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("Xtables: packet \"rejection\" target for IPv6");
  35 MODULE_LICENSE("GPL");
  36
  37 /* Send RST reply */
  38 static void send_reset(struct net *net, 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         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
  45         struct ipv6hdr *ip6h;
  46         struct dst_entry *dst = NULL;
  47         u8 proto;
  48         struct flowi fl;
  49
  50         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
  51             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
  52                 pr_debug("ip6t_REJECT: addr is not unicast.\n");
  53                 return;
  54         }
  55
  56         proto = oip6h->nexthdr;
  57         tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto);
  58
  59         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  60                 pr_debug("ip6t_REJECT: Can't get TCP header.\n");
  61                 return;
  62         }
  63
  64         otcplen = oldskb->len - tcphoff;
  65
  66         /* IP header checks: fragment, too short. */
  67         if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
  68                 pr_debug("ip6t_REJECT: proto(%d) != IPPROTO_TCP, "
  69                          "or too short. otcplen = %d\n",
  70                          proto, otcplen);
  71                 return;
  72         }
  73
  74         if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
  75                 BUG();
  76
  77         /* No RST for RST. */
  78         if (otcph.rst) {
  79                 pr_debug("ip6t_REJECT: RST is set\n");
  80                 return;
  81         }
  82
  83         /* Check checksum. */
  84         if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
  85                             skb_checksum(oldskb, tcphoff, otcplen, 0))) {
  86                 pr_debug("ip6t_REJECT: TCP checksum is invalid\n");
  87                 return;
  88         }
  89
  90         memset(&fl, 0, sizeof(fl));
  91         fl.proto = IPPROTO_TCP;
  92         ipv6_addr_copy(&fl.fl6_src, &oip6h->daddr);
  93         ipv6_addr_copy(&fl.fl6_dst, &oip6h->saddr);
  94         fl.fl_ip_sport = otcph.dest;
  95         fl.fl_ip_dport = otcph.source;
  96         security_skb_classify_flow(oldskb, &fl);
  97         dst = ip6_route_output(net, NULL, &fl);
  98         if (dst == NULL)
  99                 return;
 100         if (dst->error || xfrm_lookup(net, &dst, &fl, NULL, 0))
 101                 return;
 102
 103         hh_len = (dst->dev->hard_header_len + 15)&~15;
 104         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 105                          + sizeof(struct tcphdr) + dst->trailer_len,
 106                          GFP_ATOMIC);
 107
 108         if (!nskb) {
 109                 if (net_ratelimit())
 110                         printk("ip6t_REJECT: Can't alloc skb\n");
 111                 dst_release(dst);
 112                 return;
 113         }
 114
 115         skb_dst_set(nskb, dst);
 116
 117         skb_reserve(nskb, hh_len + dst->header_len);
 118
 119         skb_put(nskb, sizeof(struct ipv6hdr));
 120         skb_reset_network_header(nskb);
 121         ip6h = ipv6_hdr(nskb);
 122         ip6h->version = 6;
 123         ip6h->hop_limit = dst_metric(dst, RTAX_HOPLIMIT);
 124         ip6h->nexthdr = IPPROTO_TCP;
 125         ipv6_addr_copy(&ip6h->saddr, &oip6h->daddr);
 126         ipv6_addr_copy(&ip6h->daddr, &oip6h->saddr);
 127
 128         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 129         /* Truncate to length (no data) */
 130         tcph->doff = sizeof(struct tcphdr)/4;
 131         tcph->source = otcph.dest;
 132         tcph->dest = otcph.source;
 133
 134         if (otcph.ack) {
 135                 needs_ack = 0;
 136                 tcph->seq = otcph.ack_seq;
 137                 tcph->ack_seq = 0;
 138         } else {
 139                 needs_ack = 1;
 140                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 141                                       + otcplen - (otcph.doff<<2));
 142                 tcph->seq = 0;
 143         }
 144
 145         /* Reset flags */
 146         ((u_int8_t *)tcph)[13] = 0;
 147         tcph->rst = 1;
 148         tcph->ack = needs_ack;
 149         tcph->window = 0;
 150         tcph->urg_ptr = 0;
 151         tcph->check = 0;
 152
 153         /* Adjust TCP checksum */
 154         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 155                                       &ipv6_hdr(nskb)->daddr,
 156                                       sizeof(struct tcphdr), IPPROTO_TCP,
 157                                       csum_partial(tcph,
 158                                                    sizeof(struct tcphdr), 0));
 159
 160         nf_ct_attach(nskb, oldskb);
 161
 162         ip6_local_out(nskb);
 163 }
 164
 165 static inline void
 166 send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
 167              unsigned int hooknum)
 168 {
 169         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 170                 skb_in->dev = net->loopback_dev;
 171
 172         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0, NULL);
 173 }
 174
 175 static unsigned int
 176 reject_tg6(struct sk_buff *skb, const struct xt_target_param *par)
 177 {
 178         const struct ip6t_reject_info *reject = par->targinfo;
 179         struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
 180
 181         pr_debug("%s: medium point\n", __func__);
 182         /* WARNING: This code causes reentry within ip6tables.
 183            This means that the ip6tables jump stack is now crap.  We
 184            must return an absolute verdict. --RR */
 185         switch (reject->with) {
 186         case IP6T_ICMP6_NO_ROUTE:
 187                 send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
 188                 break;
 189         case IP6T_ICMP6_ADM_PROHIBITED:
 190                 send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
 191                 break;
 192         case IP6T_ICMP6_NOT_NEIGHBOUR:
 193                 send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
 194                 break;
 195         case IP6T_ICMP6_ADDR_UNREACH:
 196                 send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
 197                 break;
 198         case IP6T_ICMP6_PORT_UNREACH:
 199                 send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
 200                 break;
 201         case IP6T_ICMP6_ECHOREPLY:
 202                 /* Do nothing */
 203                 break;
 204         case IP6T_TCP_RESET:
 205                 send_reset(net, skb);
 206                 break;
 207         default:
 208                 if (net_ratelimit())
 209                         printk(KERN_WARNING "ip6t_REJECT: case %u not handled yet\n", reject->with);
 210                 break;
 211         }
 212
 213         return NF_DROP;
 214 }
 215
 216 static bool reject_tg6_check(const struct xt_tgchk_param *par)
 217 {
 218         const struct ip6t_reject_info *rejinfo = par->targinfo;
 219         const struct ip6t_entry *e = par->entryinfo;
 220
 221         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 222                 printk("ip6t_REJECT: ECHOREPLY is not supported.\n");
 223                 return false;
 224         } else if (rejinfo->with == IP6T_TCP_RESET) {
 225                 /* Must specify that it's a TCP packet */
 226                 if (e->ipv6.proto != IPPROTO_TCP
 227                     || (e->ipv6.invflags & XT_INV_PROTO)) {
 228                         printk("ip6t_REJECT: TCP_RESET illegal for non-tcp\n");
 229                         return false;
 230                 }
 231         }
 232         return true;
 233 }
 234
 235 static struct xt_target reject_tg6_reg __read_mostly = {
 236         .name           = "REJECT",
 237         .family         = NFPROTO_IPV6,
 238         .target         = reject_tg6,
 239         .targetsize     = sizeof(struct ip6t_reject_info),
 240         .table          = "filter",
 241         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 242                           (1 << NF_INET_LOCAL_OUT),
 243         .checkentry     = reject_tg6_check,
 244         .me             = THIS_MODULE
 245 };
 246
 247 static int __init reject_tg6_init(void)
 248 {
 249         return xt_register_target(&reject_tg6_reg);
 250 }
 251
 252 static void __exit reject_tg6_exit(void)
 253 {
 254         xt_unregister_target(&reject_tg6_reg);
 255 }
 256
 257 module_init(reject_tg6_init);
 258 module_exit(reject_tg6_exit);