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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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  13 #include <linux/module.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/slab.h>
  16 #include <linux/ip.h>
  17 #include <linux/udp.h>
  18 #include <linux/icmp.h>
  19 #include <net/icmp.h>
  20 #include <net/ip.h>
  21 #include <net/tcp.h>
  22 #include <net/route.h>
  23 #include <net/dst.h>
  24 #include <linux/netfilter/x_tables.h>
  25 #include <linux/netfilter_ipv4/ip_tables.h>
  26 #include <linux/netfilter_ipv4/ipt_REJECT.h>
  27 #ifdef CONFIG_BRIDGE_NETFILTER
  28 #include <linux/netfilter_bridge.h>
  29 #endif
  30
  31 MODULE_LICENSE("GPL");
  32 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  33 MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv4");
  34
  35 /* Send RST reply */
  36 static void send_reset(struct sk_buff *oldskb, int hook)
  37 {
  38         struct sk_buff *nskb;
  39         const struct iphdr *oiph;
  40         struct iphdr *niph;
  41         const struct tcphdr *oth;
  42         struct tcphdr _otcph, *tcph;
  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         oiph = ip_hdr(oldskb);
  62
  63         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
  64                          LL_MAX_HEADER, GFP_ATOMIC);
  65         if (!nskb)
  66                 return;
  67
  68         skb_reserve(nskb, LL_MAX_HEADER);
  69
  70         skb_reset_network_header(nskb);
  71         niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
  72         niph->version   = 4;
  73         niph->ihl       = sizeof(struct iphdr) / 4;
  74         niph->tos       = 0;
  75         niph->id        = 0;
  76         niph->frag_off  = htons(IP_DF);
  77         niph->protocol  = IPPROTO_TCP;
  78         niph->check     = 0;
  79         niph->saddr     = oiph->daddr;
  80         niph->daddr     = oiph->saddr;
  81
  82         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
  83         memset(tcph, 0, sizeof(*tcph));
  84         tcph->source    = oth->dest;
  85         tcph->dest      = oth->source;
  86         tcph->doff      = sizeof(struct tcphdr) / 4;
  87
  88         if (oth->ack)
  89                 tcph->seq = oth->ack_seq;
  90         else {
  91                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
  92                                       oldskb->len - ip_hdrlen(oldskb) -
  93                                       (oth->doff << 2));
  94                 tcph->ack = 1;
  95         }
  96
  97         tcph->rst       = 1;
  98         tcph->check     = tcp_v4_check(sizeof(struct tcphdr),
  99                                        niph->saddr, niph->daddr,
 100                                        csum_partial(tcph,
 101                                                     sizeof(struct tcphdr), 0));
 102
 103         addr_type = RTN_UNSPEC;
 104         if (hook != NF_INET_FORWARD
 105 #ifdef CONFIG_BRIDGE_NETFILTER
 106             || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
 107 #endif
 108            )
 109                 addr_type = RTN_LOCAL;
 110
 111         /* ip_route_me_harder expects skb->dst to be set */
 112         skb_dst_set(nskb, dst_clone(skb_dst(oldskb)));
 113
 114         if (ip_route_me_harder(nskb, addr_type))
 115                 goto free_nskb;
 116
 117         niph->ttl       = dst_metric(skb_dst(nskb), RTAX_HOPLIMIT);
 118         nskb->ip_summed = CHECKSUM_NONE;
 119
 120         /* "Never happens" */
 121         if (nskb->len > dst_mtu(skb_dst(nskb)))
 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 xt_action_param *par)
 140 {
 141         const struct ipt_reject_info *reject = par->targinfo;
 142
 143         switch (reject->with) {
 144         case IPT_ICMP_NET_UNREACHABLE:
 145                 send_unreach(skb, ICMP_NET_UNREACH);
 146                 break;
 147         case IPT_ICMP_HOST_UNREACHABLE:
 148                 send_unreach(skb, ICMP_HOST_UNREACH);
 149                 break;
 150         case IPT_ICMP_PROT_UNREACHABLE:
 151                 send_unreach(skb, ICMP_PROT_UNREACH);
 152                 break;
 153         case IPT_ICMP_PORT_UNREACHABLE:
 154                 send_unreach(skb, ICMP_PORT_UNREACH);
 155                 break;
 156         case IPT_ICMP_NET_PROHIBITED:
 157                 send_unreach(skb, ICMP_NET_ANO);
 158                 break;
 159         case IPT_ICMP_HOST_PROHIBITED:
 160                 send_unreach(skb, ICMP_HOST_ANO);
 161                 break;
 162         case IPT_ICMP_ADMIN_PROHIBITED:
 163                 send_unreach(skb, ICMP_PKT_FILTERED);
 164                 break;
 165         case IPT_TCP_RESET:
 166                 send_reset(skb, par->hooknum);
 167         case IPT_ICMP_ECHOREPLY:
 168                 /* Doesn't happen. */
 169                 break;
 170         }
 171
 172         return NF_DROP;
 173 }
 174
 175 static int reject_tg_check(const struct xt_tgchk_param *par)
 176 {
 177         const struct ipt_reject_info *rejinfo = par->targinfo;
 178         const struct ipt_entry *e = par->entryinfo;
 179
 180         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 181                 pr_info("ECHOREPLY no longer supported.\n");
 182                 return -EINVAL;
 183         } else if (rejinfo->with == IPT_TCP_RESET) {
 184                 /* Must specify that it's a TCP packet */
 185                 if (e->ip.proto != IPPROTO_TCP ||
 186                     (e->ip.invflags & XT_INV_PROTO)) {
 187                         pr_info("TCP_RESET invalid for non-tcp\n");
 188                         return -EINVAL;
 189                 }
 190         }
 191         return 0;
 192 }
 193
 194 static struct xt_target reject_tg_reg __read_mostly = {
 195         .name           = "REJECT",
 196         .family         = NFPROTO_IPV4,
 197         .target         = reject_tg,
 198         .targetsize     = sizeof(struct ipt_reject_info),
 199         .table          = "filter",
 200         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 201                           (1 << NF_INET_LOCAL_OUT),
 202         .checkentry     = reject_tg_check,
 203         .me             = THIS_MODULE,
 204 };
 205
 206 static int __init reject_tg_init(void)
 207 {
 208         return xt_register_target(&reject_tg_reg);
 209 }
 210
 211 static void __exit reject_tg_exit(void)
 212 {
 213         xt_unregister_target(&reject_tg_reg);
 214 }
 215
 216 module_init(reject_tg_init);
 217 module_exit(reject_tg_exit);