1/* IP tables module for matching the value of the IPv4 and TCP ECN bits 2 * 3 * (C) 2002 by Harald Welte <laforge@gnumonks.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/ip.h> 12#include <net/ip.h> 13#include <linux/module.h> 14#include <linux/skbuff.h> 15#include <linux/tcp.h> 16 17#include <linux/netfilter/x_tables.h> 18#include <linux/netfilter_ipv4/ip_tables.h> 19#include <linux/netfilter_ipv4/ipt_ecn.h> 20 21MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>"); 22MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag match for IPv4"); 23MODULE_LICENSE("GPL"); 24 25static inline bool match_ip(const struct sk_buff *skb, 26 const struct ipt_ecn_info *einfo) 27{ 28 return (ip_hdr(skb)->tos & IPT_ECN_IP_MASK) == einfo->ip_ect; 29} 30 31static inline bool match_tcp(const struct sk_buff *skb, 32 const struct ipt_ecn_info *einfo, 33 bool *hotdrop) 34{ 35 struct tcphdr _tcph; 36 const struct tcphdr *th; 37 38 /* In practice, TCP match does this, so can't fail. But let's 39 * be good citizens. 40 */ 41 th = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph); 42 if (th == NULL) { 43 *hotdrop = false; 44 return false; 45 } 46 47 if (einfo->operation & IPT_ECN_OP_MATCH_ECE) { 48 if (einfo->invert & IPT_ECN_OP_MATCH_ECE) { 49 if (th->ece == 1) 50 return false; 51 } else { 52 if (th->ece == 0) 53 return false; 54 } 55 } 56 57 if (einfo->operation & IPT_ECN_OP_MATCH_CWR) { 58 if (einfo->invert & IPT_ECN_OP_MATCH_CWR) { 59 if (th->cwr == 1) 60 return false; 61 } else { 62 if (th->cwr == 0) 63 return false; 64 } 65 } 66 67 return true; 68} 69 70static bool ecn_mt(const struct sk_buff *skb, struct xt_action_param *par) 71{ 72 const struct ipt_ecn_info *info = par->matchinfo; 73 74 if (info->operation & IPT_ECN_OP_MATCH_IP) 75 if (!match_ip(skb, info)) 76 return false; 77 78 if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) { 79 if (ip_hdr(skb)->protocol != IPPROTO_TCP) 80 return false; 81 if (!match_tcp(skb, info, &par->hotdrop)) 82 return false; 83 } 84 85 return true; 86} 87 88static int ecn_mt_check(const struct xt_mtchk_param *par) 89{ 90 const struct ipt_ecn_info *info = par->matchinfo; 91 const struct ipt_ip *ip = par->entryinfo; 92 93 if (info->operation & IPT_ECN_OP_MATCH_MASK) 94 return -EINVAL; 95 96 if (info->invert & IPT_ECN_OP_MATCH_MASK) 97 return -EINVAL; 98 99 if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR) && 100 ip->proto != IPPROTO_TCP) { 101 pr_info("cannot match TCP bits in rule for non-tcp packets\n"); 102 return -EINVAL; 103 } 104 105 return 0; 106} 107 108static struct xt_match ecn_mt_reg __read_mostly = { 109 .name = "ecn", 110 .family = NFPROTO_IPV4, 111 .match = ecn_mt, 112 .matchsize = sizeof(struct ipt_ecn_info), 113 .checkentry = ecn_mt_check, 114 .me = THIS_MODULE, 115}; 116 117static int __init ecn_mt_init(void) 118{ 119 return xt_register_match(&ecn_mt_reg); 120} 121 122static void __exit ecn_mt_exit(void) 123{ 124 xt_unregister_match(&ecn_mt_reg); 125} 126 127module_init(ecn_mt_init); 128module_exit(ecn_mt_exit); 129