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  * Copyright (c) 2005-2007 Patrick McHardy <kaber@trash.net>
  11  *
  12  * Based on net/ipv4/netfilter/ipt_REJECT.c
  13  *
  14  * This program is free software; you can redistribute it and/or
  15  * modify it under the terms of the GNU General Public License
  16  * as published by the Free Software Foundation; either version
  17  * 2 of the License, or (at your option) any later version.
  18  */
  19 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  20
  21 #include <linux/gfp.h>
  22 #include <linux/module.h>
  23 #include <linux/skbuff.h>
  24 #include <linux/icmpv6.h>
  25 #include <linux/netdevice.h>
  26 #include <net/ipv6.h>
  27 #include <net/tcp.h>
  28 #include <net/icmp.h>
  29 #include <net/ip6_checksum.h>
  30 #include <net/ip6_fib.h>
  31 #include <net/ip6_route.h>
  32 #include <net/flow.h>
  33 #include <linux/netfilter/x_tables.h>
  34 #include <linux/netfilter_ipv6/ip6_tables.h>
  35 #include <linux/netfilter_ipv6/ip6t_REJECT.h>
  36
  37 MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
  38 MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv6");
  39 MODULE_LICENSE("GPL");
  40
  41 /* Send RST reply */
  42 static void send_reset(struct net *net, struct sk_buff *oldskb, int hook)
  43 {
  44         struct sk_buff *nskb;
  45         struct tcphdr otcph, *tcph;
  46         unsigned int otcplen, hh_len;
  47         int tcphoff, needs_ack;
  48         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
  49         struct ipv6hdr *ip6h;
  50 #define DEFAULT_TOS_VALUE       0x0U
  51         const __u8 tclass = DEFAULT_TOS_VALUE;
  52         struct dst_entry *dst = NULL;
  53         u8 proto;
  54         __be16 frag_off;
  55         struct flowi6 fl6;
  56
  57         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
  58             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
  59                 pr_debug("addr is not unicast.\n");
  60                 return;
  61         }
  62
  63         proto = oip6h->nexthdr;
  64         tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto, &frag_off);
  65
  66         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  67                 pr_debug("Cannot get TCP header.\n");
  68                 return;
  69         }
  70
  71         otcplen = oldskb->len - tcphoff;
  72
  73         /* IP header checks: fragment, too short. */
  74         if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
  75                 pr_debug("proto(%d) != IPPROTO_TCP, "
  76                          "or too short. otcplen = %d\n",
  77                          proto, otcplen);
  78                 return;
  79         }
  80
  81         if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
  82                 BUG();
  83
  84         /* No RST for RST. */
  85         if (otcph.rst) {
  86                 pr_debug("RST is set\n");
  87                 return;
  88         }
  89
  90         /* Check checksum. */
  91         if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) {
  92                 pr_debug("TCP checksum is invalid\n");
  93                 return;
  94         }
  95
  96         memset(&fl6, 0, sizeof(fl6));
  97         fl6.flowi6_proto = IPPROTO_TCP;
  98         fl6.saddr = oip6h->daddr;
  99         fl6.daddr = oip6h->saddr;
 100         fl6.fl6_sport = otcph.dest;
 101         fl6.fl6_dport = otcph.source;
 102         security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
 103         dst = ip6_route_output(net, NULL, &fl6);
 104         if (dst == NULL || dst->error) {
 105                 dst_release(dst);
 106                 return;
 107         }
 108         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
 109         if (IS_ERR(dst))
 110                 return;
 111
 112         hh_len = (dst->dev->hard_header_len + 15)&~15;
 113         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 114                          + sizeof(struct tcphdr) + dst->trailer_len,
 115                          GFP_ATOMIC);
 116
 117         if (!nskb) {
 118                 net_dbg_ratelimited("cannot alloc skb\n");
 119                 dst_release(dst);
 120                 return;
 121         }
 122
 123         skb_dst_set(nskb, dst);
 124
 125         skb_reserve(nskb, hh_len + dst->header_len);
 126
 127         skb_put(nskb, sizeof(struct ipv6hdr));
 128         skb_reset_network_header(nskb);
 129         ip6h = ipv6_hdr(nskb);
 130         ip6_flow_hdr(ip6h, tclass, 0);
 131         ip6h->hop_limit = ip6_dst_hoplimit(dst);
 132         ip6h->nexthdr = IPPROTO_TCP;
 133         ip6h->saddr = oip6h->daddr;
 134         ip6h->daddr = oip6h->saddr;
 135
 136         skb_reset_transport_header(nskb);
 137         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 138         /* Truncate to length (no data) */
 139         tcph->doff = sizeof(struct tcphdr)/4;
 140         tcph->source = otcph.dest;
 141         tcph->dest = otcph.source;
 142
 143         if (otcph.ack) {
 144                 needs_ack = 0;
 145                 tcph->seq = otcph.ack_seq;
 146                 tcph->ack_seq = 0;
 147         } else {
 148                 needs_ack = 1;
 149                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 150                                       + otcplen - (otcph.doff<<2));
 151                 tcph->seq = 0;
 152         }
 153
 154         /* Reset flags */
 155         ((u_int8_t *)tcph)[13] = 0;
 156         tcph->rst = 1;
 157         tcph->ack = needs_ack;
 158         tcph->window = 0;
 159         tcph->urg_ptr = 0;
 160         tcph->check = 0;
 161
 162         /* Adjust TCP checksum */
 163         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 164                                       &ipv6_hdr(nskb)->daddr,
 165                                       sizeof(struct tcphdr), IPPROTO_TCP,
 166                                       csum_partial(tcph,
 167                                                    sizeof(struct tcphdr), 0));
 168
 169         nf_ct_attach(nskb, oldskb);
 170
 171 #ifdef CONFIG_BRIDGE_NETFILTER
 172         /* If we use ip6_local_out for bridged traffic, the MAC source on
 173          * the RST will be ours, instead of the destination's.  This confuses
 174          * some routers/firewalls, and they drop the packet.  So we need to
 175          * build the eth header using the original destination's MAC as the
 176          * source, and send the RST packet directly.
 177          */
 178         if (oldskb->nf_bridge) {
 179                 struct ethhdr *oeth = eth_hdr(oldskb);
 180                 nskb->dev = oldskb->nf_bridge->physindev;
 181                 nskb->protocol = htons(ETH_P_IPV6);
 182                 ip6h->payload_len = htons(sizeof(struct tcphdr));
 183                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 184                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
 185                         return;
 186                 dev_queue_xmit(nskb);
 187         } else
 188 #endif
 189                 ip6_local_out(nskb);
 190 }
 191
 192 static inline void
 193 send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
 194              unsigned int hooknum)
 195 {
 196         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 197                 skb_in->dev = net->loopback_dev;
 198
 199         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
 200 }
 201
 202 static unsigned int
 203 reject_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 204 {
 205         const struct ip6t_reject_info *reject = par->targinfo;
 206         struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
 207
 208         pr_debug("%s: medium point\n", __func__);
 209         switch (reject->with) {
 210         case IP6T_ICMP6_NO_ROUTE:
 211                 send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
 212                 break;
 213         case IP6T_ICMP6_ADM_PROHIBITED:
 214                 send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
 215                 break;
 216         case IP6T_ICMP6_NOT_NEIGHBOUR:
 217                 send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
 218                 break;
 219         case IP6T_ICMP6_ADDR_UNREACH:
 220                 send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
 221                 break;
 222         case IP6T_ICMP6_PORT_UNREACH:
 223                 send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
 224                 break;
 225         case IP6T_ICMP6_ECHOREPLY:
 226                 /* Do nothing */
 227                 break;
 228         case IP6T_TCP_RESET:
 229                 send_reset(net, skb, par->hooknum);
 230                 break;
 231         default:
 232                 net_info_ratelimited("case %u not handled yet\n", reject->with);
 233                 break;
 234         }
 235
 236         return NF_DROP;
 237 }
 238
 239 static int reject_tg6_check(const struct xt_tgchk_param *par)
 240 {
 241         const struct ip6t_reject_info *rejinfo = par->targinfo;
 242         const struct ip6t_entry *e = par->entryinfo;
 243
 244         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 245                 pr_info("ECHOREPLY is not supported.\n");
 246                 return -EINVAL;
 247         } else if (rejinfo->with == IP6T_TCP_RESET) {
 248                 /* Must specify that it's a TCP packet */
 249                 if (e->ipv6.proto != IPPROTO_TCP ||
 250                     (e->ipv6.invflags & XT_INV_PROTO)) {
 251                         pr_info("TCP_RESET illegal for non-tcp\n");
 252                         return -EINVAL;
 253                 }
 254         }
 255         return 0;
 256 }
 257
 258 static struct xt_target reject_tg6_reg __read_mostly = {
 259         .name           = "REJECT",
 260         .family         = NFPROTO_IPV6,
 261         .target         = reject_tg6,
 262         .targetsize     = sizeof(struct ip6t_reject_info),
 263         .table          = "filter",
 264         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 265                           (1 << NF_INET_LOCAL_OUT),
 266         .checkentry     = reject_tg6_check,
 267         .me             = THIS_MODULE
 268 };
 269
 270 static int __init reject_tg6_init(void)
 271 {
 272         return xt_register_target(&reject_tg6_reg);
 273 }
 274
 275 static void __exit reject_tg6_exit(void)
 276 {
 277         xt_unregister_target(&reject_tg6_reg);
 278 }
 279
 280 module_init(reject_tg6_init);
 281 module_exit(reject_tg6_exit);