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 #define DEFAULT_TOS_VALUE       0x0U
  49         const __u8 tclass = DEFAULT_TOS_VALUE;
  50         struct dst_entry *dst = NULL;
  51         u8 proto;
  52         __be16 frag_off;
  53         struct flowi6 fl6;
  54
  55         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
  56             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
  57                 pr_debug("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, &frag_off);
  63
  64         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  65                 pr_debug("Cannot 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                 pr_debug("proto(%d) != IPPROTO_TCP, "
  74                          "or too short. otcplen = %d\n",
  75                          proto, otcplen);
  76                 return;
  77         }
  78
  79         if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
  80                 BUG();
  81
  82         /* No RST for RST. */
  83         if (otcph.rst) {
  84                 pr_debug("RST is set\n");
  85                 return;
  86         }
  87
  88         /* Check checksum. */
  89         if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
  90                             skb_checksum(oldskb, tcphoff, otcplen, 0))) {
  91                 pr_debug("TCP checksum is invalid\n");
  92                 return;
  93         }
  94
  95         memset(&fl6, 0, sizeof(fl6));
  96         fl6.flowi6_proto = IPPROTO_TCP;
  97         fl6.saddr = oip6h->daddr;
  98         fl6.daddr = oip6h->saddr;
  99         fl6.fl6_sport = otcph.dest;
 100         fl6.fl6_dport = otcph.source;
 101         security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
 102         dst = ip6_route_output(net, NULL, &fl6);
 103         if (dst == NULL || dst->error) {
 104                 dst_release(dst);
 105                 return;
 106         }
 107         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
 108         if (IS_ERR(dst))
 109                 return;
 110
 111         hh_len = (dst->dev->hard_header_len + 15)&~15;
 112         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 113                          + sizeof(struct tcphdr) + dst->trailer_len,
 114                          GFP_ATOMIC);
 115
 116         if (!nskb) {
 117                 net_dbg_ratelimited("cannot alloc skb\n");
 118                 dst_release(dst);
 119                 return;
 120         }
 121
 122         skb_dst_set(nskb, dst);
 123
 124         skb_reserve(nskb, hh_len + dst->header_len);
 125
 126         skb_put(nskb, sizeof(struct ipv6hdr));
 127         skb_reset_network_header(nskb);
 128         ip6h = ipv6_hdr(nskb);
 129         *(__be32 *)ip6h =  htonl(0x60000000 | (tclass << 20));
 130         ip6h->hop_limit = ip6_dst_hoplimit(dst);
 131         ip6h->nexthdr = IPPROTO_TCP;
 132         ip6h->saddr = oip6h->daddr;
 133         ip6h->daddr = oip6h->saddr;
 134
 135         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 136         /* Truncate to length (no data) */
 137         tcph->doff = sizeof(struct tcphdr)/4;
 138         tcph->source = otcph.dest;
 139         tcph->dest = otcph.source;
 140
 141         if (otcph.ack) {
 142                 needs_ack = 0;
 143                 tcph->seq = otcph.ack_seq;
 144                 tcph->ack_seq = 0;
 145         } else {
 146                 needs_ack = 1;
 147                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 148                                       + otcplen - (otcph.doff<<2));
 149                 tcph->seq = 0;
 150         }
 151
 152         /* Reset flags */
 153         ((u_int8_t *)tcph)[13] = 0;
 154         tcph->rst = 1;
 155         tcph->ack = needs_ack;
 156         tcph->window = 0;
 157         tcph->urg_ptr = 0;
 158         tcph->check = 0;
 159
 160         /* Adjust TCP checksum */
 161         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 162                                       &ipv6_hdr(nskb)->daddr,
 163                                       sizeof(struct tcphdr), IPPROTO_TCP,
 164                                       csum_partial(tcph,
 165                                                    sizeof(struct tcphdr), 0));
 166
 167         nf_ct_attach(nskb, oldskb);
 168
 169         ip6_local_out(nskb);
 170 }
 171
 172 static inline void
 173 send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
 174              unsigned int hooknum)
 175 {
 176         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 177                 skb_in->dev = net->loopback_dev;
 178
 179         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
 180 }
 181
 182 static unsigned int
 183 reject_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 184 {
 185         const struct ip6t_reject_info *reject = par->targinfo;
 186         struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
 187
 188         pr_debug("%s: medium point\n", __func__);
 189         switch (reject->with) {
 190         case IP6T_ICMP6_NO_ROUTE:
 191                 send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
 192                 break;
 193         case IP6T_ICMP6_ADM_PROHIBITED:
 194                 send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
 195                 break;
 196         case IP6T_ICMP6_NOT_NEIGHBOUR:
 197                 send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
 198                 break;
 199         case IP6T_ICMP6_ADDR_UNREACH:
 200                 send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
 201                 break;
 202         case IP6T_ICMP6_PORT_UNREACH:
 203                 send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
 204                 break;
 205         case IP6T_ICMP6_ECHOREPLY:
 206                 /* Do nothing */
 207                 break;
 208         case IP6T_TCP_RESET:
 209                 send_reset(net, skb);
 210                 break;
 211         default:
 212                 net_info_ratelimited("case %u not handled yet\n", reject->with);
 213                 break;
 214         }
 215
 216         return NF_DROP;
 217 }
 218
 219 static int reject_tg6_check(const struct xt_tgchk_param *par)
 220 {
 221         const struct ip6t_reject_info *rejinfo = par->targinfo;
 222         const struct ip6t_entry *e = par->entryinfo;
 223
 224         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 225                 pr_info("ECHOREPLY is not supported.\n");
 226                 return -EINVAL;
 227         } else if (rejinfo->with == IP6T_TCP_RESET) {
 228                 /* Must specify that it's a TCP packet */
 229                 if (e->ipv6.proto != IPPROTO_TCP ||
 230                     (e->ipv6.invflags & XT_INV_PROTO)) {
 231                         pr_info("TCP_RESET illegal for non-tcp\n");
 232                         return -EINVAL;
 233                 }
 234         }
 235         return 0;
 236 }
 237
 238 static struct xt_target reject_tg6_reg __read_mostly = {
 239         .name           = "REJECT",
 240         .family         = NFPROTO_IPV6,
 241         .target         = reject_tg6,
 242         .targetsize     = sizeof(struct ip6t_reject_info),
 243         .table          = "filter",
 244         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 245                           (1 << NF_INET_LOCAL_OUT),
 246         .checkentry     = reject_tg6_check,
 247         .me             = THIS_MODULE
 248 };
 249
 250 static int __init reject_tg6_init(void)
 251 {
 252         return xt_register_target(&reject_tg6_reg);
 253 }
 254
 255 static void __exit reject_tg6_exit(void)
 256 {
 257         xt_unregister_target(&reject_tg6_reg);
 258 }
 259
 260 module_init(reject_tg6_init);
 261 module_exit(reject_tg6_exit);