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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  18
  19 #include <linux/gfp.h>
  20 #include <linux/module.h>
  21 #include <linux/skbuff.h>
  22 #include <linux/icmpv6.h>
  23 #include <linux/netdevice.h>
  24 #include <net/ipv6.h>
  25 #include <net/tcp.h>
  26 #include <net/icmp.h>
  27 #include <net/ip6_checksum.h>
  28 #include <net/ip6_fib.h>
  29 #include <net/ip6_route.h>
  30 #include <net/flow.h>
  31 #include <linux/netfilter/x_tables.h>
  32 #include <linux/netfilter_ipv6/ip6_tables.h>
  33 #include <linux/netfilter_ipv6/ip6t_REJECT.h>
  34
  35 MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
  36 MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv6");
  37 MODULE_LICENSE("GPL");
  38
  39 /* Send RST reply */
  40 static void send_reset(struct net *net, struct sk_buff *oldskb)
  41 {
  42         struct sk_buff *nskb;
  43         struct tcphdr otcph, *tcph;
  44         unsigned int otcplen, hh_len;
  45         int tcphoff, needs_ack;
  46         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
  47         struct ipv6hdr *ip6h;
  48         struct dst_entry *dst = NULL;
  49         u8 proto;
  50         struct flowi fl;
  51
  52         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
  53             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
  54                 pr_debug("addr is not unicast.\n");
  55                 return;
  56         }
  57
  58         proto = oip6h->nexthdr;
  59         tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto);
  60
  61         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  62                 pr_debug("Cannot get TCP header.\n");
  63                 return;
  64         }
  65
  66         otcplen = oldskb->len - tcphoff;
  67
  68         /* IP header checks: fragment, too short. */
  69         if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
  70                 pr_debug("proto(%d) != IPPROTO_TCP, "
  71                          "or too short. otcplen = %d\n",
  72                          proto, otcplen);
  73                 return;
  74         }
  75
  76         if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
  77                 BUG();
  78
  79         /* No RST for RST. */
  80         if (otcph.rst) {
  81                 pr_debug("RST is set\n");
  82                 return;
  83         }
  84
  85         /* Check checksum. */
  86         if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
  87                             skb_checksum(oldskb, tcphoff, otcplen, 0))) {
  88                 pr_debug("TCP checksum is invalid\n");
  89                 return;
  90         }
  91
  92         memset(&fl, 0, sizeof(fl));
  93         fl.proto = IPPROTO_TCP;
  94         ipv6_addr_copy(&fl.fl6_src, &oip6h->daddr);
  95         ipv6_addr_copy(&fl.fl6_dst, &oip6h->saddr);
  96         fl.fl_ip_sport = otcph.dest;
  97         fl.fl_ip_dport = otcph.source;
  98         security_skb_classify_flow(oldskb, &fl);
  99         dst = ip6_route_output(net, NULL, &fl);
 100         if (dst == NULL)
 101                 return;
 102         if (dst->error || xfrm_lookup(net, &dst, &fl, NULL, 0))
 103                 return;
 104
 105         hh_len = (dst->dev->hard_header_len + 15)&~15;
 106         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 107                          + sizeof(struct tcphdr) + dst->trailer_len,
 108                          GFP_ATOMIC);
 109
 110         if (!nskb) {
 111                 if (net_ratelimit())
 112                         pr_debug("cannot alloc skb\n");
 113                 dst_release(dst);
 114                 return;
 115         }
 116
 117         skb_dst_set(nskb, dst);
 118
 119         skb_reserve(nskb, hh_len + dst->header_len);
 120
 121         skb_put(nskb, sizeof(struct ipv6hdr));
 122         skb_reset_network_header(nskb);
 123         ip6h = ipv6_hdr(nskb);
 124         ip6h->version = 6;
 125         ip6h->hop_limit = dst_metric(dst, RTAX_HOPLIMIT);
 126         ip6h->nexthdr = IPPROTO_TCP;
 127         ipv6_addr_copy(&ip6h->saddr, &oip6h->daddr);
 128         ipv6_addr_copy(&ip6h->daddr, &oip6h->saddr);
 129
 130         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 131         /* Truncate to length (no data) */
 132         tcph->doff = sizeof(struct tcphdr)/4;
 133         tcph->source = otcph.dest;
 134         tcph->dest = otcph.source;
 135
 136         if (otcph.ack) {
 137                 needs_ack = 0;
 138                 tcph->seq = otcph.ack_seq;
 139                 tcph->ack_seq = 0;
 140         } else {
 141                 needs_ack = 1;
 142                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 143                                       + otcplen - (otcph.doff<<2));
 144                 tcph->seq = 0;
 145         }
 146
 147         /* Reset flags */
 148         ((u_int8_t *)tcph)[13] = 0;
 149         tcph->rst = 1;
 150         tcph->ack = needs_ack;
 151         tcph->window = 0;
 152         tcph->urg_ptr = 0;
 153         tcph->check = 0;
 154
 155         /* Adjust TCP checksum */
 156         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 157                                       &ipv6_hdr(nskb)->daddr,
 158                                       sizeof(struct tcphdr), IPPROTO_TCP,
 159                                       csum_partial(tcph,
 160                                                    sizeof(struct tcphdr), 0));
 161
 162         nf_ct_attach(nskb, oldskb);
 163
 164         ip6_local_out(nskb);
 165 }
 166
 167 static inline void
 168 send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
 169              unsigned int hooknum)
 170 {
 171         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 172                 skb_in->dev = net->loopback_dev;
 173
 174         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
 175 }
 176
 177 static unsigned int
 178 reject_tg6(struct sk_buff *skb, const struct xt_target_param *par)
 179 {
 180         const struct ip6t_reject_info *reject = par->targinfo;
 181         struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
 182
 183         pr_debug("%s: medium point\n", __func__);
 184         switch (reject->with) {
 185         case IP6T_ICMP6_NO_ROUTE:
 186                 send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
 187                 break;
 188         case IP6T_ICMP6_ADM_PROHIBITED:
 189                 send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
 190                 break;
 191         case IP6T_ICMP6_NOT_NEIGHBOUR:
 192                 send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
 193                 break;
 194         case IP6T_ICMP6_ADDR_UNREACH:
 195                 send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
 196                 break;
 197         case IP6T_ICMP6_PORT_UNREACH:
 198                 send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
 199                 break;
 200         case IP6T_ICMP6_ECHOREPLY:
 201                 /* Do nothing */
 202                 break;
 203         case IP6T_TCP_RESET:
 204                 send_reset(net, skb);
 205                 break;
 206         default:
 207                 if (net_ratelimit())
 208                         pr_info("case %u not handled yet\n", reject->with);
 209                 break;
 210         }
 211
 212         return NF_DROP;
 213 }
 214
 215 static int reject_tg6_check(const struct xt_tgchk_param *par)
 216 {
 217         const struct ip6t_reject_info *rejinfo = par->targinfo;
 218         const struct ip6t_entry *e = par->entryinfo;
 219
 220         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 221                 pr_info("ECHOREPLY is not supported.\n");
 222                 return -EINVAL;
 223         } else if (rejinfo->with == IP6T_TCP_RESET) {
 224                 /* Must specify that it's a TCP packet */
 225                 if (e->ipv6.proto != IPPROTO_TCP ||
 226                     (e->ipv6.invflags & XT_INV_PROTO)) {
 227                         pr_info("TCP_RESET illegal for non-tcp\n");
 228                         return -EINVAL;
 229                 }
 230         }
 231         return 0;
 232 }
 233
 234 static struct xt_target reject_tg6_reg __read_mostly = {
 235         .name           = "REJECT",
 236         .family         = NFPROTO_IPV6,
 237         .target         = reject_tg6,
 238         .targetsize     = sizeof(struct ip6t_reject_info),
 239         .table          = "filter",
 240         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 241                           (1 << NF_INET_LOCAL_OUT),
 242         .checkentry     = reject_tg6_check,
 243         .me             = THIS_MODULE
 244 };
 245
 246 static int __init reject_tg6_init(void)
 247 {
 248         return xt_register_target(&reject_tg6_reg);
 249 }
 250
 251 static void __exit reject_tg6_exit(void)
 252 {
 253         xt_unregister_target(&reject_tg6_reg);
 254 }
 255
 256 module_init(reject_tg6_init);
 257 module_exit(reject_tg6_exit);