1 /*
2 * IP6 tables REJECT target module
3 * Linux INET6 implementation
4 *
5 * Copyright (C)2003 USAGI/WIDE Project
6 *
7 * Authors:
8 * Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>
9 *
10 * Based on net/ipv4/netfilter/ipt_REJECT.c
11 *
12 * This program is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU General Public License
14 * as published by the Free Software Foundation; either version
15 * 2 of the License, or (at your option) any later version.
16 */
17 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
18
19 #include <linux/gfp.h>
20 #include <linux/module.h>
21 #include <linux/skbuff.h>
22 #include <linux/icmpv6.h>
23 #include <linux/netdevice.h>
24 #include <net/ipv6.h>
25 #include <net/tcp.h>
26 #include <net/icmp.h>
27 #include <net/ip6_checksum.h>
28 #include <net/ip6_fib.h>
29 #include <net/ip6_route.h>
30 #include <net/flow.h>
31 #include <linux/netfilter/x_tables.h>
32 #include <linux/netfilter_ipv6/ip6_tables.h>
33 #include <linux/netfilter_ipv6/ip6t_REJECT.h>
34
35 MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
36 MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv6");
37 MODULE_LICENSE("GPL");
38
39 /* Send RST reply */
send_reset(struct net * net,struct sk_buff * oldskb)40 static void send_reset(struct net *net, struct sk_buff *oldskb)
41 {
42 struct sk_buff *nskb;
43 struct tcphdr otcph, *tcph;
44 unsigned int otcplen, hh_len;
45 int tcphoff, needs_ack;
46 const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
47 struct ipv6hdr *ip6h;
48 #define DEFAULT_TOS_VALUE 0x0U
49 const __u8 tclass = DEFAULT_TOS_VALUE;
50 struct dst_entry *dst = NULL;
51 u8 proto;
52 __be16 frag_off;
53 struct flowi6 fl6;
54
55 if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
56 (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
57 pr_debug("addr is not unicast.\n");
58 return;
59 }
60
61 proto = oip6h->nexthdr;
62 tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto, &frag_off);
63
64 if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
65 pr_debug("Cannot get TCP header.\n");
66 return;
67 }
68
69 otcplen = oldskb->len - tcphoff;
70
71 /* IP header checks: fragment, too short. */
72 if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
73 pr_debug("proto(%d) != IPPROTO_TCP, "
74 "or too short. otcplen = %d\n",
75 proto, otcplen);
76 return;
77 }
78
79 if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
80 BUG();
81
82 /* No RST for RST. */
83 if (otcph.rst) {
84 pr_debug("RST is set\n");
85 return;
86 }
87
88 /* Check checksum. */
89 if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
90 skb_checksum(oldskb, tcphoff, otcplen, 0))) {
91 pr_debug("TCP checksum is invalid\n");
92 return;
93 }
94
95 memset(&fl6, 0, sizeof(fl6));
96 fl6.flowi6_proto = IPPROTO_TCP;
97 fl6.saddr = oip6h->daddr;
98 fl6.daddr = oip6h->saddr;
99 fl6.fl6_sport = otcph.dest;
100 fl6.fl6_dport = otcph.source;
101 security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
102 dst = ip6_route_output(net, NULL, &fl6);
103 if (dst == NULL || dst->error) {
104 dst_release(dst);
105 return;
106 }
107 dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
108 if (IS_ERR(dst))
109 return;
110
111 hh_len = (dst->dev->hard_header_len + 15)&~15;
112 nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
113 + sizeof(struct tcphdr) + dst->trailer_len,
114 GFP_ATOMIC);
115
116 if (!nskb) {
117 if (net_ratelimit())
118 pr_debug("cannot alloc skb\n");
119 dst_release(dst);
120 return;
121 }
122
123 skb_dst_set(nskb, dst);
124
125 skb_reserve(nskb, hh_len + dst->header_len);
126
127 skb_put(nskb, sizeof(struct ipv6hdr));
128 skb_reset_network_header(nskb);
129 ip6h = ipv6_hdr(nskb);
130 *(__be32 *)ip6h = htonl(0x60000000 | (tclass << 20));
131 ip6h->hop_limit = ip6_dst_hoplimit(dst);
132 ip6h->nexthdr = IPPROTO_TCP;
133 ip6h->saddr = oip6h->daddr;
134 ip6h->daddr = oip6h->saddr;
135
136 tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
137 /* Truncate to length (no data) */
138 tcph->doff = sizeof(struct tcphdr)/4;
139 tcph->source = otcph.dest;
140 tcph->dest = otcph.source;
141
142 if (otcph.ack) {
143 needs_ack = 0;
144 tcph->seq = otcph.ack_seq;
145 tcph->ack_seq = 0;
146 } else {
147 needs_ack = 1;
148 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
149 + otcplen - (otcph.doff<<2));
150 tcph->seq = 0;
151 }
152
153 /* Reset flags */
154 ((u_int8_t *)tcph)[13] = 0;
155 tcph->rst = 1;
156 tcph->ack = needs_ack;
157 tcph->window = 0;
158 tcph->urg_ptr = 0;
159 tcph->check = 0;
160
161 /* Adjust TCP checksum */
162 tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
163 &ipv6_hdr(nskb)->daddr,
164 sizeof(struct tcphdr), IPPROTO_TCP,
165 csum_partial(tcph,
166 sizeof(struct tcphdr), 0));
167
168 nf_ct_attach(nskb, oldskb);
169
170 ip6_local_out(nskb);
171 }
172
173 static inline void
send_unreach(struct net * net,struct sk_buff * skb_in,unsigned char code,unsigned int hooknum)174 send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
175 unsigned int hooknum)
176 {
177 if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
178 skb_in->dev = net->loopback_dev;
179
180 icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
181 }
182
183 static unsigned int
reject_tg6(struct sk_buff * skb,const struct xt_action_param * par)184 reject_tg6(struct sk_buff *skb, const struct xt_action_param *par)
185 {
186 const struct ip6t_reject_info *reject = par->targinfo;
187 struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
188
189 pr_debug("%s: medium point\n", __func__);
190 switch (reject->with) {
191 case IP6T_ICMP6_NO_ROUTE:
192 send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
193 break;
194 case IP6T_ICMP6_ADM_PROHIBITED:
195 send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
196 break;
197 case IP6T_ICMP6_NOT_NEIGHBOUR:
198 send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
199 break;
200 case IP6T_ICMP6_ADDR_UNREACH:
201 send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
202 break;
203 case IP6T_ICMP6_PORT_UNREACH:
204 send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
205 break;
206 case IP6T_ICMP6_ECHOREPLY:
207 /* Do nothing */
208 break;
209 case IP6T_TCP_RESET:
210 send_reset(net, skb);
211 break;
212 default:
213 if (net_ratelimit())
214 pr_info("case %u not handled yet\n", reject->with);
215 break;
216 }
217
218 return NF_DROP;
219 }
220
reject_tg6_check(const struct xt_tgchk_param * par)221 static int reject_tg6_check(const struct xt_tgchk_param *par)
222 {
223 const struct ip6t_reject_info *rejinfo = par->targinfo;
224 const struct ip6t_entry *e = par->entryinfo;
225
226 if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
227 pr_info("ECHOREPLY is not supported.\n");
228 return -EINVAL;
229 } else if (rejinfo->with == IP6T_TCP_RESET) {
230 /* Must specify that it's a TCP packet */
231 if (e->ipv6.proto != IPPROTO_TCP ||
232 (e->ipv6.invflags & XT_INV_PROTO)) {
233 pr_info("TCP_RESET illegal for non-tcp\n");
234 return -EINVAL;
235 }
236 }
237 return 0;
238 }
239
240 static struct xt_target reject_tg6_reg __read_mostly = {
241 .name = "REJECT",
242 .family = NFPROTO_IPV6,
243 .target = reject_tg6,
244 .targetsize = sizeof(struct ip6t_reject_info),
245 .table = "filter",
246 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
247 (1 << NF_INET_LOCAL_OUT),
248 .checkentry = reject_tg6_check,
249 .me = THIS_MODULE
250 };
251
reject_tg6_init(void)252 static int __init reject_tg6_init(void)
253 {
254 return xt_register_target(&reject_tg6_reg);
255 }
256
reject_tg6_exit(void)257 static void __exit reject_tg6_exit(void)
258 {
259 xt_unregister_target(&reject_tg6_reg);
260 }
261
262 module_init(reject_tg6_init);
263 module_exit(reject_tg6_exit);
264