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         skb_shinfo(nskb)->gso_size = 0;
  84         skb_shinfo(nskb)->gso_segs = 0;
  85         skb_shinfo(nskb)->gso_type = 0;
  86
  87         tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
  88
  89         /* Swap source and dest */
  90         tmp_addr = nskb->nh.iph->saddr;
  91         nskb->nh.iph->saddr = nskb->nh.iph->daddr;
  92         nskb->nh.iph->daddr = tmp_addr;
  93         tmp_port = tcph->source;
  94         tcph->source = tcph->dest;
  95         tcph->dest = tmp_port;
  96
  97         /* Truncate to length (no data) */
  98         tcph->doff = sizeof(struct tcphdr)/4;
  99         skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
 100         nskb->nh.iph->tot_len = htons(nskb->len);
 101
 102         if (tcph->ack) {
 103                 needs_ack = 0;
 104                 tcph->seq = oth->ack_seq;
 105                 tcph->ack_seq = 0;
 106         } else {
 107                 needs_ack = 1;
 108                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
 109                                       + oldskb->len - oldskb->nh.iph->ihl*4
 110                                       - (oth->doff<<2));
 111                 tcph->seq = 0;
 112         }
 113
 114         /* Reset flags */
 115         ((u_int8_t *)tcph)[13] = 0;
 116         tcph->rst = 1;
 117         tcph->ack = needs_ack;
 118
 119         tcph->window = 0;
 120         tcph->urg_ptr = 0;
 121
 122         /* Adjust TCP checksum */
 123         tcph->check = 0;
 124         tcph->check = tcp_v4_check(sizeof(struct tcphdr),
 125                                    nskb->nh.iph->saddr,
 126                                    nskb->nh.iph->daddr,
 127                                    csum_partial((char *)tcph,
 128                                                 sizeof(struct tcphdr), 0));
 129
 130         /* Set DF, id = 0 */
 131         nskb->nh.iph->frag_off = htons(IP_DF);
 132         nskb->nh.iph->id = 0;
 133
 134         addr_type = RTN_UNSPEC;
 135         if (hook != NF_IP_FORWARD
 136 #ifdef CONFIG_BRIDGE_NETFILTER
 137             || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
 138 #endif
 139            )
 140                 addr_type = RTN_LOCAL;
 141
 142         if (ip_route_me_harder(&nskb, addr_type))
 143                 goto free_nskb;
 144
 145         nskb->ip_summed = CHECKSUM_NONE;
 146
 147         /* Adjust IP TTL */
 148         nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 149
 150         /* Adjust IP checksum */
 151         nskb->nh.iph->check = 0;
 152         nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
 153                                            nskb->nh.iph->ihl);
 154
 155         /* "Never happens" */
 156         if (nskb->len > dst_mtu(nskb->dst))
 157                 goto free_nskb;
 158
 159         nf_ct_attach(nskb, oldskb);
 160
 161         NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 162                 dst_output);
 163         return;
 164
 165  free_nskb:
 166         kfree_skb(nskb);
 167 }
 168
 169 static inline void send_unreach(struct sk_buff *skb_in, int code)
 170 {
 171         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 172 }
 173
 174 static unsigned int reject(struct sk_buff **pskb,
 175                            const struct net_device *in,
 176                            const struct net_device *out,
 177                            unsigned int hooknum,
 178                            const struct xt_target *target,
 179                            const void *targinfo)
 180 {
 181         const struct ipt_reject_info *reject = targinfo;
 182
 183         /* Our naive response construction doesn't deal with IP
 184            options, and probably shouldn't try. */
 185         if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
 186                 return NF_DROP;
 187
 188         /* WARNING: This code causes reentry within iptables.
 189            This means that the iptables jump stack is now crap.  We
 190            must return an absolute verdict. --RR */
 191         switch (reject->with) {
 192         case IPT_ICMP_NET_UNREACHABLE:
 193                 send_unreach(*pskb, ICMP_NET_UNREACH);
 194                 break;
 195         case IPT_ICMP_HOST_UNREACHABLE:
 196                 send_unreach(*pskb, ICMP_HOST_UNREACH);
 197                 break;
 198         case IPT_ICMP_PROT_UNREACHABLE:
 199                 send_unreach(*pskb, ICMP_PROT_UNREACH);
 200                 break;
 201         case IPT_ICMP_PORT_UNREACHABLE:
 202                 send_unreach(*pskb, ICMP_PORT_UNREACH);
 203                 break;
 204         case IPT_ICMP_NET_PROHIBITED:
 205                 send_unreach(*pskb, ICMP_NET_ANO);
 206                 break;
 207         case IPT_ICMP_HOST_PROHIBITED:
 208                 send_unreach(*pskb, ICMP_HOST_ANO);
 209                 break;
 210         case IPT_ICMP_ADMIN_PROHIBITED:
 211                 send_unreach(*pskb, ICMP_PKT_FILTERED);
 212                 break;
 213         case IPT_TCP_RESET:
 214                 send_reset(*pskb, hooknum);
 215         case IPT_ICMP_ECHOREPLY:
 216                 /* Doesn't happen. */
 217                 break;
 218         }
 219
 220         return NF_DROP;
 221 }
 222
 223 static int check(const char *tablename,
 224                  const void *e_void,
 225                  const struct xt_target *target,
 226                  void *targinfo,
 227                  unsigned int hook_mask)
 228 {
 229         const struct ipt_reject_info *rejinfo = targinfo;
 230         const struct ipt_entry *e = e_void;
 231
 232         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 233                 printk("REJECT: ECHOREPLY no longer supported.\n");
 234                 return 0;
 235         } else if (rejinfo->with == IPT_TCP_RESET) {
 236                 /* Must specify that it's a TCP packet */
 237                 if (e->ip.proto != IPPROTO_TCP
 238                     || (e->ip.invflags & XT_INV_PROTO)) {
 239                         DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
 240                         return 0;
 241                 }
 242         }
 243         return 1;
 244 }
 245
 246 static struct xt_target ipt_reject_reg = {
 247         .name           = "REJECT",
 248         .family         = AF_INET,
 249         .target         = reject,
 250         .targetsize     = sizeof(struct ipt_reject_info),
 251         .table          = "filter",
 252         .hooks          = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) |
 253                           (1 << NF_IP_LOCAL_OUT),
 254         .checkentry     = check,
 255         .me             = THIS_MODULE,
 256 };
 257
 258 static int __init ipt_reject_init(void)
 259 {
 260         return xt_register_target(&ipt_reject_reg);
 261 }
 262
 263 static void __exit ipt_reject_fini(void)
 264 {
 265         xt_unregister_target(&ipt_reject_reg);
 266 }
 267
 268 module_init(ipt_reject_init);
 269 module_exit(ipt_reject_fini);