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 static inline struct rtable *route_reverse(struct sk_buff *skb,
  42                                            struct tcphdr *tcph, int hook)
  43 {
  44         struct iphdr *iph = skb->nh.iph;
  45         struct dst_entry *odst;
  46         struct flowi fl = {};
  47         struct rtable *rt;
  48
  49         /* We don't require ip forwarding to be enabled to be able to
  50          * send a RST reply for bridged traffic. */
  51         if (hook != NF_IP_FORWARD
  52 #ifdef CONFIG_BRIDGE_NETFILTER
  53             || (skb->nf_bridge && skb->nf_bridge->mask & BRNF_BRIDGED)
  54 #endif
  55            ) {
  56                 fl.nl_u.ip4_u.daddr = iph->saddr;
  57                 if (hook == NF_IP_LOCAL_IN)
  58                         fl.nl_u.ip4_u.saddr = iph->daddr;
  59                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  60
  61                 if (ip_route_output_key(&rt, &fl) != 0)
  62                         return NULL;
  63         } else {
  64                 /* non-local src, find valid iif to satisfy
  65                  * rp-filter when calling ip_route_input. */
  66                 fl.nl_u.ip4_u.daddr = iph->daddr;
  67                 if (ip_route_output_key(&rt, &fl) != 0)
  68                         return NULL;
  69
  70                 odst = skb->dst;
  71                 if (ip_route_input(skb, iph->saddr, iph->daddr,
  72                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  73                         dst_release(&rt->u.dst);
  74                         return NULL;
  75                 }
  76                 dst_release(&rt->u.dst);
  77                 rt = (struct rtable *)skb->dst;
  78                 skb->dst = odst;
  79
  80                 fl.nl_u.ip4_u.daddr = iph->saddr;
  81                 fl.nl_u.ip4_u.saddr = iph->daddr;
  82                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  83         }
  84
  85         if (rt->u.dst.error) {
  86                 dst_release(&rt->u.dst);
  87                 return NULL;
  88         }
  89
  90         fl.proto = IPPROTO_TCP;
  91         fl.fl_ip_sport = tcph->dest;
  92         fl.fl_ip_dport = tcph->source;
  93
  94         xfrm_lookup((struct dst_entry **)&rt, &fl, NULL, 0);
  95
  96         return rt;
  97 }
  98
  99 /* Send RST reply */
 100 static void send_reset(struct sk_buff *oldskb, int hook)
 101 {
 102         struct sk_buff *nskb;
 103         struct iphdr *iph = oldskb->nh.iph;
 104         struct tcphdr _otcph, *oth, *tcph;
 105         struct rtable *rt;
 106         u_int16_t tmp_port;
 107         u_int32_t tmp_addr;
 108         int needs_ack;
 109         int hh_len;
 110
 111         /* IP header checks: fragment. */
 112         if (oldskb->nh.iph->frag_off & htons(IP_OFFSET))
 113                 return;
 114
 115         oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4,
 116                                  sizeof(_otcph), &_otcph);
 117         if (oth == NULL)
 118                 return;
 119
 120         /* No RST for RST. */
 121         if (oth->rst)
 122                 return;
 123
 124         /* Check checksum */
 125         if (nf_ip_checksum(oldskb, hook, iph->ihl * 4, IPPROTO_TCP))
 126                 return;
 127
 128         if ((rt = route_reverse(oldskb, oth, hook)) == NULL)
 129                 return;
 130
 131         hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);
 132
 133         /* We need a linear, writeable skb.  We also need to expand
 134            headroom in case hh_len of incoming interface < hh_len of
 135            outgoing interface */
 136         nskb = skb_copy_expand(oldskb, hh_len, skb_tailroom(oldskb),
 137                                GFP_ATOMIC);
 138         if (!nskb) {
 139                 dst_release(&rt->u.dst);
 140                 return;
 141         }
 142
 143         dst_release(nskb->dst);
 144         nskb->dst = &rt->u.dst;
 145
 146         /* This packet will not be the same as the other: clear nf fields */
 147         nf_reset(nskb);
 148         nskb->nfmark = 0;
 149         skb_init_secmark(nskb);
 150
 151         tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
 152
 153         /* Swap source and dest */
 154         tmp_addr = nskb->nh.iph->saddr;
 155         nskb->nh.iph->saddr = nskb->nh.iph->daddr;
 156         nskb->nh.iph->daddr = tmp_addr;
 157         tmp_port = tcph->source;
 158         tcph->source = tcph->dest;
 159         tcph->dest = tmp_port;
 160
 161         /* Truncate to length (no data) */
 162         tcph->doff = sizeof(struct tcphdr)/4;
 163         skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
 164         nskb->nh.iph->tot_len = htons(nskb->len);
 165
 166         if (tcph->ack) {
 167                 needs_ack = 0;
 168                 tcph->seq = oth->ack_seq;
 169                 tcph->ack_seq = 0;
 170         } else {
 171                 needs_ack = 1;
 172                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
 173                                       + oldskb->len - oldskb->nh.iph->ihl*4
 174                                       - (oth->doff<<2));
 175                 tcph->seq = 0;
 176         }
 177
 178         /* Reset flags */
 179         ((u_int8_t *)tcph)[13] = 0;
 180         tcph->rst = 1;
 181         tcph->ack = needs_ack;
 182
 183         tcph->window = 0;
 184         tcph->urg_ptr = 0;
 185
 186         /* Adjust TCP checksum */
 187         tcph->check = 0;
 188         tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
 189                                    nskb->nh.iph->saddr,
 190                                    nskb->nh.iph->daddr,
 191                                    csum_partial((char *)tcph,
 192                                                 sizeof(struct tcphdr), 0));
 193
 194         /* Adjust IP TTL, DF */
 195         nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 196         /* Set DF, id = 0 */
 197         nskb->nh.iph->frag_off = htons(IP_DF);
 198         nskb->nh.iph->id = 0;
 199
 200         /* Adjust IP checksum */
 201         nskb->nh.iph->check = 0;
 202         nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
 203                                            nskb->nh.iph->ihl);
 204
 205         /* "Never happens" */
 206         if (nskb->len > dst_mtu(nskb->dst))
 207                 goto free_nskb;
 208
 209         nf_ct_attach(nskb, oldskb);
 210
 211         NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 212                 dst_output);
 213         return;
 214
 215  free_nskb:
 216         kfree_skb(nskb);
 217 }
 218
 219 static inline void send_unreach(struct sk_buff *skb_in, int code)
 220 {
 221         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 222 }
 223
 224 static unsigned int reject(struct sk_buff **pskb,
 225                            const struct net_device *in,
 226                            const struct net_device *out,
 227                            unsigned int hooknum,
 228                            const struct xt_target *target,
 229                            const void *targinfo,
 230                            void *userinfo)
 231 {
 232         const struct ipt_reject_info *reject = targinfo;
 233
 234         /* Our naive response construction doesn't deal with IP
 235            options, and probably shouldn't try. */
 236         if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
 237                 return NF_DROP;
 238
 239         /* WARNING: This code causes reentry within iptables.
 240            This means that the iptables jump stack is now crap.  We
 241            must return an absolute verdict. --RR */
 242         switch (reject->with) {
 243         case IPT_ICMP_NET_UNREACHABLE:
 244                 send_unreach(*pskb, ICMP_NET_UNREACH);
 245                 break;
 246         case IPT_ICMP_HOST_UNREACHABLE:
 247                 send_unreach(*pskb, ICMP_HOST_UNREACH);
 248                 break;
 249         case IPT_ICMP_PROT_UNREACHABLE:
 250                 send_unreach(*pskb, ICMP_PROT_UNREACH);
 251                 break;
 252         case IPT_ICMP_PORT_UNREACHABLE:
 253                 send_unreach(*pskb, ICMP_PORT_UNREACH);
 254                 break;
 255         case IPT_ICMP_NET_PROHIBITED:
 256                 send_unreach(*pskb, ICMP_NET_ANO);
 257                 break;
 258         case IPT_ICMP_HOST_PROHIBITED:
 259                 send_unreach(*pskb, ICMP_HOST_ANO);
 260                 break;
 261         case IPT_ICMP_ADMIN_PROHIBITED:
 262                 send_unreach(*pskb, ICMP_PKT_FILTERED);
 263                 break;
 264         case IPT_TCP_RESET:
 265                 send_reset(*pskb, hooknum);
 266         case IPT_ICMP_ECHOREPLY:
 267                 /* Doesn't happen. */
 268                 break;
 269         }
 270
 271         return NF_DROP;
 272 }
 273
 274 static int check(const char *tablename,
 275                  const void *e_void,
 276                  const struct xt_target *target,
 277                  void *targinfo,
 278                  unsigned int targinfosize,
 279                  unsigned int hook_mask)
 280 {
 281         const struct ipt_reject_info *rejinfo = targinfo;
 282         const struct ipt_entry *e = e_void;
 283
 284         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 285                 printk("REJECT: ECHOREPLY no longer supported.\n");
 286                 return 0;
 287         } else if (rejinfo->with == IPT_TCP_RESET) {
 288                 /* Must specify that it's a TCP packet */
 289                 if (e->ip.proto != IPPROTO_TCP
 290                     || (e->ip.invflags & IPT_INV_PROTO)) {
 291                         DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
 292                         return 0;
 293                 }
 294         }
 295         return 1;
 296 }
 297
 298 static struct ipt_target ipt_reject_reg = {
 299         .name           = "REJECT",
 300         .target         = reject,
 301         .targetsize     = sizeof(struct ipt_reject_info),
 302         .table          = "filter",
 303         .hooks          = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) |
 304                           (1 << NF_IP_LOCAL_OUT),
 305         .checkentry     = check,
 306         .me             = THIS_MODULE,
 307 };
 308
 309 static int __init ipt_reject_init(void)
 310 {
 311         return ipt_register_target(&ipt_reject_reg);
 312 }
 313
 314 static void __exit ipt_reject_fini(void)
 315 {
 316         ipt_unregister_target(&ipt_reject_reg);
 317 }
 318
 319 module_init(ipt_reject_init);
 320 module_exit(ipt_reject_fini);