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); 214