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
  18 #include <linux/module.h>
  19 #include <linux/skbuff.h>
  20 #include <linux/icmpv6.h>
  21 #include <linux/netdevice.h>
  22 #include <net/ipv6.h>
  23 #include <net/tcp.h>
  24 #include <net/icmp.h>
  25 #include <net/ip6_checksum.h>
  26 #include <net/ip6_fib.h>
  27 #include <net/ip6_route.h>
  28 #include <net/flow.h>
  29 #include <linux/netfilter/x_tables.h>
  30 #include <linux/netfilter_ipv6/ip6_tables.h>
  31 #include <linux/netfilter_ipv6/ip6t_REJECT.h>
  32
  33 MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
  34 MODULE_DESCRIPTION("IP6 tables REJECT target module");
  35 MODULE_LICENSE("GPL");
  36
  37 /* Send RST reply */
  38 static void send_reset(struct sk_buff *oldskb)
  39 {
  40         struct sk_buff *nskb;
  41         struct tcphdr otcph, *tcph;
  42         unsigned int otcplen, hh_len;
  43         int tcphoff, needs_ack;
  44         struct ipv6hdr *oip6h = ipv6_hdr(oldskb), *ip6h;
  45         struct dst_entry *dst = NULL;
  46         u8 proto;
  47         struct flowi fl;
  48
  49         if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
  50             (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
  51                 pr_debug("ip6t_REJECT: addr is not unicast.\n");
  52                 return;
  53         }
  54
  55         proto = oip6h->nexthdr;
  56         tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto);
  57
  58         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
  59                 pr_debug("ip6t_REJECT: Can't get TCP header.\n");
  60                 return;
  61         }
  62
  63         otcplen = oldskb->len - tcphoff;
  64
  65         /* IP header checks: fragment, too short. */
  66         if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
  67                 pr_debug("ip6t_REJECT: proto(%d) != IPPROTO_TCP, "
  68                          "or too short. otcplen = %d\n",
  69                          proto, otcplen);
  70                 return;
  71         }
  72
  73         if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
  74                 BUG();
  75
  76         /* No RST for RST. */
  77         if (otcph.rst) {
  78                 pr_debug("ip6t_REJECT: RST is set\n");
  79                 return;
  80         }
  81
  82         /* Check checksum. */
  83         if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
  84                             skb_checksum(oldskb, tcphoff, otcplen, 0))) {
  85                 pr_debug("ip6t_REJECT: TCP checksum is invalid\n");
  86                 return;
  87         }
  88
  89         memset(&fl, 0, sizeof(fl));
  90         fl.proto = IPPROTO_TCP;
  91         ipv6_addr_copy(&fl.fl6_src, &oip6h->daddr);
  92         ipv6_addr_copy(&fl.fl6_dst, &oip6h->saddr);
  93         fl.fl_ip_sport = otcph.dest;
  94         fl.fl_ip_dport = otcph.source;
  95         security_skb_classify_flow(oldskb, &fl);
  96         dst = ip6_route_output(NULL, &fl);
  97         if (dst == NULL)
  98                 return;
  99         if (dst->error || xfrm_lookup(&dst, &fl, NULL, 0))
 100                 return;
 101
 102         hh_len = (dst->dev->hard_header_len + 15)&~15;
 103         nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
 104                          + sizeof(struct tcphdr) + dst->trailer_len,
 105                          GFP_ATOMIC);
 106
 107         if (!nskb) {
 108                 if (net_ratelimit())
 109                         printk("ip6t_REJECT: Can't alloc skb\n");
 110                 dst_release(dst);
 111                 return;
 112         }
 113
 114         nskb->dst = dst;
 115
 116         skb_reserve(nskb, hh_len + dst->header_len);
 117
 118         skb_put(nskb, sizeof(struct ipv6hdr));
 119         skb_reset_network_header(nskb);
 120         ip6h = ipv6_hdr(nskb);
 121         ip6h->version = 6;
 122         ip6h->hop_limit = dst_metric(dst, RTAX_HOPLIMIT);
 123         ip6h->nexthdr = IPPROTO_TCP;
 124         ip6h->payload_len = htons(sizeof(struct tcphdr));
 125         ipv6_addr_copy(&ip6h->saddr, &oip6h->daddr);
 126         ipv6_addr_copy(&ip6h->daddr, &oip6h->saddr);
 127
 128         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
 129         /* Truncate to length (no data) */
 130         tcph->doff = sizeof(struct tcphdr)/4;
 131         tcph->source = otcph.dest;
 132         tcph->dest = otcph.source;
 133
 134         if (otcph.ack) {
 135                 needs_ack = 0;
 136                 tcph->seq = otcph.ack_seq;
 137                 tcph->ack_seq = 0;
 138         } else {
 139                 needs_ack = 1;
 140                 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
 141                                       + otcplen - (otcph.doff<<2));
 142                 tcph->seq = 0;
 143         }
 144
 145         /* Reset flags */
 146         ((u_int8_t *)tcph)[13] = 0;
 147         tcph->rst = 1;
 148         tcph->ack = needs_ack;
 149         tcph->window = 0;
 150         tcph->urg_ptr = 0;
 151         tcph->check = 0;
 152
 153         /* Adjust TCP checksum */
 154         tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 155                                       &ipv6_hdr(nskb)->daddr,
 156                                       sizeof(struct tcphdr), IPPROTO_TCP,
 157                                       csum_partial(tcph,
 158                                                    sizeof(struct tcphdr), 0));
 159
 160         nf_ct_attach(nskb, oldskb);
 161
 162         NF_HOOK(PF_INET6, NF_IP6_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 163                 dst_output);
 164 }
 165
 166 static inline void
 167 send_unreach(struct sk_buff *skb_in, unsigned char code, unsigned int hooknum)
 168 {
 169         if (hooknum == NF_IP6_LOCAL_OUT && skb_in->dev == NULL)
 170                 skb_in->dev = loopback_dev;
 171
 172         icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0, NULL);
 173 }
 174
 175 static unsigned int reject6_target(struct sk_buff **pskb,
 176                            const struct net_device *in,
 177                            const struct net_device *out,
 178                            unsigned int hooknum,
 179                            const struct xt_target *target,
 180                            const void *targinfo)
 181 {
 182         const struct ip6t_reject_info *reject = targinfo;
 183
 184         pr_debug("%s: medium point\n", __FUNCTION__);
 185         /* WARNING: This code causes reentry within ip6tables.
 186            This means that the ip6tables jump stack is now crap.  We
 187            must return an absolute verdict. --RR */
 188         switch (reject->with) {
 189         case IP6T_ICMP6_NO_ROUTE:
 190                 send_unreach(*pskb, ICMPV6_NOROUTE, hooknum);
 191                 break;
 192         case IP6T_ICMP6_ADM_PROHIBITED:
 193                 send_unreach(*pskb, ICMPV6_ADM_PROHIBITED, hooknum);
 194                 break;
 195         case IP6T_ICMP6_NOT_NEIGHBOUR:
 196                 send_unreach(*pskb, ICMPV6_NOT_NEIGHBOUR, hooknum);
 197                 break;
 198         case IP6T_ICMP6_ADDR_UNREACH:
 199                 send_unreach(*pskb, ICMPV6_ADDR_UNREACH, hooknum);
 200                 break;
 201         case IP6T_ICMP6_PORT_UNREACH:
 202                 send_unreach(*pskb, ICMPV6_PORT_UNREACH, hooknum);
 203                 break;
 204         case IP6T_ICMP6_ECHOREPLY:
 205                 /* Do nothing */
 206                 break;
 207         case IP6T_TCP_RESET:
 208                 send_reset(*pskb);
 209                 break;
 210         default:
 211                 if (net_ratelimit())
 212                         printk(KERN_WARNING "ip6t_REJECT: case %u not handled yet\n", reject->with);
 213                 break;
 214         }
 215
 216         return NF_DROP;
 217 }
 218
 219 static bool check(const char *tablename,
 220                   const void *entry,
 221                   const struct xt_target *target,
 222                   void *targinfo,
 223                   unsigned int hook_mask)
 224 {
 225         const struct ip6t_reject_info *rejinfo = targinfo;
 226         const struct ip6t_entry *e = entry;
 227
 228         if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
 229                 printk("ip6t_REJECT: ECHOREPLY is not supported.\n");
 230                 return false;
 231         } else if (rejinfo->with == IP6T_TCP_RESET) {
 232                 /* Must specify that it's a TCP packet */
 233                 if (e->ipv6.proto != IPPROTO_TCP
 234                     || (e->ipv6.invflags & XT_INV_PROTO)) {
 235                         printk("ip6t_REJECT: TCP_RESET illegal for non-tcp\n");
 236                         return false;
 237                 }
 238         }
 239         return true;
 240 }
 241
 242 static struct xt_target ip6t_reject_reg __read_mostly = {
 243         .name           = "REJECT",
 244         .family         = AF_INET6,
 245         .target         = reject6_target,
 246         .targetsize     = sizeof(struct ip6t_reject_info),
 247         .table          = "filter",
 248         .hooks          = (1 << NF_IP6_LOCAL_IN) | (1 << NF_IP6_FORWARD) |
 249                           (1 << NF_IP6_LOCAL_OUT),
 250         .checkentry     = check,
 251         .me             = THIS_MODULE
 252 };
 253
 254 static int __init ip6t_reject_init(void)
 255 {
 256         return xt_register_target(&ip6t_reject_reg);
 257 }
 258
 259 static void __exit ip6t_reject_fini(void)
 260 {
 261         xt_unregister_target(&ip6t_reject_reg);
 262 }
 263
 264 module_init(ip6t_reject_init);
 265 module_exit(ip6t_reject_fini);