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
13 #include <linux/module.h>
14 #include <linux/skbuff.h>
15 #include <linux/ip.h>
16 #include <linux/udp.h>
17 #include <linux/icmp.h>
18 #include <net/icmp.h>
19 #include <net/ip.h>
20 #include <net/tcp.h>
21 #include <net/route.h>
22 #include <net/dst.h>
23 #include <linux/netfilter/x_tables.h>
24 #include <linux/netfilter_ipv4/ip_tables.h>
25 #include <linux/netfilter_ipv4/ipt_REJECT.h>
26 #ifdef CONFIG_BRIDGE_NETFILTER
27 #include <linux/netfilter_bridge.h>
28 #endif
29
30 MODULE_LICENSE("GPL");
31 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
32 MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv4");
33
34 /* Send RST reply */
35 static void send_reset(struct sk_buff *oldskb, int hook)
36 {
37 struct sk_buff *nskb;
38 const struct iphdr *oiph;
39 struct iphdr *niph;
40 const struct tcphdr *oth;
41 struct tcphdr _otcph, *tcph;
42 unsigned int addr_type;
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 /* Check checksum */
58 if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
59 return;
60 oiph = ip_hdr(oldskb);
61
62 nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
63 LL_MAX_HEADER, GFP_ATOMIC);
64 if (!nskb)
65 return;
66
67 skb_reserve(nskb, LL_MAX_HEADER);
68
69 skb_reset_network_header(nskb);
70 niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
71 niph->version = 4;
72 niph->ihl = sizeof(struct iphdr) / 4;
73 niph->tos = 0;
74 niph->id = 0;
75 niph->frag_off = htons(IP_DF);
76 niph->protocol = IPPROTO_TCP;
77 niph->check = 0;
78 niph->saddr = oiph->daddr;
79 niph->daddr = oiph->saddr;
80
81 tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
82 memset(tcph, 0, sizeof(*tcph));
83 tcph->source = oth->dest;
84 tcph->dest = oth->source;
85 tcph->doff = sizeof(struct tcphdr) / 4;
86
87 if (oth->ack)
88 tcph->seq = oth->ack_seq;
89 else {
90 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
91 oldskb->len - ip_hdrlen(oldskb) -
92 (oth->doff << 2));
93 tcph->ack = 1;
94 }
95
96 tcph->rst = 1;
97 tcph->check = tcp_v4_check(sizeof(struct tcphdr),
98 niph->saddr, niph->daddr,
99 csum_partial(tcph,
100 sizeof(struct tcphdr), 0));
101
102 addr_type = RTN_UNSPEC;
103 if (hook != NF_INET_FORWARD
104 #ifdef CONFIG_BRIDGE_NETFILTER
105 || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
106 #endif
107 )
108 addr_type = RTN_LOCAL;
109
110 /* ip_route_me_harder expects skb->dst to be set */
111 skb_dst_set(nskb, dst_clone(skb_dst(oldskb)));
112
113 if (ip_route_me_harder(nskb, addr_type))
114 goto free_nskb;
115
116 niph->ttl = dst_metric(skb_dst(nskb), RTAX_HOPLIMIT);
117 nskb->ip_summed = CHECKSUM_NONE;
118
119 /* "Never happens" */
120 if (nskb->len > dst_mtu(skb_dst(nskb)))
121 goto free_nskb;
122
123 nf_ct_attach(nskb, oldskb);
124
125 ip_local_out(nskb);
126 return;
127
128 free_nskb:
129 kfree_skb(nskb);
130 }
131
132 static inline void send_unreach(struct sk_buff *skb_in, int code)
133 {
134 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
135 }
136
137 static unsigned int
138 reject_tg(struct sk_buff *skb, const struct xt_target_param *par)
139 {
140 const struct ipt_reject_info *reject = par->targinfo;
141
142 /* WARNING: This code causes reentry within iptables.
143 This means that the iptables jump stack is now crap. We
144 must return an absolute verdict. --RR */
145 switch (reject->with) {
146 case IPT_ICMP_NET_UNREACHABLE:
147 send_unreach(skb, ICMP_NET_UNREACH);
148 break;
149 case IPT_ICMP_HOST_UNREACHABLE:
150 send_unreach(skb, ICMP_HOST_UNREACH);
151 break;
152 case IPT_ICMP_PROT_UNREACHABLE:
153 send_unreach(skb, ICMP_PROT_UNREACH);
154 break;
155 case IPT_ICMP_PORT_UNREACHABLE:
156 send_unreach(skb, ICMP_PORT_UNREACH);
157 break;
158 case IPT_ICMP_NET_PROHIBITED:
159 send_unreach(skb, ICMP_NET_ANO);
160 break;
161 case IPT_ICMP_HOST_PROHIBITED:
162 send_unreach(skb, ICMP_HOST_ANO);
163 break;
164 case IPT_ICMP_ADMIN_PROHIBITED:
165 send_unreach(skb, ICMP_PKT_FILTERED);
166 break;
167 case IPT_TCP_RESET:
168 send_reset(skb, par->hooknum);
169 case IPT_ICMP_ECHOREPLY:
170 /* Doesn't happen. */
171 break;
172 }
173
174 return NF_DROP;
175 }
176
177 static bool reject_tg_check(const struct xt_tgchk_param *par)
178 {
179 const struct ipt_reject_info *rejinfo = par->targinfo;
180 const struct ipt_entry *e = par->entryinfo;
181
182 if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
183 printk("ipt_REJECT: ECHOREPLY no longer supported.\n");
184 return false;
185 } else if (rejinfo->with == IPT_TCP_RESET) {
186 /* Must specify that it's a TCP packet */
187 if (e->ip.proto != IPPROTO_TCP
188 || (e->ip.invflags & XT_INV_PROTO)) {
189 printk("ipt_REJECT: TCP_RESET invalid for non-tcp\n");
190 return false;
191 }
192 }
193 return true;
194 }
195
196 static struct xt_target reject_tg_reg __read_mostly = {
197 .name = "REJECT",
198 .family = NFPROTO_IPV4,
199 .target = reject_tg,
200 .targetsize = sizeof(struct ipt_reject_info),
201 .table = "filter",
202 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
203 (1 << NF_INET_LOCAL_OUT),
204 .checkentry = reject_tg_check,
205 .me = THIS_MODULE,
206 };
207
208 static int __init reject_tg_init(void)
209 {
210 return xt_register_target(&reject_tg_reg);
211 }
212
213 static void __exit reject_tg_exit(void)
214 {
215 xt_unregister_target(&reject_tg_reg);
216 }
217
218 module_init(reject_tg_init);
219 module_exit(reject_tg_exit);
220
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