net/ipv4/netfilter/ipt_REJECT.c

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