ip6t_REJECT.c

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/*
 * IP6 tables REJECT target module
 * Linux INET6 implementation
 *
 * Copyright (C)2003 USAGI/WIDE Project
 *
 * Authors:
 *  Yasuyuki Kozakai    <[email protected]>
 *
 * 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.
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/gfp.h>
#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 <[email protected]>");
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;
#define DEFAULT_TOS_VALUE   0x0U
    const __u8 tclass = DEFAULT_TOS_VALUE;
    struct dst_entry *dst = NULL;
    u8 proto;
    __be16 frag_off;
    struct flowi6 fl6;

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

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

    if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
        pr_debug("Cannot 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("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("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("TCP checksum is invalid\n");
        return;
    }

    memset(&fl6, 0, sizeof(fl6));
    fl6.flowi6_proto = IPPROTO_TCP;
    fl6.saddr = oip6h->daddr;
    fl6.daddr = oip6h->saddr;
    fl6.fl6_sport = otcph.dest;
    fl6.fl6_dport = otcph.source;
    security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
    dst = ip6_route_output(net, NULL, &fl6);
    if (dst == NULL || dst->error) {
        dst_release(dst);
        return;
    }
    dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
    if (IS_ERR(dst))
        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) {
        net_dbg_ratelimited("cannot alloc skb\n");
        dst_release(dst);
        return;
    }

    skb_dst_set(nskb, dst);

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

    skb_put(nskb, sizeof(struct ipv6hdr));
    skb_reset_network_header(nskb);
    ip6h = ipv6_hdr(nskb);
    *(__be32 *)ip6h =  htonl(0x60000000 | (tclass << 20));
    ip6h->hop_limit = ip6_dst_hoplimit(dst);
    ip6h->nexthdr = IPPROTO_TCP;
    ip6h->saddr = oip6h->daddr;
    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);
}

static unsigned int
reject_tg6(struct sk_buff *skb, const struct xt_action_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__);
    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:
        net_info_ratelimited("case %u not handled yet\n", reject->with);
        break;
    }

    return NF_DROP;
}

static int 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) {
        pr_info("ECHOREPLY is not supported.\n");
        return -EINVAL;
    } 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)) {
            pr_info("TCP_RESET illegal for non-tcp\n");
            return -EINVAL;
        }
    }
    return 0;
}

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);