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 */
send_reset(struct sk_buff * oldskb,int hook)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 tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
85 memset(tcph, 0, sizeof(*tcph));
86 tcph->source = oth->dest;
87 tcph->dest = oth->source;
88 tcph->doff = sizeof(struct tcphdr) / 4;
89
90 if (oth->ack)
91 tcph->seq = oth->ack_seq;
92 else {
93 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
94 oldskb->len - ip_hdrlen(oldskb) -
95 (oth->doff << 2));
96 tcph->ack = 1;
97 }
98
99 tcph->rst = 1;
100 tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
101 niph->daddr, 0);
102 nskb->ip_summed = CHECKSUM_PARTIAL;
103 nskb->csum_start = (unsigned char *)tcph - nskb->head;
104 nskb->csum_offset = offsetof(struct tcphdr, check);
105
106 /* ip_route_me_harder expects skb->dst to be set */
107 skb_dst_set_noref(nskb, skb_dst(oldskb));
108
109 nskb->protocol = htons(ETH_P_IP);
110 if (ip_route_me_harder(nskb, RTN_UNSPEC))
111 goto free_nskb;
112
113 niph->ttl = ip4_dst_hoplimit(skb_dst(nskb));
114
115 /* "Never happens" */
116 if (nskb->len > dst_mtu(skb_dst(nskb)))
117 goto free_nskb;
118
119 nf_ct_attach(nskb, oldskb);
120
121 ip_local_out(nskb);
122 return;
123
124 free_nskb:
125 kfree_skb(nskb);
126 }
127
send_unreach(struct sk_buff * skb_in,int code)128 static inline void send_unreach(struct sk_buff *skb_in, int code)
129 {
130 icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
131 }
132
133 static unsigned int
reject_tg(struct sk_buff * skb,const struct xt_action_param * par)134 reject_tg(struct sk_buff *skb, const struct xt_action_param *par)
135 {
136 const struct ipt_reject_info *reject = par->targinfo;
137
138 switch (reject->with) {
139 case IPT_ICMP_NET_UNREACHABLE:
140 send_unreach(skb, ICMP_NET_UNREACH);
141 break;
142 case IPT_ICMP_HOST_UNREACHABLE:
143 send_unreach(skb, ICMP_HOST_UNREACH);
144 break;
145 case IPT_ICMP_PROT_UNREACHABLE:
146 send_unreach(skb, ICMP_PROT_UNREACH);
147 break;
148 case IPT_ICMP_PORT_UNREACHABLE:
149 send_unreach(skb, ICMP_PORT_UNREACH);
150 break;
151 case IPT_ICMP_NET_PROHIBITED:
152 send_unreach(skb, ICMP_NET_ANO);
153 break;
154 case IPT_ICMP_HOST_PROHIBITED:
155 send_unreach(skb, ICMP_HOST_ANO);
156 break;
157 case IPT_ICMP_ADMIN_PROHIBITED:
158 send_unreach(skb, ICMP_PKT_FILTERED);
159 break;
160 case IPT_TCP_RESET:
161 send_reset(skb, par->hooknum);
162 case IPT_ICMP_ECHOREPLY:
163 /* Doesn't happen. */
164 break;
165 }
166
167 return NF_DROP;
168 }
169
reject_tg_check(const struct xt_tgchk_param * par)170 static int reject_tg_check(const struct xt_tgchk_param *par)
171 {
172 const struct ipt_reject_info *rejinfo = par->targinfo;
173 const struct ipt_entry *e = par->entryinfo;
174
175 if (rejinfo->with == IPT_ICMP_ECHOREPLY) {
176 pr_info("ECHOREPLY no longer supported.\n");
177 return -EINVAL;
178 } else if (rejinfo->with == IPT_TCP_RESET) {
179 /* Must specify that it's a TCP packet */
180 if (e->ip.proto != IPPROTO_TCP ||
181 (e->ip.invflags & XT_INV_PROTO)) {
182 pr_info("TCP_RESET invalid for non-tcp\n");
183 return -EINVAL;
184 }
185 }
186 return 0;
187 }
188
189 static struct xt_target reject_tg_reg __read_mostly = {
190 .name = "REJECT",
191 .family = NFPROTO_IPV4,
192 .target = reject_tg,
193 .targetsize = sizeof(struct ipt_reject_info),
194 .table = "filter",
195 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
196 (1 << NF_INET_LOCAL_OUT),
197 .checkentry = reject_tg_check,
198 .me = THIS_MODULE,
199 };
200
reject_tg_init(void)201 static int __init reject_tg_init(void)
202 {
203 return xt_register_target(&reject_tg_reg);
204 }
205
reject_tg_exit(void)206 static void __exit reject_tg_exit(void)
207 {
208 xt_unregister_target(&reject_tg_reg);
209 }
210
211 module_init(reject_tg_init);
212 module_exit(reject_tg_exit);
213