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root/net/ipv4/netfilter/ipt_REJECT.c

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DEFINITIONS

This source file includes following definitions.
  1. send_reset
  2. send_unreach
  3. reject_tg
  4. reject_tg_check
  5. reject_tg_init
  6. reject_tg_exit

/*
 * This is a module which is used for rejecting packets.
 */

/* (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/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/x_tables.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("Xtables: packet \"rejection\" target for IPv4");

/* Send RST reply */
static void send_reset(struct sk_buff *oldskb, int hook)
{
        struct sk_buff *nskb;
        const struct iphdr *oiph;
        struct iphdr *niph;
        const struct tcphdr *oth;
        struct tcphdr _otcph, *tcph;
        unsigned int addr_type;

        /* IP header checks: fragment. */
        if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
                return;

        oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
                                 sizeof(_otcph), &_otcph);
        if (oth == NULL)
                return;

        /* No RST for RST. */
        if (oth->rst)
                return;

        /* Check checksum */
        if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
                return;
        oiph = ip_hdr(oldskb);

        nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
                         LL_MAX_HEADER, GFP_ATOMIC);
        if (!nskb)
                return;

        skb_reserve(nskb, LL_MAX_HEADER);

        skb_reset_network_header(nskb);
        niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
        niph->version   = 4;
        niph->ihl       = sizeof(struct iphdr) / 4;
        niph->tos       = 0;
        niph->id        = 0;
        niph->frag_off  = htons(IP_DF);
        niph->protocol  = IPPROTO_TCP;
        niph->check     = 0;
        niph->saddr     = oiph->daddr;
        niph->daddr     = oiph->saddr;

        tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
        memset(tcph, 0, sizeof(*tcph));
        tcph->source    = oth->dest;
        tcph->dest      = oth->source;
        tcph->doff      = sizeof(struct tcphdr) / 4;

        if (oth->ack)
                tcph->seq = oth->ack_seq;
        else {
                tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
                                      oldskb->len - ip_hdrlen(oldskb) -
                                      (oth->doff << 2));
                tcph->ack = 1;
        }

        tcph->rst       = 1;
        tcph->check     = tcp_v4_check(sizeof(struct tcphdr),
                                       niph->saddr, niph->daddr,
                                       csum_partial(tcph,
                                                    sizeof(struct tcphdr), 0));

        addr_type = RTN_UNSPEC;
        if (hook != NF_INET_FORWARD
#ifdef CONFIG_BRIDGE_NETFILTER
            || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
#endif
           )
                addr_type = RTN_LOCAL;

        /* ip_route_me_harder expects skb->dst to be set */
        dst_hold(oldskb->dst);
        nskb->dst = oldskb->dst;

        if (ip_route_me_harder(nskb, addr_type))
                goto free_nskb;

        niph->ttl       = dst_metric(nskb->dst, RTAX_HOPLIMIT);
        nskb->ip_summed = CHECKSUM_NONE;

        /* "Never happens" */
        if (nskb->len > dst_mtu(nskb->dst))
                goto free_nskb;

        nf_ct_attach(nskb, oldskb);

        ip_local_out(nskb);
        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_tg(struct sk_buff *skb, const struct xt_target_param *par)
{
        const struct ipt_reject_info *reject = par->targinfo;

        /* 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(skb, ICMP_NET_UNREACH);
                break;
        case IPT_ICMP_HOST_UNREACHABLE:
                send_unreach(skb, ICMP_HOST_UNREACH);
                break;
        case IPT_ICMP_PROT_UNREACHABLE:
                send_unreach(skb, ICMP_PROT_UNREACH);
                break;
        case IPT_ICMP_PORT_UNREACHABLE:
                send_unreach(skb, ICMP_PORT_UNREACH);
                break;
        case IPT_ICMP_NET_PROHIBITED:
                send_unreach(skb, ICMP_NET_ANO);
                break;
        case IPT_ICMP_HOST_PROHIBITED:
                send_unreach(skb, ICMP_HOST_ANO);
                break;
        case IPT_ICMP_ADMIN_PROHIBITED:
                send_unreach(skb, ICMP_PKT_FILTERED);
                break;
        case IPT_TCP_RESET:
                send_reset(skb, par->hooknum);
        case IPT_ICMP_ECHOREPLY:
                /* Doesn't happen. */
                break;
        }

        return NF_DROP;
}

static bool reject_tg_check(const struct xt_tgchk_param *par)
{
        const struct ipt_reject_info *rejinfo = par->targinfo;
        const struct ipt_entry *e = par->entryinfo;

        if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
                printk("ipt_REJECT: ECHOREPLY no longer supported.\n");
                return false;
        } else if (rejinfo->with == IPT_TCP_RESET) {
                /* Must specify that it's a TCP packet */
                if (e->ip.proto != IPPROTO_TCP
                    || (e->ip.invflags & XT_INV_PROTO)) {
                        printk("ipt_REJECT: TCP_RESET invalid for non-tcp\n");
                        return false;
                }
        }
        return true;
}

static struct xt_target reject_tg_reg __read_mostly = {
        .name           = "REJECT",
        .family         = NFPROTO_IPV4,
        .target         = reject_tg,
        .targetsize     = sizeof(struct ipt_reject_info),
        .table          = "filter",
        .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
                          (1 << NF_INET_LOCAL_OUT),
        .checkentry     = reject_tg_check,
        .me             = THIS_MODULE,
};

static int __init reject_tg_init(void)
{
        return xt_register_target(&reject_tg_reg);
}

static void __exit reject_tg_exit(void)
{
        xt_unregister_target(&reject_tg_reg);
}

module_init(reject_tg_init);
module_exit(reject_tg_exit);

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