1 /* IP tables module for matching the value of the IPv4 and TCP ECN bits
2 *
3 * (C) 2002 by Harald Welte <laforge@gnumonks.org>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License version 2 as
7 * published by the Free Software Foundation.
8 */
9
10 #include <linux/in.h>
11 #include <linux/ip.h>
12 #include <net/ip.h>
13 #include <linux/module.h>
14 #include <linux/skbuff.h>
15 #include <linux/tcp.h>
16
17 #include <linux/netfilter/x_tables.h>
18 #include <linux/netfilter_ipv4/ip_tables.h>
19 #include <linux/netfilter_ipv4/ipt_ecn.h>
20
21 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
22 MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag match for IPv4");
23 MODULE_LICENSE("GPL");
24
25 static inline bool match_ip(const struct sk_buff *skb,
26 const struct ipt_ecn_info *einfo)
27 {
28 return (ip_hdr(skb)->tos & IPT_ECN_IP_MASK) == einfo->ip_ect;
29 }
30
31 static inline bool match_tcp(const struct sk_buff *skb,
32 const struct ipt_ecn_info *einfo,
33 bool *hotdrop)
34 {
35 struct tcphdr _tcph;
36 const struct tcphdr *th;
37
38 /* In practice, TCP match does this, so can't fail. But let's
39 * be good citizens.
40 */
41 th = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
42 if (th == NULL) {
43 *hotdrop = false;
44 return false;
45 }
46
47 if (einfo->operation & IPT_ECN_OP_MATCH_ECE) {
48 if (einfo->invert & IPT_ECN_OP_MATCH_ECE) {
49 if (th->ece == 1)
50 return false;
51 } else {
52 if (th->ece == 0)
53 return false;
54 }
55 }
56
57 if (einfo->operation & IPT_ECN_OP_MATCH_CWR) {
58 if (einfo->invert & IPT_ECN_OP_MATCH_CWR) {
59 if (th->cwr == 1)
60 return false;
61 } else {
62 if (th->cwr == 0)
63 return false;
64 }
65 }
66
67 return true;
68 }
69
70 static bool
71 ecn_mt(const struct sk_buff *skb, const struct net_device *in,
72 const struct net_device *out, const struct xt_match *match,
73 const void *matchinfo, int offset, unsigned int protoff, bool *hotdrop)
74 {
75 const struct ipt_ecn_info *info = matchinfo;
76
77 if (info->operation & IPT_ECN_OP_MATCH_IP)
78 if (!match_ip(skb, info))
79 return false;
80
81 if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
82 if (ip_hdr(skb)->protocol != IPPROTO_TCP)
83 return false;
84 if (!match_tcp(skb, info, hotdrop))
85 return false;
86 }
87
88 return true;
89 }
90
91 static bool
92 ecn_mt_check(const char *tablename, const void *ip_void,
93 const struct xt_match *match, void *matchinfo,
94 unsigned int hook_mask)
95 {
96 const struct ipt_ecn_info *info = matchinfo;
97 const struct ipt_ip *ip = ip_void;
98
99 if (info->operation & IPT_ECN_OP_MATCH_MASK)
100 return false;
101
102 if (info->invert & IPT_ECN_OP_MATCH_MASK)
103 return false;
104
105 if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)
106 && ip->proto != IPPROTO_TCP) {
107 printk(KERN_WARNING "ipt_ecn: can't match TCP bits in rule for"
108 " non-tcp packets\n");
109 return false;
110 }
111
112 return true;
113 }
114
115 static struct xt_match ecn_mt_reg __read_mostly = {
116 .name = "ecn",
117 .family = AF_INET,
118 .match = ecn_mt,
119 .matchsize = sizeof(struct ipt_ecn_info),
120 .checkentry = ecn_mt_check,
121 .me = THIS_MODULE,
122 };
123
124 static int __init ecn_mt_init(void)
125 {
126 return xt_register_match(&ecn_mt_reg);
127 }
128
129 static void __exit ecn_mt_exit(void)
130 {
131 xt_unregister_match(&ecn_mt_reg);
132 }
133
134 module_init(ecn_mt_init);
135 module_exit(ecn_mt_exit);
136
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