net/ipv4/netfilter/ipt_REJECT.c

   1 /*
   2  * This is a module which is used for rejecting packets.
   3  * Added support for customized reject packets (Jozsef Kadlecsik).
   4  * Added support for ICMP type-3-code-13 (Maciej Soltysiak). [RFC 1812]
   5  */
   6
   7 /* (C) 1999-2001 Paul `Rusty' Russell
   8  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   9  *
  10  * This program is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License version 2 as
  12  * published by the Free Software Foundation.
  13  */
  14
  15 #include <linux/module.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/ip.h>
  18 #include <linux/udp.h>
  19 #include <linux/icmp.h>
  20 #include <net/icmp.h>
  21 #include <net/ip.h>
  22 #include <net/tcp.h>
  23 #include <net/route.h>
  24 #include <net/dst.h>
  25 #include <linux/netfilter/x_tables.h>
  26 #include <linux/netfilter_ipv4/ip_tables.h>
  27 #include <linux/netfilter_ipv4/ipt_REJECT.h>
  28 #ifdef CONFIG_BRIDGE_NETFILTER
  29 #include <linux/netfilter_bridge.h>
  30 #endif
  31
  32 MODULE_LICENSE("GPL");
  33 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  34 MODULE_DESCRIPTION("iptables REJECT target module");
  35
  36 #if 0
  37 #define DEBUGP printk
  38 #else
  39 #define DEBUGP(format, args...)
  40 #endif
  41
  42 /* Send RST reply */
  43 static void send_reset(struct sk_buff *oldskb, int hook)
  44 {
  45         struct sk_buff *nskb;
  46         struct iphdr *iph = oldskb->nh.iph;
  47         struct tcphdr _otcph, *oth, *tcph;
  48         __be16 tmp_port;
  49         __be32 tmp_addr;
  50         int needs_ack;
  51         unsigned int addr_type;
  52
  53         /* IP header checks: fragment. */
  54         if (oldskb->nh.iph->frag_off & htons(IP_OFFSET))
  55                 return;
  56
  57         oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4,
  58                                  sizeof(_otcph), &_otcph);
  59         if (oth == NULL)
  60                 return;
  61
  62         /* No RST for RST. */
  63         if (oth->rst)
  64                 return;
  65
  66         /* Check checksum */
  67         if (nf_ip_checksum(oldskb, hook, iph->ihl * 4, IPPROTO_TCP))
  68                 return;
  69
  70         /* We need a linear, writeable skb.  We also need to expand
  71            headroom in case hh_len of incoming interface < hh_len of
  72            outgoing interface */
  73         nskb = skb_copy_expand(oldskb, LL_MAX_HEADER, skb_tailroom(oldskb),
  74                                GFP_ATOMIC);
  75         if (!nskb)
  76                 return;
  77
  78         /* This packet will not be the same as the other: clear nf fields */
  79         nf_reset(nskb);
  80         nskb->mark = 0;
  81         skb_init_secmark(nskb);
  82
  83         tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
  84
  85         /* Swap source and dest */
  86         tmp_addr = nskb->nh.iph->saddr;
  87         nskb->nh.iph->saddr = nskb->nh.iph->daddr;
  88         nskb->nh.iph->daddr = tmp_addr;
  89         tmp_port = tcph->source;
  90         tcph->source = tcph->dest;
  91         tcph->dest = tmp_port;
  92
  93         /* Truncate to length (no data) */
  94         tcph->doff = sizeof(struct tcphdr)/4;
  95         skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
  96         nskb->nh.iph->tot_len = htons(nskb->len);
  97
  98         if (tcph->ack) {
  99                 needs_ack = 0;
 100                 tcph->seq = oth->ack_seq;
 101                 tcph->ack_seq = 0;
 102         } else {
 103                 needs_ack = 1;
 104                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
 105                                       + oldskb->len - oldskb->nh.iph->ihl*4
 106                                       - (oth->doff<<2));
 107                 tcph->seq = 0;
 108         }
 109
 110         /* Reset flags */
 111         ((u_int8_t *)tcph)[13] = 0;
 112         tcph->rst = 1;
 113         tcph->ack = needs_ack;
 114
 115         tcph->window = 0;
 116         tcph->urg_ptr = 0;
 117
 118         /* Adjust TCP checksum */
 119         tcph->check = 0;
 120         tcph->check = tcp_v4_check(sizeof(struct tcphdr),
 121                                    nskb->nh.iph->saddr,
 122                                    nskb->nh.iph->daddr,
 123                                    csum_partial((char *)tcph,
 124                                                 sizeof(struct tcphdr), 0));
 125
 126         /* Set DF, id = 0 */
 127         nskb->nh.iph->frag_off = htons(IP_DF);
 128         nskb->nh.iph->id = 0;
 129
 130         addr_type = RTN_UNSPEC;
 131         if (hook != NF_IP_FORWARD
 132 #ifdef CONFIG_BRIDGE_NETFILTER
 133             || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
 134 #endif
 135            )
 136                 addr_type = RTN_LOCAL;
 137
 138         if (ip_route_me_harder(&nskb, addr_type))
 139                 goto free_nskb;
 140
 141         nskb->ip_summed = CHECKSUM_NONE;
 142
 143         /* Adjust IP TTL */
 144         nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 145
 146         /* Adjust IP checksum */
 147         nskb->nh.iph->check = 0;
 148         nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
 149                                            nskb->nh.iph->ihl);
 150
 151         /* "Never happens" */
 152         if (nskb->len > dst_mtu(nskb->dst))
 153                 goto free_nskb;
 154
 155         nf_ct_attach(nskb, oldskb);
 156
 157         NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 158                 dst_output);
 159         return;
 160
 161  free_nskb:
 162         kfree_skb(nskb);
 163 }
 164
 165 static inline void send_unreach(struct sk_buff *skb_in, int code)
 166 {
 167         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 168 }
 169
 170 static unsigned int reject(struct sk_buff **pskb,
 171                            const struct net_device *in,
 172                            const struct net_device *out,
 173                            unsigned int hooknum,
 174                            const struct xt_target *target,
 175                            const void *targinfo)
 176 {
 177         const struct ipt_reject_info *reject = targinfo;
 178
 179         /* Our naive response construction doesn't deal with IP
 180            options, and probably shouldn't try. */
 181         if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
 182                 return NF_DROP;
 183
 184         /* WARNING: This code causes reentry within iptables.
 185            This means that the iptables jump stack is now crap.  We
 186            must return an absolute verdict. --RR */
 187         switch (reject->with) {
 188         case IPT_ICMP_NET_UNREACHABLE:
 189                 send_unreach(*pskb, ICMP_NET_UNREACH);
 190                 break;
 191         case IPT_ICMP_HOST_UNREACHABLE:
 192                 send_unreach(*pskb, ICMP_HOST_UNREACH);
 193                 break;
 194         case IPT_ICMP_PROT_UNREACHABLE:
 195                 send_unreach(*pskb, ICMP_PROT_UNREACH);
 196                 break;
 197         case IPT_ICMP_PORT_UNREACHABLE:
 198                 send_unreach(*pskb, ICMP_PORT_UNREACH);
 199                 break;
 200         case IPT_ICMP_NET_PROHIBITED:
 201                 send_unreach(*pskb, ICMP_NET_ANO);
 202                 break;
 203         case IPT_ICMP_HOST_PROHIBITED:
 204                 send_unreach(*pskb, ICMP_HOST_ANO);
 205                 break;
 206         case IPT_ICMP_ADMIN_PROHIBITED:
 207                 send_unreach(*pskb, ICMP_PKT_FILTERED);
 208                 break;
 209         case IPT_TCP_RESET:
 210                 send_reset(*pskb, hooknum);
 211         case IPT_ICMP_ECHOREPLY:
 212                 /* Doesn't happen. */
 213                 break;
 214         }
 215
 216         return NF_DROP;
 217 }
 218
 219 static int check(const char *tablename,
 220                  const void *e_void,
 221                  const struct xt_target *target,
 222                  void *targinfo,
 223                  unsigned int hook_mask)
 224 {
 225         const struct ipt_reject_info *rejinfo = targinfo;
 226         const struct ipt_entry *e = e_void;
 227
 228         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 229                 printk("REJECT: ECHOREPLY no longer supported.\n");
 230                 return 0;
 231         } else if (rejinfo->with == IPT_TCP_RESET) {
 232                 /* Must specify that it's a TCP packet */
 233                 if (e->ip.proto != IPPROTO_TCP
 234                     || (e->ip.invflags & XT_INV_PROTO)) {
 235                         DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
 236                         return 0;
 237                 }
 238         }
 239         return 1;
 240 }
 241
 242 static struct xt_target ipt_reject_reg = {
 243         .name           = "REJECT",
 244         .family         = AF_INET,
 245         .target         = reject,
 246         .targetsize     = sizeof(struct ipt_reject_info),
 247         .table          = "filter",
 248         .hooks          = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) |
 249                           (1 << NF_IP_LOCAL_OUT),
 250         .checkentry     = check,
 251         .me             = THIS_MODULE,
 252 };
 253
 254 static int __init ipt_reject_init(void)
 255 {
 256         return xt_register_target(&ipt_reject_reg);
 257 }
 258
 259 static void __exit ipt_reject_fini(void)
 260 {
 261         xt_unregister_target(&ipt_reject_reg);
 262 }
 263
 264 module_init(ipt_reject_init);
 265 module_exit(ipt_reject_fini);