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/gfp.h>
  19 #include <linux/module.h>
  20 #include <linux/skbuff.h>
  21 #include <linux/icmpv6.h>
  22 #include <linux/netdevice.h>
  23 #include <net/ipv6.h>
  24 #include <net/tcp.h>
  25 #include <net/icmp.h>
  26 #include <net/ip6_checksum.h>
  27 #include <net/ip6_fib.h>
  28 #include <net/ip6_route.h>
  29 #include <net/flow.h>
  30 #include <linux/netfilter/x_tables.h>
  31 #include <linux/netfilter_ipv6/ip6_tables.h>
  32 #include <linux/netfilter_ipv6/ip6t_REJECT.h>
  33
  34 MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
  35 MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv6");
  36 MODULE_LICENSE("GPL");
  37
  38 /* Send RST reply */
  39 static void send_reset(struct net *net, struct sk_buff *oldskb)
  40 {
  41         struct sk_buff *nskb;
  42         struct tcphdr otcph, *tcph;
  43         unsigned int otcplen, hh_len;
  44         int tcphoff, needs_ack;
  45         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
  46         struct ipv6hdr *ip6h;
  47         struct dst_entry *dst = NULL;
  48         u8 proto;
  49         struct flowi fl;
  50
  51         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
  52             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
  53                 pr_debug("ip6t_REJECT: addr is not unicast.\n");
  54                 return;
  55         }
  56
  57         proto = oip6h->nexthdr;
  58         tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto);
  59
  60         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  61                 pr_debug("ip6t_REJECT: Can't get TCP header.\n");
  62                 return;
  63         }
  64
  65         otcplen = oldskb->len - tcphoff;
  66
  67         /* IP header checks: fragment, too short. */
  68         if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
  69                 pr_debug("ip6t_REJECT: proto(%d) != IPPROTO_TCP, "
  70                          "or too short. otcplen = %d\n",
  71                          proto, otcplen);
  72                 return;
  73         }
  74
  75         if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
  76                 BUG();
  77
  78         /* No RST for RST. */
  79         if (otcph.rst) {
  80                 pr_debug("ip6t_REJECT: RST is set\n");
  81                 return;
  82         }
  83
  84         /* Check checksum. */
  85         if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
  86                             skb_checksum(oldskb, tcphoff, otcplen, 0))) {
  87                 pr_debug("ip6t_REJECT: TCP checksum is invalid\n");
  88                 return;
  89         }
  90
  91         memset(&fl, 0, sizeof(fl));
  92         fl.proto = IPPROTO_TCP;
  93         ipv6_addr_copy(&fl.fl6_src, &oip6h->daddr);
  94         ipv6_addr_copy(&fl.fl6_dst, &oip6h->saddr);
  95         fl.fl_ip_sport = otcph.dest;
  96         fl.fl_ip_dport = otcph.source;
  97         security_skb_classify_flow(oldskb, &fl);
  98         dst = ip6_route_output(net, NULL, &fl);
  99         if (dst == NULL)
 100                 return;
 101         if (dst->error || xfrm_lookup(net, &dst, &fl, NULL, 0))
 102                 return;
 103
 104         hh_len = (dst->dev->hard_header_len + 15)&~15;
 105         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 106                          + sizeof(struct tcphdr) + dst->trailer_len,
 107                          GFP_ATOMIC);
 108
 109         if (!nskb) {
 110                 if (net_ratelimit())
 111                         printk("ip6t_REJECT: Can't alloc skb\n");
 112                 dst_release(dst);
 113                 return;
 114         }
 115
 116         skb_dst_set(nskb, dst);
 117
 118         skb_reserve(nskb, hh_len + dst->header_len);
 119
 120         skb_put(nskb, sizeof(struct ipv6hdr));
 121         skb_reset_network_header(nskb);
 122         ip6h = ipv6_hdr(nskb);
 123         ip6h->version = 6;
 124         ip6h->hop_limit = dst_metric(dst, RTAX_HOPLIMIT);
 125         ip6h->nexthdr = IPPROTO_TCP;
 126         ipv6_addr_copy(&ip6h->saddr, &oip6h->daddr);
 127         ipv6_addr_copy(&ip6h->daddr, &oip6h->saddr);
 128
 129         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 130         /* Truncate to length (no data) */
 131         tcph->doff = sizeof(struct tcphdr)/4;
 132         tcph->source = otcph.dest;
 133         tcph->dest = otcph.source;
 134
 135         if (otcph.ack) {
 136                 needs_ack = 0;
 137                 tcph->seq = otcph.ack_seq;
 138                 tcph->ack_seq = 0;
 139         } else {
 140                 needs_ack = 1;
 141                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 142                                       + otcplen - (otcph.doff<<2));
 143                 tcph->seq = 0;
 144         }
 145
 146         /* Reset flags */
 147         ((u_int8_t *)tcph)[13] = 0;
 148         tcph->rst = 1;
 149         tcph->ack = needs_ack;
 150         tcph->window = 0;
 151         tcph->urg_ptr = 0;
 152         tcph->check = 0;
 153
 154         /* Adjust TCP checksum */
 155         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 156                                       &ipv6_hdr(nskb)->daddr,
 157                                       sizeof(struct tcphdr), IPPROTO_TCP,
 158                                       csum_partial(tcph,
 159                                                    sizeof(struct tcphdr), 0));
 160
 161         nf_ct_attach(nskb, oldskb);
 162
 163         ip6_local_out(nskb);
 164 }
 165
 166 static inline void
 167 send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
 168              unsigned int hooknum)
 169 {
 170         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 171                 skb_in->dev = net->loopback_dev;
 172
 173         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
 174 }
 175
 176 static unsigned int
 177 reject_tg6(struct sk_buff *skb, const struct xt_target_param *par)
 178 {
 179         const struct ip6t_reject_info *reject = par->targinfo;
 180         struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
 181
 182         pr_debug("%s: medium point\n", __func__);
 183         /* WARNING: This code causes reentry within ip6tables.
 184            This means that the ip6tables jump stack is now crap.  We
 185            must return an absolute verdict. --RR */
 186         switch (reject->with) {
 187         case IP6T_ICMP6_NO_ROUTE:
 188                 send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
 189                 break;
 190         case IP6T_ICMP6_ADM_PROHIBITED:
 191                 send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
 192                 break;
 193         case IP6T_ICMP6_NOT_NEIGHBOUR:
 194                 send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
 195                 break;
 196         case IP6T_ICMP6_ADDR_UNREACH:
 197                 send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
 198                 break;
 199         case IP6T_ICMP6_PORT_UNREACH:
 200                 send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
 201                 break;
 202         case IP6T_ICMP6_ECHOREPLY:
 203                 /* Do nothing */
 204                 break;
 205         case IP6T_TCP_RESET:
 206                 send_reset(net, skb);
 207                 break;
 208         default:
 209                 if (net_ratelimit())
 210                         printk(KERN_WARNING "ip6t_REJECT: case %u not handled yet\n", reject->with);
 211                 break;
 212         }
 213
 214         return NF_DROP;
 215 }
 216
 217 static bool reject_tg6_check(const struct xt_tgchk_param *par)
 218 {
 219         const struct ip6t_reject_info *rejinfo = par->targinfo;
 220         const struct ip6t_entry *e = par->entryinfo;
 221
 222         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 223                 printk("ip6t_REJECT: ECHOREPLY is not supported.\n");
 224                 return false;
 225         } else if (rejinfo->with == IP6T_TCP_RESET) {
 226                 /* Must specify that it's a TCP packet */
 227                 if (e->ipv6.proto != IPPROTO_TCP ||
 228                     (e->ipv6.invflags & XT_INV_PROTO)) {
 229                         printk("ip6t_REJECT: TCP_RESET illegal for non-tcp\n");
 230                         return false;
 231                 }
 232         }
 233         return true;
 234 }
 235
 236 static struct xt_target reject_tg6_reg __read_mostly = {
 237         .name           = "REJECT",
 238         .family         = NFPROTO_IPV6,
 239         .target         = reject_tg6,
 240         .targetsize     = sizeof(struct ip6t_reject_info),
 241         .table          = "filter",
 242         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 243                           (1 << NF_INET_LOCAL_OUT),
 244         .checkentry     = reject_tg6_check,
 245         .me             = THIS_MODULE
 246 };
 247
 248 static int __init reject_tg6_init(void)
 249 {
 250         return xt_register_target(&reject_tg6_reg);
 251 }
 252
 253 static void __exit reject_tg6_exit(void)
 254 {
 255         xt_unregister_target(&reject_tg6_reg);
 256 }
 257
 258 module_init(reject_tg6_init);
 259 module_exit(reject_tg6_exit);