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)
  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 (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
  92                             skb_checksum(oldskb, tcphoff, otcplen, 0))) {
  93                 pr_debug("TCP checksum is invalid\n");
  94                 return;
  95         }
  96
  97         memset(&fl6, 0, sizeof(fl6));
  98         fl6.flowi6_proto = IPPROTO_TCP;
  99         fl6.saddr = oip6h->daddr;
 100         fl6.daddr = oip6h->saddr;
 101         fl6.fl6_sport = otcph.dest;
 102         fl6.fl6_dport = otcph.source;
 103         security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
 104         dst = ip6_route_output(net, NULL, &fl6);
 105         if (dst == NULL || dst->error) {
 106                 dst_release(dst);
 107                 return;
 108         }
 109         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
 110         if (IS_ERR(dst))
 111                 return;
 112
 113         hh_len = (dst->dev->hard_header_len + 15)&~15;
 114         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 115                          + sizeof(struct tcphdr) + dst->trailer_len,
 116                          GFP_ATOMIC);
 117
 118         if (!nskb) {
 119                 net_dbg_ratelimited("cannot alloc skb\n");
 120                 dst_release(dst);
 121                 return;
 122         }
 123
 124         skb_dst_set(nskb, dst);
 125
 126         skb_reserve(nskb, hh_len + dst->header_len);
 127
 128         skb_put(nskb, sizeof(struct ipv6hdr));
 129         skb_reset_network_header(nskb);
 130         ip6h = ipv6_hdr(nskb);
 131         ip6_flow_hdr(ip6h, tclass, 0);
 132         ip6h->hop_limit = ip6_dst_hoplimit(dst);
 133         ip6h->nexthdr = IPPROTO_TCP;
 134         ip6h->saddr = oip6h->daddr;
 135         ip6h->daddr = oip6h->saddr;
 136
 137         skb_reset_transport_header(nskb);
 138         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 139         /* Truncate to length (no data) */
 140         tcph->doff = sizeof(struct tcphdr)/4;
 141         tcph->source = otcph.dest;
 142         tcph->dest = otcph.source;
 143
 144         if (otcph.ack) {
 145                 needs_ack = 0;
 146                 tcph->seq = otcph.ack_seq;
 147                 tcph->ack_seq = 0;
 148         } else {
 149                 needs_ack = 1;
 150                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 151                                       + otcplen - (otcph.doff<<2));
 152                 tcph->seq = 0;
 153         }
 154
 155         /* Reset flags */
 156         ((u_int8_t *)tcph)[13] = 0;
 157         tcph->rst = 1;
 158         tcph->ack = needs_ack;
 159         tcph->window = 0;
 160         tcph->urg_ptr = 0;
 161         tcph->check = 0;
 162
 163         /* Adjust TCP checksum */
 164         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 165                                       &ipv6_hdr(nskb)->daddr,
 166                                       sizeof(struct tcphdr), IPPROTO_TCP,
 167                                       csum_partial(tcph,
 168                                                    sizeof(struct tcphdr), 0));
 169
 170         nf_ct_attach(nskb, oldskb);
 171
 172 #ifdef CONFIG_BRIDGE_NETFILTER
 173         /* If we use ip6_local_out for bridged traffic, the MAC source on
 174          * the RST will be ours, instead of the destination's.  This confuses
 175          * some routers/firewalls, and they drop the packet.  So we need to
 176          * build the eth header using the original destination's MAC as the
 177          * source, and send the RST packet directly.
 178          */
 179         if (oldskb->nf_bridge) {
 180                 struct ethhdr *oeth = eth_hdr(oldskb);
 181                 nskb->dev = oldskb->nf_bridge->physindev;
 182                 nskb->protocol = htons(ETH_P_IPV6);
 183                 ip6h->payload_len = htons(sizeof(struct tcphdr));
 184                 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
 185                                     oeth->h_source, oeth->h_dest, nskb->len) < 0)
 186                         return;
 187                 dev_queue_xmit(nskb);
 188         } else
 189 #endif
 190                 ip6_local_out(nskb);
 191 }
 192
 193 static inline void
 194 send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
 195              unsigned int hooknum)
 196 {
 197         if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 198                 skb_in->dev = net->loopback_dev;
 199
 200         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
 201 }
 202
 203 static unsigned int
 204 reject_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 205 {
 206         const struct ip6t_reject_info *reject = par->targinfo;
 207         struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
 208
 209         pr_debug("%s: medium point\n", __func__);
 210         switch (reject->with) {
 211         case IP6T_ICMP6_NO_ROUTE:
 212                 send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
 213                 break;
 214         case IP6T_ICMP6_ADM_PROHIBITED:
 215                 send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
 216                 break;
 217         case IP6T_ICMP6_NOT_NEIGHBOUR:
 218                 send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
 219                 break;
 220         case IP6T_ICMP6_ADDR_UNREACH:
 221                 send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
 222                 break;
 223         case IP6T_ICMP6_PORT_UNREACH:
 224                 send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
 225                 break;
 226         case IP6T_ICMP6_ECHOREPLY:
 227                 /* Do nothing */
 228                 break;
 229         case IP6T_TCP_RESET:
 230                 send_reset(net, skb);
 231                 break;
 232         default:
 233                 net_info_ratelimited("case %u not handled yet\n", reject->with);
 234                 break;
 235         }
 236
 237         return NF_DROP;
 238 }
 239
 240 static int reject_tg6_check(const struct xt_tgchk_param *par)
 241 {
 242         const struct ip6t_reject_info *rejinfo = par->targinfo;
 243         const struct ip6t_entry *e = par->entryinfo;
 244
 245         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 246                 pr_info("ECHOREPLY is not supported.\n");
 247                 return -EINVAL;
 248         } else if (rejinfo->with == IP6T_TCP_RESET) {
 249                 /* Must specify that it's a TCP packet */
 250                 if (e->ipv6.proto != IPPROTO_TCP ||
 251                     (e->ipv6.invflags & XT_INV_PROTO)) {
 252                         pr_info("TCP_RESET illegal for non-tcp\n");
 253                         return -EINVAL;
 254                 }
 255         }
 256         return 0;
 257 }
 258
 259 static struct xt_target reject_tg6_reg __read_mostly = {
 260         .name           = "REJECT",
 261         .family         = NFPROTO_IPV6,
 262         .target         = reject_tg6,
 263         .targetsize     = sizeof(struct ip6t_reject_info),
 264         .table          = "filter",
 265         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 266                           (1 << NF_INET_LOCAL_OUT),
 267         .checkentry     = reject_tg6_check,
 268         .me             = THIS_MODULE
 269 };
 270
 271 static int __init reject_tg6_init(void)
 272 {
 273         return xt_register_target(&reject_tg6_reg);
 274 }
 275
 276 static void __exit reject_tg6_exit(void)
 277 {
 278         xt_unregister_target(&reject_tg6_reg);
 279 }
 280
 281 module_init(reject_tg6_init);
 282 module_exit(reject_tg6_exit);