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root/net/ipv6/netfilter/ip6t_REJECT.c

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DEFINITIONS

This source file includes following definitions.
  1. send_reset
  2. send_unreach
  3. reject_tg6
  4. reject_tg6_check
  5. reject_tg6_init
  6. reject_tg6_exit

/*
 * IP6 tables REJECT target module
 * Linux INET6 implementation
 *
 * Copyright (C)2003 USAGI/WIDE Project
 *
 * Authors:
 *      Yasuyuki Kozakai        <yasuyuki.kozakai@toshiba.co.jp>
 *
 * Based on net/ipv4/netfilter/ipt_REJECT.c
 *
 * 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.
 */

#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/icmpv6.h>
#include <linux/netdevice.h>
#include <net/ipv6.h>
#include <net/tcp.h>
#include <net/icmp.h>
#include <net/ip6_checksum.h>
#include <net/ip6_fib.h>
#include <net/ip6_route.h>
#include <net/flow.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter_ipv6/ip6t_REJECT.h>

MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv6");
MODULE_LICENSE("GPL");

/* Send RST reply */
static void send_reset(struct net *net, struct sk_buff *oldskb)
{
        struct sk_buff *nskb;
        struct tcphdr otcph, *tcph;
        unsigned int otcplen, hh_len;
        int tcphoff, needs_ack;
        const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
        struct ipv6hdr *ip6h;
        struct dst_entry *dst = NULL;
        u8 proto;
        struct flowi fl;

        if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
            (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
                pr_debug("ip6t_REJECT: addr is not unicast.\n");
                return;
        }

        proto = oip6h->nexthdr;
        tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto);

        if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
                pr_debug("ip6t_REJECT: Can't get TCP header.\n");
                return;
        }

        otcplen = oldskb->len - tcphoff;

        /* IP header checks: fragment, too short. */
        if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
                pr_debug("ip6t_REJECT: proto(%d) != IPPROTO_TCP, "
                         "or too short. otcplen = %d\n",
                         proto, otcplen);
                return;
        }

        if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
                BUG();

        /* No RST for RST. */
        if (otcph.rst) {
                pr_debug("ip6t_REJECT: RST is set\n");
                return;
        }

        /* Check checksum. */
        if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
                            skb_checksum(oldskb, tcphoff, otcplen, 0))) {
                pr_debug("ip6t_REJECT: TCP checksum is invalid\n");
                return;
        }

        memset(&fl, 0, sizeof(fl));
        fl.proto = IPPROTO_TCP;
        ipv6_addr_copy(&fl.fl6_src, &oip6h->daddr);
        ipv6_addr_copy(&fl.fl6_dst, &oip6h->saddr);
        fl.fl_ip_sport = otcph.dest;
        fl.fl_ip_dport = otcph.source;
        security_skb_classify_flow(oldskb, &fl);
        dst = ip6_route_output(net, NULL, &fl);
        if (dst == NULL)
                return;
        if (dst->error || xfrm_lookup(&dst, &fl, NULL, 0))
                return;

        hh_len = (dst->dev->hard_header_len + 15)&~15;
        nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
                         + sizeof(struct tcphdr) + dst->trailer_len,
                         GFP_ATOMIC);

        if (!nskb) {
                if (net_ratelimit())
                        printk("ip6t_REJECT: Can't alloc skb\n");
                dst_release(dst);
                return;
        }

        nskb->dst = dst;

        skb_reserve(nskb, hh_len + dst->header_len);

        skb_put(nskb, sizeof(struct ipv6hdr));
        skb_reset_network_header(nskb);
        ip6h = ipv6_hdr(nskb);
        ip6h->version = 6;
        ip6h->hop_limit = dst_metric(dst, RTAX_HOPLIMIT);
        ip6h->nexthdr = IPPROTO_TCP;
        ipv6_addr_copy(&ip6h->saddr, &oip6h->daddr);
        ipv6_addr_copy(&ip6h->daddr, &oip6h->saddr);

        tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
        /* Truncate to length (no data) */
        tcph->doff = sizeof(struct tcphdr)/4;
        tcph->source = otcph.dest;
        tcph->dest = otcph.source;

        if (otcph.ack) {
                needs_ack = 0;
                tcph->seq = otcph.ack_seq;
                tcph->ack_seq = 0;
        } else {
                needs_ack = 1;
                tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
                                      + otcplen - (otcph.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;
        tcph->check = 0;

        /* Adjust TCP checksum */
        tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
                                      &ipv6_hdr(nskb)->daddr,
                                      sizeof(struct tcphdr), IPPROTO_TCP,
                                      csum_partial(tcph,
                                                   sizeof(struct tcphdr), 0));

        nf_ct_attach(nskb, oldskb);

        ip6_local_out(nskb);
}

static inline void
send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
             unsigned int hooknum)
{
        if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
                skb_in->dev = net->loopback_dev;

        icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0, NULL);
}

static unsigned int
reject_tg6(struct sk_buff *skb, const struct xt_target_param *par)
{
        const struct ip6t_reject_info *reject = par->targinfo;
        struct net *net = dev_net((par->in != NULL) ? par->in : par->out);

        pr_debug("%s: medium point\n", __func__);
        /* WARNING: This code causes reentry within ip6tables.
           This means that the ip6tables jump stack is now crap.  We
           must return an absolute verdict. --RR */
        switch (reject->with) {
        case IP6T_ICMP6_NO_ROUTE:
                send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
                break;
        case IP6T_ICMP6_ADM_PROHIBITED:
                send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
                break;
        case IP6T_ICMP6_NOT_NEIGHBOUR:
                send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
                break;
        case IP6T_ICMP6_ADDR_UNREACH:
                send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
                break;
        case IP6T_ICMP6_PORT_UNREACH:
                send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
                break;
        case IP6T_ICMP6_ECHOREPLY:
                /* Do nothing */
                break;
        case IP6T_TCP_RESET:
                send_reset(net, skb);
                break;
        default:
                if (net_ratelimit())
                        printk(KERN_WARNING "ip6t_REJECT: case %u not handled yet\n", reject->with);
                break;
        }

        return NF_DROP;
}

static bool reject_tg6_check(const struct xt_tgchk_param *par)
{
        const struct ip6t_reject_info *rejinfo = par->targinfo;
        const struct ip6t_entry *e = par->entryinfo;

        if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
                printk("ip6t_REJECT: ECHOREPLY is not supported.\n");
                return false;
        } else if (rejinfo->with == IP6T_TCP_RESET) {
                /* Must specify that it's a TCP packet */
                if (e->ipv6.proto != IPPROTO_TCP
                    || (e->ipv6.invflags & XT_INV_PROTO)) {
                        printk("ip6t_REJECT: TCP_RESET illegal for non-tcp\n");
                        return false;
                }
        }
        return true;
}

static struct xt_target reject_tg6_reg __read_mostly = {
        .name           = "REJECT",
        .family         = NFPROTO_IPV6,
        .target         = reject_tg6,
        .targetsize     = sizeof(struct ip6t_reject_info),
        .table          = "filter",
        .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
                          (1 << NF_INET_LOCAL_OUT),
        .checkentry     = reject_tg6_check,
        .me             = THIS_MODULE
};

static int __init reject_tg6_init(void)
{
        return xt_register_target(&reject_tg6_reg);
}

static void __exit reject_tg6_exit(void)
{
        xt_unregister_target(&reject_tg6_reg);
}

module_init(reject_tg6_init);
module_exit(reject_tg6_exit);

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