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 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, ip_hdrlen(oldskb),
  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, ip_hdrlen(oldskb), 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         skb_shinfo(nskb)->gso_size = 0;
  83         skb_shinfo(nskb)->gso_segs = 0;
  84         skb_shinfo(nskb)->gso_type = 0;
  85
  86         tcph = (struct tcphdr *)(skb_network_header(nskb) + ip_hdrlen(nskb));
  87
  88         /* Swap source and dest */
  89         tmp_addr = nskb->nh.iph->saddr;
  90         nskb->nh.iph->saddr = nskb->nh.iph->daddr;
  91         nskb->nh.iph->daddr = tmp_addr;
  92         tmp_port = tcph->source;
  93         tcph->source = tcph->dest;
  94         tcph->dest = tmp_port;
  95
  96         /* Truncate to length (no data) */
  97         tcph->doff = sizeof(struct tcphdr)/4;
  98         skb_trim(nskb, ip_hdrlen(nskb) + sizeof(struct tcphdr));
  99         nskb->nh.iph->tot_len = htons(nskb->len);
 100
 101         if (tcph->ack) {
 102                 needs_ack = 0;
 103                 tcph->seq = oth->ack_seq;
 104                 tcph->ack_seq = 0;
 105         } else {
 106                 needs_ack = 1;
 107                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
 108                                       oldskb->len - ip_hdrlen(oldskb) -
 109                                       (oth->doff << 2));
 110                 tcph->seq = 0;
 111         }
 112
 113         /* Reset flags */
 114         ((u_int8_t *)tcph)[13] = 0;
 115         tcph->rst = 1;
 116         tcph->ack = needs_ack;
 117
 118         tcph->window = 0;
 119         tcph->urg_ptr = 0;
 120
 121         /* Adjust TCP checksum */
 122         tcph->check = 0;
 123         tcph->check = tcp_v4_check(sizeof(struct tcphdr),
 124                                    nskb->nh.iph->saddr,
 125                                    nskb->nh.iph->daddr,
 126                                    csum_partial((char *)tcph,
 127                                                 sizeof(struct tcphdr), 0));
 128
 129         /* Set DF, id = 0 */
 130         nskb->nh.iph->frag_off = htons(IP_DF);
 131         nskb->nh.iph->id = 0;
 132
 133         addr_type = RTN_UNSPEC;
 134         if (hook != NF_IP_FORWARD
 135 #ifdef CONFIG_BRIDGE_NETFILTER
 136             || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
 137 #endif
 138            )
 139                 addr_type = RTN_LOCAL;
 140
 141         if (ip_route_me_harder(&nskb, addr_type))
 142                 goto free_nskb;
 143
 144         nskb->ip_summed = CHECKSUM_NONE;
 145
 146         /* Adjust IP TTL */
 147         nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 148
 149         /* Adjust IP checksum */
 150         nskb->nh.iph->check = 0;
 151         nskb->nh.iph->check = ip_fast_csum(skb_network_header(nskb),
 152                                            nskb->nh.iph->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);