LXR linux/net/ipv4/netfilter/ipt

   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
  13#include <linux/module.h>
  14#include <linux/skbuff.h>
  15#include <linux/ip.h>
  16#include <linux/udp.h>
  17#include <linux/icmp.h>
  18#include <net/icmp.h>
  19#include <net/ip.h>
  20#include <net/tcp.h>
  21#include <net/route.h>
  22#include <net/dst.h>
  23#include <linux/netfilter/x_tables.h>
  24#include <linux/netfilter_ipv4/ip_tables.h>
  25#include <linux/netfilter_ipv4/ipt_REJECT.h>
  26#ifdef CONFIG_BRIDGE_NETFILTER
  27#include <linux/netfilter_bridge.h>
  28#endif
  29
  30MODULE_LICENSE("GPL");
  31MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  32MODULE_DESCRIPTION("iptables REJECT target module");
  33
  34/* Send RST reply */
  35static void send_reset(struct sk_buff *oldskb, int hook)
  36{
  37        struct sk_buff *nskb;
  38        struct iphdr *niph;
  39        struct tcphdr _otcph, *oth, *tcph;
  40        __be16 tmp_port;
  41        __be32 tmp_addr;
  42        int needs_ack;
  43        unsigned int addr_type;
  44
  45        /* IP header checks: fragment. */
  46        if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
  47                return;
  48
  49        oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
  50                                 sizeof(_otcph), &_otcph);
  51        if (oth == NULL)
  52                return;
  53
  54        /* No RST for RST. */
  55        if (oth->rst)
  56                return;
  57
  58        /* Check checksum */
  59        if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
  60                return;
  61
  62        /* We need a linear, writeable skb.  We also need to expand
  63           headroom in case hh_len of incoming interface < hh_len of
  64           outgoing interface */
  65        nskb = skb_copy_expand(oldskb, LL_MAX_HEADER, skb_tailroom(oldskb),
  66                               GFP_ATOMIC);
  67        if (!nskb)
  68                return;
  69
  70        /* This packet will not be the same as the other: clear nf fields */
  71        nf_reset(nskb);
  72        nskb->mark = 0;
  73        skb_init_secmark(nskb);
  74
  75        skb_shinfo(nskb)->gso_size = 0;
  76        skb_shinfo(nskb)->gso_segs = 0;
  77        skb_shinfo(nskb)->gso_type = 0;
  78
  79        tcph = (struct tcphdr *)(skb_network_header(nskb) + ip_hdrlen(nskb));
  80
  81        /* Swap source and dest */
  82        niph = ip_hdr(nskb);
  83        tmp_addr = niph->saddr;
  84        niph->saddr = niph->daddr;
  85        niph->daddr = tmp_addr;
  86        tmp_port = tcph->source;
  87        tcph->source = tcph->dest;
  88        tcph->dest = tmp_port;
  89
  90        /* Truncate to length (no data) */
  91        tcph->doff = sizeof(struct tcphdr)/4;
  92        skb_trim(nskb, ip_hdrlen(nskb) + sizeof(struct tcphdr));
  93        niph->tot_len = htons(nskb->len);
  94
  95        if (tcph->ack) {
  96                needs_ack = 0;
  97                tcph->seq = oth->ack_seq;
  98                tcph->ack_seq = 0;
  99        } else {
 100                needs_ack = 1;
 101                tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
 102                                      oldskb->len - ip_hdrlen(oldskb) -
 103                                      (oth->doff << 2));
 104                tcph->seq = 0;
 105        }
 106
 107        /* Reset flags */
 108        ((u_int8_t *)tcph)[13] = 0;
 109        tcph->rst = 1;
 110        tcph->ack = needs_ack;
 111
 112        tcph->window = 0;
 113        tcph->urg_ptr = 0;
 114
 115        /* Adjust TCP checksum */
 116        tcph->check = 0;
 117        tcph->check = tcp_v4_check(sizeof(struct tcphdr),
 118                                   niph->saddr, niph->daddr,
 119                                   csum_partial(tcph,
 120                                                sizeof(struct tcphdr), 0));
 121
 122        /* Set DF, id = 0 */
 123        niph->frag_off = htons(IP_DF);
 124        niph->id = 0;
 125
 126        addr_type = RTN_UNSPEC;
 127        if (hook != NF_IP_FORWARD
 128#ifdef CONFIG_BRIDGE_NETFILTER
 129            || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
 130#endif
 131           )
 132                addr_type = RTN_LOCAL;
 133
 134        if (ip_route_me_harder(nskb, addr_type))
 135                goto free_nskb;
 136
 137        nskb->ip_summed = CHECKSUM_NONE;
 138
 139        /* Adjust IP TTL */
 140        niph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 141
 142        /* Adjust IP checksum */
 143        niph->check = 0;
 144        niph->check = ip_fast_csum(skb_network_header(nskb), niph->ihl);
 145
 146        /* "Never happens" */
 147        if (nskb->len > dst_mtu(nskb->dst))
 148                goto free_nskb;
 149
 150        nf_ct_attach(nskb, oldskb);
 151
 152        NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 153                dst_output);
 154        return;
 155
 156 free_nskb:
 157        kfree_skb(nskb);
 158}
 159
 160static inline void send_unreach(struct sk_buff *skb_in, int code)
 161{
 162        icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 163}
 164
 165static unsigned int reject(struct sk_buff *skb,
 166                           const struct net_device *in,
 167                           const struct net_device *out,
 168                           unsigned int hooknum,
 169                           const struct xt_target *target,
 170                           const void *targinfo)
 171{
 172        const struct ipt_reject_info *reject = targinfo;
 173
 174        /* Our naive response construction doesn't deal with IP
 175           options, and probably shouldn't try. */
 176        if (ip_hdrlen(skb) != sizeof(struct iphdr))
 177                return NF_DROP;
 178
 179        /* WARNING: This code causes reentry within iptables.
 180           This means that the iptables jump stack is now crap.  We
 181           must return an absolute verdict. --RR */
 182        switch (reject->with) {
 183        case IPT_ICMP_NET_UNREACHABLE:
 184                send_unreach(skb, ICMP_NET_UNREACH);
 185                break;
 186        case IPT_ICMP_HOST_UNREACHABLE:
 187                send_unreach(skb, ICMP_HOST_UNREACH);
 188                break;
 189        case IPT_ICMP_PROT_UNREACHABLE:
 190                send_unreach(skb, ICMP_PROT_UNREACH);
 191                break;
 192        case IPT_ICMP_PORT_UNREACHABLE:
 193                send_unreach(skb, ICMP_PORT_UNREACH);
 194                break;
 195        case IPT_ICMP_NET_PROHIBITED:
 196                send_unreach(skb, ICMP_NET_ANO);
 197                break;
 198        case IPT_ICMP_HOST_PROHIBITED:
 199                send_unreach(skb, ICMP_HOST_ANO);
 200                break;
 201        case IPT_ICMP_ADMIN_PROHIBITED:
 202                send_unreach(skb, ICMP_PKT_FILTERED);
 203                break;
 204        case IPT_TCP_RESET:
 205                send_reset(skb, hooknum);
 206        case IPT_ICMP_ECHOREPLY:
 207                /* Doesn't happen. */
 208                break;
 209        }
 210
 211        return NF_DROP;
 212}
 213
 214static bool check(const char *tablename,
 215                  const void *e_void,
 216                  const struct xt_target *target,
 217                  void *targinfo,
 218                  unsigned int hook_mask)
 219{
 220        const struct ipt_reject_info *rejinfo = targinfo;
 221        const struct ipt_entry *e = e_void;
 222
 223        if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 224                printk("ipt_REJECT: ECHOREPLY no longer supported.\n");
 225                return false;
 226        } else if (rejinfo->with == IPT_TCP_RESET) {
 227                /* Must specify that it's a TCP packet */
 228                if (e->ip.proto != IPPROTO_TCP
 229                    || (e->ip.invflags & XT_INV_PROTO)) {
 230                        printk("ipt_REJECT: TCP_RESET invalid for non-tcp\n");
 231                        return false;
 232                }
 233        }
 234        return true;
 235}
 236
 237static struct xt_target ipt_reject_reg __read_mostly = {
 238        .name           = "REJECT",
 239        .family         = AF_INET,
 240        .target         = reject,
 241        .targetsize     = sizeof(struct ipt_reject_info),
 242        .table          = "filter",
 243        .hooks          = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) |
 244                          (1 << NF_IP_LOCAL_OUT),
 245        .checkentry     = check,
 246        .me             = THIS_MODULE,
 247};
 248
 249static int __init ipt_reject_init(void)
 250{
 251        return xt_register_target(&ipt_reject_reg);
 252}
 253
 254static void __exit ipt_reject_fini(void)
 255{
 256        xt_unregister_target(&ipt_reject_reg);
 257}
 258
 259module_init(ipt_reject_init);
 260module_exit(ipt_reject_fini);
 261