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         skb_reset_transport_header(nskb);
 136         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 137         /* Truncate to length (no data) */
 138         tcph->doff = sizeof(struct tcphdr)/4;
 139         tcph->source = otcph.dest;
 140         tcph->dest = otcph.source;
 141
 142         if (otcph.ack) {
 143                 needs_ack = 0;
 144                 tcph->seq = otcph.ack_seq;
 145                 tcph->ack_seq = 0;
 146         } else {
 147                 needs_ack = 1;
 148                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 149                                       + otcplen - (otcph.doff<<2));
 150                 tcph->seq = 0;
 151         }
 152
 153         /* Reset flags */
 154         ((u_int8_t *)tcph)[13] = 0;
 155         tcph->rst = 1;
 156         tcph->ack = needs_ack;
 157         tcph->window = 0;
 158         tcph->urg_ptr = 0;
 159         tcph->check = 0;
 160
 161         /* Adjust TCP checksum */
 162         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 163                                       &ipv6_hdr(nskb)->daddr,
 164                                       sizeof(struct tcphdr), IPPROTO_TCP,
 165                                       csum_partial(tcph,
 166                                                    sizeof(struct tcphdr), 0));
 167
 168         nf_ct_attach(nskb, oldskb);
 169
 170         ip6_local_out(nskb);
 171 }
 172
 173 static inline void
 174 send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
 175              unsigned int hooknum)
 176 {
 177         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 178                 skb_in->dev = net->loopback_dev;
 179
 180         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
 181 }
 182
 183 static unsigned int
 184 reject_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 185 {
 186         const struct ip6t_reject_info *reject = par->targinfo;
 187         struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
 188
 189         pr_debug("%s: medium point\n", __func__);
 190         switch (reject->with) {
 191         case IP6T_ICMP6_NO_ROUTE:
 192                 send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
 193                 break;
 194         case IP6T_ICMP6_ADM_PROHIBITED:
 195                 send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
 196                 break;
 197         case IP6T_ICMP6_NOT_NEIGHBOUR:
 198                 send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
 199                 break;
 200         case IP6T_ICMP6_ADDR_UNREACH:
 201                 send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
 202                 break;
 203         case IP6T_ICMP6_PORT_UNREACH:
 204                 send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
 205                 break;
 206         case IP6T_ICMP6_ECHOREPLY:
 207                 /* Do nothing */
 208                 break;
 209         case IP6T_TCP_RESET:
 210                 send_reset(net, skb);
 211                 break;
 212         default:
 213                 net_info_ratelimited("case %u not handled yet\n", reject->with);
 214                 break;
 215         }
 216
 217         return NF_DROP;
 218 }
 219
 220 static int reject_tg6_check(const struct xt_tgchk_param *par)
 221 {
 222         const struct ip6t_reject_info *rejinfo = par->targinfo;
 223         const struct ip6t_entry *e = par->entryinfo;
 224
 225         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 226                 pr_info("ECHOREPLY is not supported.\n");
 227                 return -EINVAL;
 228         } else if (rejinfo->with == IP6T_TCP_RESET) {
 229                 /* Must specify that it's a TCP packet */
 230                 if (e->ipv6.proto != IPPROTO_TCP ||
 231                     (e->ipv6.invflags & XT_INV_PROTO)) {
 232                         pr_info("TCP_RESET illegal for non-tcp\n");
 233                         return -EINVAL;
 234                 }
 235         }
 236         return 0;
 237 }
 238
 239 static struct xt_target reject_tg6_reg __read_mostly = {
 240         .name           = "REJECT",
 241         .family         = NFPROTO_IPV6,
 242         .target         = reject_tg6,
 243         .targetsize     = sizeof(struct ip6t_reject_info),
 244         .table          = "filter",
 245         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 246                           (1 << NF_INET_LOCAL_OUT),
 247         .checkentry     = reject_tg6_check,
 248         .me             = THIS_MODULE
 249 };
 250
 251 static int __init reject_tg6_init(void)
 252 {
 253         return xt_register_target(&reject_tg6_reg);
 254 }
 255
 256 static void __exit reject_tg6_exit(void)
 257 {
 258         xt_unregister_target(&reject_tg6_reg);
 259 }
 260
 261 module_init(reject_tg6_init);
 262 module_exit(reject_tg6_exit);