linux/net/ipv4/netfilter/ipt_REJECT.c
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   1/*
   2 * This is a module which is used for rejecting packets.
   3 */
   4
   5/* (C) 1999-2001 Paul `Rusty' Russell
   6 * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   7 *
   8 * This program is free software; you can redistribute it and/or modify
   9 * it under the terms of the GNU General Public License version 2 as
  10 * published by the Free Software Foundation.
  11 */
  12#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  13#include <linux/module.h>
  14#include <linux/skbuff.h>
  15#include <linux/slab.h>
  16#include <linux/ip.h>
  17#include <linux/udp.h>
  18#include <linux/icmp.h>
  19#include <net/icmp.h>
  20#include <net/ip.h>
  21#include <net/tcp.h>
  22#include <net/route.h>
  23#include <net/dst.h>
  24#include <linux/netfilter/x_tables.h>
  25#include <linux/netfilter_ipv4/ip_tables.h>
  26#include <linux/netfilter_ipv4/ipt_REJECT.h>
  27#ifdef CONFIG_BRIDGE_NETFILTER
  28#include <linux/netfilter_bridge.h>
  29#endif
  30
  31MODULE_LICENSE("GPL");
  32MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  33MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv4");
  34
  35/* Send RST reply */
  36static void send_reset(struct sk_buff *oldskb, int hook)
  37{
  38        struct sk_buff *nskb;
  39        const struct iphdr *oiph;
  40        struct iphdr *niph;
  41        const struct tcphdr *oth;
  42        struct tcphdr _otcph, *tcph;
  43
  44        /* IP header checks: fragment. */
  45        if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
  46                return;
  47
  48        oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
  49                                 sizeof(_otcph), &_otcph);
  50        if (oth == NULL)
  51                return;
  52
  53        /* No RST for RST. */
  54        if (oth->rst)
  55                return;
  56
  57        if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
  58                return;
  59
  60        /* Check checksum */
  61        if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
  62                return;
  63        oiph = ip_hdr(oldskb);
  64
  65        nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
  66                         LL_MAX_HEADER, GFP_ATOMIC);
  67        if (!nskb)
  68                return;
  69
  70        skb_reserve(nskb, LL_MAX_HEADER);
  71
  72        skb_reset_network_header(nskb);
  73        niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
  74        niph->version   = 4;
  75        niph->ihl       = sizeof(struct iphdr) / 4;
  76        niph->tos       = 0;
  77        niph->id        = 0;
  78        niph->frag_off  = htons(IP_DF);
  79        niph->protocol  = IPPROTO_TCP;
  80        niph->check     = 0;
  81        niph->saddr     = oiph->daddr;
  82        niph->daddr     = oiph->saddr;
  83
  84        skb_reset_transport_header(nskb);
  85        tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
  86        memset(tcph, 0, sizeof(*tcph));
  87        tcph->source    = oth->dest;
  88        tcph->dest      = oth->source;
  89        tcph->doff      = sizeof(struct tcphdr) / 4;
  90
  91        if (oth->ack)
  92                tcph->seq = oth->ack_seq;
  93        else {
  94                tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
  95                                      oldskb->len - ip_hdrlen(oldskb) -
  96                                      (oth->doff << 2));
  97                tcph->ack = 1;
  98        }
  99
 100        tcph->rst       = 1;
 101        tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
 102                                    niph->daddr, 0);
 103        nskb->ip_summed = CHECKSUM_PARTIAL;
 104        nskb->csum_start = (unsigned char *)tcph - nskb->head;
 105        nskb->csum_offset = offsetof(struct tcphdr, check);
 106
 107        /* ip_route_me_harder expects skb->dst to be set */
 108        skb_dst_set_noref(nskb, skb_dst(oldskb));
 109
 110        nskb->protocol = htons(ETH_P_IP);
 111        if (ip_route_me_harder(nskb, RTN_UNSPEC))
 112                goto free_nskb;
 113
 114        niph->ttl       = ip4_dst_hoplimit(skb_dst(nskb));
 115
 116        /* "Never happens" */
 117        if (nskb->len > dst_mtu(skb_dst(nskb)))
 118                goto free_nskb;
 119
 120        nf_ct_attach(nskb, oldskb);
 121
 122#ifdef CONFIG_BRIDGE_NETFILTER
 123        /* If we use ip_local_out for bridged traffic, the MAC source on
 124         * the RST will be ours, instead of the destination's.  This confuses
 125         * some routers/firewalls, and they drop the packet.  So we need to
 126         * build the eth header using the original destination's MAC as the
 127         * source, and send the RST packet directly.
 128         */
 129        if (oldskb->nf_bridge) {
 130                struct ethhdr *oeth = eth_hdr(oldskb);
 131                nskb->dev = oldskb->nf_bridge->physindev;
 132                niph->tot_len = htons(nskb->len);
 133                ip_send_check(niph);
 134                if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 135                                    oeth->h_source, oeth->h_dest, nskb->len) < 0)
 136                        goto free_nskb;
 137                dev_queue_xmit(nskb);
 138        } else
 139#endif
 140                ip_local_out(nskb);
 141
 142        return;
 143
 144 free_nskb:
 145        kfree_skb(nskb);
 146}
 147
 148static inline void send_unreach(struct sk_buff *skb_in, int code)
 149{
 150        icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 151}
 152
 153static unsigned int
 154reject_tg(struct sk_buff *skb, const struct xt_action_param *par)
 155{
 156        const struct ipt_reject_info *reject = par->targinfo;
 157
 158        switch (reject->with) {
 159        case IPT_ICMP_NET_UNREACHABLE:
 160                send_unreach(skb, ICMP_NET_UNREACH);
 161                break;
 162        case IPT_ICMP_HOST_UNREACHABLE:
 163                send_unreach(skb, ICMP_HOST_UNREACH);
 164                break;
 165        case IPT_ICMP_PROT_UNREACHABLE:
 166                send_unreach(skb, ICMP_PROT_UNREACH);
 167                break;
 168        case IPT_ICMP_PORT_UNREACHABLE:
 169                send_unreach(skb, ICMP_PORT_UNREACH);
 170                break;
 171        case IPT_ICMP_NET_PROHIBITED:
 172                send_unreach(skb, ICMP_NET_ANO);
 173                break;
 174        case IPT_ICMP_HOST_PROHIBITED:
 175                send_unreach(skb, ICMP_HOST_ANO);
 176                break;
 177        case IPT_ICMP_ADMIN_PROHIBITED:
 178                send_unreach(skb, ICMP_PKT_FILTERED);
 179                break;
 180        case IPT_TCP_RESET:
 181                send_reset(skb, par->hooknum);
 182        case IPT_ICMP_ECHOREPLY:
 183                /* Doesn't happen. */
 184                break;
 185        }
 186
 187        return NF_DROP;
 188}
 189
 190static int reject_tg_check(const struct xt_tgchk_param *par)
 191{
 192        const struct ipt_reject_info *rejinfo = par->targinfo;
 193        const struct ipt_entry *e = par->entryinfo;
 194
 195        if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 196                pr_info("ECHOREPLY no longer supported.\n");
 197                return -EINVAL;
 198        } else if (rejinfo->with == IPT_TCP_RESET) {
 199                /* Must specify that it's a TCP packet */
 200                if (e->ip.proto != IPPROTO_TCP ||
 201                    (e->ip.invflags & XT_INV_PROTO)) {
 202                        pr_info("TCP_RESET invalid for non-tcp\n");
 203                        return -EINVAL;
 204                }
 205        }
 206        return 0;
 207}
 208
 209static struct xt_target reject_tg_reg __read_mostly = {
 210        .name           = "REJECT",
 211        .family         = NFPROTO_IPV4,
 212        .target         = reject_tg,
 213        .targetsize     = sizeof(struct ipt_reject_info),
 214        .table          = "filter",
 215        .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 216                          (1 << NF_INET_LOCAL_OUT),
 217        .checkentry     = reject_tg_check,
 218        .me             = THIS_MODULE,
 219};
 220
 221static int __init reject_tg_init(void)
 222{
 223        return xt_register_target(&reject_tg_reg);
 224}
 225
 226static void __exit reject_tg_exit(void)
 227{
 228        xt_unregister_target(&reject_tg_reg);
 229}
 230
 231module_init(reject_tg_init);
 232module_exit(reject_tg_exit);
 233