SAFE public projects git trees. - safe/jmp/linux-2.6/blob - 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 *niph;
  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 (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
  55                 return;
  56
  57         oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
  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, ip_hdrlen(oldskb), 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 *)(skb_network_header(nskb) + ip_hdrlen(nskb));
  88
  89         /* Swap source and dest */
  90         niph = ip_hdr(nskb);
  91         tmp_addr = niph->saddr;
  92         niph->saddr = niph->daddr;
  93         niph->daddr = tmp_addr;
  94         tmp_port = tcph->source;
  95         tcph->source = tcph->dest;
  96         tcph->dest = tmp_port;
  97
  98         /* Truncate to length (no data) */
  99         tcph->doff = sizeof(struct tcphdr)/4;
 100         skb_trim(nskb, ip_hdrlen(nskb) + sizeof(struct tcphdr));
 101         niph->tot_len = htons(nskb->len);
 102
 103         if (tcph->ack) {
 104                 needs_ack = 0;
 105                 tcph->seq = oth->ack_seq;
 106                 tcph->ack_seq = 0;
 107         } else {
 108                 needs_ack = 1;
 109                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
 110                                       oldskb->len - ip_hdrlen(oldskb) -
 111                                       (oth->doff << 2));
 112                 tcph->seq = 0;
 113         }
 114
 115         /* Reset flags */
 116         ((u_int8_t *)tcph)[13] = 0;
 117         tcph->rst = 1;
 118         tcph->ack = needs_ack;
 119
 120         tcph->window = 0;
 121         tcph->urg_ptr = 0;
 122
 123         /* Adjust TCP checksum */
 124         tcph->check = 0;
 125         tcph->check = tcp_v4_check(sizeof(struct tcphdr),
 126                                    niph->saddr, niph->daddr,
 127                                    csum_partial((char *)tcph,
 128                                                 sizeof(struct tcphdr), 0));
 129
 130         /* Set DF, id = 0 */
 131         niph->frag_off = htons(IP_DF);
 132         niph->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         niph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 149
 150         /* Adjust IP checksum */
 151         niph->check = 0;
 152         niph->check = ip_fast_csum(skb_network_header(nskb), niph->ihl);
 153
 154         /* "Never happens" */
 155         if (nskb->len > dst_mtu(nskb->dst))
 156                 goto free_nskb;
 157
 158         nf_ct_attach(nskb, oldskb);
 159
 160         NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 161                 dst_output);
 162         return;
 163
 164  free_nskb:
 165         kfree_skb(nskb);
 166 }
 167
 168 static inline void send_unreach(struct sk_buff *skb_in, int code)
 169 {
 170         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 171 }
 172
 173 static unsigned int reject(struct sk_buff **pskb,
 174                            const struct net_device *in,
 175                            const struct net_device *out,
 176                            unsigned int hooknum,
 177                            const struct xt_target *target,
 178                            const void *targinfo)
 179 {
 180         const struct ipt_reject_info *reject = targinfo;
 181
 182         /* Our naive response construction doesn't deal with IP
 183            options, and probably shouldn't try. */
 184         if (ip_hdrlen(*pskb) != sizeof(struct iphdr))
 185                 return NF_DROP;
 186
 187         /* WARNING: This code causes reentry within iptables.
 188            This means that the iptables jump stack is now crap.  We
 189            must return an absolute verdict. --RR */
 190         switch (reject->with) {
 191         case IPT_ICMP_NET_UNREACHABLE:
 192                 send_unreach(*pskb, ICMP_NET_UNREACH);
 193                 break;
 194         case IPT_ICMP_HOST_UNREACHABLE:
 195                 send_unreach(*pskb, ICMP_HOST_UNREACH);
 196                 break;
 197         case IPT_ICMP_PROT_UNREACHABLE:
 198                 send_unreach(*pskb, ICMP_PROT_UNREACH);
 199                 break;
 200         case IPT_ICMP_PORT_UNREACHABLE:
 201                 send_unreach(*pskb, ICMP_PORT_UNREACH);
 202                 break;
 203         case IPT_ICMP_NET_PROHIBITED:
 204                 send_unreach(*pskb, ICMP_NET_ANO);
 205                 break;
 206         case IPT_ICMP_HOST_PROHIBITED:
 207                 send_unreach(*pskb, ICMP_HOST_ANO);
 208                 break;
 209         case IPT_ICMP_ADMIN_PROHIBITED:
 210                 send_unreach(*pskb, ICMP_PKT_FILTERED);
 211                 break;
 212         case IPT_TCP_RESET:
 213                 send_reset(*pskb, hooknum);
 214         case IPT_ICMP_ECHOREPLY:
 215                 /* Doesn't happen. */
 216                 break;
 217         }
 218
 219         return NF_DROP;
 220 }
 221
 222 static int check(const char *tablename,
 223                  const void *e_void,
 224                  const struct xt_target *target,
 225                  void *targinfo,
 226                  unsigned int hook_mask)
 227 {
 228         const struct ipt_reject_info *rejinfo = targinfo;
 229         const struct ipt_entry *e = e_void;
 230
 231         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 232                 printk("REJECT: ECHOREPLY no longer supported.\n");
 233                 return 0;
 234         } else if (rejinfo->with == IPT_TCP_RESET) {
 235                 /* Must specify that it's a TCP packet */
 236                 if (e->ip.proto != IPPROTO_TCP
 237                     || (e->ip.invflags & XT_INV_PROTO)) {
 238                         DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
 239                         return 0;
 240                 }
 241         }
 242         return 1;
 243 }
 244
 245 static struct xt_target ipt_reject_reg = {
 246         .name           = "REJECT",
 247         .family         = AF_INET,
 248         .target         = reject,
 249         .targetsize     = sizeof(struct ipt_reject_info),
 250         .table          = "filter",
 251         .hooks          = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) |
 252                           (1 << NF_IP_LOCAL_OUT),
 253         .checkentry     = check,
 254         .me             = THIS_MODULE,
 255 };
 256
 257 static int __init ipt_reject_init(void)
 258 {
 259         return xt_register_target(&ipt_reject_reg);
 260 }
 261
 262 static void __exit ipt_reject_fini(void)
 263 {
 264         xt_unregister_target(&ipt_reject_reg);
 265 }
 266
 267 module_init(ipt_reject_init);
 268 module_exit(ipt_reject_fini);