ipt_ECN.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/* iptables module for the IPv4 and TCP ECN bits, Version 1.5
  3 *
  4 * (C) 2002 by Harald Welte <laforge@netfilter.org>
  5*/
  6#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  7#include <linux/in.h>
  8#include <linux/module.h>
  9#include <linux/skbuff.h>
 10#include <linux/ip.h>
 11#include <net/ip.h>
 12#include <linux/tcp.h>
 13#include <net/checksum.h>
 14
 15#include <linux/netfilter/x_tables.h>
 16#include <linux/netfilter_ipv4/ip_tables.h>
 17#include <linux/netfilter_ipv4/ipt_ECN.h>
 18
 19MODULE_LICENSE("GPL");
 20MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
 21MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag modification");
 22
 23/* set ECT codepoint from IP header.
 24 * 	return false if there was an error. */
 25static inline bool
 26set_ect_ip(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
 27{
 28	struct iphdr *iph = ip_hdr(skb);
 29
 30	if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
 31		__u8 oldtos;
 32		if (skb_ensure_writable(skb, sizeof(struct iphdr)))
 33			return false;
 34		iph = ip_hdr(skb);
 35		oldtos = iph->tos;
 36		iph->tos &= ~IPT_ECN_IP_MASK;
 37		iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
 38		csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
 39	}
 40	return true;
 41}
 42
 43/* Return false if there was an error. */
 44static inline bool
 45set_ect_tcp(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
 46{
 47	struct tcphdr _tcph, *tcph;
 48	__be16 oldval;
 49
 50	/* Not enough header? */
 51	tcph = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
 52	if (!tcph)
 53		return false;
 54
 55	if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
 56	     tcph->ece == einfo->proto.tcp.ece) &&
 57	    (!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
 58	     tcph->cwr == einfo->proto.tcp.cwr))
 59		return true;
 60
 61	if (skb_ensure_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
 62		return false;
 63	tcph = (void *)ip_hdr(skb) + ip_hdrlen(skb);
 64
 65	oldval = ((__be16 *)tcph)[6];
 66	if (einfo->operation & IPT_ECN_OP_SET_ECE)
 67		tcph->ece = einfo->proto.tcp.ece;
 68	if (einfo->operation & IPT_ECN_OP_SET_CWR)
 69		tcph->cwr = einfo->proto.tcp.cwr;
 70
 71	inet_proto_csum_replace2(&tcph->check, skb,
 72				 oldval, ((__be16 *)tcph)[6], false);
 73	return true;
 74}
 75
 76static unsigned int
 77ecn_tg(struct sk_buff *skb, const struct xt_action_param *par)
 78{
 79	const struct ipt_ECN_info *einfo = par->targinfo;
 80
 81	if (einfo->operation & IPT_ECN_OP_SET_IP)
 82		if (!set_ect_ip(skb, einfo))
 83			return NF_DROP;
 84
 85	if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR) &&
 86	    ip_hdr(skb)->protocol == IPPROTO_TCP)
 87		if (!set_ect_tcp(skb, einfo))
 88			return NF_DROP;
 89
 90	return XT_CONTINUE;
 91}
 92
 93static int ecn_tg_check(const struct xt_tgchk_param *par)
 94{
 95	const struct ipt_ECN_info *einfo = par->targinfo;
 96	const struct ipt_entry *e = par->entryinfo;
 97
 98	if (einfo->operation & IPT_ECN_OP_MASK)
 99		return -EINVAL;
100
101	if (einfo->ip_ect & ~IPT_ECN_IP_MASK)
102		return -EINVAL;
103
104	if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR)) &&
105	    (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
106		pr_info_ratelimited("cannot use operation on non-tcp rule\n");
107		return -EINVAL;
108	}
109	return 0;
110}
111
112static struct xt_target ecn_tg_reg __read_mostly = {
113	.name		= "ECN",
114	.family		= NFPROTO_IPV4,
115	.target		= ecn_tg,
116	.targetsize	= sizeof(struct ipt_ECN_info),
117	.table		= "mangle",
118	.checkentry	= ecn_tg_check,
119	.me		= THIS_MODULE,
120};
121
122static int __init ecn_tg_init(void)
123{
124	return xt_register_target(&ecn_tg_reg);
125}
126
127static void __exit ecn_tg_exit(void)
128{
129	xt_unregister_target(&ecn_tg_reg);
130}
131
132module_init(ecn_tg_init);
133module_exit(ecn_tg_exit);