net/ipv6/netfilter/ip6t_REJECT.c

   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 /* Send RST reply */
  38 static void send_reset(struct sk_buff *oldskb)
  39 {
  40         struct sk_buff *nskb;
  41         struct tcphdr otcph, *tcph;
  42         unsigned int otcplen, hh_len;
  43         int tcphoff, needs_ack;
  44         struct ipv6hdr *oip6h = ipv6_hdr(oldskb), *ip6h;
  45         struct dst_entry *dst = NULL;
  46         u8 proto;
  47         struct flowi fl;
  48
  49         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
  50             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
  51                 pr_debug("ip6t_REJECT: addr is not unicast.\n");
  52                 return;
  53         }
  54
  55         proto = oip6h->nexthdr;
  56         tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto);
  57
  58         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  59                 pr_debug("ip6t_REJECT: Can't get TCP header.\n");
  60                 return;
  61         }
  62
  63         otcplen = oldskb->len - tcphoff;
  64
  65         /* IP header checks: fragment, too short. */
  66         if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
  67                 pr_debug("ip6t_REJECT: proto(%d) != IPPROTO_TCP, "
  68                          "or too short. otcplen = %d\n",
  69                          proto, otcplen);
  70                 return;
  71         }
  72
  73         if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
  74                 BUG();
  75
  76         /* No RST for RST. */
  77         if (otcph.rst) {
  78                 pr_debug("ip6t_REJECT: RST is set\n");
  79                 return;
  80         }
  81
  82         /* Check checksum. */
  83         if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
  84                             skb_checksum(oldskb, tcphoff, otcplen, 0))) {
  85                 pr_debug("ip6t_REJECT: TCP checksum is invalid\n");
  86                 return;
  87         }
  88
  89         memset(&fl, 0, sizeof(fl));
  90         fl.proto = IPPROTO_TCP;
  91         ipv6_addr_copy(&fl.fl6_src, &oip6h->daddr);
  92         ipv6_addr_copy(&fl.fl6_dst, &oip6h->saddr);
  93         fl.fl_ip_sport = otcph.dest;
  94         fl.fl_ip_dport = otcph.source;
  95         security_skb_classify_flow(oldskb, &fl);
  96         dst = ip6_route_output(NULL, &fl);
  97         if (dst == NULL)
  98                 return;
  99         if (dst->error || xfrm_lookup(&dst, &fl, NULL, 0))
 100                 return;
 101
 102         hh_len = (dst->dev->hard_header_len + 15)&~15;
 103         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 104                          + sizeof(struct tcphdr) + dst->trailer_len,
 105                          GFP_ATOMIC);
 106
 107         if (!nskb) {
 108                 if (net_ratelimit())
 109                         printk("ip6t_REJECT: Can't alloc skb\n");
 110                 dst_release(dst);
 111                 return;
 112         }
 113
 114         nskb->dst = dst;
 115
 116         skb_reserve(nskb, hh_len + dst->header_len);
 117
 118         skb_put(nskb, sizeof(struct ipv6hdr));
 119         skb_reset_network_header(nskb);
 120         ip6h = ipv6_hdr(nskb);
 121         ip6h->version = 6;
 122         ip6h->hop_limit = dst_metric(dst, RTAX_HOPLIMIT);
 123         ip6h->nexthdr = IPPROTO_TCP;
 124         ipv6_addr_copy(&ip6h->saddr, &oip6h->daddr);
 125         ipv6_addr_copy(&ip6h->daddr, &oip6h->saddr);
 126
 127         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 128         /* Truncate to length (no data) */
 129         tcph->doff = sizeof(struct tcphdr)/4;
 130         tcph->source = otcph.dest;
 131         tcph->dest = otcph.source;
 132
 133         if (otcph.ack) {
 134                 needs_ack = 0;
 135                 tcph->seq = otcph.ack_seq;
 136                 tcph->ack_seq = 0;
 137         } else {
 138                 needs_ack = 1;
 139                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 140                                       + otcplen - (otcph.doff<<2));
 141                 tcph->seq = 0;
 142         }
 143
 144         /* Reset flags */
 145         ((u_int8_t *)tcph)[13] = 0;
 146         tcph->rst = 1;
 147         tcph->ack = needs_ack;
 148         tcph->window = 0;
 149         tcph->urg_ptr = 0;
 150         tcph->check = 0;
 151
 152         /* Adjust TCP checksum */
 153         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 154                                       &ipv6_hdr(nskb)->daddr,
 155                                       sizeof(struct tcphdr), IPPROTO_TCP,
 156                                       csum_partial(tcph,
 157                                                    sizeof(struct tcphdr), 0));
 158
 159         nf_ct_attach(nskb, oldskb);
 160
 161         ip6_local_out(nskb);
 162 }
 163
 164 static inline void
 165 send_unreach(struct sk_buff *skb_in, unsigned char code, unsigned int hooknum)
 166 {
 167         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 168                 skb_in->dev = init_net.loopback_dev;
 169
 170         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0, NULL);
 171 }
 172
 173 static unsigned int
 174 reject_tg6(struct sk_buff *skb, const struct net_device *in,
 175            const struct net_device *out, unsigned int hooknum,
 176            const struct xt_target *target, const void *targinfo)
 177 {
 178         const struct ip6t_reject_info *reject = targinfo;
 179
 180         pr_debug("%s: medium point\n", __FUNCTION__);
 181         /* WARNING: This code causes reentry within ip6tables.
 182            This means that the ip6tables jump stack is now crap.  We
 183            must return an absolute verdict. --RR */
 184         switch (reject->with) {
 185         case IP6T_ICMP6_NO_ROUTE:
 186                 send_unreach(skb, ICMPV6_NOROUTE, hooknum);
 187                 break;
 188         case IP6T_ICMP6_ADM_PROHIBITED:
 189                 send_unreach(skb, ICMPV6_ADM_PROHIBITED, hooknum);
 190                 break;
 191         case IP6T_ICMP6_NOT_NEIGHBOUR:
 192                 send_unreach(skb, ICMPV6_NOT_NEIGHBOUR, hooknum);
 193                 break;
 194         case IP6T_ICMP6_ADDR_UNREACH:
 195                 send_unreach(skb, ICMPV6_ADDR_UNREACH, hooknum);
 196                 break;
 197         case IP6T_ICMP6_PORT_UNREACH:
 198                 send_unreach(skb, ICMPV6_PORT_UNREACH, hooknum);
 199                 break;
 200         case IP6T_ICMP6_ECHOREPLY:
 201                 /* Do nothing */
 202                 break;
 203         case IP6T_TCP_RESET:
 204                 send_reset(skb);
 205                 break;
 206         default:
 207                 if (net_ratelimit())
 208                         printk(KERN_WARNING "ip6t_REJECT: case %u not handled yet\n", reject->with);
 209                 break;
 210         }
 211
 212         return NF_DROP;
 213 }
 214
 215 static bool
 216 reject_tg6_check(const char *tablename, const void *entry,
 217                  const struct xt_target *target, void *targinfo,
 218                  unsigned int hook_mask)
 219 {
 220         const struct ip6t_reject_info *rejinfo = targinfo;
 221         const struct ip6t_entry *e = entry;
 222
 223         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 224                 printk("ip6t_REJECT: ECHOREPLY is not supported.\n");
 225                 return false;
 226         } else if (rejinfo->with == IP6T_TCP_RESET) {
 227                 /* Must specify that it's a TCP packet */
 228                 if (e->ipv6.proto != IPPROTO_TCP
 229                     || (e->ipv6.invflags & XT_INV_PROTO)) {
 230                         printk("ip6t_REJECT: TCP_RESET illegal for non-tcp\n");
 231                         return false;
 232                 }
 233         }
 234         return true;
 235 }
 236
 237 static struct xt_target reject_tg6_reg __read_mostly = {
 238         .name           = "REJECT",
 239         .family         = AF_INET6,
 240         .target         = reject_tg6,
 241         .targetsize     = sizeof(struct ip6t_reject_info),
 242         .table          = "filter",
 243         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 244                           (1 << NF_INET_LOCAL_OUT),
 245         .checkentry     = reject_tg6_check,
 246         .me             = THIS_MODULE
 247 };
 248
 249 static int __init reject_tg6_init(void)
 250 {
 251         return xt_register_target(&reject_tg6_reg);
 252 }
 253
 254 static void __exit reject_tg6_exit(void)
 255 {
 256         xt_unregister_target(&reject_tg6_reg);
 257 }
 258
 259 module_init(reject_tg6_init);
 260 module_exit(reject_tg6_exit);