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
match_ip(const struct sk_buff * skb,const struct ipt_ecn_info * einfo)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
match_tcp(const struct sk_buff * skb,const struct ipt_ecn_info * einfo,bool * hotdrop)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
ecn_mt(const struct sk_buff * skb,const struct xt_match_param * par)70 static bool ecn_mt(const struct sk_buff *skb, const struct xt_match_param *par)
71 {
72 const struct ipt_ecn_info *info = par->matchinfo;
73
74 if (info->operation & IPT_ECN_OP_MATCH_IP)
75 if (!match_ip(skb, info))
76 return false;
77
78 if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
79 if (ip_hdr(skb)->protocol != IPPROTO_TCP)
80 return false;
81 if (!match_tcp(skb, info, par->hotdrop))
82 return false;
83 }
84
85 return true;
86 }
87
ecn_mt_check(const struct xt_mtchk_param * par)88 static bool ecn_mt_check(const struct xt_mtchk_param *par)
89 {
90 const struct ipt_ecn_info *info = par->matchinfo;
91 const struct ipt_ip *ip = par->entryinfo;
92
93 if (info->operation & IPT_ECN_OP_MATCH_MASK)
94 return false;
95
96 if (info->invert & IPT_ECN_OP_MATCH_MASK)
97 return false;
98
99 if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)
100 && ip->proto != IPPROTO_TCP) {
101 printk(KERN_WARNING "ipt_ecn: can't match TCP bits in rule for"
102 " non-tcp packets\n");
103 return false;
104 }
105
106 return true;
107 }
108
109 static struct xt_match ecn_mt_reg __read_mostly = {
110 .name = "ecn",
111 .family = NFPROTO_IPV4,
112 .match = ecn_mt,
113 .matchsize = sizeof(struct ipt_ecn_info),
114 .checkentry = ecn_mt_check,
115 .me = THIS_MODULE,
116 };
117
ecn_mt_init(void)118 static int __init ecn_mt_init(void)
119 {
120 return xt_register_match(&ecn_mt_reg);
121 }
122
ecn_mt_exit(void)123 static void __exit ecn_mt_exit(void)
124 {
125 xt_unregister_match(&ecn_mt_reg);
126 }
127
128 module_init(ecn_mt_init);
129 module_exit(ecn_mt_exit);
130