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/config.h>
  16 #include <linux/module.h>
  17 #include <linux/skbuff.h>
  18 #include <linux/ip.h>
  19 #include <linux/udp.h>
  20 #include <linux/icmp.h>
  21 #include <net/icmp.h>
  22 #include <net/ip.h>
  23 #include <net/tcp.h>
  24 #include <net/route.h>
  25 #include <net/dst.h>
  26 #include <linux/netfilter_ipv4/ip_tables.h>
  27 #include <linux/netfilter_ipv4/ipt_REJECT.h>
  28 #ifdef CONFIG_BRIDGE_NETFILTER
  29 #include <linux/netfilter_bridge.h>
  30 #endif
  31
  32 MODULE_LICENSE("GPL");
  33 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  34 MODULE_DESCRIPTION("iptables REJECT target module");
  35
  36 #if 0
  37 #define DEBUGP printk
  38 #else
  39 #define DEBUGP(format, args...)
  40 #endif
  41
  42 static inline struct rtable *route_reverse(struct sk_buff *skb,
  43                                            struct tcphdr *tcph, int hook)
  44 {
  45         struct iphdr *iph = skb->nh.iph;
  46         struct dst_entry *odst;
  47         struct flowi fl = {};
  48         struct rtable *rt;
  49
  50         /* We don't require ip forwarding to be enabled to be able to
  51          * send a RST reply for bridged traffic. */
  52         if (hook != NF_IP_FORWARD
  53 #ifdef CONFIG_BRIDGE_NETFILTER
  54             || (skb->nf_bridge && skb->nf_bridge->mask & BRNF_BRIDGED)
  55 #endif
  56            ) {
  57                 fl.nl_u.ip4_u.daddr = iph->saddr;
  58                 if (hook == NF_IP_LOCAL_IN)
  59                         fl.nl_u.ip4_u.saddr = iph->daddr;
  60                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  61
  62                 if (ip_route_output_key(&rt, &fl) != 0)
  63                         return NULL;
  64         } else {
  65                 /* non-local src, find valid iif to satisfy
  66                  * rp-filter when calling ip_route_input. */
  67                 fl.nl_u.ip4_u.daddr = iph->daddr;
  68                 if (ip_route_output_key(&rt, &fl) != 0)
  69                         return NULL;
  70
  71                 odst = skb->dst;
  72                 if (ip_route_input(skb, iph->saddr, iph->daddr,
  73                                    RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
  74                         dst_release(&rt->u.dst);
  75                         return NULL;
  76                 }
  77                 dst_release(&rt->u.dst);
  78                 rt = (struct rtable *)skb->dst;
  79                 skb->dst = odst;
  80
  81                 fl.nl_u.ip4_u.daddr = iph->saddr;
  82                 fl.nl_u.ip4_u.saddr = iph->daddr;
  83                 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
  84         }
  85
  86         if (rt->u.dst.error) {
  87                 dst_release(&rt->u.dst);
  88                 return NULL;
  89         }
  90
  91         fl.proto = IPPROTO_TCP;
  92         fl.fl_ip_sport = tcph->dest;
  93         fl.fl_ip_dport = tcph->source;
  94
  95         if (xfrm_lookup((struct dst_entry **)&rt, &fl, NULL, 0)) {
  96                 dst_release(&rt->u.dst);
  97                 rt = NULL;
  98         }
  99
 100         return rt;
 101 }
 102
 103 /* Send RST reply */
 104 static void send_reset(struct sk_buff *oldskb, int hook)
 105 {
 106         struct sk_buff *nskb;
 107         struct tcphdr _otcph, *oth, *tcph;
 108         struct rtable *rt;
 109         u_int16_t tmp_port;
 110         u_int32_t tmp_addr;
 111         int needs_ack;
 112         int hh_len;
 113
 114         /* IP header checks: fragment. */
 115         if (oldskb->nh.iph->frag_off & htons(IP_OFFSET))
 116                 return;
 117
 118         oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4,
 119                                  sizeof(_otcph), &_otcph);
 120         if (oth == NULL)
 121                 return;
 122
 123         /* No RST for RST. */
 124         if (oth->rst)
 125                 return;
 126
 127         /* FIXME: Check checksum --RR */
 128         if ((rt = route_reverse(oldskb, oth, hook)) == NULL)
 129                 return;
 130
 131         hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);
 132
 133         /* We need a linear, writeable skb.  We also need to expand
 134            headroom in case hh_len of incoming interface < hh_len of
 135            outgoing interface */
 136         nskb = skb_copy_expand(oldskb, hh_len, skb_tailroom(oldskb),
 137                                GFP_ATOMIC);
 138         if (!nskb) {
 139                 dst_release(&rt->u.dst);
 140                 return;
 141         }
 142
 143         dst_release(nskb->dst);
 144         nskb->dst = &rt->u.dst;
 145
 146         /* This packet will not be the same as the other: clear nf fields */
 147         nf_reset(nskb);
 148         nskb->nfcache = 0;
 149         nskb->nfmark = 0;
 150 #ifdef CONFIG_BRIDGE_NETFILTER
 151         nf_bridge_put(nskb->nf_bridge);
 152         nskb->nf_bridge = NULL;
 153 #endif
 154
 155         tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
 156
 157         /* Swap source and dest */
 158         tmp_addr = nskb->nh.iph->saddr;
 159         nskb->nh.iph->saddr = nskb->nh.iph->daddr;
 160         nskb->nh.iph->daddr = tmp_addr;
 161         tmp_port = tcph->source;
 162         tcph->source = tcph->dest;
 163         tcph->dest = tmp_port;
 164
 165         /* Truncate to length (no data) */
 166         tcph->doff = sizeof(struct tcphdr)/4;
 167         skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
 168         nskb->nh.iph->tot_len = htons(nskb->len);
 169
 170         if (tcph->ack) {
 171                 needs_ack = 0;
 172                 tcph->seq = oth->ack_seq;
 173                 tcph->ack_seq = 0;
 174         } else {
 175                 needs_ack = 1;
 176                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
 177                                       + oldskb->len - oldskb->nh.iph->ihl*4
 178                                       - (oth->doff<<2));
 179                 tcph->seq = 0;
 180         }
 181
 182         /* Reset flags */
 183         ((u_int8_t *)tcph)[13] = 0;
 184         tcph->rst = 1;
 185         tcph->ack = needs_ack;
 186
 187         tcph->window = 0;
 188         tcph->urg_ptr = 0;
 189
 190         /* Adjust TCP checksum */
 191         tcph->check = 0;
 192         tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
 193                                    nskb->nh.iph->saddr,
 194                                    nskb->nh.iph->daddr,
 195                                    csum_partial((char *)tcph,
 196                                                 sizeof(struct tcphdr), 0));
 197
 198         /* Adjust IP TTL, DF */
 199         nskb->nh.iph->ttl = MAXTTL;
 200         /* Set DF, id = 0 */
 201         nskb->nh.iph->frag_off = htons(IP_DF);
 202         nskb->nh.iph->id = 0;
 203
 204         /* Adjust IP checksum */
 205         nskb->nh.iph->check = 0;
 206         nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
 207                                            nskb->nh.iph->ihl);
 208
 209         /* "Never happens" */
 210         if (nskb->len > dst_mtu(nskb->dst))
 211                 goto free_nskb;
 212
 213         nf_ct_attach(nskb, oldskb);
 214
 215         NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 216                 dst_output);
 217         return;
 218
 219  free_nskb:
 220         kfree_skb(nskb);
 221 }
 222
 223 static inline void send_unreach(struct sk_buff *skb_in, int code)
 224 {
 225         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 226 }
 227
 228 static unsigned int reject(struct sk_buff **pskb,
 229                            const struct net_device *in,
 230                            const struct net_device *out,
 231                            unsigned int hooknum,
 232                            const void *targinfo,
 233                            void *userinfo)
 234 {
 235         const struct ipt_reject_info *reject = targinfo;
 236
 237         /* Our naive response construction doesn't deal with IP
 238            options, and probably shouldn't try. */
 239         if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
 240                 return NF_DROP;
 241
 242         /* WARNING: This code causes reentry within iptables.
 243            This means that the iptables jump stack is now crap.  We
 244            must return an absolute verdict. --RR */
 245         switch (reject->with) {
 246         case IPT_ICMP_NET_UNREACHABLE:
 247                 send_unreach(*pskb, ICMP_NET_UNREACH);
 248                 break;
 249         case IPT_ICMP_HOST_UNREACHABLE:
 250                 send_unreach(*pskb, ICMP_HOST_UNREACH);
 251                 break;
 252         case IPT_ICMP_PROT_UNREACHABLE:
 253                 send_unreach(*pskb, ICMP_PROT_UNREACH);
 254                 break;
 255         case IPT_ICMP_PORT_UNREACHABLE:
 256                 send_unreach(*pskb, ICMP_PORT_UNREACH);
 257                 break;
 258         case IPT_ICMP_NET_PROHIBITED:
 259                 send_unreach(*pskb, ICMP_NET_ANO);
 260                 break;
 261         case IPT_ICMP_HOST_PROHIBITED:
 262                 send_unreach(*pskb, ICMP_HOST_ANO);
 263                 break;
 264         case IPT_ICMP_ADMIN_PROHIBITED:
 265                 send_unreach(*pskb, ICMP_PKT_FILTERED);
 266                 break;
 267         case IPT_TCP_RESET:
 268                 send_reset(*pskb, hooknum);
 269         case IPT_ICMP_ECHOREPLY:
 270                 /* Doesn't happen. */
 271                 break;
 272         }
 273
 274         return NF_DROP;
 275 }
 276
 277 static int check(const char *tablename,
 278                  const struct ipt_entry *e,
 279                  void *targinfo,
 280                  unsigned int targinfosize,
 281                  unsigned int hook_mask)
 282 {
 283         const struct ipt_reject_info *rejinfo = targinfo;
 284
 285         if (targinfosize != IPT_ALIGN(sizeof(struct ipt_reject_info))) {
 286                 DEBUGP("REJECT: targinfosize %u != 0\n", targinfosize);
 287                 return 0;
 288         }
 289
 290         /* Only allow these for packet filtering. */
 291         if (strcmp(tablename, "filter") != 0) {
 292                 DEBUGP("REJECT: bad table `%s'.\n", tablename);
 293                 return 0;
 294         }
 295         if ((hook_mask & ~((1 << NF_IP_LOCAL_IN)
 296                            | (1 << NF_IP_FORWARD)
 297                            | (1 << NF_IP_LOCAL_OUT))) != 0) {
 298                 DEBUGP("REJECT: bad hook mask %X\n", hook_mask);
 299                 return 0;
 300         }
 301
 302         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 303                 printk("REJECT: ECHOREPLY no longer supported.\n");
 304                 return 0;
 305         } else if (rejinfo->with == IPT_TCP_RESET) {
 306                 /* Must specify that it's a TCP packet */
 307                 if (e->ip.proto != IPPROTO_TCP
 308                     || (e->ip.invflags & IPT_INV_PROTO)) {
 309                         DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
 310                         return 0;
 311                 }
 312         }
 313
 314         return 1;
 315 }
 316
 317 static struct ipt_target ipt_reject_reg = {
 318         .name           = "REJECT",
 319         .target         = reject,
 320         .checkentry     = check,
 321         .me             = THIS_MODULE,
 322 };
 323
 324 static int __init init(void)
 325 {
 326         return ipt_register_target(&ipt_reject_reg);
 327 }
 328
 329 static void __exit fini(void)
 330 {
 331         ipt_unregister_target(&ipt_reject_reg);
 332 }
 333
 334 module_init(init);
 335 module_exit(fini);