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, write_len: 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(sum: &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, offset: ip_hdrlen(skb), len: sizeof(_tcph), buffer: &_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, write_len: 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(sum: &tcph->check, skb,
72 from: oldval, to: ((__be16 *)tcph)[6], pseudohdr: 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(target: &ecn_tg_reg);
125}
126
127static void __exit ecn_tg_exit(void)
128{
129 xt_unregister_target(target: &ecn_tg_reg);
130}
131
132module_init(ecn_tg_init);
133module_exit(ecn_tg_exit);
134

source code of linux/net/ipv4/netfilter/ipt_ECN.c