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, par->thoff, sizeof(_tcph), &_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, 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, 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(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
168}
169
170static void __exit ecn_mt_exit(void)
171{
172	xt_unregister_matches(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
173}
174
175module_init(ecn_mt_init);
176module_exit(ecn_mt_exit);