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 * Copyright (c) 2005-2007 Patrick McHardy <kaber@trash.net>
11 *
12 * Based on net/ipv4/netfilter/ipt_REJECT.c
13 *
14 * This program is free software; you can redistribute it and/or
15 * modify it under the terms of the GNU General Public License
16 * as published by the Free Software Foundation; either version
17 * 2 of the License, or (at your option) any later version.
18 */
19 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
20
21 #include <linux/gfp.h>
22 #include <linux/module.h>
23 #include <linux/skbuff.h>
24 #include <linux/icmpv6.h>
25 #include <linux/netdevice.h>
26 #include <net/ipv6.h>
27 #include <net/tcp.h>
28 #include <net/icmp.h>
29 #include <net/ip6_checksum.h>
30 #include <net/ip6_fib.h>
31 #include <net/ip6_route.h>
32 #include <net/flow.h>
33 #include <linux/netfilter/x_tables.h>
34 #include <linux/netfilter_ipv6/ip6_tables.h>
35 #include <linux/netfilter_ipv6/ip6t_REJECT.h>
36
37 MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
38 MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv6");
39 MODULE_LICENSE("GPL");
40
41 /* Send RST reply */
42 static void send_reset(struct net *net, struct sk_buff *oldskb)
43 {
44 struct sk_buff *nskb;
45 struct tcphdr otcph, *tcph;
46 unsigned int otcplen, hh_len;
47 int tcphoff, needs_ack;
48 const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
49 struct ipv6hdr *ip6h;
50 #define DEFAULT_TOS_VALUE 0x0U
51 const __u8 tclass = DEFAULT_TOS_VALUE;
52 struct dst_entry *dst = NULL;
53 u8 proto;
54 __be16 frag_off;
55 struct flowi6 fl6;
56
57 if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
58 (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
59 pr_debug("addr is not unicast.\n");
60 return;
61 }
62
63 proto = oip6h->nexthdr;
64 tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto, &frag_off);
65
66 if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
67 pr_debug("Cannot get TCP header.\n");
68 return;
69 }
70
71 otcplen = oldskb->len - tcphoff;
72
73 /* IP header checks: fragment, too short. */
74 if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
75 pr_debug("proto(%d) != IPPROTO_TCP, "
76 "or too short. otcplen = %d\n",
77 proto, otcplen);
78 return;
79 }
80
81 if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
82 BUG();
83
84 /* No RST for RST. */
85 if (otcph.rst) {
86 pr_debug("RST is set\n");
87 return;
88 }
89
90 /* Check checksum. */
91 if (csum_ipv6_magic(&oip6h->saddr, &oip6h->daddr, otcplen, IPPROTO_TCP,
92 skb_checksum(oldskb, tcphoff, otcplen, 0))) {
93 pr_debug("TCP checksum is invalid\n");
94 return;
95 }
96
97 memset(&fl6, 0, sizeof(fl6));
98 fl6.flowi6_proto = IPPROTO_TCP;
99 fl6.saddr = oip6h->daddr;
100 fl6.daddr = oip6h->saddr;
101 fl6.fl6_sport = otcph.dest;
102 fl6.fl6_dport = otcph.source;
103 security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
104 dst = ip6_route_output(net, NULL, &fl6);
105 if (dst == NULL || dst->error) {
106 dst_release(dst);
107 return;
108 }
109 dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
110 if (IS_ERR(dst))
111 return;
112
113 hh_len = (dst->dev->hard_header_len + 15)&~15;
114 nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
115 + sizeof(struct tcphdr) + dst->trailer_len,
116 GFP_ATOMIC);
117
118 if (!nskb) {
119 net_dbg_ratelimited("cannot alloc skb\n");
120 dst_release(dst);
121 return;
122 }
123
124 skb_dst_set(nskb, dst);
125
126 skb_reserve(nskb, hh_len + dst->header_len);
127
128 skb_put(nskb, sizeof(struct ipv6hdr));
129 skb_reset_network_header(nskb);
130 ip6h = ipv6_hdr(nskb);
131 ip6_flow_hdr(ip6h, tclass, 0);
132 ip6h->hop_limit = ip6_dst_hoplimit(dst);
133 ip6h->nexthdr = IPPROTO_TCP;
134 ip6h->saddr = oip6h->daddr;
135 ip6h->daddr = oip6h->saddr;
136
137 skb_reset_transport_header(nskb);
138 tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
139 /* Truncate to length (no data) */
140 tcph->doff = sizeof(struct tcphdr)/4;
141 tcph->source = otcph.dest;
142 tcph->dest = otcph.source;
143
144 if (otcph.ack) {
145 needs_ack = 0;
146 tcph->seq = otcph.ack_seq;
147 tcph->ack_seq = 0;
148 } else {
149 needs_ack = 1;
150 tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
151 + otcplen - (otcph.doff<<2));
152 tcph->seq = 0;
153 }
154
155 /* Reset flags */
156 ((u_int8_t *)tcph)[13] = 0;
157 tcph->rst = 1;
158 tcph->ack = needs_ack;
159 tcph->window = 0;
160 tcph->urg_ptr = 0;
161 tcph->check = 0;
162
163 /* Adjust TCP checksum */
164 tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
165 &ipv6_hdr(nskb)->daddr,
166 sizeof(struct tcphdr), IPPROTO_TCP,
167 csum_partial(tcph,
168 sizeof(struct tcphdr), 0));
169
170 nf_ct_attach(nskb, oldskb);
171
172 #ifdef CONFIG_BRIDGE_NETFILTER
173 /* If we use ip6_local_out for bridged traffic, the MAC source on
174 * the RST will be ours, instead of the destination's. This confuses
175 * some routers/firewalls, and they drop the packet. So we need to
176 * build the eth header using the original destination's MAC as the
177 * source, and send the RST packet directly.
178 */
179 if (oldskb->nf_bridge) {
180 struct ethhdr *oeth = eth_hdr(oldskb);
181 nskb->dev = oldskb->nf_bridge->physindev;
182 nskb->protocol = htons(ETH_P_IPV6);
183 ip6h->payload_len = htons(sizeof(struct tcphdr));
184 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
185 oeth->h_source, oeth->h_dest, nskb->len) < 0)
186 return;
187 dev_queue_xmit(nskb);
188 } else
189 #endif
190 ip6_local_out(nskb);
191 }
192
193 static inline void
194 send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
195 unsigned int hooknum)
196 {
197 if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
198 skb_in->dev = net->loopback_dev;
199
200 icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
201 }
202
203 static unsigned int
204 reject_tg6(struct sk_buff *skb, const struct xt_action_param *par)
205 {
206 const struct ip6t_reject_info *reject = par->targinfo;
207 struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
208
209 pr_debug("%s: medium point\n", __func__);
210 switch (reject->with) {
211 case IP6T_ICMP6_NO_ROUTE:
212 send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
213 break;
214 case IP6T_ICMP6_ADM_PROHIBITED:
215 send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
216 break;
217 case IP6T_ICMP6_NOT_NEIGHBOUR:
218 send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
219 break;
220 case IP6T_ICMP6_ADDR_UNREACH:
221 send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
222 break;
223 case IP6T_ICMP6_PORT_UNREACH:
224 send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
225 break;
226 case IP6T_ICMP6_ECHOREPLY:
227 /* Do nothing */
228 break;
229 case IP6T_TCP_RESET:
230 send_reset(net, skb);
231 break;
232 default:
233 net_info_ratelimited("case %u not handled yet\n", reject->with);
234 break;
235 }
236
237 return NF_DROP;
238 }
239
240 static int reject_tg6_check(const struct xt_tgchk_param *par)
241 {
242 const struct ip6t_reject_info *rejinfo = par->targinfo;
243 const struct ip6t_entry *e = par->entryinfo;
244
245 if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
246 pr_info("ECHOREPLY is not supported.\n");
247 return -EINVAL;
248 } else if (rejinfo->with == IP6T_TCP_RESET) {
249 /* Must specify that it's a TCP packet */
250 if (e->ipv6.proto != IPPROTO_TCP ||
251 (e->ipv6.invflags & XT_INV_PROTO)) {
252 pr_info("TCP_RESET illegal for non-tcp\n");
253 return -EINVAL;
254 }
255 }
256 return 0;
257 }
258
259 static struct xt_target reject_tg6_reg __read_mostly = {
260 .name = "REJECT",
261 .family = NFPROTO_IPV6,
262 .target = reject_tg6,
263 .targetsize = sizeof(struct ip6t_reject_info),
264 .table = "filter",
265 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
266 (1 << NF_INET_LOCAL_OUT),
267 .checkentry = reject_tg6_check,
268 .me = THIS_MODULE
269 };
270
271 static int __init reject_tg6_init(void)
272 {
273 return xt_register_target(&reject_tg6_reg);
274 }
275
276 static void __exit reject_tg6_exit(void)
277 {
278 xt_unregister_target(&reject_tg6_reg);
279 }
280
281 module_init(reject_tg6_init);
282 module_exit(reject_tg6_exit);
283
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