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   1 /*
   2  * IP6 tables REJECT target module
   3  * Linux INET6 implementation
   4  *
   5  * Copyright (C)2003 USAGI/WIDE Project
   6  *
   7  * Authors:
   8  *      Yasuyuki Kozakai        <yasuyuki.kozakai@toshiba.co.jp>
   9  *
  10  * Based on net/ipv4/netfilter/ipt_REJECT.c
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License
  14  * as published by the Free Software Foundation; either version
  15  * 2 of the License, or (at your option) any later version.
  16  */
  17
  18 #include <linux/module.h>
  19 #include <linux/skbuff.h>
  20 #include <linux/icmpv6.h>
  21 #include <linux/netdevice.h>
  22 #include <net/ipv6.h>
  23 #include <net/tcp.h>
  24 #include <net/icmp.h>
  25 #include <net/ip6_checksum.h>
  26 #include <net/ip6_fib.h>
  27 #include <net/ip6_route.h>
  28 #include <net/flow.h>
  29 #include <linux/netfilter/x_tables.h>
  30 #include <linux/netfilter_ipv6/ip6_tables.h>
  31 #include <linux/netfilter_ipv6/ip6t_REJECT.h>
  32
  33 MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
  34 MODULE_DESCRIPTION("IP6 tables REJECT target module");
  35 MODULE_LICENSE("GPL");
  36
  37 #if 0
  38 #define DEBUGP printk
  39 #else
  40 #define DEBUGP(format, args...)
  41 #endif
  42
  43 /* Send RST reply */
  44 static void send_reset(struct sk_buff *oldskb)
  45 {
  46         struct sk_buff *nskb;
  47         struct tcphdr otcph, *tcph;
  48         unsigned int otcplen, hh_len;
  49         int tcphoff, needs_ack;
  50         struct ipv6hdr *oip6h = ipv6_hdr(oldskb), *ip6h;
  51         struct dst_entry *dst = NULL;
  52         u8 proto;
  53         struct flowi fl;
  54
  55         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
  56             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
  57                 DEBUGP("ip6t_REJECT: addr is not unicast.\n");
  58                 return;
  59         }
  60
  61         proto = oip6h->nexthdr;
  62         tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto);
  63
  64         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  65                 DEBUGP("ip6t_REJECT: Can't get TCP header.\n");
  66                 return;
  67         }
  68
  69         otcplen = oldskb->len - tcphoff;
  70
  71         /* IP header checks: fragment, too short. */
  72         if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
  73                 DEBUGP("ip6t_REJECT: proto(%d) != IPPROTO_TCP, or too short. otcplen = %d\n",
  74                         proto, otcplen);
  75                 return;
  76         }
  77
  78         if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
  79                 BUG();
  80
  81         /* No RST for RST. */
  82         if (otcph.rst) {
  83                 DEBUGP("ip6t_REJECT: RST is set\n");
  84                 return;
  85         }
  86
  87         /* Check checksum. */
  88         if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
  89                             skb_checksum(oldskb, tcphoff, otcplen, 0))) {
  90                 DEBUGP("ip6t_REJECT: TCP checksum is invalid\n");
  91                 return;
  92         }
  93
  94         memset(&fl, 0, sizeof(fl));
  95         fl.proto = IPPROTO_TCP;
  96         ipv6_addr_copy(&fl.fl6_src, &oip6h->daddr);
  97         ipv6_addr_copy(&fl.fl6_dst, &oip6h->saddr);
  98         fl.fl_ip_sport = otcph.dest;
  99         fl.fl_ip_dport = otcph.source;
 100         security_skb_classify_flow(oldskb, &fl);
 101         dst = ip6_route_output(NULL, &fl);
 102         if (dst == NULL)
 103                 return;
 104         if (dst->error || xfrm_lookup(&dst, &fl, NULL, 0))
 105                 return;
 106
 107         hh_len = (dst->dev->hard_header_len + 15)&~15;
 108         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 109                          + sizeof(struct tcphdr) + dst->trailer_len,
 110                          GFP_ATOMIC);
 111
 112         if (!nskb) {
 113                 if (net_ratelimit())
 114                         printk("ip6t_REJECT: Can't alloc skb\n");
 115                 dst_release(dst);
 116                 return;
 117         }
 118
 119         nskb->dst = dst;
 120
 121         skb_reserve(nskb, hh_len + dst->header_len);
 122
 123         skb_put(nskb, sizeof(struct ipv6hdr));
 124         skb_reset_network_header(nskb);
 125         ip6h = ipv6_hdr(nskb);
 126         ip6h->version = 6;
 127         ip6h->hop_limit = dst_metric(dst, RTAX_HOPLIMIT);
 128         ip6h->nexthdr = IPPROTO_TCP;
 129         ip6h->payload_len = htons(sizeof(struct tcphdr));
 130         ipv6_addr_copy(&ip6h->saddr, &oip6h->daddr);
 131         ipv6_addr_copy(&ip6h->daddr, &oip6h->saddr);
 132
 133         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 134         /* Truncate to length (no data) */
 135         tcph->doff = sizeof(struct tcphdr)/4;
 136         tcph->source = otcph.dest;
 137         tcph->dest = otcph.source;
 138
 139         if (otcph.ack) {
 140                 needs_ack = 0;
 141                 tcph->seq = otcph.ack_seq;
 142                 tcph->ack_seq = 0;
 143         } else {
 144                 needs_ack = 1;
 145                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 146                                       + otcplen - (otcph.doff<<2));
 147                 tcph->seq = 0;
 148         }
 149
 150         /* Reset flags */
 151         ((u_int8_t *)tcph)[13] = 0;
 152         tcph->rst = 1;
 153         tcph->ack = needs_ack;
 154         tcph->window = 0;
 155         tcph->urg_ptr = 0;
 156         tcph->check = 0;
 157
 158         /* Adjust TCP checksum */
 159         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 160                                       &ipv6_hdr(nskb)->daddr,
 161                                       sizeof(struct tcphdr), IPPROTO_TCP,
 162                                       csum_partial(tcph,
 163                                                    sizeof(struct tcphdr), 0));
 164
 165         nf_ct_attach(nskb, oldskb);
 166
 167         NF_HOOK(PF_INET6, NF_IP6_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 168                 dst_output);
 169 }
 170
 171 static inline void
 172 send_unreach(struct sk_buff *skb_in, unsigned char code, unsigned int hooknum)
 173 {
 174         if (hooknum == NF_IP6_LOCAL_OUT && skb_in->dev == NULL)
 175                 skb_in->dev = &loopback_dev;
 176
 177         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0, NULL);
 178 }
 179
 180 static unsigned int reject6_target(struct sk_buff **pskb,
 181                            const struct net_device *in,
 182                            const struct net_device *out,
 183                            unsigned int hooknum,
 184                            const struct xt_target *target,
 185                            const void *targinfo)
 186 {
 187         const struct ip6t_reject_info *reject = targinfo;
 188
 189         DEBUGP(KERN_DEBUG "%s: medium point\n", __FUNCTION__);
 190         /* WARNING: This code causes reentry within ip6tables.
 191            This means that the ip6tables jump stack is now crap.  We
 192            must return an absolute verdict. --RR */
 193         switch (reject->with) {
 194         case IP6T_ICMP6_NO_ROUTE:
 195                 send_unreach(*pskb, ICMPV6_NOROUTE, hooknum);
 196                 break;
 197         case IP6T_ICMP6_ADM_PROHIBITED:
 198                 send_unreach(*pskb, ICMPV6_ADM_PROHIBITED, hooknum);
 199                 break;
 200         case IP6T_ICMP6_NOT_NEIGHBOUR:
 201                 send_unreach(*pskb, ICMPV6_NOT_NEIGHBOUR, hooknum);
 202                 break;
 203         case IP6T_ICMP6_ADDR_UNREACH:
 204                 send_unreach(*pskb, ICMPV6_ADDR_UNREACH, hooknum);
 205                 break;
 206         case IP6T_ICMP6_PORT_UNREACH:
 207                 send_unreach(*pskb, ICMPV6_PORT_UNREACH, hooknum);
 208                 break;
 209         case IP6T_ICMP6_ECHOREPLY:
 210                 /* Do nothing */
 211                 break;
 212         case IP6T_TCP_RESET:
 213                 send_reset(*pskb);
 214                 break;
 215         default:
 216                 if (net_ratelimit())
 217                         printk(KERN_WARNING "ip6t_REJECT: case %u not handled yet\n", reject->with);
 218                 break;
 219         }
 220
 221         return NF_DROP;
 222 }
 223
 224 static bool check(const char *tablename,
 225                   const void *entry,
 226                   const struct xt_target *target,
 227                   void *targinfo,
 228                   unsigned int hook_mask)
 229 {
 230         const struct ip6t_reject_info *rejinfo = targinfo;
 231         const struct ip6t_entry *e = entry;
 232
 233         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 234                 printk("ip6t_REJECT: ECHOREPLY is not supported.\n");
 235                 return false;
 236         } else if (rejinfo->with == IP6T_TCP_RESET) {
 237                 /* Must specify that it's a TCP packet */
 238                 if (e->ipv6.proto != IPPROTO_TCP
 239                     || (e->ipv6.invflags & XT_INV_PROTO)) {
 240                         DEBUGP("ip6t_REJECT: TCP_RESET illegal for non-tcp\n");
 241                         return false;
 242                 }
 243         }
 244         return true;
 245 }
 246
 247 static struct xt_target ip6t_reject_reg = {
 248         .name           = "REJECT",
 249         .family         = AF_INET6,
 250         .target         = reject6_target,
 251         .targetsize     = sizeof(struct ip6t_reject_info),
 252         .table          = "filter",
 253         .hooks          = (1 << NF_IP6_LOCAL_IN) | (1 << NF_IP6_FORWARD) |
 254                           (1 << NF_IP6_LOCAL_OUT),
 255         .checkentry     = check,
 256         .me             = THIS_MODULE
 257 };
 258
 259 static int __init ip6t_reject_init(void)
 260 {
 261         return xt_register_target(&ip6t_reject_reg);
 262 }
 263
 264 static void __exit ip6t_reject_fini(void)
 265 {
 266         xt_unregister_target(&ip6t_reject_reg);
 267 }
 268
 269 module_init(ip6t_reject_init);
 270 module_exit(ip6t_reject_fini);