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Commit | Line | Data |
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1da177e4 LT |
1 | /* |
2 | * This is a module which is used for rejecting packets. | |
3 | * Added support for customized reject packets (Jozsef Kadlecsik). | |
4 | * Added support for ICMP type-3-code-13 (Maciej Soltysiak). [RFC 1812] | |
5 | */ | |
6 | ||
7 | /* (C) 1999-2001 Paul `Rusty' Russell | |
8 | * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org> | |
9 | * | |
10 | * This program is free software; you can redistribute it and/or modify | |
11 | * it under the terms of the GNU General Public License version 2 as | |
12 | * published by the Free Software Foundation. | |
13 | */ | |
14 | ||
15 | #include <linux/config.h> | |
16 | #include <linux/module.h> | |
17 | #include <linux/skbuff.h> | |
18 | #include <linux/ip.h> | |
19 | #include <linux/udp.h> | |
20 | #include <linux/icmp.h> | |
21 | #include <net/icmp.h> | |
22 | #include <net/ip.h> | |
23 | #include <net/tcp.h> | |
24 | #include <net/route.h> | |
25 | #include <net/dst.h> | |
26 | #include <linux/netfilter_ipv4/ip_tables.h> | |
27 | #include <linux/netfilter_ipv4/ipt_REJECT.h> | |
28 | #ifdef CONFIG_BRIDGE_NETFILTER | |
29 | #include <linux/netfilter_bridge.h> | |
30 | #endif | |
31 | ||
32 | MODULE_LICENSE("GPL"); | |
33 | MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>"); | |
34 | MODULE_DESCRIPTION("iptables REJECT target module"); | |
35 | ||
36 | #if 0 | |
37 | #define DEBUGP printk | |
38 | #else | |
39 | #define DEBUGP(format, args...) | |
40 | #endif | |
41 | ||
42 | static inline struct rtable *route_reverse(struct sk_buff *skb, | |
43 | struct tcphdr *tcph, int hook) | |
44 | { | |
45 | struct iphdr *iph = skb->nh.iph; | |
46 | struct dst_entry *odst; | |
47 | struct flowi fl = {}; | |
48 | struct rtable *rt; | |
49 | ||
50 | /* We don't require ip forwarding to be enabled to be able to | |
51 | * send a RST reply for bridged traffic. */ | |
52 | if (hook != NF_IP_FORWARD | |
53 | #ifdef CONFIG_BRIDGE_NETFILTER | |
54 | || (skb->nf_bridge && skb->nf_bridge->mask & BRNF_BRIDGED) | |
55 | #endif | |
56 | ) { | |
57 | fl.nl_u.ip4_u.daddr = iph->saddr; | |
58 | if (hook == NF_IP_LOCAL_IN) | |
59 | fl.nl_u.ip4_u.saddr = iph->daddr; | |
60 | fl.nl_u.ip4_u.tos = RT_TOS(iph->tos); | |
61 | ||
62 | if (ip_route_output_key(&rt, &fl) != 0) | |
63 | return NULL; | |
64 | } else { | |
65 | /* non-local src, find valid iif to satisfy | |
66 | * rp-filter when calling ip_route_input. */ | |
67 | fl.nl_u.ip4_u.daddr = iph->daddr; | |
68 | if (ip_route_output_key(&rt, &fl) != 0) | |
69 | return NULL; | |
70 | ||
71 | odst = skb->dst; | |
72 | if (ip_route_input(skb, iph->saddr, iph->daddr, | |
73 | RT_TOS(iph->tos), rt->u.dst.dev) != 0) { | |
74 | dst_release(&rt->u.dst); | |
75 | return NULL; | |
76 | } | |
77 | dst_release(&rt->u.dst); | |
78 | rt = (struct rtable *)skb->dst; | |
79 | skb->dst = odst; | |
80 | ||
81 | fl.nl_u.ip4_u.daddr = iph->saddr; | |
82 | fl.nl_u.ip4_u.saddr = iph->daddr; | |
83 | fl.nl_u.ip4_u.tos = RT_TOS(iph->tos); | |
84 | } | |
85 | ||
86 | if (rt->u.dst.error) { | |
87 | dst_release(&rt->u.dst); | |
88 | return NULL; | |
89 | } | |
90 | ||
91 | fl.proto = IPPROTO_TCP; | |
92 | fl.fl_ip_sport = tcph->dest; | |
93 | fl.fl_ip_dport = tcph->source; | |
94 | ||
95 | if (xfrm_lookup((struct dst_entry **)&rt, &fl, NULL, 0)) { | |
96 | dst_release(&rt->u.dst); | |
97 | rt = NULL; | |
98 | } | |
99 | ||
100 | return rt; | |
101 | } | |
102 | ||
103 | /* Send RST reply */ | |
104 | static void send_reset(struct sk_buff *oldskb, int hook) | |
105 | { | |
106 | struct sk_buff *nskb; | |
107 | struct tcphdr _otcph, *oth, *tcph; | |
108 | struct rtable *rt; | |
109 | u_int16_t tmp_port; | |
110 | u_int32_t tmp_addr; | |
111 | int needs_ack; | |
112 | int hh_len; | |
113 | ||
114 | /* IP header checks: fragment. */ | |
115 | if (oldskb->nh.iph->frag_off & htons(IP_OFFSET)) | |
116 | return; | |
117 | ||
118 | oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4, | |
119 | sizeof(_otcph), &_otcph); | |
120 | if (oth == NULL) | |
121 | return; | |
122 | ||
123 | /* No RST for RST. */ | |
124 | if (oth->rst) | |
125 | return; | |
126 | ||
127 | /* FIXME: Check checksum --RR */ | |
128 | if ((rt = route_reverse(oldskb, oth, hook)) == NULL) | |
129 | return; | |
130 | ||
131 | hh_len = LL_RESERVED_SPACE(rt->u.dst.dev); | |
132 | ||
133 | /* We need a linear, writeable skb. We also need to expand | |
134 | headroom in case hh_len of incoming interface < hh_len of | |
135 | outgoing interface */ | |
136 | nskb = skb_copy_expand(oldskb, hh_len, skb_tailroom(oldskb), | |
137 | GFP_ATOMIC); | |
138 | if (!nskb) { | |
139 | dst_release(&rt->u.dst); | |
140 | return; | |
141 | } | |
142 | ||
143 | dst_release(nskb->dst); | |
144 | nskb->dst = &rt->u.dst; | |
145 | ||
146 | /* This packet will not be the same as the other: clear nf fields */ | |
147 | nf_reset(nskb); | |
148 | nskb->nfcache = 0; | |
149 | nskb->nfmark = 0; | |
150 | #ifdef CONFIG_BRIDGE_NETFILTER | |
151 | nf_bridge_put(nskb->nf_bridge); | |
152 | nskb->nf_bridge = NULL; | |
153 | #endif | |
154 | ||
155 | tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl); | |
156 | ||
157 | /* Swap source and dest */ | |
158 | tmp_addr = nskb->nh.iph->saddr; | |
159 | nskb->nh.iph->saddr = nskb->nh.iph->daddr; | |
160 | nskb->nh.iph->daddr = tmp_addr; | |
161 | tmp_port = tcph->source; | |
162 | tcph->source = tcph->dest; | |
163 | tcph->dest = tmp_port; | |
164 | ||
165 | /* Truncate to length (no data) */ | |
166 | tcph->doff = sizeof(struct tcphdr)/4; | |
167 | skb_trim(nskb, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr)); | |
168 | nskb->nh.iph->tot_len = htons(nskb->len); | |
169 | ||
170 | if (tcph->ack) { | |
171 | needs_ack = 0; | |
172 | tcph->seq = oth->ack_seq; | |
173 | tcph->ack_seq = 0; | |
174 | } else { | |
175 | needs_ack = 1; | |
176 | tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin | |
177 | + oldskb->len - oldskb->nh.iph->ihl*4 | |
178 | - (oth->doff<<2)); | |
179 | tcph->seq = 0; | |
180 | } | |
181 | ||
182 | /* Reset flags */ | |
183 | ((u_int8_t *)tcph)[13] = 0; | |
184 | tcph->rst = 1; | |
185 | tcph->ack = needs_ack; | |
186 | ||
187 | tcph->window = 0; | |
188 | tcph->urg_ptr = 0; | |
189 | ||
190 | /* Adjust TCP checksum */ | |
191 | tcph->check = 0; | |
192 | tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr), | |
193 | nskb->nh.iph->saddr, | |
194 | nskb->nh.iph->daddr, | |
195 | csum_partial((char *)tcph, | |
196 | sizeof(struct tcphdr), 0)); | |
197 | ||
198 | /* Adjust IP TTL, DF */ | |
199 | nskb->nh.iph->ttl = MAXTTL; | |
200 | /* Set DF, id = 0 */ | |
201 | nskb->nh.iph->frag_off = htons(IP_DF); | |
202 | nskb->nh.iph->id = 0; | |
203 | ||
204 | /* Adjust IP checksum */ | |
205 | nskb->nh.iph->check = 0; | |
206 | nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph, | |
207 | nskb->nh.iph->ihl); | |
208 | ||
209 | /* "Never happens" */ | |
210 | if (nskb->len > dst_mtu(nskb->dst)) | |
211 | goto free_nskb; | |
212 | ||
213 | nf_ct_attach(nskb, oldskb); | |
214 | ||
215 | NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev, | |
216 | dst_output); | |
217 | return; | |
218 | ||
219 | free_nskb: | |
220 | kfree_skb(nskb); | |
221 | } | |
222 | ||
223 | static inline void send_unreach(struct sk_buff *skb_in, int code) | |
224 | { | |
225 | icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0); | |
226 | } | |
227 | ||
228 | static unsigned int reject(struct sk_buff **pskb, | |
229 | const struct net_device *in, | |
230 | const struct net_device *out, | |
231 | unsigned int hooknum, | |
232 | const void *targinfo, | |
233 | void *userinfo) | |
234 | { | |
235 | const struct ipt_reject_info *reject = targinfo; | |
236 | ||
237 | /* Our naive response construction doesn't deal with IP | |
238 | options, and probably shouldn't try. */ | |
239 | if ((*pskb)->nh.iph->ihl<<2 != sizeof(struct iphdr)) | |
240 | return NF_DROP; | |
241 | ||
242 | /* WARNING: This code causes reentry within iptables. | |
243 | This means that the iptables jump stack is now crap. We | |
244 | must return an absolute verdict. --RR */ | |
245 | switch (reject->with) { | |
246 | case IPT_ICMP_NET_UNREACHABLE: | |
247 | send_unreach(*pskb, ICMP_NET_UNREACH); | |
248 | break; | |
249 | case IPT_ICMP_HOST_UNREACHABLE: | |
250 | send_unreach(*pskb, ICMP_HOST_UNREACH); | |
251 | break; | |
252 | case IPT_ICMP_PROT_UNREACHABLE: | |
253 | send_unreach(*pskb, ICMP_PROT_UNREACH); | |
254 | break; | |
255 | case IPT_ICMP_PORT_UNREACHABLE: | |
256 | send_unreach(*pskb, ICMP_PORT_UNREACH); | |
257 | break; | |
258 | case IPT_ICMP_NET_PROHIBITED: | |
259 | send_unreach(*pskb, ICMP_NET_ANO); | |
260 | break; | |
261 | case IPT_ICMP_HOST_PROHIBITED: | |
262 | send_unreach(*pskb, ICMP_HOST_ANO); | |
263 | break; | |
264 | case IPT_ICMP_ADMIN_PROHIBITED: | |
265 | send_unreach(*pskb, ICMP_PKT_FILTERED); | |
266 | break; | |
267 | case IPT_TCP_RESET: | |
268 | send_reset(*pskb, hooknum); | |
269 | case IPT_ICMP_ECHOREPLY: | |
270 | /* Doesn't happen. */ | |
271 | break; | |
272 | } | |
273 | ||
274 | return NF_DROP; | |
275 | } | |
276 | ||
277 | static int check(const char *tablename, | |
278 | const struct ipt_entry *e, | |
279 | void *targinfo, | |
280 | unsigned int targinfosize, | |
281 | unsigned int hook_mask) | |
282 | { | |
283 | const struct ipt_reject_info *rejinfo = targinfo; | |
284 | ||
285 | if (targinfosize != IPT_ALIGN(sizeof(struct ipt_reject_info))) { | |
286 | DEBUGP("REJECT: targinfosize %u != 0\n", targinfosize); | |
287 | return 0; | |
288 | } | |
289 | ||
290 | /* Only allow these for packet filtering. */ | |
291 | if (strcmp(tablename, "filter") != 0) { | |
292 | DEBUGP("REJECT: bad table `%s'.\n", tablename); | |
293 | return 0; | |
294 | } | |
295 | if ((hook_mask & ~((1 << NF_IP_LOCAL_IN) | |
296 | | (1 << NF_IP_FORWARD) | |
297 | | (1 << NF_IP_LOCAL_OUT))) != 0) { | |
298 | DEBUGP("REJECT: bad hook mask %X\n", hook_mask); | |
299 | return 0; | |
300 | } | |
301 | ||
302 | if (rejinfo->with == IPT_ICMP_ECHOREPLY) { | |
303 | printk("REJECT: ECHOREPLY no longer supported.\n"); | |
304 | return 0; | |
305 | } else if (rejinfo->with == IPT_TCP_RESET) { | |
306 | /* Must specify that it's a TCP packet */ | |
307 | if (e->ip.proto != IPPROTO_TCP | |
308 | || (e->ip.invflags & IPT_INV_PROTO)) { | |
309 | DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n"); | |
310 | return 0; | |
311 | } | |
312 | } | |
313 | ||
314 | return 1; | |
315 | } | |
316 | ||
317 | static struct ipt_target ipt_reject_reg = { | |
318 | .name = "REJECT", | |
319 | .target = reject, | |
320 | .checkentry = check, | |
321 | .me = THIS_MODULE, | |
322 | }; | |
323 | ||
324 | static int __init init(void) | |
325 | { | |
326 | return ipt_register_target(&ipt_reject_reg); | |
327 | } | |
328 | ||
329 | static void __exit fini(void) | |
330 | { | |
331 | ipt_unregister_target(&ipt_reject_reg); | |
332 | } | |
333 | ||
334 | module_init(init); | |
335 | module_exit(fini); |