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("Xtables: packet \"rejection\" target for IPv4");
  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 *oiph, *niph;
  39         struct tcphdr _otcph, *oth, *tcph;
  40         unsigned int addr_type;
  41
  42         /* IP header checks: fragment. */
  43         if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
  44                 return;
  45
  46         oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
  47                                  sizeof(_otcph), &_otcph);
  48         if (oth == NULL)
  49                 return;
  50
  51         /* No RST for RST. */
  52         if (oth->rst)
  53                 return;
  54
  55         /* Check checksum */
  56         if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
  57                 return;
  58         oiph = ip_hdr(oldskb);
  59
  60         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
  61                          LL_MAX_HEADER, GFP_ATOMIC);
  62         if (!nskb)
  63                 return;
  64
  65         skb_reserve(nskb, LL_MAX_HEADER);
  66
  67         skb_reset_network_header(nskb);
  68         niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
  69         niph->version   = 4;
  70         niph->ihl       = sizeof(struct iphdr) / 4;
  71         niph->tos       = 0;
  72         niph->id        = 0;
  73         niph->frag_off  = htons(IP_DF);
  74         niph->protocol  = IPPROTO_TCP;
  75         niph->check     = 0;
  76         niph->saddr     = oiph->daddr;
  77         niph->daddr     = oiph->saddr;
  78
  79         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
  80         memset(tcph, 0, sizeof(*tcph));
  81         tcph->source    = oth->dest;
  82         tcph->dest      = oth->source;
  83         tcph->doff      = sizeof(struct tcphdr) / 4;
  84
  85         if (oth->ack)
  86                 tcph->seq = oth->ack_seq;
  87         else {
  88                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
  89                                       oldskb->len - ip_hdrlen(oldskb) -
  90                                       (oth->doff << 2));
  91                 tcph->ack = 1;
  92         }
  93
  94         tcph->rst       = 1;
  95         tcph->check     = tcp_v4_check(sizeof(struct tcphdr),
  96                                        niph->saddr, niph->daddr,
  97                                        csum_partial(tcph,
  98                                                     sizeof(struct tcphdr), 0));
  99
 100         addr_type = RTN_UNSPEC;
 101         if (hook != NF_INET_FORWARD
 102 #ifdef CONFIG_BRIDGE_NETFILTER
 103             || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
 104 #endif
 105            )
 106                 addr_type = RTN_LOCAL;
 107
 108         /* ip_route_me_harder expects skb->dst to be set */
 109         dst_hold(oldskb->dst);
 110         nskb->dst = oldskb->dst;
 111
 112         if (ip_route_me_harder(nskb, addr_type))
 113                 goto free_nskb;
 114
 115         niph->ttl       = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 116         nskb->ip_summed = CHECKSUM_NONE;
 117
 118         /* "Never happens" */
 119         if (nskb->len > dst_mtu(nskb->dst))
 120                 goto free_nskb;
 121
 122         nf_ct_attach(nskb, oldskb);
 123
 124         ip_local_out(nskb);
 125         return;
 126
 127  free_nskb:
 128         kfree_skb(nskb);
 129 }
 130
 131 static inline void send_unreach(struct sk_buff *skb_in, int code)
 132 {
 133         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 134 }
 135
 136 static unsigned int
 137 reject_tg(struct sk_buff *skb, const struct net_device *in,
 138           const struct net_device *out, unsigned int hooknum,
 139           const struct xt_target *target, const void *targinfo)
 140 {
 141         const struct ipt_reject_info *reject = targinfo;
 142
 143         /* WARNING: This code causes reentry within iptables.
 144            This means that the iptables jump stack is now crap.  We
 145            must return an absolute verdict. --RR */
 146         switch (reject->with) {
 147         case IPT_ICMP_NET_UNREACHABLE:
 148                 send_unreach(skb, ICMP_NET_UNREACH);
 149                 break;
 150         case IPT_ICMP_HOST_UNREACHABLE:
 151                 send_unreach(skb, ICMP_HOST_UNREACH);
 152                 break;
 153         case IPT_ICMP_PROT_UNREACHABLE:
 154                 send_unreach(skb, ICMP_PROT_UNREACH);
 155                 break;
 156         case IPT_ICMP_PORT_UNREACHABLE:
 157                 send_unreach(skb, ICMP_PORT_UNREACH);
 158                 break;
 159         case IPT_ICMP_NET_PROHIBITED:
 160                 send_unreach(skb, ICMP_NET_ANO);
 161                 break;
 162         case IPT_ICMP_HOST_PROHIBITED:
 163                 send_unreach(skb, ICMP_HOST_ANO);
 164                 break;
 165         case IPT_ICMP_ADMIN_PROHIBITED:
 166                 send_unreach(skb, ICMP_PKT_FILTERED);
 167                 break;
 168         case IPT_TCP_RESET:
 169                 send_reset(skb, hooknum);
 170         case IPT_ICMP_ECHOREPLY:
 171                 /* Doesn't happen. */
 172                 break;
 173         }
 174
 175         return NF_DROP;
 176 }
 177
 178 static bool
 179 reject_tg_check(const char *tablename, const void *e_void,
 180                 const struct xt_target *target, void *targinfo,
 181                 unsigned int hook_mask)
 182 {
 183         const struct ipt_reject_info *rejinfo = targinfo;
 184         const struct ipt_entry *e = e_void;
 185
 186         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 187                 printk("ipt_REJECT: ECHOREPLY no longer supported.\n");
 188                 return false;
 189         } else if (rejinfo->with == IPT_TCP_RESET) {
 190                 /* Must specify that it's a TCP packet */
 191                 if (e->ip.proto != IPPROTO_TCP
 192                     || (e->ip.invflags & XT_INV_PROTO)) {
 193                         printk("ipt_REJECT: TCP_RESET invalid for non-tcp\n");
 194                         return false;
 195                 }
 196         }
 197         return true;
 198 }
 199
 200 static struct xt_target reject_tg_reg __read_mostly = {
 201         .name           = "REJECT",
 202         .family         = AF_INET,
 203         .target         = reject_tg,
 204         .targetsize     = sizeof(struct ipt_reject_info),
 205         .table          = "filter",
 206         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 207                           (1 << NF_INET_LOCAL_OUT),
 208         .checkentry     = reject_tg_check,
 209         .me             = THIS_MODULE,
 210 };
 211
 212 static int __init reject_tg_init(void)
 213 {
 214         return xt_register_target(&reject_tg_reg);
 215 }
 216
 217 static void __exit reject_tg_exit(void)
 218 {
 219         xt_unregister_target(&reject_tg_reg);
 220 }
 221
 222 module_init(reject_tg_init);
 223 module_exit(reject_tg_exit);