net/ipv4/netfilter/ipt_REJECT.c

   1 /*
   2  * This is a module which is used for rejecting packets.
   3  * Added support for customized reject packets (Jozsef Kadlecsik).
   4  * Added support for ICMP type-3-code-13 (Maciej Soltysiak). [RFC 1812]
   5  */
   6
   7 /* (C) 1999-2001 Paul `Rusty' Russell
   8  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   9  *
  10  * This program is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License version 2 as
  12  * published by the Free Software Foundation.
  13  */
  14
  15 #include <linux/module.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/ip.h>
  18 #include <linux/udp.h>
  19 #include <linux/icmp.h>
  20 #include <net/icmp.h>
  21 #include <net/ip.h>
  22 #include <net/tcp.h>
  23 #include <net/route.h>
  24 #include <net/dst.h>
  25 #include <linux/netfilter_ipv4/ip_tables.h>
  26 #include <linux/netfilter_ipv4/ipt_REJECT.h>
  27 #ifdef CONFIG_BRIDGE_NETFILTER
  28 #include <linux/netfilter_bridge.h>
  29 #endif
  30
  31 MODULE_LICENSE("GPL");
  32 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  33 MODULE_DESCRIPTION("iptables REJECT target module");
  34
  35 #if 0
  36 #define DEBUGP printk
  37 #else
  38 #define DEBUGP(format, args...)
  39 #endif
  40
  41 static inline struct rtable *route_reverse(struct sk_buff *skb,
  42                                            struct tcphdr *tcph, int hook)
  43 {
  44         struct iphdr *iph = skb->nh.iph;
  45         struct dst_entry *odst;
  46         struct flowi fl = {};
  47         struct rtable *rt;
  48
  49         /* We don't require ip forwarding to be enabled to be able to
  50          * send a RST reply for bridged traffic. */
  51         if (hook != NF_IP_FORWARD
  52 #ifdef CONFIG_BRIDGE_NETFILTER
  53             || (skb->nf_bridge && skb->nf_bridge->mask & BRNF_BRIDGED)
  54 #endif
  55            ) {
  56                 fl.nl_u.ip4_u.daddr = iph->saddr;
  57                 if (hook == NF_IP_LOCAL_IN)
  58                         fl.nl_u.ip4_u.saddr = iph->daddr;
  59                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  60
  61                 if (ip_route_output_key(&rt, &fl) != 0)
  62                         return NULL;
  63         } else {
  64                 /* non-local src, find valid iif to satisfy
  65                  * rp-filter when calling ip_route_input. */
  66                 fl.nl_u.ip4_u.daddr = iph->daddr;
  67                 if (ip_route_output_key(&rt, &fl) != 0)
  68                         return NULL;
  69
  70                 odst = skb->dst;
  71                 if (ip_route_input(skb, iph->saddr, iph->daddr,
  72                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  73                         dst_release(&rt->u.dst);
  74                         return NULL;
  75                 }
  76                 dst_release(&rt->u.dst);
  77                 rt = (struct rtable *)skb->dst;
  78                 skb->dst = odst;
  79
  80                 fl.nl_u.ip4_u.daddr = iph->saddr;
  81                 fl.nl_u.ip4_u.saddr = iph->daddr;
  82                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  83         }
  84
  85         if (rt->u.dst.error) {
  86                 dst_release(&rt->u.dst);
  87                 return NULL;
  88         }
  89
  90         fl.proto = IPPROTO_TCP;
  91         fl.fl_ip_sport = tcph->dest;
  92         fl.fl_ip_dport = tcph->source;
  93         security_skb_classify_flow(skb, &fl);
  94
  95         xfrm_lookup((struct dst_entry **)&rt, &fl, NULL, 0);
  96
  97         return rt;
  98 }
  99
 100 /* Send RST reply */
 101 static void send_reset(struct sk_buff *oldskb, int hook)
 102 {
 103         struct sk_buff *nskb;
 104         struct iphdr *iph = oldskb->nh.iph;
 105         struct tcphdr _otcph, *oth, *tcph;
 106         struct rtable *rt;
 107         __be16 tmp_port;
 108         __be32 tmp_addr;
 109         int needs_ack;
 110         int hh_len;
 111
 112         /* IP header checks: fragment. */
 113         if (oldskb->nh.iph->frag_off & htons(IP_OFFSET))
 114                 return;
 115
 116         oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4,
 117                                  sizeof(_otcph), &_otcph);
 118         if (oth == NULL)
 119                 return;
 120
 121         /* No RST for RST. */
 122         if (oth->rst)
 123                 return;
 124
 125         /* Check checksum */
 126         if (nf_ip_checksum(oldskb, hook, iph->ihl * 4, IPPROTO_TCP))
 127                 return;
 128
 129         if ((rt = route_reverse(oldskb, oth, hook)) == NULL)
 130                 return;
 131
 132         hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);
 133
 134         /* We need a linear, writeable skb.  We also need to expand
 135            headroom in case hh_len of incoming interface < hh_len of
 136            outgoing interface */
 137         nskb = skb_copy_expand(oldskb, hh_len, skb_tailroom(oldskb),
 138                                GFP_ATOMIC);
 139         if (!nskb) {
 140                 dst_release(&rt->u.dst);
 141                 return;
 142         }
 143
 144         dst_release(nskb->dst);
 145         nskb->dst = &rt->u.dst;
 146
 147         /* This packet will not be the same as the other: clear nf fields */
 148         nf_reset(nskb);
 149         nskb->nfmark = 0;
 150         skb_init_secmark(nskb);
 151
 152         tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
 153
 154         /* Swap source and dest */
 155         tmp_addr = nskb->nh.iph->saddr;
 156         nskb->nh.iph->saddr = nskb->nh.iph->daddr;
 157         nskb->nh.iph->daddr = tmp_addr;
 158         tmp_port = tcph->source;
 159         tcph->source = tcph->dest;
 160         tcph->dest = tmp_port;
 161
 162         /* Truncate to length (no data) */
 163         tcph->doff = sizeof(struct tcphdr)/4;
 164         skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
 165         nskb->nh.iph->tot_len = htons(nskb->len);
 166
 167         if (tcph->ack) {
 168                 needs_ack = 0;
 169                 tcph->seq = oth->ack_seq;
 170                 tcph->ack_seq = 0;
 171         } else {
 172                 needs_ack = 1;
 173                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
 174                                       + oldskb->len - oldskb->nh.iph->ihl*4
 175                                       - (oth->doff<<2));
 176                 tcph->seq = 0;
 177         }
 178
 179         /* Reset flags */
 180         ((u_int8_t *)tcph)[13] = 0;
 181         tcph->rst = 1;
 182         tcph->ack = needs_ack;
 183
 184         tcph->window = 0;
 185         tcph->urg_ptr = 0;
 186
 187         /* Adjust TCP checksum */
 188         nskb->ip_summed = CHECKSUM_NONE;
 189         tcph->check = 0;
 190         tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
 191                                    nskb->nh.iph->saddr,
 192                                    nskb->nh.iph->daddr,
 193                                    csum_partial((char *)tcph,
 194                                                 sizeof(struct tcphdr), 0));
 195
 196         /* Adjust IP TTL, DF */
 197         nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 198         /* Set DF, id = 0 */
 199         nskb->nh.iph->frag_off = htons(IP_DF);
 200         nskb->nh.iph->id = 0;
 201
 202         /* Adjust IP checksum */
 203         nskb->nh.iph->check = 0;
 204         nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
 205                                            nskb->nh.iph->ihl);
 206
 207         /* "Never happens" */
 208         if (nskb->len > dst_mtu(nskb->dst))
 209                 goto free_nskb;
 210
 211         nf_ct_attach(nskb, oldskb);
 212
 213         NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 214                 dst_output);
 215         return;
 216
 217  free_nskb:
 218         kfree_skb(nskb);
 219 }
 220
 221 static inline void send_unreach(struct sk_buff *skb_in, int code)
 222 {
 223         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 224 }
 225
 226 static unsigned int reject(struct sk_buff **pskb,
 227                            const struct net_device *in,
 228                            const struct net_device *out,
 229                            unsigned int hooknum,
 230                            const struct xt_target *target,
 231                            const void *targinfo)
 232 {
 233         const struct ipt_reject_info *reject = targinfo;
 234
 235         /* Our naive response construction doesn't deal with IP
 236            options, and probably shouldn't try. */
 237         if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
 238                 return NF_DROP;
 239
 240         /* WARNING: This code causes reentry within iptables.
 241            This means that the iptables jump stack is now crap.  We
 242            must return an absolute verdict. --RR */
 243         switch (reject->with) {
 244         case IPT_ICMP_NET_UNREACHABLE:
 245                 send_unreach(*pskb, ICMP_NET_UNREACH);
 246                 break;
 247         case IPT_ICMP_HOST_UNREACHABLE:
 248                 send_unreach(*pskb, ICMP_HOST_UNREACH);
 249                 break;
 250         case IPT_ICMP_PROT_UNREACHABLE:
 251                 send_unreach(*pskb, ICMP_PROT_UNREACH);
 252                 break;
 253         case IPT_ICMP_PORT_UNREACHABLE:
 254                 send_unreach(*pskb, ICMP_PORT_UNREACH);
 255                 break;
 256         case IPT_ICMP_NET_PROHIBITED:
 257                 send_unreach(*pskb, ICMP_NET_ANO);
 258                 break;
 259         case IPT_ICMP_HOST_PROHIBITED:
 260                 send_unreach(*pskb, ICMP_HOST_ANO);
 261                 break;
 262         case IPT_ICMP_ADMIN_PROHIBITED:
 263                 send_unreach(*pskb, ICMP_PKT_FILTERED);
 264                 break;
 265         case IPT_TCP_RESET:
 266                 send_reset(*pskb, hooknum);
 267         case IPT_ICMP_ECHOREPLY:
 268                 /* Doesn't happen. */
 269                 break;
 270         }
 271
 272         return NF_DROP;
 273 }
 274
 275 static int check(const char *tablename,
 276                  const void *e_void,
 277                  const struct xt_target *target,
 278                  void *targinfo,
 279                  unsigned int hook_mask)
 280 {
 281         const struct ipt_reject_info *rejinfo = targinfo;
 282         const struct ipt_entry *e = e_void;
 283
 284         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 285                 printk("REJECT: ECHOREPLY no longer supported.\n");
 286                 return 0;
 287         } else if (rejinfo->with == IPT_TCP_RESET) {
 288                 /* Must specify that it's a TCP packet */
 289                 if (e->ip.proto != IPPROTO_TCP
 290                     || (e->ip.invflags & IPT_INV_PROTO)) {
 291                         DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
 292                         return 0;
 293                 }
 294         }
 295         return 1;
 296 }
 297
 298 static struct ipt_target ipt_reject_reg = {
 299         .name           = "REJECT",
 300         .target         = reject,
 301         .targetsize     = sizeof(struct ipt_reject_info),
 302         .table          = "filter",
 303         .hooks          = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) |
 304                           (1 << NF_IP_LOCAL_OUT),
 305         .checkentry     = check,
 306         .me             = THIS_MODULE,
 307 };
 308
 309 static int __init ipt_reject_init(void)
 310 {
 311         return ipt_register_target(&ipt_reject_reg);
 312 }
 313
 314 static void __exit ipt_reject_fini(void)
 315 {
 316         ipt_unregister_target(&ipt_reject_reg);
 317 }
 318
 319 module_init(ipt_reject_init);
 320 module_exit(ipt_reject_fini);