| 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 | |
| 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 |
| 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 |
| 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 enought 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 |
| 80 | ecn_tg(struct sk_buff *skb, const struct xt_target_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 | |
| 96 | static bool 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 | printk(KERN_WARNING "ECN: unsupported ECN operation %x\n", |
| 103 | einfo->operation); |
| 104 | return false; |
| 105 | } |
| 106 | if (einfo->ip_ect & ~IPT_ECN_IP_MASK) { |
| 107 | printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n", |
| 108 | einfo->ip_ect); |
| 109 | return false; |
| 110 | } |
| 111 | if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR)) |
| 112 | && (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) { |
| 113 | printk(KERN_WARNING "ECN: cannot use TCP operations on a " |
| 114 | "non-tcp rule\n"); |
| 115 | return false; |
| 116 | } |
| 117 | return true; |
| 118 | } |
| 119 | |
| 120 | static struct xt_target ecn_tg_reg __read_mostly = { |
| 121 | .name = "ECN", |
| 122 | .family = NFPROTO_IPV4, |
| 123 | .target = ecn_tg, |
| 124 | .targetsize = sizeof(struct ipt_ECN_info), |
| 125 | .table = "mangle", |
| 126 | .checkentry = ecn_tg_check, |
| 127 | .me = THIS_MODULE, |
| 128 | }; |
| 129 | |
| 130 | static int __init ecn_tg_init(void) |
| 131 | { |
| 132 | return xt_register_target(&ecn_tg_reg); |
| 133 | } |
| 134 | |
| 135 | static void __exit ecn_tg_exit(void) |
| 136 | { |
| 137 | xt_unregister_target(&ecn_tg_reg); |
| 138 | } |
| 139 | |
| 140 | module_init(ecn_tg_init); |
| 141 | module_exit(ecn_tg_exit); |