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); 218