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->mark = 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         /* Adjust TCP checksum */
 118         tcph->check = 0;
 119         tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
 120                                    nskb->nh.iph->saddr,
 121                                    nskb->nh.iph->daddr,
 122                                    csum_partial((char *)tcph,
 123                                                 sizeof(struct tcphdr), 0));
 124
 125         /* Set DF, id = 0 */
 126         nskb->nh.iph->frag_off = htons(IP_DF);
 127         nskb->nh.iph->id = 0;
 128
 129         addr_type = RTN_UNSPEC;
 130         if (hook != NF_IP_FORWARD
 131 #ifdef CONFIG_BRIDGE_NETFILTER
 132             || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
 133 #endif
 134            )
 135                 addr_type = RTN_LOCAL;
 136
 137         if (ip_route_me_harder(&nskb, addr_type))
 138                 goto free_nskb;
 139
 140         nskb->ip_summed = CHECKSUM_NONE;
 141
 142         /* Adjust IP TTL */
 143         nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 144
 145         /* Adjust IP checksum */
 146         nskb->nh.iph->check = 0;
 147         nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
 148                                            nskb->nh.iph->ihl);
 149
 150         /* "Never happens" */
 151         if (nskb->len > dst_mtu(nskb->dst))
 152                 goto free_nskb;
 153
 154         nf_ct_attach(nskb, oldskb);
 155
 156         NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 157                 dst_output);
 158         return;
 159
 160  free_nskb:
 161         kfree_skb(nskb);
 162 }
 163
 164 static inline void send_unreach(struct sk_buff *skb_in, int code)
 165 {
 166         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 167 }
 168
 169 static unsigned int reject(struct sk_buff **pskb,
 170                            const struct net_device *in,
 171                            const struct net_device *out,
 172                            unsigned int hooknum,
 173                            const struct xt_target *target,
 174                            const void *targinfo)
 175 {
 176         const struct ipt_reject_info *reject = targinfo;
 177
 178         /* Our naive response construction doesn't deal with IP
 179            options, and probably shouldn't try. */
 180         if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
 181                 return NF_DROP;
 182
 183         /* WARNING: This code causes reentry within iptables.
 184            This means that the iptables jump stack is now crap.  We
 185            must return an absolute verdict. --RR */
 186         switch (reject->with) {
 187         case IPT_ICMP_NET_UNREACHABLE:
 188                 send_unreach(*pskb, ICMP_NET_UNREACH);
 189                 break;
 190         case IPT_ICMP_HOST_UNREACHABLE:
 191                 send_unreach(*pskb, ICMP_HOST_UNREACH);
 192                 break;
 193         case IPT_ICMP_PROT_UNREACHABLE:
 194                 send_unreach(*pskb, ICMP_PROT_UNREACH);
 195                 break;
 196         case IPT_ICMP_PORT_UNREACHABLE:
 197                 send_unreach(*pskb, ICMP_PORT_UNREACH);
 198                 break;
 199         case IPT_ICMP_NET_PROHIBITED:
 200                 send_unreach(*pskb, ICMP_NET_ANO);
 201                 break;
 202         case IPT_ICMP_HOST_PROHIBITED:
 203                 send_unreach(*pskb, ICMP_HOST_ANO);
 204                 break;
 205         case IPT_ICMP_ADMIN_PROHIBITED:
 206                 send_unreach(*pskb, ICMP_PKT_FILTERED);
 207                 break;
 208         case IPT_TCP_RESET:
 209                 send_reset(*pskb, hooknum);
 210         case IPT_ICMP_ECHOREPLY:
 211                 /* Doesn't happen. */
 212                 break;
 213         }
 214
 215         return NF_DROP;
 216 }
 217
 218 static int check(const char *tablename,
 219                  const void *e_void,
 220                  const struct xt_target *target,
 221                  void *targinfo,
 222                  unsigned int hook_mask)
 223 {
 224         const struct ipt_reject_info *rejinfo = targinfo;
 225         const struct ipt_entry *e = e_void;
 226
 227         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 228                 printk("REJECT: ECHOREPLY no longer supported.\n");
 229                 return 0;
 230         } else if (rejinfo->with == IPT_TCP_RESET) {
 231                 /* Must specify that it's a TCP packet */
 232                 if (e->ip.proto != IPPROTO_TCP
 233                     || (e->ip.invflags & IPT_INV_PROTO)) {
 234                         DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
 235                         return 0;
 236                 }
 237         }
 238         return 1;
 239 }
 240
 241 static struct ipt_target ipt_reject_reg = {
 242         .name           = "REJECT",
 243         .target         = reject,
 244         .targetsize     = sizeof(struct ipt_reject_info),
 245         .table          = "filter",
 246         .hooks          = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) |
 247                           (1 << NF_IP_LOCAL_OUT),
 248         .checkentry     = check,
 249         .me             = THIS_MODULE,
 250 };
 251
 252 static int __init ipt_reject_init(void)
 253 {
 254         return ipt_register_target(&ipt_reject_reg);
 255 }
 256
 257 static void __exit ipt_reject_fini(void)
 258 {
 259         ipt_unregister_target(&ipt_reject_reg);
 260 }
 261
 262 module_init(ipt_reject_init);
 263 module_exit(ipt_reject_fini);