH);
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break;
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case IPT_ICMP_NET_PROHIBITED:
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send_unreach(skb, ICMP_NET_ANO);
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break;
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case IPT_ICMP_HOST_PROHIBITED:
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send_unreach(skb, ICMP_HOST_ANO);
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break;
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case IPT_ICMP_ADMIN_PROHIBITED:
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send_unreach(skb, ICMP_PKT_FILTERED);
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break;
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case IPT_TCP_RESET:
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send_reset(skb, 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 bool check(const char *tablename,
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const void *e_void,
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const struct xt_target *target,
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void *targinfo,
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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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const struct ipt_entry *e = e_void;
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if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
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printk("ipt_REJECT: ECHOREPLY no longer supported.\n");
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return false;
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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 & XT_INV_PROTO)) {
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printk("ipt_REJECT: TCP_RESET invalid for non-tcp\n");
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return false;
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}
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}
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return true;
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}
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static struct xt_target ipt_reject_reg __read_mostly = {
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.name = "REJECT",
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.family = AF_INET,
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.target = reject,
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.targetsize = sizeof(struct ipt_reject_info),
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.table = "filter",
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.hooks = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) |
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(1 << NF_IP_LOCAL_OUT),
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.checkentry = check,
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.me = THIS_MODULE,
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};
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static int __init ipt_reject_init(void)
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{
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return xt_register_target(&ipt_reject_reg);
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}
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static void __exit ipt_reject_fini(void)
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{
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xt_unregister_target(&ipt_reject_reg);
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}
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module_init(ipt_reject_init);
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module_exit(ipt_reject_fini);
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