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 iphdr *iph = oldskb->nh.iph;
 108         struct tcphdr _otcph, *oth, *tcph;
 109         struct rtable *rt;
 110         u_int16_t tmp_port;
 111         u_int32_t tmp_addr;
 112         unsigned int tcplen;
 113         int needs_ack;
 114         int hh_len;
 115
 116         /* IP header checks: fragment. */
 117         if (oldskb->nh.iph->frag_off & htons(IP_OFFSET))
 118                 return;
 119
 120         oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4,
 121                                  sizeof(_otcph), &_otcph);
 122         if (oth == NULL)
 123                 return;
 124
 125         /* No RST for RST. */
 126         if (oth->rst)
 127                 return;
 128
 129         /* Check checksum */
 130         tcplen = oldskb->len - iph->ihl * 4;
 131         if (((hook != NF_IP_LOCAL_IN && oldskb->ip_summed != CHECKSUM_HW) ||
 132              (hook == NF_IP_LOCAL_IN &&
 133               oldskb->ip_summed != CHECKSUM_UNNECESSARY)) &&
 134             csum_tcpudp_magic(iph->saddr, iph->daddr, tcplen, IPPROTO_TCP,
 135                               oldskb->ip_summed == CHECKSUM_HW ? oldskb->csum :
 136                               skb_checksum(oldskb, iph->ihl * 4, tcplen, 0)))
 137                 return;
 138
 139         if ((rt = route_reverse(oldskb, oth, hook)) == NULL)
 140                 return;
 141
 142         hh_len = LL_RESERVED_SPACE(rt->u.dst.dev);
 143
 144         /* We need a linear, writeable skb.  We also need to expand
 145            headroom in case hh_len of incoming interface < hh_len of
 146            outgoing interface */
 147         nskb = skb_copy_expand(oldskb, hh_len, skb_tailroom(oldskb),
 148                                GFP_ATOMIC);
 149         if (!nskb) {
 150                 dst_release(&rt->u.dst);
 151                 return;
 152         }
 153
 154         dst_release(nskb->dst);
 155         nskb->dst = &rt->u.dst;
 156
 157         /* This packet will not be the same as the other: clear nf fields */
 158         nf_reset(nskb);
 159         nskb->nfmark = 0;
 160 #ifdef CONFIG_BRIDGE_NETFILTER
 161         nf_bridge_put(nskb->nf_bridge);
 162         nskb->nf_bridge = NULL;
 163 #endif
 164
 165         tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl);
 166
 167         /* Swap source and dest */
 168         tmp_addr = nskb->nh.iph->saddr;
 169         nskb->nh.iph->saddr = nskb->nh.iph->daddr;
 170         nskb->nh.iph->daddr = tmp_addr;
 171         tmp_port = tcph->source;
 172         tcph->source = tcph->dest;
 173         tcph->dest = tmp_port;
 174
 175         /* Truncate to length (no data) */
 176         tcph->doff = sizeof(struct tcphdr)/4;
 177         skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr));
 178         nskb->nh.iph->tot_len = htons(nskb->len);
 179
 180         if (tcph->ack) {
 181                 needs_ack = 0;
 182                 tcph->seq = oth->ack_seq;
 183                 tcph->ack_seq = 0;
 184         } else {
 185                 needs_ack = 1;
 186                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
 187                                       + oldskb->len - oldskb->nh.iph->ihl*4
 188                                       - (oth->doff<<2));
 189                 tcph->seq = 0;
 190         }
 191
 192         /* Reset flags */
 193         ((u_int8_t *)tcph)[13] = 0;
 194         tcph->rst = 1;
 195         tcph->ack = needs_ack;
 196
 197         tcph->window = 0;
 198         tcph->urg_ptr = 0;
 199
 200         /* Adjust TCP checksum */
 201         tcph->check = 0;
 202         tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
 203                                    nskb->nh.iph->saddr,
 204                                    nskb->nh.iph->daddr,
 205                                    csum_partial((char *)tcph,
 206                                                 sizeof(struct tcphdr), 0));
 207
 208         /* Adjust IP TTL, DF */
 209         nskb->nh.iph->ttl = MAXTTL;
 210         /* Set DF, id = 0 */
 211         nskb->nh.iph->frag_off = htons(IP_DF);
 212         nskb->nh.iph->id = 0;
 213
 214         /* Adjust IP checksum */
 215         nskb->nh.iph->check = 0;
 216         nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph,
 217                                            nskb->nh.iph->ihl);
 218
 219         /* "Never happens" */
 220         if (nskb->len > dst_mtu(nskb->dst))
 221                 goto free_nskb;
 222
 223         nf_ct_attach(nskb, oldskb);
 224
 225         NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev,
 226                 dst_output);
 227         return;
 228
 229  free_nskb:
 230         kfree_skb(nskb);
 231 }
 232
 233 static inline void send_unreach(struct sk_buff *skb_in, int code)
 234 {
 235         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 236 }
 237
 238 static unsigned int reject(struct sk_buff **pskb,
 239                            const struct net_device *in,
 240                            const struct net_device *out,
 241                            unsigned int hooknum,
 242                            const void *targinfo,
 243                            void *userinfo)
 244 {
 245         const struct ipt_reject_info *reject = targinfo;
 246
 247         /* Our naive response construction doesn't deal with IP
 248            options, and probably shouldn't try. */
 249         if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr))
 250                 return NF_DROP;
 251
 252         /* WARNING: This code causes reentry within iptables.
 253            This means that the iptables jump stack is now crap.  We
 254            must return an absolute verdict. --RR */
 255         switch (reject->with) {
 256         case IPT_ICMP_NET_UNREACHABLE:
 257                 send_unreach(*pskb, ICMP_NET_UNREACH);
 258                 break;
 259         case IPT_ICMP_HOST_UNREACHABLE:
 260                 send_unreach(*pskb, ICMP_HOST_UNREACH);
 261                 break;
 262         case IPT_ICMP_PROT_UNREACHABLE:
 263                 send_unreach(*pskb, ICMP_PROT_UNREACH);
 264                 break;
 265         case IPT_ICMP_PORT_UNREACHABLE:
 266                 send_unreach(*pskb, ICMP_PORT_UNREACH);
 267                 break;
 268         case IPT_ICMP_NET_PROHIBITED:
 269                 send_unreach(*pskb, ICMP_NET_ANO);
 270                 break;
 271         case IPT_ICMP_HOST_PROHIBITED:
 272                 send_unreach(*pskb, ICMP_HOST_ANO);
 273                 break;
 274         case IPT_ICMP_ADMIN_PROHIBITED:
 275                 send_unreach(*pskb, ICMP_PKT_FILTERED);
 276                 break;
 277         case IPT_TCP_RESET:
 278                 send_reset(*pskb, hooknum);
 279         case IPT_ICMP_ECHOREPLY:
 280                 /* Doesn't happen. */
 281                 break;
 282         }
 283
 284         return NF_DROP;
 285 }
 286
 287 static int check(const char *tablename,
 288                  const struct ipt_entry *e,
 289                  void *targinfo,
 290                  unsigned int targinfosize,
 291                  unsigned int hook_mask)
 292 {
 293         const struct ipt_reject_info *rejinfo = targinfo;
 294
 295         if (targinfosize != IPT_ALIGN(sizeof(struct ipt_reject_info))) {
 296                 DEBUGP("REJECT: targinfosize %u != 0\n", targinfosize);
 297                 return 0;
 298         }
 299
 300         /* Only allow these for packet filtering. */
 301         if (strcmp(tablename, "filter") != 0) {
 302                 DEBUGP("REJECT: bad table `%s'.\n", tablename);
 303                 return 0;
 304         }
 305         if ((hook_mask & ~((1 << NF_IP_LOCAL_IN)
 306                            | (1 << NF_IP_FORWARD)
 307                            | (1 << NF_IP_LOCAL_OUT))) != 0) {
 308                 DEBUGP("REJECT: bad hook mask %X\n", hook_mask);
 309                 return 0;
 310         }
 311
 312         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 313                 printk("REJECT: ECHOREPLY no longer supported.\n");
 314                 return 0;
 315         } else if (rejinfo->with == IPT_TCP_RESET) {
 316                 /* Must specify that it's a TCP packet */
 317                 if (e->ip.proto != IPPROTO_TCP
 318                     || (e->ip.invflags & IPT_INV_PROTO)) {
 319                         DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n");
 320                         return 0;
 321                 }
 322         }
 323
 324         return 1;
 325 }
 326
 327 static struct ipt_target ipt_reject_reg = {
 328         .name           = "REJECT",
 329         .target         = reject,
 330         .checkentry     = check,
 331         .me             = THIS_MODULE,
 332 };
 333
 334 static int __init init(void)
 335 {
 336         return ipt_register_target(&ipt_reject_reg);
 337 }
 338
 339 static void __exit fini(void)
 340 {
 341         ipt_unregister_target(&ipt_reject_reg);
 342 }
 343
 344 module_init(init);
 345 module_exit(fini);