1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Xtables module for matching the value of the IPv4/IPv6 and TCP ECN bits
4 *
5 * (C) 2002 by Harald Welte <laforge@gnumonks.org>
6 * (C) 2011 Patrick McHardy <kaber@trash.net>
7 */
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9#include <linux/in.h>
10#include <linux/ip.h>
11#include <net/ip.h>
12#include <linux/module.h>
13#include <linux/skbuff.h>
14#include <linux/tcp.h>
15
16#include <linux/netfilter/x_tables.h>
17#include <linux/netfilter/xt_ecn.h>
18#include <linux/netfilter_ipv4/ip_tables.h>
19#include <linux/netfilter_ipv6/ip6_tables.h>
20
21MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
22MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag match");
23MODULE_LICENSE("GPL");
24MODULE_ALIAS("ipt_ecn");
25MODULE_ALIAS("ip6t_ecn");
26
27static bool match_tcp(const struct sk_buff *skb, struct xt_action_param *par)
28{
29 const struct xt_ecn_info *einfo = par->matchinfo;
30 struct tcphdr _tcph;
31 const struct tcphdr *th;
32
33 /* In practice, TCP match does this, so can't fail. But let's
34 * be good citizens.
35 */
36 th = skb_header_pointer(skb, offset: par->thoff, len: sizeof(_tcph), buffer: &_tcph);
37 if (th == NULL)
38 return false;
39
40 if (einfo->operation & XT_ECN_OP_MATCH_ECE) {
41 if (einfo->invert & XT_ECN_OP_MATCH_ECE) {
42 if (th->ece == 1)
43 return false;
44 } else {
45 if (th->ece == 0)
46 return false;
47 }
48 }
49
50 if (einfo->operation & XT_ECN_OP_MATCH_CWR) {
51 if (einfo->invert & XT_ECN_OP_MATCH_CWR) {
52 if (th->cwr == 1)
53 return false;
54 } else {
55 if (th->cwr == 0)
56 return false;
57 }
58 }
59
60 return true;
61}
62
63static inline bool match_ip(const struct sk_buff *skb,
64 const struct xt_ecn_info *einfo)
65{
66 return ((ip_hdr(skb)->tos & XT_ECN_IP_MASK) == einfo->ip_ect) ^
67 !!(einfo->invert & XT_ECN_OP_MATCH_IP);
68}
69
70static bool ecn_mt4(const struct sk_buff *skb, struct xt_action_param *par)
71{
72 const struct xt_ecn_info *info = par->matchinfo;
73
74 if (info->operation & XT_ECN_OP_MATCH_IP && !match_ip(skb, einfo: info))
75 return false;
76
77 if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
78 !match_tcp(skb, par))
79 return false;
80
81 return true;
82}
83
84static int ecn_mt_check4(const struct xt_mtchk_param *par)
85{
86 const struct xt_ecn_info *info = par->matchinfo;
87 const struct ipt_ip *ip = par->entryinfo;
88
89 if (info->operation & XT_ECN_OP_MATCH_MASK)
90 return -EINVAL;
91
92 if (info->invert & XT_ECN_OP_MATCH_MASK)
93 return -EINVAL;
94
95 if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
96 (ip->proto != IPPROTO_TCP || ip->invflags & IPT_INV_PROTO)) {
97 pr_info_ratelimited("cannot match TCP bits for non-tcp packets\n");
98 return -EINVAL;
99 }
100
101 return 0;
102}
103
104static inline bool match_ipv6(const struct sk_buff *skb,
105 const struct xt_ecn_info *einfo)
106{
107 return (((ipv6_hdr(skb)->flow_lbl[0] >> 4) & XT_ECN_IP_MASK) ==
108 einfo->ip_ect) ^
109 !!(einfo->invert & XT_ECN_OP_MATCH_IP);
110}
111
112static bool ecn_mt6(const struct sk_buff *skb, struct xt_action_param *par)
113{
114 const struct xt_ecn_info *info = par->matchinfo;
115
116 if (info->operation & XT_ECN_OP_MATCH_IP && !match_ipv6(skb, einfo: info))
117 return false;
118
119 if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
120 !match_tcp(skb, par))
121 return false;
122
123 return true;
124}
125
126static int ecn_mt_check6(const struct xt_mtchk_param *par)
127{
128 const struct xt_ecn_info *info = par->matchinfo;
129 const struct ip6t_ip6 *ip = par->entryinfo;
130
131 if (info->operation & XT_ECN_OP_MATCH_MASK)
132 return -EINVAL;
133
134 if (info->invert & XT_ECN_OP_MATCH_MASK)
135 return -EINVAL;
136
137 if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
138 (ip->proto != IPPROTO_TCP || ip->invflags & IP6T_INV_PROTO)) {
139 pr_info_ratelimited("cannot match TCP bits for non-tcp packets\n");
140 return -EINVAL;
141 }
142
143 return 0;
144}
145
146static struct xt_match ecn_mt_reg[] __read_mostly = {
147 {
148 .name = "ecn",
149 .family = NFPROTO_IPV4,
150 .match = ecn_mt4,
151 .matchsize = sizeof(struct xt_ecn_info),
152 .checkentry = ecn_mt_check4,
153 .me = THIS_MODULE,
154 },
155 {
156 .name = "ecn",
157 .family = NFPROTO_IPV6,
158 .match = ecn_mt6,
159 .matchsize = sizeof(struct xt_ecn_info),
160 .checkentry = ecn_mt_check6,
161 .me = THIS_MODULE,
162 },
163};
164
165static int __init ecn_mt_init(void)
166{
167 return xt_register_matches(match: ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
168}
169
170static void __exit ecn_mt_exit(void)
171{
172 xt_unregister_matches(match: ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
173}
174
175module_init(ecn_mt_init);
176module_exit(ecn_mt_exit);
177

source code of linux/net/netfilter/xt_ecn.c