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
  94         if (tcph->ack) {
  95                 needs_ack = 0;
  96                 tcph->seq = oth->ack_seq;
  97                 tcph->ack_seq = 0;
  98         } else {
  99                 needs_ack = 1;
 100                 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
 101                                       oldskb->len - ip_hdrlen(oldskb) -
 102                                       (oth->doff << 2));
 103                 tcph->seq = 0;
 104         }
 105
 106         /* Reset flags */
 107         ((u_int8_t *)tcph)[13] = 0;
 108         tcph->rst = 1;
 109         tcph->ack = needs_ack;
 110
 111         tcph->window = 0;
 112         tcph->urg_ptr = 0;
 113
 114         /* Adjust TCP checksum */
 115         tcph->check = 0;
 116         tcph->check = tcp_v4_check(sizeof(struct tcphdr),
 117                                    niph->saddr, niph->daddr,
 118                                    csum_partial(tcph,
 119                                                 sizeof(struct tcphdr), 0));
 120
 121         /* Set DF, id = 0 */
 122         niph->frag_off = htons(IP_DF);
 123         niph->id = 0;
 124
 125         addr_type = RTN_UNSPEC;
 126         if (hook != NF_INET_FORWARD
 127 #ifdef CONFIG_BRIDGE_NETFILTER
 128             || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
 129 #endif
 130            )
 131                 addr_type = RTN_LOCAL;
 132
 133         if (ip_route_me_harder(nskb, addr_type))
 134                 goto free_nskb;
 135
 136         nskb->ip_summed = CHECKSUM_NONE;
 137
 138         /* Adjust IP TTL */
 139         niph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
 140
 141         /* "Never happens" */
 142         if (nskb->len > dst_mtu(nskb->dst))
 143                 goto free_nskb;
 144
 145         nf_ct_attach(nskb, oldskb);
 146
 147         ip_local_out(nskb);
 148         return;
 149
 150  free_nskb:
 151         kfree_skb(nskb);
 152 }
 153
 154 static inline void send_unreach(struct sk_buff *skb_in, int code)
 155 {
 156         icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 157 }
 158
 159 static unsigned int
 160 reject_tg(struct sk_buff *skb, const struct net_device *in,
 161           const struct net_device *out, unsigned int hooknum,
 162           const struct xt_target *target, const void *targinfo)
 163 {
 164         const struct ipt_reject_info *reject = targinfo;
 165
 166         /* Our naive response construction doesn't deal with IP
 167            options, and probably shouldn't try. */
 168         if (ip_hdrlen(skb) != sizeof(struct iphdr))
 169                 return NF_DROP;
 170
 171         /* WARNING: This code causes reentry within iptables.
 172            This means that the iptables jump stack is now crap.  We
 173            must return an absolute verdict. --RR */
 174         switch (reject->with) {
 175         case IPT_ICMP_NET_UNREACHABLE:
 176                 send_unreach(skb, ICMP_NET_UNREACH);
 177                 break;
 178         case IPT_ICMP_HOST_UNREACHABLE:
 179                 send_unreach(skb, ICMP_HOST_UNREACH);
 180                 break;
 181         case IPT_ICMP_PROT_UNREACHABLE:
 182                 send_unreach(skb, ICMP_PROT_UNREACH);
 183                 break;
 184         case IPT_ICMP_PORT_UNREACHABLE:
 185                 send_unreach(skb, ICMP_PORT_UNREACH);
 186                 break;
 187         case IPT_ICMP_NET_PROHIBITED:
 188                 send_unreach(skb, ICMP_NET_ANO);
 189                 break;
 190         case IPT_ICMP_HOST_PROHIBITED:
 191                 send_unreach(skb, ICMP_HOST_ANO);
 192                 break;
 193         case IPT_ICMP_ADMIN_PROHIBITED:
 194                 send_unreach(skb, ICMP_PKT_FILTERED);
 195                 break;
 196         case IPT_TCP_RESET:
 197                 send_reset(skb, hooknum);
 198         case IPT_ICMP_ECHOREPLY:
 199                 /* Doesn't happen. */
 200                 break;
 201         }
 202
 203         return NF_DROP;
 204 }
 205
 206 static bool
 207 reject_tg_check(const char *tablename, const void *e_void,
 208                 const struct xt_target *target, void *targinfo,
 209                 unsigned int hook_mask)
 210 {
 211         const struct ipt_reject_info *rejinfo = targinfo;
 212         const struct ipt_entry *e = e_void;
 213
 214         if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
 215                 printk("ipt_REJECT: ECHOREPLY no longer supported.\n");
 216                 return false;
 217         } else if (rejinfo->with == IPT_TCP_RESET) {
 218                 /* Must specify that it's a TCP packet */
 219                 if (e->ip.proto != IPPROTO_TCP
 220                     || (e->ip.invflags & XT_INV_PROTO)) {
 221                         printk("ipt_REJECT: TCP_RESET invalid for non-tcp\n");
 222                         return false;
 223                 }
 224         }
 225         return true;
 226 }
 227
 228 static struct xt_target reject_tg_reg __read_mostly = {
 229         .name           = "REJECT",
 230         .family         = AF_INET,
 231         .target         = reject_tg,
 232         .targetsize     = sizeof(struct ipt_reject_info),
 233         .table          = "filter",
 234         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
 235                           (1 << NF_INET_LOCAL_OUT),
 236         .checkentry     = reject_tg_check,
 237         .me             = THIS_MODULE,
 238 };
 239
 240 static int __init reject_tg_init(void)
 241 {
 242         return xt_register_target(&reject_tg_reg);
 243 }
 244
 245 static void __exit reject_tg_exit(void)
 246 {
 247         xt_unregister_target(&reject_tg_reg);
 248 }
 249
 250 module_init(reject_tg_init);
 251 module_exit(reject_tg_exit);