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
22 MODULE_LICENSE("GPL");
23 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
24 MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag modification");
25
26 /* set ECT codepoint from IP header.
27 * return false if there was an error. */
28 static inline bool
set_ect_ip(struct sk_buff * skb,const struct ipt_ECN_info * einfo)29 set_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. */
47 static inline bool
set_ect_tcp(struct sk_buff * skb,const struct ipt_ECN_info * einfo)48 set_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], 0);
76 return true;
77 }
78
79 static unsigned int
ecn_tg(struct sk_buff * skb,const struct xt_action_param * par)80 ecn_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
ecn_tg_check(const struct xt_tgchk_param * par)96 static 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 pr_info("unsupported ECN operation %x\n", einfo->operation);
103 return -EINVAL;
104 }
105 if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
106 pr_info("new ECT codepoint %x out of mask\n", einfo->ip_ect);
107 return -EINVAL;
108 }
109 if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR)) &&
110 (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
111 pr_info("cannot use TCP operations on a non-tcp rule\n");
112 return -EINVAL;
113 }
114 return 0;
115 }
116
117 static struct xt_target ecn_tg_reg __read_mostly = {
118 .name = "ECN",
119 .family = NFPROTO_IPV4,
120 .target = ecn_tg,
121 .targetsize = sizeof(struct ipt_ECN_info),
122 .table = "mangle",
123 .checkentry = ecn_tg_check,
124 .me = THIS_MODULE,
125 };
126
ecn_tg_init(void)127 static int __init ecn_tg_init(void)
128 {
129 return xt_register_target(&ecn_tg_reg);
130 }
131
ecn_tg_exit(void)132 static void __exit ecn_tg_exit(void)
133 {
134 xt_unregister_target(&ecn_tg_reg);
135 }
136
137 module_init(ecn_tg_init);
138 module_exit(ecn_tg_exit);
139