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