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   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/config.h>
  16 #include <linux/module.h>
  17 #include <linux/skbuff.h>
  18 #include <linux/ip.h>
  19 #include <linux/udp.h>
  20 #include <linux/icmp.h>
  21 #include <net/icmp.h>
  22 #include <net/ip.h>
  23 #include <net/tcp.h>
  24 #include <net/route.h>
  25 #include <net/dst.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 static inline struct rtable *route_reverse(struct sk_buff *skb,
  43                                            struct tcphdr *tcph, int hook)
  44 {
  45         struct iphdr *iph = skb->nh.iph;
  46         struct dst_entry *odst;
  47         struct flowi fl = {};
  48         struct rtable *rt;
  49
  50         /* We don't require ip forwarding to be enabled to be able to
  51          * send a RST reply for bridged traffic. */
  52         if (hook != NF_IP_FORWARD
  53 #ifdef CONFIG_BRIDGE_NETFILTER
  54             || (skb->nf_bridge && skb->nf_bridge->mask & BRNF_BRIDGED)
  55 #endif
  56            ) {
  57                 fl.nl_u.ip4_u.daddr = iph->saddr;
  58                 if (hook == NF_IP_LOCAL_IN)
  59                         fl.nl_u.ip4_u.saddr = iph->daddr;
  60                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  61
  62                 if (ip_route_output_key(&rt, &fl) != 0)
  63                         return NULL;
  64         } else {
  65                 /* non-local src, find valid iif to satisfy
  66                  * rp-filter when calling ip_route_input. */
  67                 fl.nl_u.ip4_u.daddr = iph->daddr;
  68                 if (ip_route_output_key(&rt, &fl) != 0)
  69                         return NULL;
  70
  71                 odst = skb->dst;
  72                 if (ip_route_input(skb, iph->saddr, iph->daddr,
  73                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  74                         dst_release(&rt->u.dst);
  75                         return NULL;
  76                 }
  77                 dst_release(&rt->u.dst);
  78                 rt = (struct rtable *)skb->dst;
  79                 skb->dst = odst;
  80
  81                 fl.nl_u.ip4_u.daddr = iph->saddr;
  82                 fl.nl_u.ip4_u.saddr = iph->daddr;
  83                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  84         }
  85
  86         if (rt->u.dst.error) {
  87                 dst_release(&rt->u.dst);
  88                 return NULL;
  89         }
  90
  91         fl.proto = IPPROTO_TCP;
  92         fl.fl_ip_sport = tcph->dest;
  93         fl.fl_ip_dport = tcph->source;
  94
  95         xfrm_lookup((struct dst_entry **)&rt, &fl, NULL, 0);
  96
  97         return rt;
  98 }
  99
 100 /* Send RST reply */
 101 static void send_reset(struct sk_buff *oldskb, int hook)
 102 {
 103         struct sk_buff *nskb;
 104         struct iphdr *iph = oldskb->nh.iph;
 105         struct tcphdr _otcph, *oth, *tcph;
 106         struct rtable *rt;
 107         u_int16_t tmp_port;
 108         u_int32_t tmp_addr;
 109         unsigned int tcplen;
 110         int needs_ack;
 111         int hh_len;
 112
 113         /* IP header checks: fragment. */
 114         if (oldskb->nh.iph->frag_off & htons(IP_OFFSET))
 115                 return;
 116
 117         oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4,
 118                                  sizeof(_otcph), &_otcph);
 119         if (oth == NULL)
 120                 return;
 121
 122         /* No RST for RST. */
 123         if (oth->rst)
 124                 return;
 125
 126         /* Check checksum */
 127         tcplen = oldskb->len - iph->ihl * 4;
 128         if (((hook != NF_IP_LOCAL_IN && oldskb->ip_summed != CHECKSUM_HW) ||
 129              (hook == NF_IP_LOCAL_IN &&
 130               oldskb->ip_summed != CHECKSUM_UNNECESSARY)) &&
 131             csum_tcpudp_magic(iph->saddr, iph->daddr, tcplen, IPPROTO_TCP,
 132                               oldskb->ip_summed == CHECKSUM_HW ? oldskb->csum :
 133                               skb_checksum(oldskb, iph->ihl * 4, tcplen, 0)))
 134                 return;
 135
 136         if ((rt = route_reverse(oldskb, oth, hook)) == NULL)
 137                 return;
 138
 139         hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);
 140
 141         /* We need a linear, writeable skb.  We also need to expand
 142            headroom in case hh_len of incoming interface < hh_len of
 143            outgoing interface */
 144         nskb = skb_copy_expand(oldskb, hh_len, skb_tailroom(oldskb),
 145                                GFP_ATOMIC);
 146         if (!nskb) {
 147                 dst_release(&rt->u.dst);
 148                 return;
 149         }
 150
 151         dst_release(nskb->dst);
 152         nskb->dst = &rt->u.dst;
 153
 154         /* This packet will not be the same as the other: clear nf fields */
 155         nf_reset(nskb);
 156         nskb->nfmark = 0;
 157 #ifdef CONFIG_BRIDGE_NETFILTER
 158         nf_bridge_put(nskb->nf_bridge);
 159         nskb->nf_bridge = NULL;
 160 #endif
 161
 162         tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
 163
 164         /* Swap source and dest */
 165         tmp_addr = nskb->nh.iph->saddr;
 166         nskb->nh.iph->saddr = nskb->nh.iph->daddr;
 167         nskb->nh.iph->daddr = tmp_addr;
 168         tmp_port = tcph->source;
 169         tcph->source = tcph->dest;
 170         tcph->dest = tmp_port;
 171
 172         /* Truncate to length (no data) */
 173         tcph->doff = sizeof(struct tcphdr)/4;
 174         skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
 175         nskb->nh.iph->tot_len = htons(nskb->len);
 176
 177         if (tcph->ack) {
 178                 needs_ack = 0;
 179                 tcph->seq = oth->ack_seq;
 180                 tcph->ack_seq = 0;
 181         } else {
 182                 needs_ack = 1;
 183                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
 184                                       + oldskb->len - oldskb->nh.iph->ihl*4
 185                                       - (oth->doff<<2));
 186                 tcph->seq = 0;
 187         }
 188
 189         /* Reset flags */
 190         ((u_int8_t *)tcph)[13] = 0;
 191         tcph->rst = 1;
 192         tcph->ack = needs_ack;
 193
 194         tcph->window = 0;
 195         tcph->urg_ptr = 0;
 196
 197         /* Adjust TCP checksum */
 198         tcph->check = 0;
 199         tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
 200                                    nskb->nh.iph->saddr,
 201                                    nskb->nh.iph->daddr,
 202                                    csum_partial((char *)tcph,
 203                                                 sizeof(struct tcphdr), 0));
 204
 205         /* Adjust IP TTL, DF */
 206         nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 207         /* Set DF, id = 0 */
 208         nskb->nh.iph->frag_off = htons(IP_DF);
 209         nskb->nh.iph->id = 0;
 210
 211         /* Adjust IP checksum */
 212         nskb->nh.iph->check = 0;
 213         nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
 214                                            nskb->nh.iph->ihl);
 215
 216         /* "Never happens" */
 217         if (nskb->len > dst_mtu(nskb->dst))
 218                 goto free_nskb;
 219
 220         nf_ct_attach(nskb, oldskb);
 221
 222         NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 223                 dst_output);
 224         return;
 225
 226  free_nskb:
 227         kfree_skb(nskb);
 228 }
 229
 230 static inline void send_unreach(struct sk_buff *skb_in, int code)
 231 {
 232         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 233 }
 234
 235 static unsigned int reject(struct sk_buff **pskb,
 236                            const struct net_device *in,
 237                            const struct net_device *out,
 238                            unsigned int hooknum,
 239                            const struct xt_target *target,
 240                            const void *targinfo,
 241                            void *userinfo)
 242 {
 243         const struct ipt_reject_info *reject = targinfo;
 244
 245         /* Our naive response construction doesn't deal with IP
 246            options, and probably shouldn't try. */
 247         if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
 248                 return NF_DROP;
 249
 250         /* WARNING: This code causes reentry within iptables.
 251            This means that the iptables jump stack is now crap.  We
 252            must return an absolute verdict. --RR */
 253         switch (reject->with) {
 254         case IPT_ICMP_NET_UNREACHABLE:
 255                 send_unreach(*pskb, ICMP_NET_UNREACH);
 256                 break;
 257         case IPT_ICMP_HOST_UNREACHABLE:
 258                 send_unreach(*pskb, ICMP_HOST_UNREACH);
 259                 break;
 260         case IPT_ICMP_PROT_UNREACHABLE:
 261                 send_unreach(*pskb, ICMP_PROT_UNREACH);
 262                 break;
 263         case IPT_ICMP_PORT_UNREACHABLE:
 264                 send_unreach(*pskb, ICMP_PORT_UNREACH);
 265                 break;
 266         case IPT_ICMP_NET_PROHIBITED:
 267                 send_unreach(*pskb, ICMP_NET_ANO);
 268                 break;
 269         case IPT_ICMP_HOST_PROHIBITED:
 270                 send_unreach(*pskb, ICMP_HOST_ANO);
 271                 break;
 272         case IPT_ICMP_ADMIN_PROHIBITED:
 273                 send_unreach(*pskb, ICMP_PKT_FILTERED);
 274                 break;
 275         case IPT_TCP_RESET:
 276                 send_reset(*pskb, hooknum);
 277         case IPT_ICMP_ECHOREPLY:
 278                 /* Doesn't happen. */
 279                 break;
 280         }
 281
 282         return NF_DROP;
 283 }
 284
 285 static int check(const char *tablename,
 286                  const void *e_void,
 287                  const struct xt_target *target,
 288                  void *targinfo,
 289                  unsigned int targinfosize,
 290                  unsigned int hook_mask)
 291 {
 292         const struct ipt_reject_info *rejinfo = targinfo;
 293         const struct ipt_entry *e = e_void;
 294
 295         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 296                 printk("REJECT: ECHOREPLY no longer supported.\n");
 297                 return 0;
 298         } else if (rejinfo->with == IPT_TCP_RESET) {
 299                 /* Must specify that it's a TCP packet */
 300                 if (e->ip.proto != IPPROTO_TCP
 301                     || (e->ip.invflags & IPT_INV_PROTO)) {
 302                         DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
 303                         return 0;
 304                 }
 305         }
 306         return 1;
 307 }
 308
 309 static struct ipt_target ipt_reject_reg = {
 310         .name           = "REJECT",
 311         .target         = reject,
 312         .targetsize     = sizeof(struct ipt_reject_info),
 313         .table          = "filter",
 314         .hooks          = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) |
 315                           (1 << NF_IP_LOCAL_OUT),
 316         .checkentry     = check,
 317         .me             = THIS_MODULE,
 318 };
 319
 320 static int __init init(void)
 321 {
 322         return ipt_register_target(&ipt_reject_reg);
 323 }
 324
 325 static void __exit fini(void)
 326 {
 327         ipt_unregister_target(&ipt_reject_reg);
 328 }
 329
 330 module_init(init);
 331 module_exit(fini);