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