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 skb_dst_set(nskb, dst_clone(skb_dst(oldskb))); 112 113 if (ip_route_me_harder(nskb, addr_type)) 114 goto free_nskb; 115 116 niph->ttl = dst_metric(skb_dst(nskb), RTAX_HOPLIMIT); 117 nskb->ip_summed = CHECKSUM_NONE; 118 119 /* "Never happens" */ 120 if (nskb->len > dst_mtu(skb_dst(nskb))) 121 goto free_nskb; 122 123 nf_ct_attach(nskb, oldskb); 124 125 ip_local_out(nskb); 126 return; 127 128 free_nskb: 129 kfree_skb(nskb); 130 } 131 132 static inline void send_unreach(struct sk_buff *skb_in, int code) 133 { 134 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0); 135 } 136 137 static unsigned int 138 reject_tg(struct sk_buff *skb, const struct xt_target_param *par) 139 { 140 const struct ipt_reject_info *reject = par->targinfo; 141 142 /* WARNING: This code causes reentry within iptables. 143 This means that the iptables jump stack is now crap. We 144 must return an absolute verdict. --RR */ 145 switch (reject->with) { 146 case IPT_ICMP_NET_UNREACHABLE: 147 send_unreach(skb, ICMP_NET_UNREACH); 148 break; 149 case IPT_ICMP_HOST_UNREACHABLE: 150 send_unreach(skb, ICMP_HOST_UNREACH); 151 break; 152 case IPT_ICMP_PROT_UNREACHABLE: 153 send_unreach(skb, ICMP_PROT_UNREACH); 154 break; 155 case IPT_ICMP_PORT_UNREACHABLE: 156 send_unreach(skb, ICMP_PORT_UNREACH); 157 break; 158 case IPT_ICMP_NET_PROHIBITED: 159 send_unreach(skb, ICMP_NET_ANO); 160 break; 161 case IPT_ICMP_HOST_PROHIBITED: 162 send_unreach(skb, ICMP_HOST_ANO); 163 break; 164 case IPT_ICMP_ADMIN_PROHIBITED: 165 send_unreach(skb, ICMP_PKT_FILTERED); 166 break; 167 case IPT_TCP_RESET: 168 send_reset(skb, par->hooknum); 169 case IPT_ICMP_ECHOREPLY: 170 /* Doesn't happen. */ 171 break; 172 } 173 174 return NF_DROP; 175 } 176 177 static bool reject_tg_check(const struct xt_tgchk_param *par) 178 { 179 const struct ipt_reject_info *rejinfo = par->targinfo; 180 const struct ipt_entry *e = par->entryinfo; 181 182 if (rejinfo->with == IPT_ICMP_ECHOREPLY) { 183 printk("ipt_REJECT: ECHOREPLY no longer supported.\n"); 184 return false; 185 } else if (rejinfo->with == IPT_TCP_RESET) { 186 /* Must specify that it's a TCP packet */ 187 if (e->ip.proto != IPPROTO_TCP || 188 (e->ip.invflags & XT_INV_PROTO)) { 189 printk("ipt_REJECT: TCP_RESET invalid for non-tcp\n"); 190 return false; 191 } 192 } 193 return true; 194 } 195 196 static struct xt_target reject_tg_reg __read_mostly = { 197 .name = "REJECT", 198 .family = NFPROTO_IPV4, 199 .target = reject_tg, 200 .targetsize = sizeof(struct ipt_reject_info), 201 .table = "filter", 202 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) | 203 (1 << NF_INET_LOCAL_OUT), 204 .checkentry = reject_tg_check, 205 .me = THIS_MODULE, 206 }; 207 208 static int __init reject_tg_init(void) 209 { 210 return xt_register_target(&reject_tg_reg); 211 } 212 213 static void __exit reject_tg_exit(void) 214 { 215 xt_unregister_target(&reject_tg_reg); 216 } 217 218 module_init(reject_tg_init); 219 module_exit(reject_tg_exit); 220