1/* iptables module for the IPv4 and TCP ECN bits, Version 1.5
2 *
3 * (C) 2002 by Harald Welte <laforge@netfilter.org>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License version 2 as
7 * published by the Free Software Foundation.
8*/
9#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10#include <linux/in.h>
11#include <linux/module.h>
12#include <linux/skbuff.h>
13#include <linux/ip.h>
14#include <net/ip.h>
15#include <linux/tcp.h>
16#include <net/checksum.h>
17
18#include <linux/netfilter/x_tables.h>
19#include <linux/netfilter_ipv4/ip_tables.h>
20#include <linux/netfilter_ipv4/ipt_ECN.h>
21
22MODULE_LICENSE("GPL");
23MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
24MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag modification");
25
26/* set ECT codepoint from IP header.
27 * return false if there was an error. */
28static inline bool
29set_ect_ip(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
30{
31 struct iphdr *iph = ip_hdr(skb);
32
33 if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
34 __u8 oldtos;
35 if (!skb_make_writable(skb, sizeof(struct iphdr)))
36 return false;
37 iph = ip_hdr(skb);
38 oldtos = iph->tos;
39 iph->tos &= ~IPT_ECN_IP_MASK;
40 iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
41 csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
42 }
43 return true;
44}
45
46/* Return false if there was an error. */
47static inline bool
48set_ect_tcp(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
49{
50 struct tcphdr _tcph, *tcph;
51 __be16 oldval;
52
53 /* Not enough header? */
54 tcph = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
55 if (!tcph)
56 return false;
57
58 if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
59 tcph->ece == einfo->proto.tcp.ece) &&
60 (!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
61 tcph->cwr == einfo->proto.tcp.cwr))
62 return true;
63
64 if (!skb_make_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
65 return false;
66 tcph = (void *)ip_hdr(skb) + ip_hdrlen(skb);
67
68 oldval = ((__be16 *)tcph)[6];
69 if (einfo->operation & IPT_ECN_OP_SET_ECE)
70 tcph->ece = einfo->proto.tcp.ece;
71 if (einfo->operation & IPT_ECN_OP_SET_CWR)
72 tcph->cwr = einfo->proto.tcp.cwr;
73
74 inet_proto_csum_replace2(&tcph->check, skb,
75 oldval, ((__be16 *)tcph)[6], false);
76 return true;
77}
78
79static unsigned int
80ecn_tg(struct sk_buff *skb, const struct xt_action_param *par)
81{
82 const struct ipt_ECN_info *einfo = par->targinfo;
83
84 if (einfo->operation & IPT_ECN_OP_SET_IP)
85 if (!set_ect_ip(skb, einfo))
86 return NF_DROP;
87
88 if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR) &&
89 ip_hdr(skb)->protocol == IPPROTO_TCP)
90 if (!set_ect_tcp(skb, einfo))
91 return NF_DROP;
92
93 return XT_CONTINUE;
94}
95
96static int ecn_tg_check(const struct xt_tgchk_param *par)
97{
98 const struct ipt_ECN_info *einfo = par->targinfo;
99 const struct ipt_entry *e = par->entryinfo;
100
101 if (einfo->operation & IPT_ECN_OP_MASK)
102 return -EINVAL;
103
104 if (einfo->ip_ect & ~IPT_ECN_IP_MASK)
105 return -EINVAL;
106
107 if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR)) &&
108 (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
109 pr_info_ratelimited("cannot use operation on non-tcp rule\n");
110 return -EINVAL;
111 }
112 return 0;
113}
114
115static struct xt_target ecn_tg_reg __read_mostly = {
116 .name = "ECN",
117 .family = NFPROTO_IPV4,
118 .target = ecn_tg,
119 .targetsize = sizeof(struct ipt_ECN_info),
120 .table = "mangle",
121 .checkentry = ecn_tg_check,
122 .me = THIS_MODULE,
123};
124
125static int __init ecn_tg_init(void)
126{
127 return xt_register_target(&ecn_tg_reg);
128}
129
130static void __exit ecn_tg_exit(void)
131{
132 xt_unregister_target(&ecn_tg_reg);
133}
134
135module_init(ecn_tg_init);
136module_exit(ecn_tg_exit);
137