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 #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
  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         if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
  58                 return;
  59
  60         /* Check checksum */
  61         if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
  62                 return;
  63         oiph = ip_hdr(oldskb);
  64
  65         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
  66                          LL_MAX_HEADER, GFP_ATOMIC);
  67         if (!nskb)
  68                 return;
  69
  70         skb_reserve(nskb, LL_MAX_HEADER);
  71
  72         skb_reset_network_header(nskb);
  73         niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
  74         niph->version   = 4;
  75         niph->ihl       = sizeof(struct iphdr) / 4;
  76         niph->tos       = 0;
  77         niph->id        = 0;
  78         niph->frag_off  = htons(IP_DF);
  79         niph->protocol  = IPPROTO_TCP;
  80         niph->check     = 0;
  81         niph->saddr     = oiph->daddr;
  82         niph->daddr     = oiph->saddr;
  83
  84         skb_reset_transport_header(nskb);
  85         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
  86         memset(tcph, 0, sizeof(*tcph));
  87         tcph->source    = oth->dest;
  88         tcph->dest      = oth->source;
  89         tcph->doff      = sizeof(struct tcphdr) / 4;
  90
  91         if (oth->ack)
  92                 tcph->seq = oth->ack_seq;
  93         else {
  94                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
  95                                       oldskb->len - ip_hdrlen(oldskb) -
  96                                       (oth->doff << 2));
  97                 tcph->ack = 1;
  98         }
  99
 100         tcph->rst       = 1;
 101         tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
 102                                     niph->daddr, 0);
 103         nskb->ip_summed = CHECKSUM_PARTIAL;
 104         nskb->csum_start = (unsigned char *)tcph - nskb->head;
 105         nskb->csum_offset = offsetof(struct tcphdr, check);
 106
 107         /* ip_route_me_harder expects skb->dst to be set */
 108         skb_dst_set_noref(nskb, skb_dst(oldskb));
 109
 110         nskb->protocol = htons(ETH_P_IP);
 111         if (ip_route_me_harder(nskb, RTN_UNSPEC))
 112                 goto free_nskb;
 113
 114         niph->ttl       = ip4_dst_hoplimit(skb_dst(nskb));
 115
 116         /* "Never happens" */
 117         if (nskb->len > dst_mtu(skb_dst(nskb)))
 118                 goto free_nskb;
 119
 120         nf_ct_attach(nskb, oldskb);
 121
 122         ip_local_out(nskb);
 123         return;
 124
 125  free_nskb:
 126         kfree_skb(nskb);
 127 }
 128
 129 static inline void send_unreach(struct sk_buff *skb_in, int code)
 130 {
 131         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 132 }
 133
 134 static unsigned int
 135 reject_tg(struct sk_buff *skb, const struct xt_action_param *par)
 136 {
 137         const struct ipt_reject_info *reject = par->targinfo;
 138
 139         switch (reject->with) {
 140         case IPT_ICMP_NET_UNREACHABLE:
 141                 send_unreach(skb, ICMP_NET_UNREACH);
 142                 break;
 143         case IPT_ICMP_HOST_UNREACHABLE:
 144                 send_unreach(skb, ICMP_HOST_UNREACH);
 145                 break;
 146         case IPT_ICMP_PROT_UNREACHABLE:
 147                 send_unreach(skb, ICMP_PROT_UNREACH);
 148                 break;
 149         case IPT_ICMP_PORT_UNREACHABLE:
 150                 send_unreach(skb, ICMP_PORT_UNREACH);
 151                 break;
 152         case IPT_ICMP_NET_PROHIBITED:
 153                 send_unreach(skb, ICMP_NET_ANO);
 154                 break;
 155         case IPT_ICMP_HOST_PROHIBITED:
 156                 send_unreach(skb, ICMP_HOST_ANO);
 157                 break;
 158         case IPT_ICMP_ADMIN_PROHIBITED:
 159                 send_unreach(skb, ICMP_PKT_FILTERED);
 160                 break;
 161         case IPT_TCP_RESET:
 162                 send_reset(skb, par->hooknum);
 163         case IPT_ICMP_ECHOREPLY:
 164                 /* Doesn't happen. */
 165                 break;
 166         }
 167
 168         return NF_DROP;
 169 }
 170
 171 static int reject_tg_check(const struct xt_tgchk_param *par)
 172 {
 173         const struct ipt_reject_info *rejinfo = par->targinfo;
 174         const struct ipt_entry *e = par->entryinfo;
 175
 176         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 177                 pr_info("ECHOREPLY no longer supported.\n");
 178                 return -EINVAL;
 179         } else if (rejinfo->with == IPT_TCP_RESET) {
 180                 /* Must specify that it's a TCP packet */
 181                 if (e->ip.proto != IPPROTO_TCP ||
 182                     (e->ip.invflags & XT_INV_PROTO)) {
 183                         pr_info("TCP_RESET invalid for non-tcp\n");
 184                         return -EINVAL;
 185                 }
 186         }
 187         return 0;
 188 }
 189
 190 static struct xt_target reject_tg_reg __read_mostly = {
 191         .name           = "REJECT",
 192         .family         = NFPROTO_IPV4,
 193         .target         = reject_tg,
 194         .targetsize     = sizeof(struct ipt_reject_info),
 195         .table          = "filter",
 196         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 197                           (1 << NF_INET_LOCAL_OUT),
 198         .checkentry     = reject_tg_check,
 199         .me             = THIS_MODULE,
 200 };
 201
 202 static int __init reject_tg_init(void)
 203 {
 204         return xt_register_target(&reject_tg_reg);
 205 }
 206
 207 static void __exit reject_tg_exit(void)
 208 {
 209         xt_unregister_target(&reject_tg_reg);
 210 }
 211
 212 module_init(reject_tg_init);
 213 module_exit(reject_tg_exit);