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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 <[email protected]>
6 * (C) 2011 Patrick McHardy <[email protected]>
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 <[email protected]>");
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 /* this is fine for IPv6 as ecn_mt_check6() enforces -p tcp */
34 if (par->fragoff)
35 return false;
36
37 /* In practice, TCP match does this, so can't fail. But let's
38 * be good citizens.
39 */
40 th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
41 if (th == NULL)
42 return false;
43
44 if (einfo->operation & XT_ECN_OP_MATCH_ECE) {
45 if (einfo->invert & XT_ECN_OP_MATCH_ECE) {
46 if (th->ece == 1)
47 return false;
48 } else {
49 if (th->ece == 0)
50 return false;
51 }
52 }
53
54 if (einfo->operation & XT_ECN_OP_MATCH_CWR) {
55 if (einfo->invert & XT_ECN_OP_MATCH_CWR) {
56 if (th->cwr == 1)
57 return false;
58 } else {
59 if (th->cwr == 0)
60 return false;
61 }
62 }
63
64 return true;
65}
66
67static inline bool match_ip(const struct sk_buff *skb,
68 const struct xt_ecn_info *einfo)
69{
70 return ((ip_hdr(skb)->tos & XT_ECN_IP_MASK) == einfo->ip_ect) ^
71 !!(einfo->invert & XT_ECN_OP_MATCH_IP);
72}
73
74static bool ecn_mt4(const struct sk_buff *skb, struct xt_action_param *par)
75{
76 const struct xt_ecn_info *info = par->matchinfo;
77
78 if (info->operation & XT_ECN_OP_MATCH_IP && !match_ip(skb, info))
79 return false;
80
81 if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
82 !match_tcp(skb, par))
83 return false;
84
85 return true;
86}
87
88static int ecn_mt_check4(const struct xt_mtchk_param *par)
89{
90 const struct xt_ecn_info *info = par->matchinfo;
91 const struct ipt_ip *ip = par->entryinfo;
92
93 if (info->operation & XT_ECN_OP_MATCH_MASK)
94 return -EINVAL;
95
96 if (info->invert & XT_ECN_OP_MATCH_MASK)
97 return -EINVAL;
98
99 if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
100 (ip->proto != IPPROTO_TCP || ip->invflags & IPT_INV_PROTO)) {
101 pr_info_ratelimited("cannot match TCP bits for non-tcp packets\n");
102 return -EINVAL;
103 }
104
105 return 0;
106}
107
108static inline bool match_ipv6(const struct sk_buff *skb,
109 const struct xt_ecn_info *einfo)
110{
111 return (((ipv6_hdr(skb)->flow_lbl[0] >> 4) & XT_ECN_IP_MASK) ==
112 einfo->ip_ect) ^
113 !!(einfo->invert & XT_ECN_OP_MATCH_IP);
114}
115
116static bool ecn_mt6(const struct sk_buff *skb, struct xt_action_param *par)
117{
118 const struct xt_ecn_info *info = par->matchinfo;
119
120 if (info->operation & XT_ECN_OP_MATCH_IP && !match_ipv6(skb, info))
121 return false;
122
123 if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
124 !match_tcp(skb, par))
125 return false;
126
127 return true;
128}
129
130static int ecn_mt_check6(const struct xt_mtchk_param *par)
131{
132 const struct xt_ecn_info *info = par->matchinfo;
133 const struct ip6t_ip6 *ip = par->entryinfo;
134
135 if (info->operation & XT_ECN_OP_MATCH_MASK)
136 return -EINVAL;
137
138 if (info->invert & XT_ECN_OP_MATCH_MASK)
139 return -EINVAL;
140
141 if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
142 (ip->proto != IPPROTO_TCP || ip->invflags & IP6T_INV_PROTO)) {
143 pr_info_ratelimited("cannot match TCP bits for non-tcp packets\n");
144 return -EINVAL;
145 }
146
147 return 0;
148}
149
150static struct xt_match ecn_mt_reg[] __read_mostly = {
151 {
152 .name = "ecn",
153 .family = NFPROTO_IPV4,
154 .match = ecn_mt4,
155 .matchsize = sizeof(struct xt_ecn_info),
156 .checkentry = ecn_mt_check4,
157 .me = THIS_MODULE,
158 },
159 {
160 .name = "ecn",
161 .family = NFPROTO_IPV6,
162 .match = ecn_mt6,
163 .matchsize = sizeof(struct xt_ecn_info),
164 .checkentry = ecn_mt_check6,
165 .me = THIS_MODULE,
166 },
167};
168
169static int __init ecn_mt_init(void)
170{
171 return xt_register_matches(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
172}
173
174static void __exit ecn_mt_exit(void)
175{
176 xt_unregister_matches(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
177}
178
179module_init(ecn_mt_init);
180module_exit(ecn_mt_exit);